Heat treatment process for mining link chain

Abstract

A kind of heat treatment process of mining link ring, including step 1: according to preliminary treatment process, the blank of mining link ring is pre-treated;Wherein, the preliminary treatment process includes: the blank of mining link ring is kept in 900±5 DEG C car-bottom furnace for 3h, after furnace, using 15-35 DEG C tap water quenching, tempering is kept in 500 DEG C car-bottom furnace for 1h, then heated to 700 DEG C and kept for 8-10h, after furnace, air cooling to room temperature;Step 2: using controllable atmosphere furnace heating, K oil is used as quenching medium, according to quenching process, the mining link ring obtained after finishing is quenched;Step 3: the mining link ring after quenching is tempered in turn according to first tempering process and second tempering process;Step 4: the mining link ring after two times of tempering is shot blasting according to shot blasting process.The scheme has no corrosion to parts and equipment, and can improve the mechanical properties of link ring.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, and in particular to a heat treatment process for mining chain links. Background Technology

[0002] Mining connecting links are crucial transmission components on coal mine scraper conveyors. They are typically made of 23MnNiCrMo54 material, and quenching is performed in a controlled atmosphere furnace. The heat treatment process involves first pre-treating the connecting link blank, then holding the connecting link at 880℃ for 2.5 hours with a protective atmosphere carbon potential of 0.23%, followed by quenching with a (5-7)% sodium chloride aqueous solution, followed by rapid cooling for 3 minutes, then slow cooling for 5 minutes. Finally, tempering and shot peening are performed at (430±10)℃ for 3.5 hours. Hardness testing shows compliance with HRC38-42 technical requirements, and mechanical properties meet the requirements of MT / T99-1977 "Flat Connecting Links for Mining Round Link Chains" standard.

[0003] However, in the aforementioned heat treatment process, using sodium chloride aqueous solution as the quenching medium can cause corrosion to equipment and parts such as the quenching chamber iron plate, the lifting assembly of the quenching chamber, and the stirring motor assembly. This can easily lead to equipment malfunction and shutdown of the chain link quenching process. Furthermore, existing quenching processes using corrosion-resistant media materials often fail to produce chain links that meet mechanical performance requirements, resulting in a low product qualification rate. Summary of the Invention

[0004] In view of this, and to address the above shortcomings, it is necessary to propose a heat treatment process for mining chain links that is non-corrosive to mining chain link parts and quenching equipment, and that enables the produced chain links to meet mechanical performance requirements.

[0005] This invention provides a heat treatment process for mining connecting links, including the following steps:

[0006] Step 1: Pre-treat the blank of the mining connecting link according to the pre-treatment process; wherein, the pre-treatment process includes: holding the blank of the mining connecting link in a bogie-type resistance furnace at 900±5℃ for 3h, quenching it with tap water at 15-35℃ after taking it out of the furnace, tempering it in a bogie-type resistance furnace at 500℃ for 1h, then raising the temperature to 700℃ and holding it for 8-10h, and air cooling it to room temperature after taking it out of the furnace.

[0007] Step 2: The pre-treated connecting ring blank is precision machined, and K oil is used as the quenching medium to quench the precision-machined mining connecting ring according to the quenching process.

[0008] Step 3: Temper the quenched mining chain links sequentially according to the first tempering process and the second tempering process.

[0009] Step 4: Perform shot peening on the mining chain links that have undergone two tempering treatments, according to the shot peening process.

[0010] Preferably, in step 1, the loading quantity of the mining connecting ring in the bogie-type resistance furnace meets the following requirements: when the mining connecting ring is Φ26, the loading quantity is ≤400 pieces; when the mining connecting ring is Φ30, the loading quantity is ≤300 pieces; and when the mining connecting ring is Φ34, the loading quantity is ≤250 pieces.

[0011] Preferably, the quenching process in step 2 includes: keeping the mining chain link at 900℃ for 2.5 hours to protect the carbon potential at 0.3%, cooling it with K oil as the quenching medium for 10-15 minutes, and maintaining the oil outlet temperature of the mining chain link at 60-80℃.

