Composite membrane with insert and opening surrounding thickening for diaphragm pumps

Abstract

Composite diaphragm for diaphragm pumps with an elastomer body (1) having a circumferential edge (2) with a clamping surface (3), a base (4) and a flexible diaphragm section (5) connecting the circumferential edge (2) to the base (4), wherein the base (4) has an upper and a lower wall (6a, 6b) and an insert (8) is arranged at least partially between the walls (6a, 6b), characterized in that the insert (8) extends through an opening (9) in the lower wall (6b) and surrounds the lower wall (6b) in a sealing section (10), wherein the insert (8) and the lower wall (6b) are positively connected to each other in the sealing section (10) with respect to a force acting in the radial direction (R), wherein the lower wall (6b) in the sealing section (10) has a thickening (11) surrounding the opening (9) on both sides engages in a circumferential groove (12a, 12b) of the insert (8).

Description

[0001] The present invention relates to a composite membrane with an elastomer body comprising a circumferential edge with a clamping surface, a base, and a flexible membrane section connecting the circumferential edge to the base, wherein the base has an upper and a lower wall, and wherein an insert is arranged at least partially between the upper and the lower wall. Accordingly, the lower and upper walls form a chamber designed to receive the insert.

[0002] Composite diaphragms of the type described above can be used, for example, to convert differential pressures, particularly in servo elements, actuators, brake boosters, or similar devices. They can also be used in pressure reducers, pressure regulators, or flow controllers. Furthermore, they are suitable for use in valve applications, such as pressure relief valves, safety valves, shut-off valves, or check valves.

[0003] However, such composite diaphragms are preferably intended for use in pumps. These pumps can include, for example, metering pumps, mechanical pumps, diaphragm compressors, or vacuum pumps. They are particularly suitable for use in diaphragm pumps, such as air-operated diaphragm pumps.

[0004] Such composite diaphragms are typically circular and have a disc-shaped base. For this reason, they are also referred to as disc-shaped diaphragms. However, the invention is not limited to such designs but also relates to rolling diaphragms, corrugated diaphragms, dome-shaped diaphragms, and flat diaphragms. The corresponding composite diaphragm can be clamped at its edge in a diaphragm pump, while the base of the composite diaphragm performs reciprocating movements, with each reciprocating movement the flexible diaphragm section being inverted, so that rolling movements of the flexible material can be observed in a radial section. For this reason, the flexible diaphragm section is also referred to as a rolling loop in the prior art.

[0005] The insert located in the base, unlike the elastomer body, is made of an inflexible or dimensionally stable material. This means the base itself does not participate in the rolling motion but merely transmits the stroke movements to the flexible material section via a piston rod attached to the insert. For this purpose, the insert is positioned between the upper and lower walls, with the upper wall facing the conveyed medium during normal use. Similarly, the rear wall faces away from the medium during normal use.

[0006] From DE 19 634 922 A1 it is also known that the insert is part of a connecting rod which can be arranged directly by means of hook-shaped projections in the elastomer body.

[0007] The elastomer body typically has a media-side coating of polytetrafluoroethylene (PTFE) to ensure chemical resistance to the media being conveyed.

[0008] The elastomer body is made of an elastomeric material, usually rubber, and the insert is vulcanized into the elastomer body to create a stable bond. To simplify this manufacturing process, thermoplastic elastomers (TPEs) are increasingly used for the elastomer body. These are polymers that exhibit elastomeric properties in their normal state. However, by applying heat, they can be plastically deformed and thus shaped into almost any desired form.

[0009] One such design is taught, for example, in US 2011 / 0311379 A1, where the elastomer body is injection-molded from the thermoplastic elastomer around an insert. However, a particular problem with the integration of thermoplastic elastomers is that these materials do not form a sufficient bond with the insert, which is usually made of metal, without an additional chemical bonding system. Especially with larger membrane diameters, the high surface forces and loads cause the thermoplastic elastomer body to detach from the insert. This problem can also occur with other plastic materials, but it is particularly problematic with thermoplastic elastomers.Furthermore, the detachment of the elastomer body can allow compressed air to enter the resulting gap between the insert and the elastomer body, further accelerating the aforementioned process and potentially leading to the insert tearing out.

[0010] According to US 2011 / 0311379 A1, this problem can be solved by attaching the thermoplastic elastomer body to the insert via an additional adhesive layer. Furthermore, the insert has openings into which the liquid elastomer is injected during manufacturing, thus compensating for radial forces to a certain extent. However, these openings do not prevent compressed air from penetrating the space between the elastomer body and the insert, or at least they do not significantly reduce the amount of air entering. Therefore, without the additional adhesive layer, it is not possible to guarantee a permanent bond between the elastomer body and the insert.

[0011] However, the integration of such an adhesive layer is both production-intensive and cost-intensive, so the present invention aims to provide a composite membrane that is as easy to manufacture as possible and at the same time has sufficient resistance during operation.

