1. Briefly describe the working state of check valve in plasticizing, injectionand pressure maintaining process;Plasticization: on Injection molding: closing Pressure maintaining: off
2. The relationship between injection speed and injection pressure, and the relationship between packing speed and packing pressure is briefly described;
The relationship between injection pressure and injection speed is as follows:
In the process parameters of injection molding, the speed between speed and pressure is dominant, and there is no direct relationship between them.
In production, for example, when the injection speed is set at 100 mm / s, when the actual injection pressure is less than the set pressure value, the screw is molded at the injection speed of 100 mm / s. When the actual injection pressure exceeds the set pressure, the screw can not reach the injection speed of 100 mm / s. The relationship between the actual injection pressure and injection speed is that the faster the injection speed, the greater the actual pressure value. The higher the ejection speed, the more pressure you are required to set.
High set pressure is also required when the speed is very slow. That is to say, the point with the lowest injection pressure will not be at the fastest speed or at the slowest speed.
3. If the product appears burnt spot, how do you usually solve it;
Cleaning die surface
Find the location of the spot and reduce the injection speed
Reduce mold temperature
Reduce clamping force
Reduce material temperature
Die surface sticker, increase mold exhaust, generally not recommended
4. Briefly describe the influence of mold temperature on product deformation?
In the mold, the main factors affecting the deformation of plastic parts are gating system, cooling system and ejection system.
For the temperature control of the mold, the temperature difference between the moving die and the fixed mold, the mold core and the mold wall, and the mold wall and the insert should be determined according to the structure characteristics of the product, so as to control the different cooling shrinkage speed of each part of the product.
After demoulding, the product tends to bend to the side with higher temperature to offset the poor orientation shrinkage and avoid the product deformation according to the orientation law. For the products with the same shape, the mold temperature should be kept the same to balance the cooling of all parts of the product.
5. If a product has incomplete filling and flash during the production process, what are the possible reasons?
There is a gap between the die core and the broken surface of the movable and fixed die
Poor die exhaust
Insufficient clamping force of machine
Foreign matter on die surface
6. Why is it necessary to retreat after plasticizing? How to optimize?
Whether the suction is large or small will directly affect the product quality. If it is large, it will easily cause silver wire on the surface of the product. If the product is small, it is easy to have residual instability, product quality is unstable, mold runner overflow, nozzle wire drawing and so on. The general experience value shall not be less than 5mm.
How to optimize: according to the experience value, in the actual production to see the bad phenomenon of the product, fine-tuning up and down until there is no overflow and qualified products.
7. What is the effect of back pressure on the product? How to set the back pressure?
High back pressure:
The melt pressure in the front of the barrel is too high, the material temperature is high, the viscosity is decreased, and it is easy to fill, but it will increase the flash of product contour
Long storage time and long heating time of melt in barrel cause thermal decomposition and poor color difference of product surface
The screw backward is slow, the storage time is long, and the molding cycle is long, which affects the production efficiency
Due to high melt pressure, salivation is easy to occur in the mold with cold runner (the needle valve does not affect it), which causes the cold material in the flow channel to plug the rubber inlet or cold material spots appear on the surface of the product during injection molding
The mechanical wear of screw and barrel is big, which affects the service life
Low back pressure:
The screw retreats quickly, the melt density flowing into the front end of the barrel is small, air is sandwiched, and the surface of the product is silver wire
Poor plasticization, unstable material quantity, large change of product weight and size
Product surface shrinkage, cold grain, uneven luster and other adverse phenomena
Bubbles are easy to appear inside the product
Low melt temperature, high viscosity, poor melt fluidity and so on
Back pressure setting: the principle is from small to large (refer to the value given by the material supplier and the structural characteristics of the product)
8. What should you do when you find the amount of surplus material unstable?
Check whether the screw three-piece set is in good condition
Check whether the injection pressure is stable and whether the inside of the nozzle is clean
Whether there is material leakage at the nozzle
Whether the screw temperature and mold temperature machine temperature are stable and within the allowable deviation value
Whether the screw loosening value is set too small, causing cold material
9. How to quickly find out the reasonable clamping force?
Calculation method: clamping force = projected area of all products (including runner) x cavity pressure
Practical method: first set a clamping force, and set an empirical value (not too small) according to the product size and machine tonnage. When the product has no burr, gradually reduce the clamping force until the product has burr, and take the pressure value of the last (no burr) with burr
