A method of casting a large lip

Abstract

A kind of casting method of large lip, it is related to mining machinery technical field, in order to prevent lip fracture failure, by using easy cutting piece on large heat riser, adopt impact form to remove riser, on the premise of meeting basic feeding, as far as possible to reduce the generation of surface microcracks from the source, further, customer standard requires that surface crack should not be less than 7mm, before quenching and tempering, all cracks found are removed by welding repair or grinding, in the process of heat treatment, two Φ120-Φ160mm reinforcing bars are set to prevent crack caused by deformation, after quenching and tempering, all defects greater than 3mm are removed by grinding, etc., suitable for wide range of popularization and application.

Description

Technical Field

[0001] This invention relates to the field of mining machinery technology, specifically to a casting method for a large bucket lip. Background Technology

[0002] As is known, loaders are mainly divided into three types: large, medium, and small. Among them, medium and small loaders mainly use hydraulic mechanisms to load and unload materials, and their bucket capacity is mostly around 10m³. 3 Below, the slightly larger ones are hydraulic shovels, with a capacity of approximately 20m³. 3 Larger excavators, primarily driven by a wire rope and electric motor (i.e., electric shovels), typically have capacities in the tens of cubic meters (e.g., the largest bucket capacity is 62.7 cubic meters). 3 ).

[0003] Taking electric shovels as an example, wire rope electric shovels possess a massive body and astonishing digging capacity. Their buckets can have a maximum load capacity of 120 tons, and their own weight reaches 1369 tons, earning them the nickname "mining behemoths." The bucket lip is the core component of the wire rope electric shovel bucket. Existing bucket lip products weigh approximately 9 tons when finished, but due to numerous holes, the raw weight is 12 tons. The maximum dimensions are 5200mm × 1400mm × 1200mm, with a finished wall thickness of approximately 158–171mm, classifying them as large cast steel parts. During use, the bucket lip is tightly connected to the tooth tips and tooth seats via pins to scoop up material. The stress environment is relatively harsh, primarily subjected to impact loads, and the operating temperature range is approximately ±40℃. Therefore, high requirements are placed on low-temperature impact toughness.

[0004] The size of the electric shovel bucket is directly related to its working efficiency. A larger bucket results in higher efficiency, but also increases the price of the shovel, although the cost per ton of shovel extracted decreases. Currently, the gap between domestic and foreign electric shovel products mainly lies in the following two aspects:

[0005] First, due to quality factors, the life cycle of electric shovels is relatively short. The main failure modes of electric shovels are bucket lip fracture failure and bucket bottom plate fracture failure.

[0006] Second, there is a lack of design and manufacturing capabilities for large electric shovels.

[0007] Therefore, it is particularly important to provide a casting method for large punch lips. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention provides a casting method for a large bucket lip. In the heat treatment process, the present invention adopts the method of setting two tie rods to prevent deformation from causing cracks. After tempering, any defects larger than 3mm are preferentially removed by grinding, etc., which effectively prevents the bucket lip from breaking and failing.

[0009] To achieve the aforementioned inventive objectives, the present invention employs the following technical solution:

[0010] A casting method for a large punch lip, the casting method specifically includes the following steps:

[0011] Step 1, Styling:

[0012] A. First, place the casting mold on the ground and place hollow steel pipes and steel bars to strengthen the sand mold and prevent it from falling off.

[0013] B. Place and secure the heating riser sleeve, the easy-cut riser plate, and the ceramic casting tube. When placing the easy-cut riser plate, the easy-cut riser plate should be located below the heating riser sleeve. The easy-cut riser plate will make the riser easy to cut.

[0014] C. Fill with molding sand, ensuring the sand is compacted during filling;

[0015] D. After the sand mold is completed, let it stand for 1 to 3 hours until it hardens, then proceed with the demolding operation.

[0016] E. Apply paint by brushing, bake until the sand mold changes color, and then dry.

[0017] F. When making sand cores, pay attention to ensuring the air venting channels are unobstructed;

[0018] G. After the core is installed, check whether the wall thickness meets the design requirements. After confirming that it meets the design requirements, proceed with the box closing operation.

[0019] H. 1-3 hours before pouring, apply hot air at 90-110℃ for 30-60 minutes;

[0020] Step 2, Smelting and Casting:

[0021] After the casting raw materials are melted in an electric arc furnace to obtain molten steel, in order to prevent the molten steel from reacting with oxygen in the air, hot air at 90-110°C is introduced into the cavity of the casting mold 1-3 hours before pouring for 30-60 minutes to remove moisture from the cavity and the surface of the molding sand. Then, argon gas is introduced into the cavity of the casting mold. Since the density of argon gas is greater than that of air, the argon gas enters from the bottom of the cavity.

[0022] Then, the composition and temperature of the molten steel are tested. When the composition of the molten steel meets the internal control requirements and the temperature is 1560±5℃, the molten steel is poured into the cavity of the casting mold. During pouring, the flow rate of the molten steel should be controlled at 140~160kg / s, and the total pouring time should be controlled at 160~180s. When the pouring reaches the required height, the pouring is stopped. After the pouring is completed, a heating covering agent is added. After the molten steel cools down, the casting is obtained.

