In brazing and tinning, rosin is usually used as a flux. Solid rosin is a prickly transparent mass with a color of all shades of amber. For the convenience of work, solutions of rosin in alcohol or acetone are often used, which are sometimes called liquid rosin.
Alcohol solution of rosin
The main function of rosin when brazing is to protect metal surfaces from oxidation. A solution of rosin in ethyl alcohol spreads better over the metal surface than molten rosin, which makes brazing more economical and the seal itself cleaner. Rosin in the form of a solution is applied to the cleaned metal surfaces before the soldering point warms up, which in turn further prevents the oxidation of these surfaces. A solution of rosin in ethyl alcohol is the least toxic in comparison with a solution in acetone, therefore it finds the greatest application in technology.
Getting rosin
You can get the rosin yourself if needed. Spruce or pine resin is suitable as a raw material. Take an old ceramic cup and wrap the inside of it with aluminum foil. Separately, in a metal can from under canned food, melt the resin, make it boil. Throw away the debris that has floated to the surface with a metal spoon. When the boil is over, quickly pour the liquid into a foil-wrapped cup. Wait for the rosin to cool, shake it out of the cup and peel off the foil. This process is flammable; these works need to be carried out in the open air. During the dry distillation of the resin, turpentine is released, the vapors of which are toxic, they cannot be inhaled. For the same reason, resin cannot be used for soldering.
Obtaining liquid rosin
Liquid rosin can be purchased. For example, it is sold under the brand name LTI-120. But you can make it yourself. Take a small glass jar with a tight-fitting stopper. Fill it with one third of the crushed rosin and fill it with ethyl alcohol. You can take both medical and hydrolytic alcohol, but it is obligatory to use 96%. Close the container tightly with a stopper. The preparation of liquid rosin for soldering does not require special precision, and all work can be carried out "by eye". With occasional agitation at room temperature, the dissolution process will take 2-3 days. Undissolved sediment may remain at the bottom of the vessel - this is debris. Pour the solution into a clean vial without disturbing the precipitate. It is best to pour liquid rosin into vials with a brush on the stopper, such a brush is convenient for applying flux to the surface.
Alcohol rosin varnish
Rosin is a vegetable gum. Solutions of vegetable resins in alcohol are called alcohol varnishes. Liquid rosin as a varnish is used to cover wooden products, which makes them moisture-proof and non-conductive. The hardened layer of rosin is quite acid-resistant, which makes it possible to use rosin varnishes when etching printed circuit boards, facilitating their further soldering. The disadvantage of alcohol rosin varnish is some residual stickiness of the surface after it dries, especially noticeable when heated. But some craftsmen know how to turn this disadvantage into an advantage, thus creating anti-slip coatings.
