Lightweight Sealing Gasket for Low-Pressure and Non-Pressure Applications

Abstract

There is shown a pipe sealing gasket designed to be received within a seating ring provided within a receiving flared end of a plastic pipe section, the receiving flared end being assembled with a mating insert pipe end to form a plastic pipe joint. The gasket consists of a rigid plastic strip and two separate elastomeric portions, wherein the rigid plastic strip has an outer peripheral surface and an inner peripheral surface. The first separate elastomeric portion forms an outer ring around the outer peripheral surface of the rigid plastic strip. The second separate elastomeric portion forms an inner lip around the inner peripheral surface of the rigid plastic strip. During the gasket molding operation, the two separate elastomeric portions are connected by a series of spaced-apart ribs which form an elastomeric continuous body connecting the first separate elastomeric portion and the second separate elastomeric portion at spaced intervals.

Description

Field of the Invention

[0001] The present invention generally relates to a sealing washer and a sealing system for a pipe joint in a plastic pipeline, in which a plug-in pipe section is installed within a mating receiving socket pipe section to form a pipe joint. The present invention also relates to a method for manufacturing such a washer having a minimalist lightweight design particularly suitable for low-pressure or non-pressure applications (such as sewer pipelines). Background Art

[0002] Fluid sealing systems for plastic fluid conveyance pipelines are used in various industries. The pipes used in such systems are typically made of thermoplastic materials including polyolefins and PVC. In the process of forming a joint between pipe sections, a plug-in or spigot pipe end is inserted within a receiving or socket pipe end. An annular elastomeric ring or washer is typically located within a groove formed in the socket end of the thermoplastic pipe. When the spigot is inserted within the socket, the washer provides the primary sealing capability for the joint. Different types of sealing techniques have been employed to ensure the sealing integrity of the pipe joint. Importantly, the sealing washer does not fall out during joint formation and the washer is not distorted or otherwise damaged in field applications.

[0003] Prior washer sealing systems are known where a uniform rubber washer is generally deformable to allow for hand folding or bending to have a reverse curvature and the rubber washer is inserted within a mating internal seat formed in a receiving flared pipe end. A collapsible mandrel flaring tool is used at the pipe manufacturing site to pre-form the seat within the receiving pipe flared end. The prior art attempts to ensure the integrity of such pipe joints involve the use of a pipe washer having a first distinct body region made of an elastically yielding sealing material such as rubber, which is bonded to a second distinct body region made of a more rigid material such as rigid plastic. The purpose is that the rigid body region of the washer helps to keep the washer in place within the pipe groove. Other approaches to solve this problem include using a uniform rubber ring having a reinforcing band inserted within a mating groove disposed on the inner diameter of the rubber ring.

[0004] In the early 1970s, Rieber & Son in Bergen, Norway, developed a new technique known industrially as the "Rieber joint". The Rieber system uses a combination of die elements and sealing rings for sealing the joint between the socket end and the plug end of two mating pipes made of thermoplastic material. In the Rieber process, an elastomeric gasket is installed in an internal groove located in the receiving socket end of the pipe while the receiving or flared end is being formed. During the flaring operation, the Rieber process provides a prestressed and anchored elastomeric gasket rather than using a preformed groove. Since the gasket is installed while the flared pipe end is being formed, a rigid reinforcing ring can be supplied as part of the gasket. Since the pipe groove is formed around the gasket and the reinforcing ring embedded therein, the gasket is firmly held in place and does not tend to twist or flip or otherwise allow impurities to enter the sealed area of the joint, thus increasing the reliability of the joint and reducing the risk of leakage or failure due to wear. The Rieber process is described in the following U.S. patents:. U.S. Patent No. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.

[0005] Although the Rieber process provides progress, the flaring operation is somewhat complex and expensive. In addition, there are certain situations where it is desirable to manually install the gasket on-site or at a manufacturing plant, or to remove one gasket and reinstall another in a preformed seat in a selected pipe end, rather than using an integrally installed gasket where the groove in the pipe is formed around the gasket. Thus, in some instances, it may be desirable to have a gasket that can be installed by hand by simply bending the gasket and installing it in the pipe seat.

[0006] Accordingly, an object of the present invention is to provide an improved gasket that is firmly held in a preformed pipe groove without a separate retaining band.

[0007] Another object of the present invention is to provide such a sealing gasket that has the following properties: allows sealing of the gasket in a low-pressure or no-pressure state during on-site assembly without twisting, squeezing, or displacement, and the sealing gasket can also be installed by hand in the flared seat of a plastic pipe.

