Archive: Apr 2022
Galling and Non Ferrous Fasteners
Galling is one of the most common problems we see when tightening fasteners. Galling, also known as cold welding occurs when two metal surfaces slide against each other, resulting in metal from one surface becoming part of the other. This is problematic because it can lead to broken fasteners, weakened joints, and damaged threads. In some cases of galling, the fastener can be removed.
However, in more extreme cases the nut and bolt can become welded together and the installer will not be able to remove the fastener.
The science behind galling can be frustrating, and we have learned the hard way over the years. If you have experienced non-ferrous parts that have refused to play well together in your assembly or install sandbox, the following info may be of help.
Slow Down Installation Speed.
Friction and heat are the main contributors to galling. Slowing down during installation or removal will reduce the amount of heat and friction produced.
Use a Lubricant.
Reducing friction by using the proper lubricant is the most effective way to reduce galling. Even if the joint is permanent, lubrication is still required. We do not recommend spray film lubricant, instead opt for an anti-seize product.
Use a torque wrench and correct force.
Reducing contact stress will lessen the risk of galling. In order to prevent over-tightening, using a torque wrench to control the force is necessary. Ask KJ for torquing recommendations for your material application.
Ensure hardness difference of at least 50 Brinell between nut & bolt Surfaces treated so that they are harder, for example, hard chrome-plated, nitrided, carburised or cold worked surfaces are usually less prone to galling.
Avoid Damaged or Dirty Threads.
Dirt and other abrasive material between the mating surfaces will create friction and heat.
Use Extra Care With Lock Nuts.
Lock nuts are designed to add extra resistance and heat when installed, so it is recommended to avoid using them when you can. If necessary, make sure you are installing slowly to prevent extra heat production.
Dig deeper into mating materials and their compatibility… Understanding mating materials and their compatibility can help reduce galling. Mixing nut and bolt grades can be effective in preventing galling.
Having the proper fit is so important when it comes to preventing galling and minimizing thread burrs. The fit should be tight enough to prevent vibration and wear, but should still have enough clearance to prevent galling. You should keep the contact load on the components that slide to a minimum, and the contact area maximized.