What is a liquid wrench?
This name has become a household word for a class of lubricants whose main purpose is the ability to penetrate the smallest gaps of threaded joints that have “seized” together, to soften the rust binding them, to lubricate the friction surfaces where possible and to make it possible to undo a nut or bolt that seemed to be “welded” solid. When creating “liquid wrenches”, therefore, developers give priority to exactly the penetrating ability of these compositions, often deliberately sacrificing lubricating properties.
Why was molybdenum disulphide introduced into the composition of the liquid wrench?
The creators of any penetrating lubricant face a fairly difficult task. For the lubricant to penetrate the very smallest gaps well, its composition must include substances with short molecular chains. But such oils have low lubricating ability, and although that is not the main property it is important too, because it makes it easier to undo “seized” fasteners. Substances with good lubricating ability, on the contrary, have long molecular chains and, because of the “bulkiness” of their molecules, have weak penetrating properties. Molybdenum disulphide is precisely what helps to resolve this contradiction. It mixes well with oils and penetrates the very smallest gaps together with them. At the same time molybdenum disulphide bonds excellently to metals and is itself an excellent lubricant.
Why is molybdenum disulphide so good as a lubricant?
Molybdenum disulphide consists of two sulphur atoms and one molybdenum atom. Sulphur atoms bond well to metal atoms, while the sulphur atoms of neighbouring molecules are bonded to each other quite weakly. As a result the molybdenum disulphide molecules cover the metal surface with a sufficiently strong layer, while all the subsequent layers of the disulphide slide over one another very easily thanks to the low bonding of the sulphur atoms to each other. Molybdenum disulphide only needs to be delivered to the friction surfaces; it will cover them itself with a slippery and at the same time very strong film. It is notable that this film is not only a good lubricant but also protects the surface from corrosion to a certain extent.