中文版Fastener knowledge - surface treatment
Fastener knowledge - surface treatment
Surface treatment type:
The surface treatment is forms the overburden layer through certain method in the work piece surface the process, its goal is bestows on by the product surface is artistic, the corrosion preventing effect, carries on the surface treatment method sums up in the following several methods:
1st, galvanization: Will accept the galvanization the part to soak in includes by in the deposited metal compound peroxide solution, through plates the fluid by the electric current, causes the metal coating to separate out and to deposit on the part. Generally the galvanization has the galvanization, the copper, the nickel, the chromium, the cupro-nickel and so on, sometimes boils black (bluing), the phosphorization and so on also to include in which.
2nd, galvanizing by dipping: Through carbon steel part immerse temperature approximately for 510℃ the dissolve zinc plates in the trough to complete. Its result is on the steel stock surface hard zinc base alloy turns in the product outside surface gradually the deactivated zinc. Hot dipping aluminum-plating is a similar process.
3rd, the machinery plates: Attacks the product surface through the coating metal's particle, and coating cold welding to product surface.
Generally the screw selects the galvanization method, but uses in the electric power, the highway and so on outdoor hexagonal wood screw urgently needs the hot dipping zinc;
Galvanization effect:
The galvanization quality take its anti-corrosive ability as the main measurables, next is an outward appearance. The anti-corrosive ability imitates the product working conditions, establishes for the test condition, performs the corrosion test to it. The galvanization product's quality controls from the below aspect:
1st, outward appearance:
The product surface does not allow to have partial does not have coating, the air burn, rough, gloomy, the sand buckle, the mantle condition and the obvious stripe, does not allow to have the pinhole hemp spot, the black to plate the dregs, the deactivated membrane to be loose, the chap, falls off with the serious deactivated trace.
2nd, coating thickness:
Fastener's is proportional in corrosive atmosphere work life with its coating thickness. Generally suggestion economical galvanization coating thickness is 0.00015in~0.0005 in(4~12um).
Galvanizing by dipping: The standard average thickness is 54 um (name diameter ≤3/8 is 43 um), the smallest thickness is 43 um (name diameter ≤3/8 is 37 um).
3rd, coating distribution:
Uses the different deposition method, coats the accumulation way is also different on the fastener surface. When galvanization coats the metal is not deposits evenly in the circumference edge, the corner obtains coats thick. In fastener's thread part, the thickest coating located at the crest of screw thread, thins gradually along the thread side, is thinnest in the tooth bottom place deposition, but galvanizing by dipping just right opposite, the thick coating deposition in the inside lock and the thread base, the coating metal deposit tendency which and the hot dipping the machinery plates plates same, but smoother moreover thickness must be much evener on the entire surface.
4th, hydrogen embrittlement:
The fastener in processes and in the treating processes, especially before plating acid pickling and soda wash as well as in afterward galvanization process, adsorption hydrogen atom, deposition metal clad then capture hydrogen. When the important firmware screws tight, the hydrogen suffices toward the stress most centralized revolution per minute, to cause the pressure to advance to surpasses the parent metal the intensity and has the small skin breakage. The hydrogen moves in specially the crevasse which and permeates very quickly forms newly. This pressure - breakage - permeating circulation has continued to the fastener break. Usually occurs after within first secondary stress application several hours.
In order to eliminate the hydrogen embrittlement the threat, the fastener must after plating heats up quickly as far as possible cures, causes the hydrogen to seep out from coating, cures usually (176-190℃) carries on 375-4000F for 3-24 hours.
As a result of the machinery galvanization right and wrong electrolyte, this in fact eliminated the hydrogen embrittlement threat.
