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Vacuum Heat Treatment Furnace

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Production Management of Vacuum Quenching Furnace

With the popularity of vacuum quenching furnaces in the field of heat treatment, it has become more important to strengthen the management of vacuum quenching furnaces. In actual work, due to the inadequate management of the vacuum quenching furnace, problems with parts and equipment will be caused, which will greatly drag down the production, thereby causing the loss of raw materials, time and money. Therefore, it is necessary to improve equipment management awareness education, system implementation, process discipline inspection, equipment files and control measures for improvement activities, and urge relevant practitioners to do a good job in the management of vacuum quenching furnaces.

With the development of modern heat treatment manufacturing technology, vacuum heat treatment has been widely used in the heat treatment industry because it has the advantages of no oxidation, no decarburization, and good surface quality after heat treatment. Although the vacuum quenching furnace is divided into horizontal and vertical types, it is composed of a hot room and a cold room. The workpiece is heated and kept in the hot room, and the subsequent cooling is carried out in the cold room. Therefore, the double-chamber vacuum quenching furnace is the most common, and there are also vacuum quenching furnaces. The furnace adds a workpiece preparation chamber to become a three-chamber vacuum quenching furnace, the purpose of which is to enhance the continuous operability of production. Whether it is vertical or horizontal, double-chamber or three-chamber, the structural principle of the vacuum quenching furnace is basically the same. The content of equipment management and maintenance is basically the same. Vacuum furnace is a thermal processing equipment with high technical content and complex system structure. In actual work, the vacuum quenching furnace is often not managed properly, causing problems in parts and equipment.

Common problems of vacuum quenching furnace:

1.Part surface carbonization

In actual work, sometimes the hardness of the workpiece is obviously high after the vacuum quenching of the workpiece. For example, the hardness of the workpiece whose measurement material is 30CrMnSiA after vacuum quenching is 53HRC, which is higher than the usual hardness value of 44-48HRC. After the metallographic inspection of the part, it was found that there was a carburized layer of 0.2 mm on the surface of the part. The carbon content of the original 30CrMnSiA is 0.28% to 0.35%, and after the surface of the workpiece is infiltrated with carbon elements, the surface carbon content is increased, and the surface hardness after quenching is high, resulting in abnormal workpiece hardness. This batch of parts was scrapped because there was no machining allowance and the surface was carbonized.

The vacuum quenching furnace was inspected, and it was found that there was a lot of oil adhering to the inner wall of the hot inner chamber of the vacuum furnace. The residual oil is the oil on the workpiece, the quenching basket and the transfer trolley, which is brought into the hot chamber. In the vacuum state, at the quenching temperature of the workpiece, the partial pressure of oxygen in the atmosphere is lower than the equilibrium decomposition pressure of the metal oxide, so that the metal is in a reduced state, and the surface activity of the metal is strong, which is more conducive to the infiltration of carbon atoms, resulting in increased carbonization of the workpiece.

2.The vacuum furnace is not up to standard

The vacuum degree required by the vacuum quenching furnace is generally 1 to 13.3Pa. The vacuum degree in this working range is medium vacuum degree. Generally, the vacuum pump used is a combination of a mechanical pump and a Roots pump to meet the requirements. When using, start the mechanical pump first, when the vacuum degree in the furnace reaches 100 Pa, then start the Roots pump to make the vacuum degree meet the process requirements. The Roots pump uses the rotor to rotate in the pump casing to generate suction and exhaust. It can be used as a booster pump for a mechanical pump and is used in series with the previous mechanical pump. The gas pumped by the Roots pump cannot be discharged alone, but It needs to be vented to the atmosphere by a foreline mechanical pump. The long-term operation of the vacuum pump may cause wear and aging of internal parts, and the aging parts will reduce the air tightness and cannot meet the requirements of vacuum degree. In addition, if the vacuum pump oil is polluted and oxidized, it may deteriorate and become corrosive, which will cause the vacuum pump to be loosely sealed, and the cooling effect of the pump will be poor and malfunction.

