High-performance alloy steel track shoe based on PEP resin ceramsite and casting method of high-performance alloy steel track shoe

Abstract

The invention discloses a high-performance alloy steel track shoe casting method based on PEP resin ceramsite. The method comprises the steps that alloy steel for a track shoe is prepared; casting a track shoe casting by using the alloy steel by adopting a casting process of a metal mold frame and automatic line flaskless molding; a multi-stage gradient heat treatment process is adopted for carrying out heat treatment on the track shoe casting, and specifically comprises normalizing treatment, thermal refining and medium-frequency induction quenching. According to the casting method of the high-performance alloy steel track shoe based on the PEP resin ceramsite, material microalloying and casting process optimization are carried out, a flaskless PEP resin ceramsite automatic molding process is innovated, and a multi-stage gradient heat treatment technology is combined; the problems that in the prior art, a track shoe is insufficient in abrasion resistance and cracks due to quenching, sand burning is caused by poor sand mold quality, the porosity is high, the size precision is low, the size consistency is poor, and the surface is rough are solved, and stable batch production of track shoe castings is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of excavator track shoe, and particularly relates to a high-performance alloy steel track shoe based on PEP resin bead sand and a casting method thereof. BACKGROUND

[0002] As a core component of the walking structure of a hydraulic excavator, the track shoe needs to bear the self-weight of the whole machine and complex ground impact load. At present, with the expansion of the mining scale, large hydraulic excavators are increasingly widely used, and the performance requirements for the track shoes thereof are more stringent. With the improvement of the performance requirements for the track shoes of the hydraulic excavators, low-alloy high-strength steel gradually becomes the preferred material for the track shoes of the hydraulic excavators. The low-alloy high-strength steel can optimize the performance of the material through the addition of alloy elements, but the alloy steel material often has the problems of insufficient plasticity and toughness and cracking during quenching at high strength. In addition, in terms of the casting process, the traditional production mode mostly adopts manual molding and ordinary resin quartz sand (silica sand) process, and has the problems of low production efficiency, poor size consistency, sintering and sticking of sand, etc. Especially for large track shoes used for large hydraulic excavators, the structure thereof is complex, the wall thickness difference is large, the arc surface and the groove intersect, and the sticking of sand, deformation and cracking defects are more likely to occur during the casting process.

[0003] The track surface of the track shoe needs to bear the high stress meshing action with the driving wheel, the pin hole needs to bear the large tensile stress during the travel, and the impact load in special cases, so the casting needs to be subjected to quenching strengthening treatment. The traditional mode mostly adopts the whole quenching process to improve the overall hardness and strength of the casting, but is prone to cause large deformation and local quenching cracks, thereby affecting the normal delivery of the track shoe.

[0004] Therefore, it is urgent to develop an automatic casting and heat treatment integrated process for large hydraulic excavator track shoes to solve the problems of insufficient material performance, high casting defect rate, low production efficiency, quenching deformation and cracking, etc. in the prior art. SUMMARY

[0005] To solve the above-mentioned technical problems in the prior art, the present application provides a high-performance alloy steel track shoe based on PEP resin bead sand and a casting method thereof.

[0006] In the first aspect of the present application, a high-performance alloy steel track shoe casting method based on PEP resin beaded sand is provided, comprising the following steps:

[0007] (I) Preparation of materials

[0008] An alloy steel for track shoes is prepared, and the chemical composition of the alloy steel for track shoes is controlled as follows in terms of mass percentage: C≤0.45%, Mn≤1.20%, Si≤0.80%, Cr≤1.20%, Ni≤0.60%, Mo≤0.40%, V≤0.25%, Al: 0.02-0.10%, P≤0.025%, S≤0.025%, RE: 0.3-0.5%, and the balance being Fe and unavoidable impurities.

