A simulation control method for casting defects of bucket teeth for large excavators

Abstract

The present invention discloses a simulation control method for casting defects of bucket teeth for large excavators, relating to the field of liquid metal forming technology. The method comprises the following steps: presetting the casting process of bucket teeth according to the structural characteristics of large excavator bucket teeth; using 3D modeling software to draw the bucket teeth and the supporting casting system, and exporting a 3D digital model file; using casting simulation analysis software to import the 3D digital model file and perform meshing; setting the module of the simulation software casting process simulation parameters; simulation calculation and simulation operation; computer simulation result feedback and judgment evaluation; casting process plan and parameter improvement and optimization; and optimal parameter confirmation. The method uses computer simulation software to simulate and optimize the bucket tooth casting process, achieving the goals of controlling casting defects, rapid response under multiple processes, shortening the R&D cycle, reducing development costs, and improving the quality of bucket tooth castings.

Description

Technical Field

[0001] The invention relates to the technical field of liquid metal forming, in particular to a simulation control method for casting defects of bucket teeth for large excavators. Background Art

[0002] Excavators, as essential engineering machinery, play a crucial role in economic development. Bucket teeth, one of the primary wear parts of excavators, come into direct contact with materials such as ore, rock, and sand during use. Large excavators used in mining, in particular, face severe wear and tear under harsh operating conditions, placing extremely high demands on the product's wear and impact resistance. The quality of bucket teeth determines their service life and directly impacts the efficiency of the excavator. Casting, the first step in bucket tooth production, directly impacts the effectiveness of subsequent heat treatment and ultimately the tooth's service life.

[0003] Sand casting is widely used in bucket tooth casting production due to its ease of implementation and low cost. Traditional bucket tooth R&D relies on trial castings to verify the rationality and feasibility of the casting process design. Repeated revisions and trial castings waste significant manpower, material, and financial resources, resulting in low R&D efficiency and a waste of resources.

[0004] Shrinkage cavities and porosity defects during the casting process are primarily caused by a lack of replenishment of molten metal to the last areas of the casting to solidify during cooling and solidification. Bucket teeth used in large excavators, due to their larger size, are prone to macro-shrinkage cavities and micro-shrinkage porosity in the thickest areas of the casting and in hot spots, adversely affecting the mechanical properties of the casting.

[0005] Patent document CN 107891122 B describes a method for controlling solidification defects in aluminum alloy precision casting. By varying the casting temperature, optimizing the casting system, and pre-introducing gas into the mold, the patent document achieves an optimal process solution through repeated casting. Repeatedly modifying the casting process and conducting trial castings wastes significant manpower, material, and financial resources, resulting in low R&D efficiency and a waste of resources.

[0006] Patent document CN 106649986 B describes a practical method for optimizing casting parameters for copper tubes during horizontal continuous casting, based on the PROCAST simulation platform. This patent document uses PROCAST to simulate the copper tube casting process, simulating different production processes to obtain the optimal parameter combination. This method is valuable for defect control and simulation of tubular castings, but its value for simulation and defect control of engineering machinery components, such as excavator bucket teeth, is quite limited.

[0007] Patent document CN 110976830 B describes a method for controlling casting defects in an aluminum alloy shift hub. Using computer simulation, the patent reduces casting defects in the shift hub by adjusting the riser and deploying as many chillers as possible. While the chiller configuration does significantly reduce casting defects, it complicates the casting process, lengthens the casting cycle, and requires high worker proficiency, making it unsuitable for large-scale production. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a simulation control method for casting defects of bucket teeth for large excavators, overcome the shortcomings of the existing technology, and use computer software simulation to simulate and analyze the temperature field, filling field, solidification field, macro shrinkage distribution and micro shrinkage distribution in the casting process. By changing the gate position and size, riser shape, size and type, chiller size and position, etc., the bucket tooth casting process is optimized, which greatly shortens the research and development cycle of bucket tooth products and effectively reduces production costs.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A simulation control method for casting defects of bucket teeth for large excavators includes the following steps:

[0011] (1) Casting system design

[0012] Design bucket tooth casting process and casting system according to the structural characteristics of the bucket teeth to be cast;

