Model 3433 Small-Scale Powder Disperser Instruction … Overview 1 Model 3433 Small-Scale Powder Disperser Unpacking and Setting Up 2 Instruction Manual Operating the SSPD 3 Accessories

Model 3433 Small-Scale Powder Disperser

Instruction Manual

P/N 1933769, Revision E February 2003

P a r t i c l e I n s t r u m e n t s

Product Overview 1

Model 3433 Small-Scale Powder Disperser

Unpacking and Setting Up

2

Instruction Manual

Operating the SSPD 3

Accessories 4

Using the SSPD in a Powder Sizing System

5

Maintenance, Calibration, and Troubleshooting

6

Service 7

Appendixes

Manual H is tory

iv

The following is a manual history of the Model 3433 Small-Scale Powder Disperser (part number 1933769). Revision Date

First Version January 1993 A June 1993 B March 1994 C July 1996 October 1998 D July 2000 E February 2003

The Model 3433 Small-Scale Powder Disperser Instruction Manual was originally published under part number 1933433. This new manual, part number 1933769, reflects engineering changes made to the Model 3433 as well as a reorganization of the manual contents. Revision A adds a procedure used to preload a turntable. Revision B includes a new Figure 1-2 and TSI’s new customer service number. Revision C adds European Community “CE Mark” standards, revisions to Chapter 2, “Changing the Line Voltage Configuration” and “Changing Fuses,” TSI’s “Limitation of Warranty and Liability” on page iii was updated, and minor changes were made to rest of manual. In October 1998, TSI’s area code was changed from 612 to 651. In Revision D, TSI’s Limitation of Warranty and Liability was updated. In Revision E, TSI’s phone numbers and address were updated.

v

Part Number 1933769 / Revision E / February 2003

Copyright ©TSI Incorporated / May 1988–2003 / All rights reserved.

Address TSI Incorporated / 500 Cardigan Road / 500 Cardigan Road / Shoreview, MN 55126 / USA

Fax No. (651) 490-3824

E-mail Address [email protected]

Limitation of Warranty and Liability (effective July 2000)

Seller warrants the goods sold hereunder, under normal use and service as described in the operator's manual, shall be free from defects in workmanship and material for (12) months, or the length of time specified in the operator's manual, from the date of shipment to the customer. This warranty period is inclusive of any statutory warranty. This limited warranty is subject to the following exclusions:

a. Hot-wire or hot-film sensors used with research anemometers, and certain other components when indicated in specifications, are warranted for 90 days from the date of shipment.

b. Parts repaired or replaced as a result of repair services are warranted to be free from defects in workmanship and material, under normal use, for 90 days from the date of shipment.

c. Seller does not provide any warranty on finished goods manufactured by others or on any fuses, batteries or other consumable materials. Only the original manufacturer's warranty applies.

d. Unless specifically authorized in a separate writing by Seller, Seller makes no warranty with respect to, and shall have no liability in connection with, goods which are incorporated into other products or equipment, or which are modified by any person other than Seller.

The foregoing is IN LIEU OF all other warranties and is subject to the LIMITATIONS stated herein. NO OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR PARTICULAR PURPOSE OR MERCHANTABILITY IS MADE.

TO THE EXTENT PERMITTED BY LAW, THE EXCLUSIVE REMEDY OF THE USER OR BUYER, AND THE LIMIT OF SELLER'S LIABILITY FOR ANY AND ALL LOSSES, INJURIES, OR DAMAGES CONCERNING THE GOODS (INCLUDING CLAIMS BASED ON CONTRACT, NEGLIGENCE, TORT, STRICT LIABILITY OR OTHERWISE) SHALL BE THE RETURN OF GOODS TO SELLER AND THE REFUND OF THE PURCHASE PRICE, OR, AT THE OPTION OF SELLER, THE REPAIR OR REPLACEMENT OF THE GOODS. IN NO EVENT SHALL SELLER BE LIABLE FOR ANY SPECIAL, CONSEQUENTIAL OR INCIDENTAL DAMAGES. SELLER SHALL NOT BE RESPONSIBLE FOR INSTALLATION, DISMANTLING OR REINSTALLATION COSTS OR CHARGES. No Action, regardless of form, may be brought against Seller more than 12 months after a cause of action has accrued. The goods returned under warranty to Seller's factory shall be at Buyer's risk of loss, and will be returned, if at all, at Seller's risk of loss.

Buyer and all users are deemed to have accepted this LIMITATION OF WARRANTY AND LIABILITY, which contains the complete and exclusive limited warranty of Seller. This LIMITATION OF WARRANTY AND LIABILITY may not be amended, modified or its terms waived, except by writing signed by an Officer of Seller.

Service Policy Knowing that inoperative or defective instruments are as detrimental to TSI as they are to our customers, our service policy is designed to give prompt attention to any problems. If any malfunction is discovered, please contact your nearest sales office or representative, or call TSI’s Particle Instruments at 1-800-874-2811 (USA) or (651) 490-2811.

vi Model 3433 Small-Scale Powder Disperser

Safety

vii

This section gives instructions to promote safe and proper handling of the Model 3433 Small-Scale Powder Disperser (SSPD).

!

C a u t i o n If the SSPD is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.

Any powder dispersed in air (an aerosol) is potentially hazardous. The SSPD disperses extremely small quantities of powder and its aerosol output is essentially invisible. If you are handling hazardous powders, use an adequate respirator when loading or operating the Model 3433 or load and operate the Model 3433 inside a laboratory fume hood.

D e s c r i p t i o n o f C a u t i o n S y m b o l The following symbol and an appropriate caution statement are used throughout the manual and on the Model 3433 to draw attention to any steps that require you to take cautionary measures when working with the Model 3433:

!

C a u t i o n Refer to accompanying documents.

viii Model 3433 Small-Scale Powder Disperser

Contents

ix

Manual History........................................................................... iv

Safety ........................................................................................ vii Description of Caution Symbol.............................................. vii

About This Manual .................................................................... xv Organization ......................................................................... xv Related Product Literature ................................................... xvi Getting Help......................................................................... xvi Submitting Comments ........................................................ xvii

C h a p t e r s 1 Product Overview .............................................................. 1-1

Introduction........................................................................ 1-1 How the SSPD Operates ...................................................... 1-1 Applications ........................................................................ 1-3

2 Unpacking and Setting Up................................................. 2-1

Unpacking .......................................................................... 2-1 Unpacking Instructions.................................................... 2-1

Setting Up........................................................................... 2-2 Moving the Two Retaining Bumpers ................................. 2-2

Checking the Line Voltage Configuration............................. 2-3 Changing the Fuse .............................................................. 2-5

Changing Between European and American-Style Fuses .. 2-5 Connecting the Compressed Air Supply............................... 2-7

3 Operating the SSPD ........................................................... 3-1

Operating Requirements ..................................................... 3-1 SSPD Controls .................................................................... 3-1

Power Switch (back panel) ................................................ 3-1 Capillary Flow .................................................................. 3-1 Sheath Flow ..................................................................... 3-2 CCW/STOP/CW Switch.................................................... 3-2 Rotation Rate ................................................................... 3-3

Operating Procedure ........................................................... 3-3 4 Accessories ........................................................................ 4-1

Turntable Preloaded with a Range of PSL Spheres............... 4-1 Turntable for Redispersing Airborne Dusts Collected on

Membrane Filters ............................................................. 4-2

x Model 3433 Small-Scale Powder Disperser

Turntable with Three Concentric V-Shaped Grooves ........... 4-3 Alternate Motor ................................................................... 4-4 Ordering Parts .................................................................... 4-6

5 Using the SSPD in a Powder Sizing System ..................... 5-1

Connecting the Model 3433 to an APS................................. 5-2 Setting the Flowrate ............................................................ 5-5

6 Maintenance, Calibration, and Troubleshooting .............. 6-1

Maintenance ....................................................................... 6-1 Routine Maintenance ....................................................... 6-1 Cleaning........................................................................... 6-1

Calibration.......................................................................... 6-4 Troubleshooting .................................................................. 6-4

7 Service ............................................................................... 7-1

Technical Contacts.............................................................. 7-1 Returning the CPC for Service ............................................. 7-1 Moving the SSPD ................................................................ 7-1

