1, Chrome plating production line proglgue:
Copper alloy with good features of corrosion resistance, excellent heat conductivity, excellent plasticity and certain mechanical strength, etc., where widely applied in the industrial field. Chrome plated copper alloy surfaces can increase hardware parts surface hardness, wear resistance, corrosion resistance and decorative.
However, unskillful technical process operation of brass plating chrome production line, will cause white stripes, spotted, shelling, blistering, poor bonding failure on brass surface, and poor brightness chrome plating: such as the surface of gray, dark, hair spray, etc., then effect the chromic plating layer quality.
Following, we’ll from chromium plating production practices based on brass, beryllium bronze alloy parts, to analyze, summarize the key factors of chrome plated copper alloy, then to improve quality of chrome plating.
2, Material properties of the copper alloy and chrome plating process analysis and countermeasures:
Main material of brass is copper and zinc alloy, while zinc alloy is easy to dezincification corrosion and cracking, so when brass plating chrome production line in plating pre-treatment, need to prevent zinc dezincification.
HPb59-1 easy cutting brass contains a small amount of lead, in the conventional etching activation, it is difficult to dissolve lead, then often lead to chromium plate layer poor bonding. Copper is a copper alloy in addition to zinc, nickel elements, commonly used are copper tin alloy, as well as phosphor bronze, aluminum bronze, beryllium copper and so on. Beryllium bronze materials with high strength and hardness, and the fatigue limit, elastic limit, wear resistance, corrosion resistance are all very good, but also has heat conductivity, cold-resistant, non-magnetic, by the shock does not produce sparks, etc., so beryllium mostly to be used to manufacture elastic parts or wearable parts. Beryllium copper use copper as base material, containing beryllium: 1.7%～2.5%, and nickel: 0.2% ～ 0.5% and a trace titanium.
As an example QBe1.9 beryllium materials with a wide range of applications. The content of beryllium is 1.8%～2.1%, nickel: 0.2%～0.4%, titanium: 0.1%～ 0.2%, the balance being copper. Beryllium, nickel, titanium are elements of easy to passivation, beryllium bronze surface even in atmosphere air will quickly generate a dense layer of invisible passive film. And beryllium copper materials are generally required by quenching, aging processes such as heat strengthened, even with vacuum heat treatment, then surface oxide film will more denser. If parts of surface with oil, easier to generate grease, stains and so on.
So before chrome plating process, must select the appropriate pre-treatment process, make sure that the surface is in the activated state, to ensure chromium plating quality. Brass, beryllium in short time surface passivation easily when chrome plating energized, and even cause dissolve corrosion, which is the key reason of chrome plated brass quality.
3, Chrome plating production line pre-treatment:
The degreasing process before chrome plating of copper alloy not suitable for dipping alkali solution for a long time.
3.1, Brass parts corrosion activation:
Parts of the surface contain oxide or heavy black oxide film, must be pre-etching.
Temperature: room temperature;
Time: 1 ~ 5 min.
After descaling the pre-etching, to activate the surface by using of light etching.
For surface has smooth finish, minor oxide film parts, after degreasing process the surface oil purification can be fully activated in 10% sulfuric acid solution, then can be carried out for chrome plating operation.
4, Chrome plating equipment for brass:
Chrome plating production line for brass alloy parts using standard chromium plating processes. Copper alloy parts must be charged into baths, general should transmit small step cathode current power, especially for beryllium parts, cathode current density degree from 2 A/dm2 gradually rise to 5 A/dm2. Since cathodic hydrogen evolution, and the new ecological hydrogen atom precipitated with a strong reducing ability, can make the copper alloy surfaces passivation coating in particular beryllium bronze reduction and activation, that is very beneficial to improve the bonding strength of chromium plating equipment.
But be careful, charged into the tank, do not anode anti-plating, can effectively avoid passive film formed on the surface coating then to effect surface bonding force, and also avoid parts surface to dissolve corrosion to affect chrome plating quality.
Can adopt strike current (1.5～2 times compare to the normal current density) strike plating 30-60s, and this is particularly necessary for more complex shape parts.
Then resume normal current density chrome plating. In chrome plating process should always pay attention to the anode and cathode conductive good, should be appropriate to adjust the distance and position between the anode and cathode according to the shape of parts, in order to obtain a uniform layer of chrome, to make sure chrome plating quality.
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