Ningbo haijiang machinery manufacturing co.,Ltd |
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1, choose the right type: product and plastic decide the type and series.
Since there are many kinds of ejectors, it is necessary to
correctly determine which injection moulding machine or series
should be used to produce this product at first, such as general
thermoplastic or wood materials or PET raw materials, which are
monochrome, bichrome, multicolor, sandwich or mixed colors. In
addition, some products need high stability (closed loop), high
precision, ultra-high shooting speed, high shooting pressure or
rapid production (multi-loop) and other conditions, but also must
choose the appropriate series to produce.
2. Put it down: The size of the die determines the appropriateness of the “big column distance”, “die thickness”, “minimum size of the die” and “die plate size” of the stand to confirm whether the die can be put down.
The width and height of the mold should be less than or at least
one side less than that of the big column.
The width and height of the mold are preferably within the size of
the die.
The thickness of the mold should be between the mold thickness of
the injection molding machine.
The width and height of the mold should meet the minimum mold size
recommended by the injection molding machine, and it is too small.
3. It can be concluded that whether the “opening stroke” and “supporting stroke” are enough for the finished product to be taken out is determined by the die and finished product.
The opening stroke should be at least twice the height of the
finished product in the direction of the switching die, and the
length of the sprue should be included.
The mold support stroke should be enough for the finished product
to be ejection.
4, lock up: product and plastic determine the “clamping force”
tonnage.
When the material is injected into the cavity under high pressure,
a supporting force will be produced. Therefore, the locking unit of
the injection machine must provide enough “locking force” to
prevent the mould from being pushed open. The demand for clamping
force is calculated as follows:
The projected area of the finished product in the direction of the
switch die is calculated from the finished product size.
The strength of the supporting die = the projection area (cm2) *
the number of die points and the pressure inside the mold in the
direction of the switch die (kg/cm2).
The pressure in mold varies with raw material, and the raw material
takes 350 to 400kg/cm2.
_The clamping force of the machine should be greater than the
supporting force, and for the sake of safety, the clamping force of
the machine should be more than 1.17 times of the supporting force.
Up to now, the specification of clamping unit has been
preliminarily determined, and the tonnage of the type of machine
has been roughly determined. Then the following steps must be taken
to confirm which screw diameter of the injection unit is more in
line with the requirements.
5. Full shooting: Determine the required “shooting quantity” by the
weight of the finished product and the number of die holes, and
select the appropriate “screw diameter”.
Calculate the weight of the finished product.
For the sake of stability, the ejection quantity should be more
than 1.35 times the weight of the finished product, that is to say,
the weight of the finished product should be less than 75% of the
ejection quantity.
6. Good shooting: the conditions of “screw compression ratio” and “ejection pressure” are determined by plastics.
Some engineering plastics need higher injection pressure and
suitable screw compression ratio design to achieve better forming
effect. Therefore, in order to make the finished products shoot
better, the need for injection pressure and compression ratio
should also be considered in the selection of screw.
Generally speaking, a smaller diameter screw can provide higher
injection pressure.
7. Shoot fast: confirm the “ejection speed”.
Some finished products need high ejection rate to form stably, such
as ultra-thin products. In this case, it may be necessary to
confirm whether the ejection rate and ejection speed of the machine
are enough, whether the accumulator and closed-loop control devices
are needed. Generally speaking, under the same conditions, the
screw that can provide a higher injection pressure usually has a
lower injection velocity, whereas the screw that can provide a
lower injection pressure usually has a higher injection velocity.
Therefore, when choosing the diameter of screw, the injection
quantity, injection pressure and injection rate (injection speed)
need to be considered and traded off.
In addition, multi loop design can be used to shorten the molding
time by synchronous compound action.