The invention relates to a method for producing a foam body, in particular for a pressure accumulator, such as a hydraulic accumulator. A bladder- or diaphragm-shaped, elastically flexible separating layer of the accumulator separates two media chambers from each other within the accumulator, in particular a gas working chamber from a fluid chamber.
A pressure accumulator known from WO 2013/056834 A1 has at least one accumulator housing with at least one connection for a pressurizing medium, in particular in the form of a fluid, which fluid can be stored in the accumulator housing. A filling material is at least partially introduced into the accumulator housing and has cavities or forms at least one cavity for the at least partial receiving of this pressurizing medium. The inside of the accumulator housing is fully filled with the filling material, so that the filling material is in full-surface contact with a wall of the accumulator housing.
If, in the known solution, the filling material is formed as foam, in particular polyurethane foam, thickness differences in the foam material can be generated by multiple injections or applications of foam. It is then advantageously possible to obtain a gradient-type structure of the foam material such that a very thick material is used on the inlet side of the accumulator. That material then changes in the direction of the opposite side of the accumulator housing with increasingly open pores or with lesser thickness. At the point of entry of the pressurizing medium into the accumulator housing body, an increased resistance can then be built up in that the barrier property of the foam or of another filling material is increased accordingly.
A pressure accumulator in the form of a hydraulic accumulator known from WO 2013/056835 A1 has at least one elastomeric separating element, preferably in the form of a separating diaphragm or separating bladder, which divides the accumulator housing into at least two working chambers. One of the working chambers receives the one pressurizing medium, in particular in the form of a fluid. The other working chamber receives the pressurizing medium, in particular in the form of a working gas, such as nitrogen gas. A foam filling material is at least partially introduced into the accumulator housing, which filling material is delimited or surrounded by the separating element.
In order to define the storage capacity in the accumulator housing accordingly, the filling material, preferably of a polyurethane foam material, can be introduced as a solid form block into the accumulator with a predeterminable volume level. The filling material then creates a cavity at least inside the accumulator housing, which cavity can be filled with the respective working medium (fluid and/or gas). The filling material preferably is introduced in an already hardened, cellular structure as an open-pore finished foam form block into the cavity of the respective accumulator housing of a pressure accumulator.
Depending on the formation of the completely designed and produced foam-like filling material before its installation in the accumulator, a high storage capacity is obtained for the then modified accumulator. In addition, the stiffness of damping during operation of the accumulator can be correspondingly influenced. Furthermore, during operation of the accumulator, a homogenous temperature profile is obtained for the respective working media to be introduced and removed. The introduction of the already fully-foamed, in other words, hardened foam material and filling material, if appropriate, together with the accumulator bladder, into the accumulator nevertheless often presents issues. The free available installation openings of the respective accumulator housing are kept small for system-related reasons, such that avoiding damage to the foam and/or to the elastomer material of the separating layer during the introduction into the accumulator housing is not possible. In particular, dividing the accumulator housing into several segments in order to simplify the introduction of the foam is often necessary.
The segments must subsequently be joined together by a laser joint welding for example, which on the one hand involves intensive work and on the other hand compromises the homogeneity and thus the pressure stability of the wall of the accumulator housing. Because of the large number of work processes that this involves, the production of the known pressure accumulator solutions is time-intensive and thus cost-intensive. The costly production also prevents the design of the respective accumulator as a disposable component, which is a requirement of the rapidly modernizing market that is efficiency-oriented.
Based on this prior art, the problem addressed by the invention is therefore to provide an improved method for producing a pressure accumulator which, while retaining the advantages of the prior art such as the increased storage capacity and the temperature stability and pressure stability, helps to avoid the described disadvantages, and which can then be designed in a technically reliable and functionally reliable manner and can be produced with low labor costs and in a cost-efficient manner.
This problem is basically solved by a method for producing a pressure accumulator having the following method steps that are used in the production of the pressure accumulator:
By contrast with the known methods therefore, an already finished foam is not introduced in block form into the pressure accumulator with its separating layer. Rather a flow-capable, preferably fluid, foam material is introduced which, after its introduction into the pressure accumulator and with the expansion of the separating layer, which occurs simultaneously during the hardening process, to its maximum designed expanded state in the accumulator, forms the finished foam block in-situ. All of the important steps in the foam creation towards the finished state then occur directly and immediately in the accumulator and not outside of same.
