Cooling device suitable for easily oxidized steel casting and method thereof

Abstract

The cooling device comprises a box body and a box cover, a thermal insulation layer is arranged on the inner wall of the box body, a circle of sealing groove is formed in the top end of the box body in the circumferential direction, sealing sand is contained in the sealing groove, the box cover can be inversely buckled on the sealing sand, the box body is provided with an air inlet, and the air inlet is communicated with the box cover. And an air inlet pipe for feeding non-oxidizing atmosphere is arranged at the air inlet. The casting is naturally cooled in an oxygen-free state, and oxidation is effectively prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of investment casting, and in particular relates to a cooling device suitable for easily oxidized steel castings. Background Art

[0002] Investment casting is to use fusible materials (such as wax-based materials) to make a pattern, and then coat the surface of the pattern with several layers of refractory materials to make a shell. Then the pattern is melted and discharged from the shell to obtain a hollow shell. Then the molten metal is poured into the fired shell. After the metal liquid cools and solidifies in the shell, it is cleaned to obtain a precise casting. After the metal liquid is poured, it is maintained at a high temperature. During the solidification process, it is directly in contact with oxygen in the air, and the surface is easily oxidized. Pits and flow lines are formed on the surface of the casting, which affects the appearance quality of the casting. Usually, water immersion and fan fast cooling are used after pouring to accelerate cooling and avoid long-term contact with oxygen.

[0003] According to statistics from the World Steel Association, there are more than 3,500 different types of steel, each with unique physical, chemical and environmental properties. Depending on the performance required by the application, steel can be roughly divided into four categories based on chemical composition: carbon steel, alloy steel, stainless steel and tool steel. Carbon steel is a steel material with a carbon content between 0.12% and 2.0%. Due to its high carbon content, its hardness, strength and wear resistance are very high, so it is widely used in machinery manufacturing, vehicle manufacturing, building materials and other fields. Martensitic steel is a type of stainless steel, which is obtained by quenching and tempering, and has excellent properties such as high hardness, high toughness and high strength. Due to its high cost and difficult manufacturing process, it is mainly used in high-end machinery, aerospace, automobiles and cutting tools. Because the temperature of steel out of the furnace is as high as thousands of degrees, these two types of steel are extremely easy to oxidize, and oxidation will occur when they come into contact with oxygen in the air at high temperatures of thousands of degrees. If traditional water immersion rapid cooling is used, invasive pores are likely to form on the surface, and water immersion cooling is prone to the risk of bursting; if fan rapid cooling is used, it is difficult to achieve uniform cooling, and local high temperature areas will still form pits and flow lines due to oxidation. Summary of the invention

[0004] In order to solve the technical problems in the cooling process of steel castings that are easily oxidized, the present invention provides a cooling device suitable for steel castings that are easily oxidized, so that the castings can be naturally cooled in an oxygen-free state to effectively prevent oxidation.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] A cooling device suitable for easily oxidized steel castings comprises a box body and a box cover, wherein the inner wall of the box body is provided with a thermal insulation layer, the top of the box body is provided with a circle of sealing grooves in the circumference, the sealing grooves are filled with sealing sand, the box cover can be inverted on the sealing sand, the box body is provided with an air inlet, and the air inlet is provided with an air inlet pipe for introducing a non-oxidizing atmosphere.

[0007] The thermal insulation layer of the present invention is a brick layer with a thickness of 60 to 120 mm. The brick layer of this thickness has a good thermal insulation effect and is not difficult to cool because it is too thick.

[0008] The air inlet pipe of the present invention is connected to the air charging pipe inside the box body. The air charging pipe is arranged around the circumference of the box body, and a plurality of air inlet holes are evenly distributed on the air charging pipe to achieve uniform air intake in the device.

[0009] Preferably, the diameter of the air inlet hole is 8-10 mm, which can maintain an optimal air intake speed.

[0010] The non-oxidizing atmosphere of the present invention is at least one of argon, nitrogen, carbon dioxide, helium, neon, krypton and xenon.

[0011] Preferably, the non-oxidizing atmosphere is argon, which is slightly heavier than air and sinks after entering the device, and can quickly squeeze out the air, quickly forming an inert protective atmosphere around the casting.

[0012] The sealing sand of the present invention is at least one of mullite sand, magnesia sand and corundum sand.

[0013] Preferably, the sealing sand is 30-60 mesh Mullite sand, which can best maintain a certain sealing effect and at the same time has tiny gaps to allow air to be quickly discharged.

[0014] The materials of the steel castings of the present invention are carbon steel and martensitic steel, which are the most susceptible to oxidation and will oxidize during natural cooling, and are not suitable for conventional water cooling and fan cooling methods.