[0009] (II) Casting

[0010] The alloy steel is used to cast the track shoe casting by using a metal mold frame + automatic line flaskless molding casting process, using the horizontal center of the track shoe pin ear hole as the parting surface, and adopting upper and lower mold splitting and independent striking to make the mold.

[0011] (III) Heat treatment of the casting

[0012] A multi-stage gradient heat treatment process is used for heat treatment of the track shoe casting, comprising:

[0013] Normalizing treatment: the track shoe casting is heated to 620-660℃ for 1-3h, then heated to 870-960℃ for 2-8h after the completion of the heat preservation, and then air-cooled to room temperature after the end of the heat preservation;

[0014] Quenching and tempering treatment: the track shoe casting is heated to 620-660℃ for 1-3h, then heated to 860-950℃ for 2-8h after the completion of the heat preservation, and then liquid-cooled to room temperature after the end of the heat preservation, then heated to 520-620℃ for 5-15h, and then air-cooled to room temperature after the completion of the heat preservation;

[0015] Medium-frequency induction quenching: the key use parts of the track shoe casting, such as the pin hole, track surface and driving table, are subjected to medium-frequency induction quenching, comprising heating the track shoe casting to 860-950℃ for a few seconds, and then spraying liquid to cool to room temperature.

[0016] Further, in the above high-performance alloy steel track shoe casting method based on PEP resin beaded sand, the automatic line flaskless molding adopts a method of adding PEP resin binder to the new beaded sand, and the particle size distribution of the new beaded sand is controlled to be 30 / 50 mesh three-screen sand, and the particle size distribution of the regenerated sand after use is controlled to be 40 / 100 mesh four-screen sand.

[0017] Furthermore, in the above-mentioned high-performance alloy steel track plate casting method based on PEP resin beaded sand, the automated line flaskless molding operation process includes:

[0018] Sand mixing: A continuous sand mixer is used to control the sand mixing time and ensure that the PEP resin evenly coats the abrasive sand particles;

[0019] Sand injection molding: Select the appropriate sand injection pressure and control the sand injection time to ensure complete filling of complex cavities;

[0020] Curing: Adjust the curing time to ensure smooth and rapid demolding;

[0021] Flow coating: Use a flow coating gun to apply the coating to the sand mold to ensure the thickness of the dry coating.

[0022] Packing consolidation: Packing consolidation is carried out using an automatic packing consolidation machine.

[0023] Furthermore, in the above-mentioned high-performance alloy steel track plate casting method based on PEP resin bead sand, in the casting step, the gating system is set to be fully open, and the gating area is set according to ΣF_bottle:ΣF_straight:ΣF_horizontal:ΣF_inner = 1:1.8:2.6:4, where ΣF_bottle, ΣF_straight, ΣF_horizontal, and ΣF_inner are the total cross-sectional areas of the ladle holes, the total cross-sectional areas of the straight runner, the total cross-sectional areas of the horizontal runner, and the total cross-sectional areas of the ingate, respectively. The gating system is set to introduce molten steel from the bottom of the casting, and three straight cylindrical heated risers are set at the two single ears and the hot spot of the center track surface of the track plate casting.

[0024] Furthermore, in the above-mentioned high-performance alloy steel track plate casting method based on PEP resin bead sand, in the casting step, an automatic pouring machine is used for continuous pouring of multiple boxes in a single package.

[0025] In a second aspect of the invention, a track plate is provided, which is produced using the above-described high-performance alloy steel track plate casting method based on PEP resin granules.

[0026] Furthermore, in the aforementioned track plates, the chemical composition of the track plates, by mass percentage, is: C≤0.45%, Mn≤1.20%, Si≤0.80%, Cr≤1.20%, Ni≤0.60%, Mo≤0.40%, V≤0.25%, Al:0.02~0.10%, P≤0.025%, S≤0.025%, RE:0.3~0.5%, with the remainder being Fe and unavoidable impurities;

[0027] Further, in the above track shoe, the track shoe has a structure grain size of 6.5, a base hardness of 285-355 HB, a tensile strength of Rm≥950 Mpa, an impact energy KV2(-40℃)≥27 J, a surface hardened layer depth of the assembled engagement portion of ≥5 mm, a surface hardness of the assembled engagement portion of ≥48 HRC, and a surface roughness Ra≤25 um.

