|
|
| Black Spots, Brown streaks |
| Problem |
Remedy |
| Black spots and brown streaks appear as dark spots or streaks in the molded part and are usually caused by thermal damage to the melt. |
- Check the material for contamination.
- Decrease the melt temperature.
- Decrease the overall cycle time.
- Purge and/or clean the screw and barrel.
- Decrease the screw speed. High screw speeds may cause the
material to degrade.
- Material may have too much regrind content.
- Material may be overdried. Decrease drying time /
temperature. Refer to drying instructions provided by the
material supplier.
- Material may be prone to thermal degradation. It may be
necessary to use a more thermally stable material.
- Dead spots may be occurring, ensure that the alignment
between the machine nozzle and mold sprue is correct.
- Residence time may be too long, or the shot size may be too
small for the machine. It may be necessary to move the mold
to a machine with less injection capacity. |
|
| |
| Blisters (Air Entrapment) |
| Problem |
Remedy |
| Blisters are hollows created on or in the molded part. In contrast to a void (vacuum) this entrapped gas can also appear near the walls. |
- Decrease melt temperature.
- Decrease screw speed.
- Dry material.
- Increase back pressure.
- Increase mold temperature.
- Ensure regrind is not too coarse.
- Provide additional mold vents.
- Relocate gate. |
|
| |
| Brittleness |
| Problem |
Remedy |
| Brittleness is a condition where the part cracks or breaks at a much lower stress level than would normally be expected based on the virgin material properties. |
- Check for material contamination.
- Decrease amount of regrind use.
- Decrease back pressure.
- Decrease injection pressure.
- Decrease screw speed.
- Increase melt temperature.
- Dry material. Refer to the drying instructions provided by the
material supplier. |
|
| |
| top |
| Bubbles |
| Problem |
Remedy |
| Bubbles are similar to blisters in that there is air entrapped in the molded part. |
- Decrease injection speed.
- Decrease injection temperature.
- Dry material further.
- Increase injection pressure.
- Increase number and/or size of vents.
- Increase shot size. |
|
| |
| Burn Marks, Dieseling |
| Problem |
Remedy |
| Burn Marks or Dieseling show up on the finish molded parts as charred or dark plastic caused by trapped gas and is usually accompanied by a distinctive burnt smell. Note: If this problem is allowed to continue without fixing the root cause it will very quickly cause damage to the molding surface. |
- Alter gate position and/or increase gate size.
- Check for heater malfunction.
- Decrease booster time.
- Decrease injection pressure.
- Decrease injection speed.
- Decrease melt and/or mold temperature.
- Improve mold cavity venting. Vents may become smaller over
time due to wear and they will need to be brought back to
their original depth.
- Reduce clamp force to improve venting. Vents may become
smaller because they are being crushed by the clamping force.
If it is possible to reduce the clamping force without causing
flash then this should be done.
Note: This is always good practice to minimize wear on the
mold and machine.
- Improve venting at the burn location. Burn marks often occur
on deep ribs that have no venting. If possible it may be helpful
to put an ejector pin or sleeve at the burnt area to allow the
trapped gas to escape to atmosphere. |
|
| |
| Cracking, Crazing |
| Problem |
Remedy |
| Cracking or Crazing is caused by high internal molded in stress or by an external force imposed upon the part. They can also be caused by an incompatible external chemical being applied to the finished parts The cracks often don't appear until days or weeks after the parts have been molded. |
- Decrease injection pressure.
- Dry material.
- Increase cylinder temperature.
- Increase mold temperature.
- Increase nozzle temperature.
- Modify injection speed.
- If the material is partially crystalline then it may help to
reduce the mold and/or melt temperature.
- If the material is amorphous then it may help to increase the
mold and/or melt temperature. |
|
| |
| top |
| Delamination |
| Problem |
Remedy |
| Delamination occurs when single surface layers start flaking off the molded part. |
- Adjust injection speed.
- Check for material contamination. Incompatible resins or
colorants may have been accidently mixed causing this
condition to be seen.
- Dry material.
- Increase melt temperature.
- Increase mold temperature.
