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.
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.
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.
- 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
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.
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.
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)