A large wind power casting gradient chill solidification control process

Abstract

The present application relates to large wind power equipment casting sand casting technology field, and disclose a kind of large wind power casting gradient chill solidification control process, according to casting structure determines hot section area and riser feeding direction, corresponding hot section area is processed chill groove in sand mould initial blank, chill groove includes strong cooling groove section and slow cooling groove section, unslotted continuous sand body is reserved in slow cooling groove section side close to riser feeding direction, forms feeding sand bridge, feeding sand bridge is not embedded chill, and chill is respectively embedded in strong cooling groove section and slow cooling groove section, and sand backfilling is carried out, so that strong cooling groove section and slow cooling groove section form different sand covering thickness, after sand mould preparation, perform mould closing, pouring and cooling solidification, the present application keeps the continuous sand body in riser feeding direction by feeding sand bridge, and combines the cooling control of strong cooling groove section and slow cooling groove section in different regions, reduce the influence of chill groove on feeding path, reduce the situation that shrinkage and shrinkage hole concentrate on chill edge and structure transition area.

Description

Technical Field

[0001] This invention relates to the field of sand casting technology for large wind power equipment castings, and in particular to a gradient chill solidification control process for large wind power castings. Background Technology

[0002] As wind turbines develop towards larger megawatts, the size, load-bearing capacity, and internal quality requirements of large castings such as hubs, bearing housings, and frames in wind power equipment are constantly increasing. These castings typically have flange connection areas, stiffener root areas, openings, hole group connection areas, and multiple thickness transition structures. During sand casting, the heat dissipation conditions and solidification rates vary significantly in different areas. Hot spots are prone to form in locations such as the annular thick-walled area, stiffener root area, and flange transition area. To reduce shrinkage porosity and shrinkage cavities in hot spot areas, existing processes usually use risers, gating systems, and chills for solidification control. Chips are mainly used to accelerate local heat dissipation and ensure that thick parts solidify in a predetermined direction. Similar requirements for hot spot feeding and shrinkage porosity / shrinkage cavity control also exist for other thick-walled castings with similar thickness transition structures, including some copper alloy thick-walled castings.

[0003] In the existing technology, there are a number of cooling control schemes for large wind turbine castings. For example, patent CN114054672B discloses a casting method for wind turbine bases made of QT500-14 material, which sets chills in the thick parts of the wind turbine base casting and combines riser feeding to reduce shrinkage cavities and porosity defects; patent CN103111606A discloses a forced cooling method for wind turbine castings, which sets a heat exchanger in the sand core and introduces gas to enhance the heat dissipation of the sand core inside the wind turbine casting; patent CN105618675A discloses a casting method for conformal sand-coated chills, which adjusts the casting temperature field by determining the thickness of the sand-coated chill layer and coordinating with the riser action area; in addition, Ge Chunli et al., in their article "Development of Casting Process for QT500-14 Wind Turbine Main Shaft" published in "Foundry", also disclosed the prediction of defect locations through casting simulation and the adoption of process measures such as chills in the corresponding parts.

[0004] However, in actual production, hot spot areas are usually not isolated. When the pre-set riser feeds the hot spot area, the feeding path is often near the root of the stiffener, the flange transition area, or the edge of the hole group, which are areas with varying thicknesses. If the chills are arranged only according to the wall thickness or the location of the hot spot, or if the cooling intensity of the chills is changed only by adjusting the thickness of the sand covering, the area directly opposite the chills may solidify earlier, while the edges of the chills, the roots of the stiffeners, the openings, and the transition areas of the hole group still need to continue feeding. When the chill trough cuts into or occupies the continuous sand body between the riser and the hot spot area, the feeding of the molten metal at that location is affected, and shrinkage porosity and shrinkage cavities are easily transferred from the center of the hot spot to the edge of the chills or the transition area of ​​the adjacent structure. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to avoid cutting off the sand body near the feeding channel between the riser and the hot section area while using chills to cool the hot section area, and reduce the concentration of shrinkage porosity and shrinkage holes towards the edge of the chill, the root of the stiffener, the opening and the transition area of ​​the hole group. To this end, we propose a gradient chill solidification control process for large wind power castings.

[0006] To achieve the above objectives, this application adopts the following technical solution: a gradient chill solidification control process for large wind turbine castings, comprising the following steps: S1: preparing a sand mold blank according to the large wind turbine casting, and determining the hot spot region of the large wind turbine casting and the riser feeding direction corresponding to the hot spot region; S2: machining chill grooves in the sand mold blank corresponding to the hot spot region, the chill grooves including a strong cooling groove section and a slow cooling groove section, the strong cooling groove section being located close to the hot spot region, and the slow cooling groove section being located on the side of the strong cooling groove section away from the hot spot region; S3: retaining ungrooved continuous sand body on the side of the slow cooling groove section close to the feeding path, the ungrooved continuous sand body feeding along the riser feeding direction. S4: Extend and form a shrinkage-compensating sand bridge, without embedding chills in the shrinkage-compensating sand bridge; S5: Embed chills in the strong cooling groove section and the slow cooling groove section respectively, and backfill and compact the molding sand to form a first sand covering thickness between the chills in the strong cooling groove section and the corresponding cavity surface, and form a second sand covering thickness between the chills in the slow cooling groove section and the corresponding cavity surface, and the first sand covering thickness is less than the second sand covering thickness, and the thickness of the continuous sand body at the corresponding position of the shrinkage-compensating sand bridge is greater than the second sand covering thickness; S6: Keep the shrinkage-compensating sand bridge continuous along the riser shrinkage direction, and do not cut off the shrinkage-compensating sand bridge in the chill trough. After completing the embedding of chills and backfilling of molding sand, close the sand mold, pour and cool and solidify.

