PVC processing conditions

PVC processing conditions

Generic Class

PVC (Polyvinyl Chloride)

Typical Applications

Water distribution piping, home plumbing, house siding, business machine housings, electronics packaging, medical apparatus, packaging for foodstuffs, etc.

Injection Molding Processing Conditions

Drying

Not usually necessary as PVC absorbs very little water. 

Melt Temperature 

160 - 220 C (320 - 428 F) 

Mold Temperature

20 - 70 C (68 - 158 F)

Material Injection Pressure

Up to 150 MPa

Packing Pressure

Up to 100 MPa

Injection Speed

Relatively slow, to avoid material degradation

Runners and Gates

All conventional gate types may be used; pin-point and submarine gates are used for molding small components and fan gates are typically used for thick sections. The minimum diameter of pin-point or submarine gates should be 1 mm and the thickness of fan gates should not be less than 1 mm.

Sprues should be as short as possible; typical runner sizes are 6 - 10 mm and should have a full round cross-section. Insulated hot runners and certain types of hot sprue bushings may be used with PVC.

Chemical and Physical Properties

Rigid (unplasticised) PVC is one of the most widely used plastic materials. It is produced from sodium chloride and natural gas. The repeat chemical structure is vinyl chloride. Additives are mixed with PVC to make it processible. PVC grades produced by suspension or mass polymerization techniques are the major types used for melt processing. PVC is substantially an amorphous material.

Some of the additives used include stabilizers, lubricants, processing aids, pigments, impact modifiers, and fillers. Some features of PVC include low combustibility, toughness (designed to be virtually unbreakable), good weatherability (including good color and impact retention, and no loss in stiffness), and excellent dimensional stability. PVC is highly resistant to oxidizing and reducing agents, and strong acids. However, unplasticised PVC is not recommended for environmental and continuous use above 60 C (140 F). It is not resistant to concentrated oxidizing acids such as sulfuric or nitric acid and is unsuitable for use with aromatic and chlorinated hydrocarbons.

It is very important to process the material at the correct melt temperature; otherwise severe problems from decomposition (which produces hydrochloric acid which in turn accelerates decomposition) could result.

PVC is a relatively stiff flow material and has a narrow processing range. The molecular weight determines the flow characteristics. Higher molecular weight materials are more difficult to process (this could be modified by addition of lubricants). Typically, however, relatively low molecular weight grades are used in molding).

Shrinkage is fairly low (0.002 - 0.006 mm/mm or 0.2 - 0.6%).


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