A p p e n d i x A Specifications ....................................................................A-1 B Technical Paper .................................................................B-1

Abstract ..............................................................................B-1 Introduction........................................................................B-1 Description of the Dispersion Technique Used with the

SSPD................................................................................B-3 Small-Scale Powder Disperser Used in Conjunction with

a Particle Sensor ..............................................................B-7 The SSPD Used as a Disperser for Polystyrene Latex

Spheres..........................................................................B-10 The Small-Scale Powder Disperser Used to Redisperse

Airborne Dust Samples Collected on Membrane Filters ..B-14 References ........................................................................B-18

Contents xi

F i g u r e s 1-1 Model 3433 Small-Scale Powder Disperser ....................... 1-1 1-2 Schematic of the Small-Scale Powder Disperser................ 1-2 2-1 Position of the Two Retaining Bumpers During

Shipment ...................................................................... 2-2 2-2 Retaining Bumpers Relocated to Function as Limit

Stops During Regular Operation of the SSPD ................ 2-3 2-3 Power Entry, Fuse, and Voltage Module............................ 2-4 2-4 Orientation of the Voltage Selector Card ........................... 2-4 2-5 North American–Fusing Arrangement ............................... 2-6 2-6 European–Fusing Arrangement ........................................ 2-6 2-7 Fuse Block/Cover Assembly ............................................. 2-6 3-1 Control Panel.................................................................... 3-2 3-2 Standard Turntable Loaded with Dry Powder.................... 3-3 3-3 Turntable Correctly Positioned on its Support Shaft ......... 3-4 3-4 Internal O-ring Located Within the Turntable’s

Support Collar............................................................... 3-4 3-5 Turntable Positioned Beneath the Stainless-Steel

Delivery Tube ................................................................ 3-5 3-6 Schematic Showing the Positions of nuts Nos. 1, 2 and 3 . 3-6 4-1 Standard Turntable Preloaded with a Range of

Polystyrene Latex Spheres ............................................. 4-1 4-2 Turntable for Redispersing Airborne Dusts Collected

on Membrane Filters ..................................................... 4-3 4-3 Location of the Spring-Loaded Ball Plunger and the

Two Setscrews That Fasten the Upper Collar ................. 4-5 4-4 Using the Right-Angled Screwdriver to Remove the

Four Phillips-head Screws That Fasten the Motor Brackets to the Plate ..................................................... 4-5

5-1 Small-Scale Powder Disperser Configured to Function

with the Model 3310A Aerodynamic Particle Sizer ......... 5-1 5-2 Positions of the Setscrews That Retain the Aerosol

Outlet Tube (a) and the Upper Chamber to its Support Arm (b)............................................................. 5-3

5-3 Plexiglas Coupler Installed Over the Aerosol Outlet Tube .. 5-3 5-4 Final Configuration of the SSPD/APS Outlet and Inlet

Tubes and the Plexiglas Coupler.................................... 5-4

xii Model 3433 Small-Scale Powder Disperser

5-5 Back View of the SSPD/APS Configuration with the Sides and Backs of the Two Instruments in Alignment .. 5-4

6-1 (a) Upper and Lower Support Couplers Shown in

Their Regular Positions at the Top and Bottom of the Expansion Cone. (b) Upper and Lower Support Couplers Moved Up and Down, Respectively. (c) The Expansion Cone Can Now be Removed. ......................... 6-3

6-2 Two Center-Punch Marks on the Venturi Throat Aligned with the Lower Support Arm.......................................... 6-3

B-1 Cutaway Schematic of the Small-Scale Powder

Disperser.......................................................................B-4 B-2 Turntable Used for Dispersing Dry Powders; Three

Rings of Abrasive Paper are Glued to the Upper Surface of the Turntable................................................B-5

B-3 Powder Samples Dispersed With the SSPD (a) Photocopying Toner, (b) Rice Starch, (c) Arizona Road Dust, (d) Coal Dust. Scale: 20 µm ¦—¦ Magnification ×200........................................................B-8

B-4 A Powder-Sizing System Including the Small-Scale Powder Disperser and the Model 3310A Aerodynamic Particle Sizer .................................................................B-9

B-5 (a) A Distribution of Mass (mg/m3) Versus Aerodynamic Diameter for 15 µm Dynospheres (PSL) Dispersed with the SSPD; (b) Corresponding Multichannel Accumulator Data from which (a) was Calculated........B-12

B-6 (a) Multichannel Accumulator Data From an APS for 10 µm Dynospheres (Nominal) Dispersed with an SSPD; (b) Multichannel Accumulator Data From an APS for 9.89 µm PSL Spheres Manufactured Aboard the NASA Space Shuttle and Dispersed with an SSPD.B-13

B-7 Turntable Used for Redispersing Material Collected on Membrane Filters, Shown with Half the Required Number of Porous Plastic Filter Supports ....................B-15

B-8 Membrane Filter Loaded with Coal Dust; Shown with the Clean Track Generated by Rotating the Filter Beneath the SSPD’s Capillary Delivery Tube................B-15

B-9a Size Distribution of Airborne Coal Dust, Measured with an APS.................................................................B-17

B-9b Size Distribution of Coal Dust Captured on a Membrane Filter, Redispersed with the SSPD and then Sized with an APS. Note the much lower levels of concentration ..........................................................B-17

Contents xiii

B-9c Percentage Comparison Between (a) and (b). Perfect Comparison Would Produce a Square-Wave-Type Distribution.................................................................B-18

T a b l e s 2-1 SSPD Packing List ............................................................ 2-1 4-1 SSPD Parts List ................................................................ 4-6 A-1 Model 3433 Small-Scale Powder Disperser

Specifications ................................................................A-1

About This Manual

xv

P u r p o s e

This instruction manual describes how to operate and maintain the Model 3433 Small-Scale Powder Disperser (SSPD) manufactured by TSI Incorporated.

O r g a n i z a t i o n The following is a guide to the organization of the manual:

! Chapter 1: Product Overview

This chapter gives a brief description of the Model 3433 Small-Scale Powder Disperser, explains how the Disperser works, and gives a list of applications for the instrument.

! Chapter 2: Unpacking and Setting Up This chapter gives unpacking instructions, directions for moving the retaining bumpers, and SSPD power requirements.

! Chapter 3: Operating the SSPD This chapter describes the SSPD controls and gives a procedure for preparing a sample for dispersion.

! Chapter 4: Accessories This chapter describes the optional turntables and motor available for use with the SSPD along with a parts list for ordering components.

! Chapter 5: Using the SSPD in a Power Sizing System This chapter explains how the SSPD is used with the Aerodynamic Particle Sizer (APS).

! Chapter 6: Maintenance, Calibration, and Troubleshooting This chapter gives routine SSPD maintenance and cleaning operations, the venturi throat flowrate calibration procedure, and some troubleshooting information.

! Chapter 7: Service This chapter gives directions for contacting people at TSI Incorporated for technical information and directions for returning the SSPD for service.

! Appendix A: Specifications This appendix contains SSPD specifications.

xvi Model 3433 Small-Scale Powder Disperser

! Appendix B: Technical Paper This appendix consists of a technical paper by David B. Blackford, Ph.D. and Kenneth L. Rubow, Ph.D.

R e l a t e d P r o d u c t L i t e r a t u r e ! Model 3310A Aerodynamic Particle Sizer Instruction Manual

(part number 1933766) TSI Incorporated

This manual contains operating and maintenance instructions for the Aerodynamic Particle Sizer (APS), a particle sizing instrument that measures a particle’s aerodynamic diameter.

G e t t i n g H e l p To obtain assistance with this product, or to submit suggestions, either refer to Chapter 7, “Service,” or contact:

TSI Incorporated (Particle Instruments) 500 Cardigan Road St. Paul, MN 55126 USA Fax: (651) 490-3824 Telephone: 1-800-874-2811 (USA) or (651) 490-2811 E-mail Address: [email protected]

About this Manual xvii

S u b m i t t i n g C o m m e n t s TSI values your comments and suggestions on this manual. Please use the comment sheet, on the last page of this manual, to send us your opinion on the manual’s usability, to suggest specific improvements, or to report any technical errors.

