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The benefits of small gates in injection molding

by:Vowin Rapid Prototyping     2023-02-07
The gate is a critical part of the material flow channel in the gating system. Except for the sprue type gate, most of the gates are the parts with the smallest cross-sectional area in the gating system. Even the smallest part is enough for pouring up. Regardless of the size of the pouring cross-sectional area, generally speaking, injection molding with a small gate has the following advantages.

There is a large pressure difference between the front and rear ends of the small gate, which can effectively increase the shear rate of the melt and generate large shear heat, resulting in a decrease in the apparent viscosity of the melt and enhanced fluidity, which is conducive to filling mold. Greatly enhanced the rate of injection molding. This feature of the small gate is of great benefit to the molding of thin-walled products or products with fine patterns, as well as plastics such as polyethylene and other viscosities that are sensitive to shear rates.

In the injection molding process, the pressure-holding and feeding stage generally continues until the melt at the gate freezes, otherwise the melt in the cavity will flow back out of the cavity. In this way, if a small gate is used, it is possible to adjust the volume of the small gate through mold trial or mold repair, so that the melt at the gate can be frozen in time during the pressure holding process, so as to properly control the feeding time. Avoid the above phenomena from happening. This is where the benefit of a small sprue freezes in good time.

Because the small gate has a small volume and freezes quickly, when producing some products, it is not necessary to wait for the inside of the product to be completely solidified after the small gate is frozen. As long as the external solidified layer has sufficient strength and rigidity, the product can be demoulded, thereby shortening the production time. Molding cycle, improve production efficiency. This is the benefit brought by the small gate and the demoulding is faster.

According to experience, if a small gate is used in a multi-cavity unbalanced gating system, the flow resistance of the gate to the plastic melt will be much larger than that of the multi-melt flow in the runner, so it is possible to After the body fills the runner and builds up sufficient pressure, each cavity can be fed and filled at approximately the same time. Therefore, the small gate can balance the feed rate of each cavity in the multi-cavity, which is beneficial to the balance of the gating system. So as to achieve the effect of balancing the pouring speed of each cavity.

However, it should be noted that although a small gate has the above-mentioned advantages, a gate that is too small will cause great flow resistance, resulting in prolonged filling time. This is one of the disadvantages of small gates. Where there are advantages, there are bound to be disadvantages, and the disadvantages will not be repeated here. In injection molding, the location of small gates will inevitably bring many benefits to the production of products. In the product life, timely small gates are beneficial to solidify the outside, thereby improving production efficiency.
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