[0028] Compared with the prior art, the high-performance alloy steel track shoe casting method based on PEP resin bead sand of the application has the following advantages and beneficial effects:

[0029] Through micro-alloying of the material, the hardness and toughness indexes of the material are coordinated, and the terminal deoxidization is ensured without increasing the AlN brittle phase; through optimization of the casting process, the casting method of metal mold frame + automatic line no-box molding is adopted, the mold is split up and down, and the molding is independently struck, the production efficiency is improved by more than 300% compared with manual molding; the automatic molding process of no-box PEP resin bead sand is innovated, the method of adding PEP resin binder to the original bead sand is adopted, the reaction gas emission amount is reduced, the high-temperature sintering and sand sticking of the casting are eliminated, the sand mold strength is high, the sand mold surface is compact and smooth, the flow-coated coating is dense and uniform in thickness, the upper and lower mold combination precision is high, the wrong type amount is extremely small, the casting surface quality and dimensional accuracy are effectively ensured at a high level, so that the casting surface quality level can be effectively improved; the automatic pouring machine is used for single package and multi-box continuous pouring, the composition and organization consistency of the multi-box casting are effectively improved; the multi-stage gradient heat treatment technology is adopted, the gradient matching of the excellent comprehensive performance of the base and the surface wear resistance of the assembled engagement portion is realized, and the service performance of the casting is improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0031] Figure 1 is a structural schematic diagram of a track shoe casting, wherein (a) is a front view, and (b) is a top view;

[0032] Figure 2 is a casting process scheme diagram adopted by the high-performance alloy steel track shoe casting method based on PEP resin bead sand of the application;

[0033] Figure 3 is a multi-stage gradient heat treatment process timing diagram adopted by the high-performance alloy steel track shoe casting method based on PEP resin bead sand of the application. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0035] The main technical measures of the high-performance alloy steel track plate casting method based on PEP resin bead sand of the present application include: through micro-alloying of the material, optimization of the casting process, and innovative automatic molding process of the flaskless PEP resin bead sand, in combination with the multi-stage gradient heat treatment technology, the problems of insufficient wear resistance of the track plate, quenching cracking, high sand sticking and porosity caused by poor sand quality, low dimensional accuracy, poor dimensional consistency and rough surface in the prior art are solved, and batch stable production of the track plate castings is realized.

[0036] The high-performance alloy steel track plate casting method based on PEP resin bead sand of the present application includes the following steps:

[0037] (I) Preparation of materials

[0038] An alloy steel for track plate is prepared, and the chemical composition of the alloy steel for track plate is controlled as follows in terms of mass percentage: C≤0.45%, Mn≤1.20%, Si≤0.80%, Cr≤1.20%, Ni≤0.60%, Mo≤0.40%, V≤0.25%, Al: 0.02-0.10%, P≤0.025%, S≤0.025%, RE: 0.3-0.5%, and the rest is Fe and inevitable impurities.

[0039] In the alloy steel for track plate of the present application, by adjusting the content of C element, adding Cr, Ni, Mo, V elements and RE, etc., the hard and tough indexes of the material are cooperated, by controlling the content of Al between 0.02-0.1%, the final deoxidization is ensured without increasing the AlN brittle phase, by adding 0.3-0.5% of RE material, the medium-carbon low-alloy steel material is modified and cleaned, the types, forms, distribution, quantity and size of inclusions of the product are improved, and the organizational grain size is refined.