[0012] The solution to this problem and the subject matter of the invention is a composite diaphragm for diaphragm pumps according to claim 1. Accordingly, the insert extends through an opening in the lower wall and surrounds the lower wall in a sealing section, wherein the insert and the lower wall are positively connected to each other in the sealing section with respect to a force acting parallel to the lower wall.

[0013] The positive-locking connection in the sealing section ensures that radial forces acting on the elastomer body can be absorbed to a large extent, or even completely, via the positive locking mechanism between the insert and the elastomer body. This guarantees that the holding forces inherent in the manufacturing process between the elastomer body and the insert are not exceeded by the radial load, thus preventing the elastomer body from separating from the insert.

[0014] At the same time, the insert and the elastomer body in the sealing section form a sealing geometry through positive locking, effectively reducing or completely preventing the ingress of compressed air. Since the opening is typically located at the center or along a central axis of the circular composite membrane, the sealing section is also situated directly next to the opening, thus preventing the ingress of compressed air at an early stage. It should be noted that, in cross-section, a channel forms between the insert and the elastomer body, extending from the opening, with its inlet located on the rear wall directly adjacent to the opening.

[0015] To ensure a positive fit and the most effective seal possible, the lower wall in the sealing section features a thickening surrounding the opening, which engages in a circumferential groove on both sides of the insert. Accordingly, the insert also has a circumferential groove on both sides in the areas of the thickening. It should be noted that, due to the way the insert grips the elastomer body, it rests against it on both sides, so that two sides of the lower wall and the insert are in direct contact. The insert thus forms a recess extending along the circumference and opening radially, in which the lower wall and the thickening are arranged.

[0016] The combination of these thickenings and the circumferential groove(s) achieves a positive fit, as these circumferential grooves are open in an axial direction and thus effectively restrict radial movement between the lower wall of the elastomer body and the insert. At the same time, an additional seal is achieved, since any compressed air penetrating between the elastomer body and the insert must travel the additional path around the thickening to reach the area of ​​the insert, which is located between the walls of the elastomer body and whose separation from the elastomer body is particularly problematic.Furthermore, with the double-sided thickening, when sealing air enters, the lower wall presses against the area of ​​the insert located in the chamber, thus increasing the sealing force between the part of the insert positioned between the walls and the lower wall of the elastomer body. In this context, one can therefore speak of an "active sealing geometry," since the sealing forces increase with the increasing inflow of compressed air, and thus the sealing effectiveness also increases.

[0017] A particularly preferred embodiment is one in which the insert is formed from at least a first and a second insert body, wherein the first insert body is arranged substantially preferably, but preferably completely, within the chamber formed between the walls of the base, and the second insert body rests against the lower wall or preferably surrounds the lower wall. The two-part design of the insert allows for a simple form-fit connection between the insert and the elastomer body. For example, the first insert body can be overmolded with the elastomer of the elastomer body. The second insert body can then be positioned on the lower wall of the base and attached to the first insert body.The second insert body ensures that the lower wall is positioned between the first and second bodies and, in particular, that the thickening is held in the circumferential grooves of the first and second insert bodies to form the positive locking mechanism.

[0018] Alternatively, the insert bodies can first be arranged and attached to each other, with the elastomer body then being formed by an injection molding process. The molten elastomer penetrates the space between the insert bodies, with the shape of the insert bodies acting as a kind of mold, allowing the corresponding thickening to form in the elastomer body.

[0019] The design of the two-part insert can be implemented in various ways. For example, the first insert body can be completely enclosed between the walls of the elastomer body, in which case the second insert body has a T-shaped cross-section and extends through the opening of the lower wall with one axially extending leg. Alternatively, the first insert body can protrude to a certain extent from an upper surface of the lower wall that rests against the insert, allowing the second insert body to be disc-shaped.

[0020] The two insert bodies are connected in a known manner via a screw connection, an interference fit, or a positive fit. In the case of a screw connection, the first insert body has a recess or opening with an internal thread extending along its central axis. A T-shaped second insert body with an axially extending external thread is then screwed into the internal thread of the first insert body. This opening is preferably the only opening in the first insert body. If further openings are provided outside the central axis, they serve solely to reduce the weight of the insert body. Accordingly, the elastomer body does not form any additional walls or webs in the base area that are provided in the openings in the first insert body or in the insert itself.

[0021] The design of the chamber or the walls of the base depends on the shape of the insert or the first insert body, which preferably has a semi-ellipsoidal or disc-shaped base. In the case of a semi-ellipsoidal insert body, the chamber and the entire base also have an arc-shaped contour in cross-section in the area of ​​the upper wall. The lower wall, on the other hand, is straight or, in the case of a disc-shaped design, also has an arc-shaped contour.

[0022] To achieve the best possible bond strength between the insert and the elastomer body, even with respect to axial forces, an additional sealing section is provided that positively connects the insert to the elastomer body with respect to an axially acting force. These axial forces can be, for example, surface forces exerted on the upper wall of the base via the conveyed medium, e.g., in the form of a vacuum. Therefore, preferably, the upper wall of the base and an adjacent section of the insert are designed with a positive fit with respect to this axial force.