[0007] Preferably, the large wind turbine casting includes a hub casting, a bearing housing casting, a frame casting, or other wind turbine equipment castings with a thick-thin transition structure. The large wind turbine casting includes a flange connection area, a stiffener root area, an opening, a hole group connection area, and a thick-thin transition area. The hot spot area is determined based on the cavity contour, local design wall thickness, thick-thin transition position, and preset riser position of the large wind turbine casting.

[0008] Preferably, the feeding path is the molten metal connection path corresponding to the pre-set riser replenishing molten metal to the hot spot area, and the feeding sand bridge is located in the sand mold in an area adjacent to the feeding path.

[0009] Preferably, the sand bridge thickness is formed at the corresponding position of the compensation sand bridge. The sand bridge thickness is the minimum continuous sand body thickness between the cavity surface corresponding to the compensation sand bridge and the boundary of the adjacent chilled iron groove, and the sand bridge thickness is greater than the second sand covering thickness.

[0010] Preferably, based on the local design wall thickness T of the casting at the corresponding position, the first sand coating thickness is greater than 0 and not greater than 0.08T, the second sand coating thickness is 0.08T-0.20T, and the sand bridge thickness is not less than 0.20T.

[0011] Preferably, when the local design wall thickness T of the casting is 100mm-300mm, the first sand coating thickness is 3mm-8mm, the second sand coating thickness is 10mm-25mm, and the sand bridge thickness is 30mm-80mm.

[0012] Preferably, the width W of the feeding sand bridge is 0.3T-1.2T, where W is the minimum width of the feeding sand bridge in the direction perpendicular to the riser feeding direction, and T is the local design wall thickness of the casting at the corresponding position of the feeding sand bridge.

[0013] Preferably, the distance between the edge of the chilled iron groove and the edge of the opening, the outer contour of the hole group, the starting position of the fillet at the root of the stiffener, or the boundary of the flange thickness transition zone is not less than 0.3T, where T is the local design wall thickness of the casting at the corresponding position.

[0014] Preferably, the thickness of the chill in the rapid cooling tank section is 0.20T-0.50T, the thickness of the chill in the slow cooling tank section is 0.10T-0.35T, and the thickness of the chill in the rapid cooling tank section is not less than the thickness of the chill in the slow cooling tank section.

[0015] Preferably, the preheating temperature of the chilled iron in the strong cooling tank section is 80℃-180℃, the preheating temperature of the chilled iron in the slow cooling tank section is 150℃-280℃, and the preheating temperature of the chilled iron in the slow cooling tank section is higher than that in the strong cooling tank section.

[0016] The technical effects and advantages of this invention are as follows:

[0017] In this invention, chills channels are machined in the initial sand mold corresponding to the hot spot region, forming a strong cooling channel section near the hot spot region and a slow cooling channel section outside the strong cooling channel section. On the side of the slow cooling channel section near the feeding path, a continuous, ungrooved sand body is retained to form a feeding sand bridge, creating a cooling transition relationship from strong to weak between the hot spot region, the chill edge region, and the feeding path adjacent region. Compared with existing technologies, this invention not only creates chills effects with different sand coating thicknesses through the strong cooling channel section and the slow cooling channel section, but also maintains the continuous sand body state in the feeding path adjacent region through the feeding sand bridge, preventing premature cooling of the feeding path adjacent region due to the chills channel or chill action boundary. Therefore, the hot spot region can obtain necessary cooling, the cooling process of the chill edge and adjacent structural transition region tends to be moderate, and the feeding path adjacent region can maintain a relatively slow cooling state, thereby reducing the transfer of shrinkage porosity and shrinkage cavities to the chill edge region, the root region of the stiffener plate, and the transition region of the opening and hole group, and improving the internal density and solidification control stability of large wind power castings. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 This diagram shows the distribution of shrinkage porosity and shrinkage cavity defects under different process conditions of the present invention, as well as the composition of the number of defects in each region.

[0020] Figure 2 This is a statistical chart showing the total number of defects, the number of defects in the transfer zone, and the proportion of defects in the transfer zone under different process conditions of the present invention;

[0021] Figure 3 This is a comparison graph showing the cooling curves of the adjacent area of ​​the compensation path and the time it takes for the measuring points of the compensation path to drop to the reference temperature in this invention.

[0022] Figure 4 This is a comparison diagram of the number of shrinkage porosity and shrinkage defects in the feeding path and adjacent transition zones of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. The specific embodiments described below are used to illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can make adaptive adjustments to the chill size, chill material, sand coating thickness and shrinkage bridge size according to the specific size of the casting, local wall thickness, riser position and sand mold molding conditions.

[0024] This invention provides a gradient chill solidification control process for large wind turbine castings, which is mainly applicable to sand casting of large wind turbine equipment castings with flange connection area, stiffener root area, opening, hole group connection area and thickness transition area, especially applicable to hub castings, bearing seat castings, frame castings or other wind turbine equipment castings with thickness transition structure.

