Advanced urethanes provide precision electrostatic, friction to improve cash dispensing at ATMs

Advanced urethanes provide precision electrostatic, friction to improve cash dispensing at ATMs
Tags: Components, Manufacturers, North America
June 30, 2009

Banking machine applications that involve paper transport include check processing, billing and currency handling. All this equipment, particularly ATMs, requires precise movement and paper capture at high speeds and volumes, and the machines must retain these capabilities under hostile climatic conditions. Extreme heat and humidity, as well as extreme cold and dry conditions, create changes in electrostatic levels and friction in paper-transport equipment, which can cause jams and double-feeds. For the engineers who select rollers, belts, and pads for ATMs, consistent conductivity and levels of friction are vital considerations in both original and replacement parts.

Albert C. Chiang

High-performance urethane is ideal for these applications. It has clear advantages over traditional materials like rubber or silicone for rollers, wheels, belts, and pads. Urethane provides excellent shock and vibration dampening, abrasion and wear resistance, great durability and high mechanical strength.

More important to ATM manufacturers and replacement-part suppliers, it offers customizable levels of conductivity and of coefficient of friction, both of which greatly increase equipment reliability and performance and eliminate the need for overly tight tolerances in design.

Controlling conductivity

The most commonly practiced method of making urethanes semi-conductive is by "doping": adding select amounts of conductive materials to the mix during part manufacture. While this does adjust the electrostatic properties of the part, each additive comes with its own drawbacks.

Adding carbon controls conductivity, but late in the life of the part, the carbon can stain the paper it is transferring. High-voltage vacuum coating fiber offers a limited two-dimensional (surface) conductivity control, but it is expensive. Conductive metal dispersion using powdered metal in blends from 10 percent to 80 percent controls electrostatic properties fairly well, but it is difficult to achieve uniform distribution of the powder during parts manufacture, since the metal tends to settle.

Urethane belt manufactured by MPC. The urethane can be customized for electrostatic properties, coefficient of friction, and hardness to suit all paper-handling tasks.

Ammonium salt additives address static, but their conductive properties vary considerably with humidity — and at high humidity, they make the surface of the part sticky.

The molecular method

The best way to customize conductivity is to modify the urethane structure at the molecular level, making the material itself semiconductive instead of relying on additives.

Urethane parts customized in this way have a volume resistivity of 5E5 to 5E10 at a hardness of 5 Shore A -80 Shore D for solid urethanes, and 20 Shore 00 to 90 Shore A for foam. The same method can be used to create parts that are completely antistatic. Combined with a customized and constant coefficient of friction, the electrostatic properties of these parts ensure precise movement of paper at high speeds, eliminating double-feeds, feed failures, or jamming, which errors in conveying checks or currency and require costly machine service.

Getting a grip on paper transport

Urethane gear manufactured by MPC. The urethane can be customized for electrostatic properties, coefficient of friction, and hardness to suit all paper-handling tasks.

Customization of urethane can be useful above the molecular level, where controlling the grip of a belt or a roller is critical — especially for high-speed paper transport systems such as ATMs. Chemically modifying the urethane molecules during manufacture can increase the part's coefficient of friction, making it greater than rubber or silicone parts of similar hardness.

The proper coefficient of friction enables a part to grab one piece of paper at a time, move it a precise distance, and let go at the exact right moment, throughout the long life of the part. Such chemically based performance is achieved through decades of experience and fine-tuning of the formulations and manufacturing processes.

Semiconductive urethane parts for paper-transport tasks create the best balance of precision static control, coefficient of friction, abrasion resistance and toughness to ensure long-lasting, jam-free performance in ATM equipment. The result for the ATM manufacturer and service supplier is increased equipment accuracy and precision, reduced downtime and need for service calls and replacement parts and greater customer satisfaction.