Method for producing at least one part of an accumulator housing and hydraulic accumulator

Abstract

1. Method 2. The invention relates to a method for producing at least one part of an accumulator housing (10) for a hydraulic accumulator, said method having the following method steps: - providing accumulator housing parts (12, 14) which are to be connected to one another along mutually adjacent end sides (16, 18), of which at least one end side (16) has a material accumulation (20); - moving the adjacent accumulator housing parts (12, 14) together in such a way that the material accumulation (20) comes into contact with the adjacent end side (18); and simultaneously or subsequently - melting the material accumulation (20) by means of a welding process, and further moving the two accumulator housing parts (12, 14) together during the welding process with a predefinable pressing force; and simultaneously - forming a weld seam running along a connecting point (42) between the accumulator housing parts.

Description

[0001] METHOD FOR PRODUCING AT LEAST PART OF A STORAGE HOUSING AND HYDRO-ACCUMULATOR

[0002] The invention relates to a method for producing at least part of an accumulator housing for a hydraulic accumulator. The invention further relates to a hydraulic accumulator, which is produced in particular according to such a method. Fluidic storage devices in the form of hydraulic accumulators are freely available on the market in a wide variety of designs. In hydraulic systems, hydraulic accumulators serve, among other things, to hold specific volumes of pressurized fluids and to return them to the system when needed. Hydraulic systems with hydropneumatic accumulators with a separating device designed as a diaphragm are particularly common. The diaphragm separates, in particular, a liquid chamber as the working chamber from a gas chamber as a further working chamber. The diaphragm, however, takes over the decoupling of the gas and liquid chambers.Nitrogen is preferred as the working gas, and the fluid chamber for a hydraulic medium is regularly connected to a hydraulic circuit of a hydraulic system. When the pressure in the hydraulic circuit increases, the hydraulic accumulator absorbs the hydraulic medium, thereby compressing the gas. When the pressure decreases, the previously compressed gas expands again, displacing the fluid or hydraulic medium back into the hydraulic circuit.

[0003] DE 10 2015 01 7 026 A1 discloses a method for producing pressure vessels, such as hydraulic accumulators, and their parts, which are manufactured at least partially using a 3D printing process. This eliminates the need for additional molding equipment such as heated molds. Rather, a reservoir housing for a hydraulic accumulator or parts of such hydraulic accumulators, such as separating elements, can be manufactured in a single piece without the use of molds, which also significantly reduces the manual effort required during production. However, the overall time required to produce pressure vessels for hydraulic accumulators using a 3D printing process is still quite high, making additive manufacturing processes for large-scale production difficult to implement economically, at least for the time being.

[0004] DE 10 2015 012 357 A1 discloses a method for producing a hydraulic accumulator, in particular in the form of a diaphragm accumulator, comprising at least two housing parts of an accumulator housing, in which a separating element in the form of a separating diaphragm separates two media spaces within the accumulator housing. The method is characterized in that, in at least one of the housing parts of the accumulator housing, a connecting part is inserted into its housing opening and welded from the inside of the accumulator, wherein the separating diaphragm is inserted into the interior of the accumulator housing, and wherein a further housing part is placed or brought into contact with one housing part to form the accumulator housing, the two housing parts being firmly connected to one another along adjacent wall regions on the outer circumference by means of a weld seam.The weld seam is advantageously created by friction welding, electron beam welding, or laser beam welding, preferably without the use of filler metals. To prevent weld spatter from accidentally reaching the inside of the storage housing with its sensitive elastomer separating membrane during this welding process, the adjacent inside surface in the area of ​​the weld seam connection is covered by a wall shoulder of a storage housing component, and / or a retaining ring for the separating membrane covers the weld point. This ring is designed to be suitably resistant, as shown, for example, in DE 101 12 976 A1.

[0005] DE 10 2018 007 280 A1 discloses a hydraulic accumulator, again consisting of two housing parts of the accumulator housing, which can form a different material pairing with other components of the accumulator, such as a separating bellows as a separating element. For example, the housing parts can comprise titanium materials or be made of titanium, whereas the separating bellows is made of a conventional steel material. Such accumulators are characterized by very high strength and low weight, and the connection between the aforementioned components can be produced by cladding, preferably explosive cladding, which is also known in technical terms as explosive welding. This technically very complex joining process thus allows material groups to be joined together that would otherwise not be easily manufactured using conventional welding processes.

