What is the shot size in injection molding?

 Basic parameters of injection molding machine

The basic parameters of the injection molding machine can better reflect the size of the injection molding products, the work capacity of the injection molding machine, and the evaluation of the type, grade range, and product quality of the processed materials. The basis for the selection and use of injection molding machines.

1. The injection quantity —— the maximum injection quantity that the injection system can achieve when the injection screw or plunger makes a maximum injection stroke under the condition of air injection.

To a certain extent, this parameter reflects the processing capacity of the injection molding machine, marks the maximum quality of the plastic products that can be formed by the injection molding machine, and is an important parameter of the injection molding machine. The PS standard (density ρ=1.05 g/cm3) is expressed by the mass (g) of the injected melt and the volume (cm3) of the injected melt

According to the definition, the theoretical value of the maximum injection capacity of the injection screw at one time is the product of the maximum projection area of the screw head in its vertical and axis direction and the stroke of the injection screw. QL =π/4 D2 S

The injection molding machine can not reach the theoretical value in the working process, because the density of plastic changes with the change of temperature and pressure, therefore, the injection capacity needs to be corrected properly. The modified injection capacity is Q=αQL =π/4 D2 Sα,α—— ejection coefficient, which is generally 0.7∽0.9,

The processing of plastic products on injection molding machines 

the quality of generic products and the total amount of materials used in the gating system shall not exceed 25%∽70% of the injection molding quantity of the injection molding machine,

 2. Injection pressure —— the force acting on the unit area of the melt by the end face of the screw or plunger. The size of the injection pressure is related to the injection molding machine structure, flow resistance, product shape, plastic properties, plasticizing mode, plasticizing temperature, requirements.

A 、 material fluidity is good, product shape is simple, arm thickness is big, the general injection pressure is less than 340∽540 Kgf/cm2. Applicable to the processing of LDPE, PA, and other materials.

The B、 material melt viscosity is low, the product precision is general, the injection pressure is 680∽980 Kgf/cm2. Applicable to the processing of PS, HDPE, and other materials.

The melt viscosity of C 、 material is medium or high, the precision of product is required, the shape is complex, the injection pressure is 980∽1370 Kgf/cm2., and the injection pressure is Applicable to the processing of PP, PC, and other materials.

D、 material has high melt viscosity, thin wall, long process, high precision, complex shape, the injection pressure of 1370∽1670 Kgf/cm2. Suitable for reinforced nylon, polysulfone, polyphenylene ether, and other materials processing.

E 、 processing high-quality precision micro-products, injection pressure can reach 2260∽2450 Kgf/cm2.

In order to meet the processing requirements of injection molding precision products or products with complex shapes of molding structure and engineering structural parts, the processing adaptability of the injection molding machine is enhanced, the molding period is shortened, and the product quality is improved. The injection pressure has a trend of increasing.

 3. injection time (injection speed,)—— the melt began to cool after passing through the nozzle. In order to inject the melt into the mold cavity in time and obtain a dense, uniform, and high precision products, the melt must be filled with the mold cavity in a short time. In addition to sufficient injection pressure, there must be a certain flow rate.

4. plasticizing ability —— the amount of material that can be plasticized in unit time, and the plasticizing ability of general screw is related to screw speed, driving power, screw structure, material performance, and so on. The plasticizing device of the injection molding machine should be able to provide a sufficient amount of plasticized and uniform melt within the specified time, and the plasticizing ability should be coordinated with the whole molding cycle of the injection molding machine. The theoretical plasticizing ability of a general injection molding machine is more than 20% of the actual requirement.