1. What is the dimensional relationship between the nozzle of the injection machine and the main runner of the injection mold?
In order to ensure that there is no overflow between the main runner and the injector nozzle during injection molding, which will affect the demoulding. When designing the mold, the spherical surface at the beginning of the main runner must have a slightly larger radius than the spherical surface at the nozzle head of the injection machine, as shown in Figure 4.10, that is, R is 1~2mm larger than r. The diameter of the small end of the main runner is slightly larger than that of the nozzle, that is, D is 0.5~1mm larger than d.
2. How many installation forms of injection mold and injection machine?
The movable mold and fixed mold fixing plate of the injection mold shall be installed on the movable mold and fixed mold respectively. There are two methods for installing the mold on the injection machine: one is to fix it directly with screws; The screw holes on the mold fixing plate and the mold of the injection machine should be completely consistent. For large molds with large weight, it is safer to use screws to fix them directly; The other is fixed with screws and pressing plates. As long as there are screw holes near the outside of the die fixing plate where the pressing plate needs to be placed, the pressing plate can be fixed. Therefore, the fixing of the pressing plate has greater flexibility.
3. How to check the injection machine according to the maximum injection volume?
The maximum injection volume refers to the maximum volume of plastic injected by the injection machine at one time. When designing the mold, it shall be ensured that the total injection volume required for molding plastic parts is less than the maximum injection volume of the selected injection machine, namely:
——The maximum injection volume allowed by the injection machine, g or cm.
——The utilization coefficient of the maximum injection volume of the injection machine is generally 0.8;
——Mass or volume of plastic required by the gating system, g or cm;
——Mass or volume of single plastic part, g or cm;
——Number of cavities.
4. How to check the injection pressure of the injection machine?
The injection pressure required for plastic molding is determined by such factors as the type of plastic, the type of injection machine, the form of nozzle, the shape of plastic parts and the pressure loss of the gating system. For the plastic with high viscosity and the plastic parts with thin shape and long process, the injection pressure should be higher. Since the pressure loss of the plunger type injection machine is greater than that of the screw type, the injection pressure should also be larger. The verification of injection pressure is to check whether the rated injection pressure of the injection machine is greater than the injection pressure required for molding.
5. When selecting the injection molding machine, which installation dimensions should be checked?
In order to install the injection mold on the injection machine smoothly and produce qualified plastic parts, the dimensions related to the injection machine and mold installation must be checked when designing the mold. Generally, the parts that should be checked when designing the mold include the nozzle size, the size of the locating ring, the maximum and minimum thickness of the mold and the size of the mounting screw hole on the template
6. What is plastic?
Plastic is made of polymer synthetic resin as the basic raw material, with a certain amount of additives added. It can be molded into a material with a certain structural shape under a certain temperature and pressure, and can keep its shape unchanged at room temperature.
7. What are the components of plastics?
Plastics are composed of resins and additives (or additives). Resin is the main component, which determines the type (thermoplastic or thermosetting) and basic properties (such as thermal properties, physical properties, chemical properties, mechanical properties, etc.) of plastics. The role of additives is to improve the molding process performance, improve the performance of plastic parts and reduce costs. Additives include fillers, plasticizers, colorants, lubricants, stabilizers, curing agents, etc
8. According to the molecular structure and thermal properties of resins in plastics, what kinds of plastics are classified and what are their characteristics?
According to the molecular structure and thermal properties of resins in plastics, plastics are divided into two categories: thermoplastics and thermosets.
(1) Features of thermoplastic: 1) The molecular structure of the resin is linear or branched chain 2) When heated, it is softened and melted to become a flowing viscous liquid. In this state, it can be molded into a plastic part of a certain shape, and after cooling, it can maintain a fixed shape. If it is heated again, it can be softened and melted again, and can be molded into plastic parts of a certain shape again, which can be repeated many times. 3) In the above process, there are only physical changes and no chemical changes.
(2) Characteristics of thermosetting plastics: 1) The molecular structure of the resin is finally the body structure. 2) At the beginning of heating, its molecules are linear structure, plastic and soluble, and can be molded into plastic parts of a certain shape. When the heating continues, chemical bond bonding (i.e. cross-linking) is formed between the main chains of linear polymer molecules, and the molecules are in a network structure. When the temperature reaches a certain value, the cross-linking reaction further develops, and the molecules finally become body structure. The resin becomes neither molten nor dissolved, and the shape of the plastic parts is fixed and does not change. This process is called curing. If reheated, it will no longer soften and have no plasticity. 3) In the above forming process, there are both physical and chemical changes.
9. What are the main properties of plastics?
Plastics have many excellent properties, which make them widely used in various fields. Its main performance includes:
(1) Low density: the density of plastic is generally 0.83~2.2g/cm3, only 1/8~1/4 of steel. The density of foam plastic is smaller, and its density is generally less than 0.01g/cm3. The density of plastic is small, which is of great significance for reducing the weight of mechanical equipment and saving energy, especially for vehicles, ships, aircraft and space spacecraft.
(2) High specific strength and specific stiffness: the absolute strength of plastic is not as high as that of metal, but the density of plastic is small, so the specific strength（ σ b/ ρ）、 Specific stiffness (E/ ρ） Quite high. In particular, the specific strength and specific stiffness of reinforced plastics made of various high-strength fibrous, flaky and powdery metal or non-metal fillers are higher than those of metals.
(3) Good chemical stability: Most plastics have good resistance to acid, alkali, salt, water and gas. Under normal conditions, they do not react with these substances.
(4) Good electrical insulation, thermal insulation and sound insulation.
(5) Good wear resistance and self-lubricating property: plastic has small friction coefficient, good wear resistance, good self-lubricating property, high specific strength and low transmission noise. It can work effectively under liquid medium, semi dry or even dry friction conditions. It can be made into machine parts such as bearings, gears, cams and pulleys, and is very suitable for occasions with low speed and low load.
(6) Strong adhesion.
(7) Good molding and coloring properties.
10. What is the orientation behavior during plastic molding?
The orientation behavior of plastics is the phenomenon that polymer molecular chains tend to be arranged in parallel along the stress direction under the action of stress. The orientation can be divided into two cases:
(1) Flow orientation of solid filler in injection and pressure injection molded plastic parts; (2) Flow orientation of polymer molecules in injection and pressure injection molded plastic parts.