Type 76.95 requires slightly less installation space in the axial direction than the standard o-ring style designs (76.90H / 76.97H). The geometry of the housing contour is easier to manufacture, and the seal installation does not require an installation tool. In comparison to the o-ring face seals, the spring characteristic of the trapezoid elastomer parts is usually stiffer. This leads to a limitation of permitted axial movement and tolerance. Dimensional deviations have a negative influence on the resilience reserves.
This type of seal is typically used where high torques are required due to adhesion and surface drying of dirt in order to move a machine after a standing time. It frees itself from pollution and therefore resumes its axial mobility better than the 76.90.
In the 60-year history of manufacturing mechanical face seals, a number of designs have been developed for specific constructional and operational situations which can in principle be used for an extended range of applications. In all cases the seal sets have performed outstandingly well in rough daily operating conditions.
In particular, the inverted seal ring design provides a considerable savings potential with respect to the cross section and the manufacturing technology.
There are also special designs of the seal type 76.95 available, which have been developed specifically for applications with extreme mud impact.
We recommend contacting our engineering team if you plan to use the type 76.93 in your application.
Friction instabilities, such as stick-slip and oscillations in the sliding systems, cause detrimental phenomena that can generate positioning errors, poor surface roughness, noise and accelerated wear. In the automotive industry, many components could be affected by those undesired phenomena during deceleration regimes. The friction and wear behavior of mechanical face seals is ruled by lubrication conditions. Simulations based on tribo-dynamic models explain the occurring of friction instabilities during the operating conditions, describing different lubrication regimes: (i) full film or hydrodynamic lubrication regime, (ii) mixed lubrication regime and (iii) boundary lubrication regime. To avoid or limit instabilities it is fundamental selecting proper design parameters. Aim of the present paper is the set-up of a very fast and smart method to know how to reduce instabilities by tuning the correct dynamical parameters since the design phase. The proposed tool is based on ANNs that, even if it is not able to explain the frictional instability phenomena, as analytical models do, it allows to quickly investigate the ranges of parameters with respect to the operating range.
While an effective means of sealing, this method has inherent issues with longevity as the final seals are commonly elastomer based and in contact with rotating equipment at all times thus subject to friction wear. Elastomers have a limit in terms of surface speed capabilities, which diminishes over time. Incredibly tight tolerances are also required as the passages begin to narrow, driving manufacturing cost and creating installation and premature failure challenges.
Stribek Curves help determine the areas of the lowest friction and help engineers choose face materials and design seal cross sections. The lowest friction areas lie in the Elasto-Hydrodynamic region and is the ideal criteria for a long last, high performance mechanical face seal. To understand more about Stribek Curves, and the study of friction and wear, also known as Tribology, we conducted several tests with the assistance of LSU Professor Dr. Michael Khonsari where a number of materials were subjected to varying fluid media and pressures to better understand the friction and wear relationship that a pair of materials exhibits.
With all of the options available on the market today, which is the right one for you, your vessel or your customer? A number of parameters come into play such as shaft size, operating RPM, relative shaft motion, draft pressure. A mechanical face seal may seem like the robust design, but if you only have a small 2-3" diameter shaft that sees only a few hundred hours of operation a year and you can get away with a more affordable option like a Duramax Packing type seal, that may be a better route. Or you may have a system with incredibly high shaft speeds, and allows some amount of leak with regularly scheduled maintenance and you can get away by using a labyrinth seal.
In mechanical engineering, an end-face mechanical seal (often shortened to mechanical seal) is a type of seal used in rotating equipment, such as pumps, mixers, blowers, and compressors. When a pump operates, the liquid could leak out of the pump between the rotating shaft and the stationary pump casing. Since the shaft rotates, preventing this leakage can be difficult. Earlier pump models used mechanical packing (otherwise known as gland packing) to seal the shaft. Since World War II, mechanical seals have replaced packing in many applications.
An end-face mechanical seal uses both rigid and flexible elements that maintain contact at a sealing interface and slide on each other, allowing a rotating element to pass through a sealed case. The elements are both hydraulically and mechanically loaded with a spring or other device to maintain contact. For similar designs using flexible elements, see radial shaft seal (or "lip seal") and O-ring.
An end-face mechanical seal consists of rotating and stationary components which are tightly pressed together using both mechanical and hydraulic forces. Even though these components are tightly pressed together, a small amount of leakage occurs through a clearance that is related to the surface roughness.
The seal ring and mating ring are sometimes referred to as the primary sealing surfaces. The primary sealing surfaces are the heart of the end-face mechanical seal. A common material combination for the primary sealing surfaces is a hard material, such as silicon carbide, ceramic or tungsten carbide and a softer material, such as carbon. Many other materials can be used depending on pressure, temperature and the chemical properties of the liquid being sealed. The seal ring and mating ring are in intimate contact, one ring rotates with the shaft and the other ring is stationary. Either ring may be rotating or stationary. Also, either ring may be made of hard or soft material. These two rings are machined using a process called lapping in order to obtain the necessary degree of surface finish and flatness. The seal ring is flexible in the axial direction; the mating ring is not flexible.
By definition, the seal ring is the axially flexible member of the end-face mechanical seal. The design of the seal ring must allow for minimizing distortion and maximizing heat transfer while considering the secondary sealing element, drive mechanism, spring and ease of assembly. Many seal rings contain the seal face diameters, although this is not a requirement of the primary ring. The seal ring always contains the balance diameter.The shape of the seal ring may vary considerably according to the incorporation of various design features. In fact, the shape of the seal ring is often the most distinct identifying characteristic of a seal.[1]
By definition, the mating ring is the non-flexible member of the mechanical seal. The design of the mating ring must allow for minimizing distortion and maximizing heat transfer while considering ease of assembly and the static secondary sealing element. The mating ring can contain the seal face diameters, although this is not a requirement of the mating ring. To minimize primary ring motion, the mating ring must be mounted solidly and should form a perpendicular plane for the primary ring to run against. Like seal rings, mating rings are available in many different shapes.[1]
In order to keep the primary sealing surfaces in intimate contact, an actuating force is required. This actuating force is provided by a spring. In conjunction with the spring, axial forces may also be provided by the pressure of the sealed fluid acting on the seal ring. Many different types of springs are used in mechanical seals: single spring, multiple springs, wave springs, and metal bellows.[1]
The most common seal face design is a plain, flat, smooth surface but there are many special treatments intended for specific applications. The most common objective for the face treatment is to reduce the magnitude of mechanical contact. In general, face treatments provide a means of modifying the pressure distribution between the seal faces through hydrostatic or hydrodynamic topography. Seal face topography refers to the three dimensional aspects of the seal face surface.
Both the seal ring and mating must accommodate secondary sealing elements. In some designs, various retainers, sleeves and other components may also include secondary sealing elements. Whereas a simple O-ring might require only a groove for fitting, some secondary sealing elements (for example, packing) might require mechanical compression. Although O-rings are available in many elastomers, sometimes an elastomer might not be compatible with the fluid being sealed or might be considered too expensive. In such cases, a secondary sealing element might be manufactured from perfluoroelastomer and shaped in the form of a wedge, V or U.
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