1. Why do you need to open the exhaust groove
During the injection molding process, when the molten plastic enters the mold cavity, the air in the cavity needs to be exhausted instantly, including the air existing in the cavity and the gating system, and the water produced by the evaporation of moisture contained in the plastic raw material at high temperature. Steam, gas generated by plastic decomposition at high temperature, gas generated by volatilization of certain additives in plastics or chemical reactions, etc.
Reasonable opening of exhaust grooves can greatly reduce parameters such as injection pressure, injection time, holding time and clamping pressure, thereby improving production efficiency, reducing production costs, and reducing energy consumption of the machine.
2. the impact of poor exhaust on the product
(1) Scorching: The air in the cavity is compressed and immediately reaches a high temperature, and the part of the product in contact with the high-temperature air will produce local carbonization and scorching.
(2) Insufficient filling: During the injection molding process, if the gas cannot be discharged in time, it will be difficult to fill, commonly known as beer dissatisfaction.
(3) Spill: When the exhaust is not sufficient, the injection pressure is usually increased, so that the force in the clamping direction will increase, which will easily cause flash.
(4) Silver streaks and welding marks: The gas is not discharged smoothly, which makes the speed of molten plastic entering the various parts of the cavity different, and it is easy to form flow marks and fusion marks. the
(5) Bubbles: The generation of bubbles due to poor venting is especially noticeable on transparent materials.
Role of Mold Cooling, Venting, and Regrind in Process Development
3. Exhaust processing method
The special-shaped parting surface is processed by CNC, and the flat part is directly processed by ordinary gongs or grinders, and finally processed by EDM.
Generally speaking, the exhaust is divided into the exhaust groove of the sealing position and the air-inducing groove for avoiding the air. The length and width of the sealing position are relatively flexible. Specific problems are analyzed in detail.
The height shall not exceed the value of the plastic overflow edge. The data It can be known from the chapter on plastic materials in various design standards that in theory, the exhaust groove should be opened on the front mold as much as possible, and the specific situation should be analyzed in detail.
4. Various types of exhaust
- Mold base: Exhaust of guide sleeve and nylon buckle.
- Parting surface exhaust: the parting surface of the plane and the inclined surface mostly adopts the strip method of exhausting, and the parting surface of the arc surface adopts leaving enough sealing positions along the shape and then avoiding the air to vent. The mesh is It is used when the requirements for exhaust are relatively high and the overflow value is relatively strict. Generally, a grinding wheel of about 1MM is used to cut the depth of 0.003-0.005MM without avoiding the space.
- Row position exhaust: Generally, the row inserts are removed from the mosaic type of row position to open the exhaust separately.
- Inserts and pins for exhaust: On the deep bone and column positions on the product, inserts or needles are often used, which is convenient for exhaust and processing. There is also a kind of insert that is simply used for exhaust, which is generally made based on experience, or an exhaust insert that is added after the mold trial.
- Exhaust on the large contact surface: In order to facilitate the mold flying, it is necessary to avoid air after leaving enough sealing positions on the large contact surface, and then process a hole in the avoidance, which increases the function of exhaust.
- Ejector exhaust: Exhaust can be achieved by using the fit gap of the thimble cylinder. If the deep bone or column is not used as an insert, it can be used as an thimble or cylinder exhaust.
- Runner exhaust: The end of the runner or runner also needs to be exhausted.
- Exhaust with mosaic structure: the large mold is divided into multiple pieces, which is convenient for processing and exhaust. The precision mold is made of a fully inlaid structure, and the exhaust effect is also very good.
- Breathable steel: also known as exhaust steel and air-draining steel, there are breathable steel that can be directly used as inserts, and there are round breathable steel of various specifications.
- Exhaust at the waste position: A waste position is made on the outside of the junction of the plastic melts, which is convenient for ejection, elimination of welding marks, and easy exhaust.
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