METHOD FOR THE PRODUCTION OF A BLADDER ACCUMULATOR AND BLADDER ACCUMULATOR PRODUCED ACCORDING TO SAID METHOD

Abstract

The invention relates to a method for the production of a bladder accumulator (10) which separates two media chambers (16, 18) from one another in a storage housing (12) by means of a bladder body (14), comprising at least the following production steps:extruding a plastic tube over the bladder body (14);shaping the plastic tube with the integrated bladder body (14) in a molding tool that corresponds to a predeterminable plastic core container (20), andwinding at least one plastic fiber from the outside on the plastic core container (20) for the purpose of creating the storage housing (12).

Claims

1. A method for the manufacture of a bladder accumulator (10), which separates two media chambers (16, 18) from each other in an accumulator housing (12) by means of a bladder body (14), comprising at least the following production steps: extrusion of a plastic tube over the bladder body (14); moulding of the plastic tube with integrated bladder body (14) in a moulding tool that corresponds to a predeterminable synthetic core container (20), and winding at least one synthetic fibre from the outside onto the synthetic core container (20) for the purpose of creating the accumulator housing (12).

2. The method according to claim 1, characterized in that the bladder body (14), which is preferably made from an elastomeric material, is provided with an internal vacuum prior to the extrusion of the plastic tube.

3. The method according to claim 1, characterized in that the synthetic core container (20), prior to the application of windings from the outside, is stabilised from the inside through the introduction of a preferably incompressible medium to, what will later be, the gas side and/or the liquid side of the bladder accumulator (10).

4. The method according to claim 1, characterized in that a gas filling valve (24) is attached to the wall material of the bladder body (14) through vulcanising.

5. The method according to claim 1, characterized in that a valve for liquids (26) is attached to the accumulator housing (12) on the side opposite to the gas supply valve (24), wherein said valve for liquids (26) is operated and brought into a closed position through the expanding bladder body (14) when the accumulator housing (12) is empty.

6. The method according to claim 1, characterized in that the valve for liquids (26) is inserted into the synthetic core container (20) prior to the application of windings.

7. The method according to claim 1, characterized in that, when the halves of the moulding tool are closed, the valve for liquids (26) is surrounded by the free end of the plastic tube (36).

8. The method according to claim 1, characterized in that the diameter of the synthetic core container (20) in the vicinity of where the valve for liquids (26) is incorporated is chosen to be essentially the same, or in the same size range, as the diameter of the synthetic core container (20) in the vicinity of where the gas filling valve (24) is incorporated.

9. The method according to claim 1, characterized in that the wall thickness of the synthetic core container (20) and the wall thickness of the finished winding is chosen to be essentially the same overall.

10. A bladder accumulator, produced in particular according to claim 1, which separates two media chambers (16, 18) from each other in an accumulator housing (12) by means of a bladder body (14), wherein each of said media chambers (16, 18) is provided with a media valve (24, 26), characterized in that the mounting diameter of both media valves (24, 26) in accumulator housing (12) correspond to each other or are at least in the same size range, and are chosen to have preferably small opening diameters (40, 42).

Description

[0021] The following explains in greater detail the above-described method according to the invention by way of the embodiment of a bladder accumulator. The only FIGURE depicts a bladder accumulator according to the present invention shown in longitudinal section.

[0022] The bladder accumulator shown in the figure and referenced with the number 10 as a whole comprises an accumulator housing 12, which separates two media chambers 16, 18 from each other by means of a bladder body 14. The first media chamber 16 of the bladder accumulator 10 is usually used to hold process gas, such as nitrogen gas, and the second media chamber 18 accepts a liquid, such as hydraulic oil or similar. Said media chambers 16, 18 thus correspond to the usual gas and liquid side respectively of the bladder accumulator 10.

[0023] The accumulator housing 12 is constructed in the manner of a composite pressure vessel, comprising an internal synthetic core container 20, which is wound on the outer circumference with a synthetic fibre, which forms a synthetic sheath 22. Instead of using said synthetic materials for the synthetic core container 20 as well as for the synthetic sheath 22, it is possible to use metallic materials, such as aluminium for example, which is easy to mould and is well suited for drawing processes.

[0024] The synthetic core container 20 according to the depiction in the figure, technically also called liner, is preferably made from polyamide or polyethylene and is made through a blow moulding process or through rotational moulding. Such production methods are commonly known and therefore not explained in detail in this instance.

[0025] The invention provides that a gas filling valve 24 is attached to the sheath material of the bladder body 14 through vulcanising, wherein the bladder body 14 is preferably made from an elastomeric, synthetic material, including natural rubber. Said valve 24 not only serves for filling process gas, such as nitrogen gas, into the first media chamber 16 of the bladder body 14; said valve 24 can also be used to remove gas or, if required, to refill again, and wherein valve 24 is also used for gas pressure measurement via a common indicating device that is not shown. The bladder body 14 as well as the gas filling valve 24 are preferably placed together into the usual blow mould, and subsequently a plastic tube is extruded (not shown) over the bladder body 14 with gas filling valve 24 through a corresponding plastic extruder nozzle. The extruded, soft plastic tube with integrated bladder body 14 with valve 24 is then formed through a not-depicted blow moulding tool, wherein the moulding tool with its mould halves has an internal shape which produces the synthetic core container 20 according to the depiction in the figure.

[0026] So as not to obstruct the extruding of the plastic tube over the bladder body 14 with valve 24, a vacuum may be applied inside the bladder body 14, preferably via gas filling valve 24, in order to slim down the bladder body 14 so that it does not make contact with the soft plastic material of the plastic tube during the extrusion and forming processes. For the purpose of further simplifying the production process, it is preferred that a valve 26 for liquids, in particular in form of a poppet valve, is inserted into the blow mould tool opposite to the gas filling valve 24, so that also the liquid valve 26 is included by and connected to the plastic tube at its free lower end during the shaping process.

