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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…

Metal materials refer to metal elements or materials with metal characteristics mainly composed of metal elements. Including pure metals, alloys, metal materials, intermetallic compounds and special metal materials. (Note: metal oxides (such as alumina) are not metal materials) 1. Meaning: The development of metal materials is closely related to the progress of human civilization. After the stone age, the bronze age and iron age are marked by the application of metal materials. In modern times, a wide variety of metal materials have become an important material basis for the development of human society. 2. Type: Metal materials are usually divided…

The characteristics of chemical reactions between metals and other substances are called the chemical properties of metals. In practical application, the corrosion resistance and oxidation resistance of metals (also known as oxidation resistance, which refers to the resistance or stability of metals to oxidation at high temperature) and the influence of compounds formed between different metals and between metals and non metals on mechanical properties are mainly considered. In the chemical properties of metals, especially the corrosion resistance is of great significance to the corrosion fatigue damage of metals.

1. Yield point（ σ s) When the stress of steel or sample exceeds the elastic limit during tension, even if the stress is no longer increased, the steel or sample continues to have obvious plastic deformation. This phenomenon is called yield, and the minimum stress value when yield phenomenon occurs is the yield point. If PS is the external force at the yield point s and fo is the cross-sectional area of the sample, then the yield point σ s =Ps/Fo(MPa) 2. Yield strength（ σ 0.2) The yield point of some metal materials is not obvious, so it is difficult…