Mold-Masters Hot Runner User manual

Hot Runner User Manual
Hot Runner
Troubleshoong Guide
version 1
Original Instrucons

Table of Contents
Section 1 - Troubleshooting ............................................1-1
1.1 Moisture Related Issues .....................................................................................1-1
1.1.1 Resin Moisture Contamination...................................................................1-1
1.1.2 Resin Drying Issues...................................................................................1-1
1.1.3 Importance of Pre-Drying Resin ................................................................1-2
1.2 Pre-Molding Precautions ....................................................................................1-2
1.2.1 History........................................................................................................1-2
1.2.2 Material......................................................................................................1-2
1.2.3 Hardware ...................................................................................................1-2
1.2.4 Settings......................................................................................................1-3
1.3 Establishing Root Cause ....................................................................................1-3
1.4 Fault Identication ..............................................................................................1-3
1.5 Defect Types, Causes and Remedies Index ......................................................1-4
1.6 Troubleshooting Typical Problems......................................................................1-5
1.6.1 Dark Specks ..............................................................................................1-5
1.6.2 Blisters or Bubbles.....................................................................................1-6
1.6.3 Flow Marks ................................................................................................1-7
1.6.4 Burn Marks ................................................................................................1-8
1.6.5 Delaminating Parts ....................................................................................1-9
1.6.6 Dimensional Irregularities ........................................................................1-10
1.6.7 Discolored Parts ......................................................................................1-11
1.6.8 Flash........................................................................................................1-12
1.6.9 Jetting ......................................................................................................1-13
1.6.10 Pitted Parts ............................................................................................1-14
1.6.11 Rough Surface .......................................................................................1-15
1.6.12 Parts Sticking to Cavity..........................................................................1-16
1.6.13 Parts Sticking to Core............................................................................1-17
1.6.14 Short Parts.............................................................................................1-18
1.6.15 Sinks or Voids........................................................................................1-19
1.6.16 Splay......................................................................................................1-20
1.6.17 Streaks...................................................................................................1-21
1.6.18 Stringing.................................................................................................1-22
1.6.19 Warped Parts.........................................................................................1-23
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Hot Runner Troubleshooting Guide
© 2020 Mold-Masters (2007) Limited. All Rights Reserved.

Section 1 - Troubleshooting
WARNING -HOT SURFACES
Extreme heat. Avoid contact with heated surfaces. To avoid serious burns
wear safety clothing consisting of a protective heat resistant coat and heat-
resistant gloves. Use adequate ventilation for fumes. Failure to do so can
result in a serious injury.
WARNING -LOCKOUT / TAGOUT
Make sure the machine has been locked out and tagged out in accordance
to the machines documented procedures. Failure to do so may lead to
serious injury or death.
This troubleshooting information assumes that the Hot Runner has been
operational.
Basic rules for troubleshooting are:
• Dene the problem; what is seen is only a symptom of the underlying
problem.
• Develop a method to isolate the problem.
• Test one item at a time to verify results.
• Monitor the nal solution to verify that the problem has been solved.
Repeat occurrences of the same symptom may indicate other problems.
• Document the solution so that a repeat occurrence can be solved quickly.
• Consult other resources to augment the troubleshooting information in
this manual. One of the best resources may be your resin supplier.
1.1 Moisture Related Issues
Many common molding issues can be directly attributed to moisture
contamination of the production resin. Generally, manufacturing resin
is supplied from the manufacturer in ready to process pellets that are in
sealed, airtight containers. Follow manufacturers storage instructions,
keeping containers sealed until ready to use. Prior to using pellets, follow the
drying instructions, as provided by the resin supplier and molding machine
manufacturer, if applicable.
1.1.1 Resin Moisture Contamination
Moisture can be introduced into the resin in many ways:
• During transportation
• Environmental exposure (aging)
• Malfunctioning heater / dryer
• Extreme humidity in atmosphere
• Inadequate or malfunctioning facility HVAC
1.1.2 Resin Drying Issues
During the drying stage of the resin (if applicable), ensure that:
• The resin pellets are not overpacked
1-1TROUBLESHOOTING
Hot Runner Troubleshooting Guide
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• Adequate air circulation is present
• The drying system is properly sealed, according to manufacturers
instructions
1.1.3 Importance of Pre-Drying Resin
Thermoplastic resins can be hygroscopic, able to absorb moisture from the
air. Under normal processing conditions, this can lead to degradation of the
polymer during molding. Breakage of polymer chains changes the properties,
resulting in possible blisters, streaks, splay or other defects described in this
section.
Recycled resins can have higher hygroscopic properties due to greater
surface area and should be dried separately from fresh resins.
If moisture issues are ruled out, continue with the troubleshooting tables in
the following pages.
1.2 Pre-Molding Precautions
Prior to commencing production, ensure that the following conditions have
been met. This will greatly reduce any future need to troubleshoot defective
production.
1.2.1 History
• Review any documentation associated with your batch job regarding
the recipe using the mold, molding machine, thermoplastic resin,
environmental setting, etc.
• Review comments, notes, logbooks, blogs, and anything other resource
material that pertains to the batch job.
• Verify that all settings such as all time, temperature, pressure, material,
etc. are correct.
1.2.2 Material
• Ensure that the thermoplastic resin to be used is the right grade, and has
been stored and / or prepared/dried, etc, according to manufacturer’s
specications.
• Verify that the pigment / dye to be used meets manufacturer’s
specications, and is compatible with the resin / molding machine / mold.
• Verify the correct recycle ratio and adjust settings accordingly.
1.2.3 Hardware
• Make sure the mold has been properly stored, and is dry, clean, free of
rust, dirt, moisture, residual resin, pigment and any protective coating.
• Check that the temperature controller meets requirements, and is fully
1-2
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TROUBLESHOOTING
Hot Runner Troubleshooting Guide

