Hot screw compound
Hot screw compound , also called assembly or screw paste , is a grease-like special paste and serves primarily as a thermally stable and chemically largely inert release agent and less as a lubricant or corrosion protection agent for joints and sliding surfaces in difficult environmental conditions (high temperatures , aggressive chemical environment), such as Screw connections in exhaust systems or turbines .
Colloquially, hot screw compounds are known as copper paste or copper grease due to their traditionally mostly brown-red color . However, pastes of different colors, for example white, are also used; there the active substance consists of ceramic powder.
In the English-speaking world, self-tightening compound is called anti- seize or antiseize , literally "against jamming " or "against seizing ".
Components
Depending on the application, hot screw compounds consist of ceramic (e.g. titanium nitride ) or metallic powders (such as copper , aluminum , zinc ) or graphite in silicone grease or PTFE compounds as a carrier substance.
Contact grease has a similar composition , which is supposed to reduce the contact resistance of electrical contacts .
properties
Hot screw compound is characterized by a high lubricating and separating effect, high pressure resistance, good electrical and thermal conductivity , good adhesive strength and a high proportion of solid lubricants (mainly metal powder). In very narrow gaps there is a good sealing effect. It can be used at temperatures from −30 ° C to 1300 ° C and is resistant to weather, moisture and aggressive chemical environments or corrosive gases. This also prevents sticking and rusting.
Areas of application
Hot screw compounds are used as a release agent or lubricant in high-temperature environments in which the otherwise common mineral oil-based release agents can no longer be used. The purpose is to reduce oxidation or welding of the bare metal surfaces, to ensure the functionality of plain bearings or guides and the releasability of a screw connection in the long term.
Examples:
- Corrosion protection of threads of hot screw connections, e.g. B. in turbines , screw connections and separation points of exhaust pipes and screw connections of brakes
- Prevention of sticking of the pistons of muzzle loading weapons and cannons
- Lubrication of sliding surfaces and plain bearings of valves and guides
- Corrosion protection at high temperatures and sealing against corrosive gases in the petrochemical industry and in power plants
Instructions for use
The use of metal-containing hot screw compounds with aluminum materials such as engine blocks or other base metals should generally be avoided. Connections between copper (noble metal) and a base metal behave like a galvanic cell and lead to galvanic corrosion (stress corrosion). The grease contained in the metal-containing hot screw compounds can only stop this reaction to a limited extent, but moisture and especially the presence of chloride ions (e.g. from road salt) accelerate it. Ceramic-based or aluminum or graphite-containing hot screw compounds ( graphite paste ) are more suitable here.
The surfaces to be prepared with the compound should be cleaned. With screw connections, the threads must be filled to the bottom.
Hot screw compounds are not suitable as a lubricant for roller bearings , as the rolling surfaces can be eroded by the solid matter contained in the lubricant.
literature
- Hans-Jürgen Blanke, Wilfried J. Bartz, Uwe Jens Möller: Expert Practice Lexicon Tribology Plus. 2010 Terms for study and work, 2nd edition, Expert Verlag, Renningen 2000, ISBN 3-8169-0691-5 .
Web links
- Choosing the right screw paste (accessed August 16, 2018).
- Screw lubrication basics and lubricant selection (accessed on August 16, 2018).
- [1] (accessed January 22, 2019).
Footnotes
- ↑ Entry 525 , "From Professor Blume's E-Mail Basket"
- ↑ The graphite paste Helvosyt GPO 80 according to the manufacturer Voelkel for application to aluminum die casting molds and intended thermally and mechanically stressed conveyor chains, gear racks, guide rails and other stressed machine elements and can be used up to 1000 ° C; accessed in February 2020