CN113215519B - Carbon saturation control process of muffle-free tank - Google Patents

Abstract

The application relates to the technical field of heat treatment, in particular to a carbon saturation control process of a muffle tank, which comprises the following steps of: step 1: heating the hearth, and closing nitrogen, methanol and propane during heating; step 2: the main control temperature is raised to a first set temperature range, the furnace cover is opened upwards, the opening stroke of the furnace cover is smaller than the full-opening stroke, carbon burning is carried out, and nitrogen, methane and propane are closed during the carbon burning; step 3: the main control temperature keeps a first set temperature range and continues to be heated until the temperature of the area reaches a peak value and starts to fall, the first set time is prolonged after the peak value is reached, the furnace cover is closed, and the safety hand wheel is pressed; step 4: introducing nitrogen to maintain the second set time and ensuring that the furnace pressure is within the set pressure numerical range; step 5: the main control temperature is controlled in the second set temperature range, methanol and propane are introduced, and after the carbon potential is reduced to the target value, the saturated carburization is kept for a third set time.

Description

Carbon saturation control process of muffle-free tank

Technical Field

The application relates to the technical field of heat treatment, in particular to a carbon saturation control process of a muffle tank.

Background

At present, in the carburizing heat treatment industry, a main stream of a 3 m-diameter large-sized well type carburizing furnace is designed with a muffle tank, and a heating wire and a hearth atmosphere are shielded through the muffle tank, but the main disadvantage of the muffle furnace is that the muffle tank is high in replacement cost and complicated in lifting operation after the service life of the muffle tank is expired. Based on the real cost characteristics, industry produces a no muffle design, but through the design of W type quick cooling hollow heating rod that can carburize (furnace body external cooling air, through hollow heating rod in order to realize carburization work piece cooling in the furnace), cancel the muffle tank, through the forced atmosphere circulation of air duct, the biggest advantage of no muffle tank design is that there is not the huge cost problem of muffle tank, but find that it has a huge drawback after the actual use, namely no muffle furnace's furnace lining directly contacts with carburization atmosphere, the loose resistant firebrick of furnace lining is interior infiltration a large amount of carbon atoms very much after long-time carburization, lead to furnace lining surface carbon supersaturation, the supersaturation is just a large amount of carbon black that forms as a result, excessive carbon black leads to carburization carbon drop potential slowly, carburization spare is easy carbide superscalar, simultaneously no muffle design is liable to produce serious internal oxidation problem because of furnace lining owe carbon.

The large-scale muffle-free tank well type carburizing furnace has the following main defects after long-time carburization:

(1) The furnace lining participates in carburization reaction, carbon supersaturation is easy, and when the furnace hearth reduces carbon potential, the furnace lining continuously releases supersaturated carbon atoms, and the carbon potential is slow, so that the diffusion carbon potential is difficult to accurately control.

(2) The hollow W-shaped heating rod is contacted with carburizing atmosphere, supersaturated carbon black is enriched on the surface of the heating rod, the plasticity of the heating rod is reduced, the heating rod is easy to brittle failure, at the moment, the hollow design of quick cooling of carburization can be realized, a huge safety problem is generated, namely, the carburizing atmosphere overflows the outside of the furnace shell, and the problems of gas explosion and CO exceeding are easy to generate.

(3) The furnace mouth heat-insulating cotton is in direct contact with carburizing atmosphere, so that a large amount of supersaturated carbon black is easy to accumulate, and the control accuracy of the diffusion carbon potential is affected.

(4) Because the furnace lining continuously releases carbon atoms, the carbon potential in the furnace hearth is high, the oxygen probe is easy to accumulate carbon, the control of the carbon potential of the oxygen probe is invalid, the problems of carbide exceeding and hardening layer exceeding are easily generated, structural members in the furnace lining are corroded, and the service lives of an air duct, a heating rod, an air duct cover and the like are reduced.

