REINFORCED RUBBER LINER FOR CENTRIFUGAL PUMP CASINGS

Abstract: A half-shell rubber lining for a centrifugal pump reinforced in selective regions of its outer surface with a fabric mesh im­ pregnated with a thermoset resin is disclosed.

Description: REINFORCED RUBBER LINER FOR CENTRIFUGAL PUMP CASINGS Background of the Invention Field: This invention relates to elastomeric linings for centrifugal pumps and particularly to rubber linings, especially natural rubber linings, which are constructed to prevent collapse during use. State of the Art: Elastomeric linings, including rubber linings, and in particular, natural rubber linings, have been used for quite some time in centrifugal pumps, both as liners and as coverings on impellers so that the pumps could effectively handle abrasive slurries and corrosive liquids such as acids. Occasionally, during use, the pump lining will collapse, that is, the rubber lining will pull away from the casing of the pump. If this happens in a region proximate to the impeller, the impeller may chew up the lining and render the pump disabled. Even if the lining pulls away from the casing in the discharge region or in the throat region without interfering with the impeller, the sagging lining may impede flow and make the pump less effectual. One technique for precluding the collapse of rubber linings in a large centrifugal pump is to adhere the whole outer surface of the lining to the pump casing. In this manner, the lining is held fast to the casing so that it cannot collapse due to negative pressure within the pump. However, this technique is generally not desirable inasmuch as pump linings do require periodic replacement and it is difficult to remove a lining which has been firmly adhered to the pump casing. Thus, the replacement of a lining in such an instance requires much longer time than usual and results in the pump and the system that it services being down for a long period of time. In certain regions of the lining, for example, in the discharge nozzle, it would be possible to prevent collapse of the lining by inserting a circular, expandable band on the inside of the lining. While such a structure may prevent lining collapse, it would tend to act as an orifice, thereby restricting flow, and would tend to be eroded or corrode with time, failing before the lining failed and contributing some contamination to the liquid medium being pumped. The problem of collapsing linings is particularly acute with soft, natural rubber pump linings which are frequently preferred in pumps handling abrasive slurries and the like. Because natural rubber is soft, it has less inherent strength than many types of pump liners. Attempts to reinforce natural rubber liners with steel mesh and the like have not been successful. Steel is difficult to prepare with no oxide layer on its surface, which tends to interfere with adhesion between the rubber and the steel. The use of brass mesh overcomes the oxide problem, but has different thermal expansion properties than rubber and thus poses another problem. Since the rubber lining normally shrinks during the curing process, the presence of brass mesh does not permit the rubber lining to shrink so that a reinforced rubber lining made from a particular mold no longer fits the pump casing since the lining does not shrink as it normally does. The same problem is encountered with the use of hard rubber as an outer surface for the lining inasmuch as hard rubber does not shrink during curing to the same extent as soft natural rubber. Thus, from a particular mold size the lining no longer fits the casing. If such techniques were used to reinforce a pump liner, then new molds would have to be prepared whereby the mold was of a size and a design to provide a pump lining suitable for placement within a pump casing without any shrinkage of that lining. However, even such an approach may not be successful inasmuch as it would be necessary to reinforce the whole lining in such an instance so that there is no shrinkage throughout the lining. Also, if the rubber were prevented from shrinking during curing, it would tend to be in tension in the cured lining, subjecting the rubber to faster potential wear. Summary of the Invention The instant invention relates to a half-shell lining for centrifugal pumps wherein the lining is made of a natural rubber and reinforced in selective regions with a resin impregnated fabric which permits the rubber to shrink its normal amount during curing. The invention involves lining a mold with thermosetting resin impregnated fabric in those regions in which it is desired to reinforce a rubber lining made in said mold. Typically, the impregnated fabric is placed several or more layers thick in the region to be reinforced. The rubber and the thermoset impregnated fabric is cured for a time and at a temperature sufficient to bring about curing of the rubber and the resin. The instant invention is particularly advantageous inasmuch as linings may be molded in molds already sized to accommodate for shrinkage of the elastomer material during molding so that the finished liner will fit within the intended pump casing. Also, the elastomer can be cured for substantially the same time and substantially the same temperature as it is usually cured so that a fully cured liner results. Furthermore, the