Plastic processing
The term plastic processing refers to the production of plastic molded parts, semi-finished products, films, fibers, etc. which are made of plastic. Plastics are usually produced by the chemical industry, which are commercially available in various form, for example, as granules or masterbatches, sheet, powder, film or in plate form. In the area of reaction technology, chemicals are used to produce plastics.
Classification of procedures
Primary forming processes, forming processes, and connecting procedures are especially important for plastics manufacturing. The table below displays a classification of plastic processing methods.
The original molding processes
A basic molding method uses shapeless material such as powders or melts to create solid, geometric bodies. This procedure, also known as primary molding, produces molded items such as housing, pipes, and cups. These techniques are the most common type of thermoplastic molding, often known as injection molding compounds, and do not require any post-processing of the molded products. The thermosets, formerly known as molding compounds, can only be treated using main molding procedures. However, forming methods cannot be employed to process thermosets.
The injection molding
During injection molding , The plastic is heated to melting point in a plasticizing apparatus before being injected at high pressure into a mold cavity. Prior to cooling, the plastic is compacted. The injection-molded item is then expelled. The key advantage of this automated technique is that it allows you to make larger quantities of more complex molded parts in a shorter period of time. The drawback of the procedure, however, is that the molds are relatively expensive to produce.
The extrusion
During extrusion, In an extruder, the unprocessed plastic initially goes through a funnel before entering a cylinder. There, the material is melted, homogenized, and compacted. After plasticizing, a screw pushes the plastic through a nozzle. Up to this point, the technique is quite similar to injection molding, with the primary distinction being that extrusion is a continuous operation. Extrusion produces pipes, plates, profiles, textile fibers, and masterbatches.
The calendaring
Calendaring is the process of molding plastic into a desired shape by rolling it through a sequence of rollers. This manufacturing method is ideal for making foils, thin panels, and floor coverings.
The rotational molding
Rotational molding is also known as rotational casting and sintering. This is a unique manufacturing technology used to create massive, hollow, and seamless plastic components. During the processing, molten plastic grains are placed in a revolving mold. As the plastic cools, it deposits on the rotary tool’s inner surfaces.
Depending on the rotary tool design, workpieces with varying wall thicknesses can be manufactured in a single mold. Rotational molding is used to manufacture a variety of products, including transportation containers and larger housings, as well as furniture, dashboards and toys.
The foaming
Foaming refers to the process of creating foams. Procedures can be divided into three categories:
• Chemical blowing processes: Polymerization produces gases that froth the material. For example, PU foams are produced.
• The physical blowing procedure involves adding low-boiling liquids to a reaction combination. These evaporate during polymerization, forming characteristic gas bubbles. For example, foam polystyrene is produced.
• In mechanical blowing, a plastic melt is swirled and gas is blasted into it.
Pour
The discontinuous casting procedure is used to produce thermosets. Liquid substances (reactants) are combined homogeneously to produce a chemical reaction. The reactive liquid is then poured into a mold, with vacuum assisting in the filling process. The mixture, which reacts to form a thermoset plastic, solidifies inside the mold and may be removed. The slabstock foam process is a common method for casting polyurethane.
The steps for casting thermosets are as follows:
• Processing,
• Reactant mixing,
- Shed
- hardening in the mold.
• Demolding and post-hardening of the molded object in the heating cabinet. Post-processing.
The blow molding
During blow molding, a thermoplastic preform is inflated in a mold with compressed air. The air pressure presses the preform against the mold’s inner wall, holding it in the desired shape while the plastic cools. Extrusion blow molding differs from stretch blow molding. This plastic production procedure is typically used to make bottles, automobile tanks, and barrels.
Forming process
The primary characteristic of thermoplastics is that they soften when heated. When softened in this manner, thermoplastics can be molded into a new shape with modest forming forces, retaining the resulting products after they have cooled. The term “thermoforming” refers to the industrial application of thermoplastic characteristics.
Joining process
Joining in manufacturing technology, and hence in plastics processing, refers to processes that permanently connect two components together. Plastics are typically welded or glued together. Plastic components can also be connected using screws, rivets, and clinching (enforcement joining).
Welding plastics
To weld plastic, the substance must be able to melt. This feature is only found in thermoplastics, hence only these plastics are appropriate for welding. To melt the material, many heat sources can be used, including electric induction heaters for “hot-element welding,” hot compressed air for “warm gas welding,” and light or laser radiation for “radiation welding.” You can also utilize friction to generate heat. In high-frequency welding, molecules rub against one another, whereas in friction welding, mechanical friction creates the heat needed for welding.
Bonding plastics
Gluing is an effective method for connecting thermosets and elastomers for plastic manufacturing. However, the polar characteristics of the plastics to be bonded are the most important prerequisite for successful plastic bonding. To achieve the required wettability, many plastics must be prepared, such as through corona or plasma treatment. Physical adhesives can be divided into three categories. Some adhesives have a molecular structure even before they are applied. Other adhesives harden by evaporating a solvent. Finally, chemical adhesives cause curing by a chemical reaction.