Crankshaft self-tempering method

Abstract

The invention discloses a crankshaft self-tempering method which mainly comprises the following steps: accurately regulating and controlling the temperature of a crankshaft after quenching by controlling parameters such as the ratio of heating time to cooling time of crankshaft quenching, the power variable power range of a connecting rod, the quenching liquid concentration, the quenching liquid cooling speed, the quenching liquid temperature and the quenching liquid flow, and carrying out post-process processing after air cooling. A large number of experiments verify that crankshaft self-tempering is achieved, the performance such as the surface hardness, the metallographic structure, the quenching depth, the residual stress and the fatigue strength of the crankshaft reach the same effect as that of in-furnace tempering, the method can be applied to the two strengthening technologies of crankshaft journal quenching and fillet quenching, tempering furnace equipment can be omitted by adopting the self-tempering technology, and the cost is reduced. The energy consumption is reduced, the production cost is reduced, the crankshaft circulation period is shortened, the production efficiency is improved, and the development of an automatic crankshaft production line is facilitated.

Description

Technical Field

[0001] The present invention mainly relates to the manufacturing industries such as automobiles / ships, etc., and the technical field of metal processing and heat treatment, and specifically provides a method for self-tempering of crankshafts. Background Art

[0002] As one of the key components in an automotive engine, the performance of a crankshaft directly affects the reliability and service life of the engine. During the manufacturing process of the crankshaft, generally, journal quenching + fillet rolling or fillet quenching is adopted to improve the surface hardness, wear resistance, and fatigue strength of the crankshaft. In order to eliminate the quenching stress and obtain a stable structure and size, the crankshaft is subjected to a tempering treatment after quenching. However, the traditional tempering treatment after quenching often requires additional heating equipment and a long time, which not only increases energy consumption and prolongs the production cycle, but also may cause the crankshaft to deform and crack due to multiple heating and cooling, affecting the machining accuracy and increasing the production cost. Therefore, it is of great significance to develop a tempering process that is efficient, energy-saving, and can ensure the quality of the crankshaft. Summary of the Invention

[0003] The purpose of the present invention is to provide a self-tempering process for crankshafts. By raising the temperature of the crankshaft after quenching and using the residual heat of the crankshaft itself for tempering, the tempering furnace equipment can be omitted, energy consumption can be reduced, production costs can be lowered, while ensuring the performance of the crankshaft. At the same time, the turnover cycle of the crankshaft is shortened, production efficiency is improved, which is beneficial to the development of the crankshaft automated production line.

[0004] The technical solution to realize the present invention is as follows: A method for self-tempering of a crankshaft. First, a TQKC / Q type crankshaft quenching machine tool is used in the crankshaft quenching process; then, by controlling process parameters such as the ratio of heating time to cooling time during crankshaft quenching, the variable power range of the connecting rod power, the concentration of the quenching liquid, the V300 cooling rate of the quenching liquid, the temperature of the quenching liquid, and the flow rate of the quenching liquid, the temperature of the crankshaft after quenching is accurately regulated, and then air-cooled to achieve self-tempering of the crankshaft; wherein: when the crankshaft strengthening method adopts the journal quenching + sunk groove rolling process, the ratio of heating time to cooling time is 20% - 40%; when the crankshaft strengthening method adopts the fillet quenching process, the ratio of heating time to cooling time is 65% - 85%.

[0005] The method of the present invention realizes self-tempering of the crankshaft, and enables the performance of the crankshaft such as surface hardness, metallographic structure, quenching depth, residual stress, fatigue strength, etc. to reach the same effect as that of tempering in a tempering furnace after the crankshaft is quenched. In the present invention, the main function of controlling the ratio of the heating time to the cooling time is to control the temperature of the crankshaft after cooling, so that the crankshaft is maintained at 230°C to 280°C after quenching, and this temperature is the key point for realizing self-tempering; if the heating time is longer and the cooling time remains unchanged, it will cause the temperature of the crankshaft after quenching to be too high, affecting the physical and chemical properties of the crankshaft. If the heating time remains unchanged and the cooling time is too long, it will cause the temperature of the crankshaft after quenching to be insufficient, and the crankshaft cannot perform self-tempering.