invention provides reinforcement at the desired location (i.e., at the outside surface of the liner) so that the liquid within the pump contacts only the erosion and corrosion resistant liner surface. The thermosetting resin impregnated mesh sheets are generally placed in the molds so that a substantially complete arch is formed as an exterior surface of the lining or at least as much as an arch as possible so that optimum resistance to collapse is obtained with a minimum thickness of fabric layers. Brief Description of the Drawings FIG. 1 is a prospective view of the half-shell lining for a centrifugal pump casing; FIG. 2 is an elevational view of an actual lining for a centrifugal pump; FIG. 3 is an elevational view of a half-shell lining containing zones of reinforcement of said lining being for a centrifugal pump; FIG. 4 is an exploded sectional view of the liner of FIG. 1 along section lines 4-4; and FIG. 5 is a sectional view of the liner of FIG. 1 along section lines 5-5. Detailed Description of the Invention The instant invention comprises a soft elastomeric liner, particularly natural rubber liners, having unique reinforcement means in selective areas or regions of the liner. Also, the invention comprises a unique process for molding the reinforcing means and the rubber in a single process step in curing the rubber and reinforcing means at a similar temperature for the period of time. Rubber or elastomeric liners are typically provided for centrifugal pumps which handle either erosive or corrosive media. These pumps are of a very large size having diameters from about 50 centimeters up to about 150 centimeters. Although smaller centrifugal pumps having diameters as small as 15 centimeters are also provided with liners, the ratio of the liner thickness to liner size is smaller in large pumps which have a greater tendency to collapse, especially if the liner is composed of soft natural rubber. While the casing of the pump provides support for the liner and prevents the liner from being bulged in an outward direction through fluid forces occurring within the pump, generally no means exist for preventing the collapse of the liners if a negative force or pressure occurs within the pump, except the self-supporting structure of the liner itself. Although a negative pressure below atmospheric pressure may occur in the pump, especially in the suction region, for the purposes of the description of this invention, negative pressure is intended to mean a pressure substantially below the usually high pressures within the pump since rapid changes in pressure (hydraulic head) within the pump may occasionally collapse the liner. The instant invention provides reinforcement means in those regions of the liner which have been found to be most often subject to collapse and to provide such reinforcement means on the outer surface of the liner, that is, that surface of the liner which contacts the casing. Furthermore, the invention provides reinforcing means impregnated with a thermosetting resin which cures within the same temperature range as the natural rubber liner. Further description of the invention may be facilitated by reference to the attached drawings. In FIG 1, a half-shell elastomeric liner is illustrated in perspective view. A half-shell liner is a large bowl-shaped structure with a central axial aperture. Two half-shell liners are mated to form the lining protecting the entire inner casing of the centrifugal pump. The liner 10 has curved peripheral sidewalls 11 and an integral flat plate-like interior 12 with an aperture 13 which either is a throat opening to admit fluid into the pump or an opening which permits the drive shaft to pass through to connect to the impeller. If the liner has an opening to admit the drive shaft, it is referred to as the engine-side liner while if the opening in the liner is to admit fluid, then it is referred to as the suction-side liner. When a half-shell liner is mated with another half-shell liner the portion of the liner in contact with the casing substantially forms the peripheral surface of a toroid. In FIG. 2, a half-shell lining is illustrated in an elevational view with quadrants of the lining being designated A, B, C and D. Generally, it is preferred to provide reinforcement in the curved sidewall portions ll of quadrants A and D of both the engine side and suction side linings. Also, it is preferred to reinforce the discharge region 14 preferably in that portion of the discharge region from the flange 15 to the juncture 16 of the discharge nozzle with the toroidal portion of the liner. In FIG. 3, a liner is illustrated with fabric plys 17 and 18 exposed illustrating the mesh-like nature of the fabric. In FIGS. 4 and 5, the reinforcement means 17 and 18 is further illustrated. The reinforcement means 17 in the discharge region is substantially a semi-cylindrical structure substantially thinner in cross-sectional thickness than the lining and integral with the external surface of the lining. The reinforcement means 17 is generally at least about three layers thick and may preferably be 10 to 30 layers thick. The reinforcing means comprises an uncured thermosetting resin impregnated in a fine denier nylon mesh fabric. Reinforcing means 18 comprises a similar number of plys of a similar material. Reinforcement means 18 forms about