[0012] Preferably, after the oil comes out of the mining connecting chain ring, it is further cleaned using a cleaning machine at a temperature of 70-90℃.

[0013] Preferably, during quenching, at least four stirring motors are turned on simultaneously for stirring.

[0014] Preferably, the first tempering process in step 3 is: holding at 380±10℃ for 3.5h and then air-cooling to room temperature after removal from the furnace.

[0015] Preferably, the second tempering process in step 3 is as follows: after holding at 430±10℃ for 3.5h, the furnace is removed and air-cooled to room temperature.

[0016] Preferably, the shot peening process in step 4 involves splitting the connecting ring into half rings, binding the two half rings that make up a complete connecting ring with wire, and suspending the two half rings on the shot peening machine with a certain gap for shot peening treatment.

[0017] Preferably, the connecting chain links are subjected to two shot peening treatments, with each shot peening lasting 3 minutes.

[0018] As can be seen from the above technical solution, the heat treatment process for mining connecting rings provided in this solution uses K oil instead of brine in the existing process. This will not cause any corrosion to the equipment and parts, and can significantly extend the service life of the equipment. Moreover, in the pretreatment process of heat treatment, tempering is carried out in stages at 500℃ and 700℃, especially the 700℃ holding time of 8-10 hours, which makes the carbides more uniform and fine, which is more conducive to improving the mechanical properties of the parts and increasing the product qualification rate. In addition, due to the high tempering temperature and long tempering time in the pretreatment, the hardness is reduced and the stability is improved after tempering, which can greatly improve the efficiency of subsequent finishing. Attached Figure Description

[0019] Figure 1A flowchart of a heat treatment process for a mining connecting link provided in an embodiment of the present invention. Detailed Implementation

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] See Figure 1 This invention provides a heat treatment process for mining connecting links, which may include the following steps:

[0022] Step 1: Pre-treat the blank of the mining connecting link according to the pre-treatment process; wherein, the pre-treatment process includes: holding the blank of the mining connecting link in a bogie-type resistance furnace at 900±5℃ for 3h, quenching it with tap water at 15-35℃ after taking it out of the furnace, tempering it in a bogie-type resistance furnace at 500℃ for 1h, then raising the temperature to 700℃ and holding it for 8-10h, and air cooling it to room temperature after taking it out of the furnace.

[0023] Step 2: The pre-treated connecting ring blank is precision machined, and K oil is used as the quenching medium to quench the precision-machined mining connecting ring according to the quenching process.

[0024] Step 3: Temper the quenched mining chain links sequentially according to the first tempering process and the second tempering process.

[0025] Step 4: Perform shot peening on the mining chain links that have undergone two tempering treatments, according to the shot peening process.

[0026] Existing technologies use (5-7)% brine for quenching. This concentration of brine can cause electrochemical corrosion of ferrous metal parts and equipment accessories, easily leading to their scrapping. K-oil, commonly used in box-type multi-purpose furnaces for carburizing and quenching gear parts, is suitable for the quenching requirements of low- and medium-carbon alloy steel workpieces and is a medium used for protective atmosphere quenching. The material of mining chain links is 23MnNiCrMo54, which is a low-carbon alloy steel. Therefore, this solution considers using K-oil as the quenching medium when quenching chain links, which can solve the problem of brine quenching corroding equipment and parts, and achieve clean quenching of mining chain links.

[0027] Furthermore, in existing technologies, the pretreatment process is a common quenching and tempering process. Specifically, it involves using a bogie furnace, holding at 900℃ for 3 hours, quenching with tap water, then holding at (660±10)℃ for 3 hours for tempering and air cooling to room temperature. The hardness of the tempered chain link blank is HB230-260, which is inconsistent and tends to be too high. Moreover, this process, when using K-oil quenching medium, makes it difficult to achieve the required mechanical properties for mining chain links. In this embodiment, a spheroidizing treatment is considered for the connecting chain ring blank. Specifically, the blank is held in a bogie-type resistance furnace at 900±5℃ for 3 hours, then quenched with tap water at 15-35℃, and tempered at 500℃ for 1 hour. The temperature is then raised to 700℃ and held for 8-10 hours. After removal from the furnace, it is air-cooled to room temperature. Holding at 500℃ for 1 hour allows the connecting chain ring blank to form bainite, promoting uniform carbide precipitation. Holding at 700℃ for 8-10 hours yields finer and more uniform carbide particles than ordinary quenching and tempering, improving the mechanical properties of the quenched product and thus increasing the product qualification rate.

