UNION SCREW FOR A PIPELINE PROVIDED WITH AT LEAST ONE FLANGE, IN PARTICULAR A BRAKE PIPE

Abstract

A union screw (1) for pipes (2) provided with at least one flare (21) comprises a metal base body (10) which accommodates the pipe (20). The union screw (1) further comprises a screw head (12), a threaded portion (13), a contact portion (15) which is configured to abut the flare (21) of the pipe (20), and a functional layer (40) with which the base body (10) is coated at least in the region of the threaded portion (13) and the contact portion (15). The functional layer (40) is multi-layered and consists of at least one base coat (41) and a top coat (42) applied to the base coat (41) at least in some areas. The base coat (41) forms a structure for creating corrosion protection and a far-reaching invariance with regard to the material of the usual friction partners of the union screw (1) which, in addition to a binder, also contains zinc in the form of zinc-containing lamellae (43), which are oriented to lie substantially flat on the base body (10).

Claims

1. Union screw for pipelines provided with at least one flare (21), in particular brake pipes, comprising: a metal base body (10) extending in an axial direction (x) and having a through opening (11) having a diameter (D) in a radial direction (r) and adapted to receive the pipe (20); a screw head (12) formed on the base body (10), which is configured to transmit a torque to the union screw (1); a threaded portion (13) formed on the base body (10), the threaded portion (13) having an external thread (14) and being adapted to screw the union screw (1) into a tapped hole (31); a contact portion formed on the base body (10) and adapted to abut the flare (21) of the pipe (20), and a functional layer (40) with which the base body (10) is coated at least in the region of the threaded portion (13) and the contact portion (15); wherein the functional layer (40) is multi-layered and is composed of at least one base coat (41) and a top coat (42) applied to the base coat (41) at least in regions; wherein the top coat (42) contains a lubricant to provide a friction-reducing coating, and wherein the base coat (41) contains a binder and zinc to provide corrosion protection; characterized in that the base coat (41) forms a structure in which the zinc is present in the form of zinc-containing lamellae (43); wherein the zinc-containing lamellae (43) are oriented to lie substantially flat on the base body (10).

2. The union screw according to claim 1, characterized in that the zinc-containing lamellae (43) are platelet-shaped and have a length (I), a width (b) and a thickness (d); wherein preferably the length (I) and/or the width (b) and/or the thickness (d) are between 5 microns and 500 microns, preferably between 10 microns and 200 microns, and more preferably between 50 microns and 150 microns.

3. The union screw according to claim 1 or 2, characterized in that the zinc-containing lamellae (43) contain more than 50 wt. % zinc; wherein preferably the zinc-containing lamellae (43) also contain lamellae of another metal, which is preferably selected from a group comprising aluminum, tin, magnesium, nickel, cobalt or manganese.

4. The union screw according to any one of claims 1 to 3, characterized in that the zinc is alloyed with at least one further metal; wherein preferably the further metal is selected from a group comprising aluminum, tin, magnesium, nickel, cobalt or manganese; wherein further preferably the zinc-containing lamellae (43) consist of a zinc-aluminum alloy.

5. The union screw according to any one of claims 1 to 4, characterized in that the binder contains a silane; wherein preferably the silane has functional groups; wherein more preferably the silane has an epoxy group; wherein more preferably the silane is γ-glycidoxypropyltrimethoxysilane.

6. The union screw according to any one of claims 1 to 5, characterized in that the lubricant contains a hydrofluorocarbon, preferably a perfluorinated hydrocarbon, more preferably polytetrafluoroethylene.

7. The union screw according to any one of claims 1 to 6, characterized in that the base body (10) in the region of the screw head (11) is coated with the functional layer (40); wherein preferably the entire surface of the base body (10) is coated with the functional layer (40).

8. The union screw according to any one of claims 1 to 7, characterized in that the top coat (42) is applied to the entire base coat (41); and/or the base coat (41) forms the lowermost layer of the functional layer (40); and/or the top coat (42) forms the uppermost coat of the functional layer (40).