[0008] Another object of the present invention is to provide an improved sealing gasket of the plastic / rubber type that optimizes the sealing surface contact of the gasket with the pipe flare seat and with the plug end of the mating pipe while minimizing the amount of rubber material used. For example, in the case of a PP-TPE gasket, the goal would be to minimize the amount of TPE used while compensating by using more PP.

[0009] Another object of the present invention is to provide a sealing gasket of the PP-TPE type in which the ratio of the volume of TPE is less than 50%. Summary of the Invention

[0010] The sealing gasket of the present invention meets the foregoing objectives of rubber / plastic gasket design, which is designed in particular for sealing PVC pipes in low-pressure or non-pressure applications (such as sewer lines), where its minimalist and lightweight design can be advantageously used. A preferred gasket of the present invention includes an annular hard plastic band, which is made of a suitable polyolefin (e.g., polypropylene (PP)) for example. The hard plastic band supports two separate rubber or thermoplastic elastomer (i.e., TPE, preferably TPV) sealing regions, which form an outer ring and an inner lip. The main purpose of the design is to reduce the amount of TPV required and compensate by using more PP. In a particularly preferred form, the sealing gasket of the present invention contains approximately 55% PP and 45% TPV by volume. The unique design featuring an outer sealing ring, an inner sealing lip, and a plastic cup-shaped band also inherently serves the purpose of minimizing the total volume of TPV used.

[0011] As will be described more fully, the elongate PP body supports two TPE components (the ring and the lip), thus providing most of the necessary hardness to form sufficient contact pressure against the sealing surface. The outer ring is selectively sized to provide proper functioning as a sealing body. During the formation of the joint, the contact pressure on the outer diameter of the sealing gasket comes from ring compression (due to interference) as well as from the compression and bending of the PP body. The outer ring and the inner lip components effectively absorb all joint size variations. In the case of the inner diameter, the main source of the contact pressure comes from the circumferential stress generated by the stretching of the lip.

[0012] In most seals, there is no direct compression line from the outer sealing surface through the soft material to the inner sealing surface. In the design of the present invention, the internal PP bending stress becomes a means of transmitting the reaction force through the seal. By bending the gasket by hand, the gasket can be easily installed in the preformed seat of the plastic pipe. The ease of installation and the sealing performance are adjusted by making minor changes in the PP material properties or the body geometry to meet the requirements and standards. When hydrostatic pressure is applied, the shape of the V-shaped seal promotes self-energizing behavior.

[0013] The sealing washer of the present invention is injection molded using a unique molding operation. The TPV is injected onto the PP insert, from the sealing axis through two gates into the inner lip. The outer ring of the TPV is injected through a plurality of ribs located on the outer peripheral surface of the seal, and these ribs remain bonded to the finished product. In the finished product, these ribs or runners serve as buffer portions, which contribute to laterally sealing and fitting into the pipe seat groove with less material required.

[0014] In a particularly preferred form, there is shown a pipe sealing washer designed to be received within a seat provided within a receiving flared socket end of a thermoplastic pipe, the receiving flared socket end having a given inner diameter designed to receive a given outer diameter of a mating insertable thermoplastic pipe end to form a pipe joint. The washer is formed of an annular rigid plastic band having an outer peripheral surface and an inner peripheral surface. The band has two separate elastomeric portions, a first separate elastomeric portion forming an outer ring around the outer peripheral surface of the rigid plastic band, and a second separate elastomeric portion forming an inner lip around the inner peripheral surface of the rigid plastic band. These two separate elastomeric portions are connected by a series of spaced ribs which form an elastomeric continuous body around the band connecting the first and second separate elastomeric portions at spaced intervals.

[0015] The rigid plastic annular body portion together with the outer ring portion of the supported elastomer and the inner elastomeric lip form a cross-section of a V-shaped profile which, when hydrostatic pressure is applied to the pipe joint, the V-shape itself serves to promote self-energizing behavior. The rigid plastic band supports both the outer ring of the elastomer and the inner lip of the elastomer, thus providing sufficient hardness to form contact pressure between the outer ring and the seat of the flared socket end of the pipe and between the inner lip and the mating insertable pipe end when forming the pipe joint.

