PISTON-CYLINDER UNIT, METHOD FOR PRODUCING THE PISTON-CYLINDER UNIT

Abstract

The invention relates to a piston-cylinder unit (100) comprising a cylinder (110) filled with a fluid (150), a piston (120) slidably guided in the cylinder (110), a piston rod (130) attached to the piston (120), a seal (140), and a lubricant in contact with the seal (140) and with the cylinder (110), the piston (120) and/or the piston rod (130). The lubricant is a polyalphaolefin oil or a polyalkylene glycol oil. The seal (140) is made of chlorine-free acrylonitrile butadiene rubber. The invention also relates to a method for producing the piston-cylinder unit (100).

Claims

1. A piston cylinder unit (100) comprising a. a cylinder (110) filled with a fluid (150), b. a piston (120) slidably guided in the cylinder (110), c. a piston rod (130) attached to the piston (120), d. a seal (140) made of acrylonitrile butadiene rubber and e. a lubricant in contact with the seal (140) and with the cylinder (110), the piston (120) and/or the piston rod (130), characterised in that f. the lubricant is a polyalphaolefin oil or a polyalkylene glycol oil, and g. the seal (140) is chlorine-free, wherein the seal (140) contains neither chlorine or chlorine compounds added intentionally, nor chlorine or chlorine compounds transferred into the seal (140) during manufacture of the seal (140).

2. The piston-cylinder unit (100) according to claim 1, characterized in that the seal (140) is a piston rod seal, wherein a. the piston rod (130) is led out of the cylinder (110) through the seal (140), and b. the seal (140) closes the cylinder (110) tightly for the fluid (150).

3. The piston-cylinder unit (100) according to claim 1, characterized in that the seal (140) is halogen-free, wherein the seal (140) contains neither halogens or halogen compounds added intentionally, nor halogens or halogen compounds transferred into the seal (140) during manufacture of the seal (140).

4. The piston-cylinder unit (100) according to claim 1, characterized in that the lubricant contains at least one swelling additive for swelling the seal (140), wherein the swelling additive is an ester.

5. The piston-cylinder unit (100) according to claim 1, characterized in that the lubricant contains at least one friction reducing additive for reducing friction between the seal (140) and the cylinder (110), the piston (120) and/or the piston rod (130), wherein the friction reducing additive is an amphiphilic substance, a functionalised polymer, an organic molybdenum compound or a fatty acid ester.

6. The piston-cylinder unit (100) according to claim 1, characterized in that the lubricant contains at least one anti-corrosion additive for reducing corrosion of the cylinder (110), the piston (120) and/or the piston rod (130), wherein the anti-corrosion additive is a sulphonate, a cycloalkanate, a carboxylate, an alkyl succinic acid derivative or a polyol ester.

7. A method for producing a piston-cylinder unit (100) according to claim 1, characterized by the following steps: a. chlorine-free manufacture of the seal (140) of the piston-cylinder unit (100) from acrylonitrile-butadiene rubber, so that the seal (140) contains neither chlorine or chlorine compounds added deliberately, nor chlorine or chlorine compounds transferred into the seal (140) during the manufacture of the seal (140), b. assembly of the seal (140) with the cylinder (110), the piston (120) and the piston rod (130) of the piston-cylinder unit (100) and c. filling of the lubricant of the piston-cylinder unit (100) into the piston-cylinder unit (100), wherein the lubricant is a polyalphaolefin oil or a polyalkylene glycol oil.

8. The method of claim 7, characterized in that s aid the manufacture of the seal (140) comprises retarding solidification of an acrylonitrile-butadiene rubber melt with a chlorine-free reaction retarder.

9. The method of claim 7, characterised in that the manufacture of the seal (140) comprises injection moulding or injection compression moulding the seal (140) from an acrylonitrile-butadiene rubber melt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further advantages, objectives and properties of the invention are explained with reference to the following description and accompanying drawings, in which exemplary embodiments of the invention are shown.

[0037] FIG. 1 shows a schematic representation of a piston-cylinder unit according to the invention.

[0038] FIG. 2 shows the friction force acting on the piston rod of a piston-cylinder unit with a mineral oil or with a polyalkylene glycol oil as lubricant.

[0039] FIG. 3 shows the degree of corrosion of steel fingers in contact with a polyalkylene glycol oil lubricant with a seal of chlorine-containing or chlorine-free acrylonitrile butadiene rubber.

[0040] FIG. 1 shows a schematic representation of a piston-cylinder unit 100 according to the invention as a longitudinal section along a stroke axis H of the piston-cylinder unit 100, which is for example a gas pressure spring.

[0041] The piston-cylinder unit 100 shown comprises a cylinder 110 filled with a fluid 150, for example with nitrogen gas that is at an overpressure relative to an environment of the cylinder 110, and a piston 120 guided in the cylinder 110 so as to be displaceable along the stroke axis H.

[0042] The illustrated piston-cylinder unit 100 includes a piston rod 130 attached to the piston 120 and a seal 140. The seal 140 is, for example, a piston rod seal, wherein the piston rod 130 extends out of the cylinder 110 through the seal 140, and the seal 140 closes the cylinder 110 tightly to the fluid 150.

[0043] The illustrated piston-cylinder assembly 100 includes a lubricant (not shown) at least in contact with the seal 140 and the piston rod 130.

[0044] The lubricant is a polyalphaolefin oil or a polyalkylene glycol oil, and the seal 140 is made of chlorine-free acrylonitrile butadiene rubber.

[0045] FIG. 2 shows the frictional force Fin N acting on the piston rod of a prior art piston-cylinder unit designed as a gas pressure spring with a mineral oil (black columns) or a polyalkylene glycol oil (hatched columns) as lubricant.

[0046] The friction force F at the first stroke 1a, at the second stroke 1b and at the third stroke 1c directly after assembly of the piston-cylinder unit as well as the friction force F at the first stroke 2a, at the second stroke 2b and at the third stroke 2c after the piston-cylinder unit has been subjected to an endurance test and then stored for 24 h, so that the surface of the piston rod is dry at the first stroke in each case, are shown.

[0047] The friction force Fis lower with the polyalkylene glycol oil than with the mineral oil. This effect is particularly strong during the first stroke after assembly and after storage and can also be seen during the subsequent strokes.

[0048] FIG. 3 shows the degree of corrosion of steel fingers in contact with a polyalkylene glycol oil lubricant in which a seal of chlorine-containing (a) or chlorine-free (b, c) acrylonitrile butadiene rubber is inserted.

[0049] The degree of corrosion is determined using a steel finger test based on DIN ISO 7120, method B. In this test, a steel pin is suspended in a glass with the seal, the polyalkylene glycol oil and water. After a predetermined reaction time of, for example, 24 h at a constant temperature of, for example, 60 C., the degree of corrosion is evaluated on a scale from 0 (no corrosion) to 5 (complete corrosion of the surface of the steel pin).

[0050] While the steel pin shows a high degree of corrosion in contact with the polyalkylene glycol oil with a chlorine-containing seal, the degree of corrosion under the same conditions is much lower in contact with the polyalkylene glycol oil with a chlorine-free seal.

TABLE-US-00001 List of reference signs 100 Piston-cylinder unit 140 Seal 110 Cylinder 150 Fluid 120 Piston F Frictional force 130 Piston rod H Stroke axis