How to Eliminate Thread Galling in Fasteners
Galling is a common form of wear that can occur when threaded fasteners are installed or removed. With enough force and friction between threads, mating surfaces will begin to wear or gall. As the threads rub together, particles are broken off from the mating surfaces and increase friction between the threads. Once a fastener begins to gall, it will only get worse. The result of galling can be seizure, or the fastener’s inability to continue rotating. Other terms describing seizure are cold-welding, friction-welding, and/or “freezing up”. Once a fastener has seized, continuing to torque the fastener may result in it breaking.
Thread galling is a huge frustration for system designers and technicians. After designing an often-complex mechanical system, the last thing an engineer wants to address is frozen fasteners. Seized fasteners can slow down production or repair resulting in lost time and money. Because of all this, it is worth the effort to understand how galling and seizing can be avoided.
There are many factors that affect a fastener’s propensity to gall. They include:
- Installation Speed
- Thread Type
- Thread Damage
- Thread Cleanliness
Lubrication: An effective countermeasure to galling and seizing is thread lubrication. Traditional methods for lubricating threads include brushing on grease or compounds known as anti-seize. While relatively inexpensive, not all applications lend themselves to the use of these lubricants or the requirement for each fastener to be brushed with lubrication. If traditional brush-on lubrication does not meet the demands of your application, it is wise to consider a trusted dry lubrication coating that does not compromise the integrity of the fastener or tight tolerances in the system’s design.
When technicians coat fasteners with Dicronite®, a modified tungsten disulfide (WS2) coating, the lubricating particles bond to the surfaces of the threads. The result is an extremely thin (0.5 microns), lubricious film that reduces friction and eliminates galling between mating threads.
Torque: The higher the torque, or rotational force, the greater the pressure between threads. As torque increases, the likelihood of galling also increases. Using Dicronite® can help you reach the required torque for your fasteners without galling and seizing.
Installation Speed: High speed installation increases the likelihood of galling and seizing. While slowing down installation or switching to manual installation (e.g. socket wrench) can help reduce galling and seizing, this loss of time is not always acceptable. The Dicronite® coating reduces friction and wear between threads and allows installers to use significantly higher installation speeds without causing a fastener to gall and seize.
Thread Type: Rolled threads are less likely to gall than cut threads, and coarse threads resist galling more than fine threads. Dicronite® dry lube can be applied to all kinds of threads. Male, female, course, fine, rolled, and cut threads can all be coated with Dicronite®. In all cases, Dicronite® is an effective anti-galling and anti-seize coating.
Material: Generally speaking, mating parts of the same material have a higher tendency to gall. Stainless Steel, Aluminum, and Titanium are especially prone to galling. However, in some cases the operating conditions or requirements of the component or assembly limit material selection. In other cases, changing materials may simply be inconvenient. Adding Dicronite® to troublesome fasteners can effectively eliminate galling and seizing, removing the need for changes in material selection.
Thread Damage and Cleanliness: Damaged threads or dirty threads are both more likely to gall and seize. It’s a good idea to check threads for damage or contamination prior to installation.
Dicronite® DL-5® is the world’s leading dry film lubrication that eliminates galling in threaded fasteners. It is applied by professional technicians to fasteners of all kinds. Every day, customers all over the world send hundreds of fasteners for Dicronite® coating to the application facility closest to them. Trained technicians first clean the parts with a de-greaser and solvent. They then blast them with a very fine particle abrasive that removes any remaining dirt. The cleaned fasteners are then prepared for coating by masking off areas of the fastener that the customer wants no over spray. Finally, Dicronite® is impingement-applied by a high-velocity process that results in a permanent molecular bond between the fastener’s surface and the Dicronite® coating. This tungsten disulfide (WS2) coating adheres to all metals and numerous ceramics and plastics. The process is finished when inspection confirms the presence of a continuous film that is only ½ micron thick covers all the requested surfaces. It is ideal for systems requiring tight tolerances. Coated fasteners have an ultra-low coefficient of friction which ranges between .03 and .07, depending on system loads and other variables. It does not flake or attract particles; best of all, it does not gall!
Additional infromation on Dicronite® as an Anti Galling Coating.