Method for fixing ceramic preform for gravity casting-infiltration

Abstract

The application discloses a ceramic preform exhaust fixing method for gravity casting and infiltrating, and comprises the following steps: preparing a ceramic preform, reserving a positioning hole in the ceramic preform, cutting a hollow bolt in the middle, punching a hole on a wood mold at a position corresponding to the positioning hole of the ceramic preform, pre-burying the hollow bolt into the hole of the wood mold, filling sand in the wood mold, removing the wood mold after the sand core is solidified, fixing the ceramic preform on the sand core through the hollow bolt and a nut, lowering the sand core with the fixed ceramic preform into an outer sand mold, baking the preform and the sand mold to 80-100 DEG C after the mold is closed, pouring metal liquid into a cavity through a pouring gate, infiltrating the metal liquid into the preform to wrap ceramic particles, and obtaining a ceramic metal wear-resistant composite material; the ceramic preform is fixed on the sand core through the hollow bolt, the hollow bolt can introduce gas in the ceramic preform into the sand mold for exhaust, and the prepared ceramic metal wear-resistant composite material has good interface bonding effect.

Description

Technical Field

[0001] This invention belongs to the field of wear-resistant composite material technology, and relates to a method for venting and fixing ceramic preforms used in gravity casting. Background Technology

[0002] Ceramic particle-reinforced metal matrix wear-resistant composites possess characteristics such as toughness, high strength, and wear resistance. Currently, gravity casting infiltration is often used to prepare such wear-resistant composites. First, ceramic particles are made into porous preforms. Then, the preforms are placed in a sand mold and fixed at the wear location. After the metal matrix alloy is melted, it is poured into the sand mold. Through gravity, it is cast into the pores of the preform to encapsulate the preform, and finally, the wear-resistant composite material is obtained.

[0003] The above method can lead to problems such as the metal liquid not penetrating properly and the preform being washed away by the metal liquid when preparing wear-resistant composite materials. The reason for this is that the preform generates a large amount of gas when it comes into contact with the high-temperature metal liquid. The gas cannot be discharged in a short time and fills the gaps between the ceramics, preventing the metal liquid from penetrating. The preform is washed away because it is not firmly fixed or the fixing method loses its strength under the action of the high-temperature metal liquid, causing the preform to shift out of its original position. This will result in the ceramic and metal matrix failing to form a good interfacial bond in the composite material.

[0004] Existing patents describe many methods for preparing ceramic preforms, but few address the methods for venting and fixing the ceramic preforms in sand molds. Chinese invention patent CN110076322A discloses a ceramic-reinforced steel-based wear-resistant composite material and its preparation method, in which the ceramic preform is fixed on the inner surface of the mold, preheated, and vacuumed after mold closing. This patent does not describe the method for fixing the ceramic preform, and venting is done by vacuuming. However, achieving vacuuming in the preparation of wear-resistant composite materials by sand gravity casting is quite difficult in actual production, so it is necessary to seek other more feasible methods. Summary of the Invention

[0005] The purpose of this invention is to provide a method for venting and fixing ceramic preforms for gravity casting, which solves the problem that existing ceramic preforms are difficult to fix and vent in sand molds.

[0006] The technical solution adopted in this invention is a method for venting and fixing ceramic preforms used in gravity casting, comprising the following steps:

[0007] Step 1: Prepare a ceramic preform and leave positioning holes in the ceramic preform;

[0008] Step 2: Cut the hollow bolt with a length of 45mm to 55mm from the middle of the bottom surface, with a cutting depth of 18mm to 25mm;

[0009] Step 3: Place the ceramic preform on the wooden mold, drill holes at the positions corresponding to the pre-drilled positioning holes on the wooden mold and the ceramic preform, embed hollow bolts into the holes in the wooden mold with the bolts extending out of the surface of the wooden mold, fill the wooden mold with sand, remove the wooden mold after the sand core has solidified, and fix the ceramic preform on the sand core with hollow bolts and nuts.

[0010] Step 4: The sand core with the ceramic preform fixed is lowered into the outer sand mold. After the mold is closed, the preform and sand mold are baked to 80-100°C with a liquefied gas gun. Then, the molten metal is poured into the cavity through the sprue. Under the action of gravity, the molten metal penetrates into the preform and encapsulates the ceramic particles to obtain a ceramic-metal wear-resistant composite material.

[0011] In step 1, ceramic particles, binder and metal powder are uniformly mixed and filled into a graphite mold for sintering to prepare a ceramic preform.

[0012] The thickness of the ceramic preform is 12mm to 16mm.

[0013] In step 2, the hollow bolt with a length of 45mm to 55mm is cut from the middle of the bottom surface using wire cutting.

