EP3109486B1 - Cylindrical tube for a hydraulic or pneumatic cylinder - Google Patents

Description

The invention relates to a cylinder tube for a hydraulic or pneumatic cylinder. For hydraulic and pneumatic cylinders, efforts have long been made to use fiber-reinforced plastics (FRP) to reduce component weight (see, for example, the document) DE4430502 ). Disadvantage of the fiber-reinforced plastics is that they are not suitable as material for the running surfaces of the cylinder. To solve this problem, there are various approaches in the art.

For example, in the DE 196 49 133 C1 proposed a cylinder tube for a working cylinder having a metallic inner tube and a carbon fiber reinforced outer structure. Inner tube and outer structure are connected by wave-shaped areas of the lateral surface of the inner tube. The disadvantage is the weight savings due to the massive metallic inner tube within limits, so that is in question whether the manufacturing cost of the connection of inner tube and outer structure is justified.

The DE 103 13 477 B3 has the task of proposing a cylinder tube for a cylinder, which has good stiffness and low weight with good sliding properties. This object is achieved by an inner tube of thermoplastic material and a coaxially arranged outer tube made of fiber-reinforced thermoplastic material, which are connected by an intermediate layer. The intermediate layer is electrically conductive and thus heatable, so that a fusion of inner and outer tube can be achieved. The disadvantage is that the tribological properties of the inner tube of thermoplastic material are not sufficiently stable for many applications. In addition, the technological complexity and thus the production costs are very high.

The object of the present invention is to propose a cylinder tube for a hydraulic or pneumatic cylinder, which has a low weight and very good tribological properties and is simple and inexpensive to manufacture.

According to the invention, this object is achieved by a cylinder tube according to claim 1 and a method for its production according to claim 9. Preferred embodiments of the invention are the subject of dependent claims.

The cylinder tube according to the invention for a hydraulic or pneumatic cylinder has a load-bearing outer tube made of fiber-reinforced plastic and an inner metal liner with a comparatively smaller wall thickness. The outer tube and the liner are included connected by a shear-soft intermediate layer. The metallic liner gives the cylinder tube on the inside very good tribological properties in conjunction with a very good service life. In addition, the liner has a low weight due to the very small wall thickness. The liner is preferably not intrinsically stable in order to save weight. Advantageously, the shear-soft intermediate layer can compensate for temperature fluctuations, the different thermal expansion coefficients of metallic liner and the outer tube made of FRP. For example, steel has a coefficient of thermal expansion of 11.3 × 10 ^-6 × K ^-1 , while carbon fiber reinforced plastic (CFRP) has a coefficient of 2.65 × 10 ^-6 × K ^-1 in a quasi-isotropic laminate construction with unidirectional carbon fiber-reinforced individual layers , A unidirectionally reinforced CFRP monolayer has a coefficient in the fiber direction of -0.5 × 10 ^-6 × K ^-1 and perpendicular to the fiber direction of 43.0 × 10 ^-6 × K ^-1 . Visible is the large difference between the coefficients of thermal expansion, which leads to a significant difference in length of liner and outer tube with temperature fluctuations. This would lead to the release of the connection between FKV outer tube and metallic liner without the shear-soft intermediate layer.

Another advantage of the shear-soft intermediate layer is its significantly higher attenuation. Thus, vibrations during operation can be significantly reduced by the structurally inherent high damping.

Preferably, the intermediate layer consists of elastomers, such as ethylene-propylene-diene monomer (EPDM). Elastomers have extremely high elongations at break of up to several 100% and can thus excellently bridge the different thermal expansions between the FRP outer tube and the inner metallic liner. In addition, many elastomers have sufficient thermal resistance to application. For example, EPDM elastomers usually have a continuous service temperature range of -40 ° C to + 90 ° C. In addition, EPDM has a very good aging resistance under UV or ozone load.

Further preferably, the intermediate layer of thermoplastic elastomers (TPE), which combine the processing advantages of thermoplastics with the material properties of the elastomers. In contrast to pure elastomers TPE can be melted, thereby enabling easy production of the intermediate layer.

From the group of TPE are suitable for example thermoplastic elastomers based on urethane (TPU) or olefin (TPO). In addition, thermoplastic copolyesters (TPC) or styrene block polymers (TPS) from the group of TPE are also suitable.

Furthermore, the outer tube preferably consists of several layers of fiber-reinforced plastic. Advantageously, the structural mechanical properties of the outer tube can be adapted very well to the expected loads.

Further preferably, the metallic liner is made of steel. Advantageously, steel is available at low cost and has very good tribological properties.

Further preferably, the metallic inner liner has a wall thickness between 0.1 mm and 1 mm.

Last but not least, the intermediate layer has a preferred wall thickness between 0.1 mm and 0.4 mm.

The inventive production of the cylinder tube, which consists of the FKV outer tube, the metallic liner and the shear soft intermediate layer can be carried out as follows. First, the thin-walled metallic liner is manufactured using classical metallic tube manufacturing techniques such as the spin forming process.

Thereafter, the application of the shear soft intermediate layer of elastomer or TPE takes place on the outside of the thin-walled metallic liner, usually first a commercial low-viscosity primer (primer) is applied to the outside of the metallic liner. This adhesion promoter serves to achieve a good adhesive strength between the metallic liner and the shear-soft intermediate layer of elastomer or TPE. The thin-walled liner can be stabilized from the inside during the application of the primer and the shear-soft intermediate layer by a support core. This support core is preferably a metal or plastic cylinder, the z. For example, can be inserted into the cylindrical liner and is removed again after the application of the intermediate layer. As a support core but also the winding or braided core can be used, which is later used for the production of FKV outer tube.

