Type and characteristics of heat treatment furnace

First, the commonly used heat treatment furnaces include box type resistance furnaces, well type resistance furnaces, gas carburizing furnaces and salt bath furnaces.

(1) Box type resistance furnace. The working principle is to use electric current to generate heat through the electric heating elements arranged in the furnace, and to heat the parts by current and radiation. It is a widely used heating device in heat treatment workshops. Suitable for annealing, normalizing, quenching, tempering and solid carburizing of steel materials and non-steel materials (non-ferrous metals). The utility model has the advantages of simple operation, accurate temperature control, access to protective gas to prevent oxidation when parts are heated, and good working conditions.

(2) Well resistance furnace. The working principle of the well type resistance furnace is the same as that of the box type resistance furnace, and its furnace mouth is named upwards and is named as a well. Commonly used are medium temperature wells, low temperature well furnaces and gas carburizing furnaces. The well type resistance furnace adopts crane lifting parts, which can reduce the labor intensity, so it is widely used.

The medium temperature well type furnace mainly applies heat treatment such as quenching, annealing and normalizing of dry long parts, and its maximum working temperature is 950 °C. Compared with the box furnace, the well type furnace has better heat transfer, and the top of the furnace can be equipped with a fan to make the temperature distribution uniform. The vertical part of the elongated part can overcome the bending deformation caused by the self-weight when the part is horizontally placed.
 

(3) Salt bath furnace. The salt bath furnace is a furnace type that uses molten salt as a heating medium. The salt bath furnace has the advantages of simple structure, convenient manufacture, low cost, good heating quality and fast heating speed, and thus is widely used. However, when heating in a salt bath furnace, there are processes such as binding and clamping of parts, complicated operation, high labor intensity, poor working conditions, and shortcomings such as long heating time at startup. Therefore, salt bath furnaces are often used for parts that are medium to small and have high surface quality requirements.



Second, the heat treatment furnace has the following characteristics:

(1) The temperature range of the heat treatment furnace is large. The main purpose is to obtain austenitic steel with good plasticity, the temperature range is 900 ~ 1200 ° C; heat treatment due to different process requirements, the temperature is high up to 1300 ° C, the low is only about 100 ° C. The temperature difference is so great that the furnace structure is also very different. The furnace temperature is higher than 650 °C, called high-temperature heat treatment furnace, the heat transfer is mainly based on radiation, supplemented by convection; the furnace temperature is lower than 650 °C, called low-temperature heat treatment furnace, the heat transfer mainly depends on convection. The heat treatment requires uniform furnace temperature to avoid excessive local temperature, so the furnace of the heat treatment furnace is sometimes separated from the combustion chamber.

(2) The furnace temperature control of the heat treatment furnace is relatively strict. The heating before the pressure processing, the metal temperature fluctuates by one or two degrees, and generally does not have much influence on the quality. However, whether the heat treatment furnace can ensure the temperature required for the heat treatment process has a great influence on the product quality, and generally does not exceed 3~10 °C. The temperature distribution on the section of the object to be heated should be as uniform as possible, and the temperature difference must not exceed 5 to 15 °C. In terms of controlling the furnace temperature, the electric furnace is superior. In order to achieve the purpose of accurately controlling the temperature, it is preferable to uniformly arrange the flameless burner and the flat flame burner with small power, so that the segmentation control is facilitated, the burner is too small, the concentration is too concentrated, and local overheating is likely to occur. At the same time, the arrangement of the burner or the electric heater and the structure of the furnace should be beneficial to the circulation of the furnace gas, so that the temperature inside the furnace tends to be uniform, and a fan can be used in the furnace for this purpose.
 
 
(3) The heat treatment furnace should minimize the oxidation and decarburization of the metal. For the heat treatment of steel, oxidation and decarburization of the surface are not allowed, and the surface should be kept clean. Heat treatment furnaces often require sealing to control the composition of the furnace gas, and sometimes to maintain a specific atmosphere within the furnace. For example, the bright annealing of cold-worked steel is mostly carried out in a protective gas medium or in a vacuum, so the muffle cover and the radiant tube are used in many heat treatment furnaces. When the workpiece or steel is subjected to chemical heat treatment, such as carburizing, nitriding, cyanidation, etc., it must be kept in a certain medium of active medium, and a muffle furnace or a bath furnace is required.

(4) The productivity and thermal efficiency of the heat treatment furnace are low. In the heat treatment, in order to make the temperature of the metal cross section uniform and turn the crystal structure into complete, it is necessary to leave the metal in the furnace for a long time. Regardless of the heat treatment, the material has one or several soaking heat in the furnace or During the heat preservation phase, the cooling process is also often carried out in the furnace. Some varieties are heat treated and even heated, insulated and cooled. Many heat treatment furnaces are operated periodically. For the above reasons, the productivity and thermal efficiency of the heat treatment furnace are much lower than those of the forging and heating furnace.