What is the Temperature Setting for the PVC Sheet Extrusion Process?

Setting the correct extrusion temperature is crucial for producing high-quality PVC sheets, impacting both the physical properties and the efficiency of the manufacturing process.

The optimal temperature for PVC sheet extrusion is generally between 160°C and 200°C, crucial for preventing defects and ensuring consistent thickness and surface quality.

Understanding the factors that influence temperature settings can significantly enhance the performance of your PVC sheet extrusion process. Delve deeper to learn about temperature control's role in achieving superior product characteristics.

What are the Benchmarks for Temperature Optimization in the PVC Sheet Extrusion Process?

Achieving precise temperature control in PVC sheet extrusion is essential for maintaining product quality and process efficiency. This entails understanding the specific benchmarks that guide the optimal thermal conditions throughout the extrusion process.

In PVC sheet extrusion, optimize temperature for uniform plasticity and surface finish by maintaining correct barrel, die, and cooling temperatures, reducing defects, energy use, and enhancing output consistency.

Thermal Stability of PVC Resin

PVC resin is a heat-sensitive polymer. Simple PVC resin starts to degrade at 100 degrees Celsius, and the degradation accelerates at 150 degrees Celsius.

On the other hand, PVC starts to go from glassy state to visco-fluid state through high elasticity state only at 160℃. Therefore, simple PVC resin can not be directly processed, must be added to improve the thermal stability of the resin¹ by adding heat stabilizers. The general PVC resin stabilizer test is carried out at 180℃, 30min and 200℃, 20min conditions. Therefore, the plasticizing temperature and time of PVC resin should not exceed this range.

Plasticizing Degree

In PVC plastics, the degree of plasticization is the degree of crystallization of the product and the degree of fusion of the primary particles of PVC sign.

Many studies and test data show that: unmodified PVC-U plasticizing degree of 60% -65%, that is, the products of the primary particles are not yet fully plasticized, only most of the fusion, the strongest impact resistance, of which the plasticizing degree of 60%, the highest breaking strength, the plasticizing degree of 65% when the maximum elongation at break.

When the melting temperature is below 150 ℃, the plasticization degree² is zero. When the melting temperature is below 190 ℃, the primary particles in the product are clearly visible, and the plasticization degree is below 45%.

When the melting temperature is about 200 ℃, most of the primary particles in the product boundary disappear, and only a few primary particles are visible, and the plasticization degree is 70%. When the melting temperature is above 200 ℃, the primary particles in the product are completely plasticized, and the plasticization degree is up to 80% or more.

Processing Temperature of Blending System with CPE

All PVC products are added to the CPE blending toughening modified³, and CPE impact modifier temperature band is relatively narrow, a large number of tests have proved that the CPE-modified PVC at 190 ℃ and 200 ℃ under the conditions of the formation of the product, its micro-morphology is very different.

When the modifier particles are heated to 190 ℃, they form a network structure that covers the primary particles of PVC, which gives a good impact toughening effect; when the primary particles of PVC are heated to 200 ℃, they are fully plasticized, and the degree of plasticization can reach more than 80%.

When the primary particles of PVC are completely melted at 200 ℃, the network structure disappears and becomes a sphere, which is dispersed in the PVC resin matrix, resulting in a significant decrease in impact resistance⁴.

From the above discussion, we can see that the use of CPE blending⁵ modifies the processing conditions of PVC, which are relatively harsh. Additionally, PVC is a “non-characterized” polymer, meaning that the degradation of PVC is not only related to temperature, but also to time. The higher the temperature, the shorter the degradation time, and the lower the temperature, the longer the degradation time.

The temperature of the screw and barrel should be controlled between 180°C and 185°C (note that this is the actual melt temperature, not the temperature displayed on the barrel, which can be quite different). This is to prevent the melt from staying in the machine at too high a temperature for too long, which can cause it to decompose.

To complete the molding, the temperature difference between the melt in the nozzle and the mold should be controlled at 190-200°C or even higher, so that the melt can reach the optimal degree of plasticization at the moment it enters the mold. It should be extruded from the nozzle into the mold as soon as possible to achieve the optimal degree of plasticity from the state of molding, and not to stay in the high temperature and decompose for too long.

What is the Temperature Setting for PVC Sheet Extrusion Process?

Setting the correct temperature is crucial for PVC sheet extrusion, ensuring optimal product quality and process efficiency across applications.

The ideal PVC sheet extrusion temperature is 160°C-185°C, optimizing product quality, minimizing waste, and enhancing process stability.

