Lost foam casting process for lightweight nodular cast iron planet carrier

Abstract

The invention provides a light-weight nodular cast iron planet carrier evanescent mode production process. According to the method, an exothermic riser sleeve is installed on a model cluster through a riser support special for an evanescent mode. According to the method, a heat-conducting chilling block is arranged in a narrow area of a model cluster. The dead head support special for the evanescent mode comprises a dead head neck, a dead head supporting table is coaxially arranged on the dead head neck, an upper cover plate is coaxially arranged on the dead head supporting table, and the seam of the dead head supporting table and the seam of the upper cover plate are bonded in a circumferential winding mode through paper adhesive tape. The narrow area comprises a deep and narrow weight reduction groove. The method for avoiding iron infiltration in the narrow and small area by using the heat-conducting cold iron can solve the problems of damp caused by a coating procedure in the process of using an exothermic riser bush in the evanescent mode and bumping and falling in the transfer process.

Description

Technical Field

[0001] The invention belongs to the technical field of automobiles and relates to a planetary carrier, in particular to a lost foam casting process for a lightweight ductile iron planetary carrier. Background Art

[0002] Lost foam casting, also known as full-mold casting, involves embedding a coated foam model cluster in dry sand. Vibration is used to compact the sand during the molding process. Continuous negative pressure is applied during the casting and solidification processes to pull the products of foam vaporization and combustion through the coating layer. This increases the compactness of the sand and enhances cooling, allowing metal to replace the model cluster.

[0003] Planet carriers are crucial power transmission components, requiring high strength and toughness. Ductile iron planet carriers must be free of internal shrinkage holes and possess high dimensional accuracy. With the increasing demand for lightweight transmission systems, newly designed planet carriers require extensive topological optimization to reduce casting weight while maintaining performance, which complicates the casting process.

[0004] Traditionally, planetary carriers are cast using the green sand casting process, which requires at least three sets of molds: a hot core mold, a cold core mold, and a molding mold. This complex and challenging production process results in poor casting surface quality. The lightweight structure further increases the difficulty of green sand production. The development of lost foam castings for planetary carriers can significantly improve casting quality and reduce production costs.

[0005] Directly using the existing lost foam casting process to produce lightweight planetary carriers, heat accumulation in the deep and narrow weight-reducing grooves causes the molding sand to sinter, ultimately resulting in iron seepage and sand adhesion defects in the casting, which seriously affects the appearance quality and cleanliness of the casting. High-grade ductile iron castings have a high tendency to shrink and require the use of heated riser sleeves for shrinkage compensation. However, the conventional process uses heated riser sleeves during the bonding process, which can easily lead to water ingress and moisture in the riser sleeves during the coating stage and even fall off during transportation. This not only increases the difficulty of the process but also causes defects in the casting. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a lost foam casting process for a lightweight ductile iron planetary carrier, so as to solve the technical problem that the lost foam casting process in the existing technology has large casting defects when applied to a lightweight ductile iron planetary carrier.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A lightweight ductile iron planetary carrier lost foam production process, the method using a special lost foam riser holder to bond the heating riser sleeve on the model cluster;

[0009] This method sets a heat-conducting cold iron in a small area of ​​the model cluster.

[0010] The present invention also has the following technical features:

[0011] The special riser support for lost foam comprises a riser neck, a riser support platform coaxially arranged on the riser neck, and an upper cover plate coaxially arranged on the riser support platform. The joints between the riser support platform and the upper cover plate are circumferentially wrapped and bonded by paper tape.

[0012] The narrow area includes a deep and narrow weight-reducing groove.

[0013] The method comprises the following steps:

[0014] Step 1: White mold preparation:

[0015] The pre-foamed styrene-methyl methacrylate copolymer is added into the mold processed according to the parts to produce a casting white mold that meets the technical requirements of the drawing.

[0016] Its characteristics are:

[0017] Step 2: White mold bonding:

[0018] The multi-piece casting white mold is assembled, and the pouring system and the exothermic riser sleeve are bonded to the lost foam special riser support to form a model cluster.

[0019] Step 3: Dip coating:

[0020] The model cluster bonded in step 2 is dipped in a special coating for lost foam ductile iron and then dried. The model cluster is dipped in a special coating for lost foam ductile iron again and then dried.

