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Try these steps to fix injection molding problems.

* Here is a do-it-yourself guide to solving the 16 most common injection molding process problems in a step-by-step fashion. These are remedies you can try without the more drastic step of pulling the mold from the machine.

For each problem in the left column, try adjusting the variables listed across the top row in the order suggested by the numbers in the color-coded icons. Try adjusting the variable up or down as the point of the triangle indicates. In some cases (marked by diamond-shaped icons), there is no general rule about whether to raise or lower the value of the variable. So you will have to experiment.

The two right-hand columns point out two different sorts of factors that should be checked: Are nozzle heaters functioning properly? Is resin contamination occurring?

An 8.5 x 11 in. version of this chart with a protective plastic covering, suitable for posting by the molding machine, is available for free from Teknor Color.

By Joe Allbritton

Teknor Color Co.

Joe Allbritten is senior technical service engineer at Teknor Color Co.'s compounding plant in Jacksonville, Texas, which makes color and additive concentrates and precolored compounds. Allbritton has been with Teknor for 25 years as a color matcher, QC technician, laboratory manager, and in sales and technical service. He may be reached at (903) 586-0583, or e-mail

Variahles to Adjust Injection Cycle Injection Sprue/Runner
PROBLEMS Pressure Time Hold-Time Gate Size

Blush at Gate 4A 5A
Color Streaks 8A
Flash 1B 8B
Delamination 7B
Poor Dimens. Stability 3A 2A 6A
Poor Surface Finish 1A
Short Shots 2A 7A
Sink Marks 2A 3A 5A
Sprue Sticking 6B 3A 2B 4A
Sticking in Cavity 1B 3A 2B 6A
Warpage 5B 3A 7A
Wave Marks 4A 3A
Weak Weld 4A 7A 6A
Weld Burns 8B 7A

Variahles to Adjust Gate Land Nozzle Adjust Clamp
PROBLEMS Length Opening Feed Pressure

Blush at Gate
Color Streaks 9B
Flash 2A
Jetting 5B
Delamination 6B
Poor Dimens. Stability 4A
Poor Surface Finish 5A
Short Shots 8B 1C
Sink Marks 8B 1C
Sprue Sticking
Sticking in Cavity 4C
Wave Marks 1C
Weak Weld
Weld Burns 5A

Variahles to Adjust Stock Mold Injection Screw
PROBLEMS Temp. Temp Speed RPM

Blush at Gate 3C 1A 2B
Brittleness 1B 3A 7B 4B
Color Streaks 2C 3A 1B 5B
Flash 4B 5B 3B 7B
Jetting 2C 3A 1B
Delamination 3A 2A 4B
Poor Dimens. Stability 1C 4C
Poor Surface Finish 2B 3A
Short Shots 4A 5A 3A
Sink Marks 4B 5B
Sprue Sticking 1B
Sticking in Cavity 6B 5B
Warpage 2B 1B 4B
Wave Marks 5B 2B
Weak Weld 3A 1A 2A
Weld Burns 2C 1B 3B

Variahles to Adjust Back Gas Nozzle Contamination
PROBLEMS Pressure Vents Heating
Blush at Gate
Brittleness 5B 6A 2D
Color Streaks 6A 7D 4D
Flash 6B
Jetting 7D
Delamination 1D
Poor Dimens. Stability
Poor Surface Finish
Short Shots
Sink Marks 9A 6A
Sprue Sticking 4D 5D
Sticking in Cavity
Warpage 6B
Wave Marks 6A
Weak Weld 5A
Weld Burns 4B 6A

Check the key variables in the order indicated by the numbers.

A Increase
B Decrease
C Adjust up or down
D Check
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Copyright 2006, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:INJECTION MOLDING: Troubleshooter
Author:Allbritton, Joe
Publication:Plastics Technology
Date:Dec 1, 2006
Previous Article:Now plasma-treat the resin, not to the molded part.
Next Article:How to clean a flashed hot manifold: part three.

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