[0015] The present invention also provides a cooling method for a cooling device suitable for easily oxidized steel castings. In the initial 2 to 3 minutes, the flow rate of the non-oxidizing atmosphere sent into the device by the air inlet pipe is 15 to 20 L / min; then the flow rate is reduced to 9 to 11 L / min and the non-oxidizing atmosphere is continued to be introduced until the temperature of the casting is cooled to below the critical temperature Ac1 of the material, the casting is taken out, and it continues to be naturally cooled to room temperature.

[0016] The present invention first introduces a non-oxidizing atmosphere into the device at a relatively high flow rate in order to exhaust the air in the device. After the air is completely exhausted, the device is filled with the non-oxidizing atmosphere. Since the device is not completely sealed, the flow rate is reduced and the non-oxidizing atmosphere is continued to be introduced, so that a certain slight positive pressure is maintained in the device and external air cannot enter until the casting temperature is cooled to below the critical temperature Ac1 of the material. At this time, the material is not easily oxidized, and the casting can be taken out and switched to natural cooling. The cooling speed is faster than that in the device, but water cooling or air cooling cannot be used. Oxidation problems still exist under accelerated cooling conditions.

[0017] The beneficial effects of the present invention are:

[0018] 1. Inert gas is filled in from the air inlet pipe. Since there are gaps in the sealing sand layer, it will not be completely sealed. The air in the box is squeezed out from the gaps in the sand layer by the inert gas until the box is filled with inert gas, so that the casting is cooled naturally in an oxygen-free state, effectively preventing oxidation.

[0019] 2. The present invention adopts 30-60 mesh mullite sand for sealing at the box cover, which can not only ensure the discharge of air in the box, but also avoid the large loss of inert gas during the cooling process.

[0020] 3. The present invention adopts argon as the cooling atmosphere. Argon as the cooling medium can achieve air discharge and rapid temperature reduction in a short time. The outer surface of the casting is flat and uniform, ensuring the high quality of the outer surface of the casting.

[0021] 4. Use brick layers to insulate the outer shell of the box to avoid burns to workers caused by excessive outer shell temperature and improve safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a schematic structural diagram of a cooling device suitable for easily oxidized steel castings.

[0023] Figure 2 The present invention is a schematic structural diagram of a cooling device suitable for easily oxidized steel castings.

[0024] Figure 3 This is a distribution diagram of the air inlet holes of the cooling device of the present invention.

[0025] Markings in the figure are: 1. box body, 2. box cover, 3. thermal insulation layer, 4. air inlet pipe, 5. sealing groove, 6. sealing sand, 7. casting hanger, 8. inflation pipe, 81. air inlet hole. DETAILED DESCRIPTION

[0026] In order to more clearly and in detail illustrate the technical solution of the present invention, the present invention is further described below through relevant embodiments. The following embodiments are only for specific explanation of the implementation method of the present invention, and do not limit the protection scope of the present invention.

[0027] Example 1

[0028] A cooling device suitable for easily oxidized steel castings comprises a box body 1 and a box cover 2. A thermal insulation layer 3 is provided in the side wall of the box body 1. A circle of sealing grooves 5 are circumferentially provided at the top of the box body 1. Sealing sand 6 is filled in the sealing grooves 5. The box cover 2 can be inverted on the sealing sand 6. The box body 1 is provided with an air inlet, and an air inlet pipe 4 for introducing a non-oxidizing atmosphere is provided at the air inlet.

[0029] Example 2

[0030] This embodiment is based on embodiment 1:

[0031] The thermal insulation layer 3 is a brick layer with a thickness of 60 mm.

[0032] The air inlet pipe 4 is connected to the air charging pipe 8 inside the box body 1 . The air charging pipe 8 is circumferentially arranged around the box body 1 , and a plurality of air inlet holes 81 are evenly distributed on the air charging pipe 8 .

[0033] The diameter of the air inlet hole 81 is 8 mm.

[0034] Example 3

[0035] This embodiment is based on embodiment 1:

[0036] The thermal insulation layer 3 is a brick layer with a thickness of 120 mm.

[0037] The air inlet pipe 4 is connected to the air charging pipe 8 inside the box body 1 . The air charging pipe 8 is circumferentially arranged around the box body 1 , and a plurality of air inlet holes 81 are evenly distributed on the air charging pipe 8 .

[0038] The diameter of the air inlet hole 81 is 10 mm.

[0039] Example 4

[0040] This embodiment is based on embodiment 1:

[0041] The thermal insulation layer 3 is a brick layer with a thickness of 80 mm.

[0042] The air inlet pipe 4 is connected to the air charging pipe 8 inside the box body 1 . The air charging pipe 8 is circumferentially arranged around the box body 1 , and a plurality of air inlet holes 81 are evenly distributed on the air charging pipe 8 .

[0043] The diameter of the air inlet hole 81 is 9 mm.