If the comment sheet has already been used, mail your comments on another sheet of paper to:

TSI Incorporated Particle Instruments 500 Cardigan Road St. Paul, MN 55126 Fax: (651) 490-3824 E-mail Address: [email protected]

xviii Model 3433 Small-Scale Powder Disperser

C H A P T E R 1

Product Overv iew

1-1

I n t r o d u c t i o n The Model 3433 Small-Scale Powder Disperser (SSPD), shown in Figure 1-1, is designed to efficiently disperse small quantities of dry powder in the diameter range of 1 to 50 micrometers The SSPD disperses small, milligram, quantities of dry powder using a venturi aspiration technique. The SSPD has been designed to function as a stand-alone powder disperser or, when used with the Aerodynamic Particle Sizer (APS), as a powder sizing system.

Figure 1-1 Model 3433 Small-Scale Powder Disperser

H o w t h e S S P D O p e r a t e s This section gives a technical description of the Model 3433 SSPD. You can also refer to Appendix B, “Technical Paper,” for more information on this instrument.

1-2 Model 3433 Small-Scale Powder Disperser

Using Figure 1-2 as a reference, the powder to be dispersed is gently brushed over the surface of one of three annular rings of abrasive paper that is glued to the upper surface of the turntable. The powder is then removed from the turntable by means of a venturi aspirator and capillary delivery tube. The lower end of the capillary tube is positioned just above one of the abrasive paper rings, while the upper end of the tube floats in the throat of the venturi aspirator.

HighSheathFlow

4 LpmSheathFlow

FilteredAir In

AerosolOutput

5 Lpm

13.5 Lpm

FlowValve

NominalIsokineticSampleRemoval

18.5LpmExpansion

Cone HighEfficiency

Filter

16.5 Lpm

VenturiThroatHigh

Capillary∆ P

Turntable

Clean AirFlushingCollar

2 LpmCapillary Tube

Figure 1-2 Schematic of the Small-Scale Powder Disperser

Product Overview 1-3

A region of low pressure is created by the increased velocity of air through the venturi throat which draws particle flow up the capillary tube. The capillary tube thus acts as a small vacuum cleaner as the turntable rotates slowly beneath it. In the venturi throat, the entrained aerosol particles are deagglomerated. Shear forces are generated between the high-velocity gas passing through the venturi throat and the low-velocity gas-particle stream exiting the capillary tube. The gas stream passing through the venturi throat tends not only to break up the agglomerates (due to the shear forces of the near seven-fold difference in velocities), but the gas stream also acts as a sheath around the aerosol stream in the throat section. As such, it reduces particle losses to the walls. The output from the SSPD is a dilute deagglomerated aerosol generated from the source powder loaded on the turntable.

A p p l i c a t i o n s The SSPD uses three optional turntables for four specific applications: In the first application, the SSPD functions as an accessory to the Model 3310A Aerodynamic Particle Sizer (APS).* This combination makes it possible to determine a powder’s size distribution according its aerodynamic diameter over the size range of 0.5 to 30 micrometers. To accomplish this distribution, the standard turntable with three concentric rings of abrasive paper (P/N 1030737) is used. In the second application, the SSPD is used to disperse large monosized polystyrene latex (PSL) spheres in the diameter range of 2 to 30 micrometers. A standard turntable is available which has been preloaded with a range of PSL spheres (P/N 1030770). In the third application, the SSPD is used to redisperse airborne dust samples collected on 25- and 37-millimeter-diameter membrane filters (P/N 1030771). Particle size analysis is then

*In this manual, the Model 3300 APS will be referred to by model number, while the Model 3310A will be referred to as the

APS.


accomplished with the Model 3310A APS. See Chapter 5 for more information on this application.

In the fourth application, the SSPD is used to disperse small measured quantities of a powder, for example, 1 to 100 milligrams, at a controlled feed rate, using an optional turntable having three concentric V-shaped grooves (P/N 1030772). For more information on the optional turntables, refer to Chapter 4, “Accessories.”

C H A P T E R 2

Unpacking and Set t ing Up

2-1

Use the information in this chapter to unpack and set up the Model 3433 Small-Scale Powder Disperser (SSPD).

Note: When in use, do not position the SSPD so that it is difficult to disconnect from the filtered air inlet and in any way that inhibits the complete movement of the front panel.

U n p a c k i n g Table 2-1 gives the packing list for the SSPD. Each instrument component is packed in a separate box. Table 2-1 SSPD Packing List

Description Part Number SSPD (including turntable) Power cable 1303053 6-inch length of Norprene® tubing 3001168 Instruction manual 1933769 APS coupler 1503317 3/32” Allen wrench 3305006 Vacuum grease (for O-rings) 1502249

Unpacking Instructions Carefully unpack the components from the packing boxes. If anything is missing or appears to be damaged, contact your TSI representative or contact TSI Customer Service at 1-800-874-2811 (USA) or (651) 490-2811. Chapter 7, “Service,” gives instructions for returning the SSPD to TSI Incorporated.

Note: The SSPD does not come fully assembled. Using Figure 3-2 as a reference, remove the turntable and install it either in the SSPD on its support shaft or on one of the two auxiliary shafts located on the door of the SSPD housing.

®Norprene is a registered trademark of Norton Performance Plastics, Akron, Ohio, USA.


S e t t i n g U p Use the information in this section to set up the SSPD for operation. This section contains information on the following:

❑ Moving the two retaining bumpers

❑ Checking the line voltage configuration

❑ Changing the fuse (if necessary)

❑ Connecting the compressed air supply.

Moving the Two Retaining Bumpers Two retaining bumpers are included in the packaging materials to prevent the motor support plate from swinging during shipment and damaging the internal components of the SSPD. The bumpers are screwed to the base plate of the housing, one on either side of the motor support plate (Figure 2-1).

Limiting Bumper

Figure 2-1 Position of the Two Retaining Bumpers During Shipment

Using a Phillips-head screwdriver, remove both bumpers and relocate them to the two free screw holes (Figure 2-2). In these holes, the bumpers now function as limit stops and allow the motor support plate to swing underneath the capillary delivery tube during routine operation of the SSPD.

Unpacking and Setting Up 2-3

Limiting Bumper

Figure 2-2 Retaining Bumpers Relocated to Function as Limit Stops During Regular Operation of the SSPD

C h e c k i n g t h e L i n e V o l t a g e C o n f i g u r a t i o n The Model 3433 SSPD requires 100/120 volts AC at 0.5 amps or 230/240 volts AC at 0.25 amps with 50 to 60 hertz at any of the voltages. Use the information in this section to verify the line voltage configuration and fusing arrangement matches your local line voltages.

Check the back panel of the instrument for the voltage and fusing requirements. The label is located just above the power entry module. To change the voltage setting, follow these steps:

1. Disconnect the power from the 3433 SSPD and remove the line cord. Locate the power-entry module on the back panel of the 3433 SSPD (Figure 2-3).*

2. Lift off the cover of the fuse and voltage module cover on the back panel of the 3433 SSPD using a small-blade screwdriver or similar tool (Figure 2-3). Set aside the cover/fuse block assembly.

*Drawings reprinted by permission of Corcom Incorporated, Libertyville, Illinois.


Figure 2-3 Power Entry, Fuse, and Voltage Module

3. Grasp the indicator pin and pull the voltage-selector card straight out of the housing (Figure 2-3).

4. Orient the selector card so that the desired voltage is readable at the bottom.

5. Orient the indicator pin so that it points up when the desired voltage is readable at the bottom. When the pin is fixed and in place, rotate the card 90° clockwise (Figure 2-4).

Figure 2-4 Orientation of the Voltage Selector Card


6. Insert the voltage-selector card into the housing, making sure the edge containing the desired voltage is inserted first and the printed side of the card faces the IEC (power cord) connector.

7. Replace the cover, making sure that the indicator pin shows the desired voltage.

C h a n g i n g t h e F u s e

1. Disconnect the power from the 3433 SSPD and remove the line cord.

2. Lift off the power-entry module on the back panel of the 3433 SSPD using a small-blade screwdriver or similar tool (Figure 2-3).

3. Replace the fuses. Make sure the Fuse(s) are the proper size and rating for the line voltage you are using. The Fusing label is located just above the power entry module on the back panel of the 3433 SSPD.