[0016] The outer ring portion of the elastomer of the preferred washer of the present invention has an outer ring surface which is selectively sized to serve as a sealing body, whereby the contact pressure of the outer ring portion of the elastomer on the outer ring surface with the pipe flared end comes from hoop bending and compression due to interference with the pipe flared end and from bending of the polyolefin body. As explained, these outer ring and inner lip portions of the elastomer are selectively sized to absorb any dimensional variations in the pipe insertable and receiving members. In other words, the outer ring absorbs variations in the seat ID. The remaining dimensional variations (such as plug OD, joint misalignment and deflection, and the ID of the flared end (which affects joint misalignment)) are absorbed by the inner lip. In the case of the inner lip portion of the elastomer, the main source of the contact pressure comes from the circumferential stress generated by stretching the lip by the mating insertable pipe end when forming the pipe joint.

[0017] The washers of the present invention also have unique features that distinguish them from washers of the prior art. The fact that there is no direct compression line from the outer ring portion of the elastomer of the washer through the soft material to the inner lip portion of the elastomer (whereas a direct compression line exists in the case of most sealing washers) is a distinct difference in the washer design of the present invention. The washers of the present invention rely more on the internal bending stress of the rigid plastic band, which serves as a means for transmitting the reaction force through the seal to the outer ring portion of the elastomer and the inner lip portion of the elastomer.

[0018] Also shown is a method of manufacturing a pipe sealing washer having the previously described features. The simplest form of the method includes the following steps:

[0019] Provide an injection mold having an upper half and a lower half, the lower half having a rubber mold cavity;

[0020] Place a rigid plastic band in the rubber mold cavity, the rigid plastic band having an inner circumferential surface and an outer circumferential surface;

[0021] Inject rubber into the mold such that the rubber flows on both sides of the rigid plastic band, thereby creating an outer seating ring sealing surface and an inner plug sealing surface, which are separated from each other except for a series of spaced-apart ribs located at a plurality of circumferentially spaced positions on the rigid plastic band, the ribs being for facilitating the flow of rubber on the PP band to form the two separate washer sealing surfaces.

[0022] Additional objects, features, and advantages will be apparent from the following written description. Description of the Drawings

[0023] Figure 1 is an end view of a section of a plastic pipe that is partially cut away and shows the flared end and the seating ring, with the washer of the present invention in position in the seating ring and the insert pipe section positioned for insertion into the flared portion.

[0024] Figure 2 is Figure 1 a perspective view of the sealing washer of

[0025] Figure 3 is Figure 2 a cross-sectional view of the washer of the present invention taken at the location of one of the ribs shown in

[0026] Figure 4A shows the beginning step of forming a pipe joint, where the end of the insert pipe has just started to contact the Figure 2 sealing washer of

[0027] Figure 4B is similar toFigure 4A views, but showing the assembled pipe joint.

[0028] Figure 5A is a simplified illustration of the first step in the process for manufacturing the sealing washer of the present invention, showing the hard plastic strip in place in the lower half of the mold.

[0029] Figure 5B shows the next step in the manufacturing process, where the upper half of the mold is in place and the TPV material is introduced into the mold cavity.

[0030] Figure 5C shows the mold cavity, with some parts of the upper half of the mold not shown, and shows the initial direction of flow of the TPV material through the mold cavity.

[0031] Figure 5D is Figure 5C subsequent to the view of, showing the TPV material flowing through the ribs of the mold cavity and around the top of the PP insert to form part of the outer sealing portion of the washer.

[0032] Figure 5E is Figure 5D subsequent to the view of, showing the relative direction of movement of the TPV material in the mold.

[0033] Figure 5F shows the upper half of the mold cavity being raised and the finished washer of the present invention being removed from the mold cavity.

[0034] Figure 6 is a perspective view of a prior art washer made of rubber / hard plastic material.

[0035] Figure 7 is Figure 6 cross-sectional view of the prior art washer of. DETAILED DESCRIPTION

[0036] The present invention described herein and its various features and advantageous details are more fully explained with reference to the non-limiting examples shown in the accompanying drawings and described in detail below. Descriptions of well-known components and processes and manufacturing techniques are omitted so as not to unnecessarily obscure the operation of the present invention. The examples used herein are only intended to assist in understanding the manner in which the present invention may be practiced and further enable those skilled in the art to practice the present invention. Therefore, the examples should not be construed as limiting the scope of the claimed invention.

