Fastener Galling: What it is and how to prevent it

Galling is a common problem that occurs when two metal surfaces rub against each other and create a weld-like bond. This bond can cause the surfaces to become stuck, making it difficult and often impossible to separate them. If you've ever had a nut that won't come undone, you know how frustrating galling can be. Galling is a common issue with fasteners, such as bolts and screws, and can cause serious problems in mechanical systems.

Machine Screw and Nut Galling

What causes fastener galling?

Galling, also known as cold welding or seizing, occurs when two metal surfaces come into contact and experience high levels of friction. This can cause the surfaces to fuse together, leading to difficulty in separating them and potentially causing damage to the fastener. There are several factors that can contribute to galling:

  1. High levels of pressure and friction: When two metal surfaces are subjected to high levels of pressure and friction, they can become deformed and weld together. This is especially likely to occur when the surfaces are not perfectly smooth.

  2. Incorrect fastener selection: Choosing the wrong type of fastener for the job can lead to galling. For example, using a fastener with a too-smooth surface can lead to insufficient lubrication, while using a fastener with too rough a surface can cause excessive wear and damage.

  3. Poor lubrication: Insufficient lubrication can also contribute to galling. When two metal surfaces are not adequately lubricated, they can rub together and generate heat, which can cause the surfaces to fuse together.

  4. Corrosion: If the fastener is exposed to corrosive elements, such as saltwater or acidic substances, the surface of the fastener can become rough and uneven, increasing the likelihood of galling.

  5. Material compatibility: Certain metals are more prone to galling than others. For example, aluminum and stainless steel are more prone to galling than carbon steel. Using incompatible materials can increase the risk of galling.


How to prevent fastener galling

There are several ways to prevent fastener galling:

  1. Use lubrication: Applying a lubricant, such as our screw lube, to the threads of the fastener prior to tightening can help reduce the friction and heat that can cause galling.

    Anti Seize Lubricant to prevent Galling
  2. Use a different material: Using a different material for the fastener, such as a metal with a lower coefficient of friction. Stainless steel fasteners, and aluminum fasteners are particularly prone to galling, while silicon bronze fasteners are not.

  3. Use a softer metal: Using a softer metal for the fastener can also help prevent galling, as the softer metal will deform more easily under pressure, reducing the chances of the surfaces bonding together.

  4. Use a harder metal: Using a harder metal for the fastener can also help prevent galling, as the harder metal is less likely to deform under pressure and will be less prone to bonding with the other metal surface.

  5. Tighten more slowly: Taking time to tighten a nut or bolt will prevent galling because heat will not have time to build, and tightening slowly also will help prevent other issues such as over torqueing a fastener or cross threading which can be equally as frustrating as galling.

Fastener galling is a common problem that can cause serious issues in mechanical systems. By using lubrication, different materials or thread designs, or selecting a softer or harder metal for the fastener, it is possible to prevent galling and ensure the smooth operation of your mechanical systems.