Compression Molding Guidelines

8/13/2019 Compression Molding Guidelines

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3/10/2010 Chemiplastica 1

Thermoset Processing Manual

Compression Molding


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3/10/2010 2Chemiplastica

General Overview


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Description

Urochem-Compounded from Urea FormaldehydeResin, Cellulose Filler, Pigments, Flow Promoters

,lubricants Melochem- Compounded from Melamine

Formaldehyde Resin, Cellulose Filler, Pigments, FlowPromoters ,lubricants

Fenochem- Compounded from Phenolic Resin, organicand inorganic fillers, Pigments, Flow promoters,Lubricants


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Material Properties

Flow-Measures how fluid and soft material is.Lower Number= Easier Flow.

Cure Value- Measures how fast material is

formed into a Blister Free Part . Density- Measurement of weight per volume.

Good data for charge weight considerations.

Typical Urochem range 64 +/- 4 grams/100 cc.


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SAFETY FIRST

Guide to Safety

Around The PressAnd Machinery


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Ten Commandments of Safety

Safety Glasses & Ear Protection

No Loose clothing, Neckties/Necklace outside clothing

Turn off all electrical switches when investigatingmalfunction

Never use Compressed air Gun

to clean hands or clothing


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Ten Commandments of Safety

Know Location of Fire Extinguisher

Do not tie down or Block Safety Switch

Do not reach around or remove safety guards

Before starting press Make sure all people are clear of movingparts

Maintain good housekeeping and avoid dust collection


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Thermoset Molding

TermsCompression

Molding


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Terms & Definitions

Blister Raised Section in molded partGas Trap

Under cure or overcure

Breathe (Degassing) Opening and closing of mold toallow escape of gas

Cavity Part of mold which forms outersurface of molded part

Charge Amount of material required to fill

cavity

Charging The Mold Placing required amount in mold.Only automatic at CWD.


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Terms & Definitions

Cure Time required to polymerize to ahard blister free surface under heatand pressure

Cycle Time it takes to complete oneoperation

Loading and close of moldBreathe cycle

Open and discharge of parts

Draft Amount of taper on side ofmold/molded part for easy removal

Ejector Pins Steel pins in cavity or force forremoval of parts


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Terms & DefinitionsFamily Mold A multi-cavity mold containing

several cavities of different sizes andshapes

Flash The excess material that flows out ofthe mold cavity under pressure

Guide Pins Pin or bars in mold to assure properalignment of mold halves

Parting Line Part of mold which provides the cut-off of the flash from molded part

Plasticity/Flow Term to describe degree that materialflow under heat and pressure


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Terms & Definitions

Platens Top and bottom plates on press towhich mold halves are bolted

Polymerization Chemical reaction that starts withclosing of mold and ends with cure

of part

Pressure Pads Steel blocks outside cavity whichmeet during mold closure to preventtooling contact at parting line

Vent Small channels of groves to allow airand gas to escape during molding


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Material Handling

Storage and Rotation


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Material Handling

Store material in cool, dry place

First in first out (limited shelf life)

Verify material before loading

Use single batch at a time Avoid mixing batches

Avoid contamination

Avoid pressurized air for cleaning Maintain good housekeeping

Shield presses running light colors from dark colors


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Compression Molding

General Overview


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Compression Molding Molding of thermoset plastic using a compression

press Two halves of mold brought together under high

pressure

Mold is heated at 290-350F depending on material

Application of required breathe cycle

Temperature and pressure cause material to melt andflow into spaces between cavity and force

Material is set and ejected after appropriate cure time


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Compression Press

Molding press consisting of hydraulic ramhoused in large cylinder

Cylinder located at bottom for upward acting

press and in the top for downward Hydraulic pressure drives ram with platen and

mold halves attached

Force is applied depending on size of mold andoutput size of press


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Press Controls

Understand function of all controls, buttons,switches prior to operating press

Always be aware of the location of emergencybutton/controls

Never touch any unfamiliar controls

Always use safety devices


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Compression Molding

ProcessStep-By-Step Start Up Guide


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STEP ONE

Verify double load safeties are functional&Properly set. This ensures molding processremains in low pressure until the mold closes to

the proper position. If there is a part or foreignobject stuck in the mold, the press cannot closeto safety position and go into high pressure.These safeties are actually part of the molding

process


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Step TWO

Check mold temperature with pyrometer

290 to 310F for urea

5 to 10 degrees lower in cavity part

Check that temperature is even across cavities andmake adjustments.

If temperature is not correct, contact supervisor toensure thermocouples are properly working

Maintaining correct temperature is essential to qualityand workmanship


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STEP THREE

CLOSE MOLD EMPTY AND CHECK TOENSURE PSI IS WITHIN ACCEPTABLELIMITS.

25 Ton: 90 PSI Minimum 75 Ton: 2500 PSI Max and

lower on someoperations

150-300 Ton: 1000 PSI Maximum


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STEP FOUR

Check standards for cure time specified forpart

Charge Material

Close Press and hold closed at specifiedcure time

No Breath


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STEP FIVE

Open Mold and Check Molding for uniformFlash

If Heavy, Reduce weight

If Short, add weight

Repeat Steps Three and Four until you aresatisfied visually and based on experience that

you have correct weight


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STEP SIX

Finalize Weight by referring to standard weight specified foreach part using accurate scale to weigh parts Allowable limit of +/- 7%

Make adjustments based on loading board capability

Bolt and screw Insert

Check all cavities for uniformity

If flash heavy but weight is correct recheck temperature &pressure

If still heavy try softer batch

Correct weights are key to quality and waste control


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STEP SEVEN

Adjust cycle for good densified, bright, gas free, blisterfree parts

Know your material and choose settings based on

experience Traditional setting

Initial closing of press followed by one or two breath.Optimal breath spacing based on set up trial

Stop & Go setting Initial STOP for preheating of various duration followed by

press closing and perhaps short early breath.


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STEP EIGHT

Finalize cure by referring again to part standardas a guide

Adjust until you have blister free part

Add five to ten seconds to insure continuousblister free operation.

Beware that over curing can cause warpage,

brittleness and discoloration Maintaining optimal cycle is key to productivity

and profitability


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Common Quality Defects

Blister

Short Shots

Porous Parts Orange peel or

wrinkly surface

Gas Burns Gas Blush

Low Gloss

Warped Parts

Contamination

Molded in Flash Heavy or thick Flash

Broken parts

Off Color Parts Excess flash


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Trouble Shooting Techniques Temperature uniformity is Key. Always check with a

pyrometer

Note cycles, cavity layout and settings prior totrouble shooting

Watch out for any unusual and erratic occurrences One change at a time

Choose type of cycle and stick to process guidelines

Use the trouble shooting guide Check all possible causes including material, tooling,

equipment and operator set up.

Documents

Compression Molding Guidelines