Method of applying friction materials to threaded article

The method of providing a circumferentially uniform tightly adhered shaped solid deposit of a friction-producing resin in the thread grooves of a series of externally threaded articles which comprises advancing a series of articles with the thread axis vertical and the threads extending to to the lower ends of the articles, applying a very dilute solution of a flow-promoting polymer to the sides of the articles as they advance and thereby providing a thin film of flow-promoting polymer over an area extending completely around the threaded portions above the lower ends thereof, applying at a limited zone within said area a quantity of a flowable essentially aqeous fluid mixture of a powder of a cured friction-producing resin and water, causing the fluid mixture to flow around the thread grooves to form a substantially circumferentially uniform deposit of the fluid mixture filling the bottoms of the thread grooves to a depth sufficient to interfere with at least the crests of the threads of mating articles, thereafter drying the articles to leave the resin powder as an essentially circumferentially uniform solid deposit of discrete, cohered, solid resin particles having the required cross-sectional shape in planes radial of the thread axis, heating the articles to melt the particles to fuse them together to form an essentially continuous resin deposit, and finally coating the articles to solidify the fused resin into a solid substantially continuous resin deposit concentrated in the bottoms of the thread grooves throughout said area.

The method of mass producing threaded metal articles provided with a deposit of resin throughout a predetermined area of the threaded surface in which the deposit is located entirely within thread grooves within the predetermined area, is substantially solid, has a circumferentially substantially uniform cross-sectional shape transversely of the thread grooves in which it is received, and has a fused bond with the side surfaces of the thread grooves;

• the cross-sectional shape of the deposit in each thread groove being such that the deposit fills the bottom of the thread groove, extends along the side of the groove to a point adjacent the crests of the threads, has an outwardly concave outer surface, and has a thickness measured from the bottom of the thread groove to the midpoint of said outer concave surface sufficient to interfere with the crests of the threads of a mating threaded article to provide a friction lock therewith;
• such method comprising the steps of
• advancing a series of the threaded articles on a conveyor with the axes of the threads vertical and with the threads extending to the lower ends of the articles,
• applying an extremely thin film of a very dilute solution of a flow-promoting polymer in a volatile solvent uniformly over the area on which the resin is to be deposited,
• depositing on a side of the thread surface with said area of quantity of a fluid mixture of particles of a previously cured fusible resin and a liquid carrier,
• causing the mixture to flow along the thread grooves within said area to assume the defined cross-sectional shape within the thread grooves,
• drying the deposit to eliminate at least most of the liquid carrier to leave the dried deposit essentially in the form of a shaped coherent mass of resin particles,
• subjecting the articles to heat sufficient to fuse the resin particles into a fluid condition,
• and adruptly cooling the articles to solidify the fluid resin by immersion into a liquid cooling bath while the articles are separated from one another to avoid adhesion between individual articles.