[0037] Now turning to Figure 1, shows a pipe sealing gasket 11 embodying the advantageous features of the present invention. The gasket 11 is shown as being installed within a seat ring 13, which is disposed within the flared end 15 of a receiving pipe section of a thermoplastic pipe 17. The receiving pipe section 17 can be made of any of a variety of commercially available thermoplastic materials (such as polyolefins including polyethylene and polypropylene, as well as polyvinyl chloride and similar materials, most commonly PVC). This general type of thermoplastic pipe is used in a variety of industrial fields including water, sewage, and chemical industries. The flared end 15 of the thermoplastic pipe section has a mouth opening 19, which can engage with a plug end 23 of a matching insert pipe section 25 to form a pipe joint. The seat ring 13 for receiving the gasket has been preformed in the mouth opening 19 at the pipe manufacturing site, such as by using a collapsible mandrel flaring tool. The gasket of the present invention is sufficiently flexible to be installed within the seat ring 13 by hand or by using automated installation equipment.

[0038] Certain advantages of the gasket design of the present invention may be best understood by reference to the same general type of gasket of the prior art. Figure 6 and Figure 7 shows a common design generally designated by 27. In Figure 6 the profile of a prior art gasket is shown and in Figure 7 the cross-section of a prior art gasket is shown. The gasket 27 can be regarded as a circular annular member having a main gasket body 29 made of a flexible elastomeric material (such as a suitable natural rubber or synthetic rubber). The elastomeric material used to form the gasket body 29 will vary in composition depending on the end application and can include many different natural and synthetic rubbers, including for example styrene-butadiene rubber (SBR), ethylene propylene diene monomer rubber (EPDM), acrylonitrile butadiene rubber (NBR), nitrile rubber, etc.

[0039] Now turning to Figure 7 , the main gasket body 29 includes an outer sealing surface 31, which in this case is provided with a series of ribs or serrations. The main gasket body also includes a lower main sealing surface 33. As will be understood by those skilled in the art, the main sealing surface 33 is a uniformly inclined face of the gasket body that forms a combination of a lip and a compression sealing area for the gasket. The lip area is separated from the outer sealing surface 31 by a V-shaped recess (generally designated by 35 in Figure 7 ). When the matching plug end of a matching pipe section encounters the main sealing surface 33 of the gasket, the V-shaped recess allows the lip area of the gasket body to bend inwards.

[0040] As can be seen from Figure 7Becomes apparent in, the main washer body 29 of the prior art washer is reinforced by a hard plastic strip 37. Thus, the washer body can be considered to have a rubber element and a hard plastic element, and the hard plastic element serves as a reinforcing element for the washer body. However, it is worth noting that although in the case of a common two-component seal, the inner and outer sealing surfaces 31, 33, from the plug to the seat ring, are part of the same continuous block of rubber or TPV. That is, the inner sealing surface 33 (against the plug) is connected to the outer sealing surface 31 (seat ring) by an amount of continuous TPV injected in the same mold cavity where the PP retaining ring has already been placed. Additional TPV is used to fill the space between the two critical and functional contact surfaces of the sealing lip and the seat ring. This also necessarily means that the PP part of the washer must be quite wide and completely fill the part of the mold cavity of the washer (so that it does not distort), resulting in a wide bonding surface and using a large volume of PP.

[0041] This results in various complexities or limitations inherent in prior art molding techniques. For example, if the PP strip is held upright in a common mold cavity to create two separate areas in the mold for the TPV (thus minimizing the amount of TPV required), the TPV will fill around the PP strip and the PP will be distorted by the high-pressure TPV as the TPV flows into the mold cavity. Depending on the location of the mold gate, the PP strip will be pushed to one side or the other of the cavity by the high-pressure TPV. There is no way to create separate sealing surfaces of TPV on the lip and the seat ring due to being interrupted by low-cost PP.

[0042] Now referring to Figure 2 and Figure 3 , an improved sealing washer of the present invention is shown, which is generally designated by 39. The washer 39 is intended to be received within a seat ring provided in the receiving flared socket end of a thermoplastic pipe, the receiving flared socket end having a given inner diameter designed to receive a given outer diameter of a mating insertable thermoplastic pipe end to form a pipe joint (see Figure 1 ). It can be seen that the washer of the present invention has an annular hard plastic strip 41 and two separate elastomeric portions 47, 49 (see Figure 4A and Figure 4B ), the annular hard plastic strip having an outer peripheral surface 43 and an inner peripheral surface 45. The first separate elastomeric portion 47 forms an outer ring around the outer peripheral surface of the hard plastic strip, and the second separate elastomeric portion 49 forms an inner lip around the inner peripheral surface of the hard plastic strip 41. These two separate elastomeric portions 47, 49 are connected by a series of spaced ribs (refer to, for example, the ribs 51, 53, 55 in Figure 2 ), which form an elastomeric continuous body connecting the first separate elastomeric portion and the second separate elastomeric portion at spaced intervals.