[0021] Step 4: Pre-fill the narrow area with sand and set up heat-conducting cold irons:

[0022] Fill the narrow area of ​​the model cluster with resin sand, and after the resin sand is compacted, insert a heat-conducting cold iron in the middle, and dry the model cluster in a drying room.

[0023] Step 5: Set the heating riser sleeve:

[0024] Remove the upper cover plate of the special riser support for lost foam, adhere the heating riser sleeve to the riser support platform of the special riser support for lost foam, and wrap the white area at the joint between the riser support platform and the heating riser sleeve with refractory tape.

[0025] Step 6: Packing and shaping:

[0026] Put the model cluster with bonded heating riser sleeve and heat-conducting cold iron into the sand mold for molding, add sand, cover with plastic film through vibration, cover the film with surface sand again, and finally install high-temperature resistant cast iron pouring cup on the sprue of the pouring system.

[0027] Step 7: Melting and Casting:

[0028] Use medium frequency furnace to melt ductile iron according to grade, transfer and pour after inoculation and spheroidization; cast under negative pressure, maintain pressure under negative pressure after casting, cool in the sand box and then take out of the box.

[0029] Compared with the prior art, the present invention has the following technical effects:

[0030] (I) The present invention uses a method of using heat-conducting cold iron to avoid iron seepage in a narrow area, which can solve the problems of the lost foam using a heating riser sleeve during the coating process causing moisture and the problem of collision and falling during transportation.

[0031] (II) The heat-conducting cold iron method adopted in the present invention can completely solve the occurrence of iron seepage defects in deep and narrow weight-reducing grooves; the lost foam uses a heating riser sleeve process method to solve the shrinkage defects of castings and the porosity defects caused by moisture in subsequent processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a structural diagram of the riser support specifically for lost foam.

[0033] Figure 2 Schematic diagram of the heat conduction cold iron process.

[0034] Figure 3 Schematic diagram of the heating riser sleeve process.

[0035] Figure 4 Schematic diagram of the bonding process.

[0036] Figure 5 Schematic diagram of the heat-conducting cold iron and heat-generating cap process.

[0037] Figure 6 This is a real surface photo of the planet carrier in the application example.

[0038] Figure 7 This is a metallographic photograph of the planet carrier casting in the application example.

[0039] Figure 8 This is a slice photo of the planet carrier casting in the application example.

[0040] Figure 9 This is a photo of the iron-infiltrated waste product in the weight-reducing groove of the planetary carrier casting in Comparative Example 1.

[0041] Figure 10 This is a photo of the internal shrinkage cavity waste of the planetary carrier casting in Comparative Example 2.

[0042] Figure 11 This is a photo of the planetary carrier casting in Comparative Example 3 with a fallen riser and surface pores.

[0043] The meanings of the numbers in the figure are: 1-casting white mold, 2-heating riser sleeve, 3-exposed foam riser support, 4-resin sand, 5-heat-conducting chiller, 6-refractory tape, 7-pouring system, 8-high-temperature resistant cast iron pouring cup.

[0044] 301- riser neck, 302- riser support, 303- upper cover plate, 304- paper tape.

[0045] 701-sprue, 702-foam ceramic filter, 703-runner, 704-introductory runner.

[0046] The specific contents of the present invention are further explained in detail below with reference to the embodiments. DETAILED DESCRIPTION

[0047] It should be noted that, unless otherwise specified, all components, devices and methods in the present invention are components, devices and methods known in the prior art.

[0048] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0049] Example:

[0050] This embodiment provides a lost foam production process for a lightweight ductile iron planetary carrier, the method comprising the following steps:

[0051] Step 1: White mold preparation:

[0052] The pre-foamed styrene-methyl methacrylate copolymer is added into the mold processed according to the parts to produce a casting white mold 1 that meets the technical requirements of the drawing.

[0053] In this embodiment, the styrene-methyl methacrylate copolymer is a commonly used styrene-methyl methacrylate copolymer known in the art.

[0054] Specifically, in step 1, a styrene-methyl methacrylate copolymer that has been pre-expanded and matured and has a bulk density of (16-18) g / L is filled into a planetary carrier lost foam mold, and a white mold that meets the requirements of the drawing is formed under steam pressure of (0.01-0.10) MPa and temperature of (85-100)° C., and then matured at room temperature for more than 10 days.