[0028] After pretreatment of the blank using this embodiment, the hardness of the connecting ring blank is improved to HB190-210, which is lower and more stable than the existing technical solution. This can greatly improve the efficiency of subsequent connecting ring finishing and prepare for subsequent K oil quenching.

[0029] To improve the quality of the pre-treatment of the connecting chain ring blanks in step 1, in one embodiment, the loading quantity is controlled according to the size of the parts. Specifically, the loading quantity of the mining connecting chain rings in the bogie-type resistance furnace meets the following requirements: when the mining connecting chain ring is Φ26, the loading quantity is ≤400 pieces; when the mining connecting chain ring is Φ30, the loading quantity is ≤300 pieces; and when the mining connecting chain ring is Φ34, the loading quantity is ≤250 pieces. This ensures sufficient gaps between the mining connecting chain rings, achieving uniform heating, and prevents interference between the connecting chain ring parts, thereby improving the quality of the connecting chain ring pre-treatment.

[0030] It should be noted that the pretreatment is performed on the forged blank half-ring of the connecting chain link.

[0031] It is easy to understand that after the preparatory treatment in step 1, the connecting chain blank needs to be precision machined, and the connecting chain obtained after precision machining is used for quenching process.

[0032] In one embodiment, the quenching process in step 2 includes: keeping the mining chain link at 900°C for 2.5 hours to protect the carbon potential at 0.3%, cooling it with K oil as the quenching medium for 10-15 minutes, and maintaining the oil outlet temperature of the mining chain link at 60-80°C.

[0033] Currently, controlled atmosphere furnaces are used for quenching mining chain links. The protective atmosphere carbon potential is set to 0.23%, and the heating temperature is 880℃. However, the average carbon content of 23MnNiCrMo54 material is 0.23%. Due to the low heating temperature, the protective atmosphere only serves to prevent oxidation of the parts. In this embodiment, the quenching parameters are set to a protective atmosphere carbon potential of 0.3% and a heating temperature of 900℃. In addition to preventing oxidation, a slight carburizing effect occurs at 900℃, which promotes surface strengthening and improves the strength of the parts.

[0034] To achieve intense cooling, it is recommended to operate at least four stirring motors simultaneously during quenching to accelerate the cooling process.

[0035] Furthermore, because this solution uses K oil as the quenching medium, residual oil stains remain on the surface of the chain link parts after quenching. Therefore, in one embodiment, it is considered to further clean the mining chain link using a cleaning machine after the oil has drained, with a cleaning temperature of 70-90℃. This can remove the residual quenching oil stains and thus eliminate tempering fumes.

[0036] Furthermore, it should be noted that during quenching, the connecting links should be mounted vertically to ensure that more of their surface area is exposed, and that there is a certain gap between adjacent connecting links. This ensures that all parts of the connecting links are heated more thoroughly and uniformly. Specifically, a special bracket can be used to mount the connecting links vertically and maintain the gaps between them.

[0037] In the existing tempering process for heat treatment of butt chain links, the method used is a single tempering process where the chain is held at 430±10℃ for 3.5 hours. However, this method is only suitable for brine quenching in corrosive media. Therefore, in one embodiment, a two-stage tempering process is considered for tempering the butt chain links, which is applicable to quenching in K oil. Specifically, the first tempering process in step 3 is: holding at 380±10℃ for 3.5 hours and then air-cooling to room temperature. The second tempering process in step 3 is: holding at 430±10℃ for 3.5 hours and then air-cooling to room temperature.

