Peak Plastics was formed in 1971 as a high quality plastic injection moulding company producing mouldings and components covering an extensive range of applications and industries. Peak Plastics offers a complete service from product and tool design to product assembly. With the ability to accommodate long or short runs we are sure your exact requirements can be met. Located on the edge of the Peak District in the East Midlands, we are readily accessible from the M1 and other major road networks. Peak Plastics Ltd is proud to offer over 35 years worth of experience in the plastics industry so ensuring the highest degree of quality for your products.
Injection moulding is a manufacturing technique for making parts from both
thermoplastic and thermosetting plastic materials where high quality
multiple parts are required. Molten plastic is injected at high pressure
into a mould, which is the inverse of the product's shape. After the plastic
is cooled the mould is opened and the plastic shape is ready to use.
Injection moulding is typically used when mass production is required and
the expense of producing moulds is justified. Moulds are typically constructed
from hardened steel or aluminium due the hardness required and therefore
can take time to manufacture high quality moulds for injection moulding.
The moulds must 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 mould. More complex parts are formed
using more complex moulds, which may have movable sections called slides
which are inserted into the mould 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 Slides are then withdrawn to allow the part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 moulded parts to be reinserted
to allow a new plastic layer to form around the first part. This is often
referred to as overmoulding.
The basic injection cycle is as follows: Mould close - injection carriage
forward - inject plastic - metering - carriage retract - mould open - eject
part(s). The water-cooling channels that assist in cooling the mould and
the heated plastic solidifies into the part. The cycle is completed when
the mould opens and the part is ejected with the assistance of ejector pins
within the mould.
The resin, or raw material for injection molding, is usually in pellet or
granule form, and is melted by heat and shearing forces shortly before being
injected into the mould. Resin pellets are poured into the feed hopper,
a large open bottomed container, which feeds the granules down to the screw.
The screw is rotated by a motor, feeding pellets up the screw's grooves.
The depth of the screw flights decreases towards the end of the screw nearest
the mould, compressing the heated plastic. As the screw rotates, the pellets
are moved forward in the screw and they undergo extreme pressure and friction
which generates most of the heat needed to melt the pellets. Heaters on
either side of the screw assist in the heating and temperature control during
the melting process.
The channels through which the plastic flows toward the chamber will also
solidify, forming an attached frame. This frame is composed of the sprue,
which is the main channel from the reservoir of molten resin, parallel with
the direction of draw, and runners, which are perpendicular to the direction
of draw, and are used to convey molten resin to the gate(s), or point(s)
of injection. The sprue and runner system can be cut or twisted off and
recycled, sometimes being granulated next to the mould machine. Some moulds
are designed so that the part is automatically stripped through action of
the mould
Peak Plastics Ltd