[0055] Step 2: White mold bonding:

[0056] like Figure 4 As shown, multiple pieces of casting white molds 1 are assembled, and the pouring system 7 and the exothermic riser sleeve 2 are bonded to the lost foam special riser support 3 to form a model cluster.

[0057] like Figure 1 As shown, the riser support 3 for lost foam includes a riser neck 301, a riser support platform 302 coaxially arranged on the riser neck 301, and an upper cover plate 303 coaxially arranged on the riser support platform 302. The joint between the riser support platform 302 and the upper cover plate 303 is circumferentially wrapped and bonded by paper tape 304.

[0058] In this embodiment, the purpose of the dedicated riser support 3 for lost foam is to ensure the dryness of the riser during the white area coating process, to facilitate the transportation of the model cluster, and to facilitate the removal of the surface coating to achieve the installation of the heating riser sleeve before the molding process.

[0059] In this embodiment, the white area coating process is a commonly used white area coating process known in the art.

[0060] In this embodiment, the pouring system 7 adopts a pouring system commonly known in the art. Figure 4 As shown, the pouring system 7 includes a sprue 701 with a foam ceramic filter 702 . The bottom of the sprue 701 is connected to a runner 703 , and the runner 703 is connected to an ingrate 704 .

[0061] Step 3: Dip coating:

[0062] The model cluster bonded in step 2 is dipped in a special coating for lost foam ductile iron and then dried. The model cluster is dipped in a special coating for lost foam ductile iron again and then dried.

[0063] In this embodiment, the coating for lost foam ductile iron is a coating for lost foam ductile iron known in the art.

[0064] Specifically, in this embodiment, the model cluster bonded in step 2 is dip-coated with a special coating for ductile iron with a Baume degree of 65±2, and then dried for more than 6 hours; the model cluster is again dip-coated with a special coating for ductile iron with a Baume degree of 70±2, and then dried for more than 6 hours.

[0065] Step 4: Pre-fill the narrow area with sand and set up heat-conducting cold irons:

[0066] like Figure 2 and Figure 5 As shown, resin sand 4 is filled in the narrow area of ​​the model cluster, and after the resin sand 4 is compacted, a heat-conducting cold iron 5 is inserted in the middle, and the model cluster is dried in a drying room.

[0067] Confined areas include deep, narrow weight-reducing slots.

[0068] In this embodiment, the resin sand 4 adopts commonly used resin sand known in the art.

[0069] Specifically, in this embodiment, resin sand 4 with a particle size of 70-100 mesh is prepared, and the resin sand 4 is filled into the narrow structure of the dried model cluster and compacted; a prepared steel heat-conducting chiller 5 is inserted into the middle of the filled resin sand 4; then, it is dried for more than 4 hours, and then the surface is covered with a special coating for lost foam ductile iron.

[0070] Step 5: Set the heating riser sleeve:

[0071] like Figure 3 and Figure 5 As shown, the upper cover plate 303 on the upper part of the special riser support 3 for lost foam is removed, and the heating riser sleeve 2 is bonded to the riser support platform 302 of the special riser support 3 for lost foam before the black area molding process, and the refractory tape 6 is wrapped around the white area at the joint between the riser support platform 302 and the heating riser sleeve 2.

[0072] In this embodiment, the fire-resistant tape 6 is wrapped with two or more layers.

[0073] In this embodiment, the black area shaping process is a commonly used black area shaping process known in the art.

[0074] Step 6: Packing and shaping:

[0075] The model cluster with the bonded heating riser sleeve 2 and the heat-conducting cold iron 5 is placed in the sand mold for molding, sand is added, and the plastic film is covered with vibration, and the film is covered with surface sand again. Finally, the high-temperature resistant cast iron pouring cup 8 is installed on the sprue 701 of the pouring system 7.

[0076] In this embodiment, after adding sand and vibrating until the distance from the top of the sand box is 50 mm, the plastic film is covered.

[0077] Step 7: Melting and Casting:

[0078] Use medium frequency furnace to melt ductile iron according to grade, transfer and pour after inoculation and spheroidization; cast under negative pressure, maintain pressure under negative pressure after casting, cool in the sand box and then take out of the box.