- Insufficient Blending. Check melt homogeneity and
plasticizing performance. |
|
| |
| Discoloration |
| Problem |
Remedy |
| Discoloration is similar to burn marks or brown streaks but generally not as dark or severe. It may cause the part to be a darker shade than the virgin pellets and is often found nearest the gate area, however it can also appear as dark streaks throughout the part. |
- Check hopper and feed zone for contamination.
- Decrease back pressure.
- Decrease melt temperature.
- Decrease nozzle temperature.
- Move mold to smaller shot-size press.
- Provide additional vents in mold.
- Purge heating cylinder.
- Shorten overall cycle. |
|
| |
| Excessive Flash |
| Problem |
Remedy |
Excessive Flash is often seen near sealing faces, out of vent grooves, or down ejector pins. It appears as thin or sometimes thick sections of plastic where it would not be on a normal part.
Note: Flash can very quickly (within a few cycles) damage the parting line surfaces. |
- Decrease back pressure.
- Decrease cylinder temperature.
- Decrease injection hold time.
- Decrease injection pressure.
- Decrease injection speed.
- Decrease mold temperature.
- Increase clamp pressure.
- Check mold venting. Vents may have been ground too deep
for the material being used.
- Check sealing surfaces to ensure that they seal off properly
by "blueing" them in under clamp tonnage.
- Check ejector pin bore diameter to pin diameter tolerances.
The tolerances may be too large allowing plastic to flash down
the opening. The tolerances may be too large for the material
being used and can occur due to wear over time. |
|
| |
| top |
| Flow, Halo, Blush Marks |
| Problem |
Remedy |
| Flow, Halo, Blush Marks are marks seen on the part due to flow of the molten plastic across the molding surface. |
- Decrease injection speed.
- Increase cold slug area in size or number.
- Increase injection pressure.
- Increase melt temperature.
- Increase mold temperature.
- Increase nozzle temperature.
- Increase size of sprue/runner/gate. |
|
| |
| Gate Stringing, Drooling |
| Problem |
Remedy |
| The part does not break cleanly from the gate area. |
- Insufficient cooling time during the cycle.
- Excessive heat in the gate area. Check thermocouple in the
nozzle or decrease the temperature of the hot runner manifold
and nozzle.
- Increase cooling at the gate area.Ensure that you have
controllable turbulent flow in the gate area. |
|
| |
| Gels |
| Problem |
Remedy |
| Gels are bubbles, or blisters seen on or in the part due to poor melt quality. |
- Change screw speed.
- Increase back pressure.
- Increase cylinder temperature.
- Increase overall cycle time.
- Increase plasticating capacity of machine or use machine
with large plasticating capacity. |
|
| |
| Jetting |
| Problem |
Remedy |
| Jetting is caused by an undeveloped frontal flow of melt in the cavity. The uninterrupted plastic flows or "snakes" into the cavity and cools off enough so that it does not fuse homogeneously with the material that follows. |
- Decrease injection speed.
- Change the melt temperature, up or down.
- Use higher compression screw.
- Increase the gate diameter.
- Move the gate so that when the plastic first enters the cavity
it
hits an obstruction such as a rib or wall. |
|
| |
| Material Leakage |
| Problem |
Remedy |
| Material Leakage is usually caused by material forces overcoming the structural strength of the mold. NOTE: One sign that indicates that material has leaked is that the manifold reaches processing temperature very slowly. |
- Manifold locator is oversize.
- Processing temperature may be too low causing increased
pressure in the manifold.
- Manifold locator may be hobbed into the mold. Decrease
the force applied to the nozzle pad by the machine then repair
the damaged area, then check and if necessary replace
the locator.
- Insufficient number of mold assembly screws. Ensure that
the quantity, type of screw, and the location of the screws
correspond to the general assembly drawing.
- Nozzle may have overheated causing damage to the seal or
gate. Check/replace the thermocouple in the nozzle, then
check and if necessary repair the nozzle well area.
- Manifold may have overheated. Check and replace if
necessary the following components; nozzle well area,
thermocouple, valve disks, sprue disks, or pressure disks. |
|
| |
| Oversized Part |
| Problem |
Remedy |
| Part is too large when compared to the drawing specifications. |
- Decrease booster time.
- Decrease cylinder temperature.
- Decrease holding pressure.
- Decrease injection pressure.
- Decrease injection speed.