[0006] Another possibility is to at least partially nest such accumulator devices or hydraulic accumulators with their two housing parts forming an accumulator housing and to fold or flange an annular protruding edge at the free end of one accumulator housing part inward, resting against parts of the upper side of the other accumulator housing part near the edge, so that the housing parts are connected to one another in a contacting manner with a defined clamping force in this area. Since the connection between the accumulator housing parts is only maintained by clamping force and high forming forces are therefore necessary to create the clamped connection, use in large-scale production is not readily possible.

[0007] Based on this prior art, the invention is based on the object of providing an alternative manufacturing concept which, while retaining the advantages of the known solutions, ensures a high-strength connection between storage housing parts and is to be further improved towards economical large-scale production.

[0008] A corresponding object is achieved by a method having the features of patent claim 1 in its entirety and by a hydraulic accumulator, in particular produced according to such a method, having the features of patent claim 7.

[0009] The method according to the invention for producing at least part of a storage housing for a hydraulic accumulator is characterized by the following method steps:

[0010] Providing storage housing parts to be connected to one another along adjacent end faces, of which at least one end face has a material accumulation,

[0011] - Moving the adjacent storage housing parts together in such a way that the accumulation of material comes into contact with the adjacent end face, with simultaneous or subsequent

[0012] - Melting the accumulation of material by means of a welding process, and with further

[0013] - Moving the two storage housing parts together during the welding process with a predeterminable contact force while simultaneously forming a weld seam running along a connection point between the storage housing parts.

[0014] By melting the material accumulation, which is preferably an integral part of one storage housing part, the welding process can be carried out without additional welding material, creating a particularly homogeneous weld joint between the two adjacent storage housing parts. The relatively high contact force when joining or moving one storage housing part together with the other creates a very strong, homogeneous bond between the components, which reliably withstands even greater stresses during subsequent practical operation. This results in a uniform material joining pattern in the area of ​​the weld between the two housing parts.

[0015] In a preferred method, only one end face of one storage housing part carries the accumulation of material, and the other end face is provided with at least one recess into which the accumulation of material at least partially engages when the two adjacent storage housing parts are brought together. The respective recess forms, in particular, a type of circumferential groove on the free end face of the other storage housing part, which is initially left free of the accumulation of material. The recess or groove deepened in this way then serves as a centering device, in that the accumulation of material moves from its free end face into the corresponding recess as soon as the two storage housing parts are visibly brought together.

[0016] In a further preferred embodiment of the method according to the invention, the weld seam is formed in such a way that it protrudes outwardly beyond the two adjacent storage housing parts. This ensures that no concave groove can form in the area of ​​the weld seam, which could otherwise impair the subsequent pretreatment and subsequent painting of the storage housing.

[0017] In this respect, it is preferably provided that the overhang of the weld seam is selected such that a gap-free closure is created between the weld seam and adjacent storage housing parts with their respective connecting wall.

[0018] In another particularly preferred embodiment of the method according to the invention, resistance pressure welding, in particular resistance projection welding, is used as the welding process. The latter welding process is also referred to in technical terms as projection welding and represents a variant of resistance pressure welding. The welded joint is created by introducing electric current into the components to be joined, in the form of the two storage housing parts, and by applying the contact force to the workpieces to be joined using the large-area electrodes.

[0019] The accumulation of material on one of the free end faces of a storage housing part, which can also be divided into individual joining parts, appears as a projection. The energy input, i.e. the current concentration at the weld point, is then achieved via this accumulation of material, which melts in the process. During the actual welding process, the molten accumulation of material is largely reshaped by the electrode force and the heating resulting from the current flow between the two storage housing parts. However, this reshaping is often not complete, and the projection reshaped during welding then regularly forms a weld joint in the shape of a flat lens, which creates the connection in the area of ​​the two opposite end faces of the storage housing parts. The lens forms a self-contained ring that runs along the free peripheral edge of the respective storage housing part.In principle, the material accumulation can also be arranged on the end face of the other storage housing part or, if necessary, even be distributed proportionally across both free end faces of the storage housing parts. For the actual projection welding itself, however, it is advantageous to provide the material accumulation only on one free end face of a storage housing part, which can then be applied particularly easily to the other storage housing part, which is designed as a cathode, using a pressure-applied anode.

