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Polymer Processing Method - Coggle Diagram
Polymer Processing Method
Calendering
Calendering technique is used to produce rubber sheets of various lengths and thickness.It is also widely used for skin coating of fabrics including shower curtains, tablecloths and laminating film.
Calendering technique is used for high-volume, high quality plastic film and sheet, mainly used for PVC as well as for certain other modified thermoplastics.
In this process, the extrudate is extruded directly into the nip area between two rolls. The rollers have small gap and plastic is forced through the gaps by the counter rotating of the rollers.
Extrusion
Extrusion is the continuous semi-finished
product with uniform cross section.
Type of products are extend from simple semi-finished products (tubes,sheets and film) to complicated profiles.
In principle, the extrusion process comprises the forcing of molten material through a shaped die by means of pressure
General steps : First, materials fed into hopper, falls through a hole in the top the extruder (feed throat) onto the screw. The screw moves the molten plastic forward until the end of the extruder barrel to which die has been attached. Die gives shape to molten plastics when it cooled in water tank.
Compression molding
Compression molding is a common process used for both thermoplastic and thermoset stock shape materials.
Type of product : Melamine kitchenware (bowls, cups, and similar products) and fiber composites and cork.
General steps : The mould is held between the heated platens of the hydraulic press and a prepared quantity of molding compound is placed in the mould. The platen closes with sufficient pressure to minimize flash at mould parts line. The compounds softens and flow to shape, chemical cure occur as temperature increases. The press is opened and the molding removed.
Compression Moulding is a method of moulding in which the moulding material, generally preheated, is first placed in an open, heated mould cavity.
Transfer molding
Transfer molding is development of compression molding in which reservoir of the molding compound is located in the mold and upon closure is transferred via runner to the cavities.
The process is versatile and can fabricate products with embedded objects such as foam cores or other components in addition to the fiber preform.
General steps : The process consists of a mould cavity and a transfer cavity. The filled charge is initially placed in the transfer cavity, heated until softened and then pressure is applied to the ram, causing the charge to flow through the transfer port to the mould cavity.
The material most commonly used for transfer molding is a thermoset polymer. This type of polymer is easy to mold and manipulate, but upon curing, hardens into a permanent form.
Blow Molding
Blow Molding is a process in which a heated hollow thermoplastic tube (parison) is inflated into a closed mold conforming the shape of the mold cavity.
Type of polymer : The most widely used materials for Blow Molding are: Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE)
Type of products : hollow items such as milk and soda bottles.
General steps : Firstly, melt the resin-done in the extruder. It will form the molten resin into a cylinder or tube( the tube is call parison). Parison is placed inside a mold and inflated so that the plastic is pushed outward against the cavity wall. The part is allowed to cool in the mold and is then ejected. Finally, the part is trimmed.
Rotational Molding
Uses gravity inside a rotating mold to achieve a hollow form. It is an alternative to blow molding for making large, hollow shapes
It is used principally for thermoplastic polymers, but
applications for thermosets and elastomers are becoming more common.
Type of products : Some types of plastic tanks produced with this process include fuel and oil tanks, septic tanks, water treatment tanks, and shipping tanks.
General steps : A predetermined amount of polymer powder is loaded into the cavity of a split mold. The mold is then heated and simultaneously rotated on 2 perpendicular axes, so that the powder impinges on all internal surfaces of mold. While still rotating, the mold is cooled so that the plastic skin solidifies. The mold is opened, and the part is unloaded.
Pultrusion
Pultrusion is a continuous process for manufacture of spendere materials with constant cross-section (rod,
tubes, beam, etc). As opposed to extrusion, which pushes the material, pultrusion pulls the material.
Starting materials can be in the forms of preimpregnated or fiber + resin. Many resin types may be used in pultrusion including polyester, polyurethane, vinylester and epoxy.
General steps : Continuous rovings of the reinforcement are impregnated with the resins ( passing through a bath of resin). Then pulled through the heated die (compact and give shape to the composites). Curing will take place in the heated die and oven. Puller is used to pull the whole system with certain speed.
Thermoforming
Thermoforming is reshaping of plastics under the influence of heat and pressure or vacuum. The material is not melted, lower pressure are required to thermoform.
It is a manufacturing process for utilize thermoplastic sheet or film. It also can be used on large scale for the manufacture of packaging. It also can create large parts (swimming pool,motor vehicle parts).
General steps : Heat a thermoplatic sheet until it softens. Force the hot and pliable material against the contours of a mold by using either mechanical, air or vacuum pressure. Lastly, it is held against the mold and allow to cool, and plastics retain its shape.
Filament Winding
Filament winding is a fabrication technique mainly used for manufacturing open (cylinders) or closed end structures (pressure vessels or tanks). This process involves winding filaments under tension over a rotating mandrel.
Glass fibre is the fibre most frequently used for filament winding, carbon and aramid fibres are also used.
Type of products : pressure vessel, storage tanks, and
aerospace parts such as helicopter blades.
General steps : Firstly, the fibers are passed through the resin bath and then continuously wound onto the mandrel. After wounding number of layers, curing is carried out in an oven or room temperature. Lastly, the mandrel is removed.
Injection molding
Injection moulding is a manufacturing process for producing parts by injecting molten material into a mould, or mold.
Most common type of polymer used is thermoplastic and thermosetting polymers.
Type of products such as wire spools, packaging, bottle caps, automotive parts and components, toys, pocket combs, storage containers, mechanical parts (including gears), and most other plastic products
General steps : Initially, the mould is closed and a short of melt is ready in the injection unit. Injection occurs when the valve opens and the screw acting as a plunger forces the melt through the nozzle into the mold. The hold on stage when pressure is maintained during the early stages of cooling to counteract contraction. The valves closes and screw rotation starts, screw move backwards to give a fresh shot of melt in front. Meanwhile. the molding is cooling and once ready the press and the mould open and the molding is
removed. The mould closes again and the cycle repeats
Blown Film extrusion
It is a process utilize air to shape softened polymer tubes and no mold is required.
There are many types of polymers that can be used in blown film extrusion with the most common being polypropylene and polyethylene (LDPE, HDPE and LLDPE).
It is used to to produce relatively thin film and bag.
General steps : The extruded materials flow through a tubular die. The melt flow around a mandrel and exits the die as a tube. A cooling ring is at the exit of die to provide dimensional stability. Air is introduced through the back of die and flow upwards. The tube continues to expand,cool and crystallize until tensile strength = pressure of air inside. The tube is then forces into a flat sheet by collapsing guides and moved into nip rolls. Then it travels down over some rollers and sealed.