This article delves deep into the casting technologies for common hydraulic parts in grinder production. It analyzes the challenges faced in casting different types of hydraulic components, such as high reject rates and quality requirements. Through practical case studies and data – backed solutions, it presents optimized casting processes, including the use of centrifugal slag – collecting ladles, “horizontal casting and vertical casting” techniques, and one – billet – multiple – piece continuous casting. The concept of modulus is also introduced to control the cooling rate of castings effectively. This comprehensive guide aims to provide valuable insights for foundries and manufacturers to improve the quality and production efficiency of hydraulic components in grinder manufacturing.
1. Introduction
Grinders are essential machines in the manufacturing industry, and their hydraulic systems rely on a variety of hydraulic components. The most common types of hydraulic parts in grinder production include disc – cover – type, flat – plate – type, square, and short – cylinder – type components. These components, despite their seemingly simple structures, pose significant challenges in the casting process.
The cross – sectional thickness of these hydraulic parts is relatively large, and they have high technical requirements. For example, they need to have high strength, density, and a certain level of hardness. Additionally, the machining surfaces must be free from defects like pores, slag inclusions, and shrinkage cavities. In the past, conventional casting processes led to a high reject rate, typically ranging from 30% – 40%, causing substantial economic losses to manufacturers. Therefore, it is crucial to explore and optimize the casting technologies for these hydraulic components.
1.1 Significance of Hydraulic Components in Grinders
Hydraulic components play a vital role in the operation of grinders. They are responsible for functions such as the reciprocating motion of the worktable, the lateral feed motion of the grinding wheel, and the automatic clamping of workpieces. Any defect in these components can lead to abnormal operation of the grinder, affecting the quality of the machined products. For instance, if there are pores or slag inclusions in a valve body, it may cause oil leakage or incorrect fluid control, resulting in inaccurate movement of the grinder’s parts.
1.2 Challenges in Casting Hydraulic Components
The main challenges in casting hydraulic components are related to their thick cross – sections and strict quality requirements. The thick sections make it difficult to ensure uniform cooling during the casting process, which can lead to shrinkage cavities and porosity. Moreover, the need to prevent slag inclusions and other defects requires advanced gating and risering systems. In addition, the high technical requirements for surface finish and dimensional accuracy add to the complexity of the casting process.
2. Disc – Cover – Type Hydraulic Components
Disc – cover – type hydraulic components include end covers of hydraulic cylinders and valve bodies. These components usually have a small external size but a relatively large thickness. They also have multiple machining surfaces and holes for oil passage and installation.
2.1 Problem Analysis
One of the major problems in casting disc – cover – type hydraulic components is the formation of “slag eyes” in the castings. Due to the small size of the components, the molten metal cools quickly after pouring. As a result, the slag in the molten metal has difficulty floating to the top surface of the casting, and it may be trapped inside the casting, causing defects. Conventional gating systems have limited slag – removal capabilities, which leads to a high reject rate of 30% – 35% for these components.
2.2 Solution: Centrifugal Slag – Collecting Ladle
To address the slag – inclusion problem, a centrifugal slag – collecting ladle is used in the gating system design. This ladle not only serves as a slag – collecting device but also as a riser, providing a dual – function solution for slag removal and feeding.
2.2.1 Case Study 1: The Connecting Disk Casting
The connecting disk is a key component of the M224 semi – automatic internal – grinding – machine’s feed hydraulic cylinder. The casting details are shown in Table 1.
| Casting Name | Connecting Disk |
|---|---|
| Weight | 7.9 kg |
| Outline Dimensions | φ180mm×45mm |
| Material | HT200 |
| Maximum Thickness | 42mm |
| Requirements | Dense structure, no pores, slag eyes, or shrinkage cavities |
Figure 1: Connecting Disk Casting
[Insert an image of the connecting disk casting here, showing its shape and dimensions]
The original casting process used clay – sand green – sand molding with a “gating – instead – of – risering” method. However, this process resulted in a high reject rate of 35% due to slag – eye defects. The improved process replaced the straight sprue with a centrifugal slag – collecting ladle. The parameters of the slag – collecting ladle were designed according to the hot – spot circle diameter of the casting, as shown in Table 2.
| Parameter | Value |
|---|---|
| Slag – Collecting Ladle Dimensions | φ72mm×85mm |
| Distance between Sprue and Slag – Collecting Ladle Center | 90mm |
| Inner Gate (also Riser Neck) Length | 20mm |
| Gate Ratio (直横内) | 1.85: 1.5: 1 |
| Inner Gate Cross – Sectional Area (内) | |
| Cross – Gate Cross – Sectional Area (横) | |
| Straight Sprue Cross – Sectional Area (直) | (φ32mm) |
Figure 2: Connecting Disk Casting Process
[Insert an image of the connecting disk casting process, clearly showing the gating system, slag – collecting ladle, and the casting]
After implementing the improved process, the reject rate was reduced to less than 4%, demonstrating the effectiveness of the centrifugal slag – collecting ladle.