Note: Two European-style 5 × 20 mm fuses are required in the European-Fusing arrangement (Figure 2-4).

4. Replace the power-entry module cover.

Changing Between European and American-Style Fuses Before installing the 3433 SSPD, make sure the fuse is compatible with your site. The 3433 SSPD works with both North American and European-style fuses. The 100/120-volt model comes with the North American-style fuse and the 230/240-volt model is equipped with the European-style fuse. If you need to change the fuse from North American (Figure 2-5) to the European style (Figure 2-6),or vice versa, follow these steps:

1. Disconnect the power from the 3433 SSPD and remove the line cord.

2. Lift off the power-entry module on the back panel of the 3433 SSPD cover using a small-blade screwdriver or similar tool.


Jumper Bar

Fuse Block Cover

Fuse

Figure 2-5 North American–Fusing Arrangement

Fuse Block

Cover

Fuses

Jumper Bar

Figure 2-6 European–Fusing Arrangement 3. Loosen the screw on the fuse block two turns.

4. Remove the fuse block (Figure 2-7) by sliding it up and away from the screw. Lift the block from the pedestal.

FuseFuse Block

Cover Figure 2-7 Fuse Block/Cover Assembly


5. Change the fuses:

Note: Two European 5 × 20 mm fuses are required in the European-Fusing Arrangement.

Invert the fuse block and slide it back onto the screw and the pedestal.

6. Tighten the screw and replace the power-entry module cover. The fuse(s) that enters the housing first is the active one.

C o n n e c t i n g t h e C o m p r e s s e d A i r S u p p l y The air supplied to the SSPD must be filtered, dried, oil-free, and regulated air at 138 kPa (20 psi). Follow the steps below to connect the compressed air supply:

1. Remove the protective cap from the AIR INLET on the back panel.

2. Make sure the compressed air is supplied to the SSPD through a 3⁄8-inch (outside diameter) plastic tube. Insert the plastic tube into the Swagelok® fitting on the back panel.

3. Using an adjustable wrench tighten the Swagelok nut one-half turn past hand-tight.

4. Turn on the air at source.

5. Check to ensure the pressure is regulated at 138 kPa (20 psi).


C H A P T E R 3

Operat ing the SSPD

3-1

Use the information in this chapter to operate the Model 3433 Small-Scale Powder Disperser (SSPD).

O p e r a t i n g R e q u i r e m e n t s

! The Model 3433 SSPD requires 100/120 volts AC at 0.5 amps or 230/240 volts AC at 0.25 amps with 50 to 60 hertz at any of the voltages. Use the instructions in Chapter 2 to verify the voltage selection on the instrument matches local line voltage.

! Compressed air is required at a flowrate of 25 liters per minute at a pressure of 138 kPa (20 psi); the supply must also be dried and filtered. This source is connected to the Filtered Air Inlet on the pack panel of the instrument. TSI’s Model 3074 Filtered Air Supply is recommended.

S S P D C o n t r o l s The primary control functions of the SSPD are described in this section. Use Figure 3-1 as a reference.

Power Switch (back panel) When the power is on, the green indicator diode on the front panel lights.

Capillary Flow The flow-control restrictor valve controls the sample flow through the capillary tube. The enclosed calibration graph relates the pressure drop, measured with the Capsuhelic® gauge, to flowrate in liters per minute.

®Capsuhelic is a registered trademark of Dwyer Instruments, Inc., Michigan City, Indiana, USA.


Figure 3-1 Control Panel

Sheath Flow The sheath flow controls the amount of clean, dry air that flushes the surface of the turntable. It is set at approximately 4 liters per minute.

CCW/STOP/CW Switch The direction of turntable rotation is either clockwise (CW) or counterclockwise (CCW).

Operating the SSPD 3-3

Rotation Rate The potentiometer controls the rotating speed of the turntable. Its scale is marked off in arbitrary numbers.

O p e r a t i n g P r o c e d u r e Use the following instructions to operate the Model 3433 SSPD:

1. Swing out the motor support arm from underneath the stainless-steel capillary delivery tube. Remove the turntable from its support shaft.

2. Using the brush clipped to the inside of the front door, gently brush the powder to be dispersed over one of the annular rings of abrasive paper glued to the upper surface of the turntable.

3. Position the turntable over its support shaft and then gently press the turntable onto the bearing while pulling the spring-loaded lever. The latter action allows the rim of the turntable to rest against the Norprene® tubing mounted on the motor’s drive shaft (see Figures 3-2 and 3-3). The spring has sufficient tension to maintain adequate traction between turntable and drive shaft.

Figure 3-2 Standard Turntable Loaded with Dry Powder, Positioned Over its Support Bearing; at the Same Time, the Spring-Loaded Lever is Pulled to Allow the Rim of the Turntable to Rest Against the Norprene Tubing Mounted on the Motor’s Drive Shaft.


Figure 3-3 Turntable Correctly Positioned on its Support Shaft

4. The turntable support collar has an internal O-ring (Figure 3-4) which is supplied with a light coating of high-vacuum grease. To make the turntable easier to install and remove, it is recommended that the O-ring and support shaft be regreased occasionally with high-vacuum grease.

Note: Only gentle force is required to properly seat the turntable on its support shaft.

Internal O-ring

Figure 3-4 Internal O-ring Located Within the Turntable’s Support Collar

Operating the SSPD 3-5

5. Swing both the motor support arm and turntable underneath the stainless-steel capillary delivery tube (Figure 3-5). There should be minimum clearance between the tube and the surface of the abrasive paper. If not, first adjust the clearance by loosening the No. 1 and No. 2 nuts on the central support column (see Figure 3-6).

6. To move the whole venturi assembly up or down (whichever is needed), adjust the nut located immediately under the lower No. 3 nut; however, do not attempt to loosen No. 3. Once a minimum clearance has been obtained, tighten nuts No. 1 and No. 2.

Figure 3-5 Turntable Positioned Beneath the Stainless-Steel Delivery Tube

7. A spring-loaded plunger is attached to the base plate of the housing (see Figure 3-3). This plunger locates one of the nine detents, three per abrasive ring, found on the underside of the motor support plate. The detents provide preset turntable positions.

8. Powder is removed from the surface of the turntable by opening the restrictor valve and allowing air to flow through the throat of the venturi. This produces suction, which is transmitted through the capillary tube and which pulls up powder from the turntable.

Note: The aerosol is divided between the aerosol output and the filter. (See Chapter 5, “Setting the Flowrate,” for details of this configuration.)


9. The clear air-flushing collar allows dry filtered air to flush the surface of the turntable, independent of the total air flow, and prevents any room-air contamination from becoming entrained with the powder material. Set the sheath air to approximately 4 liters per minute using the sheath-air control valve and associated meter.

10. Select the required direction of rotation and adjust the speed of rotation with the feed rate potentiometer.

Figure 3-6 Schematic Showing the Positions of nuts Nos. 1, 2 and 3 Together with the Adjusting Nut for the Venturi Column Height Located Immediately Under Nut No. 3

C H A P T E R 4

Accessor ies

4-1

This chapter gives information on the optional turntables and alternate motor offered with the Model 3433 Small-Scale Powder Disperser (SSPD) as well as a list of components that can be ordered.

T u r n t a b l e P r e l o a d e d w i t h a R a n g e o f P S L S p h e r e s

This turntable option provides a quick, easy method of calibrating the particle sizer using PSL spheres ranging from 5 to 30 micrometers. Below 5 micrometers, the Constant Output Atomizer (Model 3076) is recommended, with PSL spheres ranging from 0.3 to 2 micrometers. The preloaded turntable (Figure 4-1) is used in exactly the same way as the standard, non-loaded table.

Figure 4-1 Standard Turntable Preloaded with a Range of Polystyrene Latex Spheres (5, 7, 10, 15, 20 and 30 µm)


To produce a preloaded turntable:

1. Use a syringe to remove the PSL particles from their storage bottle and deposit the spheres on the abrasive ring of the turntable.

2. To ensure the spheres are firmly attached to the ring, dry the turntable and the spheres together in a 200°F oven for ten minutes.

When the spheres are needed, loosen a thin layer with a stiff brush.

Note: To avoid contaminating the PSL, ensure you use a clean syringe for each PSL size. Also, use a clean brush when loosening each PSL size from the turntable.

