Tube and profile extrusion using the PVC pipe extrusion line

Here, we will start by looking at the line components of the extrusion process.

PVC pipe extrusion line Components: This process consists of an extruder with a barrel and spindle design suitable for the type of material to be processed. In the production of tube and profile, the most common plastic used is Polyvinyl Chloride (PVC), although Polyethylene tubing is also used for its low cost.

a) Pipe Die or Head: Four types of head can be distinguished in equipment for the production of pipe: the head with spider-mandrel, the spiral mandrel head, the head with lateral feed and the head with lateral feed and the head or die with mesh package. Each of these designs provides different flow patterns for the plastic, and the most appropriate type must be selected to avoid polymer degradation effects or quality defects in the product.

b) Pipe Calibration Systems: They provide the tube with the specified diameter and the circular shape that the product requires. Two types of calibration systems can be distinguished, based on the wall shape of the tube produced:

- Calibration for smooth-walled pipe

- Calibration for corrugated-walled pipe

c) Smooth Wall Pipe Calibration:

Vacuum Calibration. In this type of calibration, the vacuum caused on the outside of the tube causes a pressure difference that makes the polymer, still moldable due to the high temperature at which it is located, keep in contact with the metal forming tube, which have a inside diameter equal to the outside diameter specified for the product.

Pressure Calibration. This promotes the formation of the tube against the walls of the calibration tube, with the difference that in this case it is air that is injected into the inside of the tube that is extruded.

d) Corrugated Pipe Calibration:

Vacuum Calibration. The vacuum corrugated tube forming process has the same principle as for smooth tube; the corrugated wall is in continuous movement.

Pressure Calibration. In this type of calibration, pressurized air enters through ducts in the head and is injected into the still hot extruded tube. The resulting pressure difference molds the plastic wall against the movable formers, providing the product with the required rebar.

e) Cooling Unit or Tub: It is intended to remove the excess heat that the pipe conserves at the outlet of the calibration tank. The importance of cooling lies in the stability that the plastic acquires so as not to deform when passing through the draft unit, where the tube is subjected to pressures that could cause alterations in the required circular shape. Two types of cooling tubs can be found:

· Spray Cooling:

· Immersion Cooling:

f) Draft Unit: Once the passage through the cooling unit is completed, the pipeline passes to the cooling unit, the pipeline passes to the draft unit where all the force that keeps the plastic moving within a line is generated. Three types of shooting units are known:

- By Caterpillar

- Of Bands

- Of Wheels or Rollers

g) Cutting Units: There are several types of cutting units, designed to suit the work required in the production of flexible pipe. The common practice is to form rolls, which reduces cutting work, while in the production of rigid pipe. Tube cutting must be done accurately at equal length intervals.

For the selection of rigid and flexible pipe cutting units, PVC pipe extrusion line suppliers recommend that it will be necessary to take into account the following factors:

- The diameter and wall thickness

- The raw material used

- The shape and quality of the cut

- The length of the cut

h) Winding Units: It is used for flexible materials, which are those that do not suffer permanent deformation due to being wound. Polyolefin pipes and flexible PVC hoses are suitable for this process. Although they are not very complicated systems, the following considerations should be observed when using a pipe winder: