The more thin-walled products, the more away from the gate of the site, the exhaust groove opening is particularly important.In addition, for small parts or precision parts, but also attach importance to the exhaust groove opening, because it can avoid the product surface burns And the lack of injection, but also can eliminate the various defects of the product, reduce mold pollution.
The role of the exhaust groove there are two main points: First, the injection of molten material to exclude air within the mold cavity; the second is to exclude the material in the heating process produces a variety of gases.
Well, the mold cavity exhaust how to do it? In general, if the highest injection rate of injection of molten material, but did not leave the focal spot in the product, you can think of the exhaust cavity is sufficient.
1, exhaust method
There are many ways to vent the mold cavity, but each method must ensure that the exhaust slot is dimensioned to prevent the material from overflowing into the slot while exhausting it, and secondly to prevent blockage.Therefore, The surface to the outer edge of the mold cavity measurement, the length of 6-12mm longer exhaust groove portion, the groove height to enlarge about 0.25-0.4mm.
In addition, it is detrimental to have too many vent grooves, because if the clamping pressure acting on the part of the cavity where the vent grooves are not open is large enough to cause cold or crack in the cavity material, it is very dangerous of.
In addition to venting the mold cavity on the parting surface, it is also possible to achieve the purpose of venting by positioning the vent groove at the end of the stream of the casting system and by providing clearance around the ejector rod, since the vent groove The depth, width and location of the opening, if not appropriate, resulting flash burrs will affect the appearance and accuracy of the product, so the size of the gap in order to prevent flashing around the top of the rod is limited.
It should be particularly noted here is: gears such parts in the exhaust, even the tiniest flash is also undesirable, the gear parts is best to use the following exhaust:
(1) Thoroughly clear the gas in the runner;
(2) Peening the parting surface with a silicon carbide abrasive having a particle size of 200.
In addition, the exhaust system at the end of the gutter system to open the exhaust groove, mainly refers to the end of the shunt exhaust groove, its width should be equal to the width of the shunt, the height varies depending on the material.
2, design method
For the complex geometry of the product mold, the exhaust groove is best set up after several try to go to determine the mold structure design of the overall structure, the biggest drawback is the poor exhaust.
The overall cavity mold core, the following exhaust methods:
(1) the use of cavity slot or insert installation site;
(2) the use of the side of the insert seams;
(3) locally made into a spiral shape;
(4) Install slotted slats in the longitudinal position and open the hole in the process.
When the exhaust is extremely difficult, the use of mosaic structure, etc. If some of the mold is not easy to open the exhaust slot, the first should be without affecting the appearance and accuracy of the product, the appropriate mold into mosaic processing, so that not only Conducive to the processing exhaust groove, and sometimes can also improve the original processing difficulty and easy maintenance.
3, exhaust slot design size
Exhaust of thermoset materials is more important than thermoplastic materials.
First of all, the shunt in front of the gate should be exhaust.Exhaust groove width should be equal to the shunt width, the height of 0.12mm. Mold cavity should be around the exhaust, the exhaust slot should be separated by 25mm, a width of 6.5mm , The height of 0.075-0.16mm, depending on the material flow and the softer material should take a lower value.
Top of the rod should be enlarged, and in most cases, the ejection rod cylindrical surface should be worn 3-4 high 0.05mm plane, the direction of wear marks should be along the length of the top of the rod. Grinding application of smaller particle size Grinding wheel. The top end of the rod should be polished 0.12mm chamfer, so that if the formation of the flash, it will be attached to the workpiece.
4 Conclusion
Appropriate to open the exhaust groove, can greatly reduce the injection pressure, injection time, dwell time and clamping pressure, the plastic parts from difficult to become easier, thereby increasing production efficiency and reduce production costs and reduce the energy consumption of the machine.
In fact, not all have to exhaust through the exhaust groove exhaust method there are several other ways below:
(1) exhaust groove exhaust
For the molding of large and medium-sized plastic mold, the need to rule out the amount of gas, usually should be set up exhaust groove, exhaust groove is usually set aside in the parting surface of the die side of the exhaust groove to melt flow in the The end is good, the size of the exhaust groove to gas can be smoothly discharged without overflowing principle.Exhaust groove width is generally about 3-5mm, the depth of less than 0.05mm, the length of the general 0.7-1.0mm.
(2) Parting surface exhaust
In the case of small molds, the parting surface gap may be vented but the parting surface must be at the end of the melt flow.
(3) fight insert crevice vent
For the combined die or cavity, can use their split gap exhaust.
(4) putter gap exhaust
Using the push rod and the template or core with the gap exhaust, or deliberately plus the gap between the push rod and the template.
(5) powder sinter alloy block exhaust
Powder Sintered Alloy is a sintered material made of spherical particles alloy with poor strength, but with loose texture, allowing gas to pass through. An exhaust gas is required to place a piece of such alloy on the area to be vented, but the bottom pass Stomatal diameter should not be too large, in order to prevent the cavity pressure will be squeezed deformation.
(6) Exhaust gas exhaust
Outside the confluence of the plastic melt, a hole is provided to allow the gas to drain into it and a good exhaust effect can also be obtained.
(7) mandatory exhaust
In the closed gas site, set the exhaust rod, the exhaust effect of this method is good, but will leave pieces of plastic traces, so the exhaust rod should be located in the hidden parts of plastic parts.