A correct pre-plate preparation is essential to obtain the maximum adhesion between the material to be plated and electrodeposited chromium. There are three general areas of consideration for the preparation of the base material: The Base material itself, cleaning and activation.

A plater must determine the type of base material and finish prior to plate. Chromium plating magnifies and exaggerates imperfections on the surface of the base material.

To obtain a smooth chromium plated surface, it is necessary to start with a smooth and defect free surface. This smooth, defect free base material must also be clean and free of surface contamination. The source of contamination can come from a smeared layer of the base material that was not removed in the metal forming operation, embedded shot from a shot peen process or layers of films such as grease, oil or dirt. The cleaning of the base material varies with the material at hand, i.e., Cast iron, stainless, inconel or carbon steel and their subsequent finish call outs.

Many hard chrome plated materials are later mechanically ground to a finish dimension. In this case, materials are degreased, alkalined cleaned if required and blasted with aluminum oxide to specification prior to plate. After this cleaning, it is essential that the parts be moved through any masking operation and into the plating solution within a specific time so that oxidation is not permitted to occur.

Once material has been identified as to its composition and cleaned properly to specification, it is introduced into the plating solution or pre-plate etching solution for activation. The pre-plate etching procedure varies depending on the base material. Many steels are anodically or reversed etched in a chrome tank prior to plate. This microscopic etching of the base material is essential for proper adhesion of the chromium. High heat treated steels are sometimes required to be etched in a special bath consisting of sulfuric and hydrofluoric acids prior to introduction into the chromium solution for plating. Stainless steels and high nickel alloys show much greater adhesion with chromium if cathodically activated in a bath of low concentrated sulfuric acid prior to plate. The amount of time for these etchings or activation operations vary as to the material and specification. As you may suspect, many of these solutions have the ability of over-etching so care must be taken in their utilization.

Chromium and its substrate do not have an absolute bond. the bond can be broken through abusive use, improper grinding procedures that produce excessive heat or a corrosive chemical that is not compatible with the chromium deposit.

We hope this summary of pre-plate preparation gives you some insight into how essential a lean and properly prepared surface is when creating a long lasting and durable bond between a chromium deposit and a substrate.

In our next newsletter, we will give you a look at one of the most misunderstood and overlooked areas of manufacturing when using heat treated materials.