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#110 Determining the Dimensions of the Side Gate (Practice Calculations)

Category : Cavity
February 3, 2012

This time we practise the calculations for determining the side gate dimensions explained in the last issue.

Question

Let us design the side gate at one location in the case of an injection molded article made of Polyacetal (POM) plastic, when the average wall thickness of the molded article is 1.5 mm and the surface area of the molded article is 4900 mm2,
In this case, obtain the guidelines for the design dimensions of the gate depth h and width W.

Sample Answer

The side gate dimensions are determined in the following two steps.

First Step: Determining the gate depth

First, we check the wall thickness t (mm) of the molded item.
From the question, we find that t = 1.5 (mm).

Next, we obtain the coefficient n which depends on the molding material from Table 1.
In the case of Polyacetal, n = 0.7.

Therefore, the depth h of the side gate will be:

h = n ∙ t
= 0.7 x 1.5
= 1.05 (mm)

Second Step: Determining the gate width

First we obtain the surface area A (mm2) of the molded item.
From the question we find that A = 4900 (mm2).

Next, we obtain the coefficient n which depends on the molding material from Table 1.
In the case of Polyacetal, n = 0.7.

Therefore, the width W of the side gate will be:

W = n ∙ √A/30
= 0.7 x √(4900) /30
= 1.63 (mm)

In conclusion, considering the ease of machining the mold and its cost, we determine as follows:

h = 1 (mm)
W = 1.6 (mm)

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