T u r n t a b l e f o r R e d i s p e r s i n g A i r b o r n e D u s t s C o l l e c t e d o n M e m b r a n e F i l t e r s

This turntable option (see Figure 4-2) allows the dispersal and sizing of dust that has been collected on membrane filters commonly used in occupational hygiene studies. The sizing is most readily accomplished with the APS positioned atop the SSPD.

Note: The choice of membrane filter can affect the quality of redispersion. A lattice- or web-type filter matrix does not release particles as easily as a Nuclepore polycarbonate/polyester filter or a Gelman Zelfluor® filter.

®Zelfluor is a registered trademark of Gelman Sciences, Ann Arbor, MI, USA.

Accessories 4-3

Figure 4-2 Turntable for Redispersing Airborne Dusts Collected on Membrane Filters

The redispersing turntable consists of Nuclepore porous plastic (Porex®) support pads (measuring 4 by 25 millimeters and 4 by 37 millimeters in diameter). They are inset into the top surface of the turntable. The Porex pads are covered with a reusable adhesive that allows an appropriately sized, dust-loaded membrane filter to be attached to the turntable. Once attached, the turntable can be mounted in the SSPD and used in the conventional manner to remove a track of dust from the surface of the filter. The dust removed from the filter is dispersed and then sized with an APS. See Chapter 5 for more information on this option.

T u r n t a b l e w i t h T h r e e C o n c e n t r i c V - S h a p e d G r o o v e s

This turntable option allows the dispersal of small, weighed quantities of powder, from 10 to 100 milligrams, at predictable rates. The standard turntable is unsuitable here since the powder cannot be applied to a track that is sufficiently narrow to allow removal by the capillary delivery tube.

®Porex is a registered trademark of Porex Technologies, Fairburn, GA, USA.


However, not all the powder loaded onto the turntable will appear as an aerosol at the output tube. Some powder will inevitably be deposited on the walls and some will be diverted to the Gelman filter capsule. The diversion problem, however, can be virtually eliminated by placing a plug in the bottom of the capsule. A weighed quantity of dry powder is carefully loaded into the appropriate groove or grooves using a razor blade or knife as the packing tool. The loaded turntable is then placed on the support shaft of the SSPD and the powder dispersed conventionally. It is inappropriate to use this turntable to measure the size distribution of a powder, since, by nature, it generates a much higher concentration of powder than the standard turntable. In fact, such a concentration causes coincidence problems within the measurement-sensing zone of the APS.

A l t e r n a t e M o t o r The alternate stepper motor provides a ten-fold increase in the speed of turntable rotation, that is, 2.5 to 33.3 revolutions per hour. To remove the old motor and install the new one, follow these five steps.

1. Withdraw the spring-loaded ball plunger two full turns (Figure 4-3).

2. Loosen the two setscrews that fasten the upper collar to the main support shaft (Figure 4-3); raise the collar as high as possible. In this elevated position, secure the collar by carefully tightening one of the setscrews.

Note: When securing the upper collar, press down very firmly before securing the setscrews. There will probably be some vertical movement in the motor support plate after assembly. Set the spring-loaded plunger to allow for this movement.

Accessories 4-5

Setscrews

(behind upper

collar)

Ball Plunger

Figure 4-3 Location of the Spring-Loaded Ball Plunger and the Two Setscrews That Fasten the Upper Collar

3. Raise the motor support plate to allow access to the four Phillips-head screws that fasten the motor brackets to the plate. Remove the screws with a right-angled screwdriver as shown in Figure 4-4.

Figure 4-4 Using the Right-Angled Screwdriver to Remove the Four Phillips-head Screws That Fasten the Motor Brackets to the Plate


4. Remove the motor support brackets and attach them to the alternate motor.

5. To reassemble, reverse this procedure.

O r d e r i n g P a r t s When ordering parts for the SSPD, refer to Table 4-1. Table 4-1 SSPD Parts List

Description Part Number Standard turntable with three concentric rings of abrasive paper ................................................................. 1030737

Turntable preloaded with a range of polystyrene latex spheres (5, 7, 10, 15, 20 and 30 µm)................................. 1030770

Turntable for redispersing airborne dusts........................... 1030771

Turntable with three concentric V-shaped grooves.............. 1030772

Alternate motor.................................................................. 1030779

Power cable........................................................................ 1303053

APS coupler ....................................................................... 1503317

Model 3533 SSPD instruction manual................................ 1933769

6-inch length of Norprene tubing........................................ 3001168

C H A P T E R 5

Using the SSPD in a Powder S iz ing System

5-1

The SSPD is designed to operate as a powder dispersion accessory to the Model 3310A Aerodynamic Particle Sizer (APS) as (Figure 5-1).

Note: The Model 3310 APS is similar to the original APS (Model 3300) with two major differences:

! The optics chassis of the Model 3310A is user-reversible, allowing aerosol to enter from either above or below the instrument.

! An accumulator board in the Model 3310A improves the coincidence-rejection circuitry.

To upgrade any Model 3300 APS to a Model 3310A, contact your TSI representative.

Figure 5-1 Small-Scale Powder Disperser Configured to Function with the Model 3310A Aerodynamic Particle Sizer


C o n n e c t i n g t h e M o d e l 3 4 3 3 t o a n A P S This procedure describes how to connect the Model 3433 SSPD to the APS. Before you begin this procedure, ensure the capillary inlet tube has been correctly positioned above the turntable (see Chapter 3). To connect the Model 3433 SSPD to the APS, follow these seven steps:

!

C a u t i o n The APS weighs approximately 50 pounds. For safety, it is recommended that this maneuver be carried out with two people.

1. Rotate the APS upside-down and backwards or configure the APS so that the aerosol enters from below (see the APS instruction manual for details).

2. Position the APS on top of the SSPD so that the Plexiglas coupler (supplied with the SSPD) joins the aerosol outlet of the SSPD to the aerosol inlet of the APS.

3. Secure the aerosol outlet tube, leaving approximately 0.6 inch to protrude above the upper chamber of the dispersion column. Figure 5-2 shows the setscrew that retains the outlet tube.

4. Install the Plexiglas coupler over the outlet tube as shown in Figure 5-3, then loosen the retaining setscrew.

Using the SSPD in a Powder Sizing System 5-3

Figure 5-2 Positions of the Setscrews That Retain the Aerosol Outlet Tube (a) and the Upper Chamber to its Support Arm (b)

Figure 5-3 Plexiglas Coupler Installed Over the Aerosol Outlet Tube

5. Install the APS on top of the SSPD so that the APS’s inlet tube gently pushes the SSPD’s outlet tube back into the upper chamber of the SSPD. Figure 5-4 shows the final configuration of the inlet/outlet tubes and coupler.


Figure 5-4 Final Configuration of the SSPD/APS Outlet and Inlet Tubes and the Plexiglas Coupler

6. Align the sides and the back of the bottom of the APS with the sides and the back of the top of the SSPD (see Figure 5-5).

Figure 5-5 Back View of the SSPD/APS Configuration with the Sides and Backs of the Two Instruments in Alignment

Using the SSPD in a Powder Sizing System 5-5

7. Tighten the setscrew that holds the SSPD outlet tube within the SSPD’s upper chamber.

S e t t i n g t h e F l o w r a t e Although the APS demands a flowrate of only 5 liters per minute, a flowrate in excess of 5 liters per minute is required to generate suction within the venturi throat sufficient to lift powder from the turntable. Given these essentially conflicting requirements, the dimensions of the SSPD’s upper chamber and its aerosol outlet tube are designed for nominal isokinetic sample removal at 18.5 liters per minute. This means that when the sample flowrate of the SSPD is 18.5 liters per minute, and the APS is withdrawing 5 liters per minute, the velocities within the upper chamber and the aerosol outlet tube are nominally the same. Use the calibration graph, packed with the instrument, to obtain the Capsuhelic setting that corresponds to 18.5 liters per minute.


C H A P T E R 6

Maintenance, Ca l ibra t ion , and Troubleshoot ing

6-1

This chapter give maintenance, calibration, and troubleshooting procedures for the Model 3433 Small-Scale Powder Disperser (SSPD).

M a i n t e n a n c e The SSPD requires limited maintenance. This section outlines maintenance and cleaning recommendations.