[0013] (2) 3D digital model drawing

[0014] Use 3D modeling software to draw bucket teeth and their supporting casting systems, and export 3D digital model files;

[0015] (3) Grid division

[0016] Importing the 3D digital model file into the casting process simulation analysis software to perform meshing in preparation for casting process simulation;

[0017] (4) Simulation parameter settings

[0018] After completing the mesh division, in the casting process simulation parameter setting module of the simulation software, set the casting process related parameters according to the actual situation and the design plan;

[0019] (5) Simulation

[0020] After setting the casting process related parameters in the casting process simulation module of the simulation software, click Run and wait for the computer to return the simulation results;

[0021] (6) Process optimization

[0022] After optimizing the casting process plan and changing the casting system and simulation parameters, the optimized plan is repeated with steps (2)-(5) to obtain new simulation results for comparative analysis;

[0023] (7) Bucket tooth casting

[0024] After determining the best casting process plan according to the above steps (1)-(6), bucket tooth casting is carried out according to the best process plan.

[0025] (8) Bucket tooth casting inspection

[0026] Defect detection was carried out on trial-cast bucket tooth castings for large excavators and compared with simulation results to confirm the effectiveness of the control method.

[0027] Furthermore, a simulation control method for casting defects of bucket teeth for large excavators includes the following steps:

[0028] (1) Casting system design

[0029] According to the structural characteristics of the bucket teeth to be cast, select the appropriate casting form, casting speed, gate size, chill position, riser shape and size, etc. to complete the casting system design of the bucket teeth casting process;

[0030] (2) 3D digital model drawing

[0031] Use 3DS Max, CATIA, UG, Solid Works or C4D and other 3D modeling software to draw bucket teeth and their supporting casting systems, and export 3D digital model files after drawing;

[0032] (3) Grid division

[0033] Import the 3D digital model file into ProCAST casting process simulation analysis software to check the correctness and completeness of the casting system 3D digital model, repair the erroneous parts, and mesh the casting system 3D digital model after the repair is completed;

[0034] (4) Simulation parameter settings

[0035] After the meshing is completed, the pouring temperature, pouring time, sand box type, alloy type and heat transfer coefficient are set in the casting process simulation parameter setting module of the simulation software;

[0036] (5) Simulation

[0037] After setting the casting process parameters in the casting process simulation module of the simulation software, click Run and wait for the computer simulation to complete and return the simulation results such as temperature field, filling field, solidification field, macro shrinkage distribution and micro shrinkage distribution;

[0038] (6) Process optimization

[0039] Analyze the simulation results obtained in step (5), change the gate position and size, riser shape, size and type, chiller size and position, etc. in a targeted manner, optimize the casting process plan, and repeat steps (2) to (5) for the optimized plan;

[0040] (7) Bucket tooth casting

[0041] Repeat the above steps (1)-(6) until the best casting process is obtained, and then carry out bucket tooth casting according to the best process.

[0042] (8) Bucket tooth casting inspection

[0043] The trial-cast bucket tooth castings for large excavators were subjected to magnetic powder detection, X-ray detection, ultrasonic detection and casting dissection. The test results were compared with the simulation results to confirm the effectiveness of the control method.

[0044] Among them, the casting defect control method of bucket teeth for large excavators and the simulation results of the final casting process plan show that the casting filling process is smooth, the solidification process is sequential solidification without isolated liquid phase areas, and there are no macro shrinkage cavities inside the casting.

[0045] Furthermore, the gate position of the casting system in step (1) can be selected at the side, tooth tip or tail of the bucket tooth.

[0046] Furthermore, the shape of the riser of the casting system in step (1) can be circular or non-standard rectangular.

[0047] Furthermore, the casting system in step (1) can choose whether to use chilled iron according to actual conditions.

[0048] Furthermore, the size of the bucket teeth drawn in the three-dimensional modeling software in step (2) is 1.0-2.0% larger than the actual bucket teeth size.

[0049] Furthermore, the 3D digital model file described in step (2) is preferably exported to stl format.

