During injection molding, there will not be a lot of melt oozing out of the vent hole, because the melt will cool and solidify there and block the channel. The opening position of the exhaust port should not face the operator to prevent accidental injection of molten material and injury. Another, you can also use the matching clearance between the ejector rod and the ejection hole, and the matching clearance between the ejector block and the stripper plate and the core to exhaust air.
There has two important functions of exhaust groove:
(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 is, the farther it is from the gate, the opening of the exhaust groove is particularly important
Injection mold exhaust groove
In addition, for small parts or precision parts, attention should also be paid to the opening of exhaust grooves, because it can not only avoid surface burns and insufficient injection volume of products, but also eliminate various defects of products and reduce mold pollution.
So, how is the exhaust of the mold cavity considered sufficient? Generally speaking, if the melt is injected at the highest injection rate without leaving a focal spot on the product, the venting of the cavity can be considered sufficient.
Exhaust method
There are many ways to exhaust the mold cavity, but each method must ensure that: when the exhaust groove is exhausted, its size design should prevent the material from overflowing into the groove; secondly, it should prevent clogging.
Therefore, measured from the inner surface of the cavity to the outer edge of the cavity, the height of the vent groove with a length of 6-12mm or more should be increased by about 0.25-0.4mm. Also, having too many vent slots is detrimental. Because, if the clamping pressure acting on the unvented part of the cavity parting surface is very large, it is easy to cause cold flow or cracking of the cavity material, which is very dangerous.
In addition to venting the mold cavity on the parting surface, venting can also be achieved by setting a venting groove at the end of the material flow of the gating system and leaving a gap around the ejector rod, because the venting groove can achieve the purpose of venting. If the selection of the depth, width and position of the opening is not appropriate, the resulting burrs will affect the beauty and accuracy of the product. Therefore, the size of the above-mentioned gap is limited to prevent flash around the ejector rod.
Special attention should be paid here: When exhausting parts such as gears, it may be undesirable to have even the smallest flash. The best exhausted of this type of parts as follows:
(1). Clean and remove the gas in the flow channel;
(2). The mating surface of the parting surface is shot peened with 200# silicon carbide abrasive..
In addition, the vent groove is set at the end of the material flow of the gating system, mainly refers to the exhaust groove at the end of runner, its width must be equal to runner’s width, and the height depending on the material
Design method
For product molds with complex geometries, it is best to determine the opening of the exhaust groove after several mold trials. The biggest disadvantage of overall structure of mold is poor exhaust.
There are the following exhaust methods for integral cavity core:
(1). Utilize the slot or insert mounting portion of the cavity;
(2). Utilize the insert seam on the side;
(3). Partially made into a spiral shape;
(4). Fitting slotted slat cores in longitudinal position, opening process holes;
(5) When it is extremely difficult to exhaust, use an inlaid structure, etc.; if the dead corners of some molds are not easy to open exhaust grooves, first of all, the mold should be appropriately changed to inlaid processing without affecting the appearance and accuracy of the product. In this way, it is not only conducive to processing the exhaust groove, but also can sometimes improve the original processing difficulty and facilitate maintenance.
In conclusion
Properly opening the exhaust groove can greatly reduce the injection pressure, injection time, pressure holding time and clamping pressure, making the molding of plastic parts easier than difficult, so can improving production injection mold efficiency, reducing production costs and machine energy consumption.