- Decrease overall cycle time.
- Increase gate size and/or change gate location.
- Increase mold temperature. |
|
| |
| top |
| Part Sticking |
| Problem |
Remedy |
| Part is getting not pulling out of the cavity and in rarer circumstances cannot be ejected off the core. |
- Check mold for undercuts and/or insufficient draft.
- Decrease booster time.
- Decrease cylinder and nozzle temperature.
- Decrease injection pressure.
- Decrease injection-hold.
- Decrease mold cavity temperature.
- Increase clamp pressure.
- Increase mold-close time.
- Texturing on part is too deep. The parts may stick in the
cavity if a new texture or a retexturing has been performed
on the cavity half of the mold.
- If possible add undercuts to the core to allow the part to pull
out of the cavity. |
|
| |
| Short Shot (Incomplete Filled Parts) |
| Problem |
Remedy |
| Short Shots occur when the part does not completely fill. |
- Increase back pressure.
- Increase injection pressure.
- Increase injection speed.
- Increase melt temperature.
- Increase mold temperature.
- Increase nozzle temperature. Ensure that the manifold
and nozzles have reached the set temperature.
- Increase shot size and confirm cushion.
- Make sure mold is vented correctly and vents are clear.
- Confirm that the non-return valve used is not leaking
excessively.
- Increase the switch over pressure, distance, or time
(whichever method is being used) point from fill to hold so
the fill stage is used longer.
- Change part design. Thin areas of the mold may not fill
completely, especially if there is a thick to thin transition, or
there is a long rib that cannot be vented very well. If the part
design allows it, change in these areas can improve the
situation. |
|
| |
| Sink Marks |
| Problem |
Remedy |
| Sink Marks occur during the cooling process if certain areas of the part are not cooled sufficiently causing them to contract. |
- Decrease amount of regrind use.
- Decrease back pressure.
- Confirm that the non-return valve being used is not leaking
excessively.
- Decrease melt temperature. Do this if the sink marks are
near the gate or thick walled areas.
- Decrease mold temperature. Do this if the sink marks are
near the gate or thick walled areas.
- Decrease injection rate. Do this if the sink marks are near
the gate or thick walled areas.
- Dry material.
- Increase injection pressure. Do this if the sink marks are away
from the gate or in thin walled areas.
- Increase injection speed. Do this if the sink marks are away
from the gate or in thin walled areas.
- Increase mold temperature. Do this if the sink marks are away
from the gate or in thin walled areas.
- Increase injection-hold.
- Increase shot size and confirm that the a cushion is being
maintained.
- Increase size of sprue and/or runners and/or gates.
- Relocate gates on or as near as possible to thick sections.
- Increase cooling time.
- If possible change the mold design to maintain an even wall
thickness throughout the part. |
|
| |
| top |
| Splay Marks, Silver Streaks |
| Problem |
Remedy |
| Splay Marks, Silver Streaks are usually caused by water vapor blisters at the flow front burst and freeze on the wall of the molding surface. |
- Check for contamination.
- Decrease melt temperature.
- Decrease nozzle temperature.
- Dry resin pellets before use. As per the manufacturers
recommendations.
- Incorrect storage of pellets. Moisture on the pellets could be
transferred into the melt, especially if the resin is not normally
pre-dried.
- Raise mold temperature. This will prevent condensation on
the mold walls from being carried into the melt.
- Ensure the mold is not leaking water onto the cores or cavities.
Again this will prevent condensation on the mold walls from
being carried into the melt.
- Relocate gates on or as near as possible to thick sections.
- Shorten overall cycle. |
|
| |
| Sprue Sticking |
| Problem |
Remedy |
| Sprue Sticking generally occurs in a cold runner mold when the sprue is staying in the mold. |
- Check mold for undercuts and/or insufficient draft.
- Decrease booster time.
- Decrease injection pressure.
- Decrease injection speed.
- Decrease injection-hold.
- Decrease mold close time.
- Decrease nozzle temperature.
- Increase core temperature.
- Open the gates.
