Composite membrane, especially for diaphragm pumps

Abstract

The invention describes a composite membrane with a flexible membrane body (4) comprising a circumferential edge (2), a base (4) and a flexible membrane section (5) connecting the circumferential edge (2) to the base (4), wherein the membrane body (4) is at least partially formed from an ultra-high molecular weight polyethylene (PE-UHMWE).

Description

[0001] The present invention relates to a composite membrane with a flexible membrane body comprising a circumferential edge, a base, and a flexible membrane section connecting the circumferential edge to the base. The circumferential edge, in particular, forms a clamping surface over which the composite membrane can be arranged, for example, within a diaphragm pump.

[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] The invention preferably relates to composite diaphragms intended for use in diaphragm pumps and thus for pump applications. Such pumps can be, for example, metering pumps, mechanical pumps, diaphragm compressors, or vacuum pumps. Use in diaphragm pumps, e.g., pneumatic diaphragm pumps, is particularly suitable.

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

[0005] The base does not typically participate in the rolling motion, so an insert made of an inflexible or dimensionally stable material can be arranged within it. This insert is then connected to the piston rod, allowing the rolling motion to be transmitted through the insert into the composite membrane. According to the prior art, the membrane body is usually at least partially made of polytetrafluoroethylene (PTFE) and forms a media-side contact layer. This is typically provided as a separate contact film, which can then be bonded to a base material of the membrane body.

[0006] Corresponding designs are known, for example, from EP 1 892 414 B1 or US 5 217 797 A. Such composite membranes with a media-side PTFE coating are used particularly when toxic or chemically aggressive media are to be conveyed. The media side of the membrane body is typically formed entirely by the PTFE coating, with PTFE being particularly resistant to almost all known chemicals.

[0007] This design has generally proven effective in practice, although polytetrafluoroethylene can currently only be recycled in small quantities and with high energy expenditure. It should be noted that hydrofluoric acid is released during disposal, which usually involves thermal decomposition and can damage the recycling facilities themselves.

[0008] Against this background, the invention aims to provide a composite membrane which can still be used in a known manner, particularly with chemically aggressive and toxic media, but which is also characterized by better recyclability.

[0009] The object and solution of this problem is a composite membrane with a flexible membrane body having a circumferential edge, a base and a flexible membrane section connecting the circumferential edge to the base, wherein, according to the invention, the membrane body is provided to be at least partially made of ultra-high molecular weight polyethylene (PE-UHMW).

[0010] In this context, ultra-high molecular weight polyethylene is understood to mean polyethylene having an average molecular weight of at least 5000 g / mol, preferably at least 10000 g / mol, and particularly preferably at least 50000 g / mol. Typically, the average molecular weight of such polyethylenes is between 5000 and 50 million g / mol, preferably between 10000 and 10 million g / mol, and particularly preferably between 50000 and 2 million g / mol.

[0011] Ultra-high molecular weight polyethylene, like polytetrafluoroethylene, is characterized by high chemical resistance. Furthermore, tests have shown that even with the use of corresponding composite membranes and despite a high number of unwinding cycles, high structural stability of the membrane body can still be guaranteed. Based on such an inventive design, the use of polytetrafluoroethylene can therefore be dispensed with. In particular, the membrane body, preferably the entire composite membrane, is designed completely without polytetrafluoroethylene.

[0012] According to a preferred embodiment of the invention, the membrane body is formed entirely of ultra-high molecular weight polyethylene, at least on a first surface. The first surface is, in particular, the surface of the membrane body that forms the media side, or which, in the intended use, for example in a diaphragm pump, comes into contact with the medium being pumped. The complete formation of this surface from ultra-high molecular weight polyethylene ensures that only the ultra-high molecular weight polyethylene comes into contact with the medium, thus guaranteeing the chemical resistance of the composite membrane through the use of ultra-high molecular weight polyethylene.

[0013] According to a preferred embodiment, the membrane body is multilayered. In particular, the membrane body comprises a surface layer made of ultra-high molecular weight polyethylene and a base layer. Accordingly, not the entire membrane body is made of ultra-high molecular weight polyethylene. Rather, the ultra-high molecular weight polyethylene is preferably provided exclusively within a surface layer, which is then arranged on a base layer of the membrane body. The base layer can then also form a second surface, which is arranged on a side of the composite membrane facing away from the media.

[0014] The base layer is preferably formed from an elastomer. The elastomer is preferably selected from the group consisting of acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBA), ethylene propylene diene monomer rubber (EPDM), chloropene rubber (CR), styrene butadiene rubber (SBR), fluororubber (FKM), silicone rubber (VMQ), and fluorosilicone rubber (FVMQ).

