Friction is one of the most challenging factors to control for in metalworking. It can cause excessive heat, worn edges and tools, and seized-up parts. It can also lead to galling, a serious problem that affects the quality of expensive machinery and production equipment. Galling is the formation of a hard, brittle, and non-reactive surface on the contacting surfaces of two different metals. It is caused by the transfer of heat energy from the softer metal to the harder metal. The resulting adhesion is more severe than normal abrasive wear because it concentrates the frictional force into a very small area.
A common cause of galling is not using a proper lubricant. The metals used in machinery should be chosen carefully to reduce the chances of galling. Ductile metals, such as aluminium and stainless steel, are more prone to galling than harder metals, such as hardened tool steel. When unlubricated, these types of metals will weld together on the contact surfaces. In addition to selecting the right materials, reducing friction will help prevent galling.
One way to do this is to use a quality lubricant when installing and tightening fasteners. Another is to lower the wrench speed when installing and removing fasteners. Slowing down installation and removal will prevent the heat generated from friction from building up to the point where it causes galling.
Thread galling is a common problem that can be prevented by keeping the contacting threads clean, using a lubricant, and by avoiding overtightening. It is also important to ensure the contacting threads are not damaged during shipment and packaging. In some cases, thread galling is so severe that the contacted materials actually weld together. This is known as cold welding and can be very difficult to remove.
Herbivore-induced galls on beech (Fagus sylvatica) trees are known to have significant effects on plant structure and metabolism throughout the life cycle of the gall. These changes are likely to influence herbivore-induced defense responses from neighboring plants, such as the release of volatile cues that can signal a host tree to natural enemies. In addition, the release of olfactory cues from the gall may enable pollinators and seed dispersers to avoid galled areas. This would allow them to access the food resources of other, non-galled plants more efficiently and potentially reduce competition with herbivores for these scarce resources. In addition, these olfactory cues could serve as an indirect form of plant communication to other herbivores, allowing them to detect possible host plants. This is similar to the way in which predators and parasitoids are attracted to a host plant by its defense responses. This interaction between plants, herbivores, and their natural enemies provides a unique example of trophic level co-evolution in nature.
