In the manufacture of molds, mold exhaust is a very important part. Mold exhaust can represent the overall structure of the mold to the greatest extent. Even if the excellent mold is without good exhaust, it is impossible to produce stable quality products, a good mold should be airtight, and can ensure that the gas is free to discharge, rather than the gas being highly compressed. So what are the criteria for mold exhaust?
First of all, it is important to understand that unreasonable exhaust will produce the following bad.1, gas accumulation will leach mold surface and parting line;
2, color problems: color difference, so that the color becomes black or bright; bite surface bright mist is not the same
3, to increase the mold polishing: waste of time, money and make the steel easy to corrosion;
4、It is impossible to make the product reach the standard required by customers;
5、It will produce too many bonding lines (which are not strong and unattractive);
6、It will waste too much injection pressure and increase the difficulty of injection molding machine;
7, need to use too high barrel temperature (increase the difficulty of injection molding machine work, temperature control malfunction, material performance deviation, increase the cycle time);
8, will reduce the level of the material;
9, will reduce the product roundness and lead to product deformation;
10、The struggle of high-pressure gas in the mold cavity will increase the instability of the cycle, and will often need to adjust the machine to solve quality problems;
11、Make the work of technicians, QA, operators, and mold room personnel more difficult.
Secondly, let's understand the reasonable exhaust technology requirements.To do the full circumference of the exhaust structure as far as possible, the depth within the plastic overflow edge value, the full circumference of the exhaust is the best, but to leave 1/2 of the steel in the closing line to compensate for the pressure.
If you can't do full circumference exhaust due to irregular PL surface, the better way is to use a 12mm wide exhaust slot to the mother mold, the gas must eventually be exhausted to the atmosphere, to use the flat bottom with chamfered milling cutter to process the exhaust slot as far as possible, if you must use the ball milling cutter, you should calculate the processing depth and the flat bottom processing out the depth of the same before you can use, the length of exhaust sealant is one of the most easily ignored by most people, and related to the appropriate exhaust problem;
In this issue there are many not quite the same size regulations of the statement, the material supplier specifications from 3 ~ 5mm, and experience has proved that if the length is greater than 3mm will no longer play a good role, therefore, to be safe, we specify the standard for 3mm, the exhaust depth is determined by the molding material if in doubt, check the processing specifications.
One of the most common misconceptions is that too much venting leads tophi, but in fact, the opposite direction is correct, unreasonable venting requires excessive pressure, and when gas is allowed to escape, the rubber will come out with the gas, and the only cause of excessive venting and phi is the depth of the gas groove is too deep.
Usually, try to use all ejector exhaust, this is especially important for large plastic parts, this of course also determines the diameter of the ejector, if this is not possible, to grind the plane exhaust, with the appropriate length and depth, and slow down the ejector with clearance, the flow channel, especially large or long flow channel must be open exhaust.
Another common problem is that when the part can not do the full circumference of the exhaust, the last glue filling position and the second last glue filling position must be taken into account, these two must be added exhaust. Deep bone, column, and small needle dispensing or thin glue positions must be specially considered for venting, either with a flat thimble, a half-needle structure, or with venting steel, or even with a vacuum venting mount.
So what do you need to pay attention to?A part cannot be exhausted too much, even though the clamping line is capable of doing so, and this can lead to the following problems related to exhausting: there is not enough steel on the clamping line to withstand the pressure, and the exhaust is pressed together on the parting surface;
The best exhaust will eventually disappear, and after a certain material cycle, if there is not enough steel on the clamping line to compensate for the pressure, the mold will bite together and the air grooves will wear out. The clamping line should avoid the reduction of the clamping part of the mold, which is one of the biggest problems encountered in large molds. For molds with front and rear die inserts, the front and rear die kernel material cannot be closed before the die embryo parting surface is closed. The correct practice is to close the mold at the same time with a pressure-resistant block between the AB plates of the mold frame.
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