1、 Production process            

The production process of PVC door and window profile mainly includes single screw extrusion process and twin screw extrusion process. The raw materials used in the two processes are the mixed powder prepared in the previous process according to a certain formula.  

（1） Single screw extrusion

The single screw process is especially suitable for the production of small batch and small size profile. The process flow is as follows:            

Mixed powder → single screw extrusion granulation → single screw extrusion molding → setting → traction → cutting → turntable → finished product            

（2） Twin screw extrusion            

The twin-screw extrusion process can be directly molded with powder, with large production capacity, especially suitable for the production of large quantities of conventional profiles and large specifications of different profiles. The process flow is as follows:            

Mixed powder → twin screw extrusion molding → setting → traction → cutting → turning table → finished product

2、 Key points of process control for extruding hard PVC door and window profile by twin screw extruder

The extrusion process can be summarized as follows: the modified PVC mixture is mixed by screw in the barrel, and under the action of internal friction and electric heating, the material gradually changes into the molten viscous flow state, and the material spirals towards the head direction under the flow of the rotating screw. After entering the die, the die cavity of the die is divided and compressed under high temperature and high pressure to extrude the blank which is similar to the section of the product, and then the blank is vacuum cooled and shaped by the die to meet the product design requirements. Forming temperature, setting cooling, screw speed, traction speed and feeding speed are all important factors affecting the quality of profile products, which are described as follows:

（1） Temperature control

After PVC mixed powder enters the extruder, it should be compacted, transported, melted, homogenized and extruded at a lower temperature. In order to obtain high quality and high output profiles, the temperature of each section needs to be adjusted repeatedly and controlled accurately, so that the materials are always in the melting temperature and decomposition temperature range in the extrusion process. In order to set the temperature correctly, it is necessary to fully consider and guide the relevant factors of material forming temperature.

factors affecting material processing temperature

1) Formula and raw material quality have the greatest influence on the processing temperature, and the plasticization temperature of the mixture composed of different raw materials is different. After the formula is determined, the processing temperature is basically determined, which only needs to be adjusted in a small range according to the product quality; for the raw materials produced by different manufacturers of the same formula, the extrusion molding temperature is often different, and only through the production practice, according to the quality of the plastic parison, can the setting temperature be adjusted timely.

2) Under normal production conditions, increasing extrusion speed will cause friction and heat generation of materials, so the heating temperature should be properly reduced.

3) If the cooling water is not cold enough, it is easy to cause product deformation. In this case, the extrusion speed can be reduced or the processing temperature can be adjusted according to the product.

4) The heating time before start-up . The processing temperature in summer can be slightly lower than that in winter.

5) The display temperature of extruder is the temperature of screw, head and die, not the actual temperature of material. When the external heaters of temperature control points such as screw, head and die are heated, the material temperature is actually lower than the display temperature; when the external heaters of temperature control points such as screw, head and die stop heating, the material temperature may be equal to or higher than the display temperature. The corresponding relationship between material temperature, display temperature and set temperature in different extrusion conditions is the basis and benchmark for setting and controlling extrusion temperature.