[0043] It should be understood that the rigid plastic band 41 supports both the elastomeric outer ring and the elastomeric inner lip (surfaces 47, 49), thereby providing sufficient stiffness to form contact pressure between the outer ring and the seat ring ( Figure 1 13 in) of the flared socket end of the pipe and between the inner lip and the mating insert pipe end.

[0044] Referring again to Figure 4A and Figure 4B , it can be seen that the outer ring portion 47 of the elastomer includes an outer ring surface, the size of which is selectively set to serve as a sealing body, whereby the contact pressure on the outer ring surface with the flared end of the pipe ( Figure 1 17 in) comes from the ring bending and compression caused by the interference with the flared end of the pipe and from the bending of the polyolefin body, and wherein the sizes of the inner lip portion 49 and the outer ring portion 47 of the elastomer are determined to absorb any dimensional changes in the pipe insertion and receiving members. In the case of the inner lip portion 49 of the elastomer, the main source of the contact pressure comes from the circumferential stress generated by stretching the lip by the mating insert pipe end ( Figure 1 25 in) when the pipe joint is assembled.

[0045] From Figure 3 , Figure 4A and Figure 4B It will also be recognized that there is no direct compression line from the outer ring portion 47 of the elastomer of the gasket through the soft material to the inner lip portion 49 of the elastomer. Instead, the internal bending stress of the rigid plastic band 41 becomes the means for transmitting the reaction force to the outer ring portion 47 of the elastomer and the inner lip portion 49 of the elastomer through the seal. This is different from the prior art gasket designs shown in Figure 6 and Figure 7 , in which the rubber regions 31, 33 are continuous.

[0046] As can be observed in Figure 3 , the rigid plastic band 41 together with the outer ring portion 47 of the supported elastomer and the inner lip portion 49 of the elastomer forms a cross-section with a V-shaped profile, and when hydrostatic pressure is applied to the pipe joint, the V-shape itself serves to promote self-energizing behavior. In the specific example of the gasket shown in Figure 3 , both the outer ring portion of the elastomer of the gasket and the inner lip portion of the elastomer have exposed circumferential sealing surfaces, and these circumferential sealing surfaces are provided with a series of circumferential lands and grooves (e.g., lands 57 and grooves 59) for engaging the receiving pipe socket end and the mating insert pipe when the pipe joint is assembled.

[0047] As previously mentioned, the rubber portion of the washer of the present invention can be made of rubber such as thermoplastic elastomers such as thermoplastic vulcanizates or more traditional rubber materials (such as styrene-butadiene rubber, ethylene propylene diene monomer rubber or nitrile rubber). The hardness of the rubber can vary depending on the end application, but is typically in the range of about 40 to 70 Shore A hardness, preferably in the range of about 40 to 60 Shore A hardness. On the other hand, the rigid plastic strip 41 is made of a synthetic plastic material having a hardness greater than that of the rubber portion of the washer. The synthetic plastic material for the strip 41 is preferably a material that exhibits an appropriate hardness for hand application while allowing for creasing during installation.

[0048] A preferred material for the rubber portion of the washer of the present invention is "thermoplastic vulcanizate" known as TPV. These materials are part of the thermoplastic elastomer (TPE) family of polymers. However, these materials have properties that are closest to those of EPDM thermoset rubber in terms of elastomeric properties, thus combining the characteristics of vulcanized rubber with the processing properties of thermoplastics. TPV provides a combination of elastomeric properties (such as compression deformation and tensile deformation) with aging resistance and chemical resistance. TPV is generally suitable for conventional thermoplastic methods such as injection molding and extrusion and does not require mixing with different components such as reinforcing fillers (carbon black, mineral fillers), stabilizers, plasticizing oils and curing systems. Compared with processing rubber, the thermoplastic processing of TPV can often deliver in shorter cycle times, produce more parts per hour and reuse the waste generated during processing. Compared with rubber, this can result in lower part costs, fewer tools / machinery, lower waste costs and optimized material logistics costs.