[0023] Step 3: Cooling, sand removal, and cleaning:

[0024] A. After pouring, the casting is allowed to cool naturally in the sand mold for 144 to 200 hours, and the temperature after cooling is 300 to 500°C.

[0025] B. After the cooling time is up, remove the casting from the sand mold. During the cleaning process, take precautions to prevent damage to the surface of the casting.

[0026] C. Clean the loose sand from the surface of the casting to expose the metal surface;

[0027] D. Remove easily cut risers from castings by impact;

[0028] Step 4: Raw material inspection:

[0029] Inspect the dimensions and appearance of the blank; the dimensions and appearance of the blank should meet the design requirements.

[0030] Step 5, rough machining:

[0031] A. First, place the workpiece upright and find the verticality according to the non-machined side surface. Adjust the workpiece symmetrically left and right with reference to the arc top height coordinate dimension. Draw the X reference machining dimension line of the bottom surface of the workpiece. Draw the reference center line with the non-machined surfaces on both sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends.

[0032] B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference;

[0033] C. Four steel plates are intermittently welded together on the non-machined surface to serve as mounting process blocks;

[0034] D. Level and straighten the workpiece along the line, with the Y-datum plane facing the spindle; rough mill the Y-datum plane, leaving a 12-18mm allowance on each side.

[0035] E. Adjustment and installation: Install the clamp with the Y datum facing downwards and the X datum facing the spindle. Align with the line and level with the Y datum. Tighten. Rough mill the X datum, leaving a margin of 12-18mm on one side. Install the milling head and rough mill the plane, leaving a margin of 12-18mm on one side.

[0036] Step 6: Perform UT, MT, and RT flaw detection on the workpiece:

[0037] First, the rough-machined workpiece is subjected to UT flaw detection, with the flaw detection level being level 1 for the bevel and level 2 for the rest of the workpiece.

[0038] After rough machining, the workpiece is subjected to UT flaw detection and then MT flaw detection. During MT flaw detection, no linear display exceeding 2mm is allowed.

[0039] Then the workpiece is subjected to RT testing. The RT testing standard is ASTM E446 / E280 / E186, and D, E and F type defects are not allowed.

[0040] Step 7: Heat treat the casting.

[0041] The castings undergo pre-heat treatment and performance heat treatment. The pre-heat treatment is carried out before rough machining. The pre-heat treatment is normalizing and tempering, and its purpose is to homogenize the composition of the casting, stabilize the structure, eliminate stress, and prepare for subsequent processes. The performance heat treatment is quenching and tempering, and its purpose is to enable the casting to achieve the performance of the lip.

[0042] Step 8: Finish machining of the workpiece:

[0043] A. Place the workpiece upright, find the verticality according to the non-machined side surface, level the workpiece symmetrically on the left and right with reference to the arc top height coordinate dimension, and draw the X reference machining dimension line of the bottom surface of the workpiece; draw the reference center line with the non-machined surfaces on both sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends.

[0044] B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference;

[0045] C. Level and straighten the workpiece along the line, with the X datum plane facing the spindle; finish mill the X datum plane; program the finish milling of the chamfers and fillets at the inner cavity;

[0046] D. Adjustment: Orient the workpiece's Y-datum plane toward the machine bed, use the machined X-datum plane as the positioning reference to find the level, adjust and straighten it left and right along the line, and tighten it; finish mill the Y-datum plane.

[0047] E. Program and precision mill the internal cavity dimensions, one end face and adjacent table surface, and fillets;

[0048] F. Install the milling head and finish mill the right-side bevel, taking into account the bevel angle and related dimensions.

[0049] G. Adjust the milling head and finish mill the chamfer;

[0050] H. Adjust the milling head, finish mill the inclined surface and adjacent step surface, fillet the corners, take into account the relevant dimensions, program the finish milling of the waist-shaped hole and the fillet of the hole opening on the surface, and ensure that the surface inside the waist-shaped hole is perpendicular;

[0051] I. Program and fine-mill the oblong hole and the rounded corner of the hole in the inner cavity to ensure that the inner cavity surface of the oblong hole is perpendicular;

[0052] J. Adjustment: Rotate the workpiece 180° and finish mill the contour surface and adjacent table surface and fillets on one side of the dimension; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of the inner cavity, ensuring that the inner cavity surface of the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 90° and finish mill the left end face and adjacent step surface and fillets; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of this face, ensuring that the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 180° and finish mill the right end face and adjacent step surface and fillets; program the cutter to finish mill the waist hole and the fillets at the opening of this face, ensuring that the waist-shaped hole is vertical.

[0053] K. Adjustment and installation: Install the clamp with the X reference surface facing downwards and the top arc surface facing the bed. Align with the Y reference surface using a dial indicator and tighten.

[0054] L. Program and precision mill the top arc surface and all boss surfaces and fillets;

[0055] M. Inspect according to the requirements of the drawings and quality information sheet;

[0056] N. After painting and packaging according to the drawings and quality information sheet requirements, the product is put into storage.

[0057] In the casting method for the large punch lip, during the manufacturing of the casting mold in the first step, due to the large structure of the punch lip, the core box of the casting mold is segmented to prevent the sand core from being too large and difficult to produce. The mold material is compacted plywood, which is staggered on the template plate. The template plate is a steel structure to effectively prevent warping and deformation. Due to the large size of the product, the template plate adopts a split structure. The template plate is CNC machined, and then the machined template plate is assembled with the core box to obtain the required casting mold.