The conventional carbon burning process of the non-muffle tank carburizing furnace is simple, the conventional process is over 860 ℃, the open furnace cover is contacted and controlled to naturally burn for several hours, and the process has two obvious disadvantages: firstly, the burning time is long, and the cost is high; secondly, the effect of controlling the carbon saturation cannot be accurately achieved, and for extremely serious carbon supersaturation, the combustion effect may not be achieved; for the mild state of carbon supersaturation, excessive combustion is liable to occur, resulting in undercarbonation.

Disclosure of Invention

In order to solve the problem that the existing muffle-free tank cannot accurately control the carbon saturation effect in the prior art, the application provides a muffle-free tank carbon saturation control process with the accurate carbon saturation control effect.

The technical scheme adopted for solving the technical problems is as follows:

the muffle-free tank comprises a furnace shell and a furnace cover positioned above the furnace shell, wherein a furnace lining is arranged in the furnace shell, an oxygen probe and a main control thermocouple for measuring the main control temperature are arranged below the furnace cover, and a zone thermocouple for measuring the zone temperature is arranged in the furnace lining; a carbon saturation control process of a muffle tank,

the method comprises the following steps:

step 1: heating the hearth, and closing nitrogen, methanol and propane during heating;

step 2: the main control temperature is raised to a first set temperature range, the furnace cover is opened upwards, the opening stroke of the furnace cover is smaller than the full-opening stroke, and preferably, the furnace cover is opened upwards to 1/2 of the full-opening stroke, for example, the full-opening stroke of the furnace cover is about 500 mm, and only 250mm is needed here, so that an oxygen probe, a main control thermocouple and a instillation port in a hearth are ensured to be in an air environment for carbon burning, and nitrogen, methane and propane are closed during carbon burning;

step 3: the main control temperature keeps a first set temperature range and continues to be heated until the temperature of the area reaches a peak value and starts to fall, the first set time is prolonged after the peak value is reached, the furnace cover is closed, and the safety hand wheel is pressed;

step 4: introducing nitrogen to maintain the second set time and ensuring that the furnace pressure is within the set pressure numerical range;

step 5: and controlling the main control temperature within a second set temperature range, introducing methanol and propane, and maintaining saturated carburization for a third set time after the carbon potential is reduced to a target value.

Further, the first set temperature range is 930-950 ℃.

Further, the first set time is 8-12 min.

Further, the second setting time is 1 hour or more.

Further, the pressure value range is set to 200-400pa.

Further, the second set temperature range is 860-950 ℃.

Further, the nitrogen flow is at least 1 time of the volume of the hearth.

Further, the flow ratio of the nitrogen to the methanol is 1:1-1.2:1. Preferably, nitrogen: methanol=1.1:1.

Further, the third set time is 2h.

Further, in step 5, the carbon potential CP is reduced to 0.75 to 0.85%.

The beneficial effects are that:

(1) Accurately controlling the carbon saturation effect through the temperature balance time of the extreme value in the furnace;

(2) The carbon potential reduction time of the carbon saturation control process is reduced from conventional 1-3h to 1h, so that the production heating cost is greatly reduced;

(3) Accurate furnace lining carbon reservoir concentration values are realized through quick saturated carburization;

(4) Solves the problems of poor control accuracy and easy internal oxidation of the carbon potential of the large-scale muffle-free carburizing furnace, and the internal oxidation meets the ISO6336-5-2016ME level requirement;

(5) The dispersity and reliability of carburized carbon concentration of carburized pieces are improved, the dispersity of conventional 1-4-grade carbide is improved to a stable 1-grade, and the quality and the dispersity of products are greatly improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a carbon reduction potential and a steady state process for controlling the same;

FIG. 2 is a schematic diagram showing the temperature change in the carbon burning furnace;

FIG. 3 is a schematic view of the surface texture dispersion of the product obtained by the muffle-free tank carbon saturation control process of the application;

fig. 4 is a schematic view of the internal structure of the muffle-free tank.

Wherein, 1, furnace lining, 2, heating rod, 3, air duct, 41, main control thermocouple, 42, zone thermocouple, 5, oxygen probe, 6, furnace shell, 7, furnace cover.

