Racking Materials & Design (Part 2 of 2)

It’s probable that your customer has never given any thought to the material or the design of the tool that their part will be racked on, and for many of them, that’s fine. However, since a well-designed rack/tool can cut your lead time, lower your cost and provide for consistent quality, it is something that should be considered.

When is it appropriate, you ask? The answers are more complex than the simple answers here but if you process the same parts over and over, are concerned with cost, or your customer wants specific and well placed racking, you may want to consider specialized tools. High volume is NOT the only reason to consider specialized racks/tools. I have worked with many customers to design tools that specifically address concerns they have about their parts regardless of volume. In addition, many customers are willing to pay for this to insure good quality and the lowest pricing, not to mention that it is likely to reduce their turn time at the anodizer.

Usually, specialized racks mean, titanium racks. Titanium racks have long life because they are not consumed by the chemistry and they do not need stripping after anodize. They offer repeatable quality, lower part cost and/or faster turn times but these racks/tools can be expensive.

Aluminum racks/tools must be stripped after each anodize cycle and this, as well as the anodizing itself, consumes them and therefore the part price must be reflected in this. They are also seldom a perfect fit for the part but rather adjusted or adapted to the piece. While aluminum is less expensive, it is not cheap, and usually must be discarded after several cycles. In addition, since they are not specialized enough to maximize production quantities, turn times can be longer if there is even moderate volumes.

There are thousands of specialized tools/racks designed for a variety of products and your part may be a candidate for such treatment. Cost and productivity are at stake. 

This post was submitted by AAC Member Jack Tetrault, President of the Sanford Process Corporation.

 

Racking: Function and Location (Part 1 of 2)

Can you anodize a part without leaving a rack mark?

The simple answer is no, BUT, you can help reduce the potential of having rack marks become a problem by helping the anodizer understand the product or by providing a location where the mark will not be objectionable.

Racking serves two functions. 1) It provides a way to hold the part during the process and 2) It is the means by which the current (electricity) enters the part. It is the latter of the two that is often overlooked by designers and engineers and it’s the most important function because supplying the correct current is crucial to obtaining successful anodizing quality. Anodic coatings are applied as a direct relation to the surface area of the part. The contact area (rack mark) must be able to accept 10- 50 amps per square foot (ASF) depending on whether the anodic coating applied is type II and type III (hard coat). This means that the size of the mark cannot always be a pinpoint. For either case it is imperative that the contact (rack) be very tight.

 There are many, many racking methods and here are a few common practices:

1)    Squeezing the part between two or more contacts that wish to remain closed.

2)    Squeezing the contacts that wish to remain open and inserting in a hole or opening in the part.

3)    Threading a bolt into an existing threaded hole or using a nut and bolt combination in a hole and tighten to make contact.

4)    Clamping with a C-clamp device against an aluminum or titanium bar 

Often, anodizers are forced to take an educated guess as to where an acceptable rack location would be because we have not been provided any information. Providing a good place for a solid rack contact is tantamount to a successful anodic coating.

This post was submitted by AAC Member Jack Tetrault, President of the Sanford Process Corporation.  (Part two will be posted on 2-19-14.  Please return to check it out.)