[0020] The electrical contact resistance and the material or substance resistance of the joining partners involved, in particular in the form of the two storage housing parts, contribute significantly to the formation of the weld nugget, which delimits a receiving space inside the storage housing from the environment. The contact resistance between these joining partners is essentially influenced by the projection geometry, the contact force via at least one of the electrodes and the surface condition of the two storage housing parts. The weld nugget itself is surrounded by a heat-affected zone, whereby the material structure of the respective joining partner is changed, in particular homogenized, by the effect of heat. The setting parameters for creating the appropriate weld nugget are ultimately the welding current, the welding current time and the applied electrode force.

[0021] The invention further relates to a hydraulic accumulator, in particular manufactured using a method as presented above, which, in the course of completing its accumulator housing, is at least partially assembled from semi-finished products in the form of accumulator housing parts, of which one accumulator housing part has a material accumulation on its free end face and the other free end face of an adjacent accumulator housing part has a flat design or at least one recess, preferably in the form of a groove. In this way, the accumulator housing parts form semi-finished products or semi-finished products that can be produced cost-effectively in large quantities for series production before the actual welding and joining process.

[0022] Preferably, the volume of the material accumulation is a multiple of the released volume of the recess and, in particular, the volume of the material accumulation is selected such that a reliable welded connection is reliably created between the storage housing parts.

[0023] Preferably, the material accumulation, as well as the recess, extend annularly along the free end faces of the two storage housing parts. Preferably, the material accumulation and the recess can be brought into alignment with one another when the two adjacent storage housing parts are brought together, in particular when the adjacent storage housing parts are brought together coaxially to the longitudinal axis of the storage housing. This ensures in every case that at least one protruding tip of the material accumulation accurately engages the groove-shaped recess. Accordingly, guidance of the two storage housing parts is achieved by the material accumulation and the recess.

[0024] In a further preferred embodiment, the annular material accumulation is triangular in cross-section and has an opening angle of 50° to 110°, particularly preferably 70°, at the tip. The aforementioned angle values ​​ensure that the groove-shaped recess is not too deep, so that an unintentional lateral closure cannot occur during resistance welding. It has been shown that the geometric triangular shape for the projection, particularly with regard to material thickness and material strength, is particularly suitable for ensuring good force introduction as well as optimized recovery for the material accumulation in the direction of production of the weld nugget between the aforementioned joining partners in the form of the two housing parts or half-shells.

[0025] The respective recess serving as a centering for the material accumulation, formed from a circumferential groove, in particular in a V-shape, is accordingly recessed on the free end face of the other storage housing part, which is opposite the storage housing part with the material accumulation when the welded connection is produced.

[0026] Preferably, it is further provided that the groove recessed into the end face of the other storage housing part merges seamlessly into the adjacent wall sections along the corresponding end face of this storage housing part. Preferably, the material accumulation merges on the outer and / or inner circumference into a boundary surface that runs transversely to the longitudinal orientation of the material accumulation. Additional support is provided via the respective boundary surface during the reshaping process, resulting in improved weld seam bonding.Preferably, it is further provided that the free end face of the storage housing part with the groove-shaped recess, on the inner circumference side when visibly moved together with the adjacent storage housing part, protrudes beyond the inner circumference of the storage housing in the direction of the center of the storage housing, which benefits the further stiffening and in particular ensures that the welded connection runs out in the direction of the inside of the storage housing.

[0027] In a particularly preferred embodiment of the hydraulic accumulator according to the invention, it is provided that the accumulator housing part with the recess has a continuous central opening for at least the introduction of a fluid, in particular in the form of a working gas, and that the accumulator housing part with the material accumulation has a further continuous central opening, which serves at least for the introduction of a further fluid, in particular in the form of a working liquid. Due to the aforementioned central openings, the hydraulic accumulator according to the invention can be functionally connected to complete hydraulic systems, and the separating element arranged in the hydraulic accumulator separates a gas side from a liquid side in the accumulator housing.

