| OBSERVATION |
POSSIBLE CAUSES |
CORRECTIVE ACTIONS |
| Flash (over substrate or on periphery of part) |
- Poor mold fit
- Inadequate molding machine tonnage
- Poor shutoff design
- Substrate shrinkage
|
- Check by bluing the tool
- Increase tonnage or decrease injection and pack pressure
- Re-cut tool to obtain complete shutoff
- Check for substrate sinks and re-cut tool
|
| Short shots |
- Not enough material
- Not enough injection pressure
- Not enough fill speed
- Melt too cold
- Poor venting
|
- Increase shot size
- Increase injection pressure
- Increase injection speed
- Increase melt temperature
- Decrease the clamp tonnage and re-cut vents
|
| Poor quality knit lines |
- Gas trapped between polymer fronts
- Low melt temperature
|
- Improve vents
- Increase injection speed and melt/mold temperature
|
| Overmold breaks or impinges through hollow substrate |
- Improperly supported substrate
- High injection pressure and melt temperature
- Wrong location of gate
|
- Fully support the substrate to resist hydraulic injection pressures and melting
- Lower injection pressure and melt temperature
- Relocate gate
|
| Warped parts |
|
- Lower the molded in stress in both the substrate and the elastomer
- Increase the stiffness of the substrate by including glass or increasing thickness of ribs
|
| Poor adhesion |
- Incompatible materials
- Contamination
- Gate freeze-off too early
|
- Re-select correct grade of TPE
- Check for color concentrate compatibility and/or the use of a lubricated grade of substrate
- Increase the process temperatures and/or mold temperature
|
| Surface sinks |
- Material shrinkage causes non-uniform release from tool surface
- Gate freeze-off too early
|
- Increase the pack pressure/hold time and decrease material temperature
- Increase gate size
|
| Non-uniform color |
- Incompatible color concentrate
- Inadequate melting and dispersion of color concentrate
|
- Check for concentrate compatibility
- Increase rear zone temperature, back pressure, screw RPM
|
| Surface splaying (silver streaking) |
|
|
| Parts stick in the "A" side of the tool |
- Not enough draft
- Part forms a vacuum in the "A" cavity
- "A" cavity too shiny
- "A" cavity too hot
|
- Increase the draft
- Provide air assist release
- Sandblast the cavity
- Run the "A" half cooler
|
| Elastomer is sticky or smells |
|
- Check for material residence time and reduce temperature in rear zones if possible
|
