To produce final products from PVC powder or granules, most of the polymer molding processes including extrusion, blow molding, compression molding, rotational molding and injection can be used. It should be noted that the functional quality of polymer goods, including PVC, is not only dependent on the characteristics of the pure polymer and the prepared formulation, but also the type and conditions of the forming process.
Forming method of PVC products
extrusion
The extrusion process is the most common method of shaping PVC products. This process can be used not only directly and alone to produce many PVC final products, but also as one of the manufacturing steps in a number of other shaping processes. Dehi is used. During the extrusion process, the powder or PVC grains are first heated and compressed, and then become liquid and finally come out of the extruder with pressure.
Extruders generally have four main components and several auxiliary components.
Among the main components of an extruder, we can mention the electric motor, spiral, body, and unified feeding funnel.
The extruder spiral is the heart of the extruder and according to the formulation used and the final shape of the product, it is made in different designs. The spiral rotates with the help of an electric motor and a controllable speed.
Spiral extruder PVC molding
Extruder spiral is responsible for four main tasks of heating through cutting, mixing, pressure regulation and pumping. According to these tasks, the spiral has at least three distinct and recognizable areas.
The first part is the feeding area, which is located at the bottom of the feeding funnel PVC molding . In this area, the PVC powder or granules are compressed and the air in the feed is removed.
The second part, the spiral, is the transfer zone. In this area, the feed is melted and depending on the type of feed, the length of this area may be short or long. During the transition zone, the spiral root diameter increases gradually.
Twin screw extruder
This type of extruder has two spirals that are placed next to each other in different ways. Twin-screw extruders are divided into two general categories of unidirectional and unidirectional extruders according to the direction of rotation of the spirals.
The performance of double-screw extruders is similar to single-screw extruders, and powder or polymer grains are pressed together and then melted, and finally driven into the die by pressure to obtain the desired shape of the part.
Design by Hodeidah
Hodeidah is a mold through which the polymer melt is formed into the shape of this mold, which is actually the shape of the final product. Rheological studies show that for Newtonian fluids and with power law behavior, the pressure drop in Hodeidah has a direct relationship with the flow rate.
At first, spider claws were used in the pipe making industry, but sometimes the pipes produced by this method became brittle despite the fact that they were formulated. After conducting many investigations, researchers found out that the reason for the brittleness of some products is related to spider claws. Is .
Extrusion of PVC foam products
The extrusion process is also used to produce PVC foam products. In PVC foam formulations, a chemical foaming agent such as azodicarbonamide is usually used in the amount of 2-5% by weight of the polymer.
During the process, the foaming agent decomposes and produces nitrogen gas when it reaches a temperature of about 190 degrees Celsius.
Calendaring
PVC forming machine
Calendering method is used to produce some flexible and hard PVC products such as films and sheets, floor coverings, furniture coverings and some wall coverings.
In this shaping method, emulsion PVC resin is usually used in the formulation. Of course, vinyl chloride-vinyl acetate copolymer resin is sometimes used to produce hard parts by calendering method.
Two-roll calendering is similar to the process used to mix and soften elastomeric compounds. In multi-roller calendering, the first two rollers are for feeding and have the same function as two-roller calendering. The feeding rollers also have a warehouse, the amount of which depends on the dimensions of the rollers and their rotation speed.
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