Method for manufacturing large hard rock skip body

Abstract

The present application relates to a kind of large hard rock skip box manufacturing method, manufacturing step includes rolling, water jet cutting, preheating before welding, resistance welding, postweld heat treatment, stress relief annealing, lower body quenching, aging treatment, surface nitriding, shot peening and nickel plating.The tensile strength of hard rock skip box prepared by the present application is not less than 1048MPa, the lower yield strength is not less than 907MPa, the elongation after fracture is not less than 12.6%, the reduction of area is not less than 45.8%, the impact toughness is not less than 66.3J / cm 2 , hardness reaches 55.5HRC.The comprehensive mechanical performance index is improved by 14~18% compared with the skip box manufactured by existing process.

Description

Technical Field

[0001] This invention relates to a method for preparing a skip box, and more particularly to a method for preparing a large hard rock skip box. The large hard rock skip box is mainly used in underground mine shaft skip hoisting systems, where the hoisted ore is metallic hard rock. The large skip in this invention refers to a skip with a capacity of 15 cubic meters or more. Background Technology

[0002] With the continuous development of mining technology, the scale of underground metal mining is constantly expanding, leading to a corresponding increase in the demand for large skips. Due to the lack of large, specialized skips, metal mines, including gold mines, often directly use large-capacity skips previously used for coal to load hard rock. Because the hardness of metal ore is much higher than that of coal, large-capacity coal skips are prone to premature fatigue cracking when loading hard rock, resulting in a skip box lifespan of only 20% to 40% of that used for coal. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for manufacturing a large hard rock skip box, so as to further improve the comprehensive mechanical performance index of the box, making it suitable for loading hard rock and having a longer service life.

[0004] The technical solution of this invention is as follows:

[0005] The manufacturing method for a large hard rock skip box includes the following steps:

[0006] I. Preparation of raw materials:

[0007] (a) The raw materials are put into the furnace and smelted at a temperature of 1655~1685℃, and then cooled to obtain steel billets;

[0008] (ii) First, heat the steel billet to 1180~1220℃ and forge it into a steel plate with a thickness of 20.5~21.5mm. Then, roll the steel plate at room temperature 20~25 times, each time by 0.025~0.06mm. After pickling, it is made into a steel plate as a blank material.

[0009] II. Cutting of raw materials

[0010] The steel plates required for large hard rock skip boxes are obtained by water jet cutting of the blanks, with a cutting pressure of 230~240MPa and garnet sand as the abrasive.

[0011] III. Preheating and Box Welding

[0012] (a) First, the cut steel plate is preheated to 242.4~243.0℃ using induction heating, and then the box body is welded to obtain the box body;

[0013] (ii) After welding, the weld temperature is slowly reduced to 15~25℃ by controlling the cooling rate of the weld.

[0014] IV. Heat Treatment of the Enclosure

[0015] (a) Preheating: The chamber is preheated to between 638 and 645°C by slowly increasing the temperature;

[0016] (ii) Heating: Continue heating the chamber to 847.6~853.2℃, hold for 116~124 minutes, then cool it in ultra-fast quenching oil to 327~339℃, and finally cool it to room temperature;

[0017] (III) Post-processing:

[0018] First, the enclosure is reheated and kept at a constant temperature, and then artificial aging treatment is used to further improve its strength and hardness. Next, the enclosure is placed in a nitriding furnace with a pressure of 925~950Pa and a DC voltage of 875~895V for 3.4~3.6 hours. After that, the entire outer surface of the enclosure is shot-blasted, and finally, the enclosure is electroless nickel-plated with a plating thickness of 0.045~0.055mm.

[0019] Preferably, in step three (a), resistance welding is used for segmented welding during the welding process, with each weld seam welded once, and a mixture of argon and carbon dioxide gas is used for protection during the welding process.

[0020] Preferably, the slow cooling in step three (ii) refers to a cooling time of more than 15 minutes.