Detailed Description

The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present application unless it is specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.

In the description of the present application, it should be understood that the azimuth or positional relationships indicated by the azimuth terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal", and "top, bottom", etc., are generally based on the azimuth or positional relationships shown in the drawings, merely to facilitate description of the present application and simplify the description, and these azimuth terms do not indicate and imply that the apparatus or elements referred to must have a specific azimuth or be constructed and operated in a specific azimuth, and thus should not be construed as limiting the scope of protection of the present application; the orientation word "inner and outer" refers to inner and outer relative to the contour of the respective component itself.

Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present application.

The large-scale well-type carburizing furnace with the muffle tank has less carbon deposition and no supersaturated carbon atom, so the process for realizing carbon saturation in the hearth is to naturally burn supersaturated carbon black by contacting air when discharging from the furnace at 840-880 ℃ after carburization. The large-scale well type muffle-free furnace design carburizing furnace has the patent for only one carburizing furnace manufacturer in Austria in the world, the domestic quantity of the structural equipment is small, the technical shortage of easy carbon supersaturation of the structure can be accurately solved, and the problem of carbon supersaturation of the large-scale muffle-free tank carburizing furnace can not be accurately controlled by related manufacturers in China.

The internal structure of the muffle-free tank is shown in figure 4, and the muffle-free tank comprises a furnace shell 6 and a furnace cover 7 positioned above the furnace shell 6, wherein a furnace lining 1 is arranged in the furnace shell 6, an oxygen probe 5 and a main control thermocouple 41 for measuring the main control temperature are arranged below the furnace cover 7, a zone thermocouple 42 for measuring the zone temperature is arranged in the furnace lining 1, a heating rod 2, an air duct 3 and the like are also arranged in the furnace lining 1, and the surface carbon concentration of the furnace lining 1 and the like in the furnace chamber is in three states, namely, the furnace lining is saturated with carbon, namely, no excessive carbon black is accumulated, and meanwhile, no carbon is poor; secondly, supersaturation of carbon, namely excessive carbon black is accumulated on the surfaces of a furnace lining 1, a heating rod 2, an air duct 3 and the like, and the control of carbon reduction potential is affected; and thirdly, carbon is undersaturated, namely, the surface carbon concentration of a furnace lining 1, a heating rod 2, an air duct 3 and the like is insufficient, namely, carbon is poor, and the undersaturation of carbon can generate another problem, namely, after carburization enters a furnace, the establishment of carbon potential is extremely slow, the enrichment atmosphere is mainly absorbed by the furnace lining 1, the air duct 3 and other parts, redundant carbon atoms are not involved in heating exhaust and air combustion, air reacts with alloy elements on the metal surface of a workpiece at high temperature, severe internal oxidation is easily caused, and meanwhile, the slow establishment of carbon potential also means that the heating cost is increased.

The carbon saturation process of the application comprises the following steps: at high temperature of the hearth, carbon black in the hearth and the oxygen probe 5 reacts with air to form carbon slag and the like through introducing external environment air, the carbon black is burnt out to realize controllable carbon potential, the hearth is immediately subjected to saturated carburization after carbon burning, the saturated concentration value is equal to the diffusion carbon potential value of a conventional carburized piece, the saturated carburization provides a furnace lining 1 carbon reservoir foundation, and the subsequent carburized piece carbon potential control is realized rapidly, uniformly and stably. The method comprises the following specific steps:

a carbon saturation control process of a muffle-free tank comprises the following steps:

step 1: heating the hearth, and closing nitrogen, methanol and propane during heating;

step 2: the main control temperature is raised to a first set temperature range, and the first set temperature range is 930-950 ℃. The furnace cover 7 is opened upwards, the opening stroke of the furnace cover 7 is smaller than the full-opening stroke, the oxygen probe 5, the main control thermocouple 41, the drip nozzle and the like in the hearth are ensured to be in an air environment, carbon burning is carried out, and nitrogen, methane and propane are closed during the carbon burning;

when the furnace cover 7 is normally heated, the furnace cover 7 is required to be lowered to a certain position, and is automatically pressed to a limiting device, and at the moment, the program knows that the furnace cover 7 is closed, and at the moment, the power can be supplied. In the step 2, the furnace cover 7 is in a partially opened state and cannot be pressed to the limiting device, and the limiting device is needed to be pressed manually, so that the program senses the indication that the electric current can be applied for heating.

