In PVC pipe production lines, to increase the contact area between the material and the equipment and to enhance lubrication among the polymer particles—thereby facilitating processing, boosting throughput, and improving the surface finish of the finished product—1 to 5 parts of a lubricant are typically added during compounding. In actual production, it has been observed that the lubricant plays a critical role in the plasticization of the material and even in key mechanical properties such as the hydraulic pressure resistance of the pipes.

Types of Lubricants for PVC Pipe Production Lines

Based on their compatibility with polyethylene, lubricants used in PVC pipe production are classified into two categories.

1. A certain class of substances exhibits compatibility with polyethylene; their function is to reduce internal friction among the components and enhance material flowability. These are known as internal lubricants, such as stearic acid, glycerol monostearate, and xylitol stearate.

2. Another category exhibits poor compatibility with polyethylene; during processing, it migrates to the surfaces in contact with the material and equipment, thereby reducing adhesion and friction at these interfaces. These are external lubricants, such as paraffin wax, polyethylene wax, mineral oil, and silicone oil.

In actual production, the two types of lubricants are only relative; there is no strict demarcation criterion. At different processing temperatures, the roles of internal and external lubricants can shift, and they may sometimes exhibit both internal and external lubricating properties simultaneously.

The form in which lubricants are present in PVC pipe production lines

1. As a component in PVC pipe compounding, a certain amount of internal and external lubricants is typically added to maintain a balance between internal and external lubricity.

2. Most stabilizers exhibit a certain degree of lubricity. In PVC pipe production, stabilizers traditionally used include tris‑salt, dibasic salt, and hard lead compounds; in recent years, the trend has shifted toward composite, multifunctional formulations, with composite stabilizers now widely adopted. Metal soap stabilizers offer excellent internal lubrication.

A variety of composite stabilizing lubricants have emerged, integrating lead salts, rare earths, and lubricants into a single formulation.

The impact of lubricants on the production process of PVC plastic pipe manufacturing lines.

It is necessary to regularly account for variations in raw materials; due to differences in material composition, even after adjusting process parameters such as temperature and screw speed, satisfactory plasticization may still not be achieved. At present, formulations typically incorporate composite stabilizers, lubricants, PVC resin powder, and other additives.

The results indicate:

1. The compatibility of lubrication systems varies significantly among different stabilizers; an appropriate combination of lubricants is conducive to achieving excellent plasticity and lubricity.

2. For PVC resin powders with a high degree of polymerization, the amount of internal lubricant should be increased to reduce melt viscosity; for resins with poor thermal stability, the dosage of stabilizer should be raised; if a stabilizer with high lubricity is used, the amount of external lubricant should be appropriately reduced.

3. When using fillers with low activation levels, lubricants should be used sparingly.

Principles for Determining Lubricant Dosage

A mature lubrication system should, on the one hand, help reduce the viscosity of high‑temperature polyethylene melt, enhance material flowability, and minimize friction at the interface between the material and equipment, thereby facilitating the processing of fittings and pipes. On the other hand, it should prevent excessive lubricant from delaying plasticization and resulting in insufficient degree of plasticization.

The PVC resin powder, fillers, and stabilizers used in PVC pipe production lines have undergone significant changes. Moreover, differences in pipe specifications, as well as variations in extruders and die heads, necessitate appropriate adjustments to the lubricant formulation.

The amount of lubricant used should adhere to the following principles:

1. For resin powders with a high degree of polymerization, the internal lubricant should be appropriately increased.

2. When using a composite stabilizer containing lubricating components, the amount of lubricant should be appropriately reduced.

3. The internal and external lubricants in the formulation should be balanced to avoid processing difficulties.

4. For resin powders with poor stability, as the amount of stabilizer is increased, the amount of lubricant should be appropriately reduced.

5. When a large amount of filler is added, the lubricant should be increased accordingly.

6. When the processing temperature is high, the polymer tends to adhere to the processing equipment; therefore, the lubricant dosage should be appropriately increased.

7. When using larger processing equipment, the surface area of polymer adhesion increases, and the amount of lubricant should be increased.

8. Excessive lubricant can reduce the degree of material plasticization and weaken the mechanical properties of the pipe.