[0025] During the sand casting process, the wall thickness and heat dissipation conditions of different areas of the above castings are different. Hot spots are easily formed in the flange connection area, the root area of ​​the stiffener plate, and the thick-thin transition area.

[0026] The hot spot region refers to the location in a casting that solidifies later than the surrounding area and is prone to shrinkage porosity or shrinkage cavities.

[0027] The hot spot area can be determined based on the casting cavity profile, local wall thickness design, thickness transition position, riser position, and casting process experience.

[0028] In this invention, the feeding path refers to the connecting path corresponding to the replenishment of molten metal to the hot spot area by the preset riser, and the adjacent area of ​​the feeding path refers to the area in the sand mold that is adjacent to the feeding path.

[0029] A feeding sand bridge refers to an ungrooved continuous sand body retained in a sand mold. The feeding sand bridge is not fitted with chills and remains continuous along the feeding direction of the riser.

[0030] Specifically, the gradient chill solidification control process includes the following steps:

[0031] S1: Prepare a sand mold blank according to the casting structure, and determine the hot spot area and the corresponding riser feeding direction according to the casting cavity outline, local design wall thickness, thickness transition position and preset riser position.

[0032] S2: A chilled iron groove is machined in the sand mold blank corresponding to the hot spot area. The chilled iron groove includes a strong cooling groove section and a slow cooling groove section. The strong cooling groove section is located close to the hot spot area, and the slow cooling groove section is located on the side of the strong cooling groove section away from the hot spot area.

[0033] S3: On the side of the slow cooling tank section near the riser feeding direction, an ungrooved continuous sand body is retained. The ungrooved continuous sand body extends along the riser feeding direction and forms a feeding sand bridge, and the feeding sand bridge is not embedded with chills.

[0034] S4: Chills are embedded in the strong cooling tank section and the slow cooling tank section respectively, and molding sand is backfilled and compacted. In the strong cooling tank section, a first sand covering thickness is formed between the surface of the chill near the cavity and the corresponding cavity surface. In the slow cooling tank section, a second sand covering thickness is formed between the surface of the chill near the cavity and the corresponding cavity surface. The first sand covering thickness is less than the second sand covering thickness. A sand bridge thickness is formed at the corresponding position of the shrinkage sand bridge. The sand bridge thickness is the minimum continuous sand body thickness between the cavity surface corresponding to the shrinkage sand bridge and the boundary of the adjacent chill tank, and the sand bridge thickness is greater than the second sand covering thickness.

[0035] S5: Keep the feeding sand bridge continuous along the feeding direction of the riser, and do not cut the feeding sand bridge in the chill trough. After completing the chill installation, molding sand backfilling and retention of the feeding sand bridge, apply paint to the surface of the sand mold cavity, and then close the mold, pour and cool to solidify.

[0036] The strong cooling channel is located near the hot spot area to enhance the cooling of the hot spot area. The slow cooling channel is located outside the strong cooling channel to reduce the cooling abrupt change at the edge of the chill. The feeding sand bridge retains the ungrooved continuous sand body along the feeding direction of the riser, so that the chill does not cut off the sand body near the feeding channel between the riser and the hot spot area. This can reduce the impact of the chill on the feeding of the riser and reduce the concentration of shrinkage porosity and shrinkage cavities at the edge of the chill and the transition area of ​​adjacent structures.

[0037] Based on the local design wall thickness T of the casting at the corresponding position, the first sand coating thickness is greater than 0 and not greater than 0.08T, the second sand coating thickness is 0.08T-0.20T, and the sand bridge thickness is not less than 0.20T;

[0038] When the local design wall thickness T of the casting is 100mm-300mm, the first sand coating thickness is 3mm-8mm, the second sand coating thickness is 10mm-25mm, and the sand bridge thickness is 30mm-80mm.

[0039] When the wall thickness of the casting at the corresponding position in the same slot is not completely consistent, T is determined according to the design wall thickness of the casting at the center position of the slot; when T is used for the width of the shrinkage sand bridge or the distance of the chill edge, T is the local design wall thickness of the casting at the corresponding position of the shrinkage sand bridge or the corresponding position of the chill edge.

[0040] The width W of the feeding sand bridge is 0.3T-1.2T, preferably 0.5T-0.8T, where W is the minimum width of the feeding sand bridge perpendicular to the feeding direction of the riser;

[0041] The distance between the edge of the chilled iron groove and the edge of the opening, the outer contour of the hole group, the starting position of the fillet at the root of the stiffener, or the boundary of the flange thickness transition zone shall not be less than 0.3T, where T is the local design wall thickness of the casting at the corresponding position.

[0042] The thickness of the chills in the rapid cooling tank section is 0.20T-0.50T, and the thickness of the chills in the slow cooling tank section is 0.10T-0.35T, and the thickness of the chills in the rapid cooling tank section is not less than the thickness of the chills in the slow cooling tank section.

[0043] The preheating temperature of the chills in the rapid cooling tank section is 80℃-180℃, and the preheating temperature of the chills in the slow cooling tank section is 150℃-280℃. The preheating temperature of the chills in the slow cooling tank section is higher than that of the chills in the rapid cooling tank section.

