CN-121988702-A - Hydropower lower ring split casting molding method based on integral casting segmentation

CN121988702ACN 121988702 ACN121988702 ACN 121988702ACN-121988702-A

Abstract

The invention relates to the technical field of hydropower lower ring casting, in particular to a split casting molding method of a hydropower lower ring based on integral casting segmentation. The method comprises the steps of determining notch machining allowance delta according to the number N of split segments of a target lower ring, the wall thickness T and the inner diameter D, calculating the diameter delta D= (N/pi) x (delta+T/3) of a cast blank to be increased according to the notch machining allowance delta, manufacturing a casting cavity according to delta D, setting split notch marks on an outer core, performing one-time casting operation to obtain an integral annular blank, and dividing the blank into N split segments along the marks after standard machining is performed on the blank. The invention changes the traditional split casting into split casting, thereby fundamentally solving the difficult problem of inconsistent multi-split size of the scale difference, unifying the processing standard, greatly shortening the production period, improving the product quality and the circle assembling precision, and being particularly suitable for manufacturing the lower ring of the large-scale and ultra-large-scale water turbine.

Inventors

LI DAXIN
ZHAO MINGZHE
GE CHUNYU
XU JUNCHAO

Assignees

鞍钢铸钢有限公司

Dates

Publication Date: 20260508
Application Date: 20260306

Claims (9)

1. The hydropower lower ring split casting molding method based on integral casting segmentation is characterized by comprising the following steps of: s1, determining machining allowance delta required by each split notch according to a design drawing of a target split lower ring and the split number N, wherein N is an integer greater than 2; S2, calculating the diameter delta D of the integral casting blank required to be increased relative to the target lower ring according to the machining allowance delta and the split number N; s3, manufacturing a lower ring casting cavity for integral casting according to the increased diameter dimension delta D, and arranging a notch mark at the position, corresponding to each split notch design position, of the outer core of the cavity; s4, carrying out integral casting operation based on the casting cavity, and casting and forming into an integral annular casting blank; S5, after the integral annular casting blank is subjected to reference processing, dividing the integral annular casting blank into N split lower rings along the positions of the notch marks.
2. The split casting method for the hydropower lower ring based on the integral casting split according to claim 1, wherein in the step S1, the machining allowance delta is related to the wall thickness T, the inner diameter D and the coefficient A, B of the target lower ring, and the numerical range is 15mm < delta < AT+BD), wherein the units of T and D are mm.
3. A split casting method for a hydropower lower ring based on split casting according to claim 2, wherein the increased diameter dimension Δd in step S2 is calculated by the formula Δd= (N/pi) × (δ+t/3).
4. A split casting method for a hydropower lower ring based on block casting split according to any one of claims 1-3, wherein the number of split N is 3 or 4.
5. A split-casting method for a hydropower lower ring according to claim 1, wherein in step S3, the cut is marked as a score line, a groove or a protrusion provided on the working surface of the outer core.
6. The method for split casting of hydropower lower ring based on split casting according to claim 1, wherein in step S4, the split casting operation adopts a blade molding and shaft stabilizing process, and the shaft and blade are kept fixed during the whole casting process.
7. The method for split casting of a hydropower lower ring based on split casting according to claim 1, wherein in step S5, the reference processing is: Leveling the upper end face and the lower end face of the integral annular casting blank, wherein the single-end face removal amount a is 5-30 mm; Rough machining is carried out on the inner cylindrical surface and the outer cylindrical surface of the integral annular casting blank by taking the leveled end surface as a reference, and the radial removal amount b of one side is 3-20 mm; After the reference machining is completed, the flatness error of the end face of the integral annular casting blank is not more than 1.5mm, and the radial circle run-out error of the inner and outer cylindrical surfaces of the integral annular casting blank relative to the theoretical axis is not more than 2.0mm.
8. The method according to claim 1, wherein in step S5, the split ring is split by machining, the split cuts are marked and milled or cut along the cuts, and the cut surfaces formed after the splitting are finished to form welding grooves or fitting mating surfaces.
9. A split-casting method for a hydropower lower ring based on split casting according to claim 1, characterized by further comprising the step of heat-treating the whole annular casting blank after the basic processing and before the split operation in step S5.