one-half of an arch. The reinforcement means 18 extends completely around the lining substantially reinforcing all the quadrants A, B, C and D, as illustrated in FIG. 2. Full circle reinforcing of large diameter linings may be preferred for many applications. The linings represented in FIGS. 4 and 5 are two-piece linings, that is, two pieces are required to form a single half-shell lining. Separate flat disk members, such as member 12a shown in FIG. 4, join with the peripheral pieces illustrated in FIGS. 4 and 5 to form the half-shell liner. Construction of the type shown in FIGS. 4 and 5 without integral central disk members is frequently used in very large pumps. The separate flat disk-like central members interlock with the peripheral members shown in FIGS. 4 and 5 to hold the peripheral members in place. The central disk-like members are usually provided with threaded studs which project through bolt-holes in the casing so that the lining may be securely fixed to the casing. The reinforcement means in the form of multiple plys may be from about 2.5 millimeters to about 12.7 millimeters in thickness and preferably is from about 5.0 millimeters to about 10.2 millimeters in thickness, while the thickness of the rubber lining is about 19.0 milli meters to about 38.1 millimeters and is generally about 25.4 millimeters to 31.8 millimeters. The half-shell is reinforced by placing within the mold used to form a half-shell lining, a layer of a plurality of thin sheets impregnated with an uncured thermosetting resin fabric mesh. The regions of the mold in which the reinforcing is intended to be applied to the lining are completely covered with the fabric sheets. The thickness of the impregnated fabric is generally not greater than about .5 millimeters and the fabric reinforcement is applied in the mold from about three to about thirty plys thick and generally about ten to thirty plys thick. A particular material useful as reinforcement in this invention is a phenolic resin impregnated nylon fabric material which has curing conditions substantially similar to natural rubber and which shrinks about the same amount as natural rubber upon curing. It is identified in the art by MIL-P-15047. The rubber cures at a temperature of about 3000F for about 3-1/2 hours. A rubber liner prepared in this fashion has reinforcing means integrally molded in the rubber lining and being that the resin is a thermosetting and relatively rigid material, a strong arch-type support is provided in each region in which the lining is reinforced. It is advantageous to form the linings in this manner of reinforcement inasmuch as existing molds utilized to make non-reinforced linings may be utilized to make reinforced linings whereby by the shrinkage is the same, the linings fit the casings they are intended to fit.

Claims: Claims 1. A centrifugal pump reinforced rubber lining comprising: an uncured rubber lining having a volute region, a central region, an inlet region and a discharge region; reinforcement means in selective regions of said pump liner, said reinforcement means comprising a fabric mesh impregnated within a curable thermo setting resinous material which cures under substantially the same conditions as said rubber lining and which has a shrinkage factor upon curing which is substantially the same as said rubber lining. 2. 2. In a rubber lining for a centrifugal pump, the improvement comprising: arch-like reinforcement means, the external surface of such lining being integral with the lining in the discharge nozzle of said lining; semi-arch reinforcement means in at least that portion of the volute section of the lining integral with the external surface of the lining proxi mate to said discharge nozzle, wherein said reinforcement means comprises a substantially rigid resin impregnated fabric. 3. A rubber lining for a centrifugal pump having integral reinforcing means, said integral reinforcing means comprising an outer shell of multiple plys of a resin impregnated fabric, said outer shell positioned in at least the discharge nozzle and the volute section of said rubber lining. 4. The rubber lining of Claim 3 wherein a ply of resin impregnated fabric comprises a loose mesh of nylon filaments impregnated within a phenolic resin. 5. A half-shell, bowl-shaped elastomeric lining with a split cylinder discharge nozzle for a centrifugal pump, said lining having resin impregnated mesh-like substantially rigid reinforcements in half-cylinder form in said discharge region and in the two quadrants of the bowl adjacent to the discharge, said reinforcement in said quadrants located in the curved sidewall portion of the lining. 6. The lining of Claim 5, wherein said reinforcement is a resin reinforced fabric mesh. 7. The lining of Claim 6, wherein the reinforcement consists essentially of multiple plys of said resin reinforced fabric mesh. 8. The lining of Claim 5, wherein said reinforcing fabric mesh forms substantially the outer surface of the lining in those regions in which said reinforcing means is present. 9. The lining of Claim 5, wherein said fabric is a nylon material. 10. The lining of Claim 5, wherein said resin is a thermosetting phenolic resin.

Inventors: GRISZ, J. EUGENE
Applicants: BAKER HUGHES INCORPORATED
Application year: 1986
Main classification: F04D29
IPC codes: F04D29, F04D7