Surlyn® Troubleshooting Guide

Surlyn® Troubleshooting Guide
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Surlyn Troubleshooting Guide and Mold Preparation
Checklist
®
Surlyn® -- Troubleshooting Guide
Problems
Possible Causes
Possible Solutions
Sprues breaking off-sprues
sticking, disrupting cycle
Short "hold" cycle
Cold nozzle
Increase "hold" time
Check heat source and controller
for malfunction
Poor cooling around sprue bushing Increase cooling to plate containing
sprue bushing
Long Sprue with improper draft
Rework bushing to recommended
size
Fastener failures on bending
immediately after molding
Low melt temperature
Excessive fill rate
Thin wall thickness
Weak weld lines on fastener
Increase "actual" melt temperature
Decrease ram speed
Rework tool to increase wall
See weld line solutions
Fastener failures on installation
Sharp angles on internal ribs that
create notch failure
Weld line weakness in fastener wall
Undersized hold
Oversized fastener
Add radii to all internal comers
Flash on runners
Cavities too far above cavity plate
"Rolled over" runner edges
High injection pressure
Low clamp pressure
Rework tool to lower inserts
Rework cavity plates
See parting line flash solutions
See parting line flash solutions
Weld lines
Low melt temperature
Poor venting
Slow fill rate or flow restriction
Check heat source
Clean existing vents
Add vents to increase fill rate
Check rate speed, increase gate size
Non-uniform wall dimension on
fastener
Bent core pin
Core pin misaligned with cavity
Thin wall thickness
Replace, change to harder metal
Retool
Rework mold to increase wall
thickness
Parts too shiny
Improper matte finish
Low melt temperature
Sandblast
Check heat source
Use recommended melt
temperature
Check mold heater
Use recommended mold
Low mold temperature
See weld line solutions
Check receptacle specification
Check retainer specification
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temperature
Problems
Possible Causes
Possible Solutions
Parts vary in size, shot to shot
Faulty check ring
Interrupted cycles due to part
sticking sprue sticking, nozzle
freeze off
Measure ring for wear
Spray mold and sprue with release
agent, increase nozzle temperature
Excessive flash on fasteners
High injection pressure
Lower injection pressure
Refer to recommended pressure
Poor tooling, worn mold
Mold hot spot
Rework tool
Check coring for circulation
Replace inserts with high heat
dissipating metal
Part weight varies shot to shot
Faulty check ring
Faulty temperature controller
Erratic screw feed (bridging)
Poor tooling
Wet or excessive regrind
Replace ring
Repair or replace controller
Check for cooling water on hopper
Match fit to eliminate flashing
Use regrind same shift
Keep regrind ratio below 50%
Variation in part shrink-post
molding (poor fit to standard
fixture)
Melt temperature change
Mold temperature change
Unbalanced resin flow to multicavities
Check temperature controls
Check mold cooler
Standardize resin flow to cavities
Variation in dimension change
High injection pressure
Low injection pressure
Faulty check ring
High melt temperature
Low melt temperature
Check hydraulic controls
Replace if worn
Check heat source controllers Look
for excessive back pressure
Check heater bands and "actual"
melt temperature
Shiny area on part surface
Condensation
Contamination from mold release
Cold spots in mold
Poor venting
Raise mold temperature
Clean mold cavity
Check for uniform mold coring
Open vent in trouble area
Splay on surface
Moisture in resin
Contamination
Dry resin
Purge until splay disappears
Clean barrel if necessary
Problems
Possible Causes
Possible Solutions
Sink marks
Thick cross-section, low injection
pressure
Retool-using ribs
Check hydraulic controls
Add foaming agent
Recheck molding parameters
Increase gate size
Add vents to cavity ends or in
vicinity of sink
Clean existing vents
Fill more slowly
Add time-refer to checklist
Adjust feed setting, check capacity
of barrel
Poor gate design
Poor venting
Inadequate ram forward time
Not enough material
Excessive flash on parting line
Poorly tooled cavities
Low clamp pressure
Worn cavities
High injection pressure
Hot mold
Rework mold
Check hydraulic setting
Set relief valve higher
Rework mold
Check relief valve operation
Check mold heater setting
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Part deformation on ejection
Short "hold" cycle
Cavities over-filled
High mold temperature
Warpage near gate area
Excessive gate area
Excessive injection pressure
High fill rate
High melt temperature
High mold temperature
Corrosion of equipment or
tooling
Mild steel surface
Wet resin
Increase "hold" cycle
Decrease pressure
Use mold release spray
Check relief mold heater
Increase cooling water
Check coring circulation
Slow ejector pins
Rework tool to recommended size
Check pressure setting
Decrease ram speed
Check heat source and controllers
Lower controller setting
Check mold heater
Increase cooling water
Check coring circulation
Stainless steel or other corrosionresistant alloys are recommended
Pre-dry resin if moisture content is
above 0.1%
Surlyn® Mold Preparation Checklist
Introduction
The first and generally most critical step in molding parts of Surlyn® resins is proper tool design.
This checklist is designed to provide a quick reference source in reviewing the plans of new or
modified tool design. For more detailed information, see the PART AND MOLD DESIGN
MANUAL for Surlyn® resin, available from your DuPont Industrial Polymers marketing
representative or district office.