Routine Maintenance ! Because the motor and gearbox run considerably below their

maximum torque output, they should easily provide several thousand hours of operation.

! The turntable support collar has an internal O-ring (Figure 3-4) which is supplied with a light coating of high-vacuum grease. To make the turntable easier to install and remove, it is recommended that the O-ring and support shaft be regreased occasionally with high-vacuum grease.

! It is normal for the motor/gearbox unit to seep a small amount of oil during initial use. Given the orientation of the gearbox, however, oil could find its way onto the Norprene collar. Oil on this collar causes slippage of the motor spindle and the turntable will not rotate. If oil is found on the collar, make a new 3/8-inch long collar from the 6-inch length of tubing provided.

! The Gelman filter used to collect the excess aerosol has a large capacity, and because the SSPD disperses such small quantities of powder, the filter, too, should last for several thousand hours. Obtain replacements directly from Gelman Company (HEPA Capsule, Product No. 12127).

Cleaning Usually the turntable and the small brush can be adequately cleaned with a high-pressure air jet. If you prefer, you may scrub the surface of the turntable under warm running water, then immediately dry it with compressed air.


During use the internal metal surfaces of the SSPD will inevitably become lightly covered with powder. Loosely held powder can be readily removed by fully opening the restrictor valve to allow maximum flow through the dispersion column. This is also the method recommended for cleaning the venturi column between different powder samples. Under a constant flowrate, virtually any powder deposited on the walls will not be reentrained by the air flow. Under extended use, however, it is desirable to thoroughly clean the instrument. Refer to Figures 6-1 and 6-2 and the following five steps.

1. Slide the upper and lower support couplers in opposite directions. This allows the expansion cone to slide out horizontally.

2. Remove the chamber positioned above the expansion cone by removing the setscrew that secures the chamber to the upper support arm.

3. Disconnect the plastic tubing that runs to the Gelman filter. The setscrew is reached from the top of the SSPD once the Plexiglas coupler has been removed (Figure 6-2).

4. Clean the expansion cone and upper chamber with high-pressure compressed air. They may also be washed with a suitable solvent and then dried.

Note: It is recommended that the venturi throat not be removed; see “Calibration” in this chapter

5. To reassemble the components, reverse this four-step sequence.

Maintenance, Calibration, and Troubleshooting 6-3

Figure 6-1 (a) Upper and Lower Support Couplers Shown in Their Regular Positions at the Top and Bottom of the Expansion Cone. (b) Upper and Lower Support Couplers Moved Up and Down, Respectively. (c) The Expansion Cone Can Now be Removed.

Center-

punch

marks

Figure 6-2 Two Center-Punch Marks on the Venturi Throat Aligned with the Lower Support Arm


C a l i b r a t i o n Every SSPD is supplied with a calibration curve that relates the pressure drop across the venturi throat to the flowrate through the venturi throat. By nature, this calibration is approximate and should be used accordingly.

!

C a u t i o n The position of the capillary tube within the venturi throat can affect the calibration. For this reason, handle the capillary tube with care whenever the venturi throat is removed. Once removed, the venturi throat must be replaced in its original calibrated position. To facilitate this, align the two center-punch marks on the outer surface of the throat with the lower support arm (see Figure 6-2).

The four calibration steps used at TSI are:

1. Connect a bubble flowmeter to the aerosol output tube.

2. Place a plug in the bottom of the Gelman filter.

3. Calibrate the Capsuhelic gauge over its working range.

4. Plot the calibration curve. If the capillary tube is disassembled or damaged, you can calibrate the SSPD by connecting a compressed air source to the SSPD, running 18.5 L/min (measured with a bubble flowmeter) through the capillary, and recording the ∆P.

T r o u b l e s h o o t i n g At some point, it might appear that the motor is not rotating the turntable; however, recall that the turntable rotates no faster than 3¼ revolutions per hour or one-quarter of a revolution in just under 5 minutes. To confirm this rate, place a small object on the turntable, a match stick, for example, and time its rotation for a quarter of a revolution. If the turntable does not rotate, check the Norprene collar to see if it has acquired a thin film of gearbox oil. Also, check that the plug on the end of the motor cable is secure in its socket on the PC board.

C H A P T E R 7

Serv ice

7-1

This chapter gives directions for contacting people at TSI Incorporated for technical information and directions for returning the Model 3433 Small-Scale Powder Disperser (SSPD) for service.

T e c h n i c a l C o n t a c t s

! If you have any difficulty installing the SSPD, or if you have technical or application questions about this instrument, contact an applications engineer at TSI Incorporated, (651) 490-2811.

! If the SSPD fails, or if you are returning it for service, contact TSI Customer Service at 1-800-874-2811 (USA) or (651) 490-2811.

R e t u r n i n g t h e C P C f o r S e r v i c e Call TSI Customer Service at 1-800-874-2811 (USA) or (651) 490-2811 for specific return instructions. Customer Service will need this information when you call:

! The instrument model number

! The instrument serial number

! A purchase order number (unless under warranty)

! A billing address

! A shipping address.

M o v i n g t h e S S P D If you are moving the SSPD to another location or returning the SSPD to TSI, be sure that the limiting bumpers are positioned on either side of the motor support plate (see Chapter 2). Failure to do so may cause internal damage.


Use the original packing material to return the instrument to TSI. If you no longer have the original packing material, ensure the connectors on the instrument front panel are protected.

A P P E N D I X A

Speci f icat ions

A-1

Table A-1 gives the specifications for the Model 3433 Small-Scale Powder Disperser.

Note: The specifications in Table A-1 are subject to change without notice.

Table A-1 Model 3433 Small-Scale Powder Disperser Specifications

Output concentration range................ 0.3 to 4.0 mg/m with standard motor 3 to 40 mg/m3 with alternate motor

Powder feed-rate range ....................... 3 to 90 mg/h

Carrier-gas flowrate range .................. 12 to 21 lpm

Particle size range............................... Related to size of powder to be dispersed. Maximum size is approximately 50 µm aerodynamic diameter; particles smaller than 1 µm do not deagglomerate efficiently.

Turntable rotation .............................. 0.25 to 3.3 rph, clockwise or counterclockwise

Maximum filtered air inlet pressure ... 138 kPa (20 psi)

Carrier-gas flowrate (sample flow) at 18.5 lpm Flowrate through venturi throat........ 16.5 lpm Velocity through venturi throat......... 230 m/s Flowrate through capillary delivery tube ............................................... 2 lpm Velocity through capillary delivery tube ............................................... 32.5 m/s

Power requirements............................ 100/120/230/240 VAC 0.5/0.5/0.25/0.25 Amps 50 to 60 Hz at any voltage

Fuse requirements.............................. 100/120V ~ T .5A, 5B/250V 230/240V ~ T 0.25A, 5B/250V

Dimensions ........................................ 386 × 432 × 343 mm (LWH) 15.2 × 17 × 13.5 in.

Weight................................................ 18 kg 39 lbs

Environmental conditions .................. Indoor use Altitude up to 2000 m (6500 ft) Ambient temperature 5–40°C Ambient humidity 0–90% RH noncondensing Overvoltage category II Pollution degree II

A-2 Model 3433 Small-Scale Powder Disperser

A P P E N D I X B

Technica l Paper

B-1

“A Small-Scale Powder Disperser” by:

David B. Blackford, Ph.D. TSI Incorporated P.O. Box 64394 St. Paul, MN 55164

Kenneth L. Rubow, Ph.D. Particle Technology Laboratory University of Minnesota 271 Mechanical Engineering 111 Church Street SE Minneapolis, MN 55455

Presented at World Congress Particle Technology, Nuremberg, West Germany, April 1986. Printed in TIZ-Fachberiche, Vol 110, 10:645 – 655 (1986).

A b s t r a c t A method for dispersing milligram quantities of dry powder using a venturi aspiration technique is described. The new instrument that uses this method is called a Small-Scale Powder Disperser (SSPD). Following dispersion, the aerosol is available for a variety of purposes, ranging from particle size analysis with a suitable particle sensor to the seeding an exposure chamber with experimental drugs for inhalation toxicology experiments on animals. Finally, the operating characteristics of the SSPD are presented.