[0040] (II) Casting

[0041] The alloy steel is used to cast the track plate casting, and the track plate casting is as shown in Figure 1 According to the structure and the large number of track plates, the casting process of metal mold frame + automatic line flaskless molding is selected, the model is divided into two parts with the horizontal center of the pin ear hole of the track plate as the parting surface, and the molding is made by independent striking to improve the molding work efficiency, and the casting process scheme is shown in Figure 2 .

[0042] The automatic line flaskless molding adopts the method of adding PEP resin binder to the original sand of the pearl sand, controls the particle size distribution of the new pearl sand at 30 / 50 mesh three-screen sand, controls the particle size distribution of the regenerated sand after the use of the new sand at 40 / 100 mesh four-screen sand, reduces the loss caused by rubbing during mechanical regeneration, and compensates for the reduction of the strength of the regenerated sand by increasing the number of bonding bridges, the angle of the pearl sand is small, and the shape is approximately spherical, compared with the traditional silica sand, the amount of binder needed is less under the same strength condition, the amount of gas generated by the reaction of the binder during pouring is reduced, the probability of defects such as pores in the final casting is greatly reduced, and the refractoriness of the pearl sand is higher, which can effectively prevent the occurrence of high-temperature sintering and sand sticking of the casting, and effectively improve the surface quality of the casting.

[0043] The automatic line flaskless molding operation process includes sand mixing, sand shooting molding, curing, flow coating, and flask assembling, wherein:

[0044] Sand mixing: a continuous sand mixer is used to control the sand mixing time to ensure that the PEP resin uniformly wraps the pearl sand particles;

[0045] Sand shooting molding: the appropriate sand shooting pressure is selected to control the sand shooting time to ensure complete filling of complex cavities;

[0046] Curing: the curing time is adjusted to ensure smooth and rapid mold stripping;

[0047] Flow coating: a flow coating gun is used for flow coating of the sand mold to ensure the dry coating thickness;

[0048] Flask assembling: an automatic flask assembling machine is used, and the flask assembling precision is extremely high.

[0049] Through the automatic line flaskless molding, the sand mold has high strength, the sand mold surface is compact and flat, the flow coating layer is dense and uniform in thickness, the upper and lower molds have high precision, and the misalignment amount is extremely small, which effectively ensures that the casting mold surface quality and dimensional accuracy are at a high level, thereby effectively improving the casting surface quality level.

[0050] In order to ensure the steel liquid filling capacity and realize low-temperature fast pouring, the pouring system is set to be fully open, that is, the runner area is set as ΣFbag:ΣFstraight:ΣFhorizontal:ΣFin = 1:1.8:2.6:4, wherein ΣFbag, ΣFstraight, ΣFhorizontal, and ΣFin are the total cross-sectional area of the ladle hole, the total cross-sectional area of the straight runner, the total cross-sectional area of the horizontal runner, and the total cross-sectional area of the inner runner, respectively, and the pouring system is set to introduce the steel liquid from the bottom of the casting to realize the smooth rising of the steel liquid during filling, which is beneficial to the floating of the gas, inclusions (slag) and the like in the steel liquid and the mold cavity, and three straight cylindrical heating risers are arranged at the two single ears and the center track surface hot spots of the track plate casting, which can realize the feeding of the key thick parts and facilitate the collection of inclusions (slag) and the exhaust, and ensure the compactness of the internal organization of the casting.

[0051] In the casting step, the automatic pouring machine is used for single package (for example, 15 tons package) multi-box continuous pouring. Compared with manual pouring, the time for aligning the pouring cup during multi-box pouring is shortened, the temperature drop of the single package molten steel during pouring the head and tail boxes is reduced, the temperature, composition and microstructure consistency of the multi-box castings are effectively improved, and the batch stable production of track plate castings is realized.

[0052] (III) Heat treatment of the castings

[0053] The multi-stage gradient heat treatment process is used for heat treatment of the track plate castings, as shown in the following table: Figure 3 The multi-stage gradient heat treatment includes:

[0054] Normalizing treatment: the track plate castings are heated to 620-660℃ for 1-3h, then heated to 870-960℃ for 2-8h, and then air-cooled to room temperature. Through the above normalizing treatment, the refined microstructure grain size is improved, the polishing is facilitated, and the castings are polished for quenching and tempering treatment.

