Application and Advantages of Precision Rolled Seamless Steel Pipes in Mining Cylinder Manufacturing

Abstract: This paper compares the mechanical properties, processing techniques, and economic feasibility of precision rolled seamless steel pipes with those of traditional hot-rolled and cold-drawn precision seamless steel pipes. Test results indicate that, under identical specifications, precision rolled seamless steel pipes demonstrate superior overall mechanical performance. Compared to traditional hot-rolled seamless steel pipes, they significantly reduce processing time and lower production costs by approximately 2%. Compared to cold-drawn precision seamless steel pipes, they maintain similar processing efficiency but offer a cost reduction of about 13.6%. These advantages underscore the strong potential of precision rolled seamless steel pipes for widespread application in the manufacturing of mining hydraulic cylinders.

Introduction

Hot-rolled seamless steel pipes are commonly used as the primary raw material in the manufacturing of mining hydraulic cylinders. In recent years, the use of cold-drawn precision seamless steel pipes has grown steadily, driven by their superior processing efficiency. However, their high cost and relatively low impact toughness have limited their application in coal mining machinery. Precision rolled seamless steel pipes are manufactured using advanced precision tube rolling units. Throughout the hot rolling and finishing stages, dimensional accuracy is tightly controlled, producing pipes with highly precise inner and outer diameters, uniform wall thickness, and excellent straightness. These pipes are delivered in a quenched and tempered condition, following a production process that includes continuous casting, heating, perforation, precision rolling to the target diameter, quenching, tempering, straightening, non-destructive testing, and final finishing. Boasting excellent mechanical properties, high dimensional accuracy, and exceptional cost-effectiveness, precision rolled seamless steel pipes show significant potential for use in hydraulic cylinder manufacturing. Their use can facilitate technological innovation and drive industrial upgrading within the sector. This paper analyzes and compares the performance of precision rolled seamless steel pipes, hot-rolled seamless steel pipes, and cold-drawn precision seamless steel pipes in hydraulic cylinder manufacturing, focusing on three key aspects: mechanical properties, processing technology, and economic benefits.

1. Mechanical Properties of Precision Rolled Seamless Steel Pipes

27SiMn is the most commonly used material for mining hydraulic cylinders. Its high strength, excellent wear resistance, good hardenability, low cost, and balanced chemical composition make it suitable for a wide range of applications. This article uses the 27SiMn pipe for a jack cylinder with a diameter of 160 mm as an example to compare and analyze the mechanical properties of traditional hot-rolled seamless steel pipes, cold-drawn precision seamless steel pipes, and precision rolled seamless steel pipes. According to GB/T 25974.2-2010, Hydraulic Supports for Coal Mines Part 2: Technical Conditions for Columns and Jacks, the impact energy requirement for materials used in hydraulic support columns and jacks is clearly defined: the notch impact energy must be at least 27 J at -20°C. Based on this, technical requirements for steel pipes used in hydraulic cylinders have been established, and steel mills produce pipes that meet the same or similar specifications in accordance with this standard. The traditional hot-rolled seamless steel pipes selected have dimensions of 194 mm outer diameter × 22 mm wall thickness. These pipes are delivered in the hot-rolled condition and undergo quenching and tempering in a box furnace after cutting and sawing. Cold-drawn precision seamless steel pipes with dimensions of 194 mm outer diameter × 157 mm inner diameter are selected. These pipes are manufactured by quenching and tempering hot-rolled seamless steel pipes, followed by cold drawing, straightening, and stress relief annealing. The precision rolled seamless steel pipes selected have dimensions of 194 mm outer diameter × 19 mm wall thickness and are delivered in a quenched and tempered condition by the steel mill. Samples of the three types of seamless steel pipes were collected in accordance with the relevant provisions of GB/T 2975-2018, Sampling Location and Sample Preparation for Mechanical Properties Test of Steel and Steel Products. Tensile and impact tests were then performed, with the results presented in Table 1.

Table 1: Mechanical properties of three seamless steel pipes

As shown in Table 1, all three types of seamless steel pipes demonstrate relatively high strength, meeting the requirements for jack cylinders with a diameter of 160 mm. However, in terms of plasticity and toughness, the traditional hot-rolled seamless steel pipe and the precision rolled seamless steel pipe perform better than the cold-drawn precision seamless steel pipe. According to GB/T 25974.2-2010, Hydraulic Support for Coal Mines Part 2: Technical Conditions for Columns and Jacks, the notch impact energy of materials used in hydraulic support column jacks must be at least 27 J at -20°C.