I n t r o d u c t i o n The use of a venturi aspirator to disperse various dry powders or dusts is not new. To the authors’ certain knowledge, the technique was used over 25 years ago as a method of seeding a wind tunnel for developing and evaluating instrumentation for occupational hygiene studies. (For a description of this disperser, see Blackford and Heighington [1986].) In addition, Leschonski [1985] has described an aspirator-type powder disperser for use with particle size analysis equipment.

B-2 Model 3433 Small-Scale Powder Disperser

The initial operating characteristics for the SSPD were developed by Marple and Rubow [1984] at the University of Minnesota. The SSPD is unique: its design has been optimized to disperse what were impossibly small quantities of powder material. A number of interesting applications has resulted. Small particles have a natural tendency to cling together due to the considerable forces of adhesion that act between them. Generally, the smaller the particle, the greater the adhesive force and the more difficult the problem of dispersion. The adhesive forces that act between particles include van der Waals, electrostatic, magnetic, and forces due to liquid or solid bridges. Of these, van der Waals is by far the dominant one to overcome in dispersing dry powder. While electrostatic adhesion is of no importance in dispersing an agglomerate of particles, electrostatic charging may occur soon after dispersion, resulting in almost immediate reagglomeration, or adhesion, of particles to the walls of the disperser. Therefore, once dispersion has successfully taken place it is essential to keep the particles as far apart as possible. Zahradnicek [1975] concluded that to successfully disperse quartz and limestone particles between 0.5 and 10 micrometers, forces due to high rates of shear and wall impaction were required. To impart sufficient force, air velocities in excess of 100 meters per second should be used. However, there is a disadvantage in using an impaction surface: the resultant stresses tend not only to deagglomerate collections of particles but also to break the particles themselves, resulting in the production of new fine material. This potential source of contamination is undesirable in a powder disperser. It is not used in the SSPD which relies solely on shear forces generated within the venturi throat to ensure the adequate dispersion of dry powders.

Technical Paper B-3

D e s c r i p t i o n o f t h e D i s p e r s i o n T e c h n i q u e U s e d w i t h t h e S S P D

A schematic diagram of the SSPD system is shown in Figure B-1. The powder to be dispersed is gently brushed over the surface of one of three annular rings of abrasive paper which, in turn, is glued to the top of a rotating table (see Figure B-2). Powder is removed from the paper-covered turntable by means of a venturi aspirator and capillary delivery tube. The lower end of the capillary delivery tube is positioned just above an abrasive ring, while the upper end of the tube floats in the throat of the venturi. A region of low pressure is created by the increased velocity of air through the venturi throat which draws flow up through the capillary tube; the tube thus operates like a small vacuum cleaner as the turntable rotates slowly beneath it. The 5-inch-diameter turntable rotates either clockwise or counterclockwise between 0.25 and 3.3 revolutions per hour; this corresponds to an hourly powder feed rate of 3 to 90 milligrams and an output concentration (assuming unit density material) of 1 to 40 milligrams per cubic meter. An alternate motor can provide 2.5 to 33 revolutions per hour with a corresponding increase in output and, of course, reduced operating time. To increase the utility of the powder on each annular ring of abrasive paper, a set of nine detents is used on the lower side of the motor support plate. These detents are located individually with a spring-loaded plunger. In this way, each annular ring has three precisely located sample positions. Of itself, the abrasive paper serves two important functions. First, it provides a rough surface against which to brush the powder and thus promotes the primary breakup of large clumps of powder. Secondly, it does not allow the powder to move horizontally during subsequent powder removal. Only material directly below the capillary inlet is removed. The abrasive paper prevents the powder from breaking off prematurely, which occurs when powder is packed into a more conventional, grooved turntable. The result is a much better control of the powder dispersion rate.


The aspirator has been found to work well under the following operating conditions: Flowrate through venturi throat = 16.5 L/min Velocity through venturi throat = 310.0 m/s Flowrate through capillary delivery tube = 2.0 L/min Velocity through capillary delivery tube = 32.5 m/s

Figure B-1 Cutaway Schematic of the Small-Scale Powder Disperser

Technical Paper B-5

Figure B-2 Turntable Used for Dispersing Dry Powders; Three Rings of Abrasive Paper are Glued to the Upper Surface of the Turntable

To prevent room air from contaminating subsequent use of the dispersed aerosol—a factor that is important for potential pharmaceutical applications—a Plexiglas collar surrounds the capillary delivery tube and flushes the surface of the turntable with an adequate amount of dry filtered air. This flushing air is strong enough to provide a slightly positive pressure at the capillary entrance, but not strong enough to induce a downward velocity that would disturb powder from the surface of the abrasive paper. The aerosol particles are deagglomerated in the venturi throat. Shear forces are generated between the high-velocity gas that passes through the venturi and the low-velocity gas particle stream exiting the capillary tube. The gas stream passing through the venturi throat tends not only to break up the agglomerates (due to the shear forces that result from the near seven-fold difference in velocities), but it also acts as a sheath around the aerosol stream in the throat section, thus reducing particle losses to the walls.


The considerable backpressure caused by forcing air through the venturi throat provides a simple means of monitoring the flowrate through the SSPD. As long as the capillary tube remains unclogged—a reasonable assumption given a flowrate of 32.5 meters per second—the backpressure can be directly related to total flowrate after calibration with a suitable flowmeter. To accommodate the 200 to 250 inches of water gauge generated by forcing air through the venturi throat at near supersonic velocities, the SSPD incorporates a Capsuhelic® gauge that measures up to 300 inches of water gauge. Particles in the size range of 1 to 50 micrometers can be efficiently dispersed with the SSPD. This level of performance has been confirmed by collecting a variety of dispersed powders on microscope slides and evaluating the quality of the dispersion under an optical microscope. Optical micrographs for four different powders—photocopying toner, rice starch, Arizona road dust and coal dust—are shown in Figure B-3. Particles with diameters of 0.5 micrometer and smaller tend to be too tightly held together by van der Waals forces to be overcome by the shear forces experienced in the venturi throat; this establishes the lower working limit. The transportation losses for particles greater than 50 micrometers of aerodynamic diameter determine the upper working limit.

S m a l l - S c a l e P o w d e r D i s p e r s e r U s e d i n C o n j u n c t i o n w i t h a P a r t i c l e S e n s o r

Since the SSPD has been designed to function as an accessory to the Aerodynamic Particle Sizer (APS) [Remiarz et al; 1981], it is possible to determine a powder’s size distribution, according to aerodynamic diameter, over the range of 0.5 to 30 micrometers. The APS measures a particle’s aerodynamic diameter in an accelerating flow field using a laser-based, time-of-flight meas-urement technique. Due to their inertia, larger particles record a longer time of flight and thus have greater aerodynamic diameter. Before the dispersed powder can be sized with the APS sensor, the velocities generated in the venturi throat must be substantially reduced. Moreover, the combined venturi and capillary flowrate of 18.5 liters per minute exceeds the 5 liters per minute required by the APS.

Technical Paper B-7

Figure B-3 Powder Samples Dispersed With the SSPD (a) Photocopying Toner, (b) Rice Starch, (c) Arizona Road Dust, (d) Coal Dust. Scale: 20 µm ¦—¦ Magnification ×200

The velocity reduction is achieved with a fourteen-degree included-angle expansion cone positioned directly above the venturi throat (see Figure B-1). The cone has two parts joined by a sliding coupling to facilitate manufacture and internal cleaning. The flowrate disparity between the disperser and the sensor is accommodated with a nominal, isokinetic, sample-removal tube positioned at the top of the expansion cone. The excess air, at 13.5 liters per minute, can either be exhausted to a high-efficiency, Gelman HEPA capsule filter or it can be used, say, to seed an animal exposure chamber. The combined SSPD/APS are shown in Figure B–4.