[0044] The rapid cooling tank section and the slow cooling tank section are connected by a stepped transition or a sloping transition. When a stepped transition is used, the difference in sand coating thickness between adjacent steps is 5mm-15mm; when a sloping transition is used, the sand coating thickness gradually increases along the hot spot area towards the shrinkage sand bridge; the chill can be a metal chill, a steel chill, or a graphite chill.

[0045] The present invention will be further described below with reference to the embodiments and comparative examples. The embodiments and comparative examples below are all based on sand casting of large wind power castings. Unless otherwise specified, the sand mold material, coating, riser and gating system settings, pouring temperature, pouring method, cooling method, unpacking and cleaning method and inspection method are consistent.

[0046] Example 1

[0047] This embodiment provides a gradient chill solidification control process for large wind turbine castings, which specifically includes the following steps.

[0048] S1: A sand mold blank is prepared for a large wind turbine casting such as a hub. The casting includes a flange connection area, a stiffener root area, an opening and a hole group connection area, as well as multiple thickness transition parts. The sand mold blank forms a cavity profile corresponding to the above parts.

[0049] Based on the cavity profile, local design wall thickness, preset riser position, and thickness transition position, the intersection of the flange connection area and the stiffener root area is determined as the hot spot area, and the riser feeding direction for feeding the preset riser into the hot spot area is determined. In this embodiment, the local design wall thickness T near the hot spot area is 120mm.

[0050] S2: A chilled iron groove is machined in the initial sand mold corresponding to the hot spot area. The chilled iron groove includes a strong cooling groove section and a slow cooling groove section. The strong cooling groove section is located close to the hot spot area, and the slow cooling groove section is located on the side of the strong cooling groove section away from the hot spot area.

[0051] Ungrooved continuous sand body is retained on the side of the slow cooling tank section near the riser feeding direction. The ungrooved continuous sand body extends along the preset riser towards the hot spot area to form a feeding sand bridge, and the feeding sand bridge is not embedded with chills.

[0052] S3: Metal chills are embedded in the strong cooling tank section and the slow cooling tank section respectively. The thickness of the chills in the strong cooling tank section is 40mm, and the thickness of the chills in the slow cooling tank section is 25mm. The spacing between adjacent chills in the strong cooling tank section is 25mm, and the spacing between adjacent chills in the slow cooling tank section is 60mm.

[0053] Before installation, the chills in the strong cooling groove section are preheated to 120°C, and the chills in the slow cooling groove section are preheated to 220°C. After the chills are installed, molding sand is backfilled and compacted in the strong cooling groove section and the slow cooling groove section, so that the first sand covering thickness is formed between the surface of the chills in the strong cooling groove section that is close to the cavity and the surface of the cavity, and the second sand covering thickness is formed between the surface of the chills in the slow cooling groove section that is close to the cavity and the surface of the cavity, and the sand bridge thickness is formed at the corresponding position of the shrinkage sand bridge.

[0054] In this embodiment, the first sand coating thickness is 6mm, the second sand coating thickness is 18mm, the sand bridge thickness is 45mm, and a stepped transition is adopted between the strong cooling tank section and the slow cooling tank section, with a sand coating thickness difference of 8mm between adjacent steps.

[0055] S4: A feeding sand bridge is retained between the rounded transition area between the edge of the chill and the root of the stiffener, the edge of the opening, and the connecting area of ​​the hole group, so that the feeding sand bridge remains continuous along the feeding direction of the riser, and the width W of the feeding sand bridge is 70mm.

[0056] Neither the strong cooling trough section nor the slow cooling trough section cuts off the shrinkage sand bridge. The edge of the chill is not less than 60mm from the starting position of the radius of the stiffener root and not less than 50mm from the edge of the opening.

[0057] S5: After completing the machining of the chill trough, the installation of the chill, the backfilling of molding sand, and the retention of the feeding sand bridge, apply paint to the surface of the sand mold cavity, and then close the mold after setting the risers and gating according to the preset casting process. When setting the risers and gating, ensure that the feeding area of ​​the riser corresponds to the feeding sand bridge, and ensure that the feeding sand bridge is not cut off by the gating, riser seat, and other sand mold machining parts.

[0058] S6: Pour molten metal into the sand mold after the mold is closed, and allow the molten metal to cool and solidify naturally in the sand mold. After cooling, open the mold, remove the sand and clean it to obtain a large wind power casting.

[0059] Example 2

[0060] This embodiment provides a gradient chill solidification control process for large wind turbine castings. The main difference from Embodiment 1 is that a sloping transition is used between the strong cooling tank section and the slow cooling tank section, so that the thickness of the sand coating gradually increases from the hot spot area to the direction of the shrinkage sand bridge.

[0061] In this embodiment, the local design wall thickness T near the hot spot area is 140mm, the chill thickness in the strong cooling tank section is 42mm, the chill thickness in the slow cooling tank section is 28mm; the first sand coating thickness is 5mm, the second sand coating thickness is 22mm, and the sand bridge thickness is 50mm.

[0062] The chills in the strong cooling tank section are preheated to 110°C, and the chills in the slow cooling tank section are preheated to 240°C. The feeding sand bridge is not fitted with chills and remains continuous along the feeding direction of the riser. The width W of the feeding sand bridge is 80mm.

[0063] After completing the installation of chilled iron, backfilling of molding sand, and retention of shrinkage sand bridge, the coating, riser and gating system setup, mold assembly, pouring, cooling, mold opening, and cleaning are carried out in the same manner as in Example 1.

