Causes and solutions of injection molding strain

Injection molding strain refers to the phenomenon of strain or deformation of plastic parts when they are removed from the injection mold in the process of injection molding because of incomplete demoulding and uneven cooling.

The following are the causes of injection strain and solutions:

1. Reasons for injection mold:

(1) Unreasonable injection mold design, unreasonable cavity internal structure, unable to increase water or water design unreasonable factors may lead to high local temperature of injection mold, resulting in injection molding strain.

(2) Injection mold water problems, such as water road is not smooth, water pipe gasket is too thick, etc., may lead to high local temperature of injection mold.

The solution:

(1) Check the injection mold waterway to ensure that the waterway is smooth. If necessary, the waterway can be improved or adjusted.

(2) Maintain the injection mold to ensure the surface finish of the injection mold and reduce wear and damage.

2. Material reasons:

(1) The high viscosity of the material increases the flow difficulty of the melt and reduces the molding performance of the plastic parts, which is easy to cause strain in the injection molding.

(2) The thermal stability of the material is poor, and it is easy to degrade or decompose in the molding process, which affects the performance and quality of the product and increases the risk of injection strain.

The solution:

(1) Select the appropriate material, according to the material characteristics to choose the appropriate injection temperature, pressure and shear rate.

(2) Improve the material formula, improve the thermal stability and fluidity of the material.

3. Process reasons:

(1) injection molding temperature is too high or too low, will affect the molding performance and quality of products, thereby increasing the risk of injection molding strain.

(2) The pressure holding time is too long or the pressure holding pressure is too large, will make the structure of the product become tight, thus affecting the release and strength of the product, easy to cause injection strain.

The solution:

(1) Choose the appropriate injection temperature and pressure holding time.

(2) According to the molding conditions of the products, reasonable setting of pressure and time.

4. Other reasons:

(1) Damage or improper use of injection mold accessories, such as ejection parts not completely ejection, mold locking force is inappropriate, mobile components wear and other factors may lead to injection strain.

(2) Too high ambient temperature or humidity will also affect the molding performance and quality of products, thus increasing the risk of injection strain.

The solution:

(1) Check and maintain injection mold parts regularly to ensure that they are used correctly and the damage rate is within the controllable range.

(2) Pay attention to the change of ambient temperature and humidity, and try to keep the stability of the working environment.

The causes of injection-molding strain are complicated, which need to be investigated and improved from injection mold, material, process and environment. In the production process, the process should be strictly followed.