Union screw for a pipeline provided with at least one flange, in particular a brake pipe

A method of manufacturing a union screw for brake pipes having at least one flare, a metal base body extending in an axial direction and having a through opening having a diameter in a radial direction and adapted to receive the pipe;

• a screw head formed on the base body, which is configured to transmit a torque to the union screw;
• a threaded portion formed on the base body, the threaded portion having an external thread and being adapted to screw the union screw into a tapped hole;
• a contact portion formed on the base body and adapted to abut the flare of the pipe, and a functional layer with which the base body is coated at least in the region of the threaded portion and the contact portion;
• wherein the functional layer is multilayered and is composed at least of a base coat and a top coat applied to the base coat at least in regions;
• wherein the top coat contains a lubricant to provide a friction-reducing coating, and wherein the base coat comprises a binder and zinc to provide corrosion protection;
• wherein the base coat forms a structure in which the zinc is in the form of zinc-containing lamellae;
• and wherein the zinc-containing lamellae are oriented to lie substantially flat on the base body,
• the method comprising:
• a) coating the base body with a first composition comprising zinc-containing lamellae and a binder to form the base coat, wherein the zinc-containing lamellae are oriented to lie substantially flat on the base body, wherein the coating comprises applying the first composition to the base body at least once;
• wherein the base body is subjected to a heat treatment after the application of the first composition in order to dry and/or crosslink the applied composition;
• and
• b) coating the base body in at least a portion of the base coat with a second composition comprising a lubricant to produce the top coat, wherein the coating comprises applying the second composition to the base coat at least once.

The method of 17,

• wherein the first composition is an aqueous dispersion;
• or
• wherein the first composition is a suspension;
• or
• wherein the first composition comprises:
• platelet-shaped particles in the form of lamellae containing zinc, and
• a binder which contains a silane;
• and/or
• wherein the first composition further comprises:
• a solvent, which is organic, and/or
• water;
• and/or
• wherein the first composition further comprises:
• a thickening agent.