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Factors affecting the shortening of aramid reinforced PA66 plastic in molding?

Time: 2019-09-02 10:32 Author: admin Hits: Times

Aramid reinforced PA66 plastic, as a thermoplastic, has the characteristics of expanding after heating and shortening after cooling. Of course, the pressure will also shrink in the future. In the injection molding process, the molten plastic is first injected into the mold cavity. After the filling is completed, the melt cools and solidifies. When the plastic part is removed from the mold, it appears shortened. This shortening is called forming shortening. Factors affecting the shortening of aramid reinforced PA66 plastic in molding?

Within a period of time from mold removal to stabilization, the scale will still show small changes. One change is continuous shortening. This shortening is called post-shortening. Another change is that some hygroscopic plastics swell due to moisture absorption.

The mold size can be obtained from the product size plus the reduction rate. Therefore, when planning the mold, the main factors of the reduction rate need to be considered: resin pressure, resin temperature, mold temperature, gate cross-section area, injection time, cooling time, product wall thickness, Enhance data, orientation, and injection speed

Resin pressure has a great influence on the shortening rate. If the resin pressure is large, the shortening rate will be small, and the product size will be large. Even in the same cavity, the resin pressure varies depending on the shape of the product, so a difference in shortening rate occurs. In the case of multi-cavity molds, the resin pressure in each cavity simply differs, and the shortening rate of each cavity is different.

Regardless of the right or wrong crystalline resin or crystalline resin, if the mold temperature is high, the shortening rate will increase. Fine molding should maintain the mold temperature at a specific temperature. When planning the mold, pay attention to the cooling circuit planning.

Generally speaking, when the gate cross-sectional area is changed, the shortening rate also changes. The shortening rate decreases as the gate size increases, which is related to the activity of the resin.

Aramid reinforced PA66 plastic

The wall thickness of the product also affects the yield. Regarding the non-crystalline resin, the resin has a different tendency to affect the wall thickness shortening rate. The wall thickness is large, and the shortening rate is also large. On the contrary, the shortening rate becomes smaller. Regarding crystalline resins, it is necessary to avoid particularly large changes in wall thickness. In the multi-cavity mold scene, if the cavity wall thickness is different, the shortening rate will also be different.

When using glass fiber reinforced resin, the more glass fiber is added, the smaller the shortening rate is. The shortening rate in the moving direction is smaller than the transverse shortening rate. According to the resin, the difference is large. To avoid distortion and warpage, it is necessary to consider Mouth shape Hida mouth position and number of gates.

Although the orientation is quite different, it is oriented to all resins. The orientation of a crystalline resin is particularly large, and varies depending on the wall thickness and molding conditions.

The shortening rate is changed by the resin pressure. The scene of multi-point gates in single cavity mold and multi-cavity mold. To perform the same filling, gate balancing is required. Resin movement is related to the movement resistance in the runner, so it is best to take the runner balance before taking the gate balance.

In order to simplify the setting of the molding conditions, it is necessary to pay attention to the cavity arrangement. Because the molten resin will heat into the mold, in the case of a general cavity arrangement, the mold temperature spreads in a concentric circle centered on the gate. Therefore, when selecting the cavity arrangement of a multi-cavity mold, it is necessary to balance the runner easily, and also to arrange the concentric circle with the gate as the center.

The reason that the aramid reinforced PA66 plastic is deformed is that it has internal stress under uneven shortening, so it is necessary to avoid uneven shortening. In the case of a circular product with a hole in the center of the gear, a gate should be set in the center. However, when there is a large difference in the shortening rate between the movement direction of the resin and the straight direction, there is the disadvantage of an ellipse. When more precise roundness is required, it is necessary to set the gate at 3 or 6 points.

However, there is a need to pay attention to the balance of the gates. When using a side gate, the 3-point gate will increase the inner diameter of the cylindrical product, and the scene that does not allow gate marks on the surface and end faces will use less inner multi-point gates to achieve good results.

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