Feed Section

The temperature range is 185°C to 195°C. The temperature should be set to at least 185°C to ensure that the display temperature is above 185°C. The larger the extrusion volume, the higher the temperature required in this section. This allows the powder to be heated quickly and the glass to be formed into small pieces.

Our company’s extrusion production of threading pipe and drainage pipe is high-speed extrusion. Especially threading pipe, in the information I have consulted, I have not seen such a fast speed production.

So our company’s threading pipe and drainage pipe extrusion equipment for the material section of the temperature is super high, generally in the 195 ℃ or more, and individual machines even reached 210 ℃ - 220 ℃, the actual internal temperature is only between 100 ℃ - 130 ℃, in order to be the most important thing. The actual internal material temperature is only between 100℃-130℃, and it is only at the end of the feeding section that it can be close to the temperature of 150℃ which is needed for the glassy state.

Compression Section

Usually at 180 ℃; depending on the actual extrusion speed, it can be appropriately increased. The temperature of the pipe produced in this section is more than 180 ℃, up to 190 ℃ - 195 ℃, and the temperature of the pipe produced for drainage is about 180 ℃.

Melting Section

Usually at 180°C; it can also be increased depending on the actual extrusion speed. The temperature for producing threaded pipes in this section is higher than 180°C, up to 190°C-195°C. The temperature for producing drainage pipes is roughly around 180°C.

Measuring Section

The temperature control of the entire extrusion process⁶ is very important, and its importance is even greater than that of the feeding section. The temperature should generally be set at 170 ℃ ~ 180 ℃, depending on the shear performance of the extruder and the size of the extrusion volume, to ensure that the displayed temperature is ≤ 185 ℃.

Due to the large amount of heat generated by the internal shear of the metering section, it is easy to cause the melt temperature to be too high. If the melt temperature is too high, it will accelerate the decomposition of PVC, resulting in yellowing, discoloration, foaming, and other quality problems. Therefore, if necessary, the screw temperature and feeding speed should be adjusted separately.

Extrusion Mold Body Temperature

Setting the temperature for the extrusion mold die body is pretty straightforward. The main goal is to keep the melt from cooling down in the mold body. Most of the time, you’ll set it around 185°C. That works for most products you’ll make. But for some products, like bellows, you might need to set it a little higher, like 190°C.

Temperature of Mouth Mold Section

190℃ to 210℃, depending on how shiny you want the extruded product and how hard you’re pushing the extruder. In general, if you crank up the temperature of the die, you’ll get a shinier product. But you’ll also reduce the back pressure on the extruder. When you reduce the back pressure on the extruder, you naturally reduce the amount of friction and shear.

In other words, by increasing the die temperature, the internal frictional shear heat⁷ generation of the extruder can be reduced to a small extent (when the internal frictional shear heat is too large), and vice versa.

My company has been engaged in PVC extrusion production for 20 years, among which there have been some experienced extrusion operation host hand, most of them already know through the mouth mold temperature adjustment to meet the product needs of the production process.

What is the Optimization Mechanism of PVC Sheet Extrusion Process Temperature?

Optimizing the temperature in the PVC sheet extrusion process is crucial for quality control, affecting product consistency and production efficiency.

Optimizing PVC sheet extrusion temperature enhances quality by ensuring consistent thickness, minimizing waste, and reducing defects through precise heating zone control.

With a conical twin-screw extruder for PVC-U extrusion⁸ production, the whole process can be roughly divided into heating, constant temperature, insulation, and other three areas, according to the specific functions of each heating section.

The heating and temperature control⁹ mainly occur in the extruder, with the air vent as the boundary. It is divided into two relatively independent and interrelated parts: the insulation area, which is processed by the combined core, extrusion die body, and extrusion outlet mold.

First, let's be clear that there are two heat sources in the PVC-U extrusion process. One is the external heat provided by the electric heater. The other is the internal heat generated by the twin-screw shear, calendering, and friction of PVC-U materials, as well as the friction between the PVC-U itself. The two heat sources play different roles at different stages of extrusion.

The temperature control unit only controls the external heat. There is no internal heat in the extruder head, and the temperature of the die part of the mouth is generally easy to control (part of the parameters of the design of unconventional extrusion molds will also produce internal heat); the existence of internal heat, the shear is stronger, but it has not yet exceeded the needs of the material plasticization of the compression section and is mainly used for the exhaust service of the melt section, which is relatively stable and easier to control.

Shear is weak, mainly dependent on external heating, but external heating is difficult to meet the material plasticization needs of the feed section (external heating power configuration of the lower extruder is particularly prominent); shear heat has exceeded the material plasticization needs of the metering section is often not subject to the control of temperature control devices. Therefore, in the whole extrusion process of temperature control, feeding section, measuring section is the focus of temperature control and difficult.

