Galling is something that occurs in fasteners because of friction and the adhesion of metallic surfaces while sliding. During the galling process, the material from one surface is attached to another, which creates a lump and, as more lumps form, cause additional galling.
Most thread surfaces come with very small points, which create friction when fastening. This makes it hard for them to slide over one another without resulting in damage.
The material’s ductility is an important factor and one that determines how likely it is to gall. It is best to use harder materials to prevent galling because these are typically more resistant.
Thread galling occurs when the fasteners are installed. The bolt threads are often affected because of the additional pressure and friction, which seize to the threads in a trapped hole, during a process that is now known as “cold welding.” After galling has occurred, you cannot reverse the damage unless you cut the bolt or split the nut.
What Type of Fasteners Does Galling Affect?
Titanium, aluminum, steel, and stainless steel are prone to galling, more so than other materials. Don’t try to use fasteners if they have threads that are damaged or those with very fine threading. This is going to help reduce the likelihood of galling. A smart choice for applications where galling may occur is zinc-plated hardened steel bolts.
How to Prevent Galling
The good news is, while galling can’t be reversed once it happens, it can be prevented. Some tips to help prevent this from happening include:
Install the Fasteners Slowly
The heat created by adhesion and friction is the main contributor to cases of galling. Because of this, you can reduce the likelihood this will happen by slowing down how quickly you are installing the fasteners. Try to avoid using power tools when installing any type of stainless steel or other materials that are not immune to cases of galling.
Don’t Bring Joints Together Using Bolts
Bolt function doesn’t include pulling two materials into the proper position. When using bolts for this purpose, there is a much higher likelihood that galling will occur. The materials need to be installed so that the nut can be enforced to help complete the entire tightening process. You can also use clamps for holding the joints together when needed.
The likelihood of galling can be reduced if you use lubricants. These will reduce the total frication and ensure a smoother sliding process.
As you can see, there are more than a few ways you can reduce the likelihood that galling will occur. Taking the time to ensure that you use the right materials and using the prevention tips above will minimize the likelihood of galling.
Remember, galling is not able to be reversed. In most cases, you will have to throw out the affected fastener and use a new one. This is a waste of money, so preventing it is the best course of action.