Belt (mechanical)

The mechanical belt drive, using a pulley machine, was first mentioned in the text of the Dictionary of Local Expressions by the Han Dynasty philosopher, poet, and politician Yang Xiong (53–18 BC) in 15 BC, used for a quilling machine that wound silk fibres onto bobbins for weavers' shuttles.

[2][3] The belt drive was not only used in textile technologies, it was also applied to hydraulic-powered bellows dated from the 1st century AD.

Belt drives run smoothly and with little noise, and provide shock absorption for motors, loads, and bearings when the force and power needed changes.

The angular-velocity ratio may not be exactly constant or equal to that of the pulley diameters, due to slip and stretch.

Adjustment of centre distance or addition of an idler pulley is crucial to compensate for wear and stretch.

Flat belts were widely used in the 19th and early 20th centuries in line shafting to transmit power in factories.

[4] They were also used in countless farming, mining, and logging applications, such as bucksaws, sawmills, threshers, silo blowers, conveyors for filling corn cribs or haylofts, balers, water pumps (for wells, mines, or swampy farm fields), and electrical generators.

Unlike leather belts, however, rope drives were sometimes used to transmit power over relatively long distances.

Over long distances, intermediate sheaves were used to support the "flying rope", and in the late 19th century, this was considered quite efficient.

Early sewing machines utilized a leather belt, joined either by a metal staple or glued, to great effect.

The main advantage over rubber or other elastic belts is that they last much longer under poorly controlled operating conditions.

V-belts trump flat belts with their small center distances and high reduction ratios.

For high-power requirements, two or more V-belts can be joined side-by-side in an arrangement called a multi-V, running on matching multi-groove sheaves.

The fibers may be of textile materials such as cotton, polyamide (such as nylon) or polyester or, for greatest strength, of steel or aramid (such as Technora, Twaron or Kevlar).

Most models offer the same power and speed ratings as equivalently-sized endless belts and do not require special pulleys to operate.

These provide easy installation and superior environmental resistance compared to rubber belts and are length-adjustable by disassembling and removing links when needed.

[15] A multi-groove, V-ribbed, or polygroove belt[16][full citation needed] is made up of usually between 3 and 24 V-shaped sections alongside each other.

The added flexibility offers an improved efficiency, as less energy is wasted in the internal friction of continually bending the belt.

Where more must be driven, such as for modern cars with power steering and air conditioning, multiple belts are required.

[18] This ability to bend the belt at the designer's whim allows it to take a complex or "serpentine" path.

They are generally intended for low-power (less than 10 watts), high-speed uses, allowing high efficiency (up to 98%) and long life.

When correctly tensioned, they have no slippage, run at constant speed, and are often used to transfer direct motion for indexing or timing purposes (hence their name).

The helical offset tooth design forms a chevron pattern and causes the teeth to engage progressively.

Disadvantages include a relatively high purchase cost, the need for specially fabricated toothed pulleys, less protection from overloading, jamming, and vibration due to their continuous tension cords, the lack of clutch action (only possible with friction-drive belts), and the fixed lengths, which do not allow length adjustment (unlike link V-belts or chains).

However, designs for continuously variable transmissions exist that use belts that are a series of solid metal blocks, linked together as in a chain, transmitting power on the compression side of the loop.

It is midway through the surfaces in film and flat belts and dependent on cross-sectional shape and size in timing and V-belts.

The equation for power is Factors of power adjustment include speed ratio; shaft distance (long or short); type of drive unit (electric motor, internal combustion engine); service environment (oily, wet, dusty); driven unit loads (jerky, shock, reversed); and pulley-belt arrangement (open, crossed, turned).

In large speed ratios or small central distances, the angle of contact between the belt and pulley may be less than 180°.

Some of the common malfunctions or faults include the effects of belt tension, speed, sheave eccentricity and misalignment conditions.

The vibration spectrum has the tendency to move to higher frequencies as the tension force of the belt is increased.