[0058] In the casting method for the large lip described above, the molten steel in the second step comprises the following components by weight:

[0059]

[0060] In the casting method for the large cupola mentioned above, during the second step of smelting the molten steel, the impact requirements on the cupola are high, making it more sensitive to delayed cracks inside. Therefore, the H content in the casting must be reduced to below 5 PPM. Thus, all alloys must be baked during smelting, especially Ni, which has the highest proportion and a large hydrogen content. It must be baked at a high temperature of 600-800℃ for 7-9 hours to eliminate the hydrogen hazards from the raw materials to the greatest extent.

[0061] In the casting method for the large lip, during the second step of smelting the molten steel, a three-stage smelting process is carried out in an electric arc furnace, which includes a melting stage, an oxidation stage, and a reduction stage.

[0062] In the casting method for the large punch lip, during the MT flaw detection in the sixth step, a CEE-1 magnetic particle flaw detector is used, with a sensitivity test piece of 30 / 100Al, black magnetic powder, kerosene medium, and magnetization method of energization, wire winding / magnetic yoke; the inspection method is wet continuous method; working illumination: ≥500Lx; magnetization current: >44N; magnetic suspension concentration: 15g / L; demagnetization requirement: 5G.

[0063] In the casting method for the large cuppet lip, during the RT flaw detection in the sixth step, the equipment model is DZ-9 / 3000, the tube voltage is KV9Mev, the exposure time is 80-1200rad, the radiography method is single-wall single-image film, the density is 1.8-4.0, F(mm): 1630-1770, f(mm): 1500, b(mm) 130-270.

[0064] The key points of the pre-heat treatment operation in the seventh step of the casting method of the large lip are as follows: before the pre-heat treatment, it is necessary to ensure that the structure and size of the product meet the requirements of the drawing. The cut ribs, patches and risers to be removed must be clean and clear. Overcutting is strictly prohibited. The size must meet the tolerance requirements of the drawing, especially the size of the inner and outer sections. If it is not suitable, it needs to be corrected during the heat treatment.

[0065] During the preheating process, the heating rate for normalizing is ≤80℃ / h, the intermediate holding temperature is 550±10℃ for two hours, and the normalizing temperature is 920±10℃ for 10 hours.

[0066] During tempering, the heating rate is ≤80℃ / h, the tempering temperature is 580±10℃, and the holding time is 8 hours;

[0067] Both normalizing and tempering are cooled by air cooling.

[0068] The key points of the performance heat treatment operation in the seventh step of the casting method for the large bucket lip are as follows: Before performance heat treatment, it is necessary to confirm that the appearance, size and flaw detection of the casting are qualified. Due to the large stress during the tempering process, two Φ120~Φ160mm tie rods must be welded to prevent deformation. Tempering includes three parts: heating, holding and cooling. The heating rate is controlled at ≤80℃ / hour, and a holding temperature of 550~650℃ is set for 1~3 hours. The holding temperature is controlled at 870±10℃. Cooling is done by water quenching. The time from opening the furnace door to entering the water is controlled within 50 seconds. The water temperature is 30~35℃. When the tempering is finished, the temperature rise is within 5℃. The casting can be taken out of the water only when it is cooled to 50~100℃.

[0069] The casting method for the large lip described above, in the seventh step, includes testing the performance of the lip in terms of tensile properties, low-temperature impact properties, hardness, and metallographic structure. The tensile properties are tested using a tensile testing machine to measure the tensile strength, yield strength, elongation, and cross-sectional area reduction of the casting. The tensile strength of the casting is ≥724 MPa, the yield strength is ≥896 MPa, the elongation is ≥12%, and the cross-sectional area reduction is ≥25%. The low-temperature impact properties are tested by measuring the impact value of the casting at -18℃. The impact value of the casting is ≥27 J. The hardness is tested using a portable handheld hardness tester with a hammer test, and the hardness is 277–331 HB. The metallographic structure is tested by measuring the tempered martensite content of the casting to verify the tempering effect.

[0070] By employing the technical solution described above, the present invention has the following advantages:

[0071] To prevent the riser lip from breaking and failing, this invention combines a cuttable blade with a large heating riser, using an impact method to remove the riser. While ensuring basic feeding, it minimizes the generation of surface micro-cracks at the source. Furthermore, customer standards require surface cracks to be no less than 7mm. Before tempering, any cracks found are removed by welding or grinding. During heat treatment, two Φ120~Φ160mm tie rods are installed to prevent deformation from causing cracks. After tempering, any defects larger than 3mm are prioritized for grinding removal. This invention is suitable for widespread promotion and application. Attached Figure Description

[0072] Figure 1 This is a schematic diagram showing the location of the easily cut riser in an embodiment of the present invention;

[0073] Figure 2 This is a schematic diagram showing the placement of two tie rods with diameters of 120 to 160 mm in an embodiment of the present invention.

