The secondary forming is one of the plastic molding processing method.
With plastic material or parison as raw material, make its external force by
heating and a method of the shape of the products needed.
Secondary molding is a the piece, pipe, plate, such as plastic
material, heating in a kind of rubber state, deformation by external force and
moulding for all kinds of simple shape, then through cooling stereotypes and
products. Secondary molding including the hollow blow molding, thermoforming,
stretching film forming method, such as only applies to thermoplastic plastic
molding. Secondary molding is in a molding on the basis of a method.
Mainly includes the following several forming methods:
Hot forming is a thermoplastic plastic sheet is heated to softening,
the gas pressure, liquid pressure or mechanical pressure, using the appropriate
tooling or jig and make its products a molding method. Plastic thermoforming
method are many, generally can be divided into:
Molding using single mode (male die and female die) or to die, using
plus mechanical pressure or weight, to make all kinds of products from sheet
forming method, it is different from a processing molding. This method is
suitable for all thermoplastics.
Differential pressure molding using single mode (male die and female
die) or to die, also don't have to die, in the gas under the action of pressure
difference, make the heating to soft plastic sheets with mould surface, cooling
is made after forming methods of various kinds of products. Can be divided into
the vacuum forming and differential pressure molding pressure molding.
Thermoforming especially suitable for thin wall, large surface area of
the products manufacturing. The commonly used plastic varieties have various
types of polystyrene, organic glass, PVC, ABS, polyethylene, polypropylene,
polyamide, polycarbonate, and polyethylene terephthalate, etc.
Thermoforming equipment including clamping system, heating system,
vacuum and compressed air system and forming mould, etc.
Biaxial tensile
To make molecular reorientation of thermoplastic film or plate, etc,
especially above the glass transition temperature of the bidirectional tensile
process. Stretch orientation to between the glass transition temperature and
melting point of polymer, after directional tensile and rapid cooling to room
temperature, the film or monofilament, on the drawing direction has a lot to improve
mechanical properties.
Suitable for directional stretching of polymer are: polyvinyl chloride
(PVC), polyethylene terephthalate, polyvinylidene chloride, poly (methyl
methacrylate, polyethylene, polypropylene, polystyrene, and some of the styrene
copolymer.
Solid phase forming
Solid phase forming is a thermoplastic material or stock under pressure
for products with mold the molding method. In the plastic molding process of
molten (softening) under temperature (below the melting point at least 10-20 ℃). Solid phase
forming. Including plastic of non-crystalline class above the glass transition
temperature, melting point below the high elastic area processing is often
called thermoforming, and below the glass transition temperature is called cold
forming or room temperature molding processing, also often called cold working
methods or room temperature plasticity of plastic processing.
The method has the following advantages: short production cycle;
Improve the toughness and strength of products; Simple equipment, can produce
large and super large products; Cost reduction. Defect is: hard to produce
complex shape, the precision of products; It is difficult to control production
process, the products easy to be out of shape, craze.
Solid phase forming include: sheet roll, deep drawing or sheet
stamping, hydraulic forming, extrusion, cold stamping, roll forming, etc.
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