[0006] The present invention further illustrates that when the crankshaft strengthening method (i.e., the crankshaft quenching process) adopts the journal quenching + counterbore rolling process, the connecting rod power does not need to be changed; when the crankshaft strengthening method adopts the fillet quenching process, the power change angle of the connecting rod is 20° to 60°.

[0007] In the present invention, the main purpose of controlling the power change angle is to adjust the heating effect according to the thickness of the crankshaft structure to ensure that the heating temperature at each position is uniform. For example, for the connecting rod journal, the outer side is thinner and the inner side is thicker. The temperature rise rate of the thinner part during induction quenching is faster than that of the thicker part. If the same power is used, it will cause the temperature of the crankshaft to be uneven. The self-tempering effect of the part with a higher temperature is good, while that of the part with a lower temperature is worse, which is likely to cause incomplete stress elimination, resulting in crankshaft deformation or even cracking. In other words, if the temperature of the part with a higher temperature is too high, it will cause the transformation of the crankshaft structure (non-martensite), affecting the surface hardness, fatigue strength, etc. of the crankshaft.

[0008] The present invention further illustrates that the concentration of the quenching liquid is controlled at 10% to 15%, and the PAG water-based quenching liquid is used as the quenching liquid.

[0009] In the present invention, controlling the concentration of the quenching liquid is mainly to monitor the preparation of the quenching liquid, because the concentration of the quenching liquid mainly affects the cooling effect during the quenching process of the crankshaft. When the concentration of the quenching liquid is low, the cooling effect of the crankshaft is improved, and vice versa. The quality of the cooling effect is to confirm that the temperature of the crankshaft after quenching is controlled at 230°C - 280°C, because the self-tempering effect of the crankshaft is the best in this temperature range. At the same time, if the concentration of the quenching liquid is too low, high-amplitude internal stress will be formed, resulting in crankshaft deformation or even cracking.

[0010] The present invention further illustrates that the cooling rate of the quenching liquid V300 is controlled at 40°C / s to 80°C / s.

[0011] The cooling rate detection of the quenching liquid is to heat the detection probe to 850 °C, insert it into the quenching liquid for cooling, and the cooling rate detector will record the change of the detection temperature with time and the change of the cooling rate with temperature. V300 represents the cooling rate when the quenching liquid cools to 300 °C. The crankshaft belongs to medium carbon steel, and the martensite transformation start temperature Ms is about 300 °C. One of the purposes of induction quenching is to obtain a stable martensite structure through rapid cooling after heating.

[0012] The present invention further illustrates that the temperature of the quenching liquid is controlled at 15 °C to 35 °C. The temperature of the quenching liquid is one of the factors affecting the cooling effect, and the purpose is to ensure that the temperature of the crankshaft after quenching is controlled at 230 °C - 280 °C, because the self-tempering effect of the crankshaft is the best in this temperature range.

[0013] The present invention further illustrates that, characterized in that: the flow rate of the quenching liquid is controlled at 40 L / min to 100 L / min. The flow rate of the quenching liquid is one of the factors affecting the cooling effect. During the quenching and cooling process, it experiences three stages: steam film, boiling, and convection. A large flow rate will cause too large a difference in the cooling rate of each part of the crankshaft, generating large thermal stress and causing the crankshaft to deform; a small flow rate will result in untimely heat dissipation of the quenching liquid, and the crankshaft stays in the high-temperature zone for too long, resulting in austenite analysis and forming other non-martensite structures, affecting the quenching quality.

[0014] The present invention further illustrates that the temperature of the crankshaft after quenching is controlled at 230 °C to 280 °C. The self-tempering process of the crankshaft utilizes the remaining heat after quenching for tempering. The process parameter is the temperature of the crankshaft after quenching. Due to the influence of the detection method, this temperature cannot be accurately identified, and it can only be controlled by controlling the above other parameters.

