Bolt Specifications and Quality Control
- What are the common specifications of railway bolts?
Common ones include bolts of M20, M22, M24 and other specifications. M20 bolts are often used in parts with small stress such as the connection between sleepers and ballast; M22 bolts can be used for the connection of some medium - sized components, such as the fixing of clips and sleepers; M24 bolts are widely used in occasions with large stress such as the connection between fishplates and rails. The length of bolts also varies according to different usage scenarios, ranging from 80mm to 200mm. For example, the length of fishplate connecting bolts is mostly between 120 - 180mm.
- How are the strength grades of bolts divided? Which scenarios are they suitable for?
Bolt strength grades are usually divided into 4.8, 8.8, 10.9, etc. 4.8 - grade bolts have low strength and are suitable for connections with small stress, such as the fixing of some auxiliary components. 8.8 - grade bolts have high strength and can be used in medium - stress parts such as fishplate connections and clip fixing, and are widely used in ordinary railway lines. 10.9 - grade bolts have higher strength and are suitable for scenarios with extremely high requirements for connection strength such as high - speed and heavy - haul railways, such as key connection parts of high - speed turnouts.
- What are the key points of quality control in the bolt production process?
Raw material quality control requires selecting steel that meets the standards, such as No. 45 steel, 40Cr, etc., and conducting material inspection to ensure that the chemical composition and mechanical properties meet the standards. During processing, control the thread accuracy to ensure that the thread form, pitch, etc. meet the requirements, and avoid problems such as thread slipping. In the heat treatment process, the temperature and time must be strictly controlled to ensure that the bolt reaches the specified strength and hardness. For example, the hardness of 8.8 - grade bolts should be between HRC22 - 32. The surface treatment should be uniform, such as the galvanized layer thickness should be more than 8μm to improve corrosion resistance.
- What are the quality control measures during bolt installation?
Before installation, check the appearance of the bolt, which must be free of cracks, thread damage, rust and other defects, and check the thread accuracy with a thread go - no - go gauge. Use appropriate tools such as torque wrenches during installation, and tighten according to the specified torque to avoid being too loose or too tight. For high - strength bolts, apply an appropriate amount of lubricant before installation to reduce tightening resistance and ensure accurate torque. The installation sequence should be reasonable. When connecting multiple bolts, they should be tightened symmetrically and evenly to avoid uneven stress on components. After installation, check whether the bolt is perpendicular to the connecting surface and there is no skew.
- What are the quality monitoring methods of bolts during use?
Regular appearance inspection, check whether the bolts are loose, rusted, cracked, etc., and deal with problems in time. Use a torque wrench to regularly detect the tightening torque of the bolts, and timely retighten the bolts with insufficient torque. For bolts that have been used for a long time or in harsh environments, samples can be taken for mechanical performance testing, such as tensile strength and yield strength tests, to evaluate whether their performance meets the standards. In high - speed and heavy - haul lines, methods such as ultrasonic testing can be used to check whether there are hidden dangers such as fatigue cracks inside the bolts.