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Hydrauliske segl

Production

Hydrauliske forseglinger er almindeligvis fremstillet af elastomerer, naturlige og syntetiske polymerer, som har svag molekylær tiltrækning og meget elastiske egenskaber.To hovedkilder til hydrauliske forseglinger er gummi og plast (herunder PTFE, f.eks. Teflon og polyurethan).Andre elastomerer, der anvendes til fremstilling af sæler, omfatter butadien, nitril, butyl og silikone.Sæder fremstillet med disse og andre elastomeriske materialer fremstilles normalt gennem ekstrudering, selv om Teflon-forseglingerne sinistes i en ovn fra en pulverform.

Sæder kan også fremstilles af ikke-elastiske materialer som f.eks. filt og læder.Nogle særlige typer hydrauliske forseglinger (f.eks. plomber) er fremstillet af metalliske materialer (herunder messing, bronze, aluminium, kulstofstål og rustfrit stål).Alle de metalmaterialer, der anvendes til at skabe sæler, kan være belagt eller galvaniseret med henblik på yderligere oxidationsbeskyttelse og styrke.Tilslutningen mellem gummimaterialet og metal fra en bundet forsegling skabes via kemisk binding.

Major Types and Operations

Hydraulic seals are most often found in hydraulic cylinders, the mechanical actuators that convert hydraulic pressure (from oil, water, or another pressurized fluid) into unidirectional force for agriculture and forestry vehicles, construction equipment, and similar mechanisms.
Usually, hydraulic seals are located on the cylinder head, on the rod shaft, or in the piston. In these positions, seals keep fluid from leaking past the interface between the rod and head, from leaking to the outside of the cylinder, and from flowing across the piston.

Hydrauliske segl opdeles i to hovedgrupper: statiske og dynamiske.

Static seals are typically located in grooves and other confined spaces, where they act as gaskets. In this context, the term gasket refers to a mechanical seal that fills the space between two or more mating surfaces that do not have any motion between them and is held in place by pressure applied by the tightening of bolts. Although static seals vary by number and exact location depending on the specific cylinder structure, all of them serve the purpose of closing gaps between immobile surfaces. Static seals can be further broken down into groups of axial static seals and radial static seals. To achieve a secure seal, axial static seals must be squeezed between their upper and lower surfaces. Radial static seals, on the other hand, accomplish the same thing when they are compressed between their inner and outer surfaces.

Dynamic seals, which are also known as shaft seals, seal gaps between two surfaces that do share relative motion. Types of motion they work in between include reciprocation, oscillation, and rotation.

Reciprocating dynamic seals are seated within glands that hold relative motion. Here they move along an axis in between inner and outer surfaces. Most often, they’re used to power linear actuators, hydraulic cylinders, and pistons in internal combustion engines.

Oscillating seals operate with shafts that rotate using a limited number of turns around its axis. Because of the frequency with which these shafts rotate, oscillating seals are usually made of a relatively hard material and have self-lubricating capabilities.

otary seals are placed where a hydraulic device experiences rotational motion from a housing and a shaft.

Main Types of Hydraulic Seals

The specific operations of a hydraulic seal differ slightly depending on where the seal is located with regard to the hydraulic cylinder. The most common hydraulic seals are piston seals and rod seals, which are both cylinder seals with a flexible lip that rubs against the housing or shaft for improved sealing during linear movement. As such, piston seals and rod seals form the category known as lip seals. These types of seals are most often used to ensure the proper operation of revolving equipment and machinery.

Piston seals specifically work by preventing leakage or fluid flow across the piston. Many piston seals are single-acting piston seals, meaning that they concentrate pressure on only one side of a piston. This concentrated pressure buildup enables the piston to travel the bore of a cylinder and the cylinder to actually move with maximum mechanical effort. As such, (dynamic) piston seals are extremely important to maintain the efficiency of a hydraulic system. Double-acting piston seals are able to concentrate pressure on both sides of a piston, thus driving the ram that the piston is typically attached to. In contrast to the dynamic types of piston seals just described, static piston seals seal the gap between the piston and the piston rod (rather than the piston and the cylinder bore).

Rod seals specifically work by preventing external fluid leakage from the cylinder. They are usually single-acting and often enhanced with a secondary rod seal. Dynamic rod seals function in the gap between the piston rod and the cylinder head while static rod seals close gaps between the cylinder head and the cylinder bore. In addition to containing hydraulic fluid within the cylinder, rod seals help regulate lubrication fluid for the rod, the wiper seal, and the rod seal itself.

Der findes flere andre almindelige typer hydrauliske forseglinger, som normalt findes i hydrauliske cylindre.Rodviskere, også kendt som skrabere eller viskelforseglinger, forhindrer forurenende stoffer i at trænge ind i cylinderen.Nogle forurenende stoffer, der truer en hydraulisk cylinders funktion, omfatter snavs og fugt (blandt andre fremmede partikler).Gåser fjerner disse forurenende stoffer, når de trækker sig tilbage i cylinderen.

Buffer seals enhance the function of the rod seal by providing a “buffer” against excessive internal fluid pressure. They also serve to protect the rod seal from any contaminants that do manage to find their way into the cylinder (such as metal chips).

Guide rings are also known as wear rings since they serve dual purposes of centering the piston and piston rod while guiding them through the cylinder and preempting metal-on-metal contact. Wear rings can be found at both the rod and piston locations within a hydraulic cylinder.
O-rings are unique in this list since they are identified primarily by their shape rather than by their location or specific function. As their name suggests, O-rings are donut-shaped and come in many different materials (e.g. rubber, silicone, fluorocarbon) and sizes (e.g. less than an inch to several meters wide). When these types of seals are mechanically deformed by pressure, they create very effective sealing barriers. Due to their low cost and relative simplicity, O-rings are the most common type of hydraulic seal on the market today.
Beyond these common variations are more specialized types of hydraulic seals.

Oil seals, which are called metric oil seals outside of the USA, are used with hydraulic oil and made with materials that allow them to resist breaking down or malfunctioning in the face of repeated oil exposure. Such materials include polyacrylate, silicone, Teflon, and a number of fluoroelastomers. In addition to preventing leaks, oil seals retain oil and other lubricants for rotary applications.

Metalliske tætninger er karakteriseret ved, at de sidder fast på metalunderlag.

X rings (also known as quad or square rings) are, in essence, enhanced versions of O-rings. Their four-lobed design allows them to achieve up to twice the sealing power of normal O-rings with less mechanical deformation. X rings can be used both as static seals and as dynamic seals.

Applications

Da hydrauliske forseglinger er så vigtige for hydrauliske systemers effektivitet, kan de anvendes i en lang række brancher.Industriens hydrauliske forsegling omfatter luft- og rumfart, landbrug, automobilfremstilling, kemisk forarbejdning, forsvarskontrakter, fødevareforarbejdning, fremstilling af marine produkter, udvikling af medicinske og farmaceutiske produkter, kernekraft, papirmasse og papir samt bortskaffelse af affald.

The specific applications of hydraulic seals are as diverse and numerous as they industries they are found in. Hydraulic seals can be found in construction equipment, agricultural machinery, brake devices, clean rooms, conveyors, mixers, presses, valves, and test equipment.
Some hydraulic seals are made for very specific applications. Within the aerospace industry, custom seals such as silicone sealant strips serve to seal various hydraulic components within aircraft systems. Similarly, in the electronic industry, seals such as EMI shielding gaskets serve to prevent unwanted electromagnetic interference in various devices.

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