Plastic injection mold is given to the
shape and size of the molding member. Although the structure of the mold and
performance of varieties of plastic, shape, and configuration and the type of
plastics injection molding machine may be different and changing, but the basic
structure is the same. Die mainly by gating system, molded parts and structural
parts of three parts. Gating system and molded parts which are in direct
contact with the plastic part, and with the plastics and products change, the
mold is the most complex and the biggest change, the most demanding part of the
process finish and accuracy.
Gating system refers to the plastic from
the nozzle portion of the cavity before entering the flow path, including the
main channel, cold-slug, diversion channel and the gate and so on. Forming part
refers to the shape of the various parts constituting products, including
dynamic simulation, the fixed mold and cavity, core, forming rod and exhaust
ports and so on. A typical mold structure as shown.
Sprue
It is mold injection machine nozzle
connected to a shunt or cavity section channel. Sprue concave top to the nozzle
convergence. Sprue inlet diameter should be slightly larger than the diameter
of the nozzle (O.8mm) to avoid overflow and prevent the interception of
convergence between the two are not allowed to occur due. Imported products
according to the size of the diameter, usually 4-8mm. Expanding the diameter of
the main channel at an angle of 3 ° to 5 ° should be within in order to release
the flow channel thereof is superfluous.
Cold slug
It is located in the main channel at the
end of a hole to trap shoot between the ends of two injections of mouth
generated by cold material, thereby preventing the diversion channel or gate
blocked. If cold material once mixed with the cavity, then the system is easy
to produce products in the internal stress. Cold slug diameter of about eight a
lOmm, depth of 6mm. In order to facilitate mold release, normally borne by the
bottom of the release lever. Top release lever should be designed to zigzag
trench subsidence hook or set up in order to successfully pull the sprue
superfluous matter when stripping.
Shunt
It is a multi-slot die cavity connecting
the main channel and each channel. In order to melt each cavity is filled with
equal speed, diversion channel on the mold arrangement should be symmetrical
and equidistant distribution. Runner-sectional shape and size of the plastic
melt flow, and ease of mold release products has an impact. If the feeding
amount in equal flow, it places the smallest cross-section of the flow path
resistance. But because of the cylindrical flow channel surface area is small,
the cooling of the shunt superfluous material adverse, and this shunt must be
opened on the two halves of the mold, both labor-and easy alignment. Therefore,
regular use of the trapezoidal or semi-circular cross-section of the runner,
and the opening on one half of the mold with a release lever. Channel surface
polished to reduce flow resistance must provide faster filling speeds. Depends
on the size of the plastic flow channel variety, size and thickness of the
article. For most thermoplastics, the shunt section width does not exceed 8m,
up to 10 a large 12m, special small 2-3m. Under the premise of meeting the
needs of the cross-sectional area should be minimized to avoid increasing the
shunt Warts and extend the cooling time.
Gate
It is on the main road (or shunt) and the
cavity of the channel. Sectional area of the channel can be with the mainstream channel (or shunt) are equal, but are usually reduced. So it is the
smallest part of the whole system, the cross-sectional area of the flow path. The shape and size of the gate
great impact on product quality. The role of the gate is: A, control the material flow velocity: B, due to the injection can be stored in this
part of the condensate and prevent melt back earlier: C, so that the melt by
strong shear by increasing the temperature , thereby reducing the apparent
viscosity to increase flowability: D, easy separation of products, and the flow
channel system. Gate design shape, size and position depend on the nature, size
and structure of the article of plastics. The gate of the cross-sectional shape
is generally rectangular or circular cross-sectional area should be small and
the length should be short, not only based on the above effects, but also
because larger than the small gate easy, and it is very difficult to reduce the
large gate. Gate location should generally be selected in the products do not affect
the appearance of the thick places. Gate size should be designed to take into
account the nature of the plastic melt.
Cavity
It is the mold space molded plastic
products. Component as constituting the cavity collectively referred to as
molded parts. Various molded parts are often specific names. The molded article
constituting the shape of the concave part called a die (also known as the
female mold) to form the internal shape of the article (such as holes, slots,
etc.) is referred to as core or convex mold (also known as the male mold).
First, the overall structure of the cavity to be determined according to
performance, the geometry of products, dimensional tolerances and use
requirements designed plastic molded part time. Second, to select sub-surface,
the gate and the vent mode position, and release according to the determined
structure. Finally, press the control product dimensions of each part of the
design and determine the combinations between the various components. Plastic
melt with high pressure into the cavity, so the molded parts to be reasonable
selection and check the strength and stiffness. To ensure the smooth plastic
surface appearance and easy stripping, where contact with the plastic surface
roughness Ra> 0.32um, but also resistant to corrosion. Molded parts are
generally by heat treatment to improve the hardness and corrosion-resistant
steel manufacturing.
Vent
A groove which is open in a mold outlet,
and for discharging the original gas into the melt. When the molten material
into the cavity, the original is stored in the cavity from the melt into the
air and gas must be discharged through the exhaust port to die at the end of
the stream outside, otherwise it will make products with holes, bad splices,
filling dissatisfaction, even accumulated compressed air due to high
temperature and the product burns. In general, both exhaust holes provided in
the cavity of the melt flow at the end, may be provided on the mold parting
surface. The latter was set up at the side of the die deep 0.03-0.2mm, wide
shallow groove 1.5-6mm's. Injection, the vent does not have a lot of melt
leakage, because the melt is cooled and solidified in where the channel
blocked. Never open position toward the exhaust port operator, to prevent
accidental discharge wounding melt. It will also use the top of the bar with
the gap with the top of the hole, the top block and the stripper plate and with
the gap cores like exhaust.
Structural parts
It refers to the various parts
constituting the mold structure, including: orientation, ejection, core pulling
and genotyping of various parts. As the front and rear plates, after deduction
templates, pressure plate, bearing columns, guide posts, stripper, stripping
pole and the return pole and so on.
Heating or cooling means
This is to make the melt solidified
in the mold shape of the device for thermoplastic male and female mold is
typically a cooling medium passage, and by circulating cooling medium to the
cooling purposes. Pass into the cooling medium and the structure of an article
with the type of plastic and the like, cold water, hot water, hot oil and
steam. The key is uniform cooling high efficiency, uneven cooling products will
directly affect the quality and size. Should be based on the thermal properties
of the melt (including crystallization), the shape of the article and the mold
structure, consider selecting the arrangement of the cooling passage and the
cooling medium.
more information www.cnmoulding.com www.chinamoldmaker.org
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