Screw locking varnish
Screw locking varnish is a special adhesive that is attached to or in a screw connection in order to prevent or make it difficult for the screw connection to loosen independently and undesirably. It is also used to indicate unintentional or unauthorized loosening of a screw connection. The term screw locking varnish, which is common in German-speaking countries, has nothing to do with the varnishes for surface coating.
Screw locking varnish is available in different strength classes and for different temperature ranges. In addition to almost completely hardening variants, which achieve a very high level of strength and are suitable for permanent connections that can only be detached with difficulty or under the action of heat, there are also variants that remain in a viscous, sticky to rubbery state and allow the screw connection to be subsequently loosened or the Sealing of existing screw connections are used. The choice depends on the area of application. To distinguish between the different types, they are uniformly marked in different colors across all manufacturers.
General
Screw locking varnishes are based on methacrylate and cure independently of air and without evaporation of solvents in the presence of certain metals such as iron, steel, copper or brass to form a polymer . When storing screw locking varnish, these metals must be kept away and contact of the adhesive liquid with adhesive that has already polymerized must be avoided, as this would otherwise lead to premature solidification of the adhesive in the storage container. With metals such as aluminum, it may also be necessary to apply a special primer in order to safely initiate the polymerization. It may also be necessary to clean the thread before using the threadlocker.
Some screw locking varnishes are thixotropic liquids whose flow properties are time-dependent. As a result, the less firmly hardening variants have a high level of resistance to short-term impacts or vibrations , but can be loosened more easily with longer, evenly applied torque . Screw locking varnish for already existing screw connections serves as a seal, for example with adjustment screws, and therefore has a rheopexic behavior. For this application the adhesive is very thin, penetrates the thread gap and fixes the elements permanently after hardening. These screw connections can be loosened more easily with sudden torques than with a constant torque.
Some characteristic values are summarized in the following table, the torques are based on the application of a steel screw with inch thread 3/8 "-16 and a suitable steel nut .
| Type | colour | Impact torque for the solution, guide value in [Nm] |
Continuous torque for the solution, guide value in [Nm] |
|---|---|---|---|
| Low strength (thixotropic) |
7th | 3 | |
| Medium strength (thixotropic) |
12 | 6th | |
| High strength | 25th | 25th | |
| Sealing (rheopex) |
10 | 35 |
Individual evidence
- ↑ Threadlocker Gel, Application Note. Permatex, accessed August 24, 2019 .
- ↑ a b c d Threadlocking User's Guide. Henkel, accessed December 22, 2014 .