[0064] Example 3

[0065] This embodiment provides a gradient chill solidification control process for large wind turbine castings. The main difference from Embodiment 1 is that the strong cooling tank section and the slow cooling tank section use chills of different materials.

[0066] In this embodiment, the local wall thickness T near the hot spot area is 150mm. Graphite chills are embedded in the strong cooling groove section, and metal chills are embedded in the slow cooling groove section. The thickness of the graphite chills in the strong cooling groove section is 45mm, and the thickness of the metal chills in the slow cooling groove section is 30mm. The graphite chills in the strong cooling groove section are preheated to 130°C, and the metal chills in the slow cooling groove section are preheated to 230°C.

[0067] After the chills are installed, the strong cooling trough section and the slow cooling trough section are backfilled and compacted with molding sand to form the first sand covering thickness of the strong cooling trough section, the second sand covering thickness of the slow cooling trough section, and the shrinkage compensation sand bridge to form the sand bridge thickness. The first sand covering thickness is 8mm, the second sand covering thickness is 24mm, the sand bridge thickness is 60mm, and the width W of the shrinkage compensation sand bridge is 90mm.

[0068] The feeding sand bridge is not embedded with chills and remains continuous along the feeding direction of the riser; the feeding sand bridge is not cut off in either the strong cooling tank section or the slow cooling tank section. After the chills are embedded, the molding sand is backfilled and the feeding sand bridge is retained, the paint is applied, the riser and gating system are set up, the box is closed, the pouring is carried out, the cooling is performed, the box is opened and the cleaning is carried out in the same way as in Example 1.

[0069] Comparative Example 1

[0070] This comparative example uses a direct chiller arrangement, which differs from Example 1 in that: no strong cooling trough section and slow cooling trough section are set, and no ungrooved continuous sand body is retained in the area adjacent to the feeding path to form a feeding sand bridge.

[0071] Specifically, a sand mold blank is prepared according to the same casting pattern as in Example 1, and the same preset riser position and hot spot area are determined as in Example 1. Chill mounting grooves are machined near the hot spot area and metal chills are set. The sand covering thickness between the side surface of the chill near the cavity and the cavity surface is 6mm. After the chills are set, the coating is applied, risers and gating are set, the mold is closed, the casting is poured, the natural cooling is performed, the mold is opened and cleaned in the same way as in Example 1.

[0072] Comparative Example 2

[0073] This comparative example uses a uniform depth sand-covered chill arrangement, which differs from Example 1 in that: no difference in sand thickness is formed between the strong cooling trough section and the slow cooling trough section, and no ungrooved continuous sand body is retained in the area adjacent to the feeding path to form a feeding sand bridge.

[0074] Specifically, a sand mold blank is prepared according to the same large wind power casting pattern as in Example 1, and the same preset riser position, hot spot area and riser feeding direction as in Example 1 are determined. Equal depth chills grooves are machined in the sand mold blank corresponding to the hot spot area, and metal chills are embedded in the equal depth chills grooves. The sand covering thickness between the side surface of all chills near the cavity and the cavity surface is 15mm. After the chills are set, the coating is applied, risers and gating are set, the mold is closed, the casting is poured, natural cooling is performed, the mold is opened and cleaned in the same way as in Example 1.

[0075] Comparative Example 3

[0076] This comparative example uses a chilled iron arrangement with different sand covering thicknesses but without retaining a continuous feeding sand bridge. The difference from Example 1 is that although a strong cooling trough section and a slow cooling trough section are set up, and a difference is formed between the first sand covering thickness and the second sand covering thickness, no ungrooved continuous sand body is retained in the area adjacent to the feeding path.

[0077] Specifically, a sand mold blank is prepared according to the same casting pattern as in Example 1, and the same preset riser position, hot spot area and riser feeding direction as in Example 1 are determined. A strong cooling groove section and a slow cooling groove section are machined in the sand mold blank, and metal chills are embedded in the strong cooling groove section and the slow cooling groove section respectively. The first sand coating thickness between the side surface of the chill near the cavity in the strong cooling groove section and the cavity surface is 6 mm, and the second sand coating thickness between the side surface of the chill near the cavity in the slow cooling groove section and the cavity surface is 18 mm.

[0078] In this comparative example, the sand mold area where the feeding sand bridge should have been retained was occupied by the slotting of the chill trough, and a continuous unslotted sand body extending continuously along the feeding direction of the riser was not formed. After the chill was set up, the coating was applied, the riser and gating system were set up, the mold was closed, the pouring was carried out, the natural cooling was performed, the mold was opened and cleaned in the same manner as in Example 1.

[0079] Comparative Example 4

[0080] This comparative example uses a chill arrangement with a continuous feeding sand bridge but no segmented sand coating thickness difference. The difference from Example 1 is that: a continuous ungrooved sand body is retained in the area adjacent to the feeding path to form a feeding sand bridge, but the chill trough does not form a sand coating thickness difference between the strong cooling trough section and the slow cooling trough section.

[0081] Specifically, a sand mold blank is prepared according to the same casting pattern as in Example 1, and the same preset riser position, hot spot area and riser feeding direction as in Example 1 are determined. Chill grooves are machined and metal chills are embedded in the area near the hot spot area and its outer side. The sand covering thickness between the side surface of all chills near the cavity and the cavity surface is 18mm.

