Casting process of butterfly valve type steel casting

Abstract

The invention belongs to the technical field of casting forming, and particularly relates to a casting process of butterfly valve type steel castings, which comprises the following steps: step 1, adopting a flat pouring mode of horizontally placing a flange; 2, a cylindrical open riser is selected, the diameter of the riser is 80 mm, the height of the riser is 20 mm, the top of the riser is covered with a heat preservation covering agent, and the modulus of the riser is 1.2 times larger than that of a casting; 3, a metal patch is added in the thick inner circle area of the pressure-bearing wall, the thickness of the metal patch is calculated according to the thickness of a lower box flange needing feeding, and after the metal patch is added, the thickness of a feeding channel is larger than 50% of the thickness of the lower box flange; and 4, a heating patch is pre-buried on the outer side of the metal patch, the thickness of the heating patch is one third of that of the metal patch, and the distance between the heating patch and the metal patch is 5 mm during pre-burying. According to the scheme that the metal patch and the heating patch are combined, the number of feeding heads is reduced, so that the purpose of improving the process yield is achieved, and the cutting area and the grinding workload are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of casting forming, and particularly relates to a casting process for steel castings of butterfly valve type. Background Art

[0002] For steel castings of butterfly valve type, the structure has a thick flange at each end and is connected by a pressure-bearing wall thickness in the middle. When designing the casting process, it is necessary to separately consider the feeding of molten metal to the flanges at both ends and the pressure-bearing wall thickness in the middle during the cooling process. A large number of feeding risers are required, the process yield is low, the cutting area is large, and the grinding workload is large.

[0003] When designing the casting process for steel castings of butterfly valve type, it is necessary to separately consider the feeding of molten metal to the flanges at both ends and the pressure-bearing wall thickness in the middle during the cooling process. A large number of feeding risers are required, the process yield is low, the cutting area is large, and the grinding workload is large. Summary of the Invention

[0004] The purpose of the present invention is to provide a casting process for steel castings of butterfly valve type in view of the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A casting process for steel castings of butterfly valve type, including the following steps:

[0006] Step 1, adopt a flat gating method with the flanges placed horizontally;

[0007] Step 2, select a cylindrical open riser, the diameter of the riser is 80 mm, the height is 20 mm, the top is covered with a heat-insulating covering agent, and the riser modulus is more than 1.2 times the modulus of the casting;

[0008] Step 3, add a metal pad in the inner circle area of the pressure-bearing wall thickness. The thickness of the metal pad is calculated according to the thickness of the lower box flange to be fed. After adding the metal pad, the thickness of the feeding channel is more than 50% of the thickness of the lower box flange;

[0009] Step 4, pre-embed a heating pad outside the metal pad. The thickness of the heating pad is one-third of the thickness of the metal pad. When pre-embedding, it is spaced 5 mm from the metal pad, and a refractory fiber felt is filled to buffer the expansion stress;

[0010] Step 5, select a duckbill-shaped ingate to reduce the modulus at the ingate position;

[0011] Step 6, pre-embed M1.5 stainless steel bolts at the positions of the fixed sleeve, chuck and tailstock. Use a positioning tooling to ensure that the perpendicularity of the bolts is ≤ 0.1 mm / m, and the threaded part is wrapped with a high-temperature ceramic fiber sleeve.

[0012] Furthermore, the method of pre-embedding the heating pad outside the metal pad in the above Step 4 is as follows:

[0013] Make a stuffing box at the edge of the metal pad;

[0014] Mix thermite with 5% silica sol to form a heat-generating pad and fill it into the stuffing box;

[0015] After the heat-generating pad hardens and cakes, remove the stuffing box to ensure that the heat-generating pad does not deform and fits seamlessly with the metal pad.

[0016] Furthermore, the stuffing box is formed by splicing two side plates and two bottom positioning plates. A connecting plate is fixedly connected to the side plate, and the connecting plate is connected to the positioning plate through a fixing bolt.

[0017] Furthermore, a number of slots are arranged at equal distances on the side of the side plate in contact with the steel casting. An extension plate is slidably connected in the slot, and a spring connected to the extension plate is arranged in the slot.

[0018] Furthermore, the metal pad adopts a wedge-shaped pad, and its length covers the area to be compensated. The metal pad is arranged inside the hot spot at the junction of the flange and the cylinder body to form a continuous compensation channel.

[0019] Furthermore, when the heat-generating pad is embedded, there is a 5-mm interval from the metal pad, and a refractory fiber felt is filled to buffer the expansion stress.