[0074] Figure 3 These are photographs of the large lip prepared using the present invention in the embodiments of the present invention;

[0075] Figure 4 This is a schematic diagram of the main structure of the riser cuttable piece in an embodiment of the present invention;

[0076] Figure 5 yes Figure 4 A schematic diagram of the AA cross-sectional structure;

[0077] Figure 6 These are actual photographs of the riser cuttable disc in the embodiments of the present invention;

[0078] Figure 7 These are sand core photographs taken during the fabrication of the riser cuttable disc in this embodiment of the invention;

[0079] Figure 8 This is a photograph of the core box during the fabrication of the riser cuttable sheet in an embodiment of the present invention. Detailed Implementation

[0080] The present invention can be explained in more detail through the following embodiments, but the present invention is not limited to the following embodiments;

[0081] Combined with appendix Figures 1-8 The present invention discloses a casting method for a large punch lip, the casting method specifically comprising the following steps:

[0082] Step 1, Styling:

[0083] A. First, place the casting mold on the ground and place hollow steel pipes and steel bars to strengthen the sand mold and prevent it from falling off.

[0084] B. Place and secure the heating riser sleeve, the easy-cut riser plate, and the ceramic casting tube. When placing the easy-cut riser plate, the easy-cut riser plate should be located below the heating riser sleeve. The easy-cut riser plate will make the riser easy to cut.

[0085] C. Fill with molding sand, ensuring the sand is compacted during filling;

[0086] D. After the sand mold is completed, let it stand for 1 to 3 hours until it hardens, then proceed with the demolding operation.

[0087] E. Apply paint by brushing, bake until the sand mold changes color, and then dry.

[0088] F. When making sand cores, pay attention to ensuring the air venting channels are unobstructed;

[0089] G. After the core is installed, check whether the wall thickness meets the design requirements. After confirming that it meets the design requirements, proceed with the box closing operation.

[0090] H. 1-3 hours before pouring, apply hot air at 90-110℃ for 30-60 minutes;

[0091] In specific implementation, such as Figure 1 As shown, during the manufacturing of the casting mold, due to the large structure of the punch lip, the core box of the casting mold is segmented to prevent the sand core from becoming too large and difficult to produce. The mold material is compacted plywood, which is staggered on the template plate. The template plate is a steel structure to effectively prevent warping and deformation. Due to the large size of the product, the outer mold of the product also needs to be divided into two parts, which are CNC machined separately. After machining, they are connected by long bolts and fixed to the same template plate to achieve the splicing of the two models. Then, the machined template plate and the core box are assembled together to obtain the required casting mold.

[0092] Furthermore, the section of the product's inner frame that is difficult to demold has a length of 4832mm. Making it into a single sand core would result in an excessively large size, making it difficult to flip and lift. The design uses two symmetrical sand cores, each 2416mm long. A frame structure and bolted connections ensure both secure fastening and detachability, a common method in model making.

[0093] Furthermore, the risers on the casting mold are easy-cut risers; the shape and location of the easy-cut risers are detailed in the appendix. Figure 1 As shown, the shape and structure of the easily cut riser are as follows: Figure 4 , 5 As shown in Figure 6, the structure of the sand core and core box during the fabrication of the easily cut riser is as follows: Figure 7 , 8 As shown, this invention reduces the risk of cold cracking during riser cutting by using an easy-cut riser. Typical easy-cut risers are used in risers with a maximum diameter of 140mm, and the easy-cutting blade inlet is only 70mm. The riser used in this invention is 325mm in diameter, employs an easy-cutting design, and is manufactured using chromite sand combined with water glass binder. The center of the easy-cutting blade is a 90° stress concentration point, with a thickness of 30mm and a radius of radius R2 to prevent sand from falling off.

[0094] It is generally believed that when the free-cutting blade is surrounded by molten steel and remains at a high temperature for an extended period, the molten steel at the riser neck can be kept in a liquid state, thus not affecting the feeding effect of the casting. This has been fully verified in simulations and subsequent actual production.

[0095] After sand removal, the riser can be removed by impact. This reduces the drawbacks of the commonly used flame cutting method and minimizes cold cracking caused during riser cutting. It should be noted that conventional risers are usually hot-cut using an oxy-fuel torch, which easily heats the alloy and causes cracks. During cutting, poor temperature control often leads to many surface micro-cracks. While free-cutting discs are generally only used on small risers, this invention innovatively combines free-cutting discs with large, heat-generating risers, using impact to remove the riser. While meeting basic feeding requirements, it minimizes the formation of surface micro-cracks at the source.

[0096] Furthermore, since the structure of the casting mold is a conventional structure in this field, the inventor will not elaborate further here.

[0097] Step 2, Smelting and Casting:

[0098] After the casting raw materials are melted in an electric arc furnace to obtain molten steel, in order to prevent the molten steel from reacting with oxygen in the air, hot air at 90-110°C is introduced into the cavity of the casting mold 1-3 hours before pouring for 30-60 minutes to remove moisture from the cavity and the surface of the molding sand. Then, argon gas is introduced into the cavity of the casting mold. Since the density of argon gas is greater than that of air, the argon gas enters from the bottom of the cavity.

[0099] Then, the composition and temperature of the molten steel are tested. When the composition of the molten steel meets the internal control requirements and the temperature is 1560±5℃, the molten steel is poured into the cavity of the casting mold. During pouring, the flow rate of the molten steel should be controlled at 140~160kg / s, and the total pouring time should be controlled at 160~180s. When the pouring reaches the required height, the pouring is stopped. After the pouring is completed, a heating covering agent is added. After the molten steel cools down, the casting is obtained.