[0015] Depending on the elastomers used, the coating layer can be bonded to the base layer in various ways. A preferred design involves the coating layer being directly bonded to the base layer. However, this requires that sufficient adhesion be generated between the coating layer and the base layer, which can withstand the various rolling movements. This design is particularly advantageous when the base layer is made of ethylene propylene diene monomer (EPDM) rubber. In this case, the membrane body, or at least the coating layer, can be directly bonded to the base layer. This bonding is preferably achieved through compression molding.In this process, the material for the base layer is placed inside a molding press, which consists of an upper and a lower pressing part that together form the shape of the finished composite membrane. Through the application of heat and pressure, the corresponding composite membrane can then be formed from the base layer material.

[0016] It is also possible to bond the base layer and the top layer together during the compression molding process. The top layer is then provided as a separately manufactured top sheet and positioned above the base layer material within the mold. The pressure and heat vulcanize the materials together, and particularly with a combination of EPDM and UHMWPE, the bond between the base layer and the top layer has proven sufficiently strong that further measures to strengthen the bond are not strictly necessary.

[0017] If sufficient adhesion between the top layer and the base layer cannot be ensured due to the material selection and the manufacturing method, an alternative design can provide for an adhesion promoter layer between the top layer and the base layer. Accordingly, the top layer can bond to the base layer by incorporating this adhesion promoter layer. The adhesion promoter layer consists, in particular, of a polyurethane adhesive.

[0018] A preferred embodiment of the invention further provides that a reinforcing layer is arranged in the base layer. This reinforcing layer increases the strength of the membrane body. In particular, it is provided that the reinforcing layer is formed from a fabric, especially polyamide, polyester and / or high-temperature polyamide.

[0019] Within the scope of the invention, it is generally sufficient if the bearing layer forms exclusively a closed first surface. Accordingly, the bearing layer can be comparatively thin. In particular, it is provided that the bearing layer has a thickness between 0.15 and 1.5 mm, preferably between 0.2 and 1.2 mm.

[0020] Furthermore, one embodiment of the invention provides that the flexible membrane section has a plurality of nubs. According to this embodiment, the nubs can also form protrusions in the supporting layer. Preferably, the nubs are designed as spherical caps with a circular or elliptical base. The nubs create point stiffeners in the flexible membrane section. The areas between the nubs are flexible, so that the flexible membrane section can be turned inside out with minimal pressure, and no creases or fold lines form in the supporting layer due to the point stiffeners.

[0021] The composite membrane performs defined rolling movements during use, with low rolling resistance at the fold. Furthermore, the studded structure of the composite membrane on the media side ensures better adhesion between the membrane body and the ultra-high-molecular-weight polyethylene (UHMWPE) layer. This improved adhesion of the layered composite is due to an interlocking effect of the studs and / or a larger surface area resulting from the studded features.

[0022] A particularly preferred embodiment of the invention further provides that the base forms a chamber in which an insert is arranged, at least partially. The chamber is formed by an upper and a lower wall, the upper wall forming part of the first surface, and the insert being arranged between the upper and lower walls. The insert is preferably a dimensionally stable insert, which is accordingly made of a dimensionally stable material.

[0023] In particular, the insert is intended to be made of aluminum, brass, steel, stainless steel, or plastic. The insert may also have a receptacle for a piston rod. This receptacle is, in particular, a recess with an internal thread or a protrusion with an external thread, so that the piston rod can be attached to the insert via the corresponding thread.

[0024] Although the composite membrane described above can be used for a variety of applications, the invention provides that a diaphragm pump is also part of the invention, wherein the diaphragm pump has a composite membrane according to the invention.

[0025] The invention is explained in more detail below with reference to exemplary figures. These show: Fig. 1 shows a composite membrane according to the invention in an isometric view, Fig. 2 shows an alternative embodiment of the composite membrane according to Fig. 1 , Fig. 3 a composite membrane without an insert integrated into the floor.

[0026] The Fig. 1 Figure 1 shows a composite membrane according to the invention. The composite membrane has a flexible membrane body, which in turn has a clamping surface 3 on a circumferential edge 2, which is connected to a base 4 via a flexible membrane section 5. The base 4 consists of an upper and a lower wall 6a, 6b, wherein the walls 6a, 6b form a chamber 7 arranged between the walls 6a, 6b, in which an insert 8 made of a dimensionally stable material is arranged.

