Belts Flashcards
What is a V-belt
Has a wedged shaped cross section, transmits power by gripping a sides of a groove in a pulley
What are some Advantages of V-belts
Most cost effective (compared to chains and gears) Reliable, Don’t need lubrication, Absorb shock Quiet Slip on overload to protect components
What are some Limitations of V-belts
Most have fixed center distances Minimum 120° arc contact, Unsuitable first timing belts Unsuitable for high temperatures Not practice for high surface speeds because of dynamic balancing
Where might you find a V-belt?
Pump, speed changer, conveyors, fans, engine accessory’s etc.
How is a V-belt constructed
Tensile members on inside (consist of cords that carry load) Compression material (transmits power between sheave and the tensile members and support cords) Cover (protects internal parts from wear)
How do v-belts transmit power?
Friction between sides of belt and sides of sheave groove. The tensile members from the driver to the driven pulley
The amount of power a belt can transmit depends on what?
Strength of tensile members, the grip of the belt on pulley (arc contact, tension applied, coefficient of friction between belt and pulley )
What is the Pitch line
Pitch line runs through the old carrying zone, of the belt where tensile members are located. Located as close to outside diameter of the sheave so wisest cross section of belt carries load.
What is Stretch
Increase of belt over period of time
What is creep?
Loss of driving speed due to lengthening and shortening of the belt. Causes by elasticity of the belt.
What is slip? And what problems does it produce
Increasing the load with a give. Tension on the belt, the arc through which it creeps on the pulley increases. Slip produces a power loss between driver and driven, increases belt and sheave wear,
What are the types of V belts?
A,B,(commonly used for single and multiple belt drives) and C,D,E(used in multiple drives only)
Variations of the V-belts are what?
Clogged raw edge, banded, double V, and fractional horse power
Belt drives are what kind of drive
Friction, they transmit by a belt pressed tightly onto a pulley
What does the area of contact between belt and pulley surfaces depend on?
Belt width and arc of contact
What does the arc contact depend on?
Center to center distance, pulley diameter,and the take up device used.
What are 3 pulley surfaces
Flat, crowned(convex, highest point is at center) , and grooved (sheaves)
What are the most Common belt materials
Cotton, leather, rubber, nylon or other synthetic materials
How long of run in period should a new belt have
12-24 hours and then re tensioned
What are flat belts?
Used in conveyers and drip p belts , drive members carry the forces to transmit power. Can be manufactured endless or as a reel stock.
What are notched V-belts used for ?
Small sheave, short centre, hight speed drives. The notch helps cooling.
What is a high capacity V-belt
Also called wedge, hi torque or narrow v belts. 3V 5V 8V. Meaning they are 3/8, 5/8/ and 8/8. They can transmit up to 3x as Mitch horse power in the same drive space.
What is a light duty V-belt
Also called fraction so horsepower. 2L 3L 4L 5L. I dictated in 1/8 of a inch. Example 2L= 2/8 3L= 3/8. They have a neoprene cover for protection against weather-heat-chemicals.
What is a double angle v belt?
Also called a HEX belt, absorb compression and tension forces.
Where are wide V-belts used and what are they
Used in variable speed drives. A wide V-belt has cord drive members in a neoprene filler enclosed by fabric cover.
What is a positive drive belt?
Also called Timingbelts, gear belts. They have teeth inside , mesh with similarly shaped teeth in the pulley. Have the same advantages as chain or gear, but quieter. Do not last long and can’t handle heavy loads.
How do you determine the word that of a pulley.
Width of a new flat belt is determined by the width of the narrowest pulley. In general pulley face should be one inch wider when belt is up to 6” and two inches wider for anything over 6”
How should belts be stored
Cool dry place, synthetic belts should be in a cool humid place but NOT. In contact with water