[0100] In practice, when smelting the steel melt, the impact requirements on the lip of the casting are high, making it sensitive to delayed cracks inside. The hydrogen content in the casting must be reduced to below 5 PPM. Therefore, all alloys must be baked during smelting, especially Ni, which has the highest proportion and a large hydrogen content. It must be baked at a high temperature of 600-800°C for 7-9 hours to eliminate the hydrogen hazards from the raw materials to the greatest extent.

[0101] Furthermore, when smelting the steel melt, a three-stage smelting method is adopted in an electric arc furnace, which includes a melting stage, an oxidation stage, and a reduction stage.

[0102] Furthermore, the molten steel comprises the following components by weight:

[0103]

[0104] Step 3: Cooling, sand removal, and cleaning:

[0105] A. After pouring, the casting is allowed to cool naturally in the sand mold for 144 to 200 hours, and the temperature after cooling is 300 to 500°C.

[0106] B. After the cooling time is up, remove the casting from the sand mold. During the cleaning process, take precautions to prevent damage to the surface of the casting.

[0107] C. Clean the loose sand from the surface of the casting to expose the metal surface;

[0108] D. Remove easily cut risers from castings by impact;

[0109] Step 4: Raw material inspection:

[0110] Inspect the dimensions and appearance of the blank; the dimensions and appearance of the blank should meet the design requirements.

[0111] Step 5, rough machining:

[0112] A. First, place the workpiece upright and find the verticality according to the non-machined side surface. Adjust the workpiece symmetrically left and right with reference to the arc top height coordinate dimension. Draw the X reference machining dimension line of the bottom surface of the workpiece. Draw the reference center line with the non-machined surfaces on both sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends.

[0113] B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference;

[0114] C. Four steel plates are intermittently welded together on the non-machined surface to serve as mounting process blocks;

[0115] D. Level and straighten the workpiece along the line, with the Y-datum plane facing the spindle; rough mill the Y-datum plane, leaving a 12-18mm allowance on each side.

[0116] E. Adjustment and installation: Install the clamp with the Y datum facing downwards and the X datum facing the spindle. Align with the line and level with the Y datum. Tighten. Rough mill the X datum, leaving a margin of 12-18mm on one side. Install the milling head and rough mill the plane, leaving a margin of 12-18mm on one side.

[0117] Step 6: Perform UT, MT, and RT flaw detection on the workpiece:

[0118] First, the rough-machined workpiece is subjected to UT flaw detection, with the flaw detection level being level 1 for the bevel and level 2 for the rest of the workpiece.

[0119] After rough machining, the workpiece is subjected to UT flaw detection and then MT flaw detection. During MT flaw detection, no linear display exceeding 2mm is allowed.

[0120] Then the workpiece is subjected to RT testing. The RT testing standard is ASTM E446 / E280 / E186, and D, E and F type defects are not allowed.

[0121] In specific implementation, when performing MT flaw detection, a CEE-1 magnetic particle flaw detector is used, with a sensitivity test piece of 30 / 100Al, black magnetic powder, kerosene medium, and magnetization method of energization, wire winding / magnetic yoke; the inspection method is wet continuous method; working illumination: ≥500Lx; magnetization current: >44N; magnetic suspension concentration: 15g / L; demagnetization requirement: 5G;

[0122] Furthermore, when performing RT flaw detection, the equipment model is DZ-9 / 3000, the tube voltage is KV9Mev, the exposure time is 80-1200rad, the radiography method is single-wall single-image film, the density is 1.8-4.0, F(mm): 1630-1770, f(mm): 1500, b(mm) 130-270.

[0123] Step 7: Heat treat the casting.

[0124] The castings undergo pre-heat treatment and performance heat treatment. The pre-heat treatment is carried out before rough machining. The pre-heat treatment is normalizing and tempering, and its purpose is to homogenize the composition of the casting, stabilize the structure, eliminate stress, and prepare for subsequent processes. The performance heat treatment is quenching and tempering, and its purpose is to enable the casting to achieve the performance of the lip.

[0125] In specific implementation, the key points of the pre-heat treatment operation are as follows: before carrying out the pre-heat treatment, it must be determined that the structure and size of the product must meet the requirements of the drawing. The cut ribs, patches and risers to be removed must be clean and clear. Overcutting is strictly prohibited. The dimensions must meet the tolerance requirements of the drawing, especially the dimensions of the inner and outer sections. If they are not suitable, they need to be corrected during the heat treatment.

[0126] During the preheating process, the heating rate for normalizing is ≤80℃ / h, the intermediate holding temperature is 550±10℃ for two hours, and the normalizing temperature is 920±10℃ for 10 hours.

[0127] During tempering, the heating rate is ≤80℃ / h, the tempering temperature is 580±10℃, and the holding time is 8 hours;

[0128] Both normalizing and tempering are cooled by air cooling.

