Fastener knowledge

by:MPS     2020-07-18
Is through certain types of surface treatment: surface treatment methods on the workpiece surface coating process, its purpose is to assign to products is beautiful, anti-corrosion effect, the method of surface treatment are attributed to the following: 1, electroplating, will accept the plating parts immersed in aqueous solution containing was deposited metal compounds, with current through the plating solution, plating metal precipitation and deposition on the parts. General plating has galvanized iron, copper, nickel, chromium, copper, nickel alloy, etc. , sometimes cooking black ( Blue) Also including, phosphating, etc. 2, hot dip galvanized, immersion temperature about 510 ℃ by the carbon steel parts finish in melting zinc plating bath. As a result, the steel on the surface of zinc iron alloy melted into passivation of zinc on the surface of the product appearance. Hot dip aluminized is a similar process. 3, mechanical plating: through the surface coating metal particles to impact the product, and the cold welding coating on the surface of the product. Adopts the electroplating method more general screw, but used in electricity, highway and other outdoor hexagon wood screw with hot dip zinc; The cost of electroplating generally 0 per kilogram. 6 - — 0. 8 yuan, hot-dip zinc in general is 1. 5 - — 2 yuan/kg, the cost is higher. The effect of plating: plating quality for its corrosion resistance ability as the main measure, the second is the appearance. Corrosion resistant ability is imitation products work environment, is set to the test conditions, corrosion test them. Electroplating to control the quality of the products from the following aspects: 1, appearance: product surface are not allowed to have a local without coating, burning, rough, dark, peeling, the condition of crust and stripes obviously, there is no pinhole pitting, black plated slag, passivation membrane loose, crack, fall off and the serious passivation. 2, the thickness of the coating: fasteners in the operation life of corrosive atmosphere and its coating thickness is proportional to the. General advice economic plating coating thickness of 0. 在0 ~ 00015。 0005 in( 4~12um) 。 Hot dip galvanized: standard of the average thickness of 54 um ( 43 um call diameter 3/8 or less) , the minimum thickness of 43 um ( Call diameter 3/8 or less 37 um) 。 3, coating distribution: using different methods of deposit and the coating on the surface of fasteners on the way is different also. When plating coating metal is not evenly deposit weeks outside edge, corner to get thicker coating. In fasteners, threaded portion, the thickest deposit is located in the top thread, along the thread profile gradually thinning, the thinnest the sedimentation of the tooth to ascend, and the opposite of hot dip galvanized, thicker coating deposition, corner and the bottom of the thread, the mechanical plating coating metal deposition tendency of the same as the hot dip plating, but more smooth and thickness is much more evenly across the surface. 4, hydrogen embrittlement: fasteners in the process of machining and processing, especially in the acid and alkaline cleaning before plating and subsequent electroplating process, the surface absorbed hydrogen, deposition of metal coating and then capture hydrogen. When the fastener tighten, hydrogen turn towards the part of the most concentrated stress enough, cause the pressure increased to more than the strength of the matrix metal and generate small surface rupture. Hydrogen special events and quickly penetrate into the newly formed fractures. The pressure - Break - Into the cycle of continued until fasteners fracture. Usually occurs within the first hours after the stress application. In order to eliminate the threat of hydrogen embrittlement, fasteners to heated baking as soon as possible after plating, in order to make hydrogen leak out of the coating, usually in the 375 - baking 4000F( 176 - 190℃) 3 - 24 hours. Due to mechanical galvanizing is the electrolyte, which actually eliminate the threat of hydrogen embrittlement.
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