[0028] In the following, the method according to the invention and a hydraulic accumulator that can be produced using it are explained in more detail according to the drawing. In this drawing, the following are shown in principle and not to scale:

[0029] Figures 1 to 4 show in longitudinal section and in succession the basic process steps for producing an accumulator housing of a hydraulic accumulator from two accumulator housing parts;

[0030] Figures 5 and 6 show two completed hydraulic accumulators based on the basic accumulator construction according to Figures 1 to 4 with an inserted dome-shaped separating membrane, which is fixed at the edge to the inside of the accumulator housing via fixing or holding devices.

[0031] Figures 1 to 4 show the essential process steps for producing at least part of an accumulator housing 10 for a hydraulic accumulator, as shown by way of example in Figures 5 and 6.

[0032] Figure 1 shows the provision of accumulator housing parts 12, 14 to be connected to one another, along adjacent end faces 16 and 18 respectively, of which, viewed in the direction of Figure 1, the lower accumulator housing part 12 has a material accumulation 20 on its free end face. The annular material accumulation 20 is triangular in cross-section and has an opening angle of preferably 70° at its tip; however, other opening angles are also conceivable here, for example in the range from 50° to 110°. The material accumulation 20 is preferably an integral component of the other shell material for the lower accumulator housing part 12. The lower accumulator housing part 12 has, in the usual way, a central opening 22 for the inlet or outlet of a fluid, such as a hydraulic medium.The upper storage housing part 14 is provided concentrically to the lower central opening 22 with a further central opening 24 in the usual way, which serves to introduce a working gas, such as nitrogen gas.

[0033] In the central direction and opposite the tip of the material accumulation 20, a recess 26 is introduced into the upper or other end face 18 of the upper storage housing part 14, preferably in a V-groove shape, wherein the free cross-section of the recess 26 is adapted to the geometry of the material tip of the material accumulation 20. Preferably, this adaptation is selected such that the free opening cross-section for the triangular recess 26 is slightly larger than the angle for the tip of the material accumulation 20 entering the recess 26 in this area.

[0034] The recess 26 therefore preferably has a free opening angle of preferably 90° if the free opening angle of the material accumulation 20 at its tip is 70°. Within the tolerance range, the specified angle values ​​of 70° and 90° can be slightly exceeded or undercut. In any case, as shown in Figure 1, provided the two housing parts 12, 14 are concentrically positioned one above the other, a central engagement of the tip of the material accumulation 20 in the associated recess 26 is guaranteed. The guide mentioned is not absolutely necessary, so that if necessary the recess 26 can be omitted, so that the tip of the material accumulation 20 strikes a flat contact surface such as the upper free end face 18 of the upper storage housing part 14 when the storage housing parts 12 and 14 move together.Figure 2 shows, starting from the initial state shown in Figure 1, the two storage housing parts 12, 14 moving toward each other, whereby, as already described, the tip of the material accumulation then enters the V-shaped recess 26, which thus forms the centering aid in this area. At the same time, or subsequently, the material accumulation 20 melts by means of a welding process, as indicated in the illustration in Figure 3.

[0035] The welding method used according to the invention is so-called resistance pressure welding, in particular resistance projection welding. In resistance projection welding, the lower storage housing part 12 is pressed against the upper storage housing part 14 as the cathode 30 by means of a stamp-shaped anode 28 with a predeterminable contact force. When an electrical voltage or current is applied to both the anode 28 and the cathode 30, the material accumulation 20 is melted due to the resulting contact resistance when the storage housing parts 12, 14 are placed against one another, as shown in Figures 2 and 3. Due to the contact force via the anode 28, the material accumulation 20 is reformed until an annular weld nugget 32 ​​is obtained, which creates the actual welded connection 34 as shown in Figure 4 between the two storage housing parts 12, 14 after it has cooled.The annular weld nugget 32 ​​has a central region 36 in the form of a circular ring, which serves to accommodate additional hydraulic accumulator parts, which will be explained in more detail below. The anode 28 is not absolutely necessary; rather, the lower accumulator housing part 12 can also form the anode exclusively. Under the application of force, one accumulator housing part 12 can be moved toward the other accumulator housing part 14, or vice versa. Furthermore, it is possible to move both accumulator housing parts 12, 14 toward each other equally under force, forming the welded joint.

[0036] As can be further seen from Figure 1, the triangular material accumulation 20, seen in cross-section, merges into a boundary surface 38, 40 on both the outer and inner circumferences, which is perpendicular to the longitudinal or feed axis L. In this way, the annular boundary surfaces 38, 40, which adjoin the base side of the material accumulation 20, provide support for the latter during reshaping during the welding process.