[0079] In this embodiment, the casting is carried out under a negative pressure in the range of (-0.04 to -0.07) MPa; the pressure is maintained at a negative pressure in the range of (-0.02 to -0.06) MPa for more than 12 minutes, and the sintered articles are cooled in the sand box for 4 hours before being taken out of the sand box.

[0080] Application examples:

[0081] This example provides a lost foam production process for a lightweight ductile iron planetary carrier based on the above embodiment. The lightweight ductile iron planetary carrier is a lightweight QT600-3 planetary carrier for a tractor. The method includes the following steps:

[0082] Step 1: White mold preparation:

[0083] In this application example, the styrene-methyl methacrylate copolymer with a bulk density of 17 g / L is filled into the planet carrier lost foam mold, and then the white mold meeting the drawing requirements is formed under the conditions of steam pressure 0.05 MPa and temperature 95℃, and then the white mold is cured at room temperature for 15 days.

[0084] Step two, white mold bonding:

[0085] The white mold 1 is assembled, the pouring system 7 and the lost foam special riser holder 3 of the heating riser sleeve 2 are bonded, and the model cluster is formed.

[0086] Step three, coating layer:

[0087] In this application example, the model cluster bonded in step two is coated with a special coating for nodular iron with a Bome degree of 66, and then baked for 6 hours; the model cluster is again coated with a special coating for nodular iron with a Bome degree of 71, and then baked for 6 hours.

[0088] Step four, pre-fill sand in narrow area and set up heat-conducting chill:

[0089] In this application example, resin sand 4 with a particle size of 80 mesh is prepared, the resin sand 4 is filled into the narrow structure of the baked model cluster and compacted; a steel heat-conducting chill 5 with a length of 150 mm and a diameter of 5 mm is inserted into the filled resin sand 4; and then baked for 4 hours.

[0090] Step five, set up heating riser sleeve:

[0091] The upper cover plate 303 of the lost foam special riser holder 3 is removed, the heating riser sleeve 2 is bonded to the riser holder table 302 of the lost foam special riser holder 3 before the black area modeling process, and three layers of refractory tape 6 are wound around the joint between the riser holder table 302 and the heating riser sleeve 2.

[0092] Step six, box molding:

[0093] The model cluster with the heating riser sleeve 2 and the heat-conducting chill 5 is placed into the sand mold for molding, sand is added and vibrated to a distance of 50 mm from the top of the sand box, plastic film is covered, sand is again covered on the film, and finally a high-temperature-resistant cast iron pouring cup 8 is installed on the sprue 701 of the pouring system 7.

[0094] Step seven, smelting and casting:

[0095] QT600-3 ductile iron was smelted in a medium-frequency furnace according to the ingredient list. Spheroidization was performed using rare earth magnesium silicon cored wire using a wire-feed spheroidization process. Subsequently, inoculation was performed using a silicon-barium inoculant with an average particle size of 15mm. The iron was then transferred to the casting line for pouring. Casting was performed within a pressure range of -0.05MPa. After casting, the pressure was maintained at -0.04MPa for 15 minutes. The iron was then cooled in the flask for 5 hours before being removed from the flask.

[0096] After testing, the planet carrier castings produced by the lost foam casting process have no iron seepage in the weight reduction grooves. Figure 6 As shown in the figure, the surface quality meets the requirements of the drawing. Figure 7 As shown, the metallographic structure meets the standard requirements. The mechanical properties of the test are tensile strength 654MPa, yield strength 423MPa, and elongation 9%. The casting slice test, such as Figure 8 As shown, there are no shrinkage defects inside the casting, which meets the design requirements.

[0097] Comparative Example 1:

[0098] This comparative example describes a lost-foam production process for a lightweight ductile iron planetary carrier. This method differs from the method in the application example only in that the deep, narrow weight-reducing grooves in this comparative example are not equipped with heat-conducting chillers 5. The trial production results of this comparative example, based on the casting's appearance and internal quality, are shown in Table 1.

[0099] Comparative Example 2:

[0100] This comparative example describes a lost-foam production process for lightweight ductile iron planetary carriers. This method differs only from the method used in the application example in that EPS (Expandable Polystyrene) is used to create the riser. The riser measures 120 x 140 mm and features a V-notch at the top, which is then bonded directly to the surface during the bonding process. The trial production results of this comparative example, based on the casting's appearance and internal quality, are shown in Table 1.