9. The union screw according to any one of claims 1 to 8, characterized in that the base coat (41) has, at least in the region of the threaded portion (13) and/or in the region of the contact portion (15), a layer thickness (d.sub.G) which is between 0.5 microns and 30.0 microns, preferably between 1.0 microns and 20.0 microns, more preferably between 5.0 microns and 10.0 microns; and/or the top coat (42) has, at least in the region of the threaded portion (13) and/or in the region of the contact portion (15), a layer thickness (d.sub.D) which is less than 5.0 microns, preferably less than 1.0 microns, more preferably less than 0.5 microns.

10. The union screw according to any one of claims 1 to 9, characterized in that the base coat (41) has a weight per unit area (MG) which is between 5.0 g/m.sup.2 and 40.0 g/m.sup.2, preferably between 10.0 g/m.sup.2 and 30.0 g/m.sup.2, more preferably between 22.0 g/m.sup.2 and 26.0 g/m.sup.2, and/or the top coat (42) has a weight per unit area (MG) which is between 0.5 g/m.sup.2 and 15.0 g/m.sup.2, preferably between 1.0 g/m.sup.2 and 10.0 g/m.sup.2, more preferably between 3.0 g/m.sup.2 and 5.0 g/m.sup.2.

11. Use of a union screw (1) according to any one of claims 1 to 10 for a pipe (20) provided with a flare (21), in particular a brake pipe.

12. A method of manufacturing a union screw (1) according to any one of claims 1 to 10, characterized by the following process steps: a) coating the base body (10) with a first composition containing zinc-containing lamellae and a binder to produce the base coat (41); b) coating the base body (10) in at least one part of the base coat (41) with a second composition containing a lubricant to produce the top coat (42).

13. The method of claim 12, characterized in that the base body (10) in the entire area of the base coat (41) is coated with the second composition.

14. The method of claim 12 or 13, characterized in that the first composition is an aqueous dispersion; wherein preferably the first composition is a suspension; wherein more preferably the first composition comprises: platelet-shaped particles in the form of lamellae containing zinc, and a binder that preferably contains a silane; wherein more preferably the first composition further comprises: a solvent which is preferably organic, and/or water; wherein more preferably the first composition further comprises: a thickener.

15. The method according to any one of claims 12 to 14, characterized in that the second composition is an aqueous dispersion; wherein preferably the lubricant contains a hydrofluorocarbon, preferably a perfluorinated hydrocarbon, more preferably polytetrafluoroethylene.

16. The method according to any one of claims 12 to 15, characterized in that the coating according to method step a) comprises at least once, preferably several times, in particular twice, application of the first composition to the base body (10); wherein preferably the base body (10) is subjected to a heat treatment after applying the first composition in order to dry and/or crosslink the applied composition.

17. The method according to any one of claims 12 to 16, characterized in that the coating according to method step b) comprises at least once, preferably several times, application of the second composition to the base coat (41); wherein preferably the base body (10) is subjected to a heat treatment after applying the second composition to dry and/or crosslink the applied composition.

Description

[0042] Details and other advantages of the invention result from the following description of preferred embodiments. In the drawings schematically illustrative the embodiments show in detail:

[0043] FIG. 1a is a longitudinal section through a pipe connected to a connection element with a flare of form F;

[0044] FIG. 1b is a longitudinal section according to FIG. 1a with a flare of the form E;

[0045] FIG. 2a is a micrograph of a functional layer;

[0046] FIG. 3a is a diagram showing a measured axial load for union screws provided with conventional zinc-nickel and lubricant coatings;

[0047] FIG. 3b is a diagram showing a measured axial load for union screws coated according to the invention;

[0048] FIG. 3c is a diagram showing a measured pipe torque for union screws coated according to the invention; and

[0049] FIG. 4 is a representation showing the “slip” effect inherent in the invention.

[0050] The embodiment shown in FIG. 1a has a pipe 20 provided with a flare 21 of form F according to the standard DIN 74 234:1992-09, which is attached by means of a union screw 1 or pipe screw to a connection element 30, which is, for example, an aggregate of the braking system of a motor vehicle. The flare 21 has a sealing face 22 and an abutment face 23. The connection element 30 has a tapped hole 31, that is, an opening 31 provided with an internal thread 32, which leads into a passage line 33. The tapped or threaded hole 31 has a connection face 34 located at the bottom of the opening, which edges the passage line 33 and in the case of FIG. 1a is concave.

