application

The PVC pipe formulation contains: PVC resin, impact modifier, stabilizer, processing modifier, filler, pigment and external lubricant.

1. PVC resin

In order to obtain rapid and uniform plasticization, the suspension method should be used to loosen the resin.

——The resin used for double-wall corrugated pipes should have good molecular weight distribution and impurity content, so as to reduce the “fish eye” in the pipe and avoid the collapse of the pipe corrugation and the rupture of the pipe wall.

——The resin used for water supply pipes should be of “sanitary grade”, and the residual vinyl chloride in the resin should be within 1 mg/kg. In order to ensure the quality of the pipe and reduce the defective rate, the source of the resin should be stable.

2. Stabilizer

At present, the main heat stabilizers used in China are: metal soaps, composite lead salt stabilizers, rare earth composite stabilizers, and organic tin stabilizers.

Stabilizers containing heavy metals (such as Pb, Ba, Cd) are harmful to human health, and the dosage of these stabilizers in the formulation of water supply pipes is limited. In the single-screw extrusion process, the heating history of the material is longer than that in the twin-screw extrusion process, and the amount of stabilizer in the former is increased by more than 25%. The temperature of the head of the double-wall corrugated pipe is higher, the material stays in the head for a long time, and the amount of stabilizer in the formula is more than that of the ordinary pipe formula.

3. Filler

The role of fillers is to reduce costs. Try to use ultra-fine active fillers (higher price). The amount of pipe material is larger than that of profiles. Excessive amount of filler will cause the impact resistance to decrease and the pressure resistance of the pipe to decrease. Therefore, in chemical pipes and water supply pipes, the amount of filler in Less than 10 copies. The amount of filler in the drain pipe and cold-formed threading sleeve can be more, and the amount of CPE can be increased to change the drop of impact performance.

For pipes with lower requirements for pipe performance, and rain pipes, the amount of filler can be large, but the wear of the twin-screw extruder is serious.

4. Modifier

(1) Processing modifier: ordinary pipes can be used less or not; corrugated pipes and thin-walled pipes are mostly used.

(2) Impact modifier: less dosage than profiles, for two reasons: 1. Performance, low temperature resistance, tensile strength 2. Cost

(3) Other additives, colors, etc.: When the profile is used as an anti-aging agent, titanium dioxide must be added. The formula of the rigid PVC pipe is mainly pigment, mainly titanium dioxide or carbon black, which can be selected according to the appearance requirements of the pipe.

5. Matching of external lubricant and stabilizer

(1) Select the matching external lubricant according to the stabilizer

a. Organotin stabilizer. The organic tin stabilizer has good compatibility with PVC resin, and has a serious tendency to adhere to the metal wall. The cheapest external lubricant that matches it is a paraffin-based paraffin-calcium stearate system.

b. Lead salt stabilizer. Lead salt stabilizer has poor compatibility with PVC resin, and only attaches to the surface of PVC particles, which hinders the fusion between PVC particles. Usually, lead stearate-calcium stearate external lubricant is used to match it.

(2) The amount of external lubricant. If adjusting the amount of external lubricant still cannot meet the requirements of material processing, you can consider adding a small amount of internal lubricant. When the impact toughening modifier is used, due to the high melt viscosity, the possibility of adhesion to the metal surface is high, and the amount of external lubricant often needs to be increased; The thick-walled pipe requires more external lubricant. When the processing temperature is high, the tendency of the melt to adhere to the metal surface is high, and more external lubricants are added.

How are PVC Pipes Made?

PVC pipes are manufactured by extrusion of raw material PVC, and generally follow the same steps of typical pipe extrusion operations:

• Feeding of raw material pellets / powder into the PVC twin screw extruder
• Melting and heating in multiple extruder zones
• Extruding through a die to shape into a pipe
• Cooling of the shaped pipe
• Cutting of PVC pipes to the desired length