Preparation method of cast-rolling-pushing composite molded thick-wall high-performance elbow

Abstract

The invention discloses a preparation method of a cast-rolling-pushing composite molded thick-wall high-performance elbow. The preparation method is simple, convenient and efficient in process, suitable for planned mass production of thick-wall elbows, low in cost and stable in quality. According to the method, (1) an intermediate-frequency smelting furnace is firstly adopted for smelting and tempering alloy to obtain alloy melt, and then refining is performed through furnace bottom argon blowing, so that the alloy can be better refined, and the quality and the stability of the final elbow are improved; and (2) the steel wire roller brush rotates to polish and clean the inside and the outside of the pipe blank at high temperature (such as about 700 DEG C), so that impurities and dross thereof are efficiently removed. And (3) the residual temperature (about 600 DEG C) of the thick-wall cast pipe blank is utilized, the pipe blank with residual heat is repeatedly and axially rolled, and the inner diameter and the outer diameter of the pipe blank are synchronously enlarged while the thickness of the pipe wall is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of elbow processing, and in particular to a method for preparing a thick-walled high-performance elbow formed by composite casting, rolling and pushing. Background Art

[0002] In the pipeline system, the elbow is a pipe fitting that changes the direction of the pipeline. It is the largest fitting in the pipeline system and is a core component in the pipeline equipment. Among them, thick-walled high-performance elbows are widely used, mainly used in harsh working conditions such as abrasive wear, corrosive wear, erosion wear, and impact wear. Its excellent wear resistance and toughness make it an indispensable component in the industrial pipeline system. In the current preparation process of thick-walled elbows, seamless thick-walled pipes are used for preparation, but the cost is high; although centrifugal casting pipes are low in cost and have good density, they are prone to segregation during the molding process, resulting in uneven internal structure. Directly pushing elbows is very likely to cause defects such as wrinkles, interlayers, and cracks. The product quality cannot be guaranteed, so it has not been formally applied in industrial production. Therefore, it is very necessary to develop a preparation process for thick-walled high-performance elbows that is stable in quality, efficient and fast, simple in process, and low in cost, and can be planned and mass-produced. Summary of the invention

[0003] Therefore, based on the above background, the present invention provides a method for preparing a thick-walled high-performance elbow by casting, rolling and pushing composite forming, which can be suitable for planned mass production of thick-walled elbows, with simple process, high efficiency, low cost and stable quality.

[0004] The technical solution of the present invention is:

[0005] A method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing composite forming comprises the following steps:

[0006] S1: Alloy melting

[0007] S2: Centrifugal casting

[0008] Centrifugally casting the molten alloy melted in step S1 into a tubular thick-walled cast pipe blank;

[0009] S3: Horizontal rolling

[0010] The thick-walled cast pipe blank of step S2 is placed in a horizontal long-axis rolling ring expansion device, and the rolling roller and the axis roller interact with each other. When the cast pipe blank is rotated, the rolling roller is repeatedly rolled to reduce the wall thickness of the pipe and expand the inner and outer diameters of the pipe blank synchronously, so as to prepare a rolled thick-walled pipe blank;

[0011] S4: Pipe end ring cutting

[0012] Cutting the rolled thick-walled tube into hot-pushed thick-walled tubes of a certain length, wherein both end surfaces of the hot-pushed thick-walled tube are flush and perpendicular to the axial direction of the tube;

[0013] S5: Heating push

[0014] The hot-pushed thick-walled tube blank in the heat step S4 is passed through an elbow-pushing machine with a profile heating device, and is expanded, bent, sized, and shaped in sequence along a mandrel under a constant temperature condition, and finally falls off from the mandrel, thereby preparing a thick-walled elbow blank;

[0015] S6: Surface finishing

[0016] The thick-wall elbow blank obtained in step S5 is subjected to shot blasting, and its surface is micro-shaped and ground;

[0017] S7: Groove treatment

[0018] The end of the thick-walled elbow blank trimmed in step S6 is subjected to groove processing to prepare a thick-walled elbow.