[0021] Preferably, the slow heating in step four (a) refers to controlling the heating rate at 1.95~2.05℃ / minute.

[0022] Preferably, the final cooling to room temperature mentioned in step four (ii) refers to cooling to room temperature at a rate of 8.6~9.2℃ / minute.

[0023] Preferably, the artificial aging process described in step four (iii) is as follows: the box is placed in an oven, the oven is powered on, the box is heated to 141.6~147.2℃, kept warm for 9.5~9.7 hours, and then the power is turned off and it is allowed to cool naturally to room temperature.

[0024] Preferably, the shot peening of the entire outer surface of the box body in step four (iii) refers to: spraying steel shot with a diameter of 0.6~0.7mm, a shot peening time of 12~13 minutes, and a shot peening speed of 258~288m / s.

[0025] Preferably, the thickness of the electroless nickel plating on the box body in step four (iii) is 0.045~0.055mm.

[0026] Preferably, the feeding in step one (a) refers to the feeding of 20CrNiMo alloy, 25Cr2Ni4W alloy, 38CrMoAl alloy, ferromolybdenum alloy, fluorite and quicklime in a weight ratio of (145~155):(290~310):(45~48):(1.25~1.45):(0.9~1.1):1.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] First, this invention uses three alloy steels—20CrNiMo, 25Cr2Ni4W, and 38CrMoAl—as the main raw materials, supplemented with a certain proportion of ferromolybdenum, fluorite, and quicklime. A new type of alloy steel with better comprehensive performance is smelted in an electric arc furnace at a specific temperature, serving as the material for large hard rock skip boxes. The hot-forged steel billets are repeatedly cold-rolled at room temperature, improving the strength and dimensional accuracy of the steel plates.

[0029] Secondly, this invention uses garnet sand for water jet cutting to cut steel plates of various specifications and sizes required for manufacturing the skip box. Garnet sand has a very high hardness. Under the action of high-pressure water jet, the garnet sand cuts the steel plate like abrasive grains on a grinding wheel, avoiding the adverse effects of thermal cutting processes such as oxy-acetylene flame cutting and laser cutting on the crystal structure of the steel plate, and further ensuring the strength of the steel plate.

[0030] Third, the present invention preheats the steel plate to be welded to a specific temperature and completes the welding of the steel plate by resistance welding under the protection of a protective gas. After welding, the plate is slowly cooled to room temperature at a specific speed. The welded box is heated to a specific temperature and quenched using a specific method to produce a lower bainitic structure in the steel of the box. This invention employs a roll forming process to improve the strength and hardness of the blank. Water jet cutting of the roll-formed blank does not alter its crystal structure. Preheating of the blank before welding reduces welding stress and strain. Resistance welding is used to weld the blanks together. Post-weld, induction heating further reduces welding stress and strain. Stress-relief annealing eliminates residual stress in the box body. Furnace heating achieves austenitization of the box body. Oil bath treatment further austenitizes the box body steel. Aging treatment further improves the box body's strength and hardness. Nitriding treatment enhances the surface strength and hardness of the box body. Shot peening further improves the surface hardness of the box body. Nickel plating provides corrosion protection and improves the box body's impact resistance. Ultimately, a high-strength, high-hardness, and high-impact-resistant large hard rock skip box body is obtained, solving the problem of premature fatigue cracking and meeting the usage requirements of large hard rock mines for skip boxes.

[0031] Fourth, testing shows that the hard rock skip box body prepared by this invention has a tensile strength of not less than 1048 MPa, a lower yield strength of not less than 907 MPa, an elongation after fracture of not less than 12.6%, a reduction of area of ​​not less than 45.8%, and an impact toughness of not less than 66.3 J / cm². 2 The hardness reaches 55.5 HRC. The overall mechanical performance is 14-18% higher than that of skip boxes manufactured by existing processes. Under the same conditions, the service life is 35-50% longer than that of skip boxes manufactured by existing processes. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments and test data.