[0044] Example 5

[0045] A method for cooling an easily oxidized steel casting, wherein the flow rate of a non-oxidizing atmosphere sent into the device by an air inlet pipe is 15 to 20 L / min for the first 2 to 3 minutes; the flow rate is then reduced to 9 to 11 L / min and the non-oxidizing atmosphere is continued to be introduced until the casting temperature is cooled to below the critical temperature Ac1 of the material, the casting is taken out, and the casting is continued to be naturally cooled to room temperature.

[0046] The present invention uses carbon steel castings just out of the furnace as experimental objects, uses argon, nitrogen, carbon dioxide, helium, neon, krypton and xenon as oxygen-free cooling atmospheres, and uses the device of Example 4 to conduct 7 groups of cooling experiments under the same experimental conditions.

[0047] Experimental method: The initial flow rate of cooling atmosphere sent into the device through the air inlet pipe is 20L / min. After the air in the device is completely discharged, the flow rate is reduced to 10L / min and the cooling atmosphere is continued to be introduced until the casting temperature is cooled to below the critical temperature Ac1 (730℃) of the material. The casting is taken out and continues to be naturally cooled to room temperature.

[0048] Table 1 Cooling test results of different cooling atmospheres

[0049]

[0050]

[0051] As can be seen from the table above, since helium is the lightest gas and takes the longest time to exhaust the air, the casting is in contact with the air for a long time, and obvious pits and flow lines appear on the outer surface. The thermal conductivity of neon, krypton and xenon is too low, and the time to cool to the critical temperature exceeds 1 hour, which has low production efficiency and causes shrinkage defects in the casting, holes on the surface, and may also affect the mechanical properties of the casting. Carbon dioxide is an active gas that easily reacts with metals, affecting the appearance of the casting, and holes and cracks appear on the surface. Nitrogen also undergoes a certain degree of oxidation on the outer surface of the casting because it takes a long time to exhaust the air, resulting in a small amount of pits and flow lines. Only argon can achieve the goal of exhausting air in a short time and rapid cooling, and the outer surface of the casting is flat, uniform, and free of pits, flow lines and holes.

[0052] Based on the above experiments, the present invention further conducted selective experiments on sealing sand using argon as the cooling atmosphere, and compared three different high temperature resistant sands, namely 30-60 mesh mullite sand, magnesia sand and corundum sand. The high temperature resistant sand of this particle size is used because if the particle size is too small, the air exhaust time is too long, and if the particle size is too large, a large amount of atmosphere will escape from the large gap, causing waste.

[0053] Table 2 Cooling test results of different sealing sands

[0054]

[0055] As can be seen from the table above, the time for exhausting air using mullite sand is the shortest and the least affected by oxidation. A small amount of pits and flow lines appeared on the outer surface of the castings using magnesia sand and corundum sand as sealing sand. This may be because mullite sand has a smaller density and exhausts air faster.

[0056] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A cooling device suitable for easily oxidized steel castings, characterized in that: It includes a box body and a box cover. The inner wall of the box body is provided with a thermal insulation layer. The top of the box body is circumferentially provided with a circle of sealing grooves. The sealing grooves are filled with sealing sand. The box cover can be inverted on the sealing sand. The box body is provided with an air inlet. The air inlet is provided with an air inlet pipe for delivering non-oxidizing atmosphere.

2. The cooling device for easily oxidized steel castings according to claim 1, characterized in that: The thermal insulation layer is a brick layer with a thickness of 60 to 120 mm.

3. The cooling device for easily oxidized steel castings according to claim 1, characterized in that: The air inlet pipe is connected to the air charging pipe inside the box body, the air charging pipe is arranged around the circumference of the box body, and a plurality of air inlet holes are evenly distributed on the air charging pipe.

4. The cooling device for easily oxidized steel castings according to claim 3, characterized in that: The diameter of the air inlet hole is 8-10 mm.

5. The cooling device for easily oxidized steel castings according to claim 1, characterized in that: The non-oxidizing atmosphere is at least one of argon, nitrogen, carbon dioxide, helium, neon, krypton and xenon.

6. The cooling device for easily oxidized steel castings according to claim 5, characterized in that: The non-oxidizing atmosphere is argon.

7. The cooling device for easily oxidized steel castings according to claim 1, characterized in that: The sealing sand is at least one of mullite sand, magnesia sand and corundum sand.

8. The cooling device for easily oxidized steel castings according to claim 7, characterized in that: The sealing sand is 30-60 mesh Mullite sand.

9. The cooling device for easily oxidized steel castings according to claim 1, characterized in that: The materials of the steel casting are carbon steel and martensitic steel.

10. The cooling method of the cooling device according to any one of claims 1 to 9, characterized in that: In the initial 2 to 3 minutes, the flow rate of non-oxidizing atmosphere sent into the device through the air inlet pipe is 15 to 20 L / min; then the flow rate is reduced to 9 to 11 L / min and the non-oxidizing atmosphere is continued to be introduced until the temperature of the casting is cooled to below the critical temperature Ac1 of the material, the casting is taken out, and continues to cool naturally to room temperature.

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