[0038] In the tempering process of the connecting link, the entire connecting link is tempered.

[0039] In one embodiment, the shot peening process in step 4 involves splitting the connecting link into half-rings, binding the two half-rings that form a complete connecting link together with wire, and suspending them on the shot peening machine with a certain gap between them for shot peening. During shot peening, the connecting link is shot peened twice, with each shot peening session lasting 3 minutes.

[0040] It should be noted that the two half-loops bound together on the same wire are the two half-loops split from the original whole loop. For example, for whole loop A, it is split into two half-loops A1 and A2, and for whole loop B, it is split into two half-loops B1 and B2. The two half-loops bound together on the same wire can only be either A1 and A2 or B1 and B2, not A1 and B2 or A2 and B1, in order to ensure the original fit of the whole loop.

[0041] Since the connecting link is composed of two half-rings, shot peening cannot be applied to the mating surfaces of the two half-rings if the entire ring is shot peened. Therefore, this embodiment achieves a more thorough shot peening of the connecting link by splitting the entire ring into two half-rings for shot peening. Furthermore, the tempering process enhances the fatigue resistance of the connecting link.

[0042] For example, for existing quenched connecting links, the tempering process involves holding at (430±10)℃ for 3.5 hours and shot peening the entire ring. Through testing, its hardness meets the technical requirements of HRC38-42, and the breaking load and fatigue cycle count can meet the requirements of MT / T99-1997 "Flat Connecting Links for Mining Round Link Chains". However, this method is only suitable for brine quenching in corrosive media, and shot peening can only clean the surface, not the mating surfaces.

[0043] After tempering at (430±10)℃ for 3.5 hours and shot peening with a semi-ring suspension, the hardness can meet the HRC38-42 requirement, and the breaking load meets the standard requirements. However, the fatigue cycle count of 80% of the link parts is lower than the technical requirements.

[0044] Furthermore, by employing the first tempering process of holding at (380±10)℃ for 3.5 hours and the second tempering process of holding at (430±10)℃ for 3.5 hours provided by this invention, along with the use of a semi-ring suspended shot peening method, complete cleaning of the mating surfaces and other exposed surfaces of the parts can be achieved, resulting in a more thorough cleaning. Moreover, using this tempering process, the hardness, breaking load, and fatigue cycle count of the chain link parts after shot peening all meet the requirements. Among them, the fatigue cycle count of the Φ34 specification chain link even reaches 74,590 cycles (the standard requires ≥40,000 fatigue cycles).

[0045] The following comparative experiment will further illustrate this scheme.

[0046] Example 1: Comparison of conventional tempering and spheroidizing treatments in the pretreatment process.

[0047] Comparative group: The pretreatment process adopts ordinary quenching and tempering, with the following process parameters: quenching at (900±5)℃ for 3 hours, water cooling to room temperature, tempering at (660±10)℃ for 3 hours, and air cooling to room temperature.

[0048] Implementation Group: The pretreatment process adopts the spheroidizing treatment provided in this plan. The process parameters are as follows: the blank is held in a bogie-type resistance furnace at 900±5℃ for 3 hours, quenched with tap water at 15-35℃ after being taken out of the furnace, tempered in an environment of 500℃ for 1 hour, then heated to 700℃ and held for 8-10 hours, and then air-cooled to room temperature after being taken out of the furnace.

[0049] The fatigue test results are shown in Table 1:

[0050] Table 1

[0051]

[0052]

[0053] It is evident that the fatigue life of the connecting links is significantly improved through spheroidization pretreatment. Moreover, for the 5M series products, the improvement in fatigue life can even reach more than 70% compared to ordinary heat treatment.

[0054] It should be noted that in the above experiments, the quenching process after finishing was the same for both types of pre-treated parts.

[0055] Example 2: Comparison of single tempering and double tempering during K oil quenching.

