Research on Vacuum Plating Process of Chrome Plates and Circular Gratings
Research on vacuum chrome plating process with code disk and circular grating Chen Zhan1, Xue-ying Zhang2 (1. Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 2 College of Mechanical and Electrical Engineering, Changchun University of Science and Technology, Changchun 130032) The relationship between factors and The critical rotational speed of the plated part during the safe film formation provides a theoretical basis for obtaining a uniform chromium film with good compactness under vacuum conditions. 1 Membrane formation mechanism and influencing factors 1.1 Membrane formation mechanism 121 When the membrane material is heated by the evaporation source, a gasification process takes place, and the evaporated or migrated atoms or molecules carry energy while evaporating against the surface of the substrate. The atoms or molecules are adsorbed on the surface of the substrate by the dipole force, forming crystal nucleuses. The nuclei continue to grow into islands, and the islands merge and recrystallize to form the omentum. When the omentum is deposited, the thickness of the film increases. The trenches are filled to form a continuous thin film. 1.2 Factors affecting film growth and densification Vaporization temperature From the point of view of the film formation process, the higher the evaporation temperature, the more atoms or molecules will evaporate, and the greater the chance of collision, the harder the nucleus will become. The coded discs and circular gratings that affect the film layer are the core components of the precision photoelectric measurement instrument. Therefore, the uniformity of the code disc and the circular grating directly affects the measurement accuracy of the instrument. The compactness of the chromium layer and the uniformity of its thickness are important factors influencing the accuracy of the code wheel and the circular grating. In order to obtain a better chromium layer, the blank is usually vacuum-deposited. This method has the advantages of simple process, material saving, no pollution, and strong adhesion of the obtained film base, but due to the purity of the film material, vapor pressure, evaporation temperature, evaporation rate, substrate temperature, and evaporation source The distance between the substrate, the size of the parts to be plated, and the rotating speed of the parts to be plated, etc. will have different degrees of influence on the formation of the film, thereby affecting the film layer density and film thickness uniformity, resulting in reduced accuracy of the code disk, circular grating This paper analyzes the principle of vacuum coating and the mechanism of film formation to find out the intrinsic relationship between them and provides a theoretical basis for obtaining a film with good compactness and uniformity. Fund Project: The third phase of the Youth Innovation Project of the Changchun Institute of Optics, Fine Mechanics and Mechanics of the Chinese Academy of Sciences has enabled the formation of a film as soon as possible and must be prepared for a long period of time. to make. When evaporation reaches equilibrium, the relationship between the evaporation rate and the coefficient of condensation and the temperature is: a condensation coefficient, for general metals, the molecular mass of a*M vapor, the temperature of the moj T* evaporation source, K. To obtain the temperature directly The relation between the rate and the rate is obtained by transforming equation (1): obtained by the Clausius-Claiprain equation: number. Will, as shown. Such a film has anisotropy, its mechanical properties and optical properties are not stable, and it easily leads to broken wires on the coded disk and the circular grating, which affects its accuracy. The origin is approximately punctiform, and the substrate to be plated is a plane. The vertical distance between the center of the evaporation source and the substrate is h. The thickness of the film is the thickness distribution of the film. The following formula is calculated: On the plane, the above equation can be written as: It can be seen that the thickness of the deposited film in a certain period of time decreases with the square of the evaporation distance and the distance between the center and the edge of the substrate. The evaporation distance is also related to the mean free path of the molecule. Experiments show that only when the mean free path of the molecule is When the evaporation distance is greater than 10 times, a strong adhesion layer can be obtained, which provides theoretical guidance for the deposition of high-precision encoders and circular gratings. 2Determination of the critical speed of the plated part during dynamic evaporation In order to make the chromium film of the code plate and the round grating uniform, dynamic evaporation is usually used, and whether the dynamic evaporation speed is related to the thickness of the film layer and the surface of the code plate or the circular grating Forming a film has an important effect. Because during dynamic evaporation, if the object to be plated passes through the evaporation source at a very fast speed, there is a possibility that the time for the chromium vapor molecules to stay on the substrate is less than the time required for forming a dense monolayer, resulting in failure to form a film layer. The following formula determines: According to the size of the evaporation source to take the corresponding length of the plated part in the direction of movement in the direction of time T, the plated part through the evaporation source of the critical speed V*i: so when dynamic evaporation, was The uniform rotating speed v of the plating part should satisfy: In the vacuum evaporation of this experiment, the value of A, BC and D can be obtained by the speed of the plated part 21.37mm/s. This speed sets the rotating speed of the plated part in actual operation. The chromium layer has good compactness, which provides a theoretical basis for obtaining a high-quality film layer. 3 Conclusions By analyzing the principle of vacuum chrome plating and the formation mechanism of the glass surface film layer, the uniformity and compactness of the film thickness and the vapor pressure, evaporation temperature, evaporation rate, substrate temperature, distance from the evaporation source to the substrate are given. The relationship between the main influencing factors such as the size of the plated part and the critical rotational speed of the plated part during safe film formation provides a theoretical basis for obtaining a chromium film with uniform thickness and good compaction under vacuum conditions. The flat die pellet machine uses electrical motor as the power source. With gear drive instead of belt drive which can increase the efficiency to 20%. After being extruded through the die hole by the pinch roller. 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