What are the causes of the brittleness of extruded PVC profiles? And what are the solutions?

① The temperature control is unreasonable. The materials are either over-melted or not melted enough. If the temperature is set too high, the materials will be over-melted, and some components with lower molecular weights will decompose and volatilize. If the temperature is too low, the components will not fully melt together, and the molecular structure will not be stable.
② The feeding ratio is unreasonable. If the feeding ratio is too large, it will cause an increase in the heating area and shear force of the materials, resulting in an increase in pressure, which may cause over-melting; if the feeding ratio is too small, the heating area and shear force of the materials will decrease, resulting in under-melting. Whether over-melting or under-melting, it is prone to cause cracking in the profile during cutting.
③ The die head pressure is insufficient. When the pressure is insufficient, the density of the materials is poor, resulting in a loose texture and a phenomenon of profile brittleness.
④ The gas in the molten material has not been completely removed, and there are air bubbles in the product. This causes a decline in the mechanical properties of the profile.
⑤ The traction speed does not match the extrusion speed. If the traction speed is too fast, the mechanical properties of the profile will decrease due to the thin wall; if the traction speed is too slow, the profile will be subjected to a large resistance, and the product will be in a high tensile state, which will also affect the mechanical properties of the profile.
The solutions mainly include:
① Reasonably control the molding temperature. Generally, for hard PVC profiles, the temperature should be controlled between 170-190℃.
② Reasonably control the feeding ratio, feeding speed, and extrusion speed to ensure an appropriate die head pressure. Usually, the die head pressure should be controlled between 25-35 MPa.
③ Strengthen the vacuum degree of the forced exhaust system in the exhaust section of the exhaust host of the extruder. The vacuum degree is generally controlled between 0.05-0.08 MPa.
④ Determine the extrusion speed and traction speed reasonably to allow the profile to be subjected to appropriate stretching during traction, thereby improving the mechanical strength.
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