Figure B-4 A Powder-Sizing System Including the Small-Scale Powder Disperser and the Model 3310A Aerodynamic Particle Sizer

Technical Paper B-9

T h e S S P D U s e d a s a D i s p e r s e r f o r P o l y s t y r e n e L a t e x S p h e r e s

Polystyrene latex (PSL) spheres are used extensively to calibrate particle size analysis equipment. In this area, the APS is no different from a great many other particle size sensors. A recent terrestrial two-stage swelling process, developed in Norway by Ugelstad (1980) and now manufactured by Dyno Industries AS of Oslo, Norway, has produced a new range of monosized PSL spheres called Dynospheres® measuring up to 20 micrometers in diameter. These spheres are ideally suited for instrument calibration [Blackford, 1986]. In addition, PSL spheres measuring 9.89 micro-meters in diameter have been produced aboard the NASA space shuttle, Challenger, and certified by the National Bureau of Standards. The traditional method of dispersing PSL spheres has been to nebulize the aqueous suspension in which spheres are usually stored using a DeVilbiss-type or Retec nebulizer. Unfortunately, nebulizers have a tendency to produce droplets smaller than 5 micrometers in diameter. Accordingly, the nebulizer output for PSL spheres greater than 5 micrometers dramatically decreases and yields essentially no output for the size range of 10 to 15 micrometers and above. Fortunately, a very simple technique has been found to disperse large PSL spheres with the SSPD. First, a micropipette removes a heavy concentration of PSL spheres from the deposit that accumulates at the bottom of the storage bottle when PSL spheres are left standing. The heavy concentration of spheres is then deposited on one of the annular rings of abrasive paper and allowed to dry in a low-temperature oven. The stabilizers added by the manufacturer of the spheres, along with any other impurities, can first be removed by repeated washing with isopropyl alcohol and then recovered with a centrifuge. However, these additives or impurities result in the generation of particles that are much smaller than the PSL spheres of interest and can usually be easily isolated in a subsequent size analysis.

®Dynospheres is a registered trademark of Dyno Industries A.S., Oslo, Norway.


A semi-stiff brush is now used to release some of the PSL spheres that have lightly bonded to the abrasive paper by the heating and drying process. The turntable loaded with PSL spheres is rotated beneath the capillary delivery tube. In this way, PSL spheres as large as 40.5 micrometers have been successfully dispersed and sized with an APS. Figure B-5 shows an APS size distribution for 15-micrometer Dynospheres dispersed with the SSPD. Figure B-5a gives a mass versus aerodynamic diameter size distribution, while Figure B-5b details the APS Multichannel. Accumulator (MCA) data from which Figure B-5a was calculated. The counts found in channels 257 to 300 are the result of the stabilizers/impurities referred to above.

Figure B-6 shows the MCA data from the APS for two different sources of 10-micrometer PSL spheres. Figure 6a shows the MCA distribution of nominally 10-micrometer Dynospheres, while Figure B-6b shows the 9.89-micrometer NBS standard (PSL spheres) manufactured aboard the space shuttle, Challenger. The NBS spheres clearly exhibit a slightly narrower size distribution.

Technical Paper B-11

Figure B-5 (a) A Distribution of Mass (mg/m3) Versus Aerodynamic Diameter for 15 µm Dynospheres (PSL) Dispersed with the SSPD; (b) Corresponding Multichannel Accumulator Data from which (a) was Calculated


Figure B-6 (a) Multichannel Accumulator Data From an APS for 10 µm Dynospheres (Nominal) Dispersed with an SSPD; (b) Multichannel Accumulator Data From an APS for 9.89 µm PSL Spheres Manufactured Aboard the NASA Space Shuttle and Dispersed with an SSPD


T h e S m a l l - S c a l e P o w d e r D i s p e r s e r U s e d t o R e d i s p e r s e A i r b o r n e D u s t S a m p l e s C o l l e c t e d o n M e m b r a n e F i l t e r s

It is often desirable to use an APS to make a measurement of airborne particles according to aerodynamic diameter, in remote and difficult locations, for example, in coal mines and foundries. However, it may be impossible to bring the necessary hardware into such locations because of the explosion hazard presented by instrumentation that is not intrinsically safe. One solution to this problem is to collect a representative sample of airborne dust on a membrane filter and redisperse the collected sample with the SSPD. To facilitate redispersion, an alternate turntable (see Figure B-7) is required. This turntable consists of porous plastic filter supports, measuring 25 and 37 millimeters in diameter, inset into the top surface of the turntable. Each filter support is covered with a reusable adhesive to hold the dust-loaded filter in position on the turntable. The filter rotates beneath the capillary tube and the tube acts as a small vacuum cleaner, removing a narrow track of dust from the surface of the filter (see Figure B-8).


Figure B-7 Turntable Used for Redispersing Material Collected on Membrane Filters, Shown with Half the Required Number of Porous Plastic Filter Supports

Figure B-8 Membrane Filter Loaded with Coal Dust; Shown with the Clean Track Generated by Rotating the Filter Beneath the SSPD’s Capillary Delivery Tube


The choice of membrane filter can affect the efficiency of redispersion since a lattice- or web-type filter matrix does not release particles as easily as the Nuclepore polycarbonate/ polyester filter or Gelman Zelfluor filter. To investigate the efficiency of redispersion, a precision aerosol divider was constructed. It consisted of an annular filter holder surrounding the inlet nozzle of an APS. The sampled aerosol was isokinetically split into two streams; one passing directly into the APS, the other passing through the annular filter for subsequent redispersion. By keeping the sample transport distances very short, a good sample split with low losses was obtained. Figure 9a shows the results obtained for a sample of coal dust using the aerosol divider. This size distribution was measured by the APS from the direct aerosol stream and saved in memory for subsequent comparison. The corresponding annular filter was removed from the aerosol divider; the dust deposit was redispersed with the SSPD and then sized with an APS sensor. The size distribution for this sample is shown in Figure B-9b. Figure B-9c shows a percentage comparison between B-9a and B-9b, produced by the standard APS software.

Note: The relative concentration of the particles in the redispersed dust is approximately 2 percent of the concentration of the powder in the original dust. The comparison between the two size distributions clearly indicates that the size distribution of the redispersed dust is nearly the same as the size distribution of the original dust.


Figure B-9a Size Distribution of Airborne Coal Dust, Measured with an APS

Figure B-9b Size Distribution of Coal Dust Captured on a Membrane Filter, Redispersed with the SSPD and then Sized with an APS. Note the much lower levels of concentration.


Figure B-9c Percentage Comparison Between (a) and (b). Perfect Comparison Would Produce a Square-Wave-Type Distribution.

R e f e r e n c e s

1. Blackford, D. B. and Heighington, K. [1986], “The Design of an Aerosol Test Tunnel for Occupational Hygiene Investigations,” to be published in Atmospheric Environment.

2. Blackford, D. B. [1986], “The Assessment of a New Range of Large Monosized Polystyrene Spheres and Their Potential as Calibration Material for Particle Size Analysis Equipment,” to be published in Aerosol Science and Technology.

3. Leschonski, K., Röthele, S. and Menzel, U. [1984], “A Special Feeder for Diffraction Pattern Analysis of Dry Powders,” Particle Characterization, 1, volume 4, pp. 161-166.

4. Marple, V. A. and Rubow, K. L. [1984], “Instrumentation for the Measurement of Respirable Coal Mine Dust,” Coal Mine Dust Conference, Morgantown, West Virginia, Oct. 8-10, 1984. Also available from the University of Minnesota, Particle Technology Laboratory, Publication No. 542.


5. Remiarz, R. J., Agarwal, J. K., Quant, F. R. and Sem, G. J. [1981], “Real-Time Aerodynamic Particle Size Analyzer,” Vol. 3, “Instrumentation,” Proc. Int. Symp. on Aerosols in the Mining and Industrial Work Environment, Minneapolis, edited by V. A. Marple and B. Y. H. Liu, Ann Arbor Science, Michigan, pp. 879-895.

6. Ugelstad, I., Mosek, P. C., Kaggerud, K. H., Ellingsen, J. and Berge, A. [1980], “Swelling of Oligomer-Polymer Particles. New Methods of Preparations of Emulsions and Polymer Dispersions,” Advances in Colloidal Interface Sciences, 13, pp. 101-140.

7. Zahradnicek, A. [1975], “Methods for Generating Aerosols from Solid Powder Material,” in German, Staub-Reinhaltung Luft, 35, pp. 226-231.

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Documents

Model 3433 Small-Scale Powder Disperser Instruction … Overview 1 Model 3433 Small-Scale Powder Disperser Unpacking and Setting Up 2 Instruction Manual Operating the SSPD 3 Accessories