In addition to the two types of vacuum pumps, the mechanical pump and the Roots pump, the vacuum units that make up the vacuum quenching furnace also include vacuum pipelines, vacuum butterfly valves, solenoid valves, vacuum pressure gauges, vacuum gauges, and vacuum relays. The sealing rings involved are all made of non-metallic materials such as rubber, which will melt at high temperatures. Therefore, the vacuum quenching furnace is required to start the equipped water circulation system during operation. Even if the work is over, the furnace temperature is required to drop below 150 ℃ Before closing the circulating water cooling system. In order to prevent the circulating water from scaling and blocking the pipeline, resulting in poor cooling, the water used for the vacuum furnace water circulation should be soft water, and tap water should not be used directly. A heat treatment workshop found that the softening water equipment was faulty during production. In order to ensure the production progress, the workshop leader asked to use tap water for circulation directly. At that time, the vacuum equipment was also running normally, so they did not pay attention to it. After 6 months, it was found that the vacuum furnace leaked air frequently and the vacuum pump was burned out due to overheating. Once, the graphite felt in the hot room was burned out due to serious air leakage. When I asked the equipment manufacturer to repair it, it was found that the water pressure of the circulating water system was too low, and the sealing ring was deformed by heat and the sealing was not tight. The fundamental reason was that there was too much scale in the circulating pipeline.

3.The fan system is damaged

In the operation of the vacuum quenching furnace, failures will also be caused due to the operator’s inattentive work. For example, when the workpiece is cooled in the cold room, it falls out of the material basket and falls into the oil tank. When cooling the subsequent heats, it falls into the oil tank. The parts in the machine are stuck in the stirring fan, causing the oil stirring system to not work. For another example, when operating the transfer trolley between the cold room and the hot room, it should first descend, then enter the bottom of the material basket, and then raise the trolley. Some operators directly control the trolley to operate the material basket, so that the material basket falls in the hot room. As a result, the furnace chamber of the vacuum furnace heat chamber is damaged.

Related systems

The equipment manual and the heat treatment workshop of the enterprise should formulate the management system of the vacuum quenching furnace in combination with relevant standards and their own regulations, such as furnace temperature uniformity detection, cold pressure rise rate measurement, regular measurement of vacuum quenching oil, equipment operation precautions, vacuum pump oil Check the replacement cycle, etc. The inspection and inspection items of these regulations are institutionalized, and inspection results are required to be recorded, and abnormal values that occur are analyzed in a timely manner. In particular, the measurement of the pressure rise rate in the cold state is to use the static pressure rise method to pump the vacuum furnace to a certain pressure, close the vacuum valve, observe the change of the pressure in the furnace with time, and draw the pressure-time relationship curve. Determine how well the vacuum furnace maintains the degree of vacuum. If the pressure rise rate exceeds the standard requirements, the cause of the failure can be found out by analyzing the pressure-time curve. If the curve shows that the vacuum degree in the furnace increases with time and the pressure does not change, it means that the vacuum furnace does not leak air. If the vacuum degree does not go up, it is caused by the poor operation of the vacuum pump. If the pressure of the curve increases linearly with time and exceeds the requirements, it means that there is a leak in the vacuum quenching furnace, and it is necessary to find the leak point.

After the system is formulated, it must be implemented, and the data after the implementation should be analyzed, so as to facilitate the later work. The pressure rise rate is the performance of the sealing effect of the vacuum quenching furnace. By regularly detecting the air leakage of the vacuum quenching furnace, it can effectively prevent long-term work under the air leakage and avoid oxidation and burning of the graphite felt in the hot chamber.

In actual production, a factory passed the cold-state pressure rise rate test and found 7 air leaks in advance within 3 years. Among them, the gate door was not tightly sealed 3 times, the vacuum pump failed 2 times, and the temperature-controlled thermocouple and vacuum gauge were sealed. Not strict 1 time each. Early detection of air leakage can avoid equipment accidents in the later stage. The maintenance cost of the four vacuum quenching furnaces in the heat meter factory has dropped from the original total of 640,000 yuan/a to 150,000 yuan/a. The economic benefits are considerable, and it provides a guarantee for the production progress and product quality of the workshop.

Create device file

A file is established for each vacuum quenching furnace in the workshop. The content of the file includes the maintenance records of the second and third levels of the equipment, the fault repair of the equipment, and the regular inspection records. and remain in the file of the device. Every year, analyze the records of vacuum quenching furnace files, classify the phenomenon of vacuum furnace failure, analyze the reasons for equipment failure, and formulate corresponding measures. Sort out the spare parts replaced this year. For example, the graphite rod used as the heating element of the vacuum quenching furnace often needs to be replaced due to the collision of the material basket or falls off by itself, and the production is often affected by the purchase of the graphite rod. Safety stock management to ensure the smooth progress of daily production. Through the equipment file management, it is easy to identify the focus and direction of management, and the management of the vacuum quenching furnace is transformed from the previous fault repair to the preventive management.

Selection of vacuum heat treatment equipment: VOGQ series vacuum heat treatment furnaces produced by SIMUWU are high-quality products for vacuum heat treatment process. Good temperature control accuracy and temperature control uniformity ensure effective vacuum heat treatment process. The equipment is easy to manage and maintain, which greatly reduces maintenance costs. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.