How to avoid cracks in acrylic products during processing?

Cracking is a common defect in the processing of acrylic products, mainly caused by stress and deformation. Today, Jinbao will discuss with you how to avoid cracks in acrylic products during processing.

Acrylic products have cracks, which are mainly caused by residual stress. There are three reasons for residual stress: demolding, metal inlay and excess filling. We analyze from these three points:

First, if the crack of the acrylic product is caused by too much filling, it can be solved according to the following methods:

1. Because the pressure loss of the sprue is smaller, if the crack mainly occurs near the sprue, it can be replaced by multi-point distribution gate, side gate and handle gate when acrylic processing.

2. Under the premise of ensuring that the resin will not decompose and deteriorate, appropriately increasing the resin temperature can reduce the melt viscosity, improve the fluidity, and at the same time reduce the injection pressure and reduce the stress.

3. Under normal circumstances, the low temperature of the acrylic processing mold is easy to generate stress, and the temperature should be appropriately increased. However, when the injection speed is higher, the stress can be reduced even if the mold temperature is lower.

4. If the injection pressure holding time is too long, stress will also be generated. Therefore, it is recommended to shorten or switch the holding pressure time to the first time during acrylic processing.

5. Amorphous resins such as AS resin, ABS resin, and PMMA resin are more likely to generate residual stress than crystalline resins such as polyethylene and polyoxymethylene, which should be paid attention to.

Second, if it is demolded and pushed out to cause cracks

When demoulding, due to the small demoulding slope, rough mold compound and punch, the ejection force is too large, resulting in stress, and sometimes even whitening or cracking around the ejector rod. It is not difficult to solve this problem, you can replace a mold, or increase the demoulding angle.

Third, it is easy to generate stress when inserting metal parts during injection molding

This is mainly because the thermal expansion coefficients of metal and resin are very different to generate stress, and then after a period of time, the stress exceeds the strength of the resin to cause cracks. In addition, the effect of the inlay on nylon is small, and the thermal expansion coefficient of the glass fiber reinforced resin material is small, which is also more suitable for the inlay.

Preheating the metal inserts before forming also has good results.

Fourth, the external environment and external stress

In addition to residual stress, external stress and external environment can cause cracking. External stress is mainly due to stress concentration caused by unreasonable design, especially at sharp corners.

External environments such as chemical-induced water degradation, moisture absorption and excessive use of recycled materials can degrade physical properties and cause cracks.

If you have other information and questions about acrylic, please contact Jinbao.