GWP Plastics are extruders of plastic profile and clear and coloured PVC tubing used in spray pump bottles, manufacture rigid pvc edging used as board edging for the agricultural, aluminium, furniture, motor, packaging and upholstery industries.
Plastic Injection Moulding
Injection moulding is a manufacturing
process for making parts from thermoplastic and thermosetting plastic
materials using plastic injection moulding machines. Molten plastic is injected at high pressure into
a mould , which is the inverse of the
product's shape. After a product is designed by an Industrial Designer
or an Engineer, moulds are made by a mouldmaker or toolmaker from metal,
usually either steel or aluminium, and precision-machined to form the
features of the desired part. Injection moulding is widely used for manufacturing
a variety of plastic products and parts, from the smallest component to entire body panels
of cars. Injection molding is the most common method of production, with
some commonly made items including bottle caps and outdoor furniture.
Injection molding machines, also known as presses, hold the moulds in which
the components are shaped. Presses are rated by tonnage, which expresses
the amount of clamping force that the machine can generate. This pressure
keeps the mold closed during the injection process. Tonnage can vary from
less than 5 tons to 6000 tons, with the higher figures used in comparatively
few manufacturing operations.
Moulds separate into at least two halves (called the core and the cavity)
to permit the part to be extracted. In general the shape of a part must
not cause it to be locked into the mold. For example, sides of objects typically
cannot be parallel with the direction of draw (the direction in which the
core and cavity separate from each other). They are angled slightly (draft),
and examination of most plastic household objects will reveal this. Parts
that are "bucket-like" tend to shrink onto the core while cooling,
and after the cavity is pulled away. Pins are the most popular method of
removal from the core, but air ejection, and stripper plates can also be
used depending on the application. Most ejection plates are found on the
moving half of the tool, but they can be placed on the fixed half. More
complex parts are formed using more complex molds, which may have movable
sections called slides which are inserted into the mold to form features
that cannot be formed using only a core and a cavity. Slides are then withdrawn
to allow the part to be released. Some moulds allow previously molded parts
to be reinserted to allow a new plastic layer to form around the first part.
This is often referred to as overmolding. This system can allow for production
of one piece tires and wheels. 2-shot or multi shot molds are designed to
"overmold" within a single molding cycle and must be processed
on specialized injection molding machines with two or more injection units.
This can be achieved by having pairs of identical cores and pairs of different
cavities within the mold. After injection of the first material, the component
is rotated on the core from the one cavity to another. The second cavity
differs from the first in that the detail for the second material is included.
The second material is then injected into the additional cavity detail before
the completed part is ejected from the mold. Common applications include
"soft-grip" toothbrushes and freelander grab handles. The core
and cavity, along with injection and cooling hoses form the mold tool. While
large tools are very heavy (up to 60t), they can be hoisted into molding
machines for production and removed when molding is complete or the tool
needs repairing. A mold can produce several copies of the same parts in
a single "shot". The number of "impressions" in the
mold of that part is referred to as cavitation. A tool with one impression
will often be called a single cavity (impression) tool. A mold with 2 or
more cavities of the same parts will likely be referred to as multiple cavity
tooling. Some extremely high production volume molds (like those for bottle
caps) can have over 128 cavities. In some cases multiple cavity tooling
will mold a series of different parts in the same tool. Some toolmakers
call these molds family molds as all the parts are not the same but often
part of a family of parts (to be used in the same product for example).
Plastic injection moulding machine - a machine for making
plastic parts. Manufacturing products by injection moulding process.
Consist of two main parts, an injection unit and a clamping unit.
Injection moulding machines can fasten the moulds in either a horizontal or vertical position. The majority are horizontally
oriented but vertical injection moulding machines are used in some niche applications such as insert moulding, allowing the plastic injection
moulding machine to take advantage of gravity. There are many ways to fasten the tools to the platens, the most common being manual clamps
(both halves are bolted to the platens); however hydraulic clamps and magnetic clamps are also used.
The magnetic and hydraulic clamps are used where fast tool changes are
Types of injection moulding machines
Plastic injection moulding machines / plastic moulding machines are classified primarily by the type of driving systems they use: hydraulic, electric, or hybrid. Hydraulic presses have historically been the only option available to moulders until Nissei Plastic Industrial Co., LTD introduced the first all-electric injection moulding machine in 1983. The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive. Hybrid injection moulding machines take advantage of the best features of both hydraulic and electric systems. Hydraulic machines are the predominant type in most of the world. Hydraulic Injection Moulding Machines, Electric Injection Moulding Machines, Toggle Injection Moulding Machines.
Injection moulding machine - a machine for making plastic parts. Manufacturing
products by injection moulding process. Consist of two main parts, an
injection unit and a clamping unit. Injection moulding machines can fasten
the moulds in either a horizontal or vertical position. The majority is
horizontally oriented but vertical injection moulding machines are used
in some niche applications such as insert moulding, allowing the plastic
injection moulding machine to take advantage of gravity. There are many
ways to fasten the tools to the platens, the most common being manual
clamps (both halves are bolted to the platens); however hydraulic clamps
(chocks are used to hold the tool in place) and magnetic clamps are also
used. The magnetic and hydraulic clamps are used where fast tool changes
Setting Guidelines for unfilled materials
Heat Contents of Some Moulding Materials
Transducer Pressure Range
Dry Cycle Times
Calculating Mould Fill and Solidificaion Times
Clamping Force Requirements