What is Galling and How to Prevent It

Anyone who works with mechanical fasteners has likely experienced galling – or at least seen it in action when nuts and bolts get stuck or even seized. Galling is a form of material wear during sliding in which macroscopic transfer of adhesion-induced heat causes metal surfaces to stick together, creating miniature wells that can become permanent.

There is a wide range of factors that can cause galling, including debris or other objects caught between threaded parts, improper lubrication, and mismatched materials. The key ingredient for galling is friction between two metals, which drives the heat and material transfer that leads to the formation of a gall-like lump. The type of metal involved is also a significant factor – aluminium and austenitic stainless steels are particularly susceptible to galling, while harder tool steels and martensite-grade stainless steels have higher resistance to galling.

In some cases, galling can be difficult or impossible to remove, especially when the metal becomes diffusion welded to the mating surface. This is commonly seen with corrosion resistant fasteners made from austenitic stainless steel, which can be difficult to disassemble due to galling. This problem can be reduced by using a corrosion resistant lubricant or a special anti-galling coating.

It is also possible to prevent galling by using coarse-threaded or annealed metals, which tend to be less prone to galling than harder materials. In addition, the use of hand tools rather than power tools can reduce or eliminate galling by slowing down the tightening process and preventing excess heat build-up.

Galling can occur in a variety of environments and conditions, but it is most prevalent when metals come into contact with each other during sliding. This is why it is important to make sure that all moving metal components are properly lubricated.

Earlier studies have emphasized the role of a parasitoid complex as the dominant top-down factor controlling beech gall midge (Maleficentum fagi) populations. However, the present findings provide novel evidence for a bottom-up influence on M. fagi population density at the forest edge through negative effects on host defenses during gall development and heripredation by herbivores [20]. The implication is that M. fagi is more able to expand its parasitoid communities at the edge where osmotic differences between shade and sun leaves are high, leading to increased herbivore infestation and gall development. This may be related to the release of volatile chemicals induced by M. fagi in the galls that stimulate host plant defenses through the phenomenon of hypersensitivity reaction (HR). This study provides an opportunity to explore the ecological significance of these volatile cues for a multitrophic interaction, and further examine how HR impacts nearby ecological interactions via edge effects on M. fagi herbivore abundance.

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