Skip Navigation Links
Contact
Literature
Careers
Sitemap
 
Skip Navigation Links
Home
Specialty Polymers
Vinyls
Site Map
Solvay.com


 

Processing Techniques 

Each PVC compound contains a diverse assortment of materials. Polymerization techniques and additives, such as plasticizers, pigments, fillers, etc., can enhance the properties of a single polymer (flow, mechanical strength, etc.). We offer custom-made formulations in line with developments in processing technology and consumer quality requirements. After use, these plastics can be recycled or their energy value recovered by clean incineration.

 
Expand All Collapse All
Choose your processing technique

A variety of processes are used to transform raw plastics into the thousands of everyday objects that we use. To mold or shape thermoplastics, they are basically softened to allow the plastic to flow through a dye, to be injected into, or formed in or over a mold. These processes usually allow scrap materials to be recycled as well.

Below, you’ll find short explanations about some of the more common processes.

Blow moulding

In the blow moulding process, molten resins are extruded in the form of a vertical tube, which is clamped between two halves of a mould. This tube is inflated so that it takes on the shape of the mould. It is then cooled, and released as the fully formed container. For larger containers, the molten resins have to be extruded very quickly or the container will 'sag' due to gravity.
This is called intermittent extrusion, which usually only produces one or two containers for each machine cycle. For smaller containers, like those for dairy products and fruit juices, there are machines which can produce up to 16 containers at a time. This allows them to process a high quantity of containers to meet the demands of the industry.

Calendering

Calendering is a continuous process which works in much the same way as an old-fashioned clothes mangle. For plastics, there are usually four heated rollers of different sizes rotating at slightly different speeds. The material is fed into these rollers, heated and melted, then shaped into a sheet or film. This is then cooled and rolled up. The sheets can be mono-oriented during this process. The most commonly calendered material is PVC.


Cast or blow film

Blown films are created by feeding plastic granules into an extruder where they are melted and homogenised before being pumped through a circular blown film die. The melted plastic forms a continuous tube which is drawn from the die. It is inflated and simultaneously cooled by rapidly moving air so that the plastic solidifies quickly. The tube is then collapsed between rollers and wound onto a reel.
Cast films also start life as plastic granules fed into an extruder, where they too are melted. The difference is that they are fed through a flat die onto a chilled roller so that they cool extremely quickly. Once the plastic has solidified, it is wound onto a reel.

Coating

There are several different types of coating processes, such as dipping, dip forming, spraying and co-extrusion.
In the most basic coating process, a very fluid plastic paste is spread over a base material or substrate (textile, paper, non-woven fabric) and then passed through an oven to ensure that the paste forms a gel.

In the dipping process, the metallic shape is pre-heated before being dipped into a plastisol (liquid paste based on PVC and plasticiser). This process is most particularly suited to PVC paste resins (emulsion and micro-suspension process), but powder dry-blends (suspension process) can also be used for specific needs.

Extruding can produce soft or rigid items which can be compact or cellular in form. Items which require specific characteristics (e.g. aesthetic appearance, good weather resistance) are made by the co-extrusion process, which uses one (jacketing of metallic wires) or two extruders and a specially shaped die.

Extrusion

In the extrusion process, plastic pellets or powder (dry-blends) is fed into a heated cylinder where rotating screws homogenise it and squeeze it through a die to give a finished or semi-finished product. Pellets are used in single screw extruders, and powders are used in twin screw extruders. The die is designed to produce the desired shape of the end product.

Extruding can produce soft or rigid items which can be compact or cellular in form. For producing hollow articles, a special tool is required and this process is called extrusion blow moulding. Profiles which require an aesthetic appearance are made by the co-extrusion process, which uses two extruders and a specially shaped die.

Injection moulding

In injection moulding, the plastic is forced into the mould at very high pressure. The mould is then kept at a given temperature while the polymer solidifies; the halves are opened and the finished article is ejected. For small parts, lots of moulds are often mounted on one machine and the molten plastic is injected into them all simultaneously. Injection moulding can produce far more complex items than extrusion, but it isn't a continuous process.

The finished articles it produces are in their final shape and can be rigid or soft, compact or cellular. Injection blow moulding allows hollow articles to be produced.
With over-moulding (co-injection), it's possible to produce articles with rigid cores (metal or polymer) by placing the cores in the mould before the plastic is injected.

Rotational moulding

Rotational moulding, or rotomoulding, is an extremely popular and well-used process for producing items that are usually hollow. It's most often used for very large articles which are usually made in small quantities. Items such as children's toys, garden furniture and road traffic bollards are manufactured by rotational moulding.  Rotomoulding uses polyethylene in powdered form; this is introduced into the mould along with any additives such as pigments or finishers.

The mould is closed and then spun both vertically and horizontally and moved into an oven. As the powder starts to melt and the mould continues rotating, it is flung onto the walls of the mould by centrifugal force where it forms a skin. After a fixed period, the mould is removed from the oven and allowed to cool carefully to avoid the product shrinking or warping.

Thermoforming

Thermoforming is a general term for the process of making plastic parts from a flat sheet of plastic by using pressure and temperature. In its most sophisticated form, thermoforming can provide small tolerances, sharp detail and meet very stringent specifications. When advanced finishing techniques are used, high-technology thermoforming can match the results obtained through injection moulding. Thermoforming is particularly suitable for producing large panels, housings, enclosures and similar parts.

Transfer moulding

Transfer moulding, or slush moulding, is a process in which molten resin is transferred from a meltpot into a mould which is hotter than the resin. This is unlike injection moulding where the mould is cooler. The higher temperature is important for filling long moulds in order to maintain a consistent wall thickness and to compensate for shrinkage. Once the mould has cooled and the plastic solidified, the item is removed and the next charge is loaded.

 

 





 





Links 





 
 
Current Site > SolvayPlastics
 
© SOLVAY 2014 Skip Navigation Links
Last Update (6/1/2012)