[0014] The diameter of the hollow bolt is 4mm to 8mm, and the diameter of the through hole in the middle of the hollow bolt is 1.5mm to 2.5mm.

[0015] In step 3, after the sand core has solidified, remove the wooden mold, place the ceramic preform on the sand core, pass the hollow bolt through the positioning hole, and finally place the washer and fix it with the nut.

[0016] The hollow bolts, washers, and nuts are made of the same material as the molten metal.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) By pre-reserving positioning holes when preparing ceramic preforms, drilling holes at the positions corresponding to the pre-reserved positioning holes of the wooden mold and the ceramic preforms, embedding hollow bolts into the holes of the wooden mold, with the bolts extending out of the surface of the wooden mold, filling the wooden mold with sand, removing the wooden mold after the sand core has solidified, forming bolt holes in the sand core, and finally fixing the ceramic preforms on the sand core with hollow bolts and nuts, so that the ceramic preforms are fixed in their original positions and do not shift during the casting of molten metal, thus solving the problem of the ceramic preforms being washed away during the casting process;

[0019] (2) Hollow bolts are used, and then wire cutting is used to cut them in the middle. Finally, the hollow bolts and nuts are used to fix the ceramic preform on the sand core. During the casting process, the gas generated in the ceramic preform can be introduced into the sand mold through the holes in the bolts and discharged, so that the molten metal can smoothly penetrate into the pores of the ceramic preform. The prepared ceramic-metal wear-resistant composite material has a good interface bonding effect. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the fixing of the ceramic preform and the sand core;

[0021] Figure 2 It is the macroscopic morphology of the ceramic-metal composite material after gravity casting. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] A method for venting and fixing ceramic preforms used in gravity casting includes the following steps:

[0025] In step 1, ceramic particles, binder and metal powder are uniformly mixed and filled into a graphite mold and sintered to prepare a ceramic preform. Positioning holes are reserved in the ceramic preform, and the thickness of the ceramic preform is 12mm.

[0026] Step 2: Cut the 45mm long hollow bolt from the middle of the bottom surface using wire cutting, with a cutting depth of 20mm; the diameter of the hollow bolt is 4mm, and the diameter of the through hole in the middle of the hollow bolt is 1.5mm, for use in the shaping process;

[0027] Step 3, see Figure 1 During the molding process, the ceramic preform is placed on a wooden mold according to the placement of the preform. Holes are drilled at the positions corresponding to the pre-drilled positioning holes on the wooden mold and the ceramic preform. Hollow bolts are embedded in the holes of the wooden mold, with the bolts extending out of the surface of the wooden mold. Sand is then filled into the wooden mold to fill it completely. After the sand core has solidified, the wooden mold is flipped over and removed. Once the sand core has solidified, the bolts are fixed to the sand core. The ceramic preform is then placed on the sand core, with the positioning holes passing through the hollow bolts. Finally, washers are placed and nuts are used to secure it. In this way, the ceramic preform is firmly fixed in the predetermined position on the sand core and will not shift during the casting process. The hollow bolts also provide excellent venting.

[0028] Step 4: The sand core with the ceramic preform fixed is lowered into the outer sand mold. After the mold is closed, the preform and sand mold are baked to 80°C with a liquefied gas gun. Then, the molten metal is poured into the cavity through the sprue. Under the action of gravity, the molten metal penetrates into the preform and wraps the ceramic particles to obtain a ceramic-metal wear-resistant composite material. The hollow bolts, washers and nuts are made of the same material as the molten metal.

[0029] The microstructure and morphology of the obtained ceramic-metal wear-resistant composite material were observed. Figure 2 The figure shows the macroscopic morphology of the ceramic-metal wear-resistant composite material. As can be seen from the figure, the ceramic particles are encapsulated by the molten metal, forming a good interfacial bond.

[0030] Example 2

[0031] A method for venting and fixing ceramic preforms used in gravity casting includes the following steps:

[0032] In step 1, ceramic particles, binder and metal powder are uniformly mixed and filled into a graphite mold and sintered to prepare a ceramic preform. Positioning holes are reserved in the ceramic preform, and the thickness of the ceramic preform is 16mm.

[0033] Step 2: Cut the 55mm long hollow bolt from the middle of the bottom surface using wire cutting, with a cutting depth of 25mm; the diameter of the hollow bolt is 8mm, and the diameter of the through hole in the middle of the hollow bolt is 2.5mm, for use in the shaping process;

[0034] Step 3: During the molding process, place the ceramic preform on the wooden mold according to the placement of the preform. Drill holes at the positions corresponding to the pre-drilled positioning holes on the wooden mold and ceramic preform. Embed hollow bolts into the holes in the wooden mold, with the bolts extending out of the surface of the wooden mold. Fill the wooden mold with sand to fill it completely. After the sand core has solidified, remove the wooden mold. Once the sand core has solidified, the bolts will be fixed on the sand core. Place the ceramic preform on the sand core, with the positioning holes passing through the hollow bolts. Finally, place the washers and fix it with nuts. In this way, the ceramic preform is firmly fixed in the predetermined position on the sand core and will not shift during the casting process. The hollow bolts also provide excellent venting.