[0049] Various rigid plastic-type materials can be suitable candidates for use as the rigid plastic strip. These materials include materials such as polyolefins (such as polypropylene) and other materials (such as polyvinyl chloride and various "engineering plastics"). The preferred material for the present application is suitable polypropylene. Thus, a preferred sealing washer is a PP-TPV composite.

[0050] An advantage of the washer design of the present invention is that it requires less rigid plastic, thereby resulting in cost savings. The washer of the present invention contains more than 50% synthetic polyolefin. In a particularly preferred form, the washer of the present invention contains, for example, about 55% polypropylene and 45% thermoplastic elastomer by volume.

[0051] The described gasket design of the present invention is achieved only by certain unique techniques used in the molding operation. As briefly discussed, there are various complexities or limitations inherent in the prior art molding techniques. Attempting to raise the PP band to create two separate areas in the mold would subject the plastic band to the distorting forces caused by the high-pressure TPV as it flows into the mold cavity. Due to being interrupted by low-cost PP, there is no convenient way to create separate sealing surfaces of TPV on the lip and seat contact areas of the gasket.

[0052] The unique molding technique of the present invention uses the ribs or runners ( Figure 2 such as 51, 53, 55 in

[0053] previously described) and, more specifically, uses their mirror image spaces or cavities in the mold to essentially create two cavities on either side of a continuous PP band in the same mold, and uses the mold halves to hold the PP in place. Thus, TPV can be injected on both sides of the PP band without distorting the PP band as occurs in other designs due to the high-pressure TPV. When the PP band is placed in the mold, the two halves of the mold close, creating two unfilled areas in the mold. One area is on the inside of the PP band, i.e., the lip area, while the other area is on the outside of the PP band, i.e., the seat area. TPV is injected into the first open cavity and fills the cavity, creating the sealing lip. At the same time, the TPV pushes the PP band against the outer half of the mold, holding the PP band in place. The width of the small rib space in the outer half of the mold is not sufficient to push the PP band into the space and fill it, but the width of the space is sufficient for the TPV to flow around the PP and up along the rib space (which is a groove in the outer cavity) to the unfilled second cavity. Here, the PP band is held in place by the inner cavity. When the inner cavity is filled with TPV, the outer seat sealing surface is formed, and the PP band remains against the inner mold cavity so that it does not deform.

[0054] Now will be mainly referred to Figures 5A to 5F to describe the above method of manufacturing the sealed pipe gasket of the present invention. Figure 5A The lower half 61 of an injection molding die of a type familiar to those skilled in the relevant art is shown. For ease of illustration, the matching upper half 63 of the die is raised. As Figure 5AAs can be seen, the first mold half 61 has a first mold surface 65 that has a circumferential recess 67. As Figure 5A shown, in the first step of the manufacturing process, the rigid plastic strip 41 is placed within the circumferential recess 67.

[0055] The second mold half 63 has a mold surface that is substantially a mirror image of the first mold surface. The first and second mold surfaces are then joined, and a moldable rubber compound (TPV in this case) is injected into the circumferential recess. As has been briefly described, the TPV is injected onto the PP insert, through two gates into the inner lip region from the sealing axis. The TPE outer ring is injected through a mold region that ultimately travels around the front of the sealing region and holds a series of ribs or runners that are incorporated into the finished product. In the finished product, these runners serve as cushions that help to laterally seal into the seat groove of the plastic pipe, requiring less material compared to prior art gaskets. Heat and pressure are thus applied to the mold to form the annular gasket body. The heat and pressure in the mold cure the rubber sealing regions and adhere them to the rigid plastic strip portions.

[0056] Figures 5B to 5E is a simplified partial schematic view showing the steps of the flow path of the TPV (rubber) relative to the rigid plastic strip 41 during the molding operation. In Figure 5B the first part of the manufacturing operation shown, the rubber flows from a rubber source (not shown) through the gate 65, through the cavity between the mold halves to the lip region 67 of the rigid plastic strip (insert).

[0057] As Figure 5C shown, the rubber then travels circumferentially in two directions (shown by the arrows in Figure 5C ) around the lip cavity of the mold.

[0058] Figure 5D The rubber (TPV) then passes through the rib or runner region of the mold, allowing it to reach the outer ring cavity (schematically shown by the bottom curved arrow in Figure 5D ).

[0059] As again shown in Figure 5E in a slightly simplified manner, the rubber continues to travel circumferentially in the inner and outer mold cavities until the melt front of the rubber converges.

