Understanding Thread Galling in Threaded Parts

Galling refers to the wear and tear occurring between two metal surfaces due to friction when they happen to be in sliding contact with each other. Thread galling is prevalent amongst threaded fasteners which are fabricated from stainless steel, steel, aluminium or brass. Therefore, correct steps must be taken from the start in order to lower the risk and occurrence of thread galling. What are the effects of thread galling? What must precautionary measures be employed in order to protect threaded parts such as fasteners, nuts, and screws from galling? Read the following post to get answers to these questions.

How Galling Affects the Design of Threaded Parts?

Galling causes a bump, gall or tear in threaded fasteners, screws, and bolts. When the surfaces of threaded parts get eroded, they leave behind a small cavity or hole in them. This causes microscopic particles to accumulate inside the cavity of the threaded parts. This affects the design and efficiency of threaded parts such as fasteners, nuts, and screws.  Below are some negative implications of galling, which seriously affect the design and construction of the mechanical parts.

• Early Chance of Failure: Galling causes the threads to develop strain, stress, and tears. This can eventually lead to the structural distortion of threaded parts.
• Bad Operating Environment: One of the major concerns is the entry of minute particles and debris inside the threaded fasteners. These particles might affect the efficiency of mechanical parts.
• Costly Repairs: Any kind of damage to the threads of fasteners, nuts or screws may require repairs. As the structure of the threaded parts gets distorted, repairing them becomes difficult. External thread galling is easy to repair, whereas internal thread galling becomes a costly affair owing to the structure of the mechanical parts.

How to Take Care of Thread Galling?

Various effective measures are taken for protection against thread galling. Here are some measures:

• Thread Lubrication: Using special anti-galling lubricants can help reduce frictional coefficient and galling in the threaded fasteners. Also, various threads are given a Polytetrafluoroethylene (PTFE) based coating in order to eliminate any chances of rust or corrosion between the threads. These coatings are best suited for stainless steel fasteners, where abrasion and chemical resistance properties are needed.
• Minimize the Wrench Speed: Heat is the main cause of galling in fasteners. During installation of fasteners, as the wrench speed increases, more heat is generated. Hence, reducing the wrench speed helps lower the heat generated in them.
• Use Coarse Threads: Choosing coarse threads over fine threads helps to reduce galling. The coarse threads are more tolerant towards abuse during the handling process. Also, owing to the larger thread allowance (the gap between the actual and basic thread profile) helps prevent galling in fasteners and nuts.
• Ensure Tight Tolerance: Having high tolerance in the threaded fasteners can help avoid galling. This also makes fasteners less prone to any kind of sliding or friction. Thread rolling ensures the same dimension and tolerance in threaded fasteners, nuts or bolts.

All these galling prevention strategies help to increase the longevity and efficiency of a threaded fastener, nut or screw. If planned beforehand, it can also help avoid costly repairs and servicing. If you would like to know more about thread galling and prevention tips please contact Norwood Screw Machine Parts. We provide performance oriented fasteners enhanced with anti-galling defense mechanisms.