[0019] Furthermore, in step S3, before the thick-walled cast pipe blank is horizontally rolled, the thick-walled cast pipe blank still at high temperature after demoulding needs to be cleaned.

[0020] Furthermore, the thick-walled cast pipe blank is cleaned and polished by rotating wire roller brushes inside and outside.

[0021] Furthermore, after the heating and pushing in step S5, the thick-wall elbow blank needs to be solution treated before surface finishing.

[0022] Further, the operation of the solution treatment is specifically as follows:

[0023] The thick-walled elbow obtained in step S5 is heated, immersed in water and then subjected to solution treatment.

[0024] Furthermore, the operation of alloy smelting in step S1 is specifically as follows:

[0025] First, a medium frequency melting furnace is used to melt and temper the alloy, and slag is removed to obtain a molten alloy; then the molten alloy is poured into an argon blowing refining and insulation furnace, and argon is blown at the bottom of the furnace to refine the molten alloy while maintaining a certain temperature; the bottom of the refining and insulation furnace is provided with a gas supply system and a gas diffuser, and the gas supply system introduces argon gas into the molten alloy through the gas diffuser.

[0026] Furthermore, the thickness of the thick-walled elbow prepared in step S7 is 20-80 mm.

[0027] The above technical solution has the following beneficial effects:

[0028] The process of the invention is simple and efficient, can be applied to planned mass production of thick-wall elbows, has low cost and stable quality.

[0029] ① In the alloy smelting step, the present invention first adopts a medium frequency smelting furnace to smelt and temper the alloy to obtain an alloy melt, and then refines it by blowing argon from the furnace bottom;

[0030] Especially when refining is carried out by blowing argon from the furnace bottom, that is, the argon gas is introduced into the alloy liquid through the gas diffuser at the bottom of the furnace, which will cause small and dense argon bubbles to float from the bottom of the alloy liquid to the top, and at the same time bring O, N, H and inclusions out of the alloy liquid surface, so as to better refine the alloy and improve the quality and stability of the final elbow.

[0031] ② The present invention utilizes the rotation of a wire roller brush to achieve grinding and cleaning of the inside and outside of a tube blank at a high temperature (eg, about 700° C.) to efficiently remove impurities and scum.

[0032] ③ The present invention utilizes the residual temperature (about 600°C) of the thick-walled cast tube blank. The present invention repeatedly axially rolls the tube blank with residual heat to reduce the wall thickness of the tube and simultaneously expand the inner and outer diameters of the tube blank;

[0033] Compared with traditional seamless steel pipes as elbow raw materials, the processing of seamless steel pipes requires multiple steps such as steel billet pipe threading, top expansion, forging and pressing. The present invention simplifies the raw material preparation process, uses centrifugal cast pipes to replace seamless steel pipe raw materials, and obtains cast and forged pipe billets with the same material and detailed performance as seamless steel pipe raw materials through a simple rolling process, thereby reducing production costs and improving production efficiency.

[0034] ④ The present invention utilizes the double-ring cutters of the ring rolling and expanding device to simultaneously vertically cut the tube blank, thereby achieving cutting at high temperature with high efficiency. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with its embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The technical solution of the present invention:

[0037] A method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing composite forming comprises the following steps:

[0038] S1: Alloy melting

[0039] In this step, the alloy is first smelted and tempered in a medium frequency smelting furnace, and a slag removal agent is added to remove the slag, and the slag is removed to obtain a molten alloy; then the molten alloy is poured into an argon blowing refining and insulation furnace, and argon is blown at the bottom of the furnace to keep the alloy liquid refined at a certain temperature;

[0040] The furnace bottom of the refining and holding furnace is provided with a gas supply system and a gas diffuser, and the gas supply system introduces argon gas into the alloy liquid through the gas diffuser.

[0041] In this step, the present invention first adopts a medium frequency melting furnace to melt and temper the alloy to obtain a molten alloy, and then refines it by blowing argon from the furnace bottom; in particular, when refining by blowing argon from the furnace bottom, that is, argon is introduced into the alloy liquid through a gas diffuser at the bottom of the furnace, small and dense argon bubbles will float from the bottom of the alloy liquid to the top, and at the same time, O, N, H and inclusions will be taken out of the alloy liquid surface, so as to better refine the alloy and improve the quality and stability of the final elbow.

