Adjusting the injection pressure and speed depends on the size of the product. A simple mold can be quickly formed in one or two sections, while a large complex mold is generally divided into 4 sections. The quality of the finished product is better, the first section adopts slow filling to the gate of the product, and the general speed pressure is below 30% and 40bar respectively;
The second stage is injected into the convex area of the front mold, and medium speed and medium pressure (
40% ~ 60% 30 ~ 50bar)To avoid flow marks caused by too fast injection speed;
Three sections are injected into 95% of the product. At this time, it should be filled quickly to prevent the temperature of the melt from dropping too fast and affecting the molding of the product. The speed and pressure are respectively set at 40% ~ 60% 60 ~ Above 100bar, the four sections begin to adopt slow buffering and enter the pressure maintaining state to prevent the product from appearing flash.
The injection position can be determined by the short-shot method. The so-called short-shot method means that the whole cavity is first injected without slow glue, only a small part is filled at a time, and it is increased one by one. After several times of filling, finally, fill the entire mold cavity to check whether the injection molding glue is uniform.
The process setting of the whole injection molding pressure and speed is better for the mold to run smoothly without abnormal vibration. (I)Composition of injection molding machine
The injection molding machine consists of a mold locking system, a glue injection system, a computer operating system, an electrical drive system and an oil pressure transmission system;
1. Injection molding device: function: to evenly plasticize the plastic into a molten state, and inject a certain amount of molten material into the mold cavity with sufficient pressure and speed.
2. Die-locking device: function: to ensure the reliable closure of the forming mold and realize the opening and closing actions of the mold.
3. Hydraulic transmission and electrical control system: Function: ensure that the injection molding machine works accurately according to the predetermined requirements and action degree of the technological process. (II)
The working process of the injection molding machine 1. Closing and tightening: the cycle of the injection molding machine generally starts from the beginning of closing the mold, and the mold is quickly closed at low pressure, when the moving die is close to the fixed die, the power system of the die-closing is automatically replaced by low pressure and low speed. When it is confirmed that there is no foreign matter in the die, the die-closing is tightened by switching to high pressure.
2. Move the injection device forward and inject: after confirming that the mold has reached the required degree of tightness, the injection device moves forward to make the nozzle and the mold fit. When the nozzle and the mold completely fit, the pressure oil can be connected to the injection cylinder, so the screw connected with the cylinder piston injects the molten material from the head into the mold cavity at high pressure and high speed. At this time, the pressure exerted by the screw head on the molten material is called injection pressure.
3. Keep the pressure and inject the melt into the mold cavity. Due to the cooling effect of the low-temperature mold, the melt in the injection mold cavity shrinks to produce products with dense quality, therefore, it is necessary to maintain a certain pressure for feeding the molten material. At this time, the pressure exerted by the screw on the molten material is called the pressure maintaining pressure. During the pressure maintaining, the screw moves forward in a small amount due to feeding.
4. Cooling and pre-plasticizing of the product: When the molten material in the mold cavity loses the possibility of backflow from the gate, the pressure-maintaining pressure in the injection cylinder can be removed, so that the product is cooled and shaped in the mold, at this time, the screw is in the hydraulic motor (Or motor)
The backward movement of the screw during plasticization indicates the volume of melt accumulated by the screw (That is, the amount of plastic)
, Product cooling and screw plasticization are usually overlapping in time. Under normal circumstances, screw plasticization measurement time is required to be less than product cooling time.
5. The injection device retreats and opens the mold to eject the product: After the screw plasticization and metering are completed.
In order to prevent the nozzle from forming cold materials due to long-term contact with the cold mold, it is often necessary to withdraw the nozzle from the mold device and retreat. After the melt in the mold cavity is cooled and shaped, the mold closing device opens the mold and automatically ejects the product.
Product has become a standardized way of dealing with manual blow molding machines.
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