tested and operational.
• The injection molding machine has been properly maintained, cleaned,
lubricated; tolerances and dimensions veried.
• Make sure that the nozzles, cylinders, valves, gates, and any other
variable that is appropriate for the batch job has been chosen.
1.2.4 Settings
Ensure that all batch job parameters are correct:
• Temperatures
• Pressures
• Injection Speed
• Back Pressure
1.3 Establishing Root Cause
This section is to be used as a reference tool only.
When a system that has been set up according to specication and was
functioning normally suddenly produces sub-standard parts, the data in
the following pages may be used to determine the possible cause, but only
should be used as a guide.
A correct set up procedure that has been proven in will produce parts
that meet design tolerances and specications. A sudden change in any
parameter indicates a possible fault. Rather than modify other settings to
compensate for this variation, it is advisable to determine which of the original
settings has changed.
1.4 Fault Identication
The operator will need to evaluate all the possible conditions which may have
caused the defect.
• Identify the problem
• Determine the frequency
• Is the problem random or in the same location
• Review past history logs for similar occurrences and resolutions.
Review the machine settings to ensure that there is no variation from the
original set-up which was producing standard parts.
injection speed melt heating
screw speed locking
melt temperature cushion
back pressure mold heating
For a more thorough analysis of the defect, refer to the Troubleshooting
Section in the following pages.
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Hot Runner Troubleshooting Guide
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1.5 Defect Types, Causes and Remedies Index
Dark Specks ..............................................................................................19-5
Blisters or Bubbles.....................................................................................19-6
Flow Marks ................................................................................................19-7
Burn Marks ................................................................................................19-8
Delaminating..............................................................................................19-9
Dimensional Irregularities........................................................................19-10
Discolored................................................................................................ 19-11
Flash........................................................................................................19-12
Jetting......................................................................................................19-13
Pitted Parts..............................................................................................19-14
Rough Surface.........................................................................................19-15
Parts Sticking to Cavity............................................................................19-16
Parts Sticking to Core..............................................................................19-17
Short Parts...............................................................................................19-18
Sinks or Voids..........................................................................................19-19
Splay........................................................................................................19-20
Streaks ....................................................................................................19-21
Stringing ..................................................................................................19-22
Warped Parts...........................................................................................19-23
Weld Lines...............................................................................................19-24
1-4
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Hot Runner Troubleshooting Guide

1.6 Troubleshooting Typical Problems
1.6.1 Dark Specks
The nished product contains dark specks. Usually occurs when transparent
resins are used.
Probable Cause:
1. Molding Machine
• O󰀨-line for extended period
• Barrel o󰀨-line for extended period
• Barrel improperly purged
• Contamination in plasticizer
• Wrong nozzle
• Use of wrong screw
2. Mold
• Gate and / or runner has dead spots
3. Material
• Physical contamination of raw material
• Chemical contamination of raw material
• Particulate contamination from machine barrel
Solution (in sequence):
1. Purge system with appropriate material
2. Trace source of contamination and repair, remove or discard
3. Adjust melt temperature if necessary
4. Inspect for dead spots: gates, runners, nozzle, back ow valve
5. Inspect feed screw for degradation
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Hot Runner Troubleshooting Guide
© 2020 Mold-Masters (2007) Limited. All Rights Reserved.

