What is the role of the gasket in the screw with the nut?

Update:29-11-2018
Summary:

Among the screws with nuts, the role of the gasket is m […]

Among the screws with nuts, the role of the gasket is mainly to increase the contact area, reduce the pressure, prevent loosening, and protect parts and screws.

A gasket is a mechanical seal between two objects, usually used to prevent pressure, corrosion, and natural thermal expansion and contraction between the two objects. Since the machined surface is not perfect, the gasket can be used to fill the irregularities.

The gasket is usually made of sheet material such as mat paper, rubber, silicone rubber, metal, cork, felt, neoprene, nitrile rubber, fiberglass or plastic polymer (such as polytetrafluoroethylene). Gaskets for specific applications may contain asbestos.
A gasket is a hole (usually in the middle) of a thin plate (usually in the middle) that is typically a load thread fastener for dispensing. Other uses are as spacers, springs (Belleville gaskets, wave gaskets), wear pads, pre-display devices, and lock devices. Rubber gaskets are also used in faucets (valves) to cut off flowing liquids or gases. Rubber or silicon gaskets can also be used to reduce fan vibration. Usually the outer diameter of the gasket is about twice the inner diameter.

The thickness of the gasket is related to its form, material, diameter, sealing surface condition and sealing medium. For most non-metallic sheet-like sheets, a thinner 1.5 mm or 2 mm thick gasket is usually used. This is because the thinner gasket has a smaller surface area exposed to internal pressure and less leakage of the medium along the body, so the leakage rate is lower and the force of the gasket to be extruded outward is smaller; the thinner gasket has Lower creep relaxation; the thinner the gasket, the lower the price.

However, the gasket must fill the irregular flange sealing surface, and the thicker gasket has good compressibility and has a certain adaptability to the sealing surface with little damage or buckling. Therefore, the minimum thickness of the gasket depends on the surface roughness of the flange, the compressibility of the gasket, the gasket stress, the degree of deflection of the flange, and the like.