- Ensure that the correct design of nozzle tip for the material
is being used. |
|
| |
| Surface Finish (Low Gloss) |
| Problem |
Remedy |
| Surface Finish (Low Gloss). Gloss is the appearance of the surface of the molded part when light is reflected off of it. Molds that are textured or resins that are filled have an inherently reduced level of gloss when compared to highly polished mold surfaces. |
- Clean mold surface.
- If the part design allows increase the polish of the molding
surface.
- Increase cylinder temperature. This applies to molds that have
a polished surface.
- Increase injection pressure. This applies to molds that have a
polished surface.
- Increase injection speed. This applies to molds that have a
polished surface.
- Increase mold temperature. This applies to molds that have a
polished surface.
- Decrease cylinder temperature. This applies to molds that
have a textured surface.
- Decrease injection pressure. This applies to molds that have a
textured surface.
- Decrease injection speed. This applies to molds that have a
textured surface.
- Decrease mold temperature. This applies to molds that have a
textured surface.
- Increase melt temperature.
- Make sure venting is adequate. |
|
| |
| top |
| Surface Finish (Scars, Wrinkles) |
| Problem |
Remedy |
| Surface Finish (Scars, Wrinkles). Is the appearance of the ripples or wrinkles on the surface of the molded part. |
- Decrease back pressure.
- Decrease nozzle temperature.
- Increase booster time.
- Increase the melt temperature.
- Increase injection pressure.
- Increase injection speed.
- Increase overall cycle time.
- Increase shot size.
- Inspect mold for surface defects. |
|
| |
| Undersized Part |
| Problem |
Remedy |
| Part is too small when compared to the drawing specifications. |
- Decrease mold temperature.
- Increase booster time.
- Increase cylinder temperature.
- Increase hold-time.
- Increase holding pressure.
- Increase injection pressure.
- Increase injection speed.
- Inspect mold for surface defects. |
|
| |
| Valve Pin Does Not Close |
| Problem |
Remedy |
| Valve pin does not close properly. This will leave the gate protruding from the part. This may also occur if the valve pin is too hot, the material may stick to the valve pin. |
- Valve pin is too short. Check and replace if necessary.
- Valve pin fit. Ensure that the valve pin is lapped to the gate
steel when appropriate.
- Damaged gate. Check if valve pin is too long, rework if
necessary. Also check to ensure that the valve pin is concentric
with the gate, if not replace it.
- Hydraulic / Pneumatic seals may be worn. Replace as
necessary.
- Insufficient pin/land area in the gate area of the mold. Increase
the gate area cooling, or increase the valve pin land contact.
- Insufficient hydraulic or air pressure. Increase the pressure up
to but not beyond the maximum rating of the unit being used.
- Excessive hold time. Decrease the hold time. |
|
| |
| top |
| Voids |
| Problem |
Remedy |
| Voids are hollows created in the part. They are normally found in thick sectioned parts caused by material being pulled away from the hot center section towards cold mold walls leaving a void in the center. |
- Clean vents.
- Decrease injection speed.
- Decrease melt temperature.
- Dry material.
- Increase injection pressure.
- Increase injection-hold.
- Increase mold temperature.
- Increase shot length.
- Increase size of gate.
- Increase size of sprue and/or runners and/or gates. |
|
| |
| Warping, Part Distortion |
| Problem |
Remedy |
| Warping, Part Distortion is shows up as parts being bowed, warped, bent or twisted beyond the normal specification outlined on the drawing. |
- Adjust melt Temperature (increase to relieve molded-in stress,
decrease to avoid overpacking). stress, decrease to avoid over
packing). stress, decrease to avoid over packing).
- Check gates for proper location and adequate size.
- Check mold knockout mechanism for proper design and
operation.
- Equalize/balance mold temperature of both halves.
- Increase injection-hold.
- Increase mold cooling time.
- Relocate gates on or as near as possible to thick sections.
- Try increasing or decreasing injection pressure. |
|
| |
| Weld Lines |
| Problem |
Remedy |
| Weld Lines are created when two or more melt flow fronts meet possibly causing a cosmetically visible line. It can also create a weakened area in the finished molded part especially with filled resins. |
- Increase injection pressure.
- Increase injection speed.
- Increase injection hold.
- Increase melt temperature.
- Increase mold temperature.
- Make sure part contains no sharp variation in cross-sections.
- Vent cavity in the weld area. |
|
| |
| top |