[0051] The union screw 1 has a metal base body 10, which extends in an axial direction x and has a through opening 11, which in a radial direction r has a diameter D. Pipe 20 extends through the through opening 11. On the base body 10, a screw head 12 is formed, which serves to transfer a torque to the union screw 1. Furthermore, a threaded portion 13 is formed on the base body 10, which has an external thread 14 and serves to screw the union screw 1 into the internal thread 32 of the tapped hole 31. In addition, a contact portion 15 is formed on the base body 10, which serves to lie on the abutment face 23 of the flare 21 in the screwed-in state of the union screw 1.

[0052] The embodiment shown in FIG. 1b also has a pipe 20 provided with a flare 21, which is attached to a connection element 30 by means of a union screw 1. In contrast to the embodiment according to FIG. 1a, however, the flare 21 does not correspond to the form F, but to the form E according to the standard DIN 74 234:1992-09. The sealing face 22 is therefore concave and is fluid-tight to the convex connection face 34 of the connection element 30 in this case. Furthermore, it can be seen that the contact portion 15 of the union screw 1 is located on the abutment face 23 of the flare 21. The pipe 20 is thus held as in the embodiment according to FIG. 1a by means of the flare 21 between the contact portion 15 of the union screw 1 and the connection face 34.

[0053] In order to ensure that when screwing in the union screw 1 into the tapped or threaded hole 31, no torsion of the pipe 20 occurs, which led to an undesirable torsional stress in the pipe 20, it is desirable that in the contact area I between the contact portion 15 of the union screw 1 and the abutment face 23 of the flare 21, a comparatively low friction occurs. In the contact area II between the sealing face 22 of the flare 21 and the connection face 34 and in the contact area III between the external thread 14 of the union screw 1 and the internal thread 32 of the thread hole 31, on the other hand, it is advantageous, if a comparatively large friction occurs to ensure on the one hand a fluid-tight concern of the pipe 20 on the connection element 30 and on the other hand a firm and permanent fit of the union screw 1 in the threaded hole 31.

[0054] In order to meet these different requirements, the surface of the union screw 1 is provided with a functional layer 40, which causes a suitable coefficient of friction p. The coefficient of friction, also called friction coefficient, is a dimensionless number calculated from measured physical properties and depends on the type and geometry of the surfaces in contact. Test setups and test procedures for determining the friction coefficients or friction coefficients describe in particular the VDA standard 235-203 and the standard DIN EN ISO 16047:2005.

[0055] The functional layer 40, with which the base body 10 is coated at least in the area of the threaded portion 13 and the contact portion 15, is multi-layered and is composed of at least one base coat 41 and a top coat 42 applied to the base coat 41 at least partially. The base coat 41 creates a corrosion protection and, as FIG. 2 indicates, forms a structure comprising zinc-containing lamellae 43, which are substantially arranged flat on the base body 10, and a binder. The top coat 42 produces a friction-reducing coating that causes the coefficient of friction p and contains a lubricant comprising a silane.

[0056] Zinc is the essential component of lamellae 43. The lamellae 43 contain more than 50 wt.-% zinc. In addition, in the lamellae 43 another metal may be present, which is either in the form of additional lamellae made of this further metal, or is alloyed with the zinc. The other metal is preferably aluminum, tin, magnesium, nickel, cobalt or manganese. In the present embodiment, the base coat 41 comprises a mixture of zinc and aluminum lamellae 43.

[0057] The metal components of base coat 41 are connected by a matrix of a binder. The binder contains a silane. In order to enable a good bonding of the metal components, the silane has functional groups. A preferred reactive and functional chemical unit is the epoxy group. A particularly suitable representative of such an epoxysilane is γ-glycidoxypropyltrimethoxysilane.