[0129] Furthermore, such as Figure 2 As shown, the key points of the performance heat treatment operation are as follows: Before the performance heat treatment, it is necessary to confirm that the appearance, size and flaw detection of the casting are qualified. Due to the large stress during the tempering process, two Φ120~Φ160mm tie rods must be welded to prevent deformation. The tempering process includes three parts: heating, holding and cooling. The heating rate is controlled at ≤80℃ / hour, and the intermediate holding temperature is set at 550~650℃ for 1~3 hours. The holding temperature is controlled at 870±10℃. The cooling is water quenching. The time from opening the furnace door to entering the water is controlled within 50 seconds. The water temperature is 30~35℃. When the tempering is finished, the temperature rise is within 5℃. The casting can be taken out of the water only when it is cooled to 50~100℃.

[0130] Furthermore, the performance characteristics of the lip include tensile properties, low-temperature impact properties, hardness testing, and metallographic testing. The tensile properties are tested using a tensile testing machine to measure the tensile strength, yield strength, elongation, and cross-sectional expansion of the casting. The tensile strength of the casting is ≥724 MPa, the yield strength is ≥896 MPa, the elongation is ≥12%, and the cross-sectional expansion is ≥25%. The low-temperature impact properties are tested by measuring the impact value of the casting at -18℃. The impact value of the casting is ≥27 J. The hardness is tested using a portable handheld hardness tester with a hammer test, and the hardness is 277–331 HB. The metallographic testing measures the tempering martensite content of the casting to verify the tempering effect.

[0131] Step 8: Finish machining of the workpiece:

[0132] A. Place the workpiece upright, find the verticality according to the non-machined side surface, level the workpiece symmetrically on the left and right with reference to the arc top height coordinate dimension, and draw the X reference machining dimension line of the bottom surface of the workpiece; draw the reference center line with the non-machined surfaces on both sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends.

[0133] B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference;

[0134] C. Level and straighten the workpiece along the line, with the X datum plane facing the spindle; finish mill the X datum plane; program the finish milling of the chamfers and fillets at the inner cavity;

[0135] D. Adjustment: Orient the workpiece's Y-datum plane toward the machine bed, use the machined X-datum plane as the positioning reference to find the level, adjust and straighten it left and right along the line, and tighten it; finish mill the Y-datum plane.

[0136] E. Program and precision mill the internal cavity dimensions, one end face and adjacent table surface, and fillets;

[0137] F. Install the milling head and finish mill the right-side bevel, taking into account the bevel angle and related dimensions.

[0138] G. Adjust the milling head and finish mill the chamfer;

[0139] H. Adjust the milling head, finish mill the inclined surface and adjacent step surface, fillet the corners, take into account the relevant dimensions, program the finish milling of the waist-shaped hole and the fillet of the hole opening on the surface, and ensure that the surface inside the waist-shaped hole is perpendicular;

[0140] I. Program and fine-mill the oblong hole and the rounded corner of the hole in the inner cavity to ensure that the inner cavity surface of the oblong hole is perpendicular;

[0141] J. Adjustment: Rotate the workpiece 180° and finish mill the contour surface and adjacent table surface and fillets on one side of the dimension; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of the inner cavity, ensuring that the inner cavity surface of the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 90° and finish mill the left end face and adjacent step surface and fillets; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of this face, ensuring that the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 180° and finish mill the right end face and adjacent step surface and fillets; program the cutter to finish mill the waist hole and the fillets at the opening of this face, ensuring that the waist-shaped hole is vertical.

[0142] K. Adjustment and installation: Install the clamp with the X reference surface facing downwards and the top arc surface facing the bed. Align with the Y reference surface using a dial indicator and tighten.

[0143] L. Program and precision mill the top arc surface and all boss surfaces and fillets;

[0144] M. Inspect according to the requirements of the drawings and quality information sheet;

[0145] N. After painting and packaging according to the drawings and quality information sheet requirements, the prepared large bucket lips are stored in the warehouse. Figure 3 As shown.

[0146] The large-scale indenter produced using this invention, through process assurance and strict process control, results in an indenter product with a smooth appearance, minimal dimensional deformation, and dense internal structure, free from defects exceeding standards. Customer verification confirms that it fully meets the required quality requirements in terms of internal quality, appearance, and dimensions, passing the verification on the first attempt.

[0147] The large bucket lip prepared by this invention, after assembly and application, fully meets the performance requirements, fills the gap in domestic manufacturing of this type of product, and lays a solid foundation for the manufacturing of parts for large-scale engineering machinery in China.

[0148] The parts of this invention not described in detail are prior art.

[0149] The embodiments selected herein for the purpose of disclosing the inventive objectives are currently considered suitable; however, it should be understood that the invention is intended to include all variations and modifications of the embodiments that fall within the scope of this concept and invention.

