DRIVE PINS IN A MECHANICAL SEAL

Abstract: A mechanical seal provides a sealing between a rotatable shaft and a housing. The seal has a stationary part for connection to the housing and a rotary part for rotation with the shaft. Mating sealing faces are carried by the stationary and rotary parts and the rotary parts are mounted on the drive shaft for rotation therewith. Each sealing face is held relatively stationary to their respective stationary or rotary part by means of at least one link member extending therebetween. The link member is arranged for at least limited longitudinal rotation.

Description: DRIVE PINS IN A MECHANICAL SEAL This invention relates to the driving mechanism of a mechanical seal face, especially where the seal face is a soft or brittle material and its drive contact gets damage in respect of high pressure and rotation. A mechanical seal comprises a "floating" component which is mounted axially movably around the rotary shaft of, for example a pump and a "static" component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more springs. In use, one of the floating and static components rotates; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component. Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary , the seal is referred to as a stationary seal. If the sliding seal between the rotary and stationary components are assembled and pre-set prior to despatch from the mechanical seal manufacturing premises, the industry terminology for this is "cartridge seal". If however the rotary and stationary components are despatched individually (unassembled) from the mechanical seal manufacturing premises, the industry terminology for this is "component seal". Seal faces are generally held to their relevant stationary or rotary components by a mechanism that is called drive ring. One of the common mechanisms is the use of slots on the back of seal face and lugs on the drive ring or vice versa. Figure- 1 shows four slots on the seal face and four lugs on the drive ring. Figure-2 shows two lugs on the seal face and two lugs on the drive ring. Rotation will be transferred from the seal faces to the drive ring at rotary faces or vice versa at the stationary faces. Seal faces are mainly supplied from various grades of silicon carbide, tungsten carbide, ceramics and carbon. Carbon is categorised as a soft face. The contact between the slots and lugs in Figures 1 and 2 is mainly point contact. Under point contact, soft or brittle seal faces are more prone to failure than hard faces, especially in high pressure and large seal size applications. The failure may start by notch propagation around the contact point which gradually grows until it destroys the seal face. Instead of having lugs on the drive ring, some designs employ drive pins that are pressed firmly into holes in the drive ring. These pins cannot move or rotate from their location. Figure-3-2 illustrates the use of two pins to drive a lug on the seal face when the seal rotates either in clockwise or counter-clockwise direction. If the mechanical seal is designed to only rotate in one direction, one pin can be used for each lug. Alternatively, the pin may be square, cylindrical or any other shape (See Figures 4-a and 4-b). The drive ring may also be designed to drive the seal face around the outer diameter, inner diameter or axial end of said face. This is shown in Figure-4 where point contacts between the lug and slot are labelled A and B. The invention relates to a floating pin that allows the interface between the lug and the slot to be a line or face contact. Preferably the pin is of circular shank diameter, preferably with a square or rectangular head and is loosely fitted in a hole to allow free rotation of said pin about its axis. The present invention will now be described by way of example only with reference to the accompanying drawings wherein Figure-1-1 illustrates four slots on the rear of a seal face which are driven by four lugs on a drive ring which is shown in Figure- 1-2. Figure-2- 1 illustrates two lugs on the seal face and Figure-2-2 shows two slots on the drive ring. Figure 3 illustrates the use of a pins which are pressed into a hole in the drive ring and which do the same job as the lugs in Figures 1 & 2. Figure-4 illustrate a drive ring under the seal face upon which rectangular or cylindrical pins can be mounted. The point of contact is shown by A and B. Figure 5-b and c illustrate that the floating pin design can rotate around the (R) axis and provide a face or line contact (C). As shown in Figure 5 a, a fixed pin of any shape will mostly have a point contact. Figure-5-c illustrates the contact areas on a rectangular head of a floating pin. Figures 6 & 7 illustrate a different shape for the floating pin in which the surface contact is not flat but wherein face or line contact is achieved. Figure-8 is a partial longitudinal cross section through a seal of the invention, and illustrates the location of floating pins on the drive ring and slots. Figure-8 illustrates the pin design at (1) and (2). After assembly of the seal, the loose pins will be held in their location and can rotate freely in their position around their axis in the functioning seal. As shown in Figure-5-a, the use of a fixed pin/lug on the drive ring means that there is no rotation allowed to the pin/lug. The contact area is a point contact. A similar design is demonstrated in Figure-5-b using the floating pin. In this design, because it is adjustable and not fixed, the pin can adjust its contact area to line/face contact. This will minimise the possibility of point contact between the pin/lug and slot. The pin's head may have different shapes which are related to the contact area at the slot. Figure-6 illustrates a different shape for the head of the floating pin. Figure-7 illustrates a different contact area between the floating pin and its relevant slot. It should be understood that the invention may be employed for either rotary or stationary seals and single or double mechanical seals, whether designed in a cartridge or component seal format. The type of drive can be switched for rotary and stationary faces according to application. Similarly, some pieces of equipment such as shaft (3) and pin (1) in Figure 8 may be stationary and the other pin (2) may be rotary. It should be understood that the invention may be used with metallic components as well as non- metallic components. Depending upon the application of the seal, a floating pin of the present invention may be located at any position or angle relative to the seal faces.

Claims: CLAIMS 1 A mechanical seal to provide sealing between a rotatable shaft and a housing, the seal having a stationary part for connection to the housing and a rotary part for rotation with the shaft, mating sealing faces being carried by said stationary and rotary parts, said rotary parts being for mounting on the drive shaft for rotation therewith, each said sealing face being held relatively stationary to their respective stationary or rotary part by means of at least one link member extending therebetween, said link member being arranged for at least limited longitudinal rotation. 2 A mechanical seal according to claim 1 in which the link member is a floating pin. 3 A mechanical seal according to claim 2 in which the floating pin is arranged to rotate freely about its longitudinal axis. 4 A mechanical seal according any of claims 2 or claim 3 in which the floating pin is arranged for at least limited rotation about a transverse axis thereof. 5 A mechanical seal according to any of the preceding claims where the link member is located from the rotary part into a slot or lug which are located in the rotary face. 6 A mechanical seal according to any of the preceding claims where the link member is located from the stationary part into a slot or lug which are located in the stationary face. 7 A mechanical seal according to any of the preceding claims wherein the seal face is made of soft or brittle material or any other material used as a seal face or seal face holder. 8 A mechanical seal according to claim 7 wherein the seal face is made of carbon. 9 A mechanical seal according to any of the preceding claims where said rotary face and corresponding rotary part are connected with a radially located link member. 10 A mechanical seal according to any of the preceding claims where the link member is located in a direction parallel to the longitudinal axis of the seal. 11 A mechanical seal according to any of the preceding claims where the link member is located in any direction between those as claimed in claims 9 and 10. 12 A mechanical seal according to any of the preceding claims wherein the seal is a double seal having two sets of faces and link members between their rotary and stationary parts. 13 A mechanical seal according to claim 1 substantially as herein described with reference to the accompanying drawings.

Inventors: TAHERI OSKOUEI EASA, TAHERI OSKOUEI, EASA
Applicants: AES ENG LTD, TAHERI OSKOUEI EASA, AES ENGINEERING LTD, TAHERI OSKOUEI, EASA
Application year: 1999
Main classification: F16J15
IPC codes: F16J15