Sprue Bushing
z
z
z
z
Should be as short as possible.
Should have 0.75 in. taper/foot (6.2cm, taper/m.) (3° included angle) with sprue opening
equal to main runner diameter.
Should contain a generous radius into main runner.
Should have all internal surfaces sandblasted for easier release.
Runners
z
z
z
z
Should be full round, 0.200 in. (0.5cm.) diameter initially; add 0.062 in. (0.16cm.) for each
right angle turn. Do not exceed 0.375 in. (1cm.)
Should have all dead ends vented.
Should have a radius at all intersections.
Should be laid out so each cavity receives equal pressure to insure identical fill pattern.
Gates
z
z
z
z
Should have a fan or edge for minimum warpage and shorter molding cycle. Both entrance
and exit should flare into cavity Always cut with a minimum land of 0.050 in. (0.13 cm.) and
set opening initially at 0.050 in. thick x 0.750 in. (1.9 cm.) wide. Increase as needed to fill
cavity
Should be located on cavity-end, when possible.
If side-gated, should be cut into cavity wall at an angle to avoid jetting across cavity
Should begin with a single gate, with option to cut in additional gates every 12 in. (30cm.).
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Cavities
z
z
z
z
Should be liquid or air-blasted with an abrasive (i.e. aluminum oxide) for matte finished
parts. Grit size and total treatment time dependent on metal hardness.
Should have maximum wall thickness no greater than 0.250 in. (0.6 cm.). Radius all
intersections with a minimum of 0.015 in. (0.04 cm.).
Should contain rib thickness of one-half to two-thirds of main wall thickness. Radius all
intersections a minimum of 0.015 in. (0.04 cm.).
Should have fastener walls with a minimum thickness of 0.060 in. (0.15 cm.) and supporting
ribs from the cavity bottom. Radius all intersections.
Vents
z
z
z
z
Vents are needed at all dead ends, opposite all gates, and in the vicinity of all weld lines.
Preferably peripheral venting of cavity runner is suggested.
Runners-size vents to 0.0015-0.002 in. (0.04-0.05 mm.) deep over runner width. Use land
length of 0.032 in. (0.8 mm.) and increase vent depth beyond land ending to 0.032 in. (0.8
mm.). Carry channel to atmosphere.
Cavities-size vents to 0.0015-0.002 in. (0.04--0.05 mm.) deep and 0.250 in. (0.6 cm.) wide.
Same details for land. Carryout channel as runners.
Pins-grind vents to 0.0015-0.002 in. (0.04-0.05 mm.) flat or slot on pin for 0.250 in. (0.6
cm.). Open to 0.032 in. (0.8 mm.) beyond and carry to atmosphere.
Mold Cooling
z
z
z
Core the cavity side with a series of small channels, 0.437 in. (1.1 cm.) in diameter. Locate
no further than one diameter distance from the cavity surface.
Locate adequate cooling cores in the vicinity of all runners and the sprue bushing.
Use high thermal conductivity metals (beryllium, copper, etc.) where coring is not possible,
particularly in core pins that are not water cooled.
Materials of Construction
z
z
Stainless steel or other corrosion-resistant alloys are recommended. Older machines may be
attacked if they have mild steel parts.
Use of excessively wet resin accelerates the corrosion rate of mild steel.
Surlyn® Checklist for Processing Conditions
Be sure to check the following:
z
z
z
z
z
z
z
z
z
z
z
Water cooling on hopper throat is functioning
Maximum rear zone temperature is 350°F (175°C)
Melt temperature is 460°F (238°C)* (as verified by pyrometer)
Injection Pressure is 10-12,000 psi nominal* (700-850kg/sq. cm.)
Fill rate is 5 to 8 sec *
Pad (positive cavity pressure) is 0.325 in. (8 mm)
Injection forward time is 40 sec. ± 5 (For 0.125 in. (3 mm) part thickness)
Hold cycle time is 20 sec. ± 10 (For 0.125 in. (3 mm) part thickness)
Back pressure is 50-200 psi (3-14 kg/sq. cm.)
Mold temperature is 60°F ± 10°(15°C ± 5°)
Resin is dry
* Adjust as needed-only guidelines
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Safety
As with any hot material, care should be taken to protect the hands and other exposed parts of the
body when handling molten polymer. At temperatures above 250°C (482°F), Surlyn® resins can
evolve low concentrations of fumes. It is recommended that adequate ventilation be provided. For
more detailed information on the safe handling and disposal of DuPont ethylene resins, OSHA
material safety data sheets and a Product Safety Bulletin can be obtained from the sales
representative serving you.
Protective covering should be worn since molten resin is very tacky and will stick to the skin.
©1999 DuPont Company.
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The technical data contained herein are guides to the use of DuPont resins. The advice contained herein is based upon
tests and information believed to be reliable, but users should not rely upon it absolutely for specific applications
because performance properties will vary with processing conditions. It is given and accepted at user's risk and
confirmation of its validity and suitability in particular cases should be obtained independently. The DuPont Company
makes no guarantees of results and assumes no obligations or liability in connection with its advice. This publication is
not to be taken as a license to operate under, or recommendation to infringe, any patents.
CAUTION: Do not use in medical applications involving permanent implantation in the human body. For other
medical applications, see "DuPont Medical Caution Statement", H-50102.
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