Brush plating and anodizing are widely accepted for use in commercial and military applications。 With very few exceptions, brush-plated deposits and coat- ings will meet  the  performance  requirements  of their tank counterparts。 The specifications noted in Table  I  are the  industry  standards  for brush plating。

A brush-plating operation, in its simplest form, resembles painting。 The operator soaks or  dips the tool in a solution and then brushes or rubs it against the surface of the material that is to be finished。 The tools are covered with an absorbent material  that holds solutions so they can be applied to the work surface。 As  can be  seen in Figure  4, plating solution

Figure 4。 Schematic of the brush-plating process。

July 2002

touching the work surface。 The tool is always kept in motion whenever it is in contact with the work sur- face。 Movement is required to ensure a quality fin- ish。

Work surface preparation is usually accomplished through a series of electrochemical operations。 These preparatory steps are performed with the same equipment and tool types that are used for the final finishing operation。 There are  separate tools for each step of the preparatory procedure and for the final plating operation。 Good preparation of the work surface is as important as movement of the tools to produce a quality finish。

Plating a Turbine Generator Thrust Block Several alternatives were  considered  for  the  repair of a thrust block  bore  that  would  ultimately require a shrink fit onto  a mating  shaft (see Fig。  5)。

Making a new part was not cost effective。 Sleeving was ruled out because of the  dual keyways running the length of the bore。 Flame spray was seriously considered, but was then rejected due to concerns about adhesion。 Brush plating was chosen as the repair based upon the proven performance of the process, the lower cost, and quick turn time that it afforded。

The 14-in。 ID by 7-in。-deep thrust block bore had appreciable wear over its 30 years of service。 An 0。018-in。-thick deposit of nickel was plated and then ground to the finish dimension。 The repair was car- ried out by processing half the bore at a time。 The finished product was then heated and shrunk  fit onto its mating shaft。 As a side note, the shaft was misaligned on the first attempt and had to be removed and then reinstalled with  no  adverse effects  to the brush-plated  deposit。论文网

Corrosion Protection For OEM Components

A leasing manufacturer of compressors used for gas gathering and pipeline transmission uses brush plating in an OEM application where corrosion pro- tection is needed on their compressor housing bores。 A nominal thickness of 0。002 in。 of nickel is required。 After a localized degreasing operation, simplified masking techniques are used to  protect the outer face of the bore and to contain the solution within the work area。 The cast iron housing is pre- pared for the final plating operation as follows: elec- troclean, rinse, etch, rinse, desmut, rinse, and nickel preplate。 The plating  operation  is carried  out  using a mechanized system with opposing,  rotating anodes that are inserted into the bore。 Plating solu— tions is pumped through these anodes and is recov- ered and recirculated。 Nickel plating is continued until the desired  thickness  is  achieved。

Brush plating allows this manufacturer to selec- tively improve the performance characteristics on a localized area of a large and heavy component  and

SELECTIVE  ANODIZIMG

Selective anodizing is used when localized areas of large or complex aluminum assemblies need a coat- ing either to restore a previously anodized surface or to meet a specification requirement。 The principal types of selective anodized coatings are chromic, sul- furic, hard coat, phosporic, and boric-sulfuric。 In mil- itary and commercial applications, brush anodized coatings are usually applied for dimensional restoration, corrosion protection, or to provide wear resistance  to  a localized area。