Brittleness of the profile is basically fully reflected in the physical and mechanical properties of the product. Its main features are: when the material is broken, the cold bursts. There are many reasons for the poor physical and mechanical properties of fabricated products. The main manifestations are as follows:
First, the formula and mixing process is not reasonable
1, too much filler
2. Impact modifier addition type and quantity
3, too much or too little stabilizer
4, excessive use of external lubricant
5, the hot mixing sequence, temperature setting and aging time are also decisive factors for the performance of the profile
Second, the extrusion process is not reasonable
1, excessive plastic material or insufficient
2, lack of head pressure
3, the low-molecular components in the product are not discharged
4, the screw torque is too low
5, the traction speed does not match the extrusion speed
Third, the mold design is not reasonable
1. The design of the die section is irrational, especially the distribution of the inner ribs and the treatment of the interface angle. This will cause stress concentration, and it is necessary to improve the design and eliminate the right angles and acute angles at the interface.
2, die pressure is insufficient. The pressure at the die is directly determined by the compression ratio of the die, especially the length of the straight section of the die. The compression ratio of the die is too small or the straight section is too short can cause the product not to be dense and affect the physical properties. The change of the die pressure can adjust the flow resistance by changing the length of the die straight section. On the other hand, different compression ratios can be selected to change the extrusion pressure at the die design stage. However, attention must be paid to the compression ratio of the die head. The compression ratio of the extruder screw is adapted; it is also possible to change the melt pressure by changing the formulation, adjusting the extrusion process parameters, and increasing the perforated plate.
3, for the performance caused by the poor convergence of branching ribs should be appropriate to increase the length of the ribs and the outer surface, ribs and ribs confluence, or increase the compression ratio to solve.
4. The die discharge is not uniform, resulting in inconsistent thickness of the profile walls, or inconsistent density. This also caused a difference in the mechanical properties between the two sides of the profile. In the experiment, we sometimes failed to pass the cold side, which just proved it. As for the thin wall and other non-standard profiles here will not say more.
5, the cooling rate of the fixed mold. The cooling water temperature often does not cause enough attention. The role of cooling water is to cool and shape the macromolecules that are stretched in profile to achieve the purpose of use.
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