Analysis and Comparison of Forging Processes and Schemes for Large Valve Bodies

The valve body is a major component of the petroleum machinery valve; according to the pressure level there are different forming methods, such as: casting, forging, etc. Valve body material according to the different process media and different materials; commonly used materials are cast iron, cast steel, stainless steel, structural alloy steel, etc. Valve forging is divided into press die forging and forging hammer free forging; this paper mainly introduces the product through free forging forming, analysis, and comparison of various process options, and finally gives an optimal valve body forging forming process.

Process analysis of forged valve body forgings

The valve body (Figure 1 is the product parts diagram) is flange-shaped at both ends, with two symmetrical round tabs in the middle part and a polygonal design between the two tabs, allowing moderate collapse during the forging process. The overall design is an eccentric structure, the raw material is a selected ingot, the product material is AISI4130, and the weight of the product parts is 1050kg; because the forging size is large, the used ingot shape is also large. To ensure that the heart of the ingot is forged through internal inclusions and dendritic crystalline tissue can be effectively broken, and defects such as sparseness can be effectively welded together, the forging temperature range should be controlled. The higher the forging temperature is, the easier the internal defects of the ingot can be forged together, so the forging should be kept at a high temperature as much as possible.

Figure.1 Part diagram
Forging forgings with ingots, it is necessary to consider the forging ratio, the basic forging process of valve body forging billet is divided into forging ratio control and forging billet forming. According to the forging equipment forging capacity and forging material size selected 6t electro-hydraulic hammer, heating equipment selected natural gas furnace, forging material starting forging temperature of 1180 ℃, the final forging temperature of 850 ℃, forging cooling method for the pit cooling.

Forging valve body process scheme

Due to the complex shape of the forgings, and the overall forging difficulty, according to the characteristics of the part, our process personnel analyze its forming feasibility, combined with the actual production situation of our company, research, and development of three valve body forging forming process program.

Option 1

Direct forging into a square blank, 492mm × 657mm × 915mm, after forging and cooling, drawing lines on the forging blank, and finally seeing the corner on the sawing machine (Figure 2 is the forging blank diagram).

Figure.2 Forging billet diagram

Option 2

First, forging into a transition square blank, forging a square cross-section of 510mm × 690mm, to ensure the key size of the middle square, with a small round bar on both ends of the square billet for indentation, the indentation position as a benchmark with a chopper for manual parting, and then pressure shoulder pulling length, and then the forging billet on the valve body die for surface shaping (Figure 3), followed by the valve body two end faces for leveling, the final blank formed into three sections of the square body (Figure 4 ).

Figure.3 Forging billet

1 – Die 2 – Valve body

Figure.4 Forging billet

Option 3

Forge the blank into a cylindrical shape with a cross-sectional circle diameter of φ480mm, then put the die ring on the top and bottom of the blank, respectively, upsetting along the forging billet axis direction (Fig.5), when the middle forging square meets the process size, then place the forging billet and the die ring transversely on the hammer anvil to forge the eccentric structure of the blank. Finally, the die ring at both ends is removed, and the blank is leveled to ensure that the forging process dimensions and surface quality (Figure 6) meet the requirements.

Figure.5 Forging process diagram

Figure.6 Forging billet diagram

Process comparison analysis of valve body forging

• (1) Scheme one valve body forging process down weight is 2430kg, forging fire for two times; Scheme two valve body forging process down weight is 2335kg, forging fire for three times; Scheme three valve body forging process down weight is 2030kg, forging fire for three times.
• (2) Option 1 is to forge the billet as a whole into a square blank; Option 2 forging process increases the margin at both ends of the forging billet to facilitate manual parting and prevent the concave center at both ends. These two options design valve bodies in the subsequent mechanical processing process, there is a large machining allowance, and the forging flow is cut off, reducing the service life of the parts, so product quality cannot be guaranteed.
• (3) Program one after forging by sawing off two residual materials, lightweight, the use of value is not high, can only be treated as scrap while using a sewing machine to increase the loss of the saw blade and add a process, there is an additional risk of quality control, such as the existence of sawing the corner of the product sawing process may be scrap. The second option in the forging process of human division process, in the division of the material location of the remaining block, and the chopping knife is not necessarily a neat surface so that the location is easy to produce fold.

The test proves that although the forging process of option one is simple, the forging margin is large, and the material utilization rate is low; there are two production processes, the production cycle is long, and the quality control risk is high. Option 2 increases the forging allowance to facilitate manual splitting, while the splitting position is prone to cracking, and the quality control of the forging billet is difficult. Option 3 has the advantages of economic and rapid forming methods; the forging billet structure is closer to the part structure, improving the raw materials’ utilization rate. The forging process adopts the collar process, the production pace is fast, and the product quality is effectively guaranteed. Comparing the first two process options, it is clear that option three is the best process option to meet the requirements.

Conclusion

In summary, the selection of the valve body forging process should be analyzed from multiple perspectives to be combined with production costs and actual production efficiency, a comprehensive assessment of the selection of the best forging process. Only through this process of continuous optimization can we produce valve body forgings of qualified quality. The success of the test of this process scheme makes our valve body forging technology rise to another level while enhancing our competitiveness in the valve body forging market and laying a good foundation for the extension of the valve body collar process.

Source: China Valve Bodies Manufacturer – Yaang Pipe Industry (www.epowermetals.com)