1.6.2 Blisters or Bubbles
The nished product contains small gas or air lled pockets or cooling voids.
Probable Cause:
1. Molding Machine
• Low injection pressure
• Back ow valve malfunctioning
• Decompression cycle too long
• Rapid plasticizing
• Trapped air in feed
• Feed error
2. Mold
• Trapped or volatile gas
• Low mold temperature
• Poor thin/thick transition phase
• Inadequate venting
3. Material
• Overheating of resin
Solution (in sequence):
1. Verify control and / or holding pressure
2. Increase back pressure
3. Increase mold temperature
4. Inspect back ow valve
5. Ensure proper venting
6. Increase gate size
7. Decrease vent land length
1-6
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Hot Runner Troubleshooting Guide

1.6.3 Flow Marks
The nished product exhibits blush and ow marks, due to variations in
material temperature from gradients between the machine nozzle and mold
sprue bushing. Cold material in the nozzle tip section results in a halo around
the direct sprue.
Probable Cause:
1. Molding Machine
• Wrong injection speed
• Wrong injection pressure
• Hold pressure too long
2. Mold
• Insu󰀩cient mold cooling
• Temperature of mold too high around the gate
• Temperature of mold too cool
• Gate size is too small
• Gate is in wrong location
• Land length of gate is too long
• Incorrect Hot Runner system
3. Material
• Melt temperature is too low
Solution (in sequence):
1. Adjust injection speed
2. Add a large cold slug area
3. Add cold wells at the end of the runner system
4. Use hot sprue bushing
5. Identify and eliminate dead pockets / sections
1-7TROUBLESHOOTING
Hot Runner Troubleshooting Guide
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1.6.4 Burn Marks
The nished product display brown streaks. This is from the material being
overheated due to trapped air (diesel e󰀨ect), which can lighten or darken the
color.
Probable Cause:
1. Molding Machine
• High injection speed
• Backow / check ring valve malfunctioning
• High back pressure
2. Mold
• Trapped or volatile gas
• Burning due to friction
• Incorrect sprue diameter
3. Material
• Overheated / underheated melt, possible shear
Solution (in sequence):
1. Clear blocked vent channels
2. Lower injection speed
3. Lower injection pressure
4. Check heater functionality
5. Check thermocouple functionality
6. Reduce feed screw rotation
7. Reduce melt temperature
8. Increase mold cavity venting
9. Enlarge gate
10. Change gate position and / or size
1-8
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Hot Runner Troubleshooting Guide

1.6.5 Delaminating Parts
The nished product is separating into layers that can be peeled o󰀨; surface
layers are aking o󰀨. Insu󰀩cient layer bonding as a result of high shear
stresses; non homogeneous material.
Probable Cause:
1. Molding Machine
• High injection speed
2. Mold
• Cold mold
• Gate has sharp corners
• Sharp corners causing shear heat
3. Material
• Physical contamination of raw material
• Chemical contamination of raw material
• Melt too hot / poor melt
• Incompatible color dye
• High percentage of recycled material
Solution (in sequence):
1. Increase melt temperature
2. Increase mold temperature
3. Decrease injection speed
4. Eliminate contamination
5. Adjust regrind ratio
6. Adjust or change resin moisture content
7. Purge system
8. Reduce sharp corners at gate
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Hot Runner Troubleshooting Guide
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1.6.6 Dimensional Irregularities
The nished product is of a di󰀨erent dimensional value than originally
designed or previous production.
Probable Cause:
1. Molding Machine
• Low injection pressure
• Short hold pressure time
• Damaged backow / check ring valve
• Short cycle time
• Cylinder clearance too big
• Nozzle heaters malfunctioning
2. Mold
• Temperature setting too high
• Small gate size resulting in wrong pressure
• Incorrect gate location
• Incorrect mold conguration / size
3. Material
• Generally not a material related issue unless excessive regrind is
used
Solution (in sequence):
1. Increase injection pressure
2. Increase cooling time
3. Increase mold temperature
4. Ensure cycle time is consistent
5. Monitor molding machine for irregularities
6. Balance regrind ratio
7. Increase gate size
8. Decrease gate land length
9. Balance the runner and / or gate system
10. Decrease cavity quantity
1-10
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Hot Runner Troubleshooting Guide

