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Author: Site Editor Publish Time: 2025-02-11 Origin: Site
Stainless steel fasteners are widely used in many fields due to their good corrosion resistance and high strength. However, locking occurs from time to time during use, which brings many inconveniences to equipment maintenance and normal operation. The following will analyze the reasons for the locking of stainless steel fasteners from multiple angles.
The hardness of stainless steel is relatively high, and its surface hardness is usually between 200-300HV. When stainless steel fasteners are assembled, the threads squeeze each other, and the high-hardness surface is prone to produce tiny wear particles. These particles accumulate in the thread gap, hindering the normal relative movement of the threads, resulting in locking. In addition, stainless steel has a complex chemical composition and contains a variety of alloy elements such as chromium and nickel. Under specific chemical environments, these elements may react chemically with the surrounding medium to generate some difficult-to-dissolve compounds that adhere to the thread surface, further exacerbating the risk of locking.
During the assembly process, if the preload applied to the stainless steel fasteners is too large, excessive stress will be generated between the threads. When the stress exceeds the elastic limit of the material, the thread will undergo plastic deformation. This deformation changes the geometry and size of the thread, making the fit between the threads extremely tight and difficult to disassemble, which eventually leads to locking. For example, in some high-strength mechanical connections, operators may over-tighten the bolts to ensure the firmness of the connection, which in turn causes the locking problem.
Lubrication is essential for the normal operation of fasteners. If stainless steel fasteners are not properly lubricated during assembly, the friction coefficient between the threads will increase significantly. During the tightening process, high friction will cause the surface temperature of the thread to rise, which will accelerate the wear and deformation of the thread surface. At the same time, lack of lubrication will also make the thread surface more susceptible to dust, impurities, etc., which will form a "glue"-like substance when mixed with the wear particles on the thread surface, firmly adhering to the thread, making it difficult to disassemble the fastener and locking.
Although stainless steel has a certain degree of corrosion resistance, electrochemical corrosion may still occur on its surface in a humid environment. When fasteners are exposed to humid air, water molecules will form a thin layer of water film on the thread surface. This water film will undergo an oxidation-reduction reaction with elements such as chromium in stainless steel to generate corrosion products such as chromium oxide. These corrosion products will fill the thread gaps, gradually accumulate and harden over time, and eventually cause the fasteners to lock. For example, in some mechanical equipment in coastal areas, stainless steel fasteners are prone to locking due to long-term erosion by salt spray in the sea breeze.
In high temperature environments, the performance of stainless steel fasteners will also change. On the one hand, high temperature will cause the metallographic structure of stainless steel to change, resulting in a decrease in its hardness and strength. On the other hand, high temperature will accelerate the oxidation process on the surface of the thread and form a dense oxide film. This oxide film will shrink after cooling, making the gap between the threads smaller, increasing the friction and bite force between the threads. At the same time, high temperature will also accelerate the evaporation of the lubricating oil on the thread surface, lose its lubrication effect, and further increase the risk of locking. For example, in some high-temperature furnace equipment, if stainless steel fasteners are kept at high temperature for a long time, they are prone to locking.
If stainless steel fasteners are frequently disassembled and assembled, the thread surface will be worn and deformed many times. During each disassembly and assembly process, the relative movement between the threads will generate new wear particles. These particles continue to accumulate, eventually causing the thread fit clearance to become smaller and increasing the possibility of locking. Moreover, frequent disassembly and assembly may also cause the anti-corrosion coating on the thread surface to be damaged, making the thread more susceptible to corrosion, thereby aggravating the locking phenomenon.
During the use of the equipment, if there is a lack of regular inspection and maintenance of stainless steel fasteners, some potential problems may not be discovered in time. For example, corrosion on the thread surface, drying of lubricating grease, etc., if not handled in time, will gradually develop into a locking problem. Regular inspections can promptly detect abnormal conditions on the thread surface and take appropriate measures to repair or replace them, thereby effectively avoiding the occurrence of locking.
The locking of stainless steel fasteners is a complex problem with a variety of causes. To effectively avoid the occurrence of locking, it is necessary to take comprehensive measures from multiple aspects such as material selection, assembly process, use environment and maintenance. In terms of materials, you can choose some stainless steel materials that have been specially treated and have better corrosion resistance and anti-bite properties; during the assembly process, the preload should be strictly controlled to ensure adequate lubrication; during use, try to avoid exposing fasteners to harsh environments, such as humidity and high temperature; at the same time, strengthen daily inspection and maintenance of fasteners, and promptly discover and deal with potential problems. Only in this way can the occurrence of stainless steel fasteners locking be minimized to ensure the normal operation and safe use of mechanical equipment.
Stainless steel fastener locking is a common problem, but the risk of locking can be effectively reduced by taking the following preventive measures:
Choose suitable materials: Choose stainless steel materials with good corrosion resistance and appropriate strength according to the use environment. For example, in a humid environment, 316 stainless steel has better corrosion resistance than 304 stainless steel.
Reasonable selection of specifications: Ensure that fasteners of appropriate length and specifications are selected, so that 1-3 pitches of the nut are exposed after tightening.
Clean threads: Before assembly, ensure that the thread surface is clean and free of grease, impurities, solder joints and metal chips.
Use lubricants: Apply lubricants such as butter, 40# engine oil or special anti-seizure agents (such as Molylub) on the thread surface to effectively reduce the friction coefficient and prevent locking. For high temperature environments, solid lubricants containing silver, aluminum or copper particles can be used.
Uniform force: During the tightening process, the force must be uniform, avoid excessive force or locking too fast, so as to avoid a sharp rise in temperature and cause locking.
Use appropriate tools: Try to use torque wrenches or socket wrenches, and avoid using adjustable wrenches or electric wrenches.
Vertical screwing: The nut must be screwed perpendicular to the axis of the bolt to avoid tilting.
Control torque: According to the specifications and materials of the fasteners, strictly control the torque to avoid exceeding the safe torque.
Regular inspection: Regularly check whether the fasteners are loose, corroded, worn or threaded, and deal with problems in a timely manner.
Lubrication and maintenance: Apply grease regularly to keep the thread surface lubricated and reduce the wear rate.
Anti-rust measures: Apply anti-rust oil on the surface of the fastener to form a protective film to avoid long-term exposure to a humid environment.
Avoid material interchange: Try to avoid using stainless steel bolts and nuts of different materials for assembly, because different materials have different thermal expansion coefficients, which may cause locking.
Use washers: Using washers between nuts and connection surfaces can effectively prevent over-tightening.
The above measures can effectively prevent the locking of stainless steel fasteners and ensure the normal operation and maintenance of the equipment.