[0082] In this comparative example, an ungrooved continuous sand body is retained between the edge of the chill and the area adjacent to the feeding path. The ungrooved continuous sand body forms a feeding sand bridge with a width W of 70 mm. The chill trough does not cut off the feeding sand bridge. After the chill is set up, the coating is applied, risers and gating are set up, the box is closed, the pouring is carried out, the natural cooling is performed, the box is opened and the cleaning is carried out in the same manner as in Example 1.

[0083] To further illustrate the differences between the above embodiments and comparative examples in the solidification control process of castings, the castings obtained in Examples 1-3 and Comparative Examples 1-4 were tested and compared. Except for the different settings of chiller troughs, the relationship of sand coating thickness, and the retention of feeding sand bridges in each group, the sand mold materials, coatings, riser and gating settings, pouring temperature, pouring method, cooling method, unpacking and cleaning method, and testing methods in each group were kept consistent.

[0084] Experimental Example 1

[0085] The distribution of shrinkage porosity and shrinkage cavity locations in castings obtained under different process conditions was tested. Large wind power castings of the same specifications were prepared according to the process conditions of Example 1 and Comparative Examples 1-4, respectively. Three castings were prepared continuously for each group, and the average value of the test results of the three castings was used as the statistical value.

[0086] After each group of castings is unpacked, sand removed, and surface cleaned, ultrasonic testing is first performed using a straight probe, followed by rough machining for verification. During testing, the outer surface of the casting is divided into testing areas according to a grid, with each area having a grid size of 50mm × 50mm. The grid size is increased to 25mm × 25mm in the hot spot center area, chill edge area, and rib root area. During rough machining, 10-15mm of machining allowance is removed from the surface of each testing area, and any shrinkage cavities or porosity exposed after machining are verified and recorded.

[0087] The inspection area was divided into the hot spot center area, the chill opposite area, the chill edge area, the stiffener root area, the transition area of ​​the opening and hole group, and the area adjacent to the feeding path. The chill edge area is the region within 80mm outside the chill's projected boundary; the area adjacent to the feeding path is the region within 50mm on each side of the line connecting the pre-set riser to the hot spot center. The number of shrinkage porosity and shrinkage cavity defects in different inspection areas for each group of castings is shown in Table 1. Figure 1 as well as Figure 2 As shown, the number of defects in the transfer zone is the sum of the number of defects in the chill edge zone, the stiffener root zone, the transition zone of the opening and hole group, and the zone adjacent to the feeding path.

[0088] Table 1. Distribution of shrinkage porosity and shrinkage cavity defects under different process conditions

[0089]

[0090] From Table 1 and Figure 1 , 2 It can be seen that the total number of defects in the casting obtained in Example 1 is lower than that in each of the comparative examples, and the defects do not concentrate in the edge area of ​​the chill, the root area of ​​the stiffener, the opening and the transition area of ​​the hole group or the area adjacent to the feeding path. This indicates that after retaining the feeding sand bridge and setting the strong cooling groove section and the slow cooling groove section, the defects in the center area of ​​the hot spot are controlled, and no new defect concentration is formed in the edge of the chill and the transition area of ​​the adjacent structure.

[0091] The number of defects in the hot spot center area of ​​Comparative Example 1 was lower than that in Comparative Examples 2 and 4, but the number of defects in the edge area of ​​the chill, the root area of ​​the stiffener, the opening and the transition area of ​​the hole group increased. This indicates that although the direct chill can enhance local cooling, it is easy to form new defect concentrations near the edge of the chill.

[0092] Comparative Example 2 still has many defects in the hot spot center area and the chill edge area, indicating that it is difficult to take into account both the hot spot center area and the chill edge area by using only chill arrangements with uniform sand coating thickness.

[0093] The defects in the hot spot center area of ​​Comparative Example 3 were lower than those in Comparative Example 2, but the defects in the root area of ​​the stiffener plate, the opening and the transition area of ​​the hole group and the area adjacent to the feeding path increased. This indicates that even if chills with different sand covering thicknesses are set, if the chills occupy the area where the feeding sand bridge should be retained, it will still affect the riser feeding.

[0094] In Comparative Example 4, there were fewer defects in the edge area of ​​the chilled iron and the area adjacent to the feeding path, but the defects in the center area of ​​the hot section were still relatively high. This indicates that simply retaining the feeding sand bridge cannot replace the cooling control of the hot section area by the strong cooling groove section and the slow cooling groove section.

[0095] Experiment Example 2

[0096] The effect of continuous feeding sand bridge in the cooling process of the area adjacent to the feeding path was investigated. Sand molds and castings obtained from Example 1 and Comparative Example 3 were selected for comparison. Three castings were continuously prepared for each group, and the average result was used as the statistical value.

[0097] Before casting, high-temperature resistant temperature measuring elements are arranged in two sets of sand molds. The measuring ends are protected by ceramic protective tubes and fixed in the sand mold about 10mm outside the corresponding cavity surface. The measuring points include the hot spot center measuring point P1, the chill edge measuring point P2, the feeding path measuring point P3, and the stiffener / window transition measuring point P4.

