List of TOPAS® COC grades

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7. Mold design

7.2 Gates

(1) Gate size

More stable products can be molded by positioning the gate at a thick portion of the products. The gate should be sized according to the product shape so as to avoid stress concentration at the gate area. Gate type can be a generally-used side gate, fan gate, and so on. Set sprues and runners on the large side to improve pressure transmission to products.

• Gate thickness should be 60 to 70% of the molded product thickness
  (in the case of side gates).
• Gate width should be taken by 1 to 1.5 times the gate thickness
  (in the case of side gates).
• Gate land should be as short as possible (in the case of side gates).
• Gate diameter should be wall thickness or less (in the case of pin gates).

If there are no quality problems, attach a smaller gate to improve molding cycle, gate finish, etc. Also, if molded products are thin-walled (0.3 mm or less), make thickness equal to molded products to prevent pressure loss of resin.

(2) Gate position

• Gates should be positioned at the thickest portion of molded products.
• Gates should be positioned at a part that does not influence appearance of molded products.
• No gate should be positioned where a force is exerted on molded products.
• Weld lines, if becoming a problem, should also be considered.

(3) Gate shape

Commonly-used gates can be used for TOPAS® COC, which does not have any special trouble with gate shape. However, in the case of a submarine gates, gates may break depending on the shape. Fig. 7-4 shows points to be noted.

Fig. 7-4 Points to be noted for submarine gates