METHOD FOR PRODUCING A FOAM BODY

Abstract

A method for producing a foam body, in particular for a pressure accumulator, such as a hydraulic accumulator, the bubble- or diaphragm-shaped, elastically flexible separating layer (12) of which separates two media chambers from each other within the accumulator housing, in particular a gas working chamber from a liquid chamber (18), with at least the following production method steps: introducing a flowable, preferably liquid, foam material into the pressure accumulator, said foam material being at least partially surrounded by the separating layer (12), curing the foam material in the pressure accumulator, and in the processbuilding up a pressure gradient, in which the visibly curing foam material expands the separating layer (12) from an originally partially filled starting state in the direction of an end state, in which the accumulator is finally filled with the cured foam (38).

Claims

1. A method for producing a foam body, in particular for a pressure accumulator (10), such as a hydraulic accumulator, the bladder- or diaphragm-shaped, elastically flexible separating layer (12) of which separates two media chambers from each other within the accumulator housing (14), in particular a gas working chamber (16) from a fluid chamber (18), comprising at least the following production method steps: introduction of a flow-capable, preferably fluid, foam material (28) into the pressure accumulator (10), which is at least partially surrounded by the separating layer (12), hardening of the foam material (28) in the pressure accumulator (10), and thereby building up a pressure gradient, in which the increasingly hardening foam material (28) expands the separating layer (12) from an original partially-filled starting state towards a final state, in which the accumulator (10) is finally filled with the hardened foam (38).

2. The method according to claim 1, characterized in that, by means of the hardening foam material (28) that is introduced into the pressure accumulator (10) and with build-up of the associated pressure gradient, the separating layer (12) is expanded until such time as a valve provided in the fluid chamber (18) of the accumulator (10), in particular in the form of a poppet valve (24), is closed.

3. The method according to claim 1, characterized in that the flow-capable, in particular fluid, foam material (28), is sprayed or injected by means of a lance-shaped input device (36) into the pressure accumulator (10), with the one free end of said input device opening into the top half of the pressure accumulator (10) and being guided in the gas working chamber (16) and thereby penetrating the gas connection (20) of the accumulator (10) and with the other free end of the input device outside of the pressure accumulator (10) being connected to an admixing device(30).

4. The method according to claim 1, characterized in that, by means of the admixing device (30), which is formed as a dynamically or statically functioning mixing head (32), components of the flow-capable, in particular fluid foam material (28) are supplied to the mixing head (32) via at least two supply lines (34) connected to said mixing head in order to subsequently be introduced in a corresponding predeterminable mix ratio via the lance-shaped input device (36) into the gas working chamber (16) of the accumulator (10).

5. The method according to claim 1, characterized in that the individual components which are to be mixed with one another by means of the admixing device (36) in order to create the flow-capable, in particular fluid foam material (28) are selected as follows: polyols, in particular in the form of long-chain polyether polyols; foaming agents, in particular in the form of water; and crosslinkers, in particular in the form of diglycolamine, preferably supplemented with: catalysts, in particular in the form of amine catalysts and/or tin catalysts; retarders; flame retardants; and stabilizers, in particular in the form of silicone compounds.

6. The method according to claim 1, characterized in that the foam material (38) hardened in situ in the pressure accumulator (10) is formed with open cells with a recovery capability as a 3D structure of 97 to 98%.

7. The method according to claim 1, characterized in that the volumetric weight of the hardened foam material (38) is selected in a range from 50 g/dm.sup.3 to 150 g/dm.sup.3 per liter of input volume of flow-capable, in particular fluid foam material (28).

8. The method according to claim 1, characterized in that the heat capacity of the hardened foam material (38) is selected at 20 C.>1 J/gK.

9. The method according to claim 1, characterized in that the flow resistance of the foam (38) is selected in a range from 1400 to 3800 Ns/m.sup.3.

10. The method according to claim 1, characterized in that the temperature stability in a closed accumulator bladder (12) as the elastically flexible separating element and with insertion of dry inert gas as the working gas introduced into the gas working chamber (16) of the accumulator (10) is selected in a range from 40 C. to 140 C.

11. The method according to claim 1, characterized in that, on the basis of the respective selected expansion speed together with the pressure gradient values during foaming, cells are obtained in the finished foam (38) in the range from 0.01 mm.sup.3 to 375 mm.sup.3.

Description

[0019] The method according to the invention is explained in detail below with reference to an exemplary embodiment according to the drawings, in which:

[0020] FIGS. 1 to 3 show a pressure accumulator in the form of a hydraulic accumulator with an accumulator bladder in different foam filling and production states.

[0021] The hydraulic accumulator 10 depicted in the figures is designed as a bladder accumulator, wherein 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 from a fluid chamber 18, which chambers serve, in the subsequent operating state of the accumulator 10, on the one hand to receive a working gas, in particular in the form of nitrogen gas, or to receive hydraulic oil. The accumulator housing 14 is formed substantially in one piece and bottle-shaped and preferably consists of a steel material or die-cast material, with the accumulator housing 14 also being able to be formed by a wrapped plastic laminate which is not depicted in detail, which is referred to as a liner construction in technical parlance. The accumulator bladder 12 forms the bladder-like, 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 FIGS. 1 and 2. The construction of the accumulator bladder 12 in sub-segments is in particular suitable when, viewed in the axial length of the hydraulic accumulator 10, the pressure accumulator housing 14 has a correspondingly large length.

