Quality improvement achieved by the comprehension of the flaw of surface finishing process

In order the machine parts after processed with surface finishing play the normal function in the production site in use, the processing quality becomes most important. Here, you are introduced some of the typical surface finishing processing, namely, plating.  Comprehension of a series of flaw including the surface preparation would lead to the prevention of the troubles such as “Surface finishing does not have the uniformity” or “Partial peeling of plating occurred”.

Common situation of metal surface to which plating is to be struck

Plating bath which contains plating solvent and anode and flaw strainer to flaw electricity are required to strike plating to metal. But acquisition of those facilities and equipment alone are not enough to enable quality plating. In order to materialize the high adhesive coating to satisfy the required functionality of the target, it becomes essential to remove the surface fouling (metal is usually covered by mill scale) left on the surface of base metal. Generally, metal surface which is to be surface finished after the process of machining, is composed of, from the top to the down layer ①fouling layer (refuse and oil), ② layer of corrosion, ③oxide layer, ④work-decomposition layer and ⑤ diffusion layer formed of the mixture of work-decomposition layer with material metal tissue. In order to perform the quality plating, it is indispensable to remove at least ① ,② and ③layer from the meta face, occasionally depend upon the case layer ④and ⑤may also be required to remove.

Sample chart of the metal surface section to perform surface finishing processing

The surface of the base metal after the machining process has been composed of the layers of various fouling, corrosion and oxide as shown above.

 

The quality of surface finishing is decided by preparation and analysis of the base metal in advance

Effective removal method of fouling and corrosion formed on the metal face are as follows, degreasing: removal of refuse and oil, and acid treatment (activation): removal of metal surface oxidized layer and work-decomposition layer. Quality of plating largely depend not only on the freshness of plating solvent, plating bath and electrode positioning but also on the technology of surface finishing company whose ability of preparation before coat formation. Since each metal requires respective pretreatment, so the technology to correctly analyze the state of metal surface before surface finishing processing decides the difference of quality creation. In this context, it leads to the reduction of trouble happening that order placing company provides surface finishing company with sufficient information as much as possible not only notify the meatal name of being iron, stainless steel or aluminum but also in terms of JIS standard. In case of plating, “Plating layer” is not simply placed on the metal surface, but plating layer closely adheres with base metal. Plating processing brings about the perfect bonding state with interatomic power of the plating atom with the base metal atom. The reason why removal of fouling layer, corrosion layer, and oxidized layer are important, as the pretreatment of plating, is that it is a means to access metal atom to the atom of base metal. If you take the explanation granted, you may have the easier understanding of the importance of the analysis of metal materials and pretreatment for them.

 

The table of available metals for electroplating (The periodic table of element)

Depend upon the kind, surface finishing cannot be given to all metals, for reference. In case of electroplating, 35 elements are available out of 75 elements below.

The electroplating available elements are red-colored 30 elements out of 75 elements. If formed into alloy the numbers become + 5 elements.