Especially with intermediate layers of TPE, various processing methods can be used to apply the intermediate layer. For example, the metallic liner can be overmoulded with TPE. Another possibility is the use of TPE films, which are wound around the metallic liner and melted and consolidated by brief temperature increase and subsequent cooling.

After the application of the shear-soft intermediate layer of the metallic liner is preferably pushed onto a winding or braided core, the subsequent production the FKV outer tube in the winding or braiding process is used. The metallic liner with intermediate layer is quasi "wrapped" or interwoven. The winding process is usually done with preimpregnated fibers so that no subsequent resin infiltration is required. In contrast, the braiding process is generally done with dry fibers, so that subsequent infiltration in a closed tooling system is required.

Figur 1

ein erfindungsgemäßes Zylinderrohr mit Darstellung der einzelnen Schichten,

Figur 2

das Zylinderrohr mit Schnittdarstellung dessen Endes mit verschiedenen Temperaturen.

An embodiment of the invention will be explained with reference to figures, in which:

FIG. 1

an inventive cylinder tube with representation of the individual layers,

FIG. 2

the cylinder tube with sectional view of the end with different temperatures.

FIG. 1 shows the structure of a cylinder tube according to the invention 1. This has an outer tube consisting of several fiber layers 11, with different fiber orientations. The total wall thickness of the outer tube formed by the fiber layers 11 is 7 mm.

On the inside, the cylinder tube 1 has a metallic liner 13 made of stainless steel with a wall thickness of 0.4 mm. Between the fiber layers 11 and the metallic liner 13, an intermediate layer 12 of thermoplastic polyurethane (TPU) with a layer thickness of 0.2 mm is arranged. The inner diameter of the cylinder tube 1 D _i is 85 mm.

From the cylinder tube 1, a lightweight hydraulic actuator with a piston stroke of 400 mm and an operating pressure of 207 bar is produced.

FIG. 2 shows a sectional view in the sectional plane AA through the cylinder tube 1, comprising an inner diameter D _i and an outer diameter D _a at different temperatures. On the left side of the sectional view, the fiber layers 11, the intermediate layer 12 and the metallic liner 13 are the same length. The increase in temperature results on the right side in an extension of the metallic liner 13 by the difference in length 2. By the shear-soft intermediate layer 12 of the elongation difference can be compensated with the length 2, and fiber layers 11 and metallic liner 13 remain connected despite different lengths.

LIST OF REFERENCE NUMBERS

1

cylinder tube

11

fiber layer

12

interlayer

13

Metallic liner

2

length difference

D _i

Inner diameter of the cylinder tube 1

D _a

Outer diameter of the cylinder tube 1

Claims (15)

1. Cylindrical tube (1) for a hydraulic or pneumatic cylinder, comprising an outer tube made of fibre-reinforced plastics material and an inner metal liner (13), characterised in that the metal liner (13) and outer tube are connected by a shear-compliant intermediate layer (12).
2. Cylindrical tube (1) according to claim 1, characterised in that the intermediate layer (12) is made of elastomer.
3. Cylindrical tube (1) according to claim 1, characterised in that the intermediate layer (12) is made of a thermoplastic elastomer (TPE).
4. Cylindrical tube (1) according to claim 3, characterised in that the thermoplastic elastomer (TPE) is urethane-based (TPU) or olefin-based (TPO), including in the crosslinked state (TPV), or is a thermoplastic copolyester (TPC) or a styrene block polymer (TPS).
5. Cylindrical tube (1) according to any of the preceding claims, characterised in that the outer tube comprises a plurality of fibre layers (11).
6. Cylindrical tube (1) according to any of the preceding claims, characterised in that the inner metal liner (13) is produced from steel.
7. Cylindrical tube (1) according to any of the preceding claims, characterised in that the inner metal liner (13) has a thickness of between 0.1 mm and 1 mm.
8. Cylindrical tube (1) according to any of the preceding claims, characterised in that the intermediate layer (12) has a wall thickness of between 0.1 mm and 0.4 mm.
9. Method for manufacturing a cylindrical tube (1) according to any of the preceding claims, characterised by the following method steps:

   a) providing a thin-walled metal liner (13),

   b) applying the shear-compliant intermediate layer (12) to the outside of the metal liner (13),

   c) producing the fibre-plastics-composite outer tube by means of winding or braiding onto the shear-compliant intermediate layer (12),

   d) consolidating the cylinder tube (1).
10. Method according to claim 9, characterised in that, before the shear-compliant intermediate layer (1) is applied in step b), an adhesion promoter is applied to the metal liner (13).
11. Method according to either claim 9 or claim 10, characterised in that, before the shear-compliant intermediate layer (12) is applied in step b), a core is introduced into the metal liner (13).
12. Method according to any of claims 9 to 11, characterised in that the shear-compliant intermediate layer (12) is applied in step b) by overmoulding the metal liner (13) with TPE or by wrapping the metal liner (13) in TPE films and subsequently consolidating by heating for a short time.
13. Method according to any of claims 9 to 12, characterised in that the core from claim 10 is used as a winding or braiding core for producing the fibre-plastics-composite outer tube, or a winding or braiding core is introduced into the metal liner (13) before step c) is carried out.
14. Method according to any of claims 9 to 13, characterised in that the fibre-plastics-composite outer tube is produced in step c) by winding pre-impregnated fibres.
15. Method according to any of claims 9 to 13, characterised in that the fibre-plastics-composite outer tube is produced in step c) by braiding dry fibres and subsequently consolidated in step d) by infiltration in a closed mould system.

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