[0042] Although the traditional argon blowing in the ladle can achieve alloy refining, the alloy liquid cools down too quickly during the argon blowing refining process, and it is difficult to keep the argon blowing at a constant temperature for a long time, which will affect the refining effect of the alloy. The present invention introduces argon into the alloy liquid from the bottom of the furnace, which can achieve long-term constant temperature introduction of argon and better refine the alloy liquid.

[0043] S2: Centrifugal casting

[0044] The alloy liquid refined in step S1 is metered and injected into a centrifugal casting machine tube mold under a heat preservation state, and cast into a tubular thick-walled cast tube blank under the action of centrifugal force;

[0045] S3: Horizontal rolling

[0046] The thick-walled cast pipe blank of step S2 is placed in a horizontal long-axis rolling ring expansion device, and the rolling roller of the rolling ring device is started. The rolling roller and the axis roller interact with each other, and the thickness, diameter and length of the cast pipe blank are changed by repeated rolling of the rolling roller when the cast pipe blank rotates. While the wall thickness of the pipe is reduced, the inner and outer diameters of the pipe blank are expanded synchronously, so as to prepare a rolled thick-walled pipe blank;

[0047] During centrifugal casting of thick-walled cast pipe blanks, a layer of refractory coating of a certain thickness needs to be applied on the inner wall of the pipe mold as a demoulding agent. At the same time, the inner wall of the pipe blank will carry a certain amount of slag and other debris during the centrifugal forming process. Therefore, in this step, before horizontally rolling the thick-walled cast pipe blanks, the thick-walled cast pipe blanks that are still at high temperature after demoulding need to be cleaned.

[0048] Specifically, the steel wire roller brush inside and outside the thick-walled cast pipe blank is used for rotating cleaning and polishing to remove the surface coating and the debris and scum such as the slag inclusion on the inner wall. After the thick-walled cast pipe blank after centrifugal casting is demoulded, the temperature is still relatively high, which can be as high as 700°C. At present, there is no mature technology for cleaning the inside and outside of the cast pipe at high temperature. However, the present invention can use a steel wire roller brush at a high temperature of 700°C to clean the inside and outside of the cast pipe blank.

[0049] After cleaning, the crystallization of the cast tube billet has been completed, but it still maintains a relatively high residual temperature, which can be as high as 600°C. Although the centrifugal cast tube material has good density, it still has structural segregation and uneven material, which cannot meet the material requirements of direct hot push processing. Therefore, in this step, the axial line rolling process is adopted to repeatedly roll the tube billet with residual heat in the axial direction, while reducing the wall thickness of the tube, the inner and outer diameters of the tube billet are expanded synchronously.

[0050] In actual application, when the temperature of the tube billet drops too quickly, the flame blowing heating device supporting the rolling device is started to keep the tube billet within the temperature parameter range set by the rolling process (800-900°C) to ensure the rolling effect and production efficiency.

[0051] Compared with the traditional seamless steel pipe as elbow raw material, the processing of seamless steel pipe requires multiple processes such as steel billet pipe threading, top expansion, forging, etc. The present invention simplifies the raw material preparation process, uses centrifugal casting pipe to replace the seamless steel pipe raw material, and obtains the cast and forged pipe billet with the same material and detailed performance as the seamless steel pipe raw material through a simple rolling process, thereby reducing production costs and improving production efficiency. S4: Pipe end ring cutting

[0052] Cutting the rolled thick-walled tube into hot-pushed thick-walled tubes of a certain length, wherein both end surfaces of the hot-pushed thick-walled tube are flush and perpendicular to the axial direction of the tube;

[0053] The double-ring cutter of the ring rolling and expanding device is used to cut the rolled thick-walled tube. Before cutting, the distance between the double-ring cutters is adjusted, the ring cutter driving device is started, and under the push of the hydraulic system, the ring cutter slowly cuts into the tube and drives the tube to rotate until the ends of the tube are cut vertically, completing the cutting of the tube at high temperature (500℃).

