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1. What is the purpose of inserting inserts into plastic parts? The purpose of inserting inserts into plastic parts is to improve the local strength, hardness, wear resistance, conductivity and magnetic conductivity of plastic parts, or to increase the stability of the size and shape of plastic parts, or to reduce the consumption of plastic. 2. What is the working principle of single parting surface injection mold? The single parting surface injection mold is also known as the two plate injection mold. As shown in Fig. 5.4, when closing the mold, the moving mold and the fixed mold are closed…

1. What are the preparations before injection molding?  (1) Inspection of raw material appearance and determination of process performance;  (2) Preheating and drying of materials;  (3) . preheating of inserts;  (4) . cleaning of material barrel;  (5) Selection of release agent. 2. What factors limit the size of plastic parts?  (1) Limited by the fluidity of plastics. Under certain equipment and process conditions, the plastic with good fluidity can form larger plastic parts; On the contrary, the size of plastic parts that can be formed is smaller.  (2) The size of plastic parts is also limited by molding equipment. The…

1. What is the dimensional relationship between the nozzle of the injection machine and the sprue of the injection mold? In order to ensure that there is no overflow between the main channel and the nozzle of the injection machine during injection molding, which will affect the demoulding. When designing the mold, the spherical surface at the beginning of the sprue must be slightly larger than the spherical radius of 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…

1. Please take the horizontal screw injection machine as an example to describe the working process of the injection machine?  (1) , heating and pre plasticization: driven by the transmission system, the screw will transport and compact the materials from the hopper forward. Under the shear and friction of the heater outside the barrel, the screw and the barrel, the materials will gradually melt, and a certain amount of molten plastic has accumulated at the head of the barrel. Under the pressure of the melt, the screw will slowly retreat. The backward distance depends on the amount required for one…

1. What is the shrinkage of plastics and what are the basic factors affecting the shrinkage of plastics? After the plastic is taken out from the mold and cooled to room temperature, the characteristic of dimensional shrinkage is called shrinkage. Because this shrinkage is not only caused by the thermal expansion and cold shrinkage of the resin itself, but also related to various molding factors, the shrinkage of plastic parts after molding is called molding shrinkage. The main factors affecting the shrinkage rate include: (1) plastic variety; (2) Plastic structure; (3) Die structure; (4) Molding process.2. What is the fluidity…

1. The concept of stress, the force on the unit cross-sectional area inside the object is called stress. The stress caused by the action of external force is called working stress, and the stress balanced in the interior of the object without the action of external force is called internal stress (such as tissue stress, thermal stress, residual stress left after the processing process, etc.). 2. Mechanical properties: the ability of metal to resist deformation and fracture when it is subjected to external force (load) under certain temperature conditions is called the mechanical properties of metal materials (also known as…

Hardness indicates the ability of a material to resist the pressure of a hard object into its surface. It is one of the important performance indexes of metal materials. Generally, the higher the hardness, the better the wear resistance. Common hardness indicators include Brinell hardness, Rockwell hardness and Vickers hardness: 1. Brinell hardness (HB): press a hardened steel ball of a certain size (generally 10mm in diameter) into the material surface with a certain load (generally 3000kg) and keep it for a period of time. After unloading, the ratio between the load and its indentation area is the Brinell hardness…

Main forms of building metal corrosion:  (1) Uniform corrosion. The corrosion of the metal surface makes the section uniform and thin. Therefore, the annual average thickness loss value is often used as the index of corrosion performance (corrosion rate). Steel is generally uniformly corroded in the atmosphere.  (2) Pitting. The corrosion of metal is pitted and deep pits are formed. The generation of pitting corrosion is related to the nature of metal and its medium. Pitting is easy to occur in the medium containing chloride salt. The maximum hole depth is often used as the evaluation index for pitting corrosion.…

Plasticity refers to the ability of metal materials to produce permanent deformation (plastic deformation) without damage under the action of external force. When metal materials are stretched, the length and cross-sectional area will change. Therefore, the plasticity of metal can be measured by two indexes: the elongation of length (elongation) and the shrinkage of section (reduction of section). The greater the elongation and area shrinkage of metal material, the better the plasticity of the material, that is, the material can withstand large plastic deformation without damage. Generally, metal materials with elongation greater than 5% are called plastic materials (such as…

Many mechanical parts and engineering components work under alternating load. Under the action of alternating load, although the stress level is lower than the yield limit of the material, after a long time of repeated stress cycle, sudden brittle fracture will also occur. This phenomenon is called fatigue of metal materials. The characteristics of fatigue fracture of metal materials are:  (1) The load stress is alternating;  (2) The action time of load is long;  (3) The fracture occurs instantaneously;  (4) Both plastic and brittle materials are brittle in the fatigue fracture zone. Therefore, fatigue fracture is the most common and…