[0020] Furthermore, the heat-generating pad adopts an aluminothermic heat-generating agent, which is composed of Al powder, Fe3O4 and a binder.

[0021] Compared with the existing technology, the present invention reduces the number of feeding risers by using a combination of metal pads and heat-generating pads, thereby achieving the purpose of improving the process yield rate, reducing the cutting area and grinding workload. Through the design of the spring and the extension plate, it is ensured that the stuffing box fits the surface of the steel casting, which plays a key role in the filling and shape fixation of the heat-generating pad. Description of the Drawings

[0022] Figure 1 is a flowchart of a casting process for a butterfly valve type cast steel part provided by the present invention;

[0023] Figure 2 is a structural schematic diagram of a steel casting in a casting process for a butterfly valve type cast steel part provided by the present invention;

[0024] Figure 3 is a structural schematic diagram of a stuffing box in a casting process for a butterfly valve type cast steel part provided by the present invention;

[0025] Figure 4 is a structural schematic diagram of a side plate in a casting process for a butterfly valve type cast steel part provided by the present invention;

[0026] Figure 5 isFigure 4 Enlarged view at position A in the middle.

[0027] In the figure, 1 is the metal pad, 2 is the exothermic pad, 3 is the stuffing box, 4 is the side plate, 5 is the positioning plate, 6 is the connecting plate, 7 is the fixing bolt, 8 is the slot, 9 is the extension plate, 10 is the spring, 11 is the riser, 12 is the steel casting, and 13 is the gate. Specific implementation method

[0028] The following embodiments are only for illustrative purposes and are not intended to limit the scope of the present invention.

[0029] As Figures 1-5 shown, a casting process for a butterfly valve type steel casting includes the following steps:

[0030] Step 1, adopt a flat pouring method with the flange placed horizontally.

[0031] Step 2, select a cylindrical open riser with a diameter of 80 mm and a height of 120 mm, cover the top with a heat preservation covering agent, and the riser modulus is more than 1.2 times that of the casting modulus.

[0032] Step 3, add a metal pad 1 in the inner circle area of the pressure-bearing wall thickness. The thickness of the metal pad 1 is calculated according to the thickness of the lower box flange that needs to be compensated. After adding the metal pad 1, the thickness of the feeding channel is more than 50% of the thickness of the lower box flange.

[0033] Step 4, embed an exothermic pad 2 outside the metal pad 1. The thickness of the exothermic pad 2 is one-third of that of the metal pad 1. When embedding, leave a 5-mm gap from the metal pad 1, and fill with refractory fiber felt to buffer the expansion stress.

[0034] Step 5, select a duckbill-shaped ingate 13 to reduce the modulus at the position of the gate 13.

[0035] Step 6, embed M1.5 stainless steel bolts at the positions of the fixed sleeve, chuck, and tailstock. Use a positioning tooling to ensure that the bolt verticality ≤ 0.1 mm / m, and wrap the threaded part with a high-temperature ceramic fiber sleeve.

[0036] The flat gating method makes the flow direction of the molten metal in the flange area consistent with the gravity direction, reducing inclusion defects caused by turbulence. The cylindrical riser 11 extends the holding time of the liquid metal through the modulus amplification effect and cooperates with the heat-insulating covering agent to slow down heat dissipation. The metal pad 1 is arranged inside the hot spot at the junction of the flange and the cylinder body, forming a continuous feeding path through geometric thickening, transferring the shrinkage defects during solidification to the pad area. The exothermic pad 2 and the metal pad 1 are arranged at intervals to generate directional heat release, delaying the solidification speed of the outer metal and forming a solidification gradient from inside to outside to avoid the formation of isolated molten pools. The refractory fiber felt is filled in the gap between the exothermic pad and the metal pad to absorb the stress generated by thermal expansion and prevent the steel casting 12 from cracking. The duckbill-shaped ingate 1 reduces the local modulus through cross-sectional shape optimization to balance the solidification sequence between the gating area and other parts. The embedded bolts are insulated from high-temperature oxidation through ceramic fiber sleeves, and the positioning tooling ensures that the vertical accuracy meets the assembly requirements.

[0037] By using the scheme combining the metal pad 1 and the exothermic pad 2, the number of risers 11 is reduced, thereby achieving the purpose of improving the process yield rate and reducing the cutting area and grinding workload.

[0038] Compared with the existing technology, the traditional process needs to arrange multiple risers circumferentially on the flange to cover the feeding blind area. In this scheme, through the combined design of the metal pad and the exothermic pad, the linear feeding is transformed into area feeding, significantly reducing the number of risers. The conventional exothermic agent is directly attached to the surface of the casting, which is easy to cause thermal shock. In this scheme, a buffer layer is formed by arranging at intervals to avoid stress concentration in the mold. The existing bolt embedding process mostly uses manual positioning, and this scheme uses a tooling with a guiding structure to achieve sub-millimeter vertical accuracy control.