2.2.2 Case Study 2: The Clamping Hydraulic Cylinder Casting
The clamping hydraulic cylinder casting of the M224 internal – grinding – machine is a complex component with a pulley and hydraulic – cylinder function. The casting details are presented in Table 3.
| Casting Name | Clamping Hydraulic Cylinder |
|---|---|
| Weight | 11.5 kg |
| Outline Dimensions | φ186mm×120mm |
| Material | HT200 |
| Maximum Hot – Spot Diameter | 50mm |
| Requirements | Dense structure, no pores, slag eyes, or shrinkage cavities |
Figure 3: Clamping Hydraulic Cylinder Casting
[Insert an image of the clamping hydraulic cylinder casting, showing its structure with pulley and cylinder parts]
The original process used clay – sand dry – sand molding with a side – pressing gating system. But it had issues such as turbulent molten – metal flow in the straight sprue, which led to slag entrapment and a high reject rate of about 30%. The optimized process, based on the equilibrium solidification theory and the use of a centrifugal slag – collecting ladle, is shown in Table 4.
| Parameter | Value |
|---|---|
| Slag – Collecting Ladle (also Insurance Riser) Dimensions | φ65mm×90mm |
| Gate Type | Flash Gate |
| Flash Gate Dimensions | 65mm×6mm, length about 10mm |
| Inner Gate Cross – Sectional Area (内) | |
| Cross – Gate Cross – Sectional Area (横) | |
| Straight Sprue Cross – Sectional Area (直) |
Figure 4: Clamping Hydraulic Cylinder Process
[Insert an image of the clamping hydraulic cylinder casting process, highlighting the slag – collecting ladle, flash gate, and other parts of the gating system]
After the optimization, the molten – metal flow during pouring became stable, and the slag – collecting effect of the ladle was excellent. The comprehensive reject rate dropped to 3%.
3. Flat – Plate – Type Hydraulic Components
Flat – plate – type hydraulic components, such as the distribution plates and covers in the oil – supply and distribution systems of internal – grinding – machines, have all surfaces as machining surfaces. The two large planes are the most critical parts, with many oil grooves, through – holes, and installation holes.
3.1 Problem Analysis
When these components were cast with the large planes in a horizontal or inclined position, the reject rate was as high as 30% – 40%. The main defects were pores, slag eyes, and sand inclusions. These defects were mainly caused by the difficulty of gas and slag escape during the casting process when the large planes were in a horizontal or inclined position.
3.2 Solution: “Horizontal Casting and Vertical Casting” Process
The “horizontal casting and vertical casting” dry – sand – molding process was adopted. In this process, the two large planes of the casting are placed on the side during pouring, which makes it easier to ensure the quality of these planes.
3.2.1 Case Study: The Distribution Plate Casting
The distribution plate of the M224 semi – automatic internal – grinding – machine is a key part of the oil – supply and distribution system. The casting details are shown in Table 5.
| Casting Name | Distribution Plate |
|---|---|
| Weight | 48 kg |
| Outline Dimensions | 596mm×312mm×34mm |
| Material | HT200 |
| Surface Roughness of Large Planes | |
| Requirements | Dense structure, no pores, slag eyes, or shrinkage cavities |
Figure 5: Distribution Plate Part
[Insert an image of the distribution plate, clearly showing the oil grooves, holes, and the large planes]
The casting process used clay – sand dry – sand molding with a “horizontal casting and vertical casting” method. The gating system was designed with a stepped – gate form, and two castings shared the gating system. The process details are presented in Table 6.
| Parameter | Value |
|---|---|
| Machining Allowance (Side and Bottom) | 6mm |
| Machining Allowance (Top, Pouring Position) | 10mm |
| Inner Gate Cross – Sectional Area (内) | |
| Cross – Gate Cross – Sectional Area (横) | |
| Risers | One open riser in the middle of the top surface of the cavity, dimensions 200mm×70mm×70mm |
| Chemical Composition | , , , , |
Figure 6: Distribution Plate Casting Process
[Insert an image of the distribution plate casting process, showing the gating system, risers, and the position of the casting in the mold]
Since the implementation of this process, the reject rate has been basically controlled within 3%, achieving remarkable results.