[0101] Comparative Example 3:

[0102] This comparative example describes a lost-foam production process for a lightweight ductile iron planetary carrier. This method differs from the method in the application example only in that the exothermic riser sleeve 2 is bonded to the riser seat during the bonding process. The trial production results of this comparative example, based on the casting's appearance and internal quality, are shown in Table 1.

[0103] Table 1 Application examples and trial production results of comparative examples 1 to 3

[0104] Trial production quantity / piece Number of scraps / piece Causes of scrap Attached picture of waste products Application Examples 48 1 Surface damage — Comparative Example 1 58 35 Iron infiltration in weight loss tank Figure 9 Comparative Example 2 3 3 Internal shrinkage Figure 10 Comparative Example 3 12 8 Riser drop, surface pores Figure 11

[0105] From the trial production comparison in Table 1, it can be seen that if the heat-conducting cold iron 5 is not used, more than 60% of iron infiltration defects will occur; if ordinary EPS risers are used, liquid shrinkage compensation for the casting cannot be completed, resulting in shrinkage defects in the casting; the heating riser sleeve 2 is directly bonded in the bonding process, which will cause the riser sleeve to fall off in the subsequent process and the coating process to be affected by moisture, resulting in porosity defects in the casting.

[0106] The trial production comparison in Table 1 proves that the heat-conducting cold iron method 5 can completely solve the occurrence of iron seepage defects in deep and narrow weight loss grooves; the lost foam method uses a heating riser sleeve process to solve the shrinkage defect of the casting and the porosity defect caused by moisture in subsequent processes.

Claims

1. A lightweight ductile iron planetary carrier lost foam production process, characterized in that: The method adopts a special riser support (3) for lost foam to bond a heating riser sleeve (2) on a model cluster; The method sets a heat-conducting cold iron (5) in a narrow area of ​​the model cluster.

2. The lost foam production process for a lightweight ductile iron planetary carrier according to claim 1, characterized in that: The dedicated riser support (3) for lost foam foam comprises a riser neck (301), a riser support platform (302) coaxially arranged on the riser neck (301), and an upper cover plate (303) coaxially arranged on the riser support platform (302). The joint between the riser support platform (302) and the upper cover plate (303) is circumferentially wrapped and bonded by a paper tape (304).

3. The lost foam production process for a lightweight ductile iron planetary carrier according to claim 1, characterized in that: The narrow area includes a deep and narrow weight-reducing groove.

4. The lost foam production process for a lightweight ductile iron planetary carrier according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: White mold preparation: Adding pre-foamed styrene-methyl methacrylate copolymer into a mold processed according to the parts to produce a casting white mold (1) that meets the technical requirements of the drawing; Its characteristics are: Step 2: White mold bonding: Assembling multiple pieces of casting white molds (1), gating a pouring system (7) and a dedicated riser support (3) for lost foam of a heating riser sleeve (2) to form a model cluster; Step 3: Dip coating: The model cluster bonded in step 2 is dipped in a special coating for lost foam ductile iron, and then dried; the model cluster is dipped in a special coating for lost foam ductile iron again, and then dried; Step 4: Pre-fill the narrow area with sand and set up heat-conducting cold irons: Filling resin sand (4) in a narrow area of ​​the model cluster, and inserting a heat-conducting cold iron (5) in the middle after the resin sand (4) is compacted, and drying the model cluster in a drying room; Step 5: Set the heating riser sleeve: Remove the upper cover plate (303) on the upper part of the dedicated riser support (3) for lost foam, adhere the heating riser sleeve (2) to the riser support platform (302) of the dedicated riser support (3) for lost foam, and wrap the refractory tape (6) around the exposed white area at the joint between the riser support platform (302) and the heating riser sleeve (2); Step 6: Packing and shaping: The model cluster with the bonded heating riser sleeve (2) and the heat-conducting cold iron (5) is placed in a sand mold for molding, sand is added, and the plastic film is covered with vibration, and the film is covered with surface sand again, and finally a high-temperature resistant cast iron pouring cup (8) is installed on the sprue (701) of the pouring system (7); Step 7: Melting and Casting: Use medium frequency furnace to melt ductile iron according to grade, transfer and pour after inoculation and spheroidization; cast under negative pressure, maintain pressure under negative pressure after casting, cool in the sand box and then take out of the box.

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