[0054] S5: Heating push

[0055] The hot-pushed thick-walled tube blank of the heat step S4 is passed through an elbow pusher with a profile heating device, and the tube blank is heated to a temperature within the range of 1150 to 1250 degrees Celsius according to its material, and is placed under a constant temperature condition suitable for the material, and is successively expanded, bent, sized, and characterized along the mandrel and finally falls off from the mandrel, so that a thick-walled elbow blank can be prepared;

[0056] For thick-walled elbows made of high alloy steel and stainless steel, the thick-walled elbow blank prepared in this step needs to be solution treated before surface finishing. The operation of the solution treatment is as follows:

[0057] The thick-walled elbow blank obtained in step S5 is heated, immersed in water and then subjected to solution treatment.

[0058] Specifically, the thick-walled elbow blank is sent into a heating furnace for rapid heating to 1150-1250°C. When the process temperature is reached and the temperature inside and outside the pipe is consistent, the elbow is immersed in pure water at room temperature for solution treatment.

[0059] Specifically, thick-walled elbows made of low alloy steel and carbon steel do not require solution treatment.

[0060] S6: Surface finishing

[0061] The thick-wall elbow blank obtained in step S5 is subjected to shot blasting, and its surface is micro-shaped and ground;

[0062] Specifically, the solution treated or push-formed elbow pipe fittings are sent to the shot blasting machine for shot blasting, and the surface is micro-shaped and ground to make the elbow surface look consistent;

[0063] S7: Groove treatment

[0064] The end of the thick-walled elbow blank trimmed in step S6 is subjected to groove processing to prepare a thick-walled elbow.

[0065] Embodiment 1: Next, the present invention is further described by taking the production of a 90° thick-walled 20# steel cast elbow with a diameter of DN300mm, a wall thickness of 25mm, and a bending radius of R=1.5D as an example.

[0066] The preparation steps are as follows:

[0067] 1) Through medium frequency furnace smelting, tempering and refining, the carbon content of the cast tube billet is 0.17-0.23%, the silicon content is 0.17-0.37%, the manganese content is 0.50-0.80%, the sulfur content is <=0.035%, the phosphorus content is <=0.035%, the chromium content is <=0.20%, the nickel content is <=0.30, and the carbon content is about 0.20%, which meets the various parameter standards in GB / T711-2008 and Q / WTB007-2008;

[0068] 2) According to the processing coefficient of 1:1.5 between the outer diameter of the casting tube and the outer diameter of the finished elbow and 2:1 for the wall thickness, the alloy liquid at 1650°C is injected into the metering ladle in front of the centrifugal casting machine and then injected into the centrifugal casting machine after metering. The speed of the centrifuge is controlled at 600-650 rpm, so that the casting tube is formed in the centrifugal casting tube mold with the same length as the finished elbow.

[0069] 3) The tube blank with a casting temperature of 700-800°C is taken out from the tube mold and immediately placed on a cleaning device composed of a wire roller to grind and clean the inner and outer surfaces of the tube blank to obtain a centrifugally cast tube blank with a clean and smooth surface;

[0070] 4) According to the processing coefficient of 1:1.2 between the outer diameter of the cast tube and the outer diameter of the push-pushing pipe and 1:0.7 for the wall thickness, the cleaned tube with a temperature of about 600°C is put on the mandrel on the axial line rolling equipment, and the horizontal roller is driven to roll the tube to roll the wall thickness to 0.7 times of the cast tube. The inner and outer diameters of the tube are simultaneously expanded to 1.2 times the outer diameter of the cast pipe to meet the elbow push pipe parameter requirements. When the temperature of the tube drops too fast during the rolling process, the flame blowing heating device of the rolling device is started to keep the tube in the temperature parameter range of 800-900°C set by the rolling process to ensure the rolling effect and production efficiency.

[0071] 5) After rolling is completed, start the double-ring knife device installed on the ring rolling and reaming device, which is parallel to the tube blank. According to the process requirements (according to the length), the two ends of the rolled tube are cut in an annular manner, and the tube head parts at both ends of the tube blank that are in a free rolling state are cut off, and the middle section is a qualified push-pushing tube.

