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Characteristics And Description Of Electroplated Coatings For Threaded Fasteners
Jun 17, 2017

1. Thickness of plating layer for threaded fasteners

Threaded fasteners in electroplating process whether by plating, or plating process, in a number of products in each fastener for coating thickness is different, the same is the distribution of coating on the fastener is not uniform. For example, the thickness of the top of the screw thread is larger than the middle diameter and the base thickness of the tooth, and the thickness of the coating at both ends of the bolt and the bolt is thicker than the middle, and is more pronounced with the increase of the length diameter ratio. The nut is the same, because of the effects of shielding nut electroplating processing of the thickness of plating layer on the inner screw is very thin, only the two ends of the first buckle teeth than the middle part of the coating to be thick, the equivalent of six angle wrench on the surface of thickness.

2. How to describe the thickness of a batch of threaded fasteners?

In view of threaded fasteners to electrical inhomogeneity of coating thickness distribution, the standard was quoted in four on the coating thickness is defined, namely "nominal thickness, number average thickness and partial thickness" and "effective thickness". "Nominal coating thickness" means the nominal coating thickness of the threaded fasteners, which does not represent the actual coating thickness. The actual coating thickness of the threaded fasteners is described by the effective coating thickness. The "effective coating thickness" contains two aspects: "batch average thickness" and "local thickness".

In the third chapter of the standard text, the definition of "batch mean thickness" is defined. The plating layer thickness can not be threaded fasteners to the coating thickness to represent a part, regardless of the threaded fastener plating or barrel plating process, the same batch of parts in each of the parts can not reach the same thickness, but the thickness change obey normal distribution, we assume that the thickness of the coating is uniform distribution on the surface of the parts, to calculate the average thickness of the coating, which leads to the concept of "group average thickness", to describe the whole batch of threaded fasteners used for coating thickness number of average thickness value. In the standard table 1, "batch average thickness" is a range to indicate. The minimum batch thickness is the requirement to ensure the corrosion resistance of threaded fasteners, while the maximum batch thickness is the guarantee of the thread resistance of the threaded fasteners after plating.

"Local thickness" refers to the minimum local thickness in the standard, and the minimum local thickness describes the minimum value of the coating thickness that the thread fasteners should reach on the specified local test surface. The test data show that the surface of the bolt head wrench screw, screw, bolt, nut and the local coating thickness on the surface of the local test measured the specified value, the number is greater than the average thickness value, usually number average thickness values meet the requirements, the minimum local thickness can meet the requirements of. The test results also confirmed that the "nominal thickness, number average thickness and part thickness" numerical relationship is correct, which constitute the theoretical basis of the threaded fastener plating thickness testing, acceptance.

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