Vee belts (also known as V-belts or wedge ropes) solved the slippage and alignment problems that occur with flat belts. It is now the basic belt for power transmissions.
They provide the best combination of traction, speed of movement, load of the bearings, and long service life, The V-belt was developed in 1917 by John Gates of the Gates Rubber Company. They are generally endless, and their general cross-section shape is trapezoidal.
The V shape of the belt tracks in a mating groove in the pulley (or sheave), with the result being that the belt cannot slip off.
The belt also tends to wedge into the groove as the load increases, the greater the wedging action which improves torque transmission and makes the V-belt an effective solution, needing less width and tension than flat belts. V-belts trump flat belts with their small center distances and high reduction ratios.
The preferred center distance is larger than the largest pulley diameter, but less than three times the sum of both pulleys. The optimal speed range is 1,000-7,000 ft/min. V-belts need larger pulleys for their thickness than flat belts. They can be supplied at various fixed lengths or as a segmented section, where the segments are linked (spliced) to form a belt of the required length.
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 strength of these belts is obtained by reinforcements with fibers like steel, polyester, or aramid (e.g. Twaron or Kevlar). This is known as a multiple-belt drive. When an endless belt does not fit the need, jointed and link V-belts may be employed.
However, they are weaker and only usable at speeds up to 4,000 ft/min. A link V-belt is a number of rubberized fabric links held together by metal fasteners. They are length adjustable by disassembling and removing links when needed.
Timing belts, (also known as Toothed, Notch, Cog, or Synchronous belts) are a positive transfer belt and can track relative movement.
These belts have teeth that fit into a matching toothed pulley. When correctly tensioned, they have no slippage, run at a constant speed, and are often used to transfer direct motion for indexing or timing purposes (hence their name).
They are often used in lieu of chains or gears, so there is less noise and a lubrication bath is not necessary. Camshafts of automobiles, miniature timing systems, and stepper motors often utilize these belts.
Timing belts need the least tension of all belts, and are among the most efficient. They can bear up to 200 hp (150 kW) at speeds of 16,000 ft/min. Timing belts with a helical offset tooth design are available. The helical offset tooth design forms a chevron pattern and causes the teeth to engage progressively.
The chevron pattern design is self-aligning, does not make the noise that some timing belts make at idiosyncratic speeds, and is more efficient at transferring power (up to 98%). Disadvantages include a relatively high purchase cost, the need for specially fabricated toothed pulleys, less protection from overloading and jamming, and the lack of clutch action.
→ Hi-modulus polyester cord located in the belt mid-section is specially treated to maintain extreme belt loads and shock without stretching. The central position contributes to greater strength, balance, and longer life.
→ Unique raw-edged belt sidewalls grip pulleys better, to minimize belt slip, noise, and drive vibration.
→ Special 100% neoprene rubber compound supports the cord more evenly, both on top and on bottom; dissipates heat more readily, and provides better oil, heat, and ozone resistance.
→ Multiple fabric plies, on the top and bottom, relieves stress on the load carrying center cord for added flexibility. “A” belts have three plies on the top and bottom. “B” belts have four, and “C” belts have five.