[0015] The present invention further illustrates that after the crankshaft is quenched, it is air-cooled, and the air-cooling time is 20 - 30 min. The temperature of the crankshaft is relatively high after quenching, and the self-tempering time is relatively short, generally completed within more than ten seconds. At this time, the temperature of the crankshaft is still very high. If it is directly transferred to the subsequent process, it will cause the size of the crankshaft to be unstable. Therefore, it needs to be cooled to room temperature before being transferred. If it is air-cooled, the time will be 1 - 2 h, which greatly affects the efficiency. This parameter provides a method for cooling after self-tempering: air-cooling, ensuring the size stability of the crankshaft after rapid cooling.

[0016] Advantages of the present invention: 1. No additional tempering heating equipment is required, directly using the remaining heat of the quenched crankshaft, greatly reducing energy consumption and production costs.

[0017] 2. Eliminate the heating waiting time of traditional tempering, reduce the waiting time between processes, significantly shorten the production cycle, and improve production efficiency.

[0018] 3. Shorten the tempering waiting time, reduce the thermal stress caused by multiple heating and cooling of the crankshaft, lower the possibility of deformation and cracking, improve the machining accuracy, and ensure the stability of product quality. Description of the Drawings

[0019] Figure 1 is a schematic diagram of the quenching part of the crankshaft; Figure 2 is a graph showing the temperature change of the crankshaft under the in-furnace tempering and self-tempering processes; Figure 3 is a comparison chart of the surface hardness of each part of the crankshaft under the in-furnace tempering and self-tempering processes; Figure 4 is a comparison chart of the quenching depth of each part of the crankshaft under the in-furnace tempering and self-tempering processes; Figure 5 is a comparison chart of the metallographic structure of each part of the crankshaft under the in-furnace tempering and self-tempering processes; Figure 6 is a comparison chart of the residual stress of each part of the crankshaft under the in-furnace tempering and self-tempering processes; Figure 7 is a comparison chart of the fatigue limit bending moment of the crankshaft under the in-furnace tempering and self-tempering processes.

[0020] Figure 8 is a comparison chart of the safety factor in the fatigue test of the crankshaft under the in-furnace tempering and self-tempering processes.

[0021] Among them, the meanings represented by each label in the figure are as follows: Figure 1 In, 1 represents the main shaft and 2 represents the connecting rod; Figure 2 In, a represents the quenching temperature zone, b represents the self-tempering temperature zone, and c represents the in-furnace tempering temperature zone; Figure 2-6 In, Experiment represents the experimental group representing the self-tempering process, and Comparison represents the control group representing the in-furnace tempering process. Detailed Implementation Manner Example

[0022] A method for self-tempering of crankshafts. In the crankshaft quenching process, a TQKC / Q type crankshaft quenching machine tool is used. By controlling the ratio of the heating time to the cooling time of crankshaft quenching, the ratio of the heating time to the cooling time is 20% - 40% during the journal quenching + counterbore rolling process, and the ratio of the heating time to the cooling time is 65% - 85% during the fillet quenching process; the power of the connecting rod journal does not need to change during the journal quenching + counterbore rolling process, and the power change angle of the connecting rod journal is 20° - 60° during the fillet quenching process; the quenching liquid uses a PAG water-based quenching agent, and the concentration is controlled at 10% - 15%; the cooling rate of the quenching liquid V300 is controlled at 40°C / s - 80°C / s; the temperature of the quenching liquid is controlled at 15°C - 35°C; the flow rate of the quenching liquid is controlled at 40L / min - 100L / min and other parameter conditions, and the temperature of the crankshaft after quenching is accurately controlled at 230°C - 280°C. After air cooling for 20 - 30 minutes, the subsequent process machining is carried out. Example

[0023] A certain H-type crankshaft is a crankshaft for an engine project of a certain main engine factory, and our company undertakes the development and production. In the early stage, the fillet quenching + in-furnace tempering process was used for production. After a large number of experimental verifications, while ensuring the performance of the crankshaft, the crankshaft was changed from tempering in a tempering furnace to self-tempering on an intermediate frequency quenching machine tool.