The pressure gradient to be built up in order to expand the separating layer from a starting state towards its final state can be realized in a gravity-assisted manner. In other words, the introduced fluid foam material at least partially expands the separating layer simply due to its weight. However, this process takes place predominantly due to volumetric expansion when the foam material hardens with the associated cavity cell formation.
Particularly advantageously, this foam material input is in an upright manner, in other words, in the vertical orientation of the longitudinal axis of the accumulator. Because the foam material arrives in the accumulator in a flow-capable, preferably fluid state, damage to the foam material is prevented. Due to the expansion of the separating layer by the introduced, rapidly solidifying foam material, the separating layer can be fully filled with the foam material upon its hardening, so that a particularly high storage capacity of foam filling material to be introduced is obtained. If, during hardening of the foam material, bubble formation occurs for the purpose of creation of the preferably open-pore foam structure, any excess material can be expelled from the inlet point for the foam material back into the environment. This means that there is neither overstressing of the pressure accumulator wall or of the elastically flexible, in particular elastomeric separating layer, which is often in the form of an accumulator bladder or in the form of a separating diaphragm of the kind that is customary in diaphragm accumulators.
In one preferred embodiment of the method according to the invention, by the hardening foam material that is introduced into the pressure accumulator and with build-up of the associated pressure gradient, the bladder-shaped or diaphragm-shaped separating layer is expanded until such time as a valve provided on the fluid side of the accumulator, in particular in the form of a poppet valve, is closed. On the basis of the described functional position of the valve, an easily verifiable conclusion can be reached as to whether there is sufficient foam material in the accumulator after the hardening process, or whether this is not yet the case, which can trigger an additional top-up operation as described above.
In one particularly preferred embodiment of the method according to the invention, the initially flow-capable, in particular fluid foam material is sprayed or injected by a lance-shaped input device into the accumulator housing with the separating element. The one free end of the input device preferably opens into the top half of the pressure accumulator and is to this extent guided in the gas working chamber of the accumulator. The input device furthermore penetrates the gas connection of the accumulator and is connected by its other free end to an admixing device for the foam material. This procedure permits introducing the not yet hardened foam material into the pressure accumulator in a very targeted manner and, after removal of the input device from the accumulator, the hardening operation for the foam material can take place in an unimpeded manner.
By the admixing device, which is formed as a dynamically or statically functioning mixing head, components of the flow-capable, in particular fluid, foam material are supplied to the mixing head via at least two supply lines connected to the mixing head in order to subsequently be introduced, in a corresponding predeterminable mix ratio and via the lance-shaped input device, into the gas working chamber of the accumulator, which gas working chamber is separated via the separating layer from the fluid chamber of the accumulator.
In particular, by the mixing head the lance-shaped input device can be rotated about its longitudinal axis inside the accumulator body, so that a consistent foam material input towards the separating layer of the accumulator is realized. Several dispensing nozzles also are able to be arranged at predeterminable discrete intervals from one another on the free opening end of the input device in order to allow standardization of the input. Furthermore, the input device can be adjusted, if necessary, viewed in the longitudinal direction of the accumulator, with respect to its effective axial input length, in order to then allow coverage of different accumulator sizes.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention.
Referring to the drawings that form a part of this disclosure:
The hydraulic accumulator 10 depicted in the figures is designed as a bladder accumulator. The elastically flexible, in particular deformable, accumulator bladder 12 separates two media chambers from each other within a pressure accumulator housing 14. In particular, a gas working chamber 16 is separated from a fluid chamber 18, which chambers, in the subsequent operating state of the accumulator 10, receive a working gas, in particular in the form of nitrogen gas, and hydraulic oil, respectively. The accumulator housing 14 is formed substantially in one piece, is bottle-shaped and preferably is made of a steel material or die-cast material. The accumulator housing 14 can also be formed by a wrapped plastic laminate that is not depicted in detail, which housing is referred to as a liner construction in technical parlance. The accumulator bladder 12 forms the bladder-shaped, elastically flexible separating layer of the accumulator 10 and is pieced together, in particular vulcanized together, from sub-segments in accordance with the depictions of
The accumulator housing 14 has on its opposite longitudinal end sides two openings 20, 22. The bottom opening 20 receives a conventional closing valve, such as a poppet valve 24. The top opening 22 is provided with a closing valve device 26 (cf.
