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Ingot bottom vacuum heat treatment
The spindle is one of the main components of twisting and winding on the spinning machine, and it is an assembly with a slender rotary shaft supported by two points as the main body. There are spindles on the roving frame, spinning frame and twisting frame. The roving spindle is a round steel rod with a groove on the top to support and drive the spindle to rotate together. The spindle tip at the lower end is supported by the spindle foot oil cup, and the spindle sleeve is used as the upper bearing of the spindle in the middle. Spinning spindle is composed of spindle rod, spindle disk, supporting parts (commonly known as spindle bladder), spindle hook, spindle foot, brake and so on. The number and speed of the spindles have a direct impact on the production capacity of the corresponding process, especially the spinning spindles. It is customary to use its number to indicate the equipment scale and production capacity of the spinning mill. The quality of the spindle is closely related to the quality of the yarn, power consumption, environmental noise, and labor productivity.
GCr15 spindle base is one of the components of the spindle of winding mechanism of spinning frame. When it works, it forms a pair of friction pairs with the spindle rod, the speed is as high as 16000r/min, and the required amplitude is ≤0.08mm. High precision is required, and the deformation of the entire ingot bottom shall not be greater than 0.02mm. At the same time, the requirements for its wear resistance are also high, with a hardness of HRC62-66.
The GCr15 ingot bottom was quenched in an electric heating rotary furnace in the past. When the rotary furnace is used for quenching, the parts are seriously oxidized and decarburized, and the roughness cannot meet the technical requirements. Therefore, after quenching, water sand rolling and grinding must be done to improve the finish. However, the shape of the inner hole at the bottom of the ingot is not guaranteed, and it may be annealed, and the qualified rate of the product is low. If the grinding powder remaining in the inner hole of the ingot bottom is not cleaned thoroughly, it will also cause abrasive wear of the product during use, thus affecting the service life of the entire set of ingots.
Vacuum quenching heat treatment has the advantages of safe operation, cleanness, no pollution, and the treated workpiece has a bright surface, no oxidation, no decarburization, small deformation, and long service life. Therefore, vacuum heat treatment technology has developed rapidly in recent years. Vacuum heat treatment is now a widely used premium process when treating ingots.
In order to pursue high hardness, the upper limit temperature of quenching is often used, mainly because there are more oxide inclusions in the raw material. At present, with the improvement of smelting level, the content of oxides in steel has been greatly reduced, so the harmful effects of oxides have been greatly reduced. Therefore, the ingot bottom quenching temperature is selected as 840°C. Vacuum heating conducts heat by radiation, and the thermal conductivity is poor. In actual production, in order to ensure the uniformity of heat transmission of the workpiece, we preheat the workpiece at 550°C for a period of time to achieve the purpose of uniform heating. When the ingot bottom is vacuum quenched, the holding time should not be less than 40 minutes, so that the internal and external structure and hardness distribution can be uniform.
When vacuum quenching, the selection of oil surface pressure is very important. When selecting the pressure of the oil surface, factors such as the cross-sectional size of the workpiece and the amount of furnace loading should be considered. When the cross-sectional size of the workpiece is large and the amount of furnace loading is large, in order to improve the cooling capacity of the vacuum quenching oil, appropriate consideration should be given to increasing the oil surface pressure. On the contrary, in order to reduce deformation, a higher vacuum quenching should be used as much as possible.
After vacuum quenching, the condition is good, and the appearance and inner hole are silvery white, which is obviously better than that of rotary furnace quenching. This is mainly because vacuum heat treatment has the function of vacuum protection and surface purification. Since the partial pressure of oxygen is lower than the decomposition pressure of the oxide, the oxidation is inhibited and the purpose of no oxidation is achieved. In addition, when heated in vacuum, the oxide on the surface of the workpiece will transform into sub-oxide, and the sub-oxide will sublimate when heated in vacuum, so that the treated metal surface will be purified. Due to these two chemical and physical reactions, the surface of the ingot bottom is sometimes better than before heat treatment after vacuum heat treatment.
Vacuum heat treatment can improve the mechanical properties and service life of the workpiece, and the comprehensive economic benefits are high. It has been used so far and has been well reflected. It not only has high quenching quality, automation and working conditions, but also achieved obvious economic benefits. Its advantages are mainly reflected in the following two points:
1) Cancellation of rolling, grinding and other processes saves man-hours.
2) After vacuum quenching, the service life of the ingot bottom is increased by 3 times compared with the original one. Calculated on the basis of an annual output of 1.2 million ingot bases, 400,000 ingots can be saved, and 0.5 yuan per ingot can be used to save 200,000 yuan a year.
Equipment selection: VOGQ series vacuum oil quenching furnace produced by SIMUWU company is a high-quality product for this kind of processing. It has the characteristics of high vacuum degree, temperature uniformity and high temperature control precision. SIMUWU has a team of experienced engineers to provide customers with the best quality vacuum equipment services.