In the mold test and production, there are often insufficient filling, compressed air burns, high internal stress inside the product, surface flow lines and fusion lines. In addition to these phenomena, in addition to the first adjustment of the injection molding process, it is also necessary to consider whether the mold gate is reasonable. When both the injection molding process and the gate are eliminated, the exhaust of the mold is the main problem. The main means to solve this problem is to open the vent.
The main role of the exhaust vent:
1. When the mold is glued, the air in the cavity is excluded.
2. It is to exclude various gases generated during the heating process of the rubber compound.
First, the size of the exhaust slot:
There are two points to note when opening the vent:
1. While the exhaust groove is exhausted, its size should be designed to prevent the material from overflowing into the groove.
2. Prevent the venting groove from being blocked.
Exhaust groove width size:
Should be between 4-10mm according to the size of the mold, see Figure 1.
Exhaust groove front end depth dimension A:
To be less than the edge value of the rubber, the length of the front end of the exhaust groove is 3-6mm, see Table 1.
Detach groove rear end depth dimension:
Should be between 0.3-0.6mm according to the size of the mold, as shown in Figure 1.
Exhaust tank size table
※Exhaust gas affects the size of the contact area of ​​the parting surface, so it is harmful to have too many exhaust grooves.
Second, the injection mold exhaust method:
There are several exhaust methods for the cavity core:
1, the water outlet:
2. Partition surface exhaust:
3, inserts and inserts exhaust:
For insert cavities or cores, they can be vented with their split gaps.
4, thimble and cylinder exhaust:
The ejector pin and the cylinder are vented with the matching gap of the core.
5, breathable steel exhaust:
Breathable steel is a material sintered from a spherical granular alloy. The pre-hardened steel is inferior in strength but loose in texture, allowing gas to pass. Place such an alloy in the part to be vented to meet the requirements of the exhaust, but the diameter of the bottom vent should not be too large to prevent the cavity pressure from squeezing and deforming.
6, exhaust well exhaust:
On the outside of the junction of the plastic melts, a cavity is provided to allow the gas to be discharged therein, and a good exhaust effect can also be obtained.
7. Mandatory exhaust:
An exhaust rod is provided at a portion where the gas is enclosed. This method has good exhaust effect but leaves a trace of the rod on the plastic part, so the exhaust rod should be placed in the concealed part of the plastic part.
Third, the exhaust should be noted when designing the exhaust:
1. When the exhaust is extremely difficult, the insert structure is adopted. If the dead angle of some molds is not easy to open the exhaust groove, the mold should be appropriately changed into the insert processing without affecting the appearance and precision of the product, which is not only beneficial for processing. Exhaust can also improve the original processing difficulty and ease of maintenance.
2. At the closed shape of the plastic product, the thimble must be added for exhaust to prevent burns and fusion marks.
3. For product molds with complex geometries, the opening of the venting groove is best determined after several trials.
4. The thinner the wall product, the farther away from the gate, the opening of the venting groove is particularly important.
5. For small parts or precision parts, we must also pay attention to the opening of the venting groove, because it can avoid the defects of the product surface and the injection volume.
Fourth, summary:
Appropriate opening of the venting groove can greatly reduce the injection pressure, injection time, holding time and clamping pressure, making the molding of the plastic parts from difficulty to easy, thereby improving production efficiency, reducing production costs, and reducing the energy consumption of the machine.
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