[0072] 6) The hot-pushed thick-walled tube obtained after hot cutting is installed on an elbow pushing machine equipped with a profiling heating device and locked. The forming mandrel in the pushing device is preheated to a working temperature of 800-900°C by a heating device, and then the tube is pushed to the preheating station to heat the front 1 / 3 of the tube to a pushing temperature of 1150-1250°C. The pushing device is started to allow the tube to complete diameter expansion, bending, sizing, and quality determination along the mandrel under constant temperature conditions and fall off from the mandrel, and finally the forming is completed.

[0073] 7) Surface finishing: After the push-formed thick-wall elbow blank is naturally cooled to room temperature, it is sent to the shot blasting machine for shot blasting. After shot blasting, the surface of the pipe is checked and the surface flaws are micro-shaped and polished to make the surface of the elbow consistent;

[0074] 8) Beveling processing: The end of the thick-walled elbow blank with surface trimming is processed by a beveling machine to complete the processing and preparation of the thick-walled high-performance elbow.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a thick-walled high-performance elbow by casting, rolling and pushing composite forming, characterized in that: The steps include: S1: Alloy melting S2: Centrifugal casting Centrifugally casting the molten alloy melted in step S1 into a tubular thick-walled cast pipe blank; S3: Horizontal rolling The thick-walled cast pipe blank of step S2 is placed in a horizontal long-axis rolling ring expansion device, and the rolling roller and the axis roller interact with each other. When the cast pipe blank is rotated, the rolling roller is repeatedly rolled to reduce the wall thickness of the pipe and expand the inner and outer diameters of the pipe blank synchronously, so as to prepare a rolled thick-walled pipe blank; S4: Pipe end ring cutting Cutting the rolled thick-walled tube into hot-pushed thick-walled tubes of a certain length, wherein both end surfaces of the hot-pushed thick-walled tube are flush and perpendicular to the axial direction of the tube; S5: Heating push The hot-pushed thick-walled tube blank in the heat step S4 is passed through an elbow-pushing machine with a profile heating device, and is expanded, bent, sized, and shaped in sequence along a mandrel under a constant temperature condition, and finally falls off from the mandrel, thereby preparing a thick-walled elbow blank; S6: Surface finishing The thick-wall elbow blank obtained in step S5 is subjected to shot blasting, and its surface is micro-shaped and ground; S7: Groove treatment The end of the thick-walled elbow blank trimmed in step S6 is subjected to groove processing to prepare a thick-walled elbow.

2. The method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing according to claim 1, characterized in that: In step S3, before the thick-walled cast pipe blank is horizontally rolled, the thick-walled cast pipe blank still at high temperature after demoulding needs to be cleaned.

3. The method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing according to claim 2, characterized in that: Use a wire roller brush to rotate and clean the inside and outside of the thick-walled cast pipe.

4. The method for preparing a thick-walled high-performance elbow formed by composite casting, rolling and pushing according to claim 1, characterized in that: After heating and pushing in step S5, the thick-wall elbow blank needs to be solution treated before surface finishing.

5. The method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing according to claim 4 is characterized in that: The specific operation of solution treatment is as follows: The thick-walled elbow blank obtained in step S5 is heated, immersed in water and then subjected to solution treatment.

6. The method for preparing a thick-walled high-performance elbow formed by casting, rolling and pushing according to claim 1, characterized in that: The operation of alloy smelting in step S1 is specifically as follows: First, the alloy is melted and tempered in a medium frequency melting furnace, and slag is removed to obtain a molten alloy; then the molten alloy is poured into an argon blowing refining and holding furnace, and argon is blown at the bottom of the furnace to keep the alloy liquid refined at a certain temperature; The furnace bottom of the refining and holding furnace is provided with a gas supply system and a gas diffuser, and the gas supply system introduces argon gas into the alloy liquid through the gas diffuser.

7. The method for preparing a thick-walled high-performance elbow formed by composite casting, rolling and pushing according to claim 1, characterized in that: The thickness of the thick-walled elbow prepared in step S7 is 20-80 mm.