The quality and performance of PVC profile products and extrusion machinery are intricately linked to several factors in pvc processing. It includes material composition, processing conditions, and equipment maintenance.
Raw Materials in PVC Processing
1. During the extrusion process of PVC resin particles, only about 30% of the surface will melt. This is why even a small amount of heat stabilizer can be effective. At the same time, most profile products do not fully utilize the theoretical mechanical properties of the resin. The discontinuous distribution of the molten surface and the unmelted core makes profile products very sensitive to notches.
PVC materials
2. Profile products using certain calcium-zinc stabilization systems may experience a decrease in welding mechanical properties over time. This shortens the shelf life of the profile. This phenomenon, known as welding performance attenuation, can also occur in lead salt stabilizers. However, the mechanical properties of the welded products generally remain unchanged. It is recommended that the inventory of profiles not exceed three months.
3. A low-melting-point component (e.g., 50°C) of wax in lubricants may precipitate from the surface of profiles when exposed to sunlight in the summer. This can cause high-temperature discoloration of profiles and lead to cyclic reactions under photothermal effects, as evidenced by studies.
4. The key indicators for the use of rutile titanium dioxide in profiles are the coating and particle size, not the titanium dioxide or rutile titanium dioxide content. The composition of the coating layer affects the dispersion of titanium dioxide and the fluidity of dry powder. Additionally, the particle size and its distribution in the PVC phase affect the mechanics of the profile. Both of them impact the aging performance of the product.
Extrusion Machinery for PVC Processing
1. Puffy white stripes often appear on the surface of the profile, particularly on the lower part in the extrusion direction. After a while, black fine lines may appear. This indicates a “bite” between the screws or the barrel. The gap between the screw and the barrel should be checked.
2. When the vacuum port is emitting material, the gap between the screw and the barrel on this side is usually larger. The reason is often that the thrust bearing of the screw on this side is severely worn, causing the screw to extrude and retract, leading to insufficient shear friction.
3. If the temperature of the extruder is normal but the color of the profile alternates between yellow and green. This is usually caused by a blockage in the oil temperature system inside the screw, which results in fluctuating melt temperatures.
4. If the extruder temperature is normal but the color of the profile suddenly turns green, check that other factors are normal. This may indicate that the heating plate—particularly the heating plate in the lower half of the first zone of the barrel—has burned out or is not heating properly.
5. When the extruded profile is yellow and poorly plasticized, and fluctuations in raw materials have been ruled out, it is recommended to check the heating system of zones 3 and 4 of the extruder. Typically, the overall temperature of the machine body is low, but the actual temperature of a single zone may be 30-40°C higher than the displayed temperature, which can cause this issue. For zones 3 and 4, it is also recommended to check whether the thermal sensor and the meter (model KJ type) are mismatched.
Profile Products in PVC Processing
Some common problems
When the material is soft, it usually means that the profile strength is low. The essence of strength lies in the intermolecular force of the continuous phase. The weak interaction between the molecular chains of polymer materials is much lower than the bond energy, which is why the strength of polymer materials is much lower than that of metals and is greatly influenced by processing.
When the material is brittle, it usually means that the material has poor toughness. Toughness refers to the amount of energy the material can absorb when damaged by external forces. It is related to the internal defects and strength of the material. Improving the strength, uniformity, and toughness of the material is effective, and the product of tensile strength and elongation is associated with the material’s toughness.
Hardness represents the stress a material experiences under compressive strain, while strength represents the stress the material experiences under either tensile or compressive strain.
When the material deforms at high temperatures in summer, it usually means that the material has poor high-temperature creep resistance. This should not be confused with welding strength. Materials with low hardness typically have poor high-temperature creep performance.
Advantages of the plastic doors and windows
Plastic doors and windows generally have better sealing and thermal insulation properties than thermally-insulated aluminum doors and windows. In addition to the low thermal conductivity of the material, plastic is easily deformed and flexible. When locked, the frame, sash, and rubber strips have greater sealing contact, reducing air leakage. The presence of more locking points significantly enhances sealing. In contrast, thermally-insulated aluminum doors and windows have higher strength and rigidity. The locking points have a limited effect on sealing. When large gaps arise due to improper installation, the sealing performance of doors and windows is difficult to adjust through the locking points.
Conclusion
In summary, by carefully monitoring and addressing issues such as strength, brittleness, and high-temperature performance, manufacturers can optimize the durability and functionality of their products. Additionally, a holistic approach that considers raw materials, processing parameters, and machinery upkeep is essential for ensuring high-quality profiles that meet customer expectations and industry standards.