4. Square and Short – Cylinder – Type Hydraulic Components
Square and short – cylinder – type hydraulic components, such as valve bodies of various control valves in grinders, have simple external shapes but high – precision requirements for internal structures.
4.1 Problem Analysis
These components require high hardness ( > 170HBW) for wear resistance due to the frequent movement of the valve core. They also need a dense structure to prevent oil leakage and ensure uniform material hardness to avoid machining problems. One – piece – per – blank casting often results in a high reject rate of 35% – 40% due to pores and slag holes on the upper surface of the casting in the pouring position. Additionally, the thick cross – section makes it difficult to ensure internal structure density through material selection.
4.2 Solution: One – Billet – Multiple – Piece Continuous Casting and “Horizontal Casting and Vertical Casting” Process
The combination of one – billet – multiple – piece continuous casting and the “horizontal casting and vertical casting” process is an effective solution. This process can improve the process yield and ensure the quality of the castings.
4.2.1 Case Study: The Reciprocating Control Box Casting
The reciprocating control box casting is an important component in the grinder. The casting details are shown in Table 7.
| Casting Name | Reciprocating Control Box |
|---|---|
| Weight | 19 kg |
| Outline Dimensions | 148mm×150mm×108mm |
| Material | HT300 |
| Valve – Hole Surface Roughness | |
| Valve – Hole Cylindricity Error | 0.005mm |
| Hardness Requirement | > 170HBW |
| Requirements | No slag eyes, sand eyes, or pores |
Figure 7: Reciprocating Control Box
[Insert an image of the reciprocating control box, showing its shape and the positions of valve holes and other features]
The adopted continuous – casting and vertical – casting process is as follows: Four castings are made from one blank, and the blank dimensions are 108mm×810mm×150mm. The casting process details are presented in Table 8.
| Parameter | Value |
|---|---|
| Blank Dimensions | 108mm×810mm×150mm (604mm part for castings, 206mm part for riser) |
| Single – Blank Weight (including riser) | 99.7 kg |
| Molding Method | Horizontal casting and vertical casting, two – cavity – per – mold |
| Gating System | Stepped – gate form in the middle of the two cavities |
| Chemical Composition | , , , , |
| In – Furnace Control | Triangle test piece, white – mouth 10 – 12mm |
Figure 8: Reciprocating Control Box Casting Process
[Insert an image of the reciprocating control box casting process, showing the continuous – casting setup, gating system, and the position of the blank in the mold]
After implementing this process, the process yield reached 80.5%, and the reject rate was within 4%, indicating a good process effect.
5. Ensuring Material Performance
5.1 Chemical Composition Control
The performance requirements of hydraulic components, such as strength, hardness, and density, are closely related to the chemical composition of the casting material. According to the performance requirements and wall – thickness conditions of the castings, appropriate chemical compositions should be selected, and the furnace – charge ratio should be accurately calculated. At the same time, the quality of raw materials should be strictly controlled to ensure stable composition. For example, in the production of HT200 and HT300 castings, the content of carbon (C), silicon (Si), manganese (Mn), sulfur (S), and phosphorus (P) needs to be precisely adjusted to meet the mechanical – property requirements of the castings.
5.2 Cooling Rate Control
The cooling rate during the casting process has a significant impact on the microstructure and properties of the castings. In the past, the “wall – thickness consistency” was often used as a basis for considering the cooling situation. However, for different geometric shapes, such as flat – plate – type, rectangular – rod – type, and cylindrical – type parts, it is not accurate to directly compare the wall – thickness values.
The concept of modulus is introduced to solve this problem. The modulus of different geometric shapes can be calculated using the formulas shown in Table 9.
By calculating and comparing the moduli of various geometric bodies, when the moduli of castings of the same grade are consistent or similar, they can be placed in the same sand box during molding or their sand molds can be placed together. This not only facilitates production organization but also ensures the material – performance requirements of the castings.
6. Conclusion
In the production of hydraulic components for grinders, different casting technologies have been developed and optimized for various types of components. The use of centrifugal slag – collecting ladles in disc – cover – type hydraulic components effectively solves the problems of slag removal and feeding, significantly improving the process yield and product quality. The “horizontal casting and vertical casting” process for flat – plate – type hydraulic components meets the high – quality requirements of the two large planes. The combination of one – billet – multiple – piece continuous casting and the “horizontal casting and vertical casting” process for square and short – cylinder – type hydraulic components ensures the quality of thick – section castings.