[0055] Quenching and tempering treatment: the track plate castings are heated to 620-660℃ for 1-3h, then heated to 860-950℃ for 2-8h, then liquid-cooled to room temperature, then heated to 520-620℃ for 5-15h, and then air-cooled to room temperature. Through the above quenching and tempering treatment, the uniformity of the casting matrix microstructure and the excellent comprehensive performance are ensured.

[0056] Medium-frequency induction quenching: the key use positions of the track plate castings, such as the pin hole, track surface and driving platform, are subjected to medium-frequency induction quenching to improve the hardness value and wear resistance of the assembled engagement position, which specifically includes heating the track plate castings to 860-950℃ for a few seconds, and then liquid-cooling to room temperature.

[0057] Through the above multi-stage gradient heat treatment of normalizing + quenching and tempering + induction quenching, the gradient matching of the excellent comprehensive performance of the casting matrix and the surface wear resistance of the assembled engagement position is realized. Through actual production detection, the casting matrix microstructure grain size is 6.5 level, the casting matrix hardness is 285-355HB, the tensile strength is Rm≥950Mpa, the impact energy KV2(-40℃) is ≥27J, the surface hardened layer depth of the assembled engagement position is ≥5mm, the surface hardness of the assembled engagement position is ≥48HRC, the casting surface roughness is Ra≤25um, the casting porosity is ≤0.5%, the casting quenching cracking rate is ≤1%, and the castings do not have sand sticking defects.

[0058] In summary, the high-performance alloy steel track plate casting method based on PEP resin bead sand of the present application realizes micro-alloying of material quality, cooperates with hard and tough indexes of material quality, and ensures full final deoxidization without increasing brittle phase of AlN; through casting process optimization, the casting method of metal mold frame + automatic line no-box molding is adopted, the mold is split up and down, the molding is independently struck, the production efficiency is improved by more than 300% compared with manual molding; the automatic molding process of no-box PEP resin bead sand is innovated, the method of adding PEP resin binder to the bead sand is adopted, the reaction gas emission is reduced, the high-temperature sintering and sand sticking of the casting are eliminated, the sand mold strength is high, the sand mold surface is compact and smooth, the flow coating layer is dense and uniform in thickness, the upper and lower mold combining precision is high, the wrong type amount is extremely small, the casting surface quality and size precision are effectively guaranteed at a high level, so that the casting surface quality level can be effectively improved; the automatic pouring machine is adopted for single package and multi-box continuous pouring, the composition and organization consistency of multi-box castings are effectively improved; the multi-stage gradient heat treatment technology is adopted, the gradient matching of excellent comprehensive performance of the matrix and surface wear resistance of the assembled meshing part is realized, and the use performance of the casting is improved.

[0059] It should be noted that in this document, the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the object or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such object or device.

[0060] It should also be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the present application.

