Coating Rods

Published: October 31, 2004, By Donald M. McLeod, Industry Tech

The Great Equalizer

A century of evolution has gone into wire-wound coating rods. Still called Mayer rods, after Charles W. Mayer (rhymes with wire), they continue to be popular 100 years later because they're inexpensive, accurate, and easy to use. Mayer named them “equalizers.” They also are called metering rods, coating rods, applicator bars, and even “Myrods.”

Mayer applied for his first patent in 1904 when he was 32. He developed the first successful coating machine, which applied liquid or powder materials to a moving web of paper. He formed Mayer Coating Machine Co. in Rochester, NY, which incorporated in 1905.

His machine was an immediate success. Mayer particularly was proud of his equalizer bars, the key element in his coating system. These rods could spread coating material accurately and evenly across the entire width of the web. In one patent, he wrote, “I consider…the wire-wound equalizer to be a very valuable and important feature of the invention….”

The first metering rods were made of crude materials. In an age when most metalworking was done in a blacksmith shop, rods were made of carbon steel bars wound with piano wire. The wire sometimes was wrapped unevenly on the core rod and would break during use.

Early rods were inconsistent and unpredictable. Some had spaces between the wire, and they would rust. In spite of these problems, rod coating was an improvement over the brushes and rollers used at the time, and the basic theory behind wire-wound rods was sound. Users found chrome plating could control rust and also offered a hard shell over the wire that would wear longer than the piano wire used at the time.

This advanced level of coating was a breakthrough. For the first time, makers of waxed and carbon paper could manufacture in production quantities. Coating thickness could be changed by switching rods. Converters began ordering rods with different wire sizes. Mayer found a growing market for replacement rods, which became more profitable as more coating machines were shipped.

Mayer's success in the coating machine industry attracted competition. Other processes were introduced, which cut into his machine business. However, every Mayer machine required new rods as old ones wore out, and many competitive machines used these wire-wound rods. As his machine orders declined, the market for rods continued to expand.

In the 1970s, the industry became more diversified in coatings and web materials. Metering rod manufacturers standardized on precision stainless steel core rods and wire, with closer tolerances and smoother finishes, and made them on high-speed winding machines.

Mayer rods became precision tools. Coating thickness could be controlled within one-tenth of a mil (0.0001 in.). Spring-tempered wire offered longer rod life. Coaters could select rods for a wide range of coat weights. Double- and triple-wound Mayer rods produced heavyweight coatings at a single pass. Rods coated with Teflon, hard nickel, and titanium nitride prolonged rod life and eliminated quality problems. Heated rods allowed hot melt adhesives to be coated at production speeds.

Manual and motor-diven drawdown machines were introduced for the laboratory in the 1980s and 1990s. These use wire-wound rods and allow scientists and technicians to make accurate coated samples for evaluation and study. With modern trends toward shorter production runs and customer demands for higher levels in quality, Mayer bars continue to be popular. Bottom-line economics encourage converters to consider rods as an alternative to other coating methods. Some have added rod stations to existing machines to take advantage of the flexibility, ease of use, and dollar savings associated with the Mayer rod.

It has been 100 years since the first rods were made. They continue to meet the increased demands of the converting industry in the 21st century.

Donald M. MacLeod is founder and president of Industry Tech, Oldsmar, FL, a manufacturer of coating rods and laboratory test equipment. He has a mechanical engineering degree from Rensselaer Polytechnic Inst., Troy, NY, and 21 years of experience in the coatings industry.