[0033] The specific steps of the preparation embodiment of the large hard rock skip box of the present invention are as follows:

[0034] I. Preparation of raw materials:

[0035] (a) Raw materials for furnace feeding

[0036] The following materials were added: 20CrNiMo alloy, 25Cr2Ni4W alloy, 38CrMoAl alloy, ferromolybdenum alloy, fluorite, and quicklime, in a weight ratio of 150:300:46.65:1.35:1:1.

[0037] (II) Smelting process

[0038] The raw materials are melted using an electric arc furnace, heated by three graphite electrodes, and simultaneously heated by natural gas. Oxygen is injected into the furnace using an oxygen lance, and the temperature is raised to 1672°C. The slag on the surface of the furnace is removed, and the remainder is poured into a bucket to cool and obtain steel billets.

[0039] (III) Forging and Steel Plate Rolling

[0040] First, the steel billet is heated to 1200℃ and forged into a steel plate with a thickness of 20.5mm. Then, the steel plate is rolled 20 times at room temperature, with each roll reducing the thickness by 0.03~0.04mm. After each roll, the surface skin of the steel plate is removed, and after pickling, it is finally made into a steel plate used as raw material.

[0041] The measured chemical composition of the blank material by mass percentage is as follows: C=0.275%, Si=0.172%, Mn=0.540%, Cr=1.07%, Mo=0.241%, Ni=2.661%, W=0.564%, Al=0.083%, with the balance being Fe and undetected impurity elements.

[0042] The reasons why the elements added to the feed material do not completely correspond to the measured chemical composition of the blank material include, but are not limited to, the following: 1. The carbon content increases after the graphite electrode is worn out; 2. The addition of calcium oxide removes some of the Si and Mn; 3. Oxygen spraying reduces the Cr content.

[0043] II. Cutting of raw materials

[0044] The blank was cut using water jet cutting at a pressure of 235-236 MPa. 240-mesh garnet sand was used as the abrasive. The water jet cut produced steel plates of various sizes required for manufacturing large hard rock skip boxes.

[0045] III. Preheating and Box Welding

[0046] First, the cut steel plate is preheated to 243.0℃ using induction heating. Then, the box body is welded, using resistance welding in sections, with each weld seam welded once. During the welding process, a mixture of argon and carbon dioxide gas with a volume ratio of 94:6 is used for protection.

[0047] After welding, induction heating is used to control the cooling rate of the weld, allowing it to cool down slowly. The cooling time is 16-19 minutes, until the temperature drops to 20°C. This reduces residual stress in the weld, prevents defects such as cracks, and improves the strength of the welded area.

[0048] IV. Heat Treatment of the Enclosure

[0049] (a) Preheating: The residual stress of the chamber is eliminated by stress-relief annealing, and the chamber is preheated to 640℃ by slow heating, with the heating rate controlled at 1.95~2.05℃ / minute.

[0050] (ii) Heating: Continue heating the chamber to 850℃ and hold for 120 minutes to release residual stress. Then cool it to 330℃ in ultra-fast quenching oil (the standard for ultra-fast quenching oil is SH / T 0564-1993 heat treatment oil), and then cool it to room temperature at a rate of 8.6~9.2℃ / minute.

[0051] (III) Post-processing:

[0052] 1. Reheat the enclosure to 145℃ and maintain it for 9.6 hours. This artificial aging process further improves the enclosure's strength and hardness.

[0053] The specific steps of the artificial aging process are as follows: the chamber is placed in an oven, the oven is powered on, the chamber is heated to 145°C, kept at that temperature for 9.6 hours, then the power is turned off and it is allowed to cool naturally to room temperature. The chamber is then removed from the oven, thus completing the artificial aging process of the chamber.

[0054] 2. Place the chamber into the nitriding furnace, apply a pressure of 950 Pa and a DC voltage of 880 volts, and maintain the pressure for 3.5 hours.

