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Sigilli idraulici

Production

Le guarnizioni idrauliche sono generalmente costituite da elastomeri, polimeri naturali e sintetici, che possiedono una debole attrazione molecolare e proprietà altamente elastiche.Due fonti principali per le guarnizioni idrauliche sono gomma e plastica (tra cui PTFE, come Teflon e poliuretano).Altri materiali elastomeri utilizzati per fabbricare sigilli includono butadiene, nitrile, butile e silicone.I sigilli realizzati con questi e altri materiali elastomerici sono di solito fabbricati con estrusione, anche se i sigilli Teflon sono sinterizzati in un forno a forma di polvere.

I sigilli possono anche essere costituiti da materiali non elastici come feltro e cuoio.Alcuni particolari tipi di sigilli idraulici (ad esempio sigilli legati) sono costituiti da materiali metallici (compresi ottone, bronzo, alluminio, acciaio al carbonio e acciaio inox).Tutti i materiali metallici utilizzati per la creazione di sigilli possono essere placcati o zincati per la protezione e la resistenza di ossidazione aggiunti.L'aderenza tra il materiale di gomma e il metallo di una guarnizione legata è creata attraverso un legame chimico.

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.

Le guarnizioni idrauliche sono suddivise in due gruppi principali: statiche e dinamiche.

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.

Ci sono diversi altri tipi comuni di sigilli idraulici generalmente trovati nei cilindri idraulici.I tergicristalli, noti anche come raschiatori o guarnizioni dei tergicristalli, impediscono ai contaminanti di entrare nel cilindro.Alcuni contaminanti che minacciano la funzionalità di un cilindro idraulico includono sporcizia e umidità (tra le altre particelle estranee).Le guarnizioni dei Wiper rimuoveno questi contaminanti quando si ritraggono nel cilindro.

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.

Le guarnizioni metalliche sono caratterizzate dal modo in cui sono incollate alle rondelle metalliche.

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

Poiché i sigilli idraulici sono così critici per l'efficienza dei sistemi idraulici, sono applicabili in un'ampia gamma di industrie.I sigilli idraulici per le industrie comprendono la produzione aerospaziale, l'agricoltura, la produzione automobilistica, la lavorazione chimica, l'appalto della difesa, la trasformazione alimentare, la produzione di prodotti marini, lo sviluppo di prodotti medici e farmaceutici, l'energia nucleare, la pasta e la carta, e lo smaltimento dei rifiuti.

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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