The application process of injecting bakelite powder can be controlled according to its performance characteristics, improve the finished product rate, reduce the working load of the injection machine, reduce the wear on the screw barrel, shorten the molding cycle, and improve the appearance of the workpiece. s help. Reasonable use of injection wood powder can extend the service life of general nitriding steel screws to 8-12 months and improve damage to the mold.
First, the concept:
The material must be sufficiently melt-plasticized in the barrel by the screw under appropriate temperature conditions to give it a good melt state and fluidity, so that it has the best injection molding process. Injectable bakelite powder has good thermal stability of the barrel. It can be kept in the barrel for more than 10 minutes at 120 °C, and it has the best melt flow state at 85-100 °C. The barrel retention time can reach 20 minutes.
Second, it is recommended to set the conditions of the barrel temperature:
1. Two-stage temperature-controlled barrel: the first 90-95 ° C, the latter 75-85 ° C;
2. Three-stage temperature controlled barrel: the first 90-100 ° C, the middle 80-90 ° C, the latter 70-80 ° C;
3. Material flow according to the requirements of the compounding process can be adjusted by appropriately raising or lowering the temperature of the front barrel.
Third, the relationship between back pressure:
The injected bakelite powder is basically granular. In addition to the temperature required to melt it, the back pressure must be adjusted to complete and perfect the pre-plasticization of the material, so that the fluidity during the injection process is good, and the addition amount is uniform and stable.
The adjustment of the back pressure can generally control the proper flow of the nozzle when the feeding is loosened, and the feeding is stable during the injection process, depending on the machine, about 3-5kg/cm2.
Fourth, pressure and injection (shot) speed:
Since the material has sufficient melt flowability, the cavity can be filled without requiring a high injection pressure, and the load on the machine tool can be greatly reduced and reduced, and the injection molding requirement can be generally satisfied at about 60 kg. Rapid rubbing of shots and nozzles, runners, gates, molds can create excessive temperatures and exacerbate wear on the screw barrel. Especially for the injection machine controlled by single proportional valve, the high pressure and high speed damage to the screw mold is more serious, so the injection speed should not be too fast. Too slow will affect efficiency and is not desirable. Generally, depending on the size of the part and the gate form, it is controlled at 10-25 grams per second. It is better not to inject the hard foam and gas against the workpiece.
Fifth, mold temperature and shape retention time:
Injection bakelite has a faster forming speed and can meet its molding requirements at 170 °C. The proofing time is reduced by 14 seconds per millimeter and as the thickness increases, the amount of time increases. The average cycle time of a typical part is 60-80 seconds.
The above conditions shall be adjusted according to the conditions of the machine tool, the mold, the runner gate, and the shape and thickness of the workpiece. The batch-to-batch and large-scale continuous stability of the injected bakelite powder is more convenient for the user to use.