[0035] Step 4: The sand core with the ceramic preform fixed is lowered into the outer sand mold. After the mold is closed, the preform and sand mold are baked to 100°C with a liquefied gas gun. Then, the molten metal is poured into the cavity through the sprue. Under the action of gravity, the molten metal penetrates into the preform and wraps the ceramic particles to obtain a ceramic-metal wear-resistant composite material. The hollow bolts, washers and nuts are made of the same material as the molten metal.

[0036] Example 3

[0037] A method for venting and fixing ceramic preforms used in gravity casting includes the following steps:

[0038] In step 1, ceramic particles, binder and metal powder are uniformly mixed and filled into a graphite mold and sintered to prepare a ceramic preform. Positioning holes are reserved in the ceramic preform, and the thickness of the ceramic preform is 14mm.

[0039] Step 2: Cut the 50mm long hollow bolt from the middle of the bottom surface using wire cutting, with a cutting depth of 18mm; the diameter of the hollow bolt is 6mm, and the diameter of the through hole in the middle of the hollow bolt is 2mm, for use in the shaping process;

[0040] Step 3: During the molding process, place the ceramic preform on the wooden mold according to the placement of the preform. Drill holes at the positions corresponding to the pre-drilled positioning holes on the wooden mold and ceramic preform. Embed hollow bolts into the holes in the wooden mold, with the bolts extending out of the surface of the wooden mold. Fill the wooden mold with sand to fill it completely. After the sand core has solidified, remove the wooden mold. Once the sand core has solidified, the bolts will be fixed on the sand core. Place the ceramic preform on the sand core, with the positioning holes passing through the hollow bolts. Finally, place the washers and fix it with nuts. In this way, the ceramic preform is firmly fixed in the predetermined position on the sand core and will not shift during the casting process. The hollow bolts also provide excellent venting.

[0041] Step 4: The sand core with the ceramic preform fixed is lowered into the outer sand mold. After the mold is closed, the preform and sand mold are baked to 90°C with a liquefied gas gun. Then, the molten metal is poured into the cavity through the sprue. Under the action of gravity, the molten metal penetrates into the preform and wraps the ceramic particles to obtain a ceramic-metal wear-resistant composite material. The hollow bolts, washers and nuts are made of the same material as the molten metal.

Claims

1. A method for venting and fixing ceramic preforms used in gravity casting, characterized in that, Includes the following steps: Step 1: Prepare a ceramic preform and leave positioning holes in the ceramic preform; Step 2: Cut the hollow bolt with a length of 45mm to 55mm from the middle of the bottom surface, with a cutting depth of 18mm to 25mm; Step 3: Place the ceramic preform on the wooden mold, drill holes at the positions corresponding to the positioning holes of the ceramic preform in the wooden mold, embed hollow bolts into the holes in the wooden mold with the bolts extending out of the surface of the wooden mold, fill the wooden mold with sand, remove the wooden mold after the sand core has solidified, and fix the ceramic preform on the sand core with hollow bolts and nuts. Step 4: The sand core with the ceramic preform fixed is lowered into the outer sand mold. After the mold is closed, the preform and sand mold are baked to 80-100°C with a liquefied gas gun. Then, the molten metal is poured into the cavity through the sprue. Under the action of gravity, the molten metal penetrates into the preform and encapsulates the ceramic particles to obtain a ceramic-metal wear-resistant composite material.

2. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 1, characterized in that, In step 1, ceramic particles, binder and metal powder are uniformly mixed and filled into a graphite mold for sintering to prepare a ceramic preform.

3. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 2, characterized in that, The thickness of the ceramic preform is 12mm to 16mm.

4. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 3, characterized in that, In step 2, the hollow bolt with a length of 45mm to 55mm is cut from the middle of the bottom surface using wire cutting.

5. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 1, characterized in that, The hollow bolt has a diameter of 4mm to 8mm, and the through hole in the middle of the hollow bolt has a diameter of 1.5mm to 2.5mm.

6. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 1, characterized in that, In step 3, after the sand core has solidified, the wooden mold is removed, the ceramic preform is placed on the sand core, the positioning hole is passed through the hollow bolt, and finally the washer is placed and fixed with the nut.

7. The method for venting and fixing ceramic preforms for gravity casting and infiltration according to claim 6, characterized in that, The hollow bolts, washers, and nuts are made of the same material as the molten metal.

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