[0037] Starting from the two boundary surfaces 38, 40, the material accumulation 20 forms an isosceles triangle, and during the recovery process, the boundary surfaces 38, 40 remain intact for a relatively long time, as can be seen from Figure 3, which relates to the formation of the weld nugget 32 ​​in the transition area between the two housing parts 12, 14. As the material accumulation 20 melts, a weld seam or weld joint 34 is simultaneously formed along a connection point 42 between the storage housing parts 12, 14, as shown in Figure 4, as the two storage housing parts 12, 14 are further brought together during projection welding with a predeterminable contact force.

[0038] Viewed in cross-section, the weld seam 34 is still essentially lens-shaped and protrudes beyond the outer circumference of the storage housing 10 in this connection area. This projection 44 can be removed during further processing, creating a closed outer surface for the purpose of applying protective coatings, including a paint finish (not shown). The projection 44 for the weld seam 34 is in any case selected such that a gap-free seal is achieved between the weld seam 34 and the adjacent storage housing part 12, 14.

[0039] Figure 5 shows a hydropneumatic pressure accumulator or hydraulic accumulator shortly before completion, i.e., the two accumulator housing parts 12, 14 are not yet welded together. Before the welding process, a movable, elastomeric separating element 46 is inserted into the central region 36 of the accumulator. This separating element will later, after the completion of the hydraulic accumulator, separate a first media chamber, in particular gas chamber 48, from a second media chamber, in particular liquid chamber 50, in a media-tight manner. The separating element 46 or the separating membrane is positioned in the conventional manner (DE 101 12 976 AI) by means of a circumferential retaining ring 52 in the lower accumulator housing part 12, as shown.The retaining ring 52, which is designed to be flexible on the upper circumferential part via longitudinal slots, has a protective ring 54 on the outer circumference in a corresponding circumferential groove, which helps to prevent unwanted material from entering the inside of the storage housing 10 during welding, so that not only the separating element 46 is protected, but also the retaining ring 52, which may be constructed from sensitive plastic materials.

[0040] On the underside, the separating element 56 has a buttoned closure part 56, which, in the maximum deflection position of the separating element 46, closes the lower central opening 22 for fluid transfer into the interior of the accumulator in this area. Extending from the central opening 22, a connecting piece 58 is located underneath, which is firmly connected to the lower accumulator housing part 12 via an additional welded connection, such as a fillet weld 59. This connecting piece 58 is typically used to establish a connection between fluid- or media-carrying parts of a hydraulic circuit (not shown) and the hydraulic accumulator.In the embodiment according to Figure 6, compared to the illustration in Figure 5, the upper accumulator housing part 14 is now also provided with an additional connecting piece 60, which serves to supply a working gas into the hydraulic accumulator for the purpose of creating a gas storage space on the gas side of the hydraulic accumulator, formed by the gas space 48. The additional upper connecting piece 60 is firmly connected to the upper side of the upper accumulator housing part 14 by means of an additional weld seam 62. The production of this additional weld seam 62 is disclosed in the subsequently published DE 10 2022 129 348.3 of the patent holder. For the lower connecting piece 58, a circumferential welding bed 64 is prepared on the outer circumference at the upper end in the region of the transition to the lower accumulator housing part 12, which serves to accommodate the fillet weld 59 yet to be applied, as shown in Figure 5.

[0041] A further difference between the hydraulic accumulator solution according to Figure 6 and that according to Figure 5 is that the annular clamping device 66, which in turn holds an edge-shaped stiffener 68 of the separating element 46, is arranged below the horizontal plane with the welded connection 34. In this respect, the annular separating device 66 preferably consists of a spring-elastic metal material, so that under the spring preload of the clamping device 66, the edge bead 68 of the separating element 46 is fixed in a defined manner against the inside of the lower accumulator housing part 12. This type of fixing of a separating element in a hydraulic accumulator housing 10 is also common and is shown by way of example in DE 10 2015 012 357 A1.

[0042] Overall, the projection welding process for the two half-shells 12, 14 for producing a storage housing 10 achieves a high-strength connection between them, whereby a particularly gentle welded connection is produced, which can be used on an economically interesting scale for large-scale production of hydraulic accumulators.