Claims

1. A method of casting a large lip, characterized by: The casting method specifically includes the following steps: Step 1, Styling: A. First, place the casting mold on the ground and place hollow steel pipes and steel bars to strengthen the sand mold and prevent it from falling off. B. Place and secure the heating riser sleeve, the easy-cut riser plate, and the ceramic casting tube. When placing the easy-cut riser plate, the easy-cut riser plate should be located below the heating riser sleeve. The easy-cut riser plate will make the riser easy to cut. C. Fill with molding sand, ensuring the sand is compacted during filling; D. After the sand mold is completed, let it stand for 1 to 3 hours until it hardens, then proceed with the demolding operation. E. Apply paint by brushing, bake until the sand mold changes color, and then dry. F. When making sand cores, pay attention to ensuring the air venting channels are unobstructed; G. After the core is installed, check whether the wall thickness meets the design requirements. After confirming that it meets the design requirements, proceed with the box closing operation. Step 2, Smelting and Casting: After the casting raw materials are melted in an electric arc furnace to obtain molten steel, in order to prevent the molten steel from reacting with oxygen in the air, hot air at 90-110°C is introduced into the cavity of the casting mold 1-3 hours before pouring for 30-60 minutes to remove moisture from the cavity and the surface of the molding sand. Then, argon gas is introduced into the cavity of the casting mold. Since the density of argon gas is greater than that of air, the argon gas enters from the bottom of the cavity. Then, the composition and temperature of the molten steel are tested. When the composition of the molten steel meets the internal control requirements and the temperature is 1560±5℃, the molten steel is poured into the cavity of the casting mold. During pouring, the flow rate of the molten steel is first controlled at 140~160kg / s, and the total pouring time is controlled at 160~180s. When the pouring reaches the required process height, the pouring is stopped. After the pouring is completed, a heating covering agent is added. After the molten steel cools down, the casting is obtained. Step 3: Cooling, sand removal, and cleaning: A. After pouring, the casting is allowed to cool naturally in the sand mold for 144 to 200 hours, and the temperature after cooling is 300 to 500°C. B. After the cooling time is up, remove the casting from the sand mold; C. Clean the loose sand from the surface of the casting to expose the metal surface. During the cleaning process, prevent damage to the surface of the casting. D. Remove easily cut risers from castings by impact; Step 4: Raw material inspection: Inspect the dimensions and appearance of the blank; the dimensions and appearance of the blank should meet the design requirements. Step 5: Heat treatment of the casting: The castings undergo pre-heat treatment and performance heat treatment. The pre-heat treatment is carried out before rough machining. The pre-heat treatment is normalizing and tempering, and its purpose is to homogenize the composition of the casting, stabilize the structure, eliminate stress, and prepare for subsequent processes. The performance heat treatment is quenching and tempering, and its purpose is to enable the casting to achieve the performance of the lip. Step 6, Rough machining: A. First, place the workpiece upright and find the verticality according to the non-machined side surface. Adjust the workpiece symmetrically left and right with reference to the arc top height coordinate dimension. Draw the X reference machining dimension line of the bottom surface of the workpiece. Draw the reference center line with the non-machined surfaces on both sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends. B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference; C. Four steel plates are intermittently welded together on the non-machined surface to serve as mounting process blocks; D. Level and straighten the workpiece along the line, with the Y-datum plane facing the spindle; rough mill the Y-datum plane, leaving a 12-18mm allowance on each side. E. Adjustment and installation: Install the clamp with the Y datum facing downwards and the X datum facing the spindle. Align with the line and level with the Y datum. Tighten. Rough mill the X datum, leaving a margin of 12-18mm on one side. Install the milling head and rough mill the plane, leaving a margin of 12-18mm on one side. Step 7: Perform UT, MT, and RT flaw detection on the workpiece: First, the rough-machined workpiece is subjected to UT flaw detection, with the flaw detection level being level 1 for the bevel and level 2 for the rest of the workpiece. After rough machining, the workpiece is subjected to UT flaw detection and then MT flaw detection. During MT flaw detection, no linear display exceeding 2mm is allowed. Then the workpiece is subjected to RT testing. The RT testing standard is ASTM E446 / E280 / E186, and D, E and F type defects are not allowed. Step 8: Finish machining of the workpiece: A. Place the workpiece upright, find the verticality according to the side non-machined surface, level the workpiece symmetrically with reference to the arc top height coordinate dimension, and draw the X reference machining dimension line of the bottom surface of the workpiece; draw the reference center line with the two sides of the inner cavity as the reference, and draw the machining dimension lines of the left and right outer ends. B. Draw the Y-datum surface machining dimension line using the non-machined arc surface as the reference; C. Level and straighten the workpiece along the line, with the X datum plane facing the spindle; finish mill the X datum plane; program the finish milling of the chamfers and fillets at the inner cavity; D. Adjustment: Orient the workpiece's Y-datum plane toward the machine bed, use the machined X-datum plane as the positioning reference to find the level, adjust and straighten it left and right along the line, and tighten it; finish mill the Y-datum plane. E. Program and precision mill the internal cavity dimensions, one end face and adjacent table surface, and fillets; F. Install the milling head and finish mill the right-side bevel, taking into account the bevel angle and related dimensions. G. Adjust the milling head and finish mill the chamfer; H. Adjust the milling head, finish mill the inclined surface and adjacent step surface, fillet the corners, take into account the relevant dimensions, program the finish milling of the waist-shaped hole and the rounded corner of the hole on the inclined surface, and ensure that the waist-shaped hole is perpendicular to the inclined surface; I. Program and fine-mill the oblong hole and the rounded corner of the hole in the inner cavity to ensure that the inner cavity surface of the oblong hole is perpendicular; J. Adjustment: Rotate the workpiece 180° and finish mill the contour surface on one side of the dimension, as well as the adjacent table surface and fillets; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of the inner cavity, ensuring that the inner cavity surface of the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 90° and finish mill the left end face, the adjacent step surface, and fillets; program the cutter to finish mill the waist-shaped hole and the fillets at the opening of the inclined surface, ensuring that the waist-shaped hole is vertical. Adjustment: Rotate the workpiece 180° and finish mill the right end face, the adjacent step surface, and fillets; program the cutter to finish mill the waist hole and the fillets at the opening of the inclined surface, ensuring that the waist-shaped hole is perpendicular to the inclined surface. K. Adjustment and installation: Install the clamp with the X reference surface facing downwards and the top arc surface facing the bed. Align with the Y reference surface using a dial indicator and tighten. L. Program and precision mill the top arc surface and all boss surfaces and fillets; M. Inspect according to the requirements of the drawings and quality information sheet; N. After painting and packaging according to the drawings and quality information sheet requirements, the product is put into storage.