[0050] Furthermore, in step (3), the repaired 3D digital model of the casting system has no overlap between faces and no redundant faces in the model.

[0051] Furthermore, the types of sand boxes in step (4) include: quartz sand, resin sand, glass sand, iron sand and ceramic sand, etc.

[0052] Furthermore, the alloy types in step (4) are classified according to the alloy structure to include martensitic steel, bainitic steel, martensite-austenite dual-phase steel, etc.

[0053] Furthermore, if the filling field simulation result is not needed in step (5), the simulation can be started directly from the solidification stage to save computer simulation time.

[0054] Furthermore, the riser in step (6) can be an open riser or a hidden riser.

[0055] Furthermore, in the optimal process solution described in step (7), in some cases, defects with a diameter of less than 2.0 mm are allowed to exist below 1.5 cm on the bucket tooth surface without affecting the use of the bucket tooth.

[0056] Furthermore, in the optimal process solution described in step (7), in some cases, defects with a diameter of less than 1.0 mm are allowed to exist below 2.0 cm on the bucket tooth surface without affecting the use of the bucket tooth.

[0057] Furthermore, the optimal process solution in step (7) does not use cold iron.

[0058] Bucket tooth castings for large excavators are characterized by their large size, heavy weight, and demanding mechanical properties, placing high demands on the casting process. Traditional bucket tooth R&D relies on trial castings to verify the rationality and feasibility of the casting process design. Repeated revisions and trial castings waste significant manpower, material, and financial resources, resulting in low R&D efficiency and high development costs. Using computer software simulation allows for simulation analysis and optimization of the casting process, significantly improving bucket tooth R&D efficiency.

[0059] In order to deal with the shrinkage cavities and shrinkage defects generated inside the casting during the bucket tooth casting process, R&D personnel generally reduce the defects inside the casting by adjusting the size of the riser and adding chills at the wall thickness and hot spots. The use of chills can effectively reduce shrinkage cavities and shrinkage defects inside the casting, but the introduction of chills makes the mold molding process more complicated in the actual production process, the production cycle becomes longer, and the quality requirements for production workers become higher, which is not conducive to large-scale production, and the economic and social benefits of the products are low. In response to this, the inventors found that by changing the position of the gate and combining it with a non-standard rectangular riser method, it is possible to eliminate the internal casting defects of the bucket teeth without using chills.

[0060] Bucket tooth research and development tasks are carried out using computer simulation software, trial production is carried out based on the optimal casting process plan obtained from the simulation, and the trial castings are dissected and analyzed. While verifying the reliability of the simulation analysis results, a bucket tooth casting defect control analysis model is established, providing an experimental reference for future internal defect control of bucket tooth castings and even internal defect control of engineering machinery castings.

[0061] Compared with the prior art, the beneficial effects of the above technical solution of the present invention are as follows:

[0062] (1) The present invention provides a simulation control method for casting defects of bucket teeth for large excavators, which improves the product qualification rate, shortens the R&D cycle, saves manpower and material resources, and reduces development costs.

[0063] (2) The optimal casting process scheme obtained by the present invention is easy to implement and simple to operate, and is easy to achieve large-scale production, thereby promoting product promotion.

[0064] (3) The present invention adopts a method that combines simulation and practice, which has good extensibility. The defect control analysis model established has a high reference value for the design of various large excavator bucket tooth molds and even engineering machinery casting molds. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 Shows the bucket tooth casting defect simulation control flow chart;

[0066] Figure 2 The bucket tooth casting process casting system of Example 1 is shown;

[0067] Figure 3 The distribution position of the macro shrinkage cavities of Example 1 is shown;

[0068] Figure 4 The bucket tooth casting process casting system of Example 2 is shown;

[0069] Figure 5 Shows the distribution position of the macro shrinkage cavities of Example 2. DETAILED DESCRIPTION

[0070] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a more detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0071] The present invention provides a simulation control method for casting defects of bucket teeth for large excavators, the method comprising the following steps:

[0072] (1) Casting system design

[0073] According to the structural characteristics of the bucket teeth to be cast, select the appropriate casting form, casting speed, gate size, chill position, riser shape and size, etc. to complete the casting system design of the bucket teeth casting process;

