What are Seamless Steel Tubes for Hydraulic Props?
Seamless steel tubes for hydraulic props are special steel tubes specifically designed for manufacturing hydraulic supports (critical equipment used in coal mine longwall mining faces to support the roof and prevent collapse), cylinders, and hydraulic systems for engineering equipment. They use 27SiMn alloy structural steel as the core material and undergo salt bath quenching at 920℃±10℃ and tempering at 550℃-600℃. This results in high strength, wear resistance, and corrosion resistance, making them suitable for mining, construction, and heavy industry applications.
Steel pipes are classified into two categories based on their manufacturing process: seamless steel pipes and welded steel pipes. Seamless steel pipes are steel pipes without weld seams produced by piercing steel ingots, billets, or bars. They are not ordinary seamless pipes but high-end precision cold-drawn seamless steel pipes with extremely high requirements for materials, dimensional accuracy, and performance.
Technical Requirements:
Due to their direct impact on mine safety, hydraulic support pipes must meet the following extremely stringent technical requirements:
1. Mechanical Properties
High Strength: Must possess extremely high yield strength to withstand enormous internal pressure and external loads.
High Toughness: Prevents brittle fracture under impact loads.
2. Dimensional Accuracy
Inner Diameter Accuracy: Extremely strict inner diameter tolerances are required to ensure precise fit with pistons and seals, preventing leakage.
Wall Thickness Uniformity: Uniform wall thickness must be guaranteed circumferentially; any eccentricity will lead to uneven pressure distribution and premature failure.
3. Surface Quality
Inner Surface Smoothness: The inner wall must be mirror-smooth (roughness Ra typically ≤ 0.4μm) to minimize wear on seals, ensure long-term sealing effectiveness, and reduce frictional resistance.
4. Processing Performance
Deep Hole Machinability: The pipe must possess excellent honing properties to achieve the final dimensional and surface finish requirements through subsequent processing.
Common Materials and Standards:
Common materials for seamless hydraulic prop tubes include 27SiMn, 30CrMoSi, and 35CrMo.
27SiMn: High-strength alloy steel. This steel was specifically developed for mining hydraulic props and features high strength, good hardenability, and excellent toughness. Higher strength options include 30CrMnSi and 35CrMo.
Hydraulic prop tubes are made by adding one or more alloying elements to high-quality carbon structural steel to improve its strength, toughness, and hardenability. After manufacturing, this type of steel typically undergoes heat treatment such as quenching and tempering, chemical heat treatment, and surface quenching. Compared to high-quality carbon structural steel, it has better comprehensive mechanical properties and is often rolled into round, square, or flat shapes for use as important structural components in machinery or machines.
Hydraulic prop tubes are not stainless steel, so their corrosion resistance is not as good. However, their wear resistance and machinability are much better than stainless steel.
Execution Standard:
China has a specific industry standard, GB/T 33160-2016 "Seamless Steel Tubes for Hydraulic Supports," which details the technical requirements. High-standard precision seamless tube specifications, such as DIN 2391, are also commonly followed.
Application Areas: Seamless steel tubes for hydraulic supports are mainly used in the manufacture of hydraulic supports, cylinders, and columns for coal mines, as well as other hydraulic cylinders and columns.
Other applications include hydraulic systems, plastics machinery, injection molding machinery, rubber machinery, forging machinery, die-casting machinery, construction machinery, automotive industry, shipbuilding industry, metal processing, military industry, diesel engines, internal combustion engines, construction machinery, agricultural and forestry machinery, automation machinery, petrochemicals, aerospace, hydraulic and pneumatic systems, air conditioning, and shoemaking machinery.
Manufacturing Process: The manufacturing process of seamless tubing for hydraulic supports is highly precise: High-quality round billet → Hot rolling → Cold drawing/cold rolling → Heat treatment (quenching and tempering: quenching + high-temperature tempering) → Straightening → Internal honing → Non-destructive testing → Inspection and warehousing
Advantages and Disadvantages of Hydraulic Transmission:
Advantages of Hydraulic Transmission:
Compared with mechanical and electrical transmissions, hydraulic transmission has the following advantages:
1. Various components of hydraulic transmission can be conveniently and flexibly arranged according to needs.
2. Lightweight, small in size, low inertia, and fast response speed.
3. Convenient operation and control, enabling stepless speed regulation over a wide range (speed range up to 2000:1).
4. Automatic overload protection.
5. Generally uses mineral oil as the working medium, allowing for self-lubrication of moving surfaces and a long service life.
6. Easily achieves linear motion.
7. Easily automates machines; when using electro-hydraulic combined control, not only can a higher degree of automatic control be achieved, but remote control is also possible.
Disadvantages of hydraulic systems:
1. Low efficiency due to high fluid flow resistance and leakage. Improper handling can lead to contamination of the work area and potentially fires and explosions.
2. Performance is easily affected by temperature changes, making them unsuitable for operation in very high or very low temperatures.
3. High manufacturing precision is required for hydraulic components, resulting in higher prices.
4. Due to leakage and compressibility of the liquid medium, precise transmission ratios cannot be achieved.
5. Difficulty in diagnosing hydraulic transmission malfunctions; high technical skills are required for use and maintenance.
Read more: Which is Better Seamless or Welded Pipe?
