Galling is a metalworking issue that can be very frustrating for engineers, design professionals and other industry leaders who rely on high-quality fasteners to ensure safe and efficient work. It happens when a threaded component or bolt that is being tightened or installed begins to seize up and becomes impossible to loosen or remove.
While there are many different reasons why galling occurs, it is most often the result of friction between two sliding contacting surfaces. In the most severe cases, the metals may shear and weld together and prevent further advancement or removal.
Fortunately, there are methods that can be used to mitigate galling and even eliminate it completely. These include the use of lubricants, low-friction coatings like molybdenum disulfide and titanium nitride, and increasing the hardness of the metals through processes like case hardening. However, one of the most effective and easiest methods for preventing galling is to simply reduce the amount of friction that occurs between the contacting metals.
This can be done by using a system in which the bolt load is eliminated before turning the nut. Additionally, the use of specialty anti-galling devices and fasteners can also help to reduce the likelihood of galling.
A simple way to measure the occurrence of galling is through a button and block test that is conducted by deadweight loading a button and a block specimen in a Brinell hardness tester. The resulting stress levels are then measured and used to determine the point at which galling occurs. This threshold stress level is called the unlubricated threshold galling stress and is a good indicator of the sensitivity of a material pair to galling.
Several factors contribute to the formation of galls, including heritable genetic traits, bottom-up induced plant defense responses like hypersensitivity reactions (HR), and environmental conditions. However, it has not been well understood how these various factors interact to affect gall development and persistence in the beech tree F. sylvatica.
We have shown that a mixture of heritable and environment-related characteristics are necessary to determine the fate of a beech gall. These factors may include interactions with a herbivore, the presence of other herbivores or parasitoids, and interaction with the host plants. In addition, interactions between beech trees and their natural enemies such as birds could also have a profound influence on the fate of the galls and their associated heritable traits.
These results suggest that a multitrophic approach to understanding the dynamics of gall formation is needed, especially when considering how interactions between different taxa can shape ecosystems and landscapes. The multitrophic aspect of these studies also allows us to consider a broader range of eavesdropping effects such as those from induced volatiles that interact with the gall structures and their associated heritable traits. This can reveal important information that is not otherwise readily available through the direct interactions of single taxa. This can lead to a deeper understanding of the dynamic interactions that occur in our forests.