The auto industry turns to noise reducing synthetic grease.

The motor industry has turned to noise reducing synthetic grease in recent years because background noise in vehicle interiors has decreased dramatically in hybrid, EV’s and luxury cars. As a result, noise reducing synthetic grease is already finding use in car air conditioners, because the grease has both excellent noise reduction and low temperature performance.

What is the composition of noise reducing synthetic grease?

The primary purpose of lubrication is separation of solid surfaces moving relative to one another to minimise the effects of friction and wear. Grease compositions consist primarily of a fluid lubricant, such as synthetic oil, and a thickener and are widely used to lubricate mechanical components such as joints and bearings.

Synthetic greases are employed in applications where high pressures exist and where oil drip is undesirable or where the motion of the contacting surfaces is discontinuous so that it is difficult to maintain a separating film in a bearing.

Bearings are supports provided to locate a revolving or reciprocating shaft and are widely used in automotive electric motor applications. When in use bearings may be subjected to extreme rotational forces which can lead to noise and vibrations. Such noise is detrimental to the condition of a bearing and can lead to the bearing shaking or juddering resulting in unacceptable bearing noise. Such noise associated problems can prevent the use of bearings in low vibration applications, which has led to the interest in noise reducing synthetic grease.

It is known that the lubrication of mechanical parts with grease compositions may reduce friction and wear, such as in WO 96/02615 which relates to a grease composition for constant velocity joints which comprises (a) a base oil; (b) a lithium-containing thickener selected from the group consisting of lithium soap and lithium complex soap; (c) an organic molybdenum compound selected from the group consisting of molybdenum dithiophosphates and molybdenum dithiocarbamates; and (d) a zinc dithiophosphate.
 On page 7, line 3 of WO 96/02615 it is stated that the organic molybdenum compound as the component (c) undergoes self-decomposition on the surface to be lubricated to thus form a film of a high molecular weight compound having viscoelasticity, which covers the metallic parts on the portions to be lubricated, or to form, through the self-decomposition molybdenum disulfide which serves to reduce the frictional force acting on the parts or any wear thereof.

However, there is little information available on noise reducing synthetic grease specifically designed to reduce noise or vibration. Further, in use bearings become extremely hot, causing the viscosity of a grease composition to fall and the noise or vibration to increase.

How does noise reducing synthetic grease work?

During bearing rotation sound pressure is generated by collision velocity and material properties (ex. Poisson ratio, Young's modulus). However, when the grease is applied to the area around the collision point, collision velocity is reduced because of the viscous resistance of the grease. Therefore, it is effective to use highly viscous synthetic base oil in noise reducing synthetic grease. Regular mineral base oil would detrimentally influences low temperature performance. That is to say, noise reducing synthetic grease for air conditioner requires two conflicting properties of low viscosity under low temperature and high viscosity under collision pressure.

To accomplish this high pressure viscosity is improved as shown in the Barus equation, where performance is affected by atmospheric viscosity and viscosity-pressure coefficient, alpha. Therefore, to meet both excellent noise reduction and low temperature performance, alpha of the base oil is critical.

To refine alpha, the base oil has a high-alpha-polymer added to it. PAO(Poly-Alpha-Olefin) and polybutene are commonly used as a base oil because these have high alpha and few weaknesses. A new noise reducing synthetic grease comprising a mixture PAO and polybutene as the base oil and silica as the thickener has been developed. This grease simultaneously demonstrates excellent noise reducing and low temperature performance.

Although noise reducing synthetic grease is finding popularity there are other synthetic greases that are already widely used in automotive applications, aerospace and industry. Habot Oil produce a wide range of high quality synthetic lubricants suitable for most applications.