Galling can happen for several reasons, but none make it any less frustrating. Top-quality metal and industry-regulated material is susceptible to this common issue, but there are ways to prevent it.
What is Galling in Metal?
Though it is most common in stainless steel, galling can happen in a variety of metals. The term is used to describe a type of wear on metal when it unintentionally adheres to another sliding surface. When metal galls, some of the material is pulled with the contacting surface.
Galling is defined as friction and adhesion between the two metal surfaces, followed by tearing the structure beneath the surface. When this happens, the metal separates from the component it was originally attached to when provided with enough adhesion energy, often due to friction.
Galling is also known as cold-welding. This is the process that can happen when the surfaces of a nut and bolt threads are placed under pressure. They begin to weld together due to friction and force.
Stainless steel and aluminum are the most common metals to encounter the issue of galling, but it can happen in any metal. Unfortunately, this common issue occurs even in nuts and bolts that pass all required inspections such as threads, material, mechanical, and more.
What Causes Galling?
There are several reasons why metal galls, but one of the most common, is a significant force compressing the surface of the two metals together. This generally occurs when two or more metals under high loads are in contact with one another.
Another one of the major causes of this issue can be the difference in cuts between nuts, bolts, and screws. There is a difference in the threading method between screws and most nuts and bolts. Thus, there can be issues when the two parts are threaded to each other and put under high pressure or friction.
The material has a crystal structure and is ductile, which promotes cohesive attraction. However, due to the atomic structure of their atoms, certain metals are more prone to galling than others.
When cohesive attraction, friction, and ductility are combined – galling can occur. However, there are several methods to help prevent this frustrating event.
Which Metals Are More Prone to Galling?
Since galling is more frequent in softer metals, it is seen prominently in metals such as aluminum and austenitic stainless steel. Martensitic stainless steels and other hardened steels are less likely to have galling issues due to their hardened structure.
Galling is most common in aluminum and stainless-steel fasteners due to the high friction force that they undergo when they are torqued. However, any metal machinery that is subjected to high friction may be at risk for galling.
What Causes Galling in Stainless Steel?
This issue is well-known, though it is seldom understood by many who experience it. Galling occurs when using power tools, hand tools, or even hand tightening fasteners.
Stainless steel may not look like it, but it is relatively soft compared to other common metals. When high amounts of friction are built up, it causes the metal to deform, creating more friction. At this point, the metal begins to adhere to the metal it is in contact with, often tearing away in lumps.
How Do You Prevent Stainless Steel from Galling?
Though stainless steel may be more prone to galling, it is still an excellent choice for material. A few tips to follow when using fittings or fasteners are:
This method to prevent galling is the most common. The lubricant allows the two metals to slide past one another without creating friction or heat. Most manufacturers provide anti-seizing grease already applied to the threads. Still, it is always a good idea to add your own before installation.
Though there are many anti-seizing compounds, most of these greases will contain copper, aluminum, or calcium oxide.
Higher speeds cause more friction, which significantly increases the chance of galling or shredding of the material.
At a slower speed, you may be able to feel when beginning the galling and prevent further irreversible damage. The slower rate will help reduce the friction between the two metals, lessening the chance of the issue.
What Does Anti-Seize Lubricant Do and Does It Cause Bolts to Loosen?
Anti-seizing is used to prevent metal from corroding and locking up. A screw stretches under a torque load, and there is a narrow channel where air travels its length. This air can release condensation along this channel, causing rust and weakening the material.
When corrosion sets in and the metal are weakened, it causes more force to loosen it, leading to breakage or rounding corners of the tool.
Anti-seizing is used to fill this gap with material that will prevent corrosion and stay in place even at high temperatures. The tension of the anti-seize lubricant keeps the bolt tight and prevents rust or damage to the metal.
Can You Use Anti-Seize on Stainless Steel?
Yes, and even in high-quality stainless steel, you should use anti-seize to prevent galling and seizing. This is because there is air that can get between the nuts and bolts during the threading process. In the air, there is condensation which will cause seizing, corrosion, or other damage.
The anti-seizing helps this, creating a smooth threading and proper mating between the fasteners. This helps when putting them together but also later when removing the hardware.
Where to Get Top Grade Stainless Steel?
Now that you know what galling is and how it occurs, you can prevent it. At South Austin Metals, we produce the highest quality metals in the Austin area. Our dedicated representatives are here to turn your ideas into a reality.
We have a large selection of steel for your project needs and work with a supplier to get the material needed for your ideas.
Whether you are just looking for a quote or need help with fabricating your next project, South Austin Metals is here to help. Contact us today to get the proper assistance with your next project.