supply ZJSB brand spiral drill collar

ZJSB Sprial Drill Collars are manufactured from 4145H modified alloy steel . The full length of heat treatment adopts the original medium frequency inductance heating method. Strict metallurgical specifications are followed to insure that full length heat treating produces a consistent maximum depth of hardness. After this, a hardness range of 285 to 341 BHN are guaranteed one inch below the surface at room temperature.The bores are held to close tolerances by trepanning and are drifted to API specifications. The minimum external surface finish is hot-rolled and mill-finished. Connections are machined to API specifications and monogrammed with the API symbol. Connections are also machined to prevent galling. Thread roots are cold rolled to provide longer fatigue life.