Polyvinyl chloride, better known as PVC, is a type of plastic widely used for its low cost, but also for its multiple applications. This plastic has the characteristic of not degrading with the action of sunlight, in addition to being incredibly resistant to water and wind. But, how is PVC machining done?
The benefits of PVC for the industry
Polyvinyl chloride is a plastic derivative that originates due to the polymerization of vinyl chloride monomer transforming into polyvinyl chloride. To obtain this polymer, two peculiar elements are required: sodium chloride or natural salt and petroleum or natural gas and it is obtained by following any of the four production processes that exist to create it: emulsion, suspension, mass, and solution.
Among its physical characteristics, we find that PVC is white, amorphous, and opaque; it softens at 80 °C and, to decompose, requires the temperature to rise to 140 °C. Thanks to its physical characteristics, PVC machining is very simple and economical.
PVC is one of the most widely used plastics worldwide, particularly due to its low cost, and from its manufacturing, this plastic is very economical when compared to others. During the production processes, the physical and chemical characteristics of PVC are maintained, making it a very versatile material capable of being adapted to multiple areas and tasks. For example, it is very common to find it in construction, but also in food preservation, among many others.
Characteristics of PVC
To begin with, PVC is a plastic very resistant to the environment, fire and it even has excellent electrical resistance, which is why it is widely used for making electrical connections and installations. Another characteristic of PVC is that it can change its shape if the right pressure is applied (it is ductile), but it also has a lot of toughness; toughness refers to a property of materials; it is the total deformation energy a material can withstand before breaking. PVC can withstand up to 60 years! Furthermore, this plastic is stable.
Types of PVC
Due to its resistance, PVC is divided into two: rigid (PVC-U) and flexible (PVC-P). Rigid PVC is most commonly used for contact with pipes, for example, as it is non-corrosive. Flexible PVC is more frequently found protecting cables.
Processes for PVC machining
Plastics have a lower thermal conductivity than metals, which is why it is essential to dissipate the heat generated during machining. And as we have already mentioned, PVC requires high temperatures to begin deforming, and when these temperatures rise above 200 °C, toxic and harmful substances may be produced.
When you want to machine PVC, the most common thing is to use one of these processes:
- Injection molding: where a polymer, ceramic, or molten metal is injected into a mold that closes under pressure and is cold. The injection is done through a small hole or gate.
- Extrusion: molding is done using a continuous flow of pressure and thrust. The plastic passes through a mold that gives it shape.
- Pressing: plastic molding by pressing is when the plastic is poured onto a mold that closes, with another mold on top of it, and heat and pressure are applied.
- Lamination, resin mixed with a catalyst or hardener is used, and a mold is soaked with this mixture. The goal of this method is to use a reinforced piece.
CNC Machining
For PVC machining, it is possible to use the vast majority of machine tools used for machining metals and wood, but they must have a ground tool for use on plastic. The speed must be controlled and lower than when machining metals; also, the feed rate should be high and lack cutting depth. To properly disperse heat, it is possible to use water or compressed air; this allows for cooling procedures to be carried out after machining.
One of the most used machine tools for PVC machining is the numerically controlled milling machine. This milling machine allows for chip removal but also performs various other tasks such as flattening, grooving, drilling, threading, etc. Thanks to the programs with which the milling machine's computer operates, it will be possible to choose the type of work you want to do on the piece and indicate that the material to be worked on is plastic; it is also possible to program and adjust the speed of the milling cutter, which is the cutting tool of this machine.
