Racking techniques affect the most important aspects of your business: profitability and quality. This direct relationship between racking and the bottom line is frequently overlooked by anodizers, mainly because racking is usually the first and simplest operation in a series of steps. Before we discuss the many forms and characteristics of racking, lets recall its two basic functions. First, it must provide an efficient method of transferring parts from tank to tank while holding them securely during anodizing. Second, it must form a positive link in the electrical circuit for carrying current to the parts. Some anodizers, reading this "textbook" information, may feel that it is so obvious that it needs little attention. The fact, however, is that it is the key to profitability and quality and no anodizer can afford to overlook its importance.

Internal and External Factors

Racking characteristics can be divided into two groups: internal and external. Internal factors relate to the part itself weight, surface area, shape, finish required, etc. External factors include the process environment: tank size, hoist or manual lift capacity, rectifier capacity, etc. Analyzing these factors in a methodical way will result in guidelines for proper racking. This type of analysis is called the "Ruling Characteristic Method." Used mostly in medium to high volume jobs, it requires study of both internal and external factors in relation to each other, with the result that many of each eventually cancel others. The remaining factors become your guidelines for racking and pricing. Study the steps in the example to understand the basics of this method, which ensures that all factors have been considered.

Contact Quality

The importance for quality work of this second consideration in racking can scarcely be exaggerated. It comprises two concepts: surface area and pressure. With surface areas there are typical or standard guidelines for the appropriate contact patch for a specific size of part. Pressure, in the majority of cases should not be varied. Its purpose is simply to hold the part securely enough that arcing does not occur during anodizing. The idea is simple, but proper pressure is crucial to good quality anodizing.

There are, however, certain cases in which great pressure may satisfactorily replace numerous contact points. Great pressure ensures that however poor the conductivity of titanium, it will be optimized. This type of racking may be applicable when rack marks must be kept to a minimum. For example, one titanium screw clamp may hold a part securely enough to pass the required current. When using high-pressure racking, always be sure to check whether the clamp is deforming the part by leaving a dimple. This may be unacceptable, ruling out this method.

Whether you design your tooling with surface area or pressure as the dominating factor, or a satisfactory combination of both, the racking must prevent the contact point(s) from breaking or wandering. If this happens, resistance will build up and anodizing will stop or arcing will occur. Any movement of a part during anodizing will result in inferior work.

The fact that titanium does not anodize leads to an interesting observation about resistance. Compare a part held on an aluminum rack (Case 1) with that same part held on a titanium rack (Case 2). If movement of the part on a prong occurred in Case 1, there would, in effect, be double resistance, as both the part and the rack would be anodized. If movement occurred in Case 2, resistance would be only because of the anodic coating. The conclusion may be drawn that in Case 2 the resistance may be low enough to permit completion of the anodizing process. It should be pointed out that Case 2 is predicated on movement occurring during the first ten percent of the anodizing time, and that use of a titanium rack may permit recovery from an undesirable situation. Recovery at a later stage in Case 2 may not be possible.

Configuration

The experienced anodizer must look at a part and anticipate problem areas. The most frequent problem related to the parts themselves is blind holes. The result of not addressing this problem correctly is "bleeding" from the holes because of chemical entrapment. The only solution is high pressure rinsing directly into the holes. Avoiding this problem should be a major consideration in racking configuration. Difficult areas should be as accessible as possible. For this reason atones blind holes must be included in the ruling characteristic method.

There are two basic types of configuration: picture-frame and bookend. The number of pieces possible per rack is far greater with bookend configuration, but parts having blind holes may require lower density racking to permit access for good rinsing as shown.

To summarize, keep in mind the following guidelines. They will help in substantially increasing profitability and quality.

1. Use the "Ruling Characteristic Method" to determine the lowest allowable factor. This is your guide for pricing and rack engineering.

2. Look at parts as an experienced anodized pinpointing potential problem areas. Include them as factors in your analysis.

3. Consider efficiency factors of aluminum and titanium, as discussed in this column last month to choose the proper material for rack construction.

4. Use the sample worksheet shown to analyze all your volume jobs.