How is PVC machining done?

The polyvinyl chloride, better known as PVC, is a type of plastic widely used because of its low cost, but also because of its many applications. This plastic has the property of not degrading under sunlight, and it is also incredibly resistant to water and wind. But how do you go about PVC machining?

The benefits of PVC for industry

Polyvinyl chloride is a plastic derivative that results from the polymerization of vinyl chloride monomer as it turns into polyvinyl chloride. Two particular raw materials are needed to obtain this polymer: sodium chloride or natural salt, and oil or natural gas , and it is obtained by any of the four production processes used to create it: emulsion, suspension, bulk and solution. 

In terms of its physical properties, PVC is white, amorphous and opaque; it softens at 80 °C and only decomposes when the temperature rises to 140 °C. Thanks to its physical properties, PVC machining is very simple and economical.

PVC is one of the most widely used plastics in the world, particularly because of its low cost: from the moment it is produced, this plastic is very cheap compared with others. During production processes, the physical and chemical properties of PVC are maintained, making it a very versatile material that can be adapted to many areas and tasks. For example, it is very common in construction, but also in food preservation, among many others.

Properties of PVC

To begin with, PVC is a plastic that is highly resistant to the environment and to fire and it even has excellent electrical resistance, which is why it is widely used for electrical connections and installations. Another property of PVC is that it can change shape if the right pressure is applied (it is ductile), but it also has great toughness; toughness is a property of materials: the total deformation energy a material can absorb before breaking. PVC can last up to 60 years! In addition, this plastic is stable.

Types of PVC

Based on its strength, PVC is divided into two types: rigid (PVC-U) and flexible (PVC-P). Rigid PVC is the one most used for pipes, for example, since it is non-corrosive. Flexible PVC is more commonly found protecting cables. 

Processes for PVC machining

Plastics have lower thermal conductivity than metals, which is why it is essential to dissipate the heat generated during machining. As already mentioned, PVC requires high temperatures to start deforming and, when these temperatures exceed 200 °C, toxic and harmful substances may be produced. 

When you want to machine PVC , the most common approach is to use one of these processes:

• Injection molding: a molten polymer, ceramic or metal is injected into a cold mold that is closed under pressure. Injection takes place through a small opening or gate.
• Extrusion: molding is carried out using a continuous flow of pressure and thrust. The plastic passes through a die that gives it its shape.
• Compression molding: in compression molding, the plastic is poured into a mold that is closed by another mold on top, and heat and pressure are applied.
• Lamination, resin mixed with a catalyst or hardener is used to wet a mold. The aim of this method is to produce a reinforced part.

CNC machining

For PVC machining most of the machine tools used to machine metal and wood can be used, but they must have a ground tool for use on plastic. Speed must be controlled and kept lower than when machining metals; in addition, the feed rate must be high with a shallow depth of cut. To dissipate heat properly, water or compressed air can be used; this makes it possible to carry out cooling procedures after machining. 

One of the most widely used machine tools for PVC machining is the numerically controlled milling machine. This milling machine removes chips, but it can also perform many other jobs such as face milling, grooving, drilling, threading, etc. Thanks to the programs run by the milling machine's computer, you can choose the type of work to be done on the part and specify that the material to be machined is plastic; you can also program and adjust the speed of the milling cutter, which is the cutting tool of this machine.