Drives Flashcards
What are some advantages of v-belts?
Cheap
Reliable
No lubrication
Absorb shock
Will slip when overloaded to prevent damage
What are the limitations of V-belts?
Operate with fixed distances only
Minimum of 120 degree arc of contact
Unsuitable for positive drives(timing)
Unsuitable for high temp environments
Not suitable for high surface speeds
What does the tensile member of the belt do?
Carry the load
What does the compression section of the belt do?
Transmits power between the sheave and tensile members and supports the cords
What does the cover do?
Protects the internal parts from wear, weather, and other harmful substances
How does the v belt transmit power?
Friction between the sides of the belt and sides of the sheave
and the tensile members from the driver to the driven pulley.
The amount of power a belt can transmit depends on what?
The strength of the tensile members
The grip of the belt on the pulley
- arc of contact
- tension
- coefficient of friction between belt and pulley
Describe pitch line?
The line that runs through the load carrying zone of the belt where the tensile members are located.
Describe creep?
The loss of driving speed due to the lengthening and shortening of the belt as it cycles from the slack side to the right side
What are the factors that friction depends on?
The coefficient of friction
The arc of contact
Tension on the belt
What belts are commonly used in single belt drives?
A and B
What belts are typically used in multi belt drives?
C, D, and E
What are the different types of v-belts?
Classic series - A, B, c, d, e
Cogged raw edge - greater flexibility, enhanced airflow
Banded - solve belt vibration, whip and turnover problems
Double V - belts - transmit power on either side
Fractional horsepower - usually on
drives less then 1hp
High capacity belts - 3v 5v 8v
Poly V belts - J K L M and H for small sheaves
Variable speed belts - snowmobile
Open ended - use when cannot get closed belt in
Link belts
Round belts
What are the advantages of a high capacity V-belt?
Compact - allowing for use of smaller diameter sheaves
Higher power capacity
What are the disadvantages of high capacity V-belt?
Require higher tension
Higher side wall loading accelerates wear in dusty environments
What are the advantages of classic V belts?
Highest tolerance in poor operating conditions
Reliability where maintenance is infrequent
Reliable for unusual drives
Widest selection of belt and sheave sizes
What are the Four variations of the classic belt?
Cogged raw edge
Banded
Double v
Fractional horsepower
What are the advantages of Cogged belts ?
Greater flexibility, enhanced airflow
Bend around small sheaves
Raw edged belt fits more accurate around sheave
Raw edge belts have higher coefficient of friction
What are the disadvantages of Cogged belts?
Cleanliness and sheave alignment more critical
Cannot be used on clutching drives, drives subject to shock or with changing centre distances
Cannot be subject to reverse bending
Cannot be used where slippage occurs
What are the advantages of round belts?
Suitable for 1/4 turn drives
Suitable for serpentine drives
Can be joined easily
What are the limitations of round belts?
Light duty fractional horsepower
How do you read the RMA (rubber manufacturers association) code?
The letter is the size of the cross section A is the smallest standard cross section, H is the smallest poly v belt cross section
The letter is followed be the length in inches
The third number is a decimal of an inch
What size should your outside tensioner pulley be?
At least 1.5 times the diameter of the smaller pulley
What is the advantage of outside pulley?
Increases the arc of contact
Where do you position the outside idler pulley?
As close to the smaller sheave as possible on the slack side
What is the disadvantage of outside idler on a belt drive system?
Puts backward bend on the belt which can reduce the life of the belt
What is better, outside idler pulley or inside idler pulley?
Inside if you can maintain adequate arc of contact
Using a grooved pulley on an inside idler it provides what?
Better tracking
Where do you place the grooved idler?
On the slack side, where you can achieve equal arcs.
If using a flat pulley locate it away from the sheave that the belt is travelling toward
When would you use a contact idler?
If there is a problem with belt whip(vibration).
Check alignment and belt tension first
Where do you locate the contact idler?
1/3 the span from the larger pulley on the slack side. Make sure there is no back bend.
Why are automatic take ups preferred?
Provide uniform belt tension
When do you recheck the tension of a belt?
During the first 24 to 48 hours
Every 8 hours for 24 hours
What are synchronus belts used for?
Also called positive drive belts or timing belts.
Used on drives that cannot tolerate any slippage.
Used now to replace roller chains.
What are the advantages of synchronous belts?
Last 3 times as long and chain drives
Require less tension
Do not require re-tensioning
Highly effective power transmission 98%
Very wide speed range (30 000 rpm)
Wide range of power ratings
Ideal for multiple shafts
What are the disadvantages of synchronous belts?
No overload protection
Expensive
Not suitable for shock loads
More sensitive to dirt and other contaminants
What are synchronous belts not rated for?
Aircraft
Lift systems
Braking systems
What is the arc of contact for synchronous belts?
At least 60 degrees and a minimum of 6 teeth of contact
What are the types of synchronous belts?
Trapezoidal tooth
Rounded tooth
Twin toothed
Helical offset
What is the proper tension for a flat toothed belt?
Just remove slack from the unloaded span