Precision Slitting

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Slitter Tooling Oxidation and Etch Fade

Two of the most common problems associated with the use of slitter tooling are spacer rust accumulation and the tendency of the etched thickness markings on thinner parts to fade over time.

Rust problems are particularly troublesome with high-tolerance shimless tooling sets that have been manufactured to thickness tolerances of ±.000040 of an inch. Since shims are not used to correct thickness discrepancies, even minor buildups of rust on the spacers can lead to less than perfect setup associated with shimless tooling. Even conventional tooling (±.0002" thickness tolerance) sets can be affected by excessive oxidation, since individual pieces within a thickness size group may have values outside of the tolerance range, leading to time-consuming adjustments in the setup.

How can one overcome the natural tendency of steel to oxidize or rust over time?

Certainly, the least expensive method is to carefully handle and maintain the tools before and after each usage (see DIENES' flyer on Slitting Tool Care and Maintenance).

Raised nicks or gouges in the spacers should be carefully field-dressed using the proper stones. Minor oxidation can be removed using "Scotch Brite™ " or fine grit (#500+) abrasive paper. After usage, tools should be wiped clean and coated with a light application of oil.

Another method of prohibiting rust formation is to treat spacer tooling with a protective coating during the manufacture of the tool. This method is especially effective in regions that are subject to warm/moist climate conditions, or areas that have wide temperature fluctuations, where even the best maintenance techniques cannot prevent minor rust formation.

DIENES offers two types of protective coating for spacers. The least expensive is a black oxide treatment. This hot-dip process is nondimensional (not affecting the thickness tolerance), and therefore is done as a final operation. The impregnated tool resists oxidation over an extended period of time and stands up to repeated solvent wipedowns. The continual maintenance associated with unprotected tools is reduced, but the tools still require care in handling since the oxide coating is not abrasion resistant.

A second, more expensive, method for protecting tools from oxidation is to nickel-coat the parts. Since this process does add dimensioning to the part, finish operations are completed after the nickel coating is applied. Nickel coating will provide rust protection for the life of the tool, with the added benefit of being extremely abrasion resistant. It should be noted that, for the most part, both coatings can be applied to existing tooling once the surfaces have been properly prepared.

A third method for inhibiting the formation of rust is to specify stainless steel as the spacer material. The term "stainless" is somewhat misleading when applied to spacer tooling. Higher carbon contents are needed to achieve the standard hardness levels required for spacers (56-58 RHC). These higher carbon levels make the parts somewhat prone to rust formation, but only if greatly neglected. Generally, spacers made of "stain-resistant" hardenable stainless steels offer excellent rust and corrosion and protection as well as superior abrasion resistance.

Besides rust formation, another frustrating aspect of slitter tooling use is the tendency for the tech, indication thickness size, to fade with usage. After the etch has faded, an operator may have to continually measure his thin spacers to prevent mistakes occurring in the setup by use of the wrong spacer size. Setup time, product quality, and general slitter efficiencies can be affected by faded or hard-to-read thickness markings on the tooling.

In response to this problem, DIENES has developed a permanent marking technique, using laser engraving technology, that is far superior to the standard acid etch method. All tools that do not have dirt grooves have their thickness values indelibly marked with laser imprinting. DIENES' laser-etched tooling provides "at-a-glance" confirmation of a spacer's size for the life of the tool and helps prevent any chance of tooling mix-ups.

Please let our experienced Sales Engineers know if rust formation or etch fade are causing production problems at your facility. We would be happy to discuss possible solutions.