Design Guide 5 - Dirt and Wear Resistant Magnetic Head Design & Coatings

Extreme Technology for Extreme Environments

The increased traffic, higher performance requirements and greater versatility of new mass transit installations has placed new pressure on the development of magnetic head coatings and design. These new system requirements have necessitated the development of a new generation of magnetic heads that will last for several million transactions and require minimal cleaning.

The CoMolyExtreme™ Magnetic Head was designed to

• Repel the Adherence of Dirt
• Reduce the Effects of Scalloping
• Provide Long Life
• Require Minimal or No Cleaning

As magnetic fare collection systems evolved and software became more creative, the Transit Authorities saw ways to expand system capabilities. Authorities now have systems that use stored value cards, time based cards, plastic cards and paper tickets, all in the same system and in some toll roads and bank credits cards. In addition, many systems have to cope with different ticket (card) thickness. In new systems, paper tickets are almost obsolete and reusable plastic tickets have become the norm. Patrons can now check the value on their card, reload it, or dispose of it and purchase a new card. In some instances, systems have become inter-modal, where the same card can be used to ride the subway or a bus.

With the introduction of multiple-use, numerous-pass tickets coupled with more stringent read/write requirements, a new problem was encountered - dirt. In older systems where paper tickets were used, the absorbent properties of paper and the abrasive slurry media made the system somewhat self-cleaning for the magnetic heads. With plastic tickets that are used over and over again, we now see a buildup of a tar-like substance on the magnetic heads. The buildup of this substance causes read and write errors due to spacing losses (see Figure 3). Laboratory analysis of the material indicated it was a mixture of body oils, dirt, metal rail dust and other biological substances not unlike oils found in lipstick or used to make French fries.

In order to maintain the desired performance of the magnetic heads in these new systems, more frequent cleaning was required, resulting in increased maintenance costs and reduced system performance. The CoMolyExtreme™ head was designed to relieve this problem while meeting all of the performance requirements.

The CoMolyExtreme™ head is a combination of a new coating material called CoMoly™ and a new "bridged" head design. CoMoly™ is a non-ceramic, hard, plasma coating containing Cobalt, Molybdenum and Chromium. This is a material that is adaptable for long wearing, low-friction applications. The bridged design ensures that the only material that comes in contact with the card (magnetic media) is core material or CoMoly™.

Brush Industries has been using CoMolyExtreme™ technology at sites in New York City and in China since 1998. System-wide performance was increased from 75% to 87% first swipe acceptance with the introduction of the new CoMolyExtreme™ head technology. Additionally dramatic increases in magnetic head performance with substantially less cleaning have been documented.