1.6.7 Discolored Parts
The nished product varies in color on di󰀨erent surfaces.
Probable Cause:
1. Molding Machine
• Contamination
2. Mold
• Incorrect sprue diameter
• Inadequate venting
3. Material
• Physical contamination of raw material
• Chemical contamination of raw material
• Melt too hot / poor melt
• Incompatible color dye
• Residence time too high
Solution (in sequence):
1. Purge heating cylinder
2. Lower resin temperature by:
• reducing cylinder temperature
• reducing screw speed
• reducing back pressure
3. Decrease nozzle temperature
4. Adjust residence time
5. Adjust regrind ratio
6. Adjust cycle time
7. Check for external contamination sources
8. Ensure proper cooling in all areas
9. Increase mold venting
1-11TROUBLESHOOTING
Hot Runner Troubleshooting Guide
© 2020 Mold-Masters (2007) Limited. All Rights Reserved.

1.6.8 Flash
Also known as “ns” or “spew”. The nished product contains a thin lm of
material attached at the mold parting line.
Probable Cause:
1. Molding Machine
• Low clamping pressure
• High injection pressure
• High injection speed
2. Mold
• Inadequate mold supports
• Low clamping force
• Damaged mold
• Projected area too large for machine capacity
3. Material
• Low melt viscosity
• High melt temperature
Solution (in sequence):
1. Reduce the injection speed
2. Reduce the injection pressure
3. Reduce the injection time
4. Increase clamping force
5. Inspect the mold for irregularities
6. Reduce the melt temperature
7. Inspect vent depth
8. Switch to higher tonnage clamping machine
9. Establish correct transfer position
10. Reduce hold pressure
1-12
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Hot Runner Troubleshooting Guide

1.6.9 Jetting
The nished product exhibits serpentine ow patterns on the surface as a
result of the melt cooling prior to complete lling of the mold.
Probable Cause:
1. Molding Machine
• High injection speed
2. Mold
• Cold mold
• Small gate
• Wrong gate land length
• Wrong gate location
3. Material
• Cold melt
Solution (in sequence):
1. Decrease injection speed
2. Verify nozzle temperature
3. Increase mold temperature
4. Increase melt temperature
5. Increase gate size
6. Modify gate location
1-13TROUBLESHOOTING
Hot Runner Troubleshooting Guide
© 2020 Mold-Masters (2007) Limited. All Rights Reserved.

1.6.10 Pitted Parts
The nished product contains unmelted particles or small holes on the
surface.
Probable Cause:
1. Molding Machine
• Improper or worn out feed screw
• Low melt temperature
• Low injection speed
2. Mold
• Gating shear
• Sharp corners
3. Material
• Resin used is not homogeneous
• External contamination
Solution (in sequence):
1. Reduce shear
2. Reduce back pressure
3. Reduce injection speed
4. Modify temperature
5. Modify regrind ratio
6. Modify shot size
7. Inspect Hot Runner and nozzles
1-14
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Hot Runner Troubleshooting Guide

1.6.11 Rough Surface
The nished product exhibits patterns on the surface similar to grooves on
a record, due to rapid cooling of the melt as it nears mold surface, followed
over and over again by fresh melt.
Probable Cause:
1. Molding Machine
• Low injection speed
• Low injection pressure
2. Mold
• Cold mold
• Irregularities in mold surface, defective polishing
3. Material
• Cold melt
Solution (in sequence):
1. Increase injection speed
2. Increase injection pressure
3. Increase melt temperature
4. Increase mold temperature
5. Inspect mold surface
1-15TROUBLESHOOTING
Hot Runner Troubleshooting Guide
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1.6.12 Parts Sticking to Cavity
The nished product does not properly release from the mold (female side).
Probable Cause:
1. Molding Machine
• High injection pressure
• High injection speed
• Long holding time
• High material feed
2. Mold
• Hot cavity
• Cold mold
• Defective mold surface
3. Material
• Melt too hot
Solution (in sequence):
1. Conrm cycle time for cooling
2. Reduce injection pressure
3. Reduce injection hold time
4. Reduce injection speed
5. Reduce injection time
6. Adjust feed
7. Inspect mold nish
8. Increase mold opening cycle
9. Lower mold temperature
10. Adjust di󰀨erential temperatures
11. Inspect for appropriate mold release
1-16
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TROUBLESHOOTING
Hot Runner Troubleshooting Guide