[0098] P3 is set in the area adjacent to the feeding path when feeding from the pre-set riser to the hot spot area. In Example 1, P3 corresponds to the area where the continuous feeding sand bridge is located. In Comparative Example 3, P3 corresponds to the sand mold area that should have retained the feeding sand bridge but was occupied by the slotting of the chiller. After casting, the temperature change of each measuring point is continuously recorded. The sampling interval is 5 minutes in the first hour and 10 minutes thereafter.

[0099] This experimental example compares the relative cooling rates of different regions under two sets of process conditions by measuring the time it takes for each measuring point to reach 950℃. 950℃ is only used as a unified reference temperature for relative cooling rates under different process conditions and is not used as a limitation on the liquidus, solidus, or solidification endpoint of the casting material. The results are shown in Table 2 below. Figure 3 As shown.

[0100] Table 2. Time required for each measuring point to cool to 950℃

[0101]

[0102] From Table 2 and Figure 3 It can be seen that the P3 curve in Example 1 is generally higher than that in Comparative Example 3, and the time when the P3 measuring point on the feeding path drops to 950°C is later than that in Comparative Example 3. This indicates that after the continuous feeding sand bridge is retained, the area adjacent to the feeding path is less affected by the direct cooling of the cold iron trough.

[0103] In Comparative Example 3, the temperature of measuring point P3 on the feeding path dropped to 950℃ earlier than that of measuring point P1 at the center of the hot spot, indicating that when the continuous feeding sand bridge was not retained, the chilled iron trough had a more direct cooling effect on the area adjacent to the feeding path.

[0104] After cooling, both sets of castings underwent unpacking, sand removal, cleaning, and ultrasonic testing. Following rough machining, shrinkage porosity and defects in the chill edge area, rib root area, opening and hole transition area, and adjacent areas of the feeding path were rechecked. The testing areas and defect statistics were the same as in Experiment 1. The defect counts for the relevant areas are shown in Table 3 below. Figure 4 As shown.

[0105] Table 3 Number of defects in the feeding path and adjacent transition zone

[0106]

[0107] From Table 3 and Figure 4 It can be seen that in Example 1, the total number of defects in the edge area of ​​the chill, the root area of ​​the stiffener, the transition area of ​​the opening and the hole group, and the area adjacent to the feeding path is 0.6 per piece, while in Comparative Example 3 it is 6.0 per piece. According to Table 2, although Comparative Example 3 has chills with different sand coating thicknesses, due to the lack of continuous ungrooved sand in the area adjacent to the feeding path, the area adjacent to the feeding path cools down earlier, and more shrinkage and shrinkage defects appear in the root area of ​​the stiffener, the transition area of ​​the opening and the hole group, and the area adjacent to the feeding path.

[0108] In Example 1, the continuous feeding sand bridge was not embedded with chills and was not cut off by the chill trough. A continuous sand body was formed in the sand mold corresponding to the area adjacent to the feeding path. This continuous sand body reduced the direct impact of the chill trough on the area adjacent to the feeding path, so that the area had a longer cooling time than Comparative Example 3, thereby reducing the concentration of shrinkage porosity and shrinkage holes in the root area of ​​the stiffener plate, the transition area of ​​the opening and the hole group, and the area adjacent to the feeding path.

[0109] Experimental Example 3

[0110] The defects of segmented chilled iron channels and continuous feeding sand bridges were compared. Example 1, Comparative Example 3 and Comparative Example 4 were selected for comparison. Three castings were continuously prepared in each group, and the average test result of a single casting was used as the statistical value.

[0111] After each group of castings was unpacked, removed from the sand, and cleaned, ultrasonic testing was performed on the hot spot center area, the chilled iron facing area, the chilled iron edge area, the stiffener root area, the opening and hole group transition area, and the area adjacent to the feeding path. After rough machining, the defects were checked. The number of defects in the chilled iron edge area, stiffener root area, opening and hole group transition area, and the area adjacent to the feeding path were combined and recorded as the number of defects in the transfer area. The defect count of each group of castings is shown in Table 4 below.

[0112] Table 4. Defect statistics under the condition of segmented chilled iron trough and continuous feeding sand bridge.

[0113]

[0114] While counting defects, high-temperature resistant temperature measuring elements were arranged in the hot spot center area, chill edge area and feeding path adjacent area of ​​each sand mold. The distance between the measuring end and the corresponding cavity surface was kept consistent. Temperature changes were continuously recorded after casting, and the relative cooling order of different areas was compared by the time it took for each measuring point to drop to 950℃. The results are shown in Table 5 below.

[0115] Table 5. Statistics on the time it takes for the temperature in key areas to drop to 950℃.

[0116]

[0117] As shown in Table 4, the number of defects in the hot spot center area and the number of defects in the transfer area of ​​Example 1 are both at a low level, indicating that the process can not only control the cooling of the hot spot center area, but also prevent defects from concentrating in the edge area of ​​the chilled iron, the root area of ​​the stiffener plate, the opening and hole group transition area, and the area adjacent to the feeding path.

[0118] Although Comparative Example 3 had a first and a second sand covering thickness, resulting in a lower number of defects in the central area of ​​the hot spot compared to Comparative Example 4, the number of defects in its transfer area increased. This indicates that without retaining the continuous feeding sand bridge, relying solely on the difference in sand covering thickness makes it difficult to prevent defects from concentrating in the area adjacent to the feeding path and the transition area of ​​adjacent structures.

