The numerical simulation software ProCAST was used to simulate the column socket of the ZY10000/17/35D hydraulic support, and found that the hot spot was near the hollow ball cap. After optimizing the design, the riser was changed to an insulation riser and the riser size was increased, so that the riser has enough area for feeding, will not increase the hot spot of the casting itself, and reduces the thermal impact of the casting. After production verification, the designed casting process meets the technical requirements, and the quality of the casting is guaranteed.
1. Introduction
Hydraulic supports play a crucial role in underground mining operations. As the mining face continuously advances, the cantilever of the old roof elongates, gradually sinks, and ultimately fractures. This leads to a massive influx of gangue and a powerful airflow, exposing the support to horizontal forces. Additionally, instantaneous pressure from the roof subjects the support to tremendous impact forces. Consequently, the support primarily endures vertical pressure, overturning moments, and horizontal forces. The majority of these forces are transmitted to the column socket through the support’s pillars, placing stringent demands on the production of column sockets. Casting is the primary means of manufacturing column sockets and caps, and the quality of the casting directly impacts the support strength and service life of the support. In the case of casting defects, prolonged use underground can lead to cracks or fractures in the column sockets and caps, severely affecting mining efficiency and safety. Utilizing numerical simulation methods to identify and adjust areas prone to casting defects before casting can effectively address this issue.
This paper takes the ZY10000/17/35D hydraulic support as an example, establishes a finite element model of the column socket, simulates the casting process, and optimizes the casting process. Simulation results indicate that increasing the riser size and utilizing insulating risers can reduce casting defects and enhance casting quality.
2. Materials and Casting Process Flow of Hydraulic Support Column Sockets
The material commonly used for column sockets is ZG28NiCrMo, with its chemical composition outlined in Table 1 and mechanical properties detailed in Table 2. These mechanical properties meet the requirements for long-term use.
Table 1: Chemical Composition of ZG28NiCrMo (%)
Element | C | Si | Mn | P | S | Cr | Ni | Mo |
---|---|---|---|---|---|---|---|---|
Content | 0.270 | 0.560 | 0.790 | 0.011 | 0.002 | 0.670 | 0.530 | 0.460 |
Table 2: Mechanical Properties of ZG28NiCrMo
Property | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Impact Absorption Energy (J) (at 20°C) |
---|---|---|---|---|
Value | ≥878 | ≥756 | 13 | 44 |
The casting process flow for column sockets includes:
- Production Process Preparation: This includes preparing the production process plan, process documents, casting process drawings, etc.
- Production Preparation: This entails preparing materials for melting, core boxes, sand boxes, and other process equipment.
- Molding and Core Making: During the molding process, it is essential to ensure the compactness of the sand mold. After the sand mold is prepared, nitrogen is uniformly injected into various parts of the sand mold. A vertical gating well is left at the bottom of the vertical runner, and after mold closing, a hose is used to suck out the broken sand in the mold cavity.
- Melting and Pouring.
- Sand Dropping, Cleaning, and Casting Inspection, among other main processes.
3. Finite Element Simulation
3.1 Simulation Before Optimization
During the pouring and molding process, ProCAST can predict issues occurring during the casting filling process, such as excessive cavity cooling, slow pouring speed, and low molten metal temperature. It can also quickly formulate and verify corresponding improvement schemes.
The Pro/E software was used to create a three-dimensional solid model of the column socket. The column socket measures 550 mm in length, 440 mm in width, and is made of ZG28NiCrMo with a heat treatment of 240~280HB and a mass of 182.09 kg. Based on the column socket structure, the entire workpiece is placed in the lower box. The three-dimensional model of the column socket is imported into the ProCAST software for mesh division with 248,226 numbers and a total of 50,926 nodes. The average wall thickness of the sand mold is 30 mm, with a shrinkage rate of 5.5%. According to the pouring system design principles for steel castings, the diameter of the vertical gating is φ55 mm, with a height of 360 mm and a vertical gating well of 40 mm; the horizontal gating length is 385 mm, with a trapezoidal cross-section of 40 mm (lower base), 30 mm (upper base), and 40 mm (height); the ingate length is 140 mm, with a trapezoidal cross-section of 40 mm (lower base), 36 mm (upper base), and 20 mm (height). The casting model of the column socket sand box is shown in Figure 1.
Relevant parameters for numerical simulation were set, with the casting method selected as conventional gravity casting, a pouring temperature of 1580°C, and an initial ambient temperature of 25°C. The general heat transfer coefficients selected were: metal-metal: 1100~5100 W/(m²·K); metal-sand: 300~1000 W/(m²·K); sand-sand: 210~310 W/(m²·K); solid-air: 4~9 W/(m²·K); solid-cold air: 150~1100 W/(m²·K). Velocity and temperature boundary conditions were applied to the corresponding nodes in the model.
The filling time of the column socket pouring is shown in Figure 2, indicating the sequence of steel liquid arrival in various parts of the mold. Figure 2 reveals that, due to the ingate positioned at the top of the model, some areas at the front of the column socket are filled later.
The solidification time of the column socket pouring is shown in Figure 3, indicating the sequence of solidification of the steel liquid in various parts of the mold. Figure 3 indicates that the bottom of the column socket, the cross ribs, and the riser are the last to solidify.
The locations prone to shrinkage porosity during column socket pouring are shown in Figure 4. Figure 4 indicates that shrinkage porosity occurs at the bottom of the cross ribs of the column socket and at the pouring gate and riser, with significant shrinkage defects at the central cross rib at the bottom of the column socket.
3.2 Casting Process Optimization and Simulation
Through simulation analysis of the traditional process, the main cause of defects in column socket castings is that liquid shrinkage and solidification shrinkage are greater than solid-state shrinkage, and the crystallization temperature range is wide, tending towards volume solidification, leading to poor feeding effectiveness of the riser. The solution is to improve the feeding efficiency of the riser. Compared to traditional sand-type risers, insulating exothermic risers can slow down the cooling rate, effectively enhancing the feeding efficiency of the riser and reducing defect formation.
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