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Our Top 10 Design Tips for TPE

1. Gating:

Gate location and sizing are critical to the processing, part appearance, warpage, and physical properties. Gate size should equal 40%- 50% of wall thickness for cold runner systems with a minimum size of 0.030”. Gate location should be in the thickest section of the part and located so that an even fill of the part will occur.

2. Runners:

A round runner is recommended. This allows the most efficient material flow and tends to induce the least chilling effect on the material. Runners should be balanced for multi-cavity tools to ensure that each cavity receives equal flow and pressure simultaneously. Venting and cold slugs incorporated into your runner system will give you a higher quality finished part.

3. Barrel:

Barrel size should be sufficient to ensure proper mixing and residence time. The barrel capacity should not be below 30%, or above 75% of the total shot size. Total shot size equals all parts including runners.

4. Wall Thickness:

Uniformity in wall thickness is critical to minimize warpage, distortion, internal stresses, uneven shrinkage across part and cycle times. When non-uniform wall thicknesses are unavoidable, gradual blending should be used between sections. Wall thickness over 0.250” may cause sink in parts.

5. Undercuts:

  • 45-55 Shore A      maximum undercut 2.00 mm (0.080”) 
  • 64-73 Shore A      maximum undercut 1.6 mm (0.065”) 
  • 80-95 Shore A      maximum undercut 1.00 mm (0.040”) 
  • 40-50 Shore D      maximum undercut 0.75 mm (0.030”)

Taper the undercut well to allow for expansion and slippage: this avoids tearing during ejection

6. Screws:

General Purpose polyolefin screws with a compression ratio of 2:1 to 2.5:1 and a length to diameter ratio between 16:1 and 20:1 in most cases. Audia Elastomers does not recommend low shear screws, such as those used in PVC processing.

7. Nozzles:

Audia Elastomers TPE's do not drool or degrade at normal processing temperatures and therefore do not require a special nozzle. Nozzle length should be minimized to prevent temperature loss.

8. Clamp Force:

Clamp force should be 3 – 5 tons/in²

9. Sprue Design:

A minimum taper of .5° or .75 over the length of the sprue. A reverse taper of 1.5” for harder grades (85 shore A and above) and 1.3”-2.5” for softer grades.

10. Venting:

Venting is a very important aspect of producing quality parts. The following dimensions are recommended.

General Purpose: D 0.0015” (0.038 mm); W .2” – .5” (5.0-12.0 mm); Land length .15” – .20” (3.8-5 mm)

High Flow: D .0010”   (0.025 mm); W .2” - .5” (5.0-12.0 mm); Land length .15” – .20” (3.8-5 mm)

 

 

 

 

 

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