What are the main reasons for the overall size of the profile being too small during the extrusion process? What are the solutions?

What are the main reasons for the overall size of the profile being too small during the extrusion process? What are the solutions?

During the extrusion process of the profiles, the overall size of the profiles becomes too small.
The main reasons for this are:
① The pulling speed is too fast relative to the extrusion speed, resulting in a large stretch ratio, causing excessive shrinkage of the profile. This leads to a corresponding reduction in the overall cross-sectional size (including the wall thickness) of the profiles, and a greater deformation in the direction away from the die. 
② The profiles are not cooled sufficiently. After leaving the water tank, the profiles still need to be cooled, which leads to creep and causes the overall size to shrink. This is the main reason why the profiles in high-speed molds often have an overall size that is too small. 
③ The size allowance is too small. When designing the mold, if the overall size allowance is too small, even if the mold's size allowance is well-matched, it will still result in the overall size of the profile being too small after extrusion. 
The measures for resolution mainly include: 
①Control the appropriate stretch ratio, appropriately reduce the pulling speed of the profile or increase the extrusion speed, and reduce the stretch contraction rate. 
② Appropriately increase the length of the mold and the water tank to enhance the cooling effect; 
③ When designing the mold, the free shrinkage rate of the extruded material, the structural characteristics of each component of the profile, the trend of shape and size changes during the cooling and shaping process, as well as the trend of traction resistance caused by the deformation of the profile and the balance of resistance among different parts should all be taken into consideration.
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