Galling is an issue that occurs with some fasteners. It happens because of the combined effect of adhesion of the metallic surfaces and friction, which occurs during sliding. Because of galling, material from one surface adheres to another, creating a lump. This results in the build-up of excessive lumps that can cause additional galling.
Thread surfaces come with small points to create friction when used for fastening. This makes it hard for them to slide over one another without causing damage.
The tendency a fastener has to gall depends on the ductility of the material. It is best to use harder materials to help avoid cases of galling, as they are typically more resistant.
Usually, thread galling occurs during installation. The threads of a bolt are affected because of excess friction and pressure. This pressure and friction cause the seizing of threads of a tapped hole. When this happens, it is called “cold welding.” After galling occurs, you cannot reverse the damage without cutting the bolt or splitting the nut – these are the only ways you can move forward.
Types of Bolts Susceptible to Galling
Several materials are susceptible to galling. Some of the most common materials this issue occurs in include titanium, steel variations, aluminum, and stainless steel. Try to avoid using fasteners that have damaged threads or ones that use fine threading. By doing this, you can reduce the possibility of galling. An ideal option for these applications is zinc-plated hardened steel bolts.
Tips to Avoid Galling
There are a few things you can do to help prevent galling. These tips are found here.
The heat resulting from adhesion and friction is the main factor that leads to galling. By slowing down the installation speed, you can prevent this from occurring. Try to avoid using power tools when installing stainless steel or other materials that are not immune to galling.
Do Not Use Bolts to Bring the Joints Together
The function of a bolt is not to pull materials together or into the proper position. If you use bolts to do this, there is a much higher likelihood of galling occurring. You need to put the materials in a way that the nut can be enforced and tightened. If necessary, use clamps to bring the joint together.
Use a Lubricant
You can reduce the likelihood of galling if you use lubricants. This is going to help reduce friction and allow a much smoother sliding process.
Avoid Using Dirty, Dented, or Damaged Threads
If threads are damaged, skip using that fastener. This is especially important with finer threads. Standard nuts should work well with a bolt when put on by hand. If this does not work, it may be because the treads are dented or dirty.
If you want to ensure your fasteners are damage-free and ready to be used without issue, buy from a quality supplier. Being informed and knowing how to prevent galling is also beneficial.