At Fasteners Inc. in Denver, we would like to share some pointers on bolts and thread galling. Thread galling is also known as cold welding and although that may sound like a good thing, it’s actually not! Once galling has taken place, the only way to get the bolt out again is to split the nut. Thread galling happens when the heat, pressure, and friction of a bolt being fastened causes it to seize to the nut, unable to move in or out again. If you’ve only secured the nut halfway, this can be very frustrating.
What actually happens during the process of thread galling is that the microscopic surfaces of the bolt thread have high points. Generally, they are passed over without incident, but sometimes those high points are too high, and they get sheared off increasing heat and friction. This in turns builds upon itself with more heat and friction, to the eventual point that it seizes and no longer turns.
Fine and damaged threads are particularly susceptible to thread galling. Most often, galling happens with titanium, aluminum, and stainless steel, especially when using lock nuts. These fasteners come with a protective oxide coating to prevent corrosion. Sometimes that film can get rubbed off or get scraped off. When that happens, the layer is no longer there to prevent metal on metal contact. This greatly increases friction, hence heat, and the chances of thread galling when fastening bolts with nuts. On the other hand, hardened steel bolts, particularly when plated with zinc, seldom gall.
Prevention is the key when it comes to bolts and thread galling. Here are a few tips.
Clean and Undamaged
Make sure that you are using clean and undamaged bolts, especially when it comes to fine threaded bolts. Check each one as you get ready to use it to ensure that there are not particles stuck in the threads and that the threads are even and aligned.
Stop if Galling Starts
Stop immediately, if you notice extra friction while fastening. Wait a couple of minutes for the nut and bolt to cool down, then back it out and start fresh with a new set.
There are a number of lubricants for this very purpose on the market. They are called either anti-seizing or anti-galling. Some nuts offer a waxed finish in order to prevent galling before it starts.
Even though we like to work at a quick pace, slowing it down a bit is going to help avoid galling. With less heat and friction happening, you will see fewer instances of thread galling. In some cases, it is best to avoid using power tools when working with stainless steel and nylon insert lock nuts.
Avoid Pulling Together Joints
Remember, that bolts are not made to bring joints together. Joints should already be held together (use a clamp if necessary) before using a bolt to fasten. Otherwise, your chances of thread galling are substantially increased. It’s worth the extra effort to avoid thread galling at all costs.
Extra Caution with Lock Nuts
When working with nylon insert lock nuts and torque nuts, they generate a significant amount of heat and friction. Try to keep your speed down or consider switching to an alternative locking mechanism.
Now you have a real handle on bolts and thread galling. And you’re better equipped to have a successful project without this issue to deter your results. Count on the experts at Fasteners, Inc. to help you not only find the right fastener system but be more productive by avoiding thread galling.