In order to obtain an operational hydraulic accumulator 10, the hydraulic accumulator must be correspondingly filled with a foam material, as will be described in detail below. For the input of the flow-capable, in particular fluid foam material, an admixing device 30 is employed. Admixing device 30 contains a statically or dynamically functioning mixing head 32 that, in accordance with the exemplary embodiment of
The foam components that can be supplied via the respective supply line 34 form, once they are brought together in the mixing head 32, a flow-capable mixture of polyols, isocyanate, catalysts, retarders, crosslinkers and stabilizers and, if appropriate, water. In particular, long-chain polyether polyols are used and the catalysts can be amine catalysts or tin catalysts. Diglycolamine is particularly preferably used as crosslinker material. However, amino compounds, butanediol and alcohols can also be used. As stabilizer input material, silicone compounds have proven to be successful. The foam material components can also be supplemented with commercially available flame retardants. The above-mentioned individual components can, having been be combined with one another in advance in an obvious manner, be fed to the mixing head 32 via the supply lines 34 for further input into the accumulator bladder 12. Preferably, the components are supplied to the mixing head 32 separately from one another in a consecutive sequence. The mixing head then initiates the mixing and the input via the input device 36.
If the polymer polyol used for the foam has hardened, a polyurethane (PU) soft foam 38 is created, which is crosslinked by the additional material or the additional components in the form of the crosslinker diglycolamine. The particular polyol used substantially produces the elastic foam behavior and the high recovery capability of the introduced hardened foam 38. The preferably open-cell foam 38 has a recovery capability of 97% to 98%. The above-mentioned 3D structure of the foam 38 ensures an optimal heat transfer.
As can be seen in particular from
The desired volumetric weight for the finished foam 38 ranges from 50 g/dm3 and 150 g/dm3. The heat capacity of the PU foam 38 should be 20° C.>1 J/gK, and should particularly preferably be a value between 1.4 J/gK and 1.9 J/gK, with the latter value corresponding to an operating temperature of approximately 120° C. If the introduced PU soft foam 38 has a flame retardant added to it, it is then also possible to increase the heat capacity, in particular if the flame retardant is introduced into the foam 38 as a solid. The flow resistance, which is considered to be a measure for the porosity of the foam 38, should preferably be within a value range from 1400 to 3800 Ns/m3. However, the elasticity of the foam 38 is in any case such that the foam 38 in the ready-for-use state of the accumulator 10 can be compressed by 40% of the maximum possible foam volume input. Higher values are possible. If a dry inert gas is inserted on the gas working chamber side 16, such as nitrogen, helium, argon, xenon, CF4 or SF6, for example, a temperature stability of between −40° C. and 140° C. is obtained in the case of a degree of crosslinking of the PU input material of >90% and when there are no volatile components.
Because the foam 38 is surrounded by the accumulator bladder 12 and also has no contact with the inside wall of the accumulator housing 14 or with the respective sealing materials (TPU, NBR, IIR, ECO, FKM), which are standard in accumulator construction, there is also no corresponding chemical reaction with the sealing material, which contributes to the longevity of the accumulator construction. If damage results in destruction of the hardened foam material 38 in the operational state of the accumulator according to
As another embodiment, which is not however depicted or described in detail, the possibility exists to apply the method according to the invention together with the foam input in pressure accumulators which are designed as diaphragm accumulators, of the kind presented in the prior art for example in
With the hydraulic accumulator solution according to the invention and using the described production method, accumulators can be realized having increased storage capacity and with good temperature stability and pressure stability, which prove to be very functionally-reliable during operation and which can be produced with little labor outlay and expense. There is no equivalent of this solution in the prior art.
While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.
Number | Date | Country | Kind |
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10 2015 003 673 | Mar 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/000073 | 1/15/2016 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2016/150535 | 9/29/2016 | WO | A |
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1 240 264 | May 1967 | DE |
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Entry |
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International Search Report (ISR) dated Mar. 22, 2016 in International (PCT) Application No. PCT/EP2016/000073. |
Number | Date | Country | |
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20180038391 A1 | Feb 2018 | US |