[0119] Comparative Example 4 retained the continuous feeding sand bridge, and its number of defects in the transfer area was lower than that in Comparative Example 3, but the number of defects in the hot spot center area was higher than that in Example 1. This shows that simply retaining the ungrooved continuous sand body in the area adjacent to the feeding path cannot replace the cooling control of the hot spot center area by the strong cooling tank section and the slow cooling tank section.

[0120] As can be seen from Table 5, in Example 1, the central area of ​​the hot spot cooled to 950°C earlier than the adjacent area of ​​the feeding path, indicating that the central area of ​​the hot spot could be cooled first, while the adjacent area of ​​the feeding path still retained a certain cooling time difference. In Comparative Example 3, the adjacent area of ​​the feeding path cooled to 950°C earlier than the central area of ​​the hot spot, indicating that when the continuous feeding sand bridge was not retained, the adjacent area of ​​the feeding path was easily affected by the chilled iron trough. In Comparative Example 4, although the adjacent area of ​​the feeding path cooled to 950°C later than the central area of ​​the hot spot, the overall cooling time of the central area of ​​the hot spot was later than that of Example 1, indicating that when only the continuous feeding sand bridge was retained and the segmented sand-coated thickness chilled iron trough was lacking, the cooling of the central area of ​​the hot spot was insufficient.

[0121] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A gradient chill solidification control process for large wind turbine castings, characterized in that, Includes the following steps: S1: Prepare a sand mold blank according to the large wind turbine casting, and determine the hot spot area of ​​the large wind turbine casting and the riser feeding direction corresponding to the hot spot area; S2: A chilled iron groove is machined in the initial sand mold corresponding to the hot spot area. The chilled iron groove includes a strong cooling groove section and a slow cooling groove section. The strong cooling groove section is located close to the hot spot area, and the slow cooling groove section is located on the side of the strong cooling groove section away from the hot spot area. S3: On the side of the slow cooling tank section near the feeding path, an ungrooved continuous sand body is retained. The ungrooved continuous sand body extends along the feeding direction of the riser and forms a feeding sand bridge. The feeding sand bridge is not fitted with chills. S4: Chills are embedded in the strong cooling tank section and the slow cooling tank section respectively, and molding sand is backfilled and compacted to form a first sand covering thickness between the chills in the strong cooling tank section and the corresponding cavity surface, and a second sand covering thickness between the chills in the slow cooling tank section and the corresponding cavity surface. The first sand covering thickness is less than the second sand covering thickness, and the thickness of the continuous sand body at the corresponding position of the shrinkage sand bridge is greater than the second sand covering thickness. S5: Keep the feeding sand bridge continuous along the feeding direction of the riser, and do not cut off the feeding sand bridge with the chill trough. After the chill is installed and the molding sand is backfilled, the sand mold is closed, poured and cooled to solidify.

2. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The large wind power castings include hub castings, bearing housing castings, frame castings, or other wind power equipment castings with thick and thin transition structures. The large wind power castings include flange connection areas, stiffener root areas, openings, hole group connection areas, and thick and thin transition areas. The hot spot region is determined based on the cavity profile, local wall thickness, thickness transition position, and preset riser position of the large wind turbine casting.

3. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The feeding path is the molten metal connection path corresponding to the pre-set riser replenishing molten metal to the hot spot area, and the feeding sand bridge is located in the sand mold in the area adjacent to the feeding path.

4. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The corresponding position of the compensation sand bridge forms a sand bridge thickness, which is the minimum continuous sand body thickness between the cavity surface corresponding to the compensation sand bridge and the boundary of the adjacent chilled iron groove, and the sand bridge thickness is greater than the second sand covering thickness.

5. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: Based on the local design wall thickness T of the casting at the corresponding position, the first sand coating thickness is greater than 0 and not greater than 0.08T, the second sand coating thickness is 0.08T-0.20T, and the sand bridge thickness is not less than 0.20T.

6. The gradient chill solidification control process for large wind turbine castings according to claim 5, characterized in that: When the local design wall thickness T of the casting is 100mm-300mm, the first sand coating thickness is 3mm-8mm, the second sand coating thickness is 10mm-25mm, and the sand bridge thickness is 30mm-80mm.

7. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The width W of the feeding sand bridge is 0.3T-1.2T, where W is the minimum width of the feeding sand bridge in the direction perpendicular to the riser feeding direction, and T is the local design wall thickness of the casting at the corresponding position of the feeding sand bridge.

8. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The distance between the edge of the chilled iron groove and the edge of the opening, the outer contour of the hole group, the starting position of the fillet at the root of the stiffener, or the boundary of the flange thickness transition zone shall not be less than 0.3T, where T is the local design wall thickness of the casting at the corresponding position.

9. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The thickness of the chill in the rapid cooling tank section is 0.20T-0.50T, and the thickness of the chill in the slow cooling tank section is 0.10T-0.35T, and the thickness of the chill in the rapid cooling tank section is not less than the thickness of the chill in the slow cooling tank section.

10. The gradient chill solidification control process for large wind turbine castings according to claim 1, characterized in that: The preheating temperature of the chilled iron in the strong cooling tank section is 80℃-180℃, and the preheating temperature of the chilled iron in the slow cooling tank section is 150℃-280℃, and the preheating temperature of the chilled iron in the slow cooling tank section is higher than that of the chilled iron in the strong cooling tank section.

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