The temperature control of extrusion mainly refers to the temperature of the material, not the temperature of the screw, barrel, and die. The set temperature is only a means, and the displayed temperature is different under different working conditions, and there is a corresponding relationship between the material temperature and the displayed temperature (the material temperature in the feeding section is lower than the displayed temperature, and the material temperature in the metering section is higher than the displayed temperature).

In addition, the installation position of the thermocouple also affects the displayed temperature, so the displayed temperature only partially reflects the material temperature, and it is only the basis and reference for setting the temperature. The following describes the specific temperature setting mechanism and the key points of each section.

What are the Overload Extrusion, Temperature Uncontrolled State and Countermeasures?

Overload extrusion poses significant challenges in manufacturing, particularly when temperature control fails, affecting material integrity and process efficiency.

Overload extrusion disrupts processing due to excess force or temperature issues; countermeasures include maintenance, precise temperature control, and monitoring to maintain stability and quality.

The new idea above has a premise. It is that under normal extrusion conditions, the display temperature is controlled as the benchmark. If the extrusion efficiency is not properly improved, it will also happen that the heat supplied by the feed section is difficult to meet the heat requirements of the material plasticization, the display temperature is not controlled, often lower than the set temperature, the material to the vent failed to plasticize well, there are still some powders that are vacuumed out of the vent.

Most operators will increase the temperature of the rear section to compensate for the compression section and the melting section. The harm is not too big. The main harm is in the metering section. The total heat in the metering section exceeds the heat required by the melt at a constant temperature.

This is because the increase in extrusion speed increases the heat generated by the shear friction in the metering section. The temperature is often higher than the set temperature, resulting in localized overheating and decomposition of the extruded product. This phenomenon becomes more serious as the extrusion efficiency increases.

This phenomenon varies with the magnitude of extrusion efficiency. The higher the extrusion efficiency, the greater the temperature difference between the set temperature and the display temperature, and the more serious the adverse consequences. This phenomenon is especially prominent in extruders with low shear heat or external heating power configuration in the feed section screw.

When the display temperature doesn’t match the set temperature, process optimization is a waste of time. This is a sign that the heat being put into the extruder isn’t the same as the heat needed to melt the plastic.

The temperature difference between the set temperature of the feeding section and the display temperature shows if there is not enough external heating or shear heat, and the temperature difference between the set temperature of the metering section and the display temperature shows how much extra shear heat there is.

Currently, China's extruder production in the feed section of the heating matching, respectively, take two measures: one is to improve the power of the heating coil, such as 6 5/132 conical twin-screw extruder feed section power configuration has reached 9 kW; the second is to reform the screw thread structure, in the feed section or compression section of the double-head thread after the setting of a single-head thread, effectively improving the compression ratio of the screw groove.

The lack of heat supply in the extruder feed section has improved a lot in recent years. However, the excessive shear heat in the metering section still limits the improvement of extrusion efficiency.

We also did a special study on this problem. Now all our twin-screw extruders are specially customized. We adjusted their parameters to increase the metering section of the screw elements and the gap between the screw elements to adapt to our ultra-high-speed extrusion. In addition to the shear heat caused by the screw structure, the shear heat is also directly affected by the ratio of the feed rate to the extrusion speed.

What are the Failure States and Countermeasures for Equipment, Electrical Appliances ?

Understanding failure states and effective countermeasures is crucial for maintaining the reliability and safety of equipment and electrical appliances across various sectors.

Equipment failures like overheating and wear are countered by regular maintenance, protective components, and quality materials, enhancing longevity and reducing downtime.

When you’re extruding, the key to success is controlling the melt temperature. You can set the temperature correctly, but if you overload the extruder or if something goes wrong with the equipment or the electrical system, the melt temperature will go out of control. And when the melt temperature goes out of control, you’re going to have a problem.

Conclusion

The PVC sheet extrusion process is a complex one that requires precise temperature control to achieve the desired plasticity and product properties. Because PVC resins are sensitive to heat, heat stabilizers must be added. The temperature settings for each section are as follows: the temperature of the feed section should be above 185°C, the compression and melt sections should be around 180°C, and the metering section should be less than 185°C.

The temperature of the mold section is about 185°C, and the temperature of the orifice section is 190°C-210°C. The extrusion process involves the balance of external and internal heat sources, especially the temperature of the feeding and metering section needs to be controlled in order to avoid overheating decomposition. Optimization of extrusion equipment and conditions is the key to improving efficiency.