[0023] According to a preferred embodiment, this can be achieved by the insert having a radially inwardly projecting and circumferentially extending projection on a side adjacent to the upper wall, which interacts positively with one or more radially projecting retaining lugs of the elastomer body with respect to an axially acting force. The retaining lug of the elastomer body is also preferably designed as a projection extending along the circumferential direction, so that the projections of the elastomer body and the insert interlock and thus prevent movement of the elastomer body relative to the insert in the vertical direction.

[0024] Preferably, the insert further includes a connection device for a piston rod, which, particularly in a two-part design, is provided in or on the second insert body. In principle, a connection can be achieved via a screw connection, an interference fit, or a positive fit, although a screw connection is the preferred embodiment because it allows the piston rod to be easily and detachably connected to the composite membrane. In a two-part design, the connection device is preferably provided in the second insert body, wherein an axial section of the second insert body has at least one internal thread. This internal thread serves to receive the piston rod, which accordingly has an external thread that interacts with the internal thread. However, it is also conceivable that the internal thread is provided in the first insert body.

[0025] The positive-locking connection between the insert and the elastomer body, especially in combination with an active sealing geometry, makes it possible to preferably form the elastomer body from a thermoplastic polymer (TPE).

[0026] The insert or insert bodies are preferably made of a metal, e.g., aluminium, copper, steel, especially stainless steel.

[0027] The invention will now be explained in more detail using a purely exemplary embodiment. The figures show: Fig. 1 the composite membrane according to the invention in a sectional view Fig. 2 a detailed view of the base of the composite membrane Fig. 3. The operating principle of the composite membrane compared to a state-of-the-art membrane Fig. 4 the composite membrane in an isometric view

[0028] The Fig. Figure 1 shows the composite membrane according to the invention in a cross-sectional view looking at the upper, media-side surface. The composite membrane has an elastomer body 1 made of a thermoplastic elastomer, a circumferential edge 2 with a clamping surface 3, a base 4, and a flexible membrane section 5 connecting the circumferential edge 2 to the base 4. The base 4 is formed from an upper and a lower wall 6a, 6b, wherein the walls 6a, 6b form a chamber 7 arranged between the walls 6a, 6b, and wherein an insert 8 is arranged in the chamber 7 between the walls 6a, 6b.

[0029] The insert 8 extends through an opening 9 in the lower wall 6b and surrounds the lower wall 6b in a sealing section 10. This allows the insert 8 and the lower wall 6b to be positively connected to each other in the sealing section 10 with respect to a force acting in the radial direction R.

[0030] The exact nature of the positive-locking connection can be seen in particular from the detailed view according to Fig. Figure 2 clearly shows only the base 4 of the composite membrane. It is clearly visible that the lower wall 6b has a thickening 11 surrounding the opening 9, which engages on both sides in a circumferential groove 12a, 12b of the insert 8.

[0031] The functionality of such a sealing geometry becomes particularly clear from a comparative representation with the Fig. Figure 3 highlights the fact that the left side shows a composite membrane from the prior art and the right side a composite membrane according to the invention. It should be noted that only the base 4 is shown in each case. Due to the lifting motion of the composite membrane, forces F are generated, which in particular have a radial component and, in the case of a composite membrane from the prior art, lead to a spreading apart between the elastomer body 1 and the insert 8. This creates a channel between these two components into which compressed air can penetrate, as is clearly visible in the highlighted detail view. At the same time, surface forces A also act, which in particular can cause the upper wall 6a to detach from the insert 8. This makes the channel increasingly larger, so that the compressed air can penetrate into large areas between the insert 8 and the elastomer body 1 and lead to component failure.

[0032] The positive-locking connection in the sealing section 10 ensures that the bond between the insert 8 and the elastomer body 1 remains intact even under the influence of a radial force F, preventing the channel for compressed air from enlarging during operation. Simultaneously, the thickening 11, together with the circumferential grooves 12a and 12b, acts as an active sealing geometry, ensuring that even if compressed air were to penetrate, the channel between the insert 8 and the elastomer body 1 is blocked at an early stage.

[0033] In order to sufficiently prevent detachment between the upper wall 6a and the insert 8, e.g. due to surface forces A, the insert 8 has a circumferential groove 14 on the upper wall 6a of the base 4, wherein a retaining lug 13 of the elastomer body 1 extending along the circumferential direction engages in the circumferential groove 14.

[0034] Based on the Fig. 1 and Fig. Figure 2 further shows that the insert 8 is designed in two parts and has a first insert body 8a and a second insert body 8b, wherein the first insert body 8a is arranged completely within the chamber 7 and is connected to the second insert body 8b via a screw connection. Here, the lower wall 6b lies in the sealing section 10 between the two insert bodies 8a, 8b, wherein the circumferential grooves 12a, 12b formed in the respective insert bodies 8a, 8b positively engage the thickening 11.

[0035] According to the Fig. 4 further makes clear that the second insert body 8b has an internal thread for receiving and connecting a piston rod and that the second insert body 8b is flush with the lower wall 6b on a lower side.

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