A gasket is a mechanical seal that fills the space between two objects, generally to prevent leakage between the two objects while under compression. Gaskets save money by allowing less precise mating surfaces on machine parts which can use a gasket to fill irregularities. Gaskets are commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicone, metal, cork, felt, Neoprene, fiberglass, or a plastic polymer (such as polychlorotrifluoroethylene). It is usually desirable that the gasket be made from a material that is to some degree compressible such that it tightly fills the space it is designed for, including any slight irregularities.
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One of the more desirable properties of an effective gasket in industrial applications for compressed fiber gasket material is the ability to withstand high compressive loads. Most industrial gasket material applications involve bolts exerting compression well into the 14 MPa (2000 psi) range or higher. Generally speaking, there are several truisms that allow for best gasket performance. One of the more tried and tested is: "The more compressive load exerted on the gasket, the longer it will last". There are several ways to measure a gasket material's ability to withstand compressive loading. The "hot compression test" is probably the most accepted of these. Most manufacturers of gasket materials will provide or publish these results.
Gaskets come in many different designs based on industrial usage, budget, chemical contact and physical parameters. The main types of gaskets are Sheet, Solid Material, Spiral Wound, Double Jacketed and "Kammprofile".
Sheet Gaskets are by the far the cheapest option for gaskets. The premise is simple in that a sheet of gasket material has the gasket shape "punched out" of it. This leads to a very crude, fast and cheap gasket. These gaskets can fill many chemical requirements based on the inertness of the material used and fit many budgetary restraints. Common practice prevents these gaskets from being used in many industrial processes based on temperature and pressure concerns.
Solid material gaskets are quite cost-effective. The idea behind solid material is to use metals which cannot be punched out of sheets but are still cheap to produce. These gaskets generally have a much higher level of quality control than sheet gasket material and generally can withstand much higher temperatures and pressures. A downside is that solid metal must be greatly compressed in order to become flush with a flange head and prevent leakage. Process contamination and oxidation are real time concerns as well. In addition, the metal used must be softer than the flange to prevent the flange from warping, thus preventing sealing with future gaskets.
Spiral wound gasket utilizes a mix of metallic material and "filler.” Generally the gasket has a chosen metal, normally a carbon rich or stainless steel, wound outwards in a circle with the filler material, generally flexible graphite, starting at the opposite side of the circle and winding in the same direction. This leads to a growing circle of alternating layers of filler and metal. These gaskets have proven to be reliable in most applications. More expensive than solid material they do not require as high of a bolt force to be effective. This is possible mainly because the graphite makes the primary seal with the flange and the metal only keeps the gasket structurally sound.
Double Jacketed gaskets are another combination of filler material and metallic materials. In this application, a tube with ends that resemble a "C" is made of the metal with an additional piece made to fit inside of the "C" making the tube thickest at the meeting points. The filler is pumped between the shell and piece. When in use the compressed gasket material has a larger amount of metal at the two tips where contact is made. These two places bear the burden of sealing the process. Since all that is needed is a shell and piece, these gaskets can be made from almost any material that can be made into a sheet and a filler can then be inserted.
Kammprofile gaskets are used in many older seals since they have both a flexible nature and are great sealers. Kammprofiles work by having a solid corrugated core with a flexible covering layer. This arrangement allows for very high compression and an extremely tight seal along the ridges of the gasket. Kammprofile has a high initial cost for most applications but this can be justified both by long term savings and increased reliability.