Claims

Patent claims 1 . Method for producing at least part of a storage housing (10) for a hydraulic accumulator, comprising the following method steps: Providing storage housing parts (12, 14) to be connected to one another along adjacent end faces (16, 18), of which at least one end face (16) has a material accumulation (20), - Moving the adjacent storage housing parts (12, 14) together in such a way that the material accumulation (20) comes into contact with the adjacent end face (18), with simultaneous or subsequent - melting the material accumulation (20) by means of a welding process, and with further - Moving the two storage housing parts (12, 14) together during the welding process with a predeterminable contact force and simultaneous Forming a weld seam (32) running along a connection point (42) between the storage housing parts.

2. Method according to claim 1, characterized in that only one end face (16) carries the material accumulation (20) and the other end face (18) is provided with at least one recess (26) into which the material accumulation (20) at least partially engages when the two adjacent storage housing parts (12, 14) are moved together.

3. Method according to claim 1 or 2, characterized in that the formation of the weld seam (34) is carried out in such a way that it projects outwards with a projection (44) beyond the two adjacent storage housing parts (12, 14).

4. Method according to one of the preceding claims, characterized in that the projection (44) of the weld seam (34) is selected such that a gap-free closure is created between the weld seam (34) and adjacent storage housing parts (12, 14).

5. Method according to one of the preceding claims, characterized in that resistance pressure welding, in particular resistance projection welding, is used as the welding method.

6. Method according to one of the preceding claims, characterized in that in the context of resistance projection welding, one storage housing part (12) serves as an anode or is applied by means of an anode (28) against the other storage housing part (14) as a cathode (30) with the predeterminable contact force.

7. Hydraulic accumulator, in particular manufactured using a method according to one of the preceding claims, which, in the course of completing its accumulator housing (10), is at least partially assembled from semi-finished products in the form of accumulator housing parts (12, 14), of which one accumulator housing part (12) has a material accumulation (20) on its free end face (16) and the other free end face (18) of an adjacent accumulator housing part (14) is flat or has at least one recess (26).

8. Hydraulic accumulator according to claim 7, characterized in that the volume of the material accumulation (20) is a multiple of the volume of the recess (26).

9. Hydraulic accumulator according to claim 7 or 8, characterized in that the material accumulation (20) as well as the recess (26) extend annularly along the free end faces (16, 18) of the two accumulator housing parts (12, 14).

10. Hydraulic accumulator according to one of claims 7 to 9, characterized in that the material accumulation (20) and the recess (26) can be brought into alignment with one another when the two adjacent accumulator housing parts (12, 14) are moved together, in particular are arranged coaxially to the longitudinal axis of the accumulator housing (10) during the moving together of the adjacent accumulator housing parts (12, 14).

11. Hydraulic accumulator according to one of claims 7 to 10, characterized in that the annular material accumulation (20) is triangular in cross-section and has an opening angle of 50° to 110°, particularly preferably 70°, at the tip.

12. Hydraulic accumulator according to one of claims 7 to 1 1, characterized in that the recess (26) serving as a centering for the material accumulation (20) of one accumulator housing part (12) is formed from a circumferential groove, in particular in V-shape, in the free end face (18) of the other accumulator housing part (14).

13. Hydraulic accumulator according to one of claims 7 to 12, characterized in that the groove recessed in the end face (18) of the other accumulator housing part (14) merges without protrusion into the adjacent wall parts along the associated end face (18) of this accumulator housing part (14).

14. Hydraulic accumulator according to one of claims 7 to 13, characterized in that the material accumulation (20) merges on the outer and / or inner circumference into a boundary surface (38, 40) which runs transversely to the longitudinal orientation of the material accumulation (20).

15. Hydraulic accumulator according to one of claims 7 to 14, characterized in that the free end face (18) of the accumulator housing part (14) with the groove-shaped recess (26), on the inner circumference side in the visibly retracted state with the adjacent accumulator housing part (12), over its inner circumference in the direction of the center (36) of the storage housing.

16. Hydraulic accumulator according to one of claims 7 to 15, characterized in that the accumulator housing part (14) with the recess (26) has a continuous central opening (24) for at least the introduction of a fluid, in particular in the form of a working gas, and the accumulator housing part (12) with the material accumulation (20) has a further continuous central opening (22) which serves at least for the introduction of a further fluid, in particular in the form of a working liquid.

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