[0055] 3. Shot blast the entire outer surface of the housing with steel shot of 0.6~0.7mm in diameter for 12.5 minutes at a speed of 278.5m / s.

[0056] 4. Electroless nickel plating of the enclosure, with a plating thickness of 0.045~0.055mm.

[0057] The skip box prepared in the above embodiment has a volume of 17m³. 3 The tested mechanical properties are as follows: tensile strength not less than 1048 MPa, lower yield strength not less than 907 MPa, elongation after fracture not less than 12.6%, reduction of area not less than 45.8%, and impact toughness not less than 66.3 J / cm². 2 Its hardness reaches 55.5 HRC, and its comprehensive mechanical properties are 14-18% higher than those of the skip box manufactured by the most advanced existing technology.

Claims

1. A method for manufacturing a large hard rock skip box, characterized in that... The steps are as follows: I. Preparation of raw materials: Step 1.1 After the raw materials are fed into the furnace, they are smelted at a temperature of 1655~1685℃ and then cooled to obtain steel billets; The raw materials refer to 20CrNiMo alloy, 25Cr2Ni4W alloy, 38CrMoAl alloy, ferromolybdenum alloy, fluorite and quicklime, which are added in a weight ratio of (145~155):(290~310):(45~48):(1.25~1.45):(0.9~1.1):

1. Step 1.2 First, heat the steel billet to 1180~1220℃ and forge it into a steel plate with a thickness of 20.5~21.5mm. Then, roll the steel plate at room temperature 20~25 times, each time pressing down by 0.025~0.06mm. After pickling, it is made into a steel plate as a blank material. II. Cutting of raw materials The steel plates required for large hard rock skip boxes are obtained by water jet cutting of the blanks, with a cutting pressure of 230~240MPa and garnet sand as the abrasive. III. Preheating and Box Welding Step 3.1 First, the cut steel plate is preheated to 242.4~243.0℃ using induction heating, and then the box body is welded to obtain the box body; Step 3.2 After welding, the weld temperature is slowly reduced to 15~25℃ by controlling the cooling rate of the weld. IV. Heat Treatment of the Enclosure Step 4.1 Preheating: Preheat the chamber to between 638 and 645°C by slowly increasing the temperature; the slow temperature increase refers to controlling the temperature increase rate at 1.95 to 2.05°C / minute. Step 4.2 Heating: Continue heating the chamber to 847.6~853.2℃, hold for 116~124 minutes, then cool it in ultra-fast quenching oil to 327~339℃, and finally cool it to room temperature; the final cooling to room temperature means cooling to room temperature at a rate of 8.6~9.2℃ / minute. Step 4.3 Post-processing: First, the enclosure is reheated and kept at a constant temperature, and then artificial aging treatment is used to further improve its strength and hardness. Next, the enclosure is placed in a nitriding furnace with a pressure of 925~950Pa and a DC voltage of 875~895V for 3.4~3.6 hours. After that, the entire outer surface of the enclosure is shot-blasted, and finally, the enclosure is electroless nickel-plated with a plating thickness of 0.045~0.055mm. The steps of the artificial aging process are as follows: the chamber is placed in an oven, the oven is powered on, the chamber is heated to 141.6~147.2℃, kept at that temperature for 9.5~9.7 hours, and then the power is turned off and it is allowed to cool naturally to room temperature; The shot peening of the entire outer surface of the box refers to: spraying steel shot with a diameter of 0.6~0.7mm for 12~13 minutes and a shot peening speed of 258~288m / s; The thickness of the electroless nickel plating on the enclosure is 0.045~0.055mm.

2. The method for manufacturing a large hard rock skip box as described in claim 1, characterized in that: Step 3.1: Resistance welding is used in segments during the welding process, with each weld seam welded once. Argon and carbon dioxide mixed gas are used for protection during the welding process.

3. The method for manufacturing a large hard rock skip box as described in claim 1, characterized in that: The slow cooling mentioned in step 3.2 refers to a cooling time of more than 15 minutes.