[0039] Specifically, the method of embedding the exothermic pad 2 outside the metal pad 1 in step 4 is as follows:

[0040] Make a packing frame 3 at the edge of the metal pad 1;

[0041] Mix the thermite with 5% silica sol to form the exothermic pad 2 and fill it into the packing frame 3;

[0042] After the exothermic pad hardens and cakes, remove the packing frame 3 to ensure that the exothermic pad 2 does not deform and fits seamlessly with the metal pad 1.

[0043] The physical limit of the unhardened exothermic material is carried out through the packing frame 3, maintaining its shape and size during the filling process. The bonding effect of the silica sol makes the thermite particles form a dense block, which has the stability against pouring impact after hardening. When the packing frame is removed, since the exothermic pad has formed a self-supporting structure, it can maintain a close fit with the metal pad, eliminating the gap caused by expansion stress.

[0044] The stuffing box 3 is formed by splicing two side plates 4 and two bottom positioning plates 5. A connecting plate 6 is fixedly connected to the side plate 4. The connecting plate 6 is connected to the positioning plate 5 through a fixing bolt 7. The side plate 4 and the positioning plate 5 form a detachable connection structure through the connecting plate 1. Before the fixing bolt 7 is tightened, the relative positions of the side plate 4 and the positioning plate 5 are allowed to be adjusted. When the fixing bolt 7 is fully locked, a stable rectangular frame is formed. During the aluminothermic agent filling process, when the side plate 4 is subjected to an expansion force, the rigid connection between the connecting plate 6 and the positioning plate 5 can prevent the frame from being distorted and deformed. The grooved structure of the side plate 4 allows the installation of an extension plate to expand the height of the frame to adapt to metal subsidy 1 areas of different sizes.

[0045] A number of grooves 8 are arranged at equal intervals on the side of the side plate 4 in contact with the steel casting. An extension plate 9 is slidably connected in the groove 8. A spring 10 connected to the extension plate 9 is arranged in the groove 8. During the assembly process of the stuffing box, when there is a sunken area on the surface where the side plate 4 contacts the casting, the spring 10 pushes the extension plate 9 to slide outwards to fill the gap in the sunken part; when there is a protrusion on the contact surface, the extension plate 9 is compressed and retracted to avoid rigid collision. And because the surface of the steel casting is a curved surface, this dynamic adjustment mechanism enables the stuffing box 3 to always maintain a surface contact state with the casting surface, eliminating the assembly gap caused by casting deformation. The elastic characteristics of the spring 10 can absorb the thermal expansion difference between the metal subsidy 1 and the heating subsidy 2 under high-temperature working conditions, preventing plastic deformation of the side plate.

[0046] Compared with the prior art, the traditional stuffing box adopts a fixed side plate structure and cannot adapt to the shape deviation of the casting surface, easily forming a filling blind area in the sunken part. This solution realizes the adaptive adjustment of the contact pressure through the combination of a slidable extension plate and an elastic support structure, solving the problem of incomplete cavity filling caused by uneven surfaces.

[0047] The metal subsidy 1 adopts a wedge-shaped subsidy, and the length covers the area to be compensated. The metal subsidy 1 is arranged inside the hot spot at the junction of the flange and the cylinder body to form a continuous compensation channel. During the solidification process of the casting, the thickness gradient of the wedge-shaped subsidy causes a pressure difference when the molten metal flows from the riser to the flange direction, driving the liquid metal to continuously fill the shrinkage gap. The subsidy length covers the entire hot spot area at the junction of the flange and the cylinder body, avoiding shrinkage cavities in local areas due to insufficient compensation. By setting the subsidy inside the high-temperature area of the hot spot and taking advantage of the later solidification time of this area, the compensation period of the riser for the casting is extended. The continuous compensation channel integrates the originally scattered riser compensation paths into a unified network, enabling the liquid metal to flow along a predetermined direction, thereby reducing the number of risers set.

[0048] When the heating patch 2 is embedded, it is spaced 5mm apart from the metal patch 1 and filled with refractory fiber felt to buffer the expansion stress. When the heating patch 2 is arranged outside the metal patch 1, the distance between the two is controlled at 5mm by positioning tooling. This distance reserves a deformation margin for the volume expansion caused by the thermite reaction. The refractory fiber felt filled in the gap is compressed and deformed at high temperature, and the expansion pressure is offset by elastic restoring force. When the heating patch 2 expands due to heat, the pore structure of the fiber felt allows part of the material to move. At the same time, its low thermal conductivity reduces additional heat conduction to the metal patch, avoiding the aggravation of local temperature gradients.

