How to solve the uneven shrinkage of PBT plastic during injection molding

Polybutylene terephthalate (PBT) is a high-performance thermoplastic that is widely used in the injection molding industry due to its excellent mechanical strength, excellent heat resistance and outstanding electrical properties. Although PBT performs well in many applications, it may experience uneven shrinkage during the injection molding process. This phenomenon not only affects the dimensional accuracy and appearance quality of the finished product, but may also lead to a decline in its overall performance.

Analysis of the causes of uneven shrinkage
Material factors
Although the shrinkage rate of PBT is relatively small, there may be differences in shrinkage rates between raw materials from different batches or different suppliers. This difference may cause uneven shrinkage of the finished product during the injection molding process.
Mold design
The design of the mold plays a vital role in the quality of injection molding. Factors such as the location and number of gates, the configuration of the cooling system, and the distribution of wall thickness can significantly affect the shrinkage of the finished product. Unreasonable gate design may cause uneven flow of molten material in the mold, resulting in local shrinkage. In addition, the unevenness of the cooling system may cause differences in the cooling speed of various parts of the product, further exacerbating the phenomenon of uneven shrinkage.
Injection molding process parameters
The setting of process parameters such as injection pressure, injection speed, holding time and cooling time also has an important impact on shrinkage. If the injection pressure and speed are insufficient, the molten material may not be fully filled, resulting in shrinkage; while insufficient holding time and pressure may cause the product to shrink in volume during the cooling process, forming a significant dent.
Environmental factors
The temperature and humidity of the environment during the injection molding process also affect the shrinkage of PBT. For example, excessive humidity may cause the water in the raw material to evaporate during the injection molding process, resulting in bubbles and uneven shrinkage.

Solutions for uneven shrinkage
Optimize mold design
By properly designing the location and number of gates, the uniform flow of molten material in the mold can be ensured, thereby reducing the risk of local shrinkage. At the same time, optimize the cooling system to ensure that the cooling speed of each part of the mold is consistent to avoid shrinkage differences caused by uneven cooling. In addition, controlling the wall thickness of the product to ensure its uniform thickness can also effectively reduce the possibility of uneven shrinkage.
Adjust injection molding process parameters
According to the shape and size of the finished product, the injection pressure and speed should be reasonably set to ensure that the molten material can fully fill the mold. During the holding stage, the holding time is extended and the holding pressure is increased to compensate for the volume shrinkage of the molten material during the cooling process. At the same time, the cooling time is adjusted to ensure that the product is fully solidified before demolding to reduce the occurrence of shrinkage.
Control the quality of raw materials
It is crucial to select PBT raw materials with stable quality and consistent shrinkage. Fully drying the raw materials to ensure that their moisture content is lower than the specified standard can effectively avoid bubbles and uneven shrinkage caused by moisture.
Improve the injection molding environment
Strictly controlling the environment of the injection molding workshop to ensure that the temperature and humidity remain within a stable range will help improve the stability of the injection molding process. In addition, regularly cleaning the injection molding machine and mold to avoid the impact of impurities and contaminants on product quality.
Use advanced injection molding technology
Introducing mold flow analysis software to simulate and optimize the injection molding process can effectively predict the shrinkage of the product and provide guidance for mold design and process parameter setting. By adopting advanced injection molding machine control systems, precise control of injection pressure, speed, holding time and cooling time can be achieved, which can greatly improve the quality and consistency of the finished product.