Motion System Design

Silencing the synchronous belt

A different approach to synchronous-belt tooth design pays a sound dividend: it stops the whining in the workplace

A new design synchronous belt promises to squelch belt noise and vibration on industrial equipment. The Eagle Pd belt, from Goodyear, features a helical tooth design that cuts belt noise way down.

Supplied with mating sprockets, the new belt lowers operating noise by up to 19 dBA, says Ron Maltarich, manager of PT products at Goodyear. “It can mean the difference between meeting OSHA sound requirements and incurring high costs associated with work area monitoring, training, and testing.”

How it works

All synchronous belts have teeth that engage mating teeth on a sprocket. Though quieter than their metal counterparts (chain), they still generate noise as the belt teeth engage and disengage the sprockets. The reason: the straight teeth on conventional synchronous belts engage the mating grooves between sprocket teeth one-at-a-time. “As each belt tooth contacts the sprocket, its impact generates a continuous whine at frequencies determined by tooth pitch and operating speed,” says chief engineer Loren Danhauer.

By contrast, the teeth on an Eagle Pd belt are positioned at an angle and arranged in two opposing sets centered across the belt width, Figure 1. The result is a chevron pattern, analogous to the tread on tractor tires, or teeth on double helical gears.

Because the teeth are angled, they gradually roll into engagement with the mating sprocket, with two or more teeth engaged simultaneously, rather than the abrupt engagement of a single straight tooth. This continuous rolling engagement cuts noise and vibration. Engineers achieved even further cutbacks by offsetting the teeth on one side by one-half pitch with respect to the other side.

The new belt produces a sound level equivalent to that of a V-belt, a condition reportedly unheard of with synchronous belts until now. Tests show that it also reduces noise and vibration levels compared to conventional synchronous belts with round teeth, Figure 2 and Figure 3.

Better tracking. The opposed teeth on the new belt generate opposing side forces that cancel each other, making the belt self-tracking, and eliminating the need for guide flanges on the sprocket.

This self-tracking feature also eliminates irritating rubbing noises, energyrobbing friction, and belt wear related to flange contact.

Material upgrade

The belt is comprised of HiBrex rubber, a new compound, plus Flexten tensile members, and a Plioguard fabric facing.

HiBrex rubber is characterized by Goodyear engineers as a cross-linked elastomer that resists tooth deformity and increases tooth rigidity. It offers more than double the load capacity of similar conventional belts. For this reason, a narrower belt can be used, along with a flangeless sprocket, to achieve a more compact drive.

The tensile members consist of Flexten cord — five times stronger than steel by weight — to resist flex fatigue, elongation, and shock loads. Thus, the belt requires little retensioning, once installed.

The Plioguard facing is a low-friction material that reduces tooth engagement friction and resists wear and abrasion. It also resists attack by oils and chemicals.

Saving energy

Because of its smooth rolling engagement between belt and sprocket teeth, combined with self-tracking and consistent tension, the Eagle Pd belt operates at a fairly constant 98% efficiency, thereby saving energy. By contrast, a properly tensioned V-belt is about 97% efficient and can quickly drop to 91% with slippage.


The belt and sprocket are installed in much the same way as with other synchronous belt drives. Placing the belt on each sprocket is one area where installers need to be careful. They must orient the V-shaped belt teeth in the same direction as the sprocket teeth before engaging the two.

When can I get it?

The new belt will be introduced in March 1997. Its two tooth pitch sizes — 8 mm and 14 mm — offer capacities ranging up to 550 hp at speeds to 6,000 rpm. For the first time, Goodyear is offering mating sprockets, ranging from 5/8 to 57/8-in. bore sizes and 1.75 to 29.365-in. OD, thereby providing a complete drive package.

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