To deliver the expected level of quality while controlling costs, many manufacturers are turning to specially formulated lubricants, called damping compounds. These products help deliver high-quality feel, quiet and motion control at a fraction of the cost of precision mechanical devices, special materials, or re-design.

Quality without Cost

The need for higher levels of quality in consumer applications is most evident in the automotive industry, especially with the expansion of electric hybrid vehicles (EHVs). Because of the reduced engine noise produced by these cars, drivers demand a heightened level of quiet and smoothness. This expectation has expanded to other consumer products as well. Beyond consumer applications, quiet, smooth operation is a key design criterion for such high-tech equipment as medical devices and aerospace systems.

In the past, meeting these requirements required using precision manufactured parts or special materials. Now, specially formulated greases, called damping compounds, can deliver high-quality feel, noise reduction, and sensitive motion control.

Damping compounds can be useful tools for a design engineer faced with the challenge of reducing product cost without sacrificing quality. These materials reduce wear and seal out dust and moisture like traditional greases. But their primary use is to control motion and noise in mechanical and electromechanical devices. They can transform a device plagued by jerky, noisy motion into one with a smooth feel and virtually silent operation for only fractions of a penny.

Expanding the Range

The concept of damping compounds has been around for more than 60 years. They were first used to fine tune the motion of microscopes, telescopes and binoculars. Their use did not extend far beyond optical instruments for many years because early formulations had limited low-temperature capabilities. Those materials worked well at room temperature but became so viscous at low temperatures that they made parts difficult to move. This changed with the introduction of synthetic damping compounds that could operate over a broad temperature range.

Switch manufacturers were among the first to take advantage of the new materials, especially in the automotive industry where the low-temperature design goal is typically minus 40 degrees C. Switch designers found that a small amount of damping compound on switch detents could effectively reduce the noise created by plastic-on-plastic contact, which consumers perceived as poor quality.

In addition, damping compounds provided a smooth feel to hand-actuated switches without the expense of building parts to tighter tolerances or using more expensive materials. Over the years, damping compounds found their way into a wide variety of industries on components such as potentiometers, clutches, springs, screws, gears, hinges, solenoids, steering shafts and sliding mechanisms.

How They Work

Conventional greases are formulated by combining oil with a thickener that holds the oil in place. Oil is released to lubricate the moving parts when shear is applied to the grease by a rotating bearing, sliding element or other device. The primary difference between conventional grease and damping compounds is shear resistance, which is related to the internal structure of the lubricant. Damping compounds are typically formulated with viscous, high-molecular weight synthetic fluids that give them a much higher shear resistance than conventional greases.

In addition to reducing friction between mating surfaces, this shear resistance provides a greater degree of damping compared to conventional greases. This, in turn, gives damping compounds the capacity to control motion precisely and reduce or eliminate noise.

Damping compounds can be applied by automated dispensing equipment, air jetting, spraying or brushing. Because the compounds readily adhere to moving parts, mating surfaces do not contact. Instead, they move within the compound itself, silencing the noise normally associated with metal-on-metal, metal-on-plastic, or plastic-on-plastic contact.

The result is quiet operation. Whats more, because a certain force is required to move a part through the grease, the high shear resistance prevents backlash and coasting while ensuring smooth, incremental motion.

Damping compounds give a designer the ability to adjust the amount of torque required to actuate a device. This allows them to design the user experience cost-effectively. The amount of force required to move a device lubricated with a damping compound depends primarily on the base fluid. As molecular weight increases so do shear resistance and torque. Higher-molecular-weight fluids have greater internal shear resistance, which requires more torque or force to move a component.

By controlling shear resistance, a designer can precisely fine-tune the feel of hand-operated devices. As an additional benefit, the viscous consistency of damping compound helps seal out moisture, dust and other pollutants, thereby extending component life.

Whats the Buzz?

Consumers frequently judge quality by how a device feels and sounds. These perceptions are so important that many manufacturers, particularly in the automotive industry, have developed special engineering groups devoted to eliminating buzz, squeak and rattle (BSR) or noise, vibration and harshness (NVH).

Damping compounds are important materials in helping designers meet tactile feel and acoustical design goals. Typically, high-viscosity synthetic hydrocarbon fluids are custom formulated for a specific set of operating conditions for use in these applications.

The key factors in formulating a damping compound are more complex than simply producing the right apparent viscosity – a measure of grease stiffness under shear – or the right kinematic viscosity.

Instead, custom damping compounds are developed by working cooperatively with a customer to understand their mechanical design and goals for measurable properties like sliding torque and noise, as well as subjective ones like feel.

This approach was used, for example, to correct a design issue with an intermediate steering shaft that exhibited high sliding torque and noise. The customer was faced with a recall because of this problem, and set a severe target for the damping compound to produce shear resistance and sliding torque that changed very little from room temperature to minus 40 degrees C. Typically, a silicone material would be used in this application, but silicones are prohibited in many automotive applications because they can ruin paint finishes.

A solution was found by developing a custom-formulated compound with a unique molecular structure to match the shear profile of the steering shaft. This solution allowed the shaft to provide almost constant sliding torque across the temperature range with smooth and quiet operation.

In another application, a manufacturer of a luxury electric hybrid vehicle had trouble dialing in the right damping profile for a gear motor operating the automatic headrest. Data from an acoustical study showed that the motor produced unacceptable noise as it strained to move the gears. The noise was eliminated by reducing the viscosity of the damping compound used on the gears.

Selecting a Compound

Selection of a damping compound is based on both objective and subjective criteria. First, as noted, the compound must retain its properties over the application temperature range, which relates directly to the viscosity index of the oil. Typically, synthetic hydrocarbon materials are suitable for applications operating from minus 40 to plus 125 degrees C, whereas silicone-based compounds are functional from minus 60 to plus 200 degrees C.

Material compatibility is another important consideration. Synthetic hydrocarbons may weaken polyethylene, polystyrene, polyvinyl chloride and some low-density elastomers. While material manufacturers offer compatibility charts, the best way to ensure compatibility is by actually testing the two components.

High-viscosity, silicone-based damping compounds are available for applications where material compatibility or high temperatures are issues. These products are typically thickened with PTFE and are compatible with all but silicone-based rubber. Although silicone tends to migrate in some applications, the molasses-like viscosity of the base oil gelled in PTFE virtually eliminates migration.

Subjective design considerations primarily involve the feel a designer wants to produce. A typical rule of thumb is that as the amount of torque required by a device drops so does the required molecular weight and viscosity of the damping compound. A variety of consistencies, from very light to ultra-heavy, is available to meet the needs of every application.

Also, when moving from a hydrocarbon compound to a silicone base, the pressure-viscosity difference should be considered. Because of silicones compressibility, applications using them typically require a viscosity double that of a hydrocarbon.

The ideal application for damping compounds is one for which a small amount of lubricant can control free motion, provide a smooth feel, reduce noise, or any combination of these properties. In these and other applications, damping compounds provide a cost-effective way to keep todays demanding consumers happy.

Jason Galary is manager of technical support, applications and engineering, at Nye Lubricants Inc. in Fairhaven, Mass. For more information about this article, e-mail him at jgalary@nyelubricants.com or phone+1 (508) 996-6721.

Lube Report Asia will occasionally include articles originally published in sister publications of LNG Publishing Co. This article appeared in the November 2012 issue of LubesnGreases – Volume 18, Issue 11 – under the headline, Dial D for Damping.