Step 3: the main control temperature keeps the first set temperature range and continues to heat until the zone temperature reaches the peak value and starts to decrease, as an example, the zone temperature comprises three zone temperatures, namely, the heating rod 2 is arranged in the upper, middle and lower three zones in the furnace body, namely, three circles are distributed in the upper, middle and lower, and the temperatures of the upper, middle and lower three zones are measured through the zone thermocouples 42 in fig. 3, as in fig. 2, the three zone temperatures generally reach the peak value at the same time. And after reaching the peak value, the furnace cover 7 is closed again after the first set time is prolonged, and the first set time is 8-12 min.

Step 4: and introducing nitrogen to maintain the second set time, wherein the flow rate of the nitrogen is at least 1 time of the volume of the hearth. The second set time is 1 hour or more. And ensuring that the furnace pressure is within a set pressure numerical range; the pressure value range is set to be 200-400pa.

Step 5: the main control temperature is controlled within a second set temperature range, and the second set temperature range is 860-950 ℃. And introducing methanol and propane, reducing the carbon potential CP to 0.75-0.85%, and keeping the saturated carburization for a third set time. The flow ratio of the nitrogen to the methanol is 1:1-1.2:1. The third set time is 2h.

The carbon potential reduction time of the carbon saturation control process of the muffle-free tank is reduced from conventional 1-3h to 1h as shown in figure 1, so that the production heating cost is greatly reduced; the dispersity and reliability of carburized carbon concentration of carburized pieces are improved, the dispersity of conventional 1-4-grade carbide is improved to the steady-state 1 grade as shown in figure 3, and the quality and dispersity of products are greatly improved.

The present application is not limited to the above-mentioned embodiments, and any person skilled in the art, based on the technical solution of the present application and the inventive concept thereof, can be replaced or changed within the scope of the present application.

Claims (1)

1. A carbon saturation control process of a muffle-free tank is characterized in that:

the muffle-free tank comprises a furnace shell and a furnace cover positioned above the furnace shell, wherein a furnace lining is arranged in the furnace shell; an oxygen probe and a main control thermocouple for measuring the main control temperature are arranged below the furnace cover, a zone thermocouple for measuring the zone temperature is arranged in the furnace lining, and a heating rod and an air duct are also arranged in the furnace lining;

the method comprises the following steps:

step 1: heating the hearth, and closing nitrogen, methanol and propane during heating;

step 2: the main control temperature in the area below the furnace cover is raised to a first set temperature range, the first set temperature range is 930-950 ℃, the furnace cover is opened upwards, the opening stroke of the furnace cover is smaller than the full-opening stroke, the oxygen probe, the main control thermocouple and the instillation port in the hearth are ensured to be in an air environment, carbon burning is carried out, and nitrogen, methane and propane are closed during the carbon burning;

step 3: the main control temperature keeps a first set temperature range and continues to be heated until the temperature of the area inside the furnace lining reaches a peak value and starts to fall, the first set time is prolonged after the peak value is reached, and then the furnace cover is closed, wherein the first set time is 8-12 min;

step 4: introducing nitrogen to maintain a second set time, wherein the nitrogen flow is at least 1 time of the volume of the hearth, the second set time is more than 1 hour, the furnace pressure is ensured to be within a set pressure numerical range, and the set pressure numerical range is 200-400 pa;

step 5: the main control temperature is controlled within a second set temperature range, the second set temperature range is 860-950 ℃, methanol and propane are introduced, the flow ratio of nitrogen to methanol is 1:1-1.2:1, and after the carbon potential CP is reduced to 0.75-0.85%, saturated carburization is kept for a third set time, and the third set time is 2 hours.