BASIC FUNCTIONS OF A JIG AND RACK

Proper jigging is a critical part of anodizing and must successfully accomplish at least three basic functions:

• Hold the part securely during transfer between process tanks and while immersed in a vigorously agitated solution
• Provide contacts with the work that will safely conduct enough current from the source to the part to provide a uniform coating
• Provide adequate drainage of the work, leaving no pockets of residual solution trapped in the components

FACTORS IN JIG AND RACK DESIGN

The following factors need to be taken into account in jig and rack design and the way in which components are secured on racks:

1) Suitability for the process sequence and solution used

2) Ease of loading and unracking of parts

3) Prevision of secure contact points which ensure a uniform coating

4) Location of jig marks in positions accep­table to the customer

5) Density of loading of the components must balance the economics of bath loa­ding against dangers of local overheating and shielding

6) The rack must be cost effective in terms of the quantity required and the revenue from the job

FUNCTIONAL FEATURES

The basic need is to secure properly the components on the jig and for them to be retained throughout subsequent processing. The choice of design is often a matter

of experience and judgment. The follo­wing factors have to be taken into account:

• The size and weight of the part
• Sensitivity of work surfaces to prevent damages from clamping
• The locations where trapped gas or liquid pockets may occur
• The amount of current required by the parts on the jig
• The position and number of points where contact marks may be allowed

MATERIALS FOR ANODIZING JIGS AND RACKS

In the early development of anodizing racks and jigs were made exclusively of alumi­nium, usually pure aluminium, which had the disadvantage of being soft and readily damaged. However, this has been overcome to a large extent by the use of heat treata­ble alloys, such as 6061 and 2024. In high volume applications, titanium has now become widely used. Aluminium has the fol­lowing advantages:

1) Low initial cost

2) Ease of fabrication

3) High level conductivity

4) Proper conductivity for electrocolouring

Offsetting these factors are the following disadvantages:

• Progressive weakening by chemical attack in etching and by chemical polishing
• Less robustness in handling terms