[0074] (2) 3D digital model drawing

[0075] Use 3DS Max, CATIA, UG, Solid Works or C4D and other 3D modeling software to draw bucket teeth and their supporting casting systems, and export 3D digital model files after drawing;

[0076] (3) Grid division

[0077] Import the 3D digital model file into ProCAST casting process simulation analysis software to check the correctness and completeness of the casting system 3D digital model, repair the erroneous parts, and mesh the casting system 3D digital model after the repair is completed;

[0078] (4) Simulation parameter settings

[0079] After the meshing is completed, the pouring temperature, pouring time, sand box type, alloy type and heat transfer coefficient are set in the casting process simulation parameter setting module of the simulation software;

[0080] (5) Simulation

[0081] After setting the casting process parameters in the casting process simulation module of the simulation software, click Run and wait for the computer simulation to complete and return the simulation results such as temperature field, filling field, solidification field, macro shrinkage distribution and micro shrinkage distribution;

[0082] (6) Process optimization

[0083] Analyze the simulation results obtained in step (5), change the gate position and size, riser shape, size and type, chiller size and position, etc. in a targeted manner, optimize the casting process plan, and repeat steps (2) to (5) for the optimized plan;

[0084] (7) Bucket tooth casting

[0085] Repeat the above steps (1)-(6) until the best casting process is obtained, and then carry out bucket tooth casting according to the best process.

[0086] (8) Bucket tooth casting inspection

[0087] The trial-cast bucket tooth castings for large excavators were subjected to defect detection such as magnetic powder detection, X-ray detection, ultrasonic detection and casting dissection. The detection results were compared with the simulation results to confirm the effectiveness of the control method.

[0088] Example 1: The casting in this example is a bucket tooth for a large excavator, which adopts a traditional sand casting process. The steps of the casting defect simulation control method are as follows:

[0089] (1) Gravity casting is selected according to the structural characteristics of bucket tooth castings. The pouring time is 15 s. The bucket tooth casting process casting system is as follows: Figure 2 As shown, the gate is located at the front end of the bucket tooth and the gate size is 48*25 mm 2 The riser adopts a spherical insulation blind riser with a riser neck diameter of 100 mm and a spherical riser diameter of 180 mm.

[0090] (2) Use Solid Works 3D modeling software to draw the bucket teeth and their supporting casting system, and export the 3D digital model file in STL format after the drawing is completed.

[0091] (3) Import the 3D digital model file into the ProCAST casting process simulation analysis software to check the correctness and completeness of the 3D digital model of the casting system, repair the erroneous parts, and mesh the 3D digital model of the casting system after the repair is completed.

[0092] (4) After the meshing is completed, in the simulation software casting process simulation parameter setting module, set the pouring temperature to 1580℃, the casting time to 15 s, the sand box type to resin sand sand box, the alloy type to low carbon low alloy, and the heat transfer coefficient to 498W / (m 2 ·K).

[0093] (5) After setting the casting process parameters in the casting process simulation module of the simulation software, click Run and wait for the computer simulation to complete to obtain the simulation results of the filling field, solidification field and macro shrinkage distribution. According to the simulation results, it is concluded that the casting process is filling smoothly, there is no isolated liquid phase area in the solidification process, and the macro shrinkage distribution position is shown in Figure 2. Figure 3 shown.

[0094] Example 2: The casting in this example is a bucket tooth for a large excavator, and a conventional sand casting process is used. The steps of the casting defect simulation control method are the same as those in Example 1. Compared with Example 1, the difference is that in step (1), the diameter of the spherical riser neck is increased to 120 mm, and two pieces of chill iron are added to the upper sand mold, with a size of about 40*40*20 mm. 3 Bucket tooth casting process casting system such as Figure 4 According to the simulation results, the casting process is smooth, there is no isolated liquid phase during the solidification process, and there is no macro shrinkage cavity inside the casting. Figure 5 shown.

