What is Thread Galling?
Fastening components together using threaded surfaces is a widespread practice across a range of industries. During installation, bolt threads can be affected by increased pressure and friction, leading to a phenomenon named "cold welding." This occurrence traps the threads, causing thread galling. It's important to be aware that these surfaces have tiny high points that can potentially come into contact during fastening procedures. Usually, this isn't an issue since they slide smoothly over one another without causing harm or damage; however, there are occasions when they fail to bypass one another correctly - which results in the shearing and locking of these high points instead. Consistent tightening adds pressure which increases both friction and heat, leading to even more material being shaved off until such point where failure occurs.
Unfortunately, once thread galling has taken place, the damage is irreversible, and cutting the bolt or splitting the nut is the only way to rectify the issue. Understand the impacts of thread galling to prevent irreparable damage to your fasteners. Don't let thread galling cost you time and money – in this blog, we’re going to provide details on what thread galling is, what causes it, and how to take preventive measures to protect your fasteners.
Thread Galling Causes
Thread galling is a common issue with stainless steel fasteners. Although it may occur naturally, several factors can increase its risk. Dirty or damaged threads, fastening under load or too quickly, poor environmental conditions, the absence of lubricants, and the use of locking fasteners can all lead to thread galling. Knowing these thread galling causes can help prevent it from happening in the first place. Galling is much less common with steel parts.
Fasteners That Are Susceptible to Galling
Stainless steel thread galling is a common problem, and aluminum and titanium fasteners are also susceptible to thread galling, especially when using lock nuts or damaged threads. Fine threads are also particularly susceptible to galling. Fortunately, hardened steel bolts that are zinc plated rarely experience galling. These soft metals create a thin protective oxide film on their surfaces, which reduces friction and prevents corrosion during the fastening process. However, this protective film can become scraped off under the pressure and movement of the fastener, leading to direct metal-to-metal contact. As friction increases, the risk of thread galling also increases significantly.
How to Prevent Thread Galling
For thread galling prevention, it's important to follow a few key practices. First and foremost, slow down your installation speed. Excessive heat generated by friction is a major contributor to galling, so taking your time can make all the difference. Avoid using power tools when installing stainless steel and other fasteners prone to thread galling and be particularly cautious when using nylon insert lock nuts, which can greatly increase the risk of galling.
In addition, avoid using bolts to pull joints together, as this can significantly increase the chances of galling. Instead, ensure that the materials being bolted are already in position, and use clamps if necessary to hold the joint together during bolting.
Using a lubricant can also help dramatically reduce the risk of galling. Lubricants include anti-seize compounds, thread lockers such as Vibratite and Loctite, light machine oils, or a product such as WD-40. Please keep in mind that adding lubricants to a bolted joint will affect the joint’s torque holding capacity and maximum tightening torque. It is possible to over torque a lubricated joint beyond the bolt’s capacity and stretch the bolt. Additionally, keep in mind that some nuts come with a waxed finish to help reduce the risk of galling.
Finally, take care to avoid damaged or dirty threads on your fasteners. Check for damage to the threads of each bolt, and always use clean and preferably new parts to reduce the risk of debris in the threads. When working with lock nuts, such as nylon insert or prevailing torque nuts, extra care is required due to the increased friction and heat generated during installation. If you're having thread galling issues, consider a different locking mechanism or simply slow down your installation speed.
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