[0022] The accumulator housing 14 has on its opposite end sides two openings 20, 22, with the bottom opening 20 serving to receive a conventional closing valve, such as a poppet valve 24, and the top opening 22 is provided with a closing valve device 26 (cf. FIGS. 2 and 3), which serves for subsequent supply of the working gas and which, if necessary, permits top-up operations with the working gas. Otherwise, the closing valve device 26 usually remains closed during operation of the accumulator. If the poppet valve 24 is in an opened position, as depicted in FIGS. 1 and 2, the working fluid, commonly in the form of hydraulic oil, can reach the fluid chamber side 18 of the accumulator 10 and be stored there until the stored pressure quantity and/or filling quantity is in turn required in the hydraulic circuit (not depicted) to which the accumulator 10 can be connected. This operating method corresponds to standard accumulator operation, and accordingly it will not be addressed in further detail here. However, if the accumulator bladder 12 is in its fully elongated or expanded state, as depicted in FIG. 3, said accumulator bladder 12 presses by means of its bottom end with force-locking contact against the poppet valve 24 and thus closes the valve. An input pressure of the fluid medium is then required on the fluid side of the accumulator, which pressure is greater than the counter pressure in the accumulator bladder 12, in order to thus effect an opening operation for the poppet valve 24.

[0023] In order to obtain an operational hydraulic accumulator 10, said 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 identified as a whole with the reference numeral 30 is employed, which contains a statically or dynamically functioning mixing head 32 which, in accordance with the exemplary embodiment of FIG. 1 has two supply lines 34 connected to the mixing head 32 and which is to be placed from the outside onto the accumulator 10 to be filled. Furthermore, a lance-shaped input device 36 is connected to the mixing head 32 on the bottom side thereof, with the one free end of said input device opening into the top half of the pressure accumulator 10 and being guided in the gas working chamber 16 and with its other end the input device penetrates the top opening 22 of the accumulator housing 14, which is provided for the subsequent receiving of the closing valve device 26. For the input of the foam material, in accordance with the depiction of FIG. 1, the input device 36 is provided with corresponding spray openings or nozzle openings (not depicted in detail) in the region of the bottom end of the lance of the input device 36 in order to thus obtain a consistent foam input into the inside of the accumulator.

[0024] The foam components which 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, it is also possible to use amino compounds, butanediol and alcohols. 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; however, there is also the possibility to preferably supply the components to the mixing head 32 separately from one another in a consecutive sequence, which mixing head then initiates the mixing and the input via the input device 36.

[0025] If the polymer polyol used for the foam has hardened, a polyurethane (PU) soft foam 38 is created, which is crosslinked by means of 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% and the above-mentioned 3D structure of the foam 38 ensures an optimal heat transfer.

[0026] As can be seen in particular from FIG. 2, the still fluid foam material 28 is collected in the bottom accumulator bladder end 40 with the input amount individually required for the respective accumulator type, and then the accumulator 10 is closed in a pressure-tight manner via the closing valve device 26 at the top end. As a result of the introduced components of the foam material 28, the latter then hardens and thereby expands in volume up to the final state according to the depiction of FIG. 3, in which the poppet valve 24 is then closed. In particular, the build-up of a pressure gradient occurs during the hardening of the foam material 28 in the pressure accumulator 10, during which build-up the increasingly hardening foam material 28 expands the separating layer in the form of the accumulator bladder 12 from the original partially filled starting state in accordance with the depiction of FIG. 2 towards the final state, in which the accumulator 10 is finally and fully filled with the hardened foam 38 with the poppet valve 24 being closed. Due to the recovery capability of the foam 38, in the case of an opening poppet valve 24, said foam can, by means of the fluid pressure of the hydraulic circuit which is not depicted in detail, to which the accumulator 10 is connected, be forced back, in particular, compressed with regards to the open-porosity of the foam cells, so that the fluid chamber 18 in the hydraulic accumulator 10 can be filled with the oil medium until another retrieval occurs and it can thus be stored there under pressure from the compressed foam material.

[0027] The desired volumetric weight for the finished foam 38 ranges from 50 g/dm.sup.3 and 150 g/dm.sup.3. The heat capacity of the PU foam 38 should be 20 C.>1 J/gK, and it 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 thus 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/m.sup.3. 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, CF.sub.4 or SF.sub.6, 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.

[0028] Because the foam 38 is surrounded by the accumulator bladder 12 and thus 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 FIG. 3, the accumulator 10 itself does not become unuseable, instead there is merely a return to the behavior of a standard accumulator without foam input. In addition, the above-mentioned sealing system of the accumulator 10 manages with a reduced lubricating film on the gas side and thus conforms with dry-run properties. If, contrary to expectations, foam particles or foam cells pass through via the seal or the separating layer material to the fluid side 18 of the accumulator 10, this input of foreign materials into the fluid does not lead to damage of the hydraulic system, because the PU foam does not have any observable damaging effect in this regard.

[0029] 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 FIGS. 1 and 2 of the already mentioned PCT publication WO 2013/056835 A1.

[0030] With the hydraulic accumulator solution according to the invention and using the described production method it is possible to realize accumulators 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.