[0024] Quenching of a certain H-type crankshaft uses a TQKC / Q type crankshaft quenching machine tool. During the quenching process, by controlling the ratio of the heating time to the cooling time of the crankshaft, the heating time is 10 - 14s, the cooling time is 7 - 10s, and the time ratio is about 70% - 80%. The power change angle of the connecting rod journal is 20°. The quenching liquid uses a PAG water-based quenching agent, and the concentration is controlled at 10% - 15%. The cooling rate of the quenching liquid V300 is controlled at 50 - 80°C / s, the temperature of the quenching liquid is controlled at 25°C, the flow rate of the quenching liquid is controlled at 50 - 90L / min, and the temperature of the crankshaft after quenching is accurately controlled at 230°C - 260°C. After air cooling for 25 minutes, the subsequent process machining is carried out.

[0025] See Figure 2 - Figure 6 , after a certain H-type crankshaft is self-tempered by controlling the cooling parameters during the fillet quenching process, the performance of the crankshaft such as surface hardness, quenching depth, metallographic structure, fillet residual stress, fatigue strength, etc. reaches the same level as that of in-furnace tempering.

[0026] The present invention aims to reduce costs and increase efficiency in the heat treatment of crankshafts. By controlling conditions such as the heating time to cooling time ratio during crankshaft quenching, the concentration of the quenching liquid, the cooling rate of the quenching liquid, the temperature of the quenching liquid, and the flow rate of the quenching liquid, the temperature of the crankshaft after quenching is precisely regulated. Then, after air cooling, self-tempering of the crankshaft is achieved. Using this method can eliminate the need for a tempering furnace, reduce energy consumption, and lower production costs. At the same time, it shortens the turnover cycle of the crankshaft and improves production efficiency, which is beneficial to the development of the crankshaft automated production line. The present invention can be applied to two induction hardening processes: crankshaft journal quenching and fillet quenching.

[0027] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0028] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for crankshaft self-tempering, characterized in that: The crankshaft quenching process uses a TQKC / Q type crankshaft quenching machine tool. By controlling the heating time and cooling time ratio of the crankshaft quenching, the power range of the connecting rod, the quenching liquid concentration, the quenching liquid V300 cooling rate, the quenching liquid temperature and the quenching liquid flow rate, the temperature of the crankshaft after quenching is accurately controlled, and then it is cooled by air to achieve self-tempering of the crankshaft; among them: when the crankshaft strengthening method adopts the journal quenching + sink groove rolling process, the heating time and cooling time ratio is 20%~40%; when the crankshaft strengthening method adopts the fillet quenching process, the heating time and cooling time ratio is 65%~85%.

2. The method for crankshaft self-tempering according to claim 1, characterized in that: When the crankshaft strengthening method adopts the journal quenching + groove rolling process, the connecting rod power does not need to be changed; when the crankshaft strengthening method adopts the fillet quenching process, the connecting rod power change angle is 20°~60°.

3. The method for crankshaft self-tempering according to claim 1, characterized in that: The concentration of the quenching liquid is controlled at 10% to 15%, and the quenching liquid adopts PAG water-based quenching liquid.

4. The method for crankshaft self-tempering according to claim 1, characterized in that: The cooling rate of the quenching liquid V300 is controlled at 40°C / s to 80°C / s.

5. The method for crankshaft self-tempering according to claim 1, characterized in that: The temperature of the quenching liquid is controlled at 15°C to 35°C.

6. The method for crankshaft self-tempering according to claim 1, characterized in that: The quenching liquid flow rate is controlled at 40L / min to 100L / min.

7. The method for crankshaft self-tempering according to claim 1, characterized in that: The temperature of the crankshaft after quenching is controlled at 230°C to 280°C.

8. The method for crankshaft self-tempering according to claim 1, characterized in that: The crankshaft is air-cooled after quenching, and the air-cooling time is 20 to 30 minutes.

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