[0058] The base coat 41 has a layer thickness d.sub.G in the region of the threaded portion 13 and/or in the region of the contact portion 15, which is usually between 0.5 μm and 30.0 μm, in the present case between 5.0 μm and 10.0 μm. Base coat 41 has a weight per unit area MG, which is usually between 5.0 g/m.sup.2 and 40.0 g/m.sup.2, in this case between 22.0 g/m.sup.2 and 26.0 g/m.sup.2.

[0059] The relatively thin top coat 42 compared to the base coat 41 has a layer thickness d.sub.D in the region of the threaded portion 13 and/or in the region of the contact portion 15, which is usually less than 5.0 μm, in the present case less than 1.0 μm. The weight per unit area MG of the top coat 41 is usually between 0.5 g/m.sup.2 and 15.0 g/m.sup.2, in the present case between 3.0 g/m.sup.2 and 5.0 g/m.sup.2.

[0060] The method of manufacturing the union screw 1 comprises the following process steps. First, the base body 10 is coated with a first composition containing zinc-containing lamellae and a binder to create the base coat 41. Thereafter, the base body 10 is coated in at least one part of the base coat 41 with a second composition containing a lubricant to produce the top coat 42. The base body 10 can be coated in the entire area of the base coat 41 with the second composition, but a coating is usually sufficient in the areas relevant for friction with the friction partners, i.e. the abutment face 23 and the internal thread 32, in particular in threaded portion 13 and in contact portion 15.

[0061] In the preparation of the base coat 41, a suspension of the lamellae 43 is preferably used in a liquid phase. The dispersant is preferably water, wherein in the suspension advantageously a thickener, is present to increase its viscosity.

[0062] The lubricant in the top coat 42 is a polymeric fluorocarbon, in particular a perfluorinated hydrocarbon, more preferably polytetrafluoroethylene. In the preparation preferably a lubricant dispersion is used, in particular polytetrafluoroethylene is suspended in a liquid, for example water.

[0063] Coating with the first composition is carried out by applying the first composition to the base body 10 at least once, in particular two or three times. Subsequently, the base body 10 is subjected to a heat treatment to dry and/or crosslink the applied composition.

[0064] The coating with the second composition is also carried out by at least once, preferably several times, application of the second composition to the base coat 41. Subsequently, the base body 10 is subjected to a heat treatment to dry and/or crosslink the applied composition.

[0065] FIGS. 3a to 3c show the values resulting from the functional layer 40 for different materials that make up the friction partners for a measured axial load and a measured pipe torque, i.e. the moment acting on a brake pipe, for example. The diagram according to FIG. 3a shows the axial load resulting from conventionally coated union screws. The diagrams according to FIGS. 3b and 3c clearly show that, in contrast to conventional coatings, with the usual materials aluminum (AL) and steel (ST) the values for the axial load and the values for the tube torque in the invention coated union screws in each case in two measurement sequences relatively are close to each other. Thus, the functional layer 40 allows an invariance of the union screw 1 with regard to the friction partners, which takes into account a practical handling.

[0066] The FIG. 4. illustrates that a reduction in pipe torque is a function of the flatness of the zinc lamellae and their parallelism to the base coat. During the tightening of the union screw, the shear stresses in the base coat caused by the turning of the screw connection are not resisted to the same extent as the vertical forces. This allows, as FIG. 4 also shows, a “slipping” between the lamellae or slats in the direction in which the slats lie.

TABLE-US-00001 List of reference signs  1 union screw 10 base body 11 through opening 12 screw head 13 threaded portion 14 external thread 15 contact portion 20 pipe 21 flare 22 sealing face 23 abutment face 30 connection element 31 tapped hole 32 internal thread 33 passage line 34 connection face 40 functional layer 41 base coat 42 top coat 43 zinc-containing lamellae x axial direction r radial direction d.sub.G layer thickness of the base coat d.sub.D layer thickness of the top coat M.sub.G weight per unit area of the base coat M.sub.D weight per unit area of the top coat μ coefficient of friction l length b width d thickness D Diameter of the through opening I contact area with comparatively low friction II contact area with comparatively high friction III contact area with comparatively high friction