[0095] Example 3: The casting in this example is a bucket tooth for a large excavator, using a traditional sand casting process. The steps of the casting defect simulation control method are the same as those in Example 1. Compared with Example 1, the difference is that the spherical riser in step (1) is replaced with a circular riser with a riser size of R68×188. Analysis of the simulation results shows that the casting process is smooth, the solidification process does not contain isolated liquid phase regions, and a large number of macro shrinkage cavities are present in the wall thickness directly below the riser.

[0096] Example 4: This example casting is a bucket tooth for a large excavator, using a conventional sand casting process. The steps for simulating and controlling casting defects are the same as those in Example 1. The difference from Example 1 is that the riser in step (1) is changed to a rectangular riser with a size of R68×188. Analysis of the simulation results indicates that the casting process is smooth, no isolated liquid phase region exists during solidification, and macroscopic shrinkage cavities are present in the wall thickness just below the riser and at the rear of the bucket tooth.

[0097] Example 5: The casting in this example is a bucket tooth for a large excavator, and the conventional sand casting process is used. The steps of the casting defect simulation control method are the same as those in Example 1. Compared with Example 4, the difference is that the feed port in step (1) is moved to the tail of the casting, and the size is 55×30 mm. 2 According to the simulation results, the casting process is filled smoothly, there is no isolated liquid phase during the solidification process, and there is only macro shrinkage cavity in the wall thickness just below the riser.

[0098] Example 6: The casting in this example is a bucket tooth for a large excavator, using a traditional sand casting process. The steps of the casting defect simulation control method are the same as those in Example 1. Compared with Example 5, the difference is that the size of the rectangular riser in step (1) is increased to R75×208. Based on the simulation results, it is found that the casting process is smooth, the solidification process is suspected to have an isolated liquid phase region, and macro shrinkage cavities are only present in the wall thickness directly below the riser.

[0099] Example 7: This example casting is a bucket tooth for a large excavator, using a traditional sand casting process. The steps for simulating and controlling casting defects are the same as those in Example 1. The difference from Example 6 is that the size of the rectangular riser in step (1) is increased to R85×228, and in step (5) the micro-shrinkage that may exist in the casting is simulated. Analysis of the simulation results indicates that the casting process is smooth, no isolated liquid phase regions exist during solidification, and no macro-shrinkage cavities exist within the casting, with only a few scattered micro-shrinkage cavities present.

[0100] Example 8: The casting in this example is a bucket tooth for a large excavator, and the conventional sand casting process is used. The steps of the casting defect simulation control method are the same as those in Example 1. Compared with Example 7, the difference is that the feed port in step (1) is changed to the side of the casting, and the size is 48×28 mm. 2According to the simulation results, it is concluded that there is turbulence in the casting process, there is no isolated liquid phase area in the solidification process, and there is no macro shrinkage cavity inside the casting.

[0101] Comparative Example 1: This comparative example casting is a bucket tooth for a large excavator, using a traditional sand casting process. The steps of the casting defect simulation control method are the same as those in Example 2. Compared with Example 2, the difference is that the size of the two chills in step (1) is reduced to 20*20*20 mm3. According to the simulation results, the casting filling process is smooth and there is no isolated liquid phase during the solidification process. However, due to the reduction in the volume of the chill, a small amount of macro shrinkage cavities reappear in the wall thickness just below the riser.

[0102] Comparative Example 2: The casting in this comparative example is a bucket tooth for a large excavator, which is cast using a traditional sand casting process. The steps of the casting defect simulation control method are the same as those in Example 7. Compared with Example 7, the difference is that the casting time in step (1) is reduced to 12 seconds. According to the simulation results, it is concluded that due to the shortened casting time and the increased speed, turbulence occurs during the casting and filling process, there is no isolated liquid phase region during the solidification process, there is no macro shrinkage cavity inside the casting, and the probability of micro shrinkage is slightly increased.

[0103] Comparative Example 3: This comparative example casting is a bucket tooth for a large excavator, using a conventional sand casting process. The steps for simulating and controlling casting defects are the same as those in Example 8. The difference from Example 8 is that the feed port size in step (1) is reduced to 48 × 25 mm. Analysis of the simulation results indicates that turbulence during the casting process is intensified, no isolated liquid phase regions exist during the solidification process, and no macroscopic shrinkage cavities exist within the casting.

