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8/13/2019 Compression Molding Guidelines
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3/10/2010 Chemiplastica 1
Thermoset Processing Manual
Compression Molding
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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.
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