The impact energy of the cold-drawn precision seamless steel pipe is 31 J. Although this meets the standard, the margin is narrow. By comparison, the impact energy of traditional hot-rolled seamless steel pipes and precision rolled seamless steel pipes is 68 J and 79 J respectively, both exceeding the standard by a significant margin. The primary reason for the difference in toughness among these pipes, despite being made from the same material, lies in the processing method used for the cold-drawn precision seamless steel pipe. This pipe is first quenched and tempered, then subjected to cold drawing. The plastic deformation introduced during cold drawing induces work hardening within the material, which increases its strength and hardness but reduces its toughness.

2. Processing Technology

The typical structure of a mining hydraulic cylinder body is shown in Figure 1. The cylinder barrel is generally manufactured from traditional hot-rolled seamless steel pipes or cold-drawn precision seamless steel pipes.

(a) Cylinder bottom (b) Cylinder barrel

Figure 1 Typical structure of a mining hydraulic cylinder

The dimensions and manufacturing processes of hydraulic cylinders made from traditional hot-rolled seamless steel pipes and cold-drawn precision seamless steel pipes are presented in Table 2.

Table 2. Dimensions and Manufacturing Processes of Seamless Steel Pipes Commonly Used in Hydraulic Cylinders

2. Processing Characteristics of Seamless Steel Pipes

As shown in Table 2, traditional hot-rolled seamless steel pipes generally exhibit poor straightness due to their large inner bore machining allowance and the lack of straightening treatment after quenching and tempering. Therefore, when traditional hot-rolled seamless steel pipes are used in hydraulic cylinder production, the pipe must undergo two flattening processes, and the inner bore requires rough boring. In contrast, cold-drawn precision seamless steel pipes have an inner bore machining allowance of only 2–4 mm and typically maintain a straightness tolerance within 0.3 mm/m. As a result, when using cold-drawn precision seamless steel pipes, only a single flattening operation is required, and rough boring of the inner bore is unnecessary. Scraping and rolling can be performed directly after flattening, resulting in significantly higher processing efficiency compared to traditional hot-rolled seamless steel pipes. Precision rolled seamless steel pipes have an inner bore machining allowance of 4–8 mm and, after straightening, achieve a straightness of no greater than 1.5 mm/m. Their machining allowance and straightness fall between those of cold-drawn precision seamless steel pipes and traditional hot-rolled seamless steel pipes. To assess the processing characteristics of precision rolled seamless steel pipes, trials were carried out following the same procedures used for cold-drawn precision seamless steel pipes. The precision rolled seamless steel pipes used in the processing test had an outer diameter of 194 mm and a wall thickness of 19 mm, with a measured inner bore machining allowance of 5–6 mm. The processing equipment included a CNC sawing machine, CNC lathe, and scraping machine, all of which were used in the processing trials. The results demonstrated that precision rolled seamless steel pipes eliminate the need for rough boring and the two flattening steps. When scraping without rough boring, the scraping feed rate reached 400 mm/min, matching the processing efficiency of cold-drawn precision seamless steel pipes. Overall, the comprehensive processing efficiency of the inner bore is estimated to be 50% higher than that of traditional hot-rolled seamless steel pipes. The processing test for the 194 mm × 19 mm precision rolled seamless steel pipe is shown in Figure 2. After cutting, flattening, welding (for accessories), scraping and rolling, stoppering, and beveling, all measured parameters—including inner bore dimensions and surface roughness—met quality standards. The machining conditions were favorable, demonstrating an efficient processing technology.

(a) Flattening (b) Scraping and rolling (c) Inner bore after scraping and rolling (d) Frame nest state

Figure 2 Processing test of 194 mm × 19 mm precision rolled seamless steel pipe

3. Promotion Economy

An economic analysis of the three types of seamless steel pipes discussed above was conducted. Taking a jack cylinder with specifications of 160 mm inner diameter × 1,200 mm length as an example, the material cost, processing cost, and iron scrap were calculated. Here, the processing cost refers to the total cost from initial machining through scraping and rolling. The statistical results are presented in Table 3.

Table 3 Statistics of Economic Benefits of Three Types of Seamless Steel Pipes

According to the above statistics, cold-drawn precision seamless steel pipes have the poorest economy and highest production costs, whereas precision rolled seamless steel pipes offer the best economic efficiency. For a jack cylinder with specifications of 160 mm × 1,200 mm, using precision rolled seamless steel pipe can reduce costs by approximately 2%.

4. Conclusion

• Precision rolled seamless steel pipes exhibit excellent overall mechanical properties. For pipes of the same specifications, their strength and impact energy are comparable to or exceed those of traditional hot-rolled and cold-drawn precision seamless steel pipes.
• Compared to traditional hot-rolled seamless steel pipes, precision rolled seamless steel pipes eliminate the need for inner bore rough boring and two flattening steps, significantly shortening factory processing time and reducing costs by approximately 2%.
• The processing efficiency of precision rolled seamless steel pipes matches that of cold-drawn precision seamless steel pipes, while providing cost savings of approximately 13.6%, making them well-suited for broader application in the manufacturing of mining cylinders.