[0104] After comparative analysis, the inventors found that the simulation results of the casting process scheme of Example 7 showed no macroscopic shrinkage defects within the casting, a small amount of microscopic shrinkage defects were evenly distributed, the casting and filling process was smooth, the process parameter conditions were wide, no chill addition was required, and the on-site operation requirements were low. Therefore, Example 7 was determined to be the optimal casting process scheme. Trial castings of bucket teeth were carried out according to the process scheme of Example 7. The trial-cast bucket teeth for large excavators were tested for defects such as magnetic powder deficiency, X-ray testing, ultrasonic testing, and casting dissection. The test results were compared with the simulation results and were consistent with the simulation results.

[0105] It is necessary to point out that the above embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A simulation control method for casting defects of bucket teeth for large excavators, characterized in that The steps are as follows: (1) Casting system modeling; According to the structural characteristics of the bucket teeth to be cast, the appropriate casting form, casting speed, gate size, chill position, and riser shape and size are selected to complete the casting system modeling of the bucket teeth casting process; (2) 3D digital model drawing; Use 3DS Max, CATIA, UG or Solid Works 3D modeling software to draw bucket teeth and their supporting casting systems, and export 3D digital model files after drawing is completed; (3) Grid division; Importing the 3D digital model file into ProCAST casting process simulation analysis software, checking the correctness and completeness of the 3D digital model of the casting system, repairing the erroneous parts, and meshing the 3D digital model of the casting system after the repair is completed; (4) Simulation parameter setting; After the meshing is completed, the casting temperature, casting time, sand box type, alloy type and heat transfer coefficient are set in the casting process simulation parameter setting module of the simulation software; (5) Simulation; After setting the casting process related parameters in the casting process simulation module of the simulation software, click Run, wait for the computer simulation to complete and return the simulation results of temperature field, filling field, solidification field, macro shrinkage distribution and micro shrinkage distribution; (6) Process optimization; Analyze the simulation results obtained in step (5), change the gate position and size, riser shape, size and type, chiller size and position in a targeted manner, optimize the casting process plan, and repeat steps (2) to (5) for the optimized plan; (7) Bucket tooth casting; According to the above steps (1)-(6) until the best casting process scheme is obtained, bucket tooth casting is carried out according to the best process scheme; (8) Bucket tooth casting inspection; The trial-cast bucket tooth castings for large excavators were tested for magnetic powder defects, X-ray testing, ultrasonic testing, and casting planing defect detection. The test results were compared with the simulation results to confirm the effectiveness of the control method. The simulation results of the final casting process show that the casting filling process is smooth, the solidification process is sequential solidification without isolated liquid phase areas, and there are no macro shrinkage cavities inside the final casting; The gate position is selected at the tail of the bucket tooth; The shape of its riser is a non-standard rectangle; No cold iron is used.

2. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 1, characterized in that The size of the bucket teeth drawn in the 3D modeling software in step (2) is 1.0-2.0% larger than the actual bucket teeth size.

3. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that The 3D digital model file described in step (2) is exported to stl format.

4. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that In step (3), the 3D digital model of the repaired casting system has no overlap between faces and no redundant faces in the model.

5. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that The types of sand boxes in step (4) include: quartz sand, resin sand, ferrochrome sand and ceramic sand.

6. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that The alloy types described in step (4) are classified according to the alloy structure to include martensitic steel, bainitic steel, and martensite-austenite dual-phase steel.

7. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that In step (5), if the filling field simulation result is not needed, directly choose to start the simulation from the solidification stage.

8. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 2, characterized in that The risers described in step (6) include open risers and hidden risers.

9. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 1, characterized in that The optimal process solution described in step (7) allows, in some cases, defects with a diameter of less than 2.0 mm below 1.5 cm on the bucket tooth surface.

10. The method for simulating and controlling casting defects of bucket teeth for large excavators according to claim 1, characterized in that The optimal process solution described in step (7) allows, in some cases, defects with a diameter of less than 1.0 mm below 2.0 cm on the bucket tooth surface.

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