[0060] Figure 5F The separated mold halves 61, 63 and the completed gasket 39 removed from the mold are shown at the end of the molding operation.

[0061] The present invention already has several advantages. The sealing gaskets of the present invention are ideally suited for low-pressure or non-pressure sealing operations due to the lightweight and minimalist aspects of the design. These gaskets belong to the family of PP-TPE type gaskets and are also manufactured using the least amount of TPE, thereby providing cost savings. In a preferred embodiment, the finished sealing gasket is approximately 55% PP and 45% TPE. The elongated PP strip supports two separate rubber sealing surfaces and provides most of the necessary hardness to create sufficient contact pressure against the sealing surfaces of the pipe joint (the flared seat ring and the outside of the matching plug joint). The outer sealing surface on the outside of the PP strip only has the appropriate dimensions to serve as the sealing body, thus providing material savings compared to prior art gaskets. The unique sealing aspect of the gaskets of the present invention is partly due to the fact that the contact pressure on the OD of the seal comes from ring compression (interference) and from the compression and bending of the PP body. The main source of the contact pressure on the ID of the gasket comes from the circumferential stress generated by the stretching of the lip region of the gasket. The internal bending stress of the PP strip becomes the means for transmitting the reaction force through the seal. When a hydrostatic pressure is applied to the resulting pipe joint, the V-shaped sealing shape of the gasket promotes self-energizing (self-sealing) behavior.

[0062] While the present invention is shown in only one of its forms, the present invention is not limited thereto, but is susceptible to various changes and modifications without departing from the spirit of the present invention.

Claims

1. A pipe sealing gasket designed to be received within a seating ring disposed within a receiving flared socket end of a thermoplastic pipe, the receiving flared socket end having a given inner diameter designed to receive a given outer diameter of a mating thermoplastic insert pipe end to form a pipe joint, the gasket comprising: An annular rigid plastic band having an outer peripheral surface and an inner peripheral surface; And two separate elastomeric portions, a first separate elastomeric portion forming an outer ring covering and surrounding a portion of the outer peripheral surface of the rigid plastic band, and a second separate elastomeric portion forming an inner lip covering and surrounding a portion of the inner peripheral surface of the rigid plastic band, the outer ring formed by the first separate elastomeric portion having a width substantially less than the exposed width of the outer peripheral surface of the rigid plastic band, the first separate elastomeric portion (47) and the second separate elastomeric portion (49) being connected by a series of spaced-apart ribs located on the outer peripheral surface (43) of the annular rigid plastic band (41), the connection points only at these spaced-apart ribs constituting an elastomeric continuous body connecting the first separate elastomeric portion and the second separate elastomeric portion at spaced-apart intervals; And wherein the rigid plastic band supports both the outer ring of elastomer and the inner lip of elastomer, thereby providing sufficient stiffness to create contact pressure between the outer ring and the seating ring of the flared socket end of the pipe and between the inner lip and the mating insert pipe end.

2. The pipeline sealing gasket according to claim 1, wherein The rigid plastic band is made of synthetic polyolefin.

3. The pipeline sealing washer according to claim 2, wherein The rigid plastic band is made of polypropylene.

4. The pipe sealing gasket according to claim 1, wherein, The two separate elastomeric portions are each made of thermoplastic elastomer.

5. The pipeline sealing gasket according to claim 1, wherein, The gasket contains more than 50% synthetic polyolefin.

6. The pipe sealing gasket according to claim 5, wherein, The gasket contains approximately 55% polypropylene and 45% thermoplastic elastomer by volume.

7. The pipeline sealing gasket according to claim 1, wherein, The outer ring portion of the elastomer has an outer ring surface, and the dimensions of the outer ring portion of the elastomer are selectively set to act as a sealing body, whereby the contact pressure of the outer ring portion of the elastomer on the outer ring surface with the flared pipe end results from ring compression due to interference with the flared pipe end and from bending of the polyolefin body, and wherein the inner lip portion of the elastomer and the outer ring surface are sized to absorb any dimensional variations in the pipe insert and receiving members.

8. The pipeline sealing gasket according to claim 7, wherein, In the case of the inner lip portion of the elastomer, the main source of the contact pressure comes from the circumferential stress generated by stretching the lip when forming the pipe joint by the mating insert pipe end.