[0027] The bladder accumulator 10 shown in the figure has a fluid-conducting connection to a not-depicted hydraulic line of a hydraulic circuit via the liquid supply valve or poppet valve 26. If the pressure at the liquid end is greater than the pressure at the process gas end in form of the media chamber 16, the poppet valve 28, under the additional effect of a compression spring 30 applied thereto, opens up and the second media chamber 18 fills with liquid. Depending on the pressure conditions inside the accumulator, the bladder body 14 with its compressible process gas is compressed, which simultaneously increased the gas pressure inside the first media chamber 16. If liquid is released from the second media chamber 18 of the bladder accumulator 10 through the open liquid valve 26, the elastomeric bladder body 14 is able to expand and potentially apply pressure with its underside on the disk 28 of the poppet valve 26, which then is brought into the closed position against the effect of the compression spring 30, as shown in the figure. The valve disk 28, which is guided longitudinally moveable in a valve housing 32, is provided at its top with a convex surface to make the contact of the accumulator bladder 14 with the top of the disk 28 as gentle as possible.

[0028] The valve housing 32 is provided at its outer circumference with an annular groove for retaining a sealing ring 34, which on the outer circumference is in contact with a connection sleeve 36 that protrudes downwards and is part of the completed synthetic core container 20. The liquid valve or poppet valve 26 may be retained in position inside the connection sleeve 36 through a connecting nut 38, for example via a thread connection (not shown).

[0029] Since the synthetic core container 20 is rather thin-walled, for example having a wall thickness of 2 mm, an incompressible medium such as water or alcohol is introduced in a predeterminable quantity via the first and/or second media chamber 16, 18 so as to build up a counter-pressure from the inside of the accumulator housing 12 onto the synthetic core container 20, so that windings can be applied to it from the outside without the concern that the liner 20 may buckle or fold to the inside. As a result of the incompressible medium on the inside of the bladder accumulator 10, the thin-walled synthetic core container 20 is retained in position and reinforced in such a way that the windings may be applied without difficulty.

[0030] Said liner or synthetic core container 20 is reinforced by fibre windings that are applied at the outside in the manner of a second synthetic sheath 22. The reinforcing windings consist, for example, of fibre reinforcing in the form of rovings, such as carbon fibres, aramit fibres, glass fibres, boron fibres, AL.sub.2O.sub.3 fibres or a blend thereof, which are called hybrid yarns, and which are embedded in a base matrix of duromers (epoxy resins or phenolic resins) or in thermoplastics (PA6, PA12, PP). The fibre-reinforced composite material that forms the supporting shell contains fibre strands (rovings) that cross each other, that can extend in longitudinal and circumferential direction and are embedded in synthetic resin. However, the supporting shell 22 consists preferably of each other crossing fibre strands (rovings) that are inclined in longitudinal and circumferential direction and, in an expedient further development, are inversely inclined along the longitudinal axis of the synthetic core container 20 in relation to each other. The longitudinal and circumferential forces, also seen in axial direction of the accumulator, can thus be optimally retained by the pressure vessel as a whole.

[0031] The representation according to the figure demonstrates to those skilled in the art of this field immediately that, in contrast to other solutions in the prior art (DE 10 2006 004 120 A1, DE 10 2011 111 098 A1), the free cross-sectional openings or insertion openings 40, 42 for the gas filling valve 24 and the liquid valve 26 respectively are very small with regard to their diameter, and may be in the vicinity of 50 mm or 60 mm respectively for a 10 litre bladder accumulator 10, for example. This has not been achieved in the prior art so far because, in technically comparable solutions, it was always necessary, with a finished accumulator housing 12, to pull the bladder body 14, or the accumulator bladder respectively, with its gas filling valve 24, attached through vulcanising, via the liquid connection and the inside of the accumulator in the direction of the gas end of the accumulator housing and to attach it there through the respective opening in the accumulator housing. Since, in the solution according to the invention, the synthetic core container 20 yet to be completed has already integrated the bladder body 14 with valve 24 in the forming step, it is no longer necessary to pull it through the inside of the housing at a later stage. Since, as already described, the gas filling valve 24 is already attached, preferably through vulcanising, to the top of the bladder body 14, when closing the moulding tool for the extruded plastic tube under formation of the synthetic core container or liner 20, a kind of annular pinch gap 44 forms at the top of the plastic tube material which, when the plastic tube as liner 20 has hardened, provides a secure attachment location for the gas filling valve 24 in the accumulator housing 12. In a similar manner, a corresponding annular-shaped pinch gap for the liquid valve 26 is formed through the cylindrical connection sleeve 36 of the plastic tube. Nevertheless, it is fundamentally possible to attach the valves 24 and/or 26 later to the finished liner 22 once the accumulator bladder 14 is located inside the accumulator and to affix the valve 24 to bladder body 24 [sic] through an adhesive, for example.

[0032] Since, as described, the opening cross-sections for the openings 40, 42 are very small, it is possible to keep the winding angle in this section flat so that even in the section for the valve connection of the synthetic sheath 22 an even and thin layer structure is achieved that does not tend to delaminate but still has the required axial strength. Overall it is possible to achieve a wall thickness for the synthetic sheath 22 of 10 mm for a bladder or accumulator size of 10 litres. The accumulator solution according to the invention permits a direct application of the fibre layers onto the annular pinch gap 44 for the cylindrical connection sleeve 36 for the gas filling valve 24 and for the liquid valve 26 respectively without any intermediary metallic collar components. Since it is possible to completely omit metallic collar components, the accumulator according to the invention is easily constructed but still highly pressure-resistant.