[0056] Comparative group: K oil quenching was performed using a single tempering process with a holding temperature of 420℃ for 3.5 hours;

[0057] Experimental group: K oil quenching was carried out using a two-stage tempering process, with the temperature held at 380℃ for 3.5 hours and at 420℃ for 3.5 hours.

[0058] The results of the experimental comparison are shown in Tables 2 and 3:

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] As shown in Tables 2 and 3 above, when using a single tempering process in K oil quenching, 3 out of 4 tested parts failed the fatigue performance test. However, when using a double tempering process, all 6 tested parts met the standard, and the fatigue test values ​​were significantly stronger than those of the single tempering process.

[0064] Example 3: Comparison of semi-ring shot peening and full-ring shot peening

[0065] Table 4 below shows the comparison results of the mechanical properties of the shot peening tests conducted on the half-ring and the full-ring respectively.

[0066] Table 4

[0067]

[0068] As can be seen from Table 4, shot peening using a semi-ring suspension method significantly improves the mechanical properties of the connecting link, such as fatigue number and hardness HRC.

[0069] The modules or units in the device of this invention can be merged, divided, and deleted according to actual needs. The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments and making equivalent changes according to the claims of this invention still fall within the scope of the invention.

Claims

1. A heat treatment process for mining connecting links, characterized in that, Includes the following steps: Step 1: Pre-treat the blank of the mining connecting link according to the pre-treatment process; wherein, the pre-treatment process includes: holding the blank of the mining connecting link in a bogie-type resistance furnace at 900±5℃ for 3h, quenching it with tap water at 15-35℃ after taking it out of the furnace, tempering it in a bogie-type resistance furnace at 500℃ for 1h, then raising the temperature to 700℃ and holding it for 8-10h, and air cooling it to room temperature after taking it out of the furnace. Step 2: The pre-treated connecting ring blank is precision machined, and K oil is used as the quenching medium to quench the precision-machined mining connecting ring according to the quenching process. Step 3: Temper the quenched mining chain links sequentially according to the first tempering process and the second tempering process. Step 4: Perform shot peening on the mining chain links that have undergone two tempering treatments, according to the shot peening process.

2. The heat treatment process for mining connecting links according to claim 1, characterized in that, In step 1, the loading quantity of the mining connecting ring in the bogie-type resistance furnace meets the following requirements: when the mining connecting ring is Φ26, the loading quantity is ≤400 pieces; when the mining connecting ring is Φ30, the loading quantity is ≤300 pieces; and when the mining connecting ring is Φ34, the loading quantity is ≤250 pieces.

3. The heat treatment process for mining connecting links according to claim 1, characterized in that, The quenching process in step 2 includes: keeping the mining chain link at 900℃ for 2.5 hours to protect the carbon potential at 0.3%, cooling it with K oil as the quenching medium for 10-15 minutes, and maintaining the oil outlet temperature of the mining chain link at 60-80℃.

4. The heat treatment process for mining connecting links according to claim 2, characterized in that, After the oil is discharged from the mining chain link, it is further cleaned using a cleaning machine at a temperature of 70-90℃.

5. The heat treatment process for mining connecting links according to claim 3, characterized in that, During quenching, at least four stirring motors should be turned on simultaneously for stirring.

6. The heat treatment process for mining connecting links according to claim 1, characterized in that, The first tempering process in step 3 is as follows: after holding at 380±10℃ for 3.5 hours, the furnace is removed and air-cooled to room temperature.

7. The heat treatment process for mining connecting links according to claim 1 or 6, characterized in that, The second tempering process in step 3 is as follows: after holding at 430±10℃ for 3.5h, the furnace is removed and air-cooled to room temperature.

8. The heat treatment process for mining connecting links according to claim 1, characterized in that, The shot peening process in step 4 involves splitting the connecting ring into half rings, binding the two half rings that make up a complete connecting ring with wire, and suspending them on the shot peening machine with a certain gap between the two half rings for shot peening treatment.

9. The heat treatment process for mining connecting links according to claim 1 or 8, characterized in that, The connecting chain links were shot peened twice, with each shot peening session lasting 3 minutes.

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