9. The pipe sealing gasket according to claim 1, wherein The rigid plastic band together with the outer ring portion of the elastomer and the inner lip portion of the elastomer supported by the rigid plastic band form a cross-section with a V-shaped profile, which itself acts to promote self-energizing behavior when hydrostatic pressure is applied to the pipe joint.

10. The pipe sealing gasket according to claim 1, wherein, Both the outer ring portion of the elastomer of the washer and the inner lip portion of the elastomer have exposed circumferential sealing surfaces, and both of these circumferential sealing surfaces are provided with a series of circumferential lands and grooves for engaging a receiving pipe socket end and the matching insert pipe when forming the pipe joint.

11. A method of manufacturing a pipe sealing gasket, the pipe sealing gasket being designed to be received within a seat provided within a receiving flared socket end of a thermoplastic pipe, wherein, The receiving flared socket end has a given inner diameter which is designed to accommodate the given outer diameter of a matching insert thermoplastic pipe end to form a pipe joint, and the method includes the following steps: Provide an injection mold having an upper half and a lower half, the lower half having a rubber mold cavity; Place a hard plastic strip in the rubber mold cavity, the hard plastic strip having an inner circumferential surface and an outer circumferential surface; Inject rubber into the mold such that the rubber flows on both sides of the hard plastic strip, thereby creating an outer seat ring sealing surface and an inner plug sealing surface, and these two surfaces are separated from each other except for a series of spaced ribs located at spaced circumferential positions on the hard plastic strip.

12. The method according to claim 11, wherein, The rubber is TPV rubber.

13. The method according to claim 11, wherein, The hard plastic strip is made of polyolefin.

14. The method according to claim 13, wherein, The hard plastic strip is polypropylene.

15. A method of manufacturing a pipe sealing gasket, the pipe sealing gasket being designed to be received within a seating ring disposed within a receiving flared socket end of a thermoplastic pipe, wherein, The receiving flared socket end has a given inner diameter which is designed to accommodate the given outer diameter of a matching insert thermoplastic pipe end to form a pipe joint, and the method includes the following steps: Provide an injection mold having an upper half and a lower half, the lower half having a rubber mold cavity, and the mold cavity having a series of circumferentially spaced ribbed spaces; Place a hard plastic strip in the rubber mold cavity, the hard plastic strip having an inner circumferential surface and an outer circumferential surface; Inject rubber into the mold such that the rubber flows on both sides of the hard plastic strip through the series of circumferentially spaced ribbed spaces, thereby creating an outer seat ring sealing surface and an inner plug sealing surface, and these two surfaces are separated from each other except for the series of spaced ribs formed in the ribbed spaces due to the molding operation, thereby forming the pipe seal washer; Wherein, the resulting pipe seal washer has two separate elastomer parts, a first separate elastomer part forms an outer ring around the outer circumferential surface of the hard plastic strip, and a second separate elastomer part forms an inner lip around the inner circumferential surface of the hard plastic strip, and the two separate elastomer parts are connected by a series of spaced ribs, and the ribs form an elastomeric narrow continuous body connecting the first separate elastomer part and the second separate elastomer part at spaced intervals.

16. The method according to claim 15, wherein, The hard plastic strip supports both the outer ring of the elastomer and the inner lip of the elastomer, thereby providing sufficient hardness to create contact pressure between the outer ring and the seat ring of the flared socket end of the pipe and between the inner lip and the matching insert pipe end.

17. The method according to claim 16, wherein The hard plastic strip is made of polypropylene.

18. The method according to claim 16, wherein The two separate elastomer parts are both made of thermoplastic elastomer.

19. The method according to claim 16, wherein, The resulting seal washer includes more than 50% synthetic polyolefin.

20. The method according to claim 16, wherein, The outer ring portion of the resulting elastomer has an outer ring surface, and the dimensions of the outer ring portion of the elastomer are selectively set to serve as a sealing body, whereby during the assembly of the pipe joint, the contact pressure of the outer ring portion of the elastomer with the flared end of the pipe on the outer ring surface results from ring bending and compression caused by interference with the flared end of the pipe and from bending of the polyolefin body, and wherein the inner lip portion and the outer ring portion of the elastomer are dimensioned to absorb any dimensional variations in the pipe insert member and the receiving member.

21. The method according to claim 16, wherein In the case of the inner lip portion of the elastomer, the main source of the contact pressure results from the circumferential stress generated by stretching the lip by the inserted pipe end that mates when forming the pipe joint.

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