1, the coating thickness of threaded fasteners
Plating processing for threaded fasteners used in plating or a plating process, in a number of products in each of the fasteners of the thickness of the coating obtained is different, the coating is the same on fasteners is not evenly distributed. Top of thread coating thickness than the diameter and thickness of the root, coating thickness thicker than the middle of both ends of the screws, bolts, and increasing with the more significant aspect ratio. Nuts are the same, due to the shielding effect of screw machining, plating layer thickness on the internal thread is very thin, only ends the first detention than the middle part of the coating thicker, or hex wrench screw on the surface of thickness.
2, how to describe a number of the coating thickness of threaded fasteners
In view of threaded fasteners-electroplated coatings of thickness unevenness, four on coating thickness of the standards referenced in the definition of "nominal thickness", "average" and "partial thickness" and "effective thickness". "Nominal thickness" means the nominal coating thickness of threaded fasteners, not representative of the actual thickness. The actual coating thickness of threaded fasteners is to use "effective thickness" to describe. "Effective thickness" contains a "thickness" and "partial thickness" two aspects of it.
In the standards body 3rd chapter of "average" was defined. Thread tight firmware of plating layer thickness cannot to a parts of coating thickness to representative, regardless of used hanging plating or roll plating process processing of thread tight firmware, with batch parts in the each parts cannot reached also of coating thickness, but thickness of changes is obey distribution of, we assumes that coating thickness is uniform distribution in the batch parts of surface, to calculation coating of average thickness, this on leads has "batch average thickness" of concept, can with batch average thickness value to description whole batch thread tight firmware of coating thickness situation. Standards in table 1 "thickness" is expressed as a range. Is to ensure that the minimum average thickness corrosion-resistant requirements for threaded fasteners, and a group of average thickness is guaranteed post thread in screw-threaded fasteners.
"Partial thickness" actually refers to the minimum local thickness in the standard, description of minimum local thickness is threaded fasteners within the specified local coating thickness of the test surface should reach the minimum specified value. Test data show that the heads of screws, bolts and screws, bolt, nut wrench screw surface, which local local coating thickness values measured on the test surface, are greater than the average thickness value, usually average thickness value meets the requirements, minimum local thickness can meet the requirements. Test results have confirmed the "nominal thickness", "average" and "partial thickness" values are correct, this constitutes threaded fasteners-electroplated coatings of thickness, and acceptance of the theory.