Cast iron is the carbon content as high as 2% (
The mass fraction)
Above, iron carbon alloy material is only a small amount of the carbon in the form solid solution with iron, mostly in the form of graphite or cementite exist, because the graphite will reduce the deposition potential of hydrogen, which hindered the deposition of zinc.
At the same time due to the material surface is too rough, across the sand holes and shrinkage cavity, composition containing phosphorus, sulfur, silicon and graphite and titanium, and other elements, thus appeared the overpotential of hydrogen in the process of plating is too low, easy to cause hydrogen evolution, brings to the metal deposition difficulties;
And pickling and can increase the adsorption quantity of hydrogen atoms, part into hydrogen adsorption of hydrogen atoms, in addition to send out into the air, it will be a part of the hydrogen atoms to spread in the cast iron matrix, the more hydrogen pressure, not only affects the mechanical properties of cast iron itself, in the process of electroplating can also cause a large amount of hydrogen evolution, not only seriously influence the coating fastness, still can cause JiJu current efficiency drops, to further increase the difficulty of electroplating.
Iron plating after for some improvement on the quality of the coating obtained from appearance can get satisfactory effect, but due to the particularity of its material itself has, coating on the substrate of the protective far can not meet the requirements.
For this, put forward the following Suggestions, reference for structure designer and mechanical, plating the technologist.
Plating pieces of the structure design of casting
forming technology on less as far as possible, especially in the use of a bad environment conditions.
Must be the casting molding, suggest the aluminum die casting or copper alloy casting.
Other coating process instead of electroplating, such as paint, plastic spraying.
After the workpiece forming can increase the sandblasting process before plating.
Using potassium chloride galvanized instead of zincate zinc plating.
This problem the author take the following measures at four o 'clock.
1) wipe brush oil removal instead of electricity to remove oil.
Because iron castings with shrinkage cavity, porosity and sand holes and component contains many impurities, therefore not suitable for oil by electric lift.
Otherwise it will because of severe seepage hydrogen or difficulty increases when the oxidation of iron itself to electroplating.
Using chemical degreasing dip in with cotton whitewash brush brush again after oil removal method of combining instead of electricity to remove oil is relatively ideal, the brush brush in water with brown brush after again, can make into sand holes of the place such as dirt washed clean.
(2) sand instead of pickling.
Using sand instead of pickling to avoid acid hydrogen permeability, reduce the pressure of hydrogen, in case of affect the mechanical properties of casting itself, to improve current efficiency, help to metal deposition and enhanced the adhesion strength of the coating.
(3) adjustment process of the activation solution formula.
Adjust the process of the activation solution formula is in order to adapt to the needs of iron itself characteristics.
Experiments show that by applying this process of cast iron parts before plating activation formula has the strong ability of activation.
Formula and technological conditions for 50 ml/L hydrochloride, hydrofluoric acid, 50 ml/L, room temperature, time 0.
5 ~ 1分钟。
(4) the early impact current when plating.
After plating pieces into the slot with 3 ~ 5 times higher than normal current electroplating current density, can make the casting surface after 1 ~ 2 min first to form a thin layer of coating, and coating on this with slightly higher than the normal current density can be deposit out of normal coating, which effect is remarkable.
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comes in a vast array of styles and quenching furnace manufacturers depending on which quenching furnace manufacturersis used.