2. The method of casting a large lip as set forth in claim 1, wherein: In the first step, during the manufacturing of the casting mold, due to the large structure of the lip, the core box of the casting mold is segmented to prevent the sand core from being too large and difficult to produce. The mold material is compacted plywood, which is staggered on the template plate. The template plate is a steel structure to effectively prevent warping and deformation. Due to the large size of the product, the template plate adopts a split structure. The template plate is CNC machined, and then the machined template plate is assembled with the core box to obtain the required casting mold.

3. The method of casting a large lip as set forth in claim 1, wherein: The molten steel in the second step comprises the following components by weight: C 0.16~0.24 parts; Mn 0.90~1.20 parts; Cr 1.00–1.20 parts; Ni 1.6–1.9 parts; Mo 0.30~0.50 parts; Si 0.35~0.60 parts; S ≤ 0.015 parts; P ≤ 0.015 parts; Al ≤ 0.060 parts; CE ≤0.067 copies.

4. The method of casting a large lip as defined in claim 1, wherein: In the second step, when smelting the steel melt, the impact requirements on the lip are high, making it more sensitive to delayed cracks inside. The H content in the casting must be reduced to below 5 PPM. Therefore, all alloys must be baked during smelting. Since Ni has the highest proportion and a large hydrogen content, it must be baked at a high temperature of 600-800℃ for 7-9 hours to eliminate the hydrogen hazards from the raw materials to the greatest extent.

5. The method of casting a large lip as defined in claim 1 wherein: In the second step, when smelting the steel melt, a three-stage smelting method is adopted through an electric arc furnace, which includes a melting stage, an oxidation stage, and a reduction stage.

6. The method of casting a large lip as defined in claim 1 wherein: In the seventh step, when performing MT flaw detection, a CEE-1 magnetic particle flaw detector is used, with a sensitivity test piece of 30 / 100Al, black magnetic powder, kerosene medium, and magnetization method of energization, wire winding / magnetic yoke; inspection method of wet continuous method; working illumination: ≥500Lx; magnetization current: >44N; magnetic suspension concentration: 15g / L; demagnetization requirement: 5G.

7. The method of casting a large lip as defined in claim 1 wherein: When performing RT flaw detection in the seventh step, the equipment model is DZ-9 / 3000, the tube voltage is KV9Mev, the exposure time is 80-1200rad, the radiography method is single-wall single-image film, the density is 1.8-4.0, F (mm): 1630-1770, f (mm): 1500, b (mm) 130-270.

8. The method of casting a large lip as defined in claim 1 wherein: The key points of the pre-heat treatment operation in the fifth step are as follows: before the pre-heat treatment, it must be ensured that the structure and size of the product meet the requirements of the drawing. The cut ribs, patches and risers to be removed must be clean and clear. Overcutting is strictly prohibited. The size must meet the tolerance requirements of the drawing. If the size of the inner and outer sections is not suitable, it needs to be corrected during the heat treatment. During the preheating process, the heating rate for normalizing is ≤80℃ / h, the intermediate holding temperature is 550±10℃ for two hours, and the normalizing temperature is 920±10℃ for 10 hours. During tempering, the heating rate is ≤80℃ / h, the tempering temperature is 580±10℃, and the holding time is 8 hours; Both normalizing and tempering are cooled by air cooling.

9. The method of casting a large lip as defined in claim 1 wherein: The key points of the performance heat treatment in the fifth step are as follows: Before performance heat treatment, it is necessary to confirm that the appearance, dimensions, and flaw detection of the casting are qualified. Due to the large stress during the tempering process, two Φ120~Φ160mm tie rods must be welded to prevent deformation. Tempering includes three parts: heating, holding, and cooling. The heating rate is controlled at ≤80℃ / hour, and an intermediate holding temperature of 550~650℃ is set for 1~3 hours. The holding temperature is controlled at 870±10℃. Cooling is done by water quenching. The time from opening the furnace door to entering the water is controlled within 50 seconds, and the water temperature is 30~35℃. When the tempering is finished, the temperature rise is within 5℃. The casting can be removed from the water only when it is cooled to 50~100℃.

10. The method of casting a large lip as defined in claim 1 wherein: The performance characteristics of the lip in the fifth step include tensile properties and low-temperature impact properties. The tensile properties are tested using a tensile testing machine to measure the tensile strength, yield strength, elongation, and cross-sectional expansion of the casting. The tensile strength of the casting is ≥724 MPa, the yield strength is ≥896 MPa, the elongation is ≥12%, and the cross-sectional expansion is ≥25%. The low-temperature impact properties are tested by measuring the impact value of the casting at -18℃. The impact value of the casting is ≥27 J.

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