Adding a dry film lubricant or anti-seize compound to the threaded portion of stainless steel fasteners will prevent galling. Also, specifying a lower torque on the bolts and tightening them slowly will help reduce friction and heat.
Also, when possible use coarse threads rather than fine – they generate less heat. Finally, controlling the speed of power tools will greatly reduce the chances of galling.
High-Friction Materials
Many types of metal machinery is susceptible to thread galling. The most common cases involve stainless steel or aluminum fasteners that have been subjected to excess friction during tightening or removal. This is because these materials tend to produce high amounts of heat during friction that can cause the fusion or seizing of their mating surfaces.
When a bolt or screw meets its mating surface, the initial contact creates an area of plastic deformation and elevated pressure within the contact zone. This can also produce a localized increase in energy density and temperature that promotes inter-surface adhesion and galling.
The best way to avoid galling is to lubricate the threads of your fasteners with an anti-seize compound prior to installation. Several methods are available, including dry film lubricants like molybdenum disulfide or titanium nitride, and thin-film coatings such as PTFE or Teflon. Slowing down the RPM speed of the wrench during installation can also significantly reduce or eliminate the occurrence of galling.
Dirty Fasteners
While stainless, aluminum and titanium fasteners typically form a thin protective oxide film during tightening, this can break down under high installation pressures allowing the soft metals to come into direct contact with each other. The resulting friction quickly generates heat that fuses and locks the surfaces together, causing thread galling.
Pre-applied lubrication significantly reduces the chances of thread galling. Lubricants with substantial amounts of molybdenum disulfide (moly), graphite, mica or talc are effective as well as extreme pressure waxes. Nickel based anti-seize products are ideal for use with stainless steel.
Damaged or dirty fasteners increase the friction between the components increasing the likelihood of galling. A standard nut should work easily with a bolt when placed together by hand, if it binds this may indicate the threads are damaged or dirty. Slowing down the installation process will also limit the friction and give the fasteners time to cool reducing the chances of galling. Lastly, using fasteners with the correct torque rating will prevent the problem from occurring in the first place.
Damaged Fasteners
It is important to use the proper fasteners when working on projects, as galling can damage a bolt thread and make it unusable. It also increases maintenance and repair costs, as the fasteners will have to be forcibly removed and replaced.
The most common cause of galling is shear between the microscopic surfaces of a fastener’s threads. This shear creates high points that can lock together and generate frictional heat, causing the threads to fuse together. In severe cases, the fasteners will seize to each other and can’t be separated.
There are a few ways to avoid thread galling, including the use of premium stainless steel fasteners with clean and undamaged threads. Slowing the installation process can also reduce the chance of galling by limiting the amount of frictional heat generated. Using lubricants such as anti-seize products can also help to prevent galling, but the type of lubricant used should be selected based on the environment where the fasteners will be installed.
Fastener Installation
While galling is a natural process that can’t be avoided, there are some things you can do to minimize the chances of it occurring. For instance, slowing down the RPM speed during installation can reduce or even eliminate the issue. This is because rapid tightening generates a lot of heat that can’t dissipate quickly and often leads to galling.
Also, selecting fasteners with the right material grades is important for resistance to galling. Fasteners made of harder grades are more resistant than softer ones. Also, it is recommended that you use a premium quality lubricant to reduce the friction between mating threads and avoid galling.
Dry film lubricants with anti-seize properties are excellent for reducing the friction between stainless steel bolts and nuts. These products can be pre-applied or applied on-site and help reduce galling. They contain additives like molybdenum disulfide, graphite, mica, talc and extreme pressure waxes that are effective at reducing friction between the two components.