Description

Hydropower lower ring split casting molding method based on integral casting segmentation Technical Field The invention relates to the technical field of hydropower lower ring casting, in particular to a split casting molding method of a hydropower lower ring based on integral casting segmentation. Background The construction of large hydropower stations places extremely high demands on the size and performance of the turbine runner components. Because of the limitations of transportation conditions, the overrun turbine lower ring is typically not manufactured in its entirety at the manufacturing plant and transported to the power plant site. Therefore, "split (flap) manufacture, split transportation, and site group round welding" have become the current and future production modes of the main flow of the lower ring of large-sized water turbines. The mode requires that a manufacturing plant firstly produces a plurality of split lower ring castings, and the split lower ring castings are assembled into complete annular components through welding after being transported to a site. To accommodate this production model, one of the central tasks of the manufacturing plant is to efficiently and quality produce single split lower ring castings with precise dimensions and controllable form and position tolerances. In the prior art, the main casting process is a 'bottom-to-top core' method. Specifically, in the production of each split casting, a sand core for molding (referred to as "butt core") is provided in advance at the parting position of one side face (i.e., the future welding butt face) to directly cast out a partial shape of the face. When a complete multi-lobed lower ring set is to be produced, each lobe is individually shaped, cored and cast. However, this traditional "split casting, core-setting-in-mouth" process exposes a number of drawbacks in practical applications that are difficult to overcome: 1. The operation is complex, the production efficiency is low, and a series of operations such as stable installation of the shaft bar, scraping of molded lines, lower alignment of the core, box closing and the like are required to be repeated every time one split is produced. For example, a three-flap lower ring is produced, the shaft bar and the scraping plate need to be moved and adjusted for many times in the whole molding process, the process links are many, the production period is long, and the utilization rate of key production resources such as pits is low. 2. The problem of accumulation of dimensional errors (scale differences) is serious, and as each split is an independent cast individual, the modeling standard, shrinkage control and heat treatment deformation of the split have independent differences. Multiple repeated molding operations introduce unavoidable incidental errors that make it difficult to maintain consistent the final cast segments in critical dimensions (e.g., arc length, chord height, thickness). The 'ruler difference' can bring great difficulty to round assembling, butt joint and welding of a construction site, and directly affects welding quality and unit operation stability. 3. The deformation of the heat treatment is uncontrollable, and when each split is used as an independent casting for heat treatment, the deformation trend and degree of the split are difficult to predict and uniformly control. Even if a single split meets the tolerance requirement, the roundness of the whole welded assembly can be out of tolerance due to uncoordinated deformation, the subsequent correction workload is large, and the material performance can be damaged. 4. The machining standard is not uniform, namely, when the split castings are machined, the split castings need to be aligned respectively, and the machining standard is built. Due to the difference of the as-cast shapes, the established benchmarks are difficult to ensure complete consistency, further amplifying assembly errors of the final product. Disclosure of Invention In order to overcome the defects in the prior art, the invention provides a split casting molding method of a hydropower lower ring based on integral casting and segmentation. On the premise of ensuring the necessity of split manufacturing of the lower ring of the large-sized water turbine, the remarkable improvement of product quality, production efficiency and cost control is realized. In order to achieve the above purpose, the invention is realized by adopting the following technical scheme: a hydropower lower ring split casting molding method based on integral casting segmentation comprises the following steps: s1, determining machining allowance delta required by each split notch according to a design drawing of a target split lower ring and the split number N, wherein N is an integer greater than 2; S2, calculating the diameter delta D of the integral casting blank required to be increased relative to the target lower ring according to the machining allowance delta a