[0049] Compared with the existing technology, in the traditional process, the heating pad and the metal pad 1 are directly attached, resulting in the inability to release the expansion stress at high temperature. This solution uses the combined structure of the spacer and the buffer material to transform the rigid contact into a flexible buffer while maintaining the effectiveness of the shrinkage channel, thereby avoiding the concentrated stress transmission to the casting body.

[0050] The heating subsidy 2 adopts an aluminothermic heating agent, which is a mixture of Al powder, Fe3O4 and a binder. The aluminum powder and ferroferric oxide react with aluminothermic reaction under the trigger of the molten steel temperature to generate aluminum oxide and iron element and release high heat. The heat is transmitted to the adjacent metal subsidy area through radiation, extending the solidification time of the shrinkage feeding channel. The porous structure formed by the binder allows gas diffusion to avoid pore defects in the reaction process. At the same time, its thermal decomposition characteristics match the solidification curve of the casting to ensure continuous heat release in the critical stage of shrinkage feeding. The high-density alumina covering layer generated by the reaction can replace the traditional riser insulation covering agent to form a self-sustaining shrinkage feeding heat field environment.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A casting process for a butterfly valve type cast steel part, characterized in that, The following steps are involved: Step 1: Use the flat pouring method with the flange placed horizontally; Step 2, select a cylindrical open riser with a diameter of 80 mm and a height of 120 mm, cover the top with a thermal insulation covering agent, and the riser modulus is greater than 1.2 times the casting modulus; Step 3, adding a metal subsidy (1) to the inner circle area of the pressure-bearing wall thickness, the thickness of the metal subsidy (1) is calculated according to the thickness of the lower box flange that needs to be compensated, and after adding the metal subsidy (1), the thickness of the compensation channel is greater than 50% of the thickness of the lower box flange; Step 4, pre-embed the heating pad (2) outside the metal pad (1), the thickness of the heating pad (2) is one third of the metal pad (1), and the interval between the heating pad (2) and the metal pad (1) is 5 mm during pre-embedding, and the heating pad (2) is filled with refractory fiber felt to buffer the expansion stress; Step 5, select a duckbill type gate (13) to reduce the modulus of the gate (13) position; Step 6: Pre-embed M1.5 stainless steel bolts at the fixed sleeve, chuck and chuck tail, use positioning tooling to ensure that the verticality of the bolts is ≤0.1mm / m, and wrap the threaded part with a high-temperature ceramic fiber sleeve.

2. The casting process of the butterfly valve type cast steel part according to claim 1, characterized in that, The method of pre-embedding the heating patch (2) outside the metal patch (1) in step 4 is as follows: Making a stuffing frame (3) on the edge of the metal patch (1); Aluminum thermite and 5% silica sol are mixed to form a heating pad (2) and filled into a filling frame (3); After the heating pad is hardened and agglomerated, the filling frame (3) is removed to ensure that the heating pad (2) does not deform and fits seamlessly with the metal pad (1).

3. The casting process of the butterfly valve type cast steel parts according to claim 2, characterized in that, The packing frame (3) is formed by splicing two side plates (4) and two bottom positioning plates (5); a connecting plate (6) is fixedly connected to the side plates (4); and the connecting plate (6) is connected to the positioning plate (5) via fixing bolts (7).

4. The casting process of the butterfly valve type cast steel part according to claim 3, characterized in that, A plurality of slots (8) are arranged at equal intervals on a side of the side plate (4) in contact with the steel casting, an extension plate (9) is slidably connected in the slot (8), and a spring (10) connected to the extension plate (9) is arranged in the slot (8).

5. The casting process of the butterfly valve type cast steel part according to claim 1, characterized in that, The metal patch (1) is a wedge-shaped patch, the length of which covers the area to be compensated. The metal patch (1) is arranged on the inner side of the hot spot where the flange and the cylinder meet, forming a continuous compensation channel.

6. The casting process of the butterfly valve type cast steel part according to claim 1, characterized in that, The heating patch (2) is pre-buried at a distance of 5 mm from the metal patch (1) and is filled with refractory fiber felt to buffer expansion stress.

7. The casting process of the butterfly valve type cast steel part according to claim 1, characterized in that, The heating pad (2) adopts an aluminothermic heating agent, which is a mixture of Al powder, Fe3O4 and a binder.

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