Claims

1. A method for casting high-performance alloy steel track plates based on PEP resin-bonded abrasive, characterized in that, Includes the following steps: (I) Material preparation Alloy steel for track plates is prepared, wherein the chemical composition of the alloy steel for track plates is controlled by mass percentage as follows: C≤0.45%, Mn≤1.20%, Si≤0.80%, Cr≤1.20%, Ni≤0.60%, Mo≤0.40%, V≤0.25%, Al:0.02~0.10%, P≤0.025%, S≤0.025%, RE:0.3~0.5%, with the remainder being Fe and unavoidable impurities; (II) Casting The casting process using metal mold frame + automated line boxless molding utilizes the aforementioned alloy steel to cast track plate castings, with the horizontal center of the track plate pin lug hole as the parting surface, and adopts upper and lower mold separation and independent impact molding. (III) Heat Treatment of Castings A multi-stage gradient heat treatment process is used to heat treat the track plate castings, including: Normalizing treatment: Heat the track plate casting to 620-660℃ and hold for 1-3 hours. After holding, heat the track plate casting to 870-960℃ and hold for 2-8 hours. After holding, air cool the track plate casting to room temperature. Heat treatment: Heat the track plate casting to 620-660℃ and hold for 1-3 hours. After holding, heat the track plate casting to 860-950℃ and hold for 2-8 hours. After holding, liquid cool the track plate casting to room temperature. Then heat the track plate casting to 520-620℃ and hold for 5-15 hours. After holding, air cool to room temperature. Medium-frequency induction hardening: Medium-frequency induction hardening is performed on key components of track plate castings, such as pin holes, track surfaces, and drive platforms. This involves heating the track plate castings to 860–950°C, holding them at that temperature for several seconds, and then spraying liquid cooling to room temperature.

2. The high-performance alloy steel track plate casting method based on PEP resin-bonded abrasive as described in claim 1, characterized in that, The automatic line for boxless molding uses raw abrasive sand mixed with PEP resin binder to control the particle size distribution of the new abrasive sand to 30 / 50 mesh three-sieve sand. After the new sand is used, the particle size distribution of the recycled sand is controlled to 40 / 100 mesh four-sieve sand.

3. The high-performance alloy steel track plate casting method based on PEP resin-bonded abrasive as described in claim 2, characterized in that, The automated boxless molding process includes: Sand mixing: A continuous sand mixer is used to control the sand mixing time and ensure that the PEP resin evenly coats the abrasive sand particles; Sand injection molding: Select the appropriate sand injection pressure and control the sand injection time to ensure complete filling of complex cavities; Curing: Adjust the curing time to ensure smooth and rapid demolding; Flow coating: Use a flow coating gun to apply the coating to the sand mold to ensure the thickness of the dry coating. Packing consolidation: Packing consolidation is carried out using an automatic packing consolidation machine.

4. The high-performance alloy steel track plate casting method based on PEP resin-bonded abrasive as described in claim 1, characterized in that, In the casting process, the gating system is set to be fully open, and the gating area is set according to ΣF_ladle:ΣF_straight:ΣF_horizontal:ΣF_inner = 1:1.8:2.6:4, where ΣF_ladle, ΣF_straight, ΣF_horizontal, and ΣF_inner are the total cross-sectional areas of the ladle holes, the total cross-sectional areas of the straight runner, the total cross-sectional areas of the horizontal runner, and the total cross-sectional areas of the ingate, respectively. The gating system is set to introduce molten steel from the bottom of the casting, and three straight cylindrical heated risers are set at the two single ears and the hot spot on the center track surface of the track plate casting.

5. The high-performance alloy steel track plate casting method based on PEP resin-bonded abrasive as described in claim 1, characterized in that, In the casting process, an automatic pouring machine is used for continuous pouring of multiple containers in a single package.

6. A track pad, characterized in that, The track plate is produced using the high-performance alloy steel track plate casting method based on PEP resin granules as described in any one of claims 1 to 5.

7. The track plate as described in claim 6, characterized in that, The chemical composition of the track plate, by mass percentage, is: C≤0.45%, Mn≤1.20%, Si≤0.80%, Cr≤1.20%, Ni≤0.60%, Mo≤0.40%, V≤0.25%, Al:0.02~0.10%, P≤0.025%, S≤0.025%, RE:0.3~0.5%, with the remainder being Fe and unavoidable impurities.

8. The track plate as described in claim 6, characterized in that, The track plate has a grain size of 6.5, a matrix hardness of 285~355HB, a tensile strength of Rm≥950Mpa, an impact energy of KV2(-40℃)≥27J, a surface hardening layer depth of ≥5mm at the assembly meshing parts, a surface hardness of ≥48HRC at the assembly meshing parts, and a surface roughness Ra≤25um.

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