Belts Flashcards
Stretch
-means the increase in length of the belt over the period of time that it’s in service
Pitch line
- runs through the load carrying zone of the belt where the tensile members are located
- it’s where you measure from
V belt Construction
- Tensile members consist of cords that carry the load
- compression material transmits the power between the sheave, the tensile member and supports the load
- cover protects the internal parts
Transmit power from?
- Friction between the sides of the belt and the sides of the sheave groove
- tensile members from the driver to the driven pulley
Power depends on?
-Strength of the tensile members
Creep
-loss of driving speed due to the lengthening and shortening of the belt as it cycles from the slack side to the tight side
Slip
-When you increase the load and the arc of creep extends all the way around the pulley
Friction
-The grip between the belt and the pulley
Coefficient of friction
-Depends on the nature of the surfaces in contact
Tension on the belt
-Determines the force between the belt and the pulley
Gripping
-On sides of both the sheave and belt, never the bottom
What is a classical/standard series of belts?
A,B,C & D
Cogged “Raw” edge advantages?
- greater flexibility and cooling
- the raw edges have a higher coefficient of friction than wrapped belts and can thus transmit more power
An ‘x’ after the classical series letter
-mean its “Cogged raw edge”
Banded Belts
- the belts are constructed by joining two or more standard belts with a common backing
- high speed
- designed to solve belt whip, vibration &turnover
Double V
- ‘hexagonal’ designated with AA, BB,CC & DD
- used for serpentine drives
High Capacity
- higher side walls of belts and sheaves giving greater tension
- know 3/8 = 3V, 5/8 = 5V, 1” = 8V
High capacity belt designation
3/8 = 3V, 5/8 = 5V, 1” = 8V
Disadvantage of high capacity belts
-require higher tension which causes higher bearing loads
Fractional horsepower designation (light duty)
- 2L, 3L, 4L & 5L
- generally used for less than 1 horsepower
Poly V or Micro V
- Designation J,K,L & M
- for high speed
- shape is several v’s together
Open-ended Belting
- can only carry 1/3 of the load of a corresponding endless belt
- same code as ABCD but have a VO at the end
Link Belt
- available with the same power ratings as classical v belts
- they do not like high RPM
Round belts
- rely on surface area contact
- for quarter turn drives & serpentine drives, low power cause no grab
- code gives diameter in 1/16 so 5 x 33 would by 5/16 diameter
Serpentine drives
- When the belt or chain is weaving in and out of sprockets and using both sides of the chain or belt
- think snakes
Checking the sheave groove?
- a gauge or new belt. Both should be level with the top of the sheave
- belt should never touch the bottom of the sheave
Max sheave misalignment
-1/16 inch per foot
Max axial runout?
-.005
Idler
- Increase belt tension
- Increase the arc of contact (move idler to equal contact)
- Prevent whip
- allows goes on the loose side
- 1/3 of the span distance
When should you recheck tension on v belt.
-during the first 24-48 hours of operation
What’s the rule for readjusting the tension on a synchronous belt?
-set it and forget it
Synchronous Belts (positive drive or timing belt)
- Output shaft must be synchronized with the input shaft
- flat belt with moulded teeth that engage in special toothed sprockets
- for positive drive, high speed
Advantages of synchronous belts
- do not require re-tensioning
- no lubrication needed
- 98% efficient
- very wide speed range 30,000 RPM
Disadvantages of synchronous belts
- not suitable for large shock loads
- require more accurate alignment than v belts
Belt operation
-the depend on positive engagement of the teeth on the belt with the teeth on the sprocket
Arc of contact
- v belts 120 degrees
- Synchronous 60 degrees or 6 teeth
Types of synchronous belts
- trapezoid
- rounded
- twin
- helical offset
Trapezoid
-flat sides
Rounded tooth profile
- replaces some of the sliding friction with rolling friction
- stronger tooth profile then flat
Twin toothed
-have teeth on both sides of the belt, making more compact and efficient.
Helical Offset
- highest power rating
- lowest sound rating
- very little backlash
Synchronous codes
- 22.5 L 075
- pitch length, tooth pitch, width
A pulley
-a wheel used to transmit power from its rim to a belt
A Sheave
-a pulley with a groove that runs around the circumference of the rim
A sprocket
-A special form of flat belt pulley that has grooves across its face to match the teeth in a synchronous drive belt
Sprocket code
-16 L 075
Number of grooves, tooth pitch, width
Code for poly v pulley
-6 L 48
Number of grooves, cross section, diameter
Taper-Bored Hubs
-the key may be eliminated on very high speed drives for more accurate dynamic balancing.
QD hub
- Bushing is split on barrel and flange
- keyed on shaft
Tapered bushing hub
- Bushing is split only on barrel
- keyed on shaft and bushing
Tapered loc hub
-bushing has no flange
Pulley Diameter
-avoid sub-minimum diameter sheaves as they cause excessive bending stresses in the undercord, higher belt tensions and higher temperatures
Poly V-belts pulley
- have no crown on the driving surface
- has a number of circumferential grooves to grip and guide the belt
Belt whip
-vibration in the vertical plane
Automatic take-ups
-a spring on a moveable motor mount or an idler to maintain belt tension
Quarter turn drive
- Transmits power from a horizontal shaft to a vertical shaft
- centrelines must be in line.
- derate horsepower to 90% of normal rating
Excessive vibration
-caused by misalignment or runout or long span
Uneven sprocket tooth wear
-caused by misalignment
Variable speed belt
-notches and ribs on underbelly
-reduced side angle to move up and down in
Flanges as the separate
Chirps
-indicate dirt or dust in sheave grooves
