During injection molding, there will not be a lot of
molten material in the vent hole, because the molten material will cool and
solidify at the place and block the channel. The opening position of the vent hole
should not be facing the operator to prevent accidental spraying of molten
material and hurting people.
Properly opening the vent slot can greatly reduce the
injection pressure, injection time, holding pressure time and clamping
pressure, making the molding of plastic parts easy, thereby improving
production efficiency, reducing production costs, and reducing machine energy
consumption.
The clearance between the ejector rod and the ejector
hole, the clearance between the ejector block and the stripper plate and the
core can also be used for exhaust.
一. The role of the vent slot
There are two main functions of the vent slot:
1》When injecting molten material, remove
the air in the mold cavity;
2》Exclude all kinds of gases generated
during the heating process of the material.
The thinner the product, the farther away from the gate,
the opening of the vent slot becomes particularly important.
For small parts or precision parts, attention should
also be paid to the opening of the vent slot. In addition to avoiding surface
burns and insufficient injection volume, it can also eliminate various defects
of the product and reduce mold contamination.
Generally speaking, if the melt is injected at the
highest injection rate without a burns on the product, the exhaust in the
cavity is sufficient.
二. Exhaust method
There are many ways to vent the mold cavity, but each
method must be guaranteed: the size design of the vent slot should be prevented
the material from overflowing into the slot while venting; secondly, it should
prevent blockage.
1> "Using the parting face to exhaust the mold
cavity. In addition, too many vent slot are harmful. Because, if the clamping
pressure acting on the parting surface of the mold cavity without opening the
vent slot is very large, it is easy to cause cold flow or cracking of the mold
cavity material, which is very dangerous.
2>Set an vent slot at the end of the material flow of
the gating system,
3>The method of leaving a gap around the ejector rod
achieves the purpose of exhaust, because the depth, width and position of the vent
slot , if not appropriate, the flash burrs will affect the appearance and
accuracy of the product. Therefore, the size of the gap is limited to
preventing flash around the ejector rod.
三. Design method
For product molds with complex geometric shapes, it is
best to determine the opening of the vent slot after several mold trials. The
biggest disadvantage of the integrity structure in the mold structure design is
poor vent.
For the integral cavity core, there are the following
exhaust methods:
1> Use the groove or insert installation position of the
cavity ;
2> Use side insert seams;
3> Partially made into a spiral shape;
4> Install the slotted slat core and open the process hole
in the longitudinal position;
When the exhaust is extremely difficult, the insert structure is adopted; if the dead corners of some molds are not easy to open the vent slot, first of all, the mold should be appropriately changed to insert processing without affecting the appearance and accuracy of the product, which is not only beneficial to processing The vent slot can sometimes improve the original processing difficulty and facilitate maintenance.
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