Galling is a common and potentially serious problem that occurs when metallic surfaces move against each other under pressure. This process is caused by a combination of friction and adhesion between the surfaces. When galling occurs, material is pulled from one surface and adheres to the other in the form of a lump. These lumps lead to even more galling, creating a vicious cycle that can quickly exacerbate the situation.
Why does galling occur?
The risk of a material galling depends on its ductility. Softer materials tend to be more prone to galling because they deform more easily under pressure, whereas harder materials are more resistant. This is particularly relevant in threaded fasteners, where galling can lead to significant problems.
Galling in threaded fasteners
When a threaded fastener is tightened, pressure builds up between the contact surfaces and the sliding surfaces of the threads. This situation is especially common if the fastener is made of materials such as stainless steel, aluminum, titanium, or other alloys. If the galling becomes severe, it can lead to seizing – a condition where the threads become stuck together and the fastener cannot be budged. Continued tightening under these conditions can result in the bolt breaking or the threads being stripped.
How you can prevent galling
Fortunately, there are several effective solutions for preventing galling and seizing in threaded fasteners:
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Lubricating the threads: By lubricating the internal and/or external threads, friction is reduced, which decreases the risk of galling. Choose a lubricant that is compatible with the materials you are working with.
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Controlled tightening: Tighten the threaded fastener at a slower pace to avoid the rapid increase in pressure that can lead to galling. Using a torque wrench can help ensure that the correct tightening torque is applied.
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Material selection: Choose a different stainless alloy for the bolt and the nut to achieve different hardness levels. An important principle is that the nut must always be stronger than the bolt to avoid damage to the threads.
Practical tips
- Clean the threads: Ensure the threads are clean and free from dirt and particles that can increase friction.
- Use the right lubricant: Use a lubricant that is specifically designed for the materials used in the threaded fastener.
- Regular maintenance: Inspect and maintain threaded fasteners regularly to detect early signs of galling or seizing.
By following these guidelines, you can significantly reduce the risk of galling and seizing in your threaded fasteners, which improves both the durability and functionality of your mechanical joints. Understanding and preventing galling is an important part of maintenance and can save both time and money in the long run.