[0027] The membrane body 4 is multilayered and consists essentially of a base layer 9 made of an elastomer and a support layer 10 arranged on it. In addition, a reinforcement layer 11 is arranged within the base layer 9, which is intended to increase the strength of the membrane body.

[0028] According to the invention, the coating layer 11 is now made of ultra-high molecular weight polyethylene (UHMWPE). In contrast to previously known solutions, the polytetrafluoroethylene (PTFE), which has been frequently used until now, is replaced by ultra-high molecular weight polyethylene. Like polytetrafluoroethylene, this exhibits high chemical resistance and is therefore suitable for use with toxic or chemically aggressive media. At the same time, ultra-high molecular weight polyethylene can be recycled much more easily and in a more environmentally friendly manner.

[0029] The Fig.1 Furthermore, the figure shows that the support layer 10 is located on a first surface 12 facing the media side. The base layer 9 can be co-extruded together with the support layer 10, resulting in sufficient bond strength between the base layer 9 and the support layer 10. However, it is also conceivable to provide the support layer 10 as a separate support film, which is then bonded to the base layer 9 by incorporating an adhesion promoter layer (not shown in detail). In this case, it is also possible to use materials for the base layer 9 that would otherwise not form sufficient bond strength with the support layer 10 without the inclusion of an adhesion promoter layer. In particular, especially in the case of EPDM, it is intended that the base layer 9 be co-extruded together with the support layer 10.

[0030] The second surface of the membrane body 1 is formed by the base layer 9, which is accordingly the side facing away from the medium. The second surface 13 has an opening in the base 4 through which the insert 8 extends. Furthermore, the insert 8 has an internal thread 14 via which a membrane piston (not shown) can be connected to the insert 8.

[0031] The Fig. 2 shows a further development of the composite membrane according to the Fig. 1 , whereby the clamping surface 3 is now formed by thickenings on the edge.

[0032] Furthermore, a large number of studs 15 are provided in the area of ​​the flexible membrane section 5, which are also located in the Fig. 1 are shown, but according to the Fig. 2 These nubs form 15 elevations in the support layer 10. This further improves the bond strength between the base layer 9 and the support layer 10.

[0033] The one in Fig. 3 The composite membrane shown has a design that largely corresponds to that described in the Fig. 1 and 2 The composite membranes shown are shown, but now the bottom 4 has only a wall 6 which does not form a chamber 7, so that accordingly no insert 8 can be arranged within a corresponding chamber 7.

Claims

1. Composite diaphragm, in particular for diaphragm pumps, with a flexible diaphragm body (4) having a circumferential edge (2), a base (4) and a flexible diaphragm section (5) connecting the circumferential edge (2) to the base (4), characterized by the fact that the membrane body (4) is at least partially formed from an ultra-high molecular weight polyethylene (PE-UHMWE) and the base layer (9) is formed from an elastomer selected from the group consisting of acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), ethylene propylene diene rubbers (EPDM), chloroprene rubber (CR), styrene butadiene rubber (SBR), fluororubber (FKR), silicone rubber (VMQ) and fluorosilicone rubber (FVMQ).

2. Composite membrane according to claim 1, characterized by the fact that the membrane body (4) is formed entirely from ultra-high molecular weight polyethylene at least on a first surface (12).

3. Composite membrane according to claim 1 or 2, characterized by the fact thatthe membrane body (4) is multilayered.

4. Composite membrane according to claim 3, characterized by the fact that the membrane body (4) has a surface layer (10) made of ultra-high molecular weight polyethylene and a base layer (9).

5. Composite membrane according to claim 4, characterized by the fact that the top layer (10) is directly adjacent to the base layer (9).

6. Composite membrane according to claim 4 or 5, characterized by the fact that the top layer (10) connects to the base layer (9) by incorporating an adhesion promoter layer.

7. Composite membrane according to one of claims 4 to 6, characterized by the fact that a reinforcement layer (11) is arranged in the base layer (9) and / or between the base layer (9) and the support layer (10).

8. Composite membrane according to one of claims 4 to 7, characterized by the fact that the support layer (10) has a thickness between 0.15 and 1.5 mm, in particular between 0.2 and 1.2 mm.

9. Composite membrane according to any one of claims 1 to 8, characterized by the fact that the flexible membrane section (5) has a multitude of bumps (15).

10. Composite membrane according to one of claims 1 to 9, characterized by the fact that the floor (4) forms a chamber (7) in which an insert (8) is arranged at least partially.

11. Diaphragm pump with a composite diaphragm according to one of claims 1 to 10.

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