Block 16 Drum Plants 13

Drum PlantsConstruction 1

HMA Production

Senior/GraduateHMA Course


What you will learn….

• How gradation is controlled in a drum-mixer• How asphalt is controlled in a drum-mixer• Different styles of drum-mixers• Using RAP with a drum plant


Drum-Mix Production

Hot Mix Asphalt production characterized by:

• Gradation Control at Cold Feed• Measure aggregate flow with belt scale• Meter asphalt binder to aggregate flow• Produce HMA continuously



Cold Feed Proportioning

Composite gradation is controlled at cold feed by proportioning material from individual bins.

Gradation and quality of the individual materials is controlled at the quarry.




Variation in material flow from individual bins:

• Based on variable speed motor on belt• Adjustable manual gates help control

minimum and maximum flow



• Accomplished by calibrating the feeders• Material output is charted against belt speed

in calibration charts• Different charts are created for different gate

settings on the same feeder



Cold Feed Gradation Control

Many styles of feeder controls found in field.

All can perform satisfactory proportioning.



Asphalt Binder Proportioning

Asphalt binder must proportion to aggregate flow.

First step in asphalt binder proportioning is measuring aggregate flow.

Belt scale is used.



How a Belt Scale Works

• Weigh bridge measures weight of aggregate.• Speed sensor measures speed of belt.• “Integrator / Totalizer” calculates aggregate

flow in ton (tonnes) per hour• “Integrator / Totalizer” reports flow rate to

plant control system




Asphalt Binder Proportioning

Asphalt binder must proportion to aggregate flow.

Second step is regulating asphalt binder flow.

Asphalt binder pumping / metering unit is used.




How the Asphalt Binder Proportioning System Works

• Controls system reads wet aggregate flow from belt scale.• Controls accepts moisture content entered by operator to

establish dry flow rate of aggregate• Control system accepts target asphalt content entered by

operator.• Control system drives pumping/metering unit flow control

device.• Control system adjusts asphalt binder flow control system

based on signal received back from meter



Plant Automation

Many types of systems and levels of complexity found in the field.



Drum-Mix Plant Calibration


Step 1 - Calibrating Belt Scales


Step 1 - Calibrate Belt Scale

• Verify belt scale reads zero per manufacturers guidelines

• Set the cold feed gates at an opening that will allow a good material feed

• Start main conveyor belt• Run the variable speed belt feeder for the coarse

aggregate bin - about 50% of desired production rate• Record the belt feeder speed and weight indicated on

the belt scale.


Step 1 - Calibrate Belt Scale (cont.)

• Stop belt and remove a six foot section of material from the conveyor

• Weigh the material removed• Repeat process to get an average of two weights• Adjust instrument so that it reads correctly


Example

• Conveyor is run at 225 feet per minute• Run the belt feeder until the digital readout reads 90

tons per hour• Weight of material on a six ft section of belt = 76 lbs

and 78 lbs for an average of 77 lbs


Example - cont.

• Determine the aggregate weight in lbs per minute.WR r

where Q = weight of aggregate, lbs/min

W = wt of agg measured, lbs

R = speed of belt

r = length of belt from which material was removed

Q =


Example - cont

• Therefore the aggregate weight in lbs/min is:

q = WR/r = 77 x 225 = 2887.5 lbs/min

• To convert to tons per hour (q x 60)/2000

2887.5 x 60 = 86.63 tph < 90 tph

6

2000


Example - cont

• Adjust instrument per manufacturer’s guidelines so that next test it reads 86.63

• Repeat test, adjust, until two consecutive readings are within acceptable tolerance

(Unlike batch plant no department spec on this scale tolerance - because mix purchased from silo weigh tickets)


Step 1 - AlternateCalibrating Belt Scale

• Verify belt scale reads zero per manufacturers guidelines

• Set the cold feed gates at an opening that will allow a good material feed

• Start main conveyor belt• Run the variable speed belt feeder for the coarse

aggregate bin - about 50% of desired production rate• Starting with empty belt run material in tared truck

and stop material flow to end with empty belt


Step 1 - AlternateCalibrating Belt Scale

• Record the total weight indicated on the belt scale.• Compare weight total on belt scale with actual weight

on truck.• Following manufacturers guidelines, adjust belt scale

instrument based on weight difference.• Repeat test, adjusting instrument, until two

consecutive tests are within tolerance.


Example

• Start belt scale and verify reads zero• Tare empty truck at 22,375#• Record belt scale totalizer at 437897.65• Start feeder at approximately 50% flow • Fill truck and stop and empty belt• Record belt scale totalizer at 437906.87• Calculate tonnage on scale at 9.22 tons (437906.87 -

437897.65 = 9.22 tons)


Example - cont.

• Weigh truck at 41,401#• Calculate weight in truck at 9.51 ton (41,401- 22,375

= 19,026 ÷ 2,000 = 9.51 ton) • Recall “span” value of instrument at 897654• Adjust span value by 1.0314 (9.51 ÷ 9.22 = 1.0314)• New span value = 925,840 (897654 x 1.0314 =

925,840)• Re-test, re-adjust, until two tests pass


Asphalt Binder Distribution in Drum-Mix Plants


Asphalt Binder Distribution

Understanding asphalt binder distribution…..

• Calculating Flow Requirements• Calibrating Asphalt Binder Meter


Asphalt Binder DistributionCalculating AC Flow

Need to know the number of gallons/minute of asphalt binder that is to be delivered

R = P x T x 2000 x 1

Where R = asphalt binder to be delivered, gpm P = optimum asphalt binder

T = production rate, tons per hourW = unit weight of asphalt binder (typically about 8.4 lb/gal)

W 60100


This example, Asphalt Binder target is 6.0% of 200 tons per hour

R = P x T x 2000 x 1

Where R = asphalt binder to be delivered, gpm

P = 6

T = 200

W = 8.4

W 60

Example – Asphalt Binder Flow Required

100


This example, Asphalt binder target is 6.0% of 200 tons per hour

R = 6 x 200 x 2000 x 1

Where R = asphalt binder to be delivered, gpm

P = 6

T = 200

W = 8.4

8.4 60


100


This example, Asphalt Binder target is 6.0% of 200 tons per hour

R = .06 x 200 x 238.095 x .0167

R = 47.71 gpm



QUESTIONS ?

Documents

Block 16 Drum Plants 13