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
How much tension for a curved tooth belt?
Enough tension to compress the tooth into engagement.
How much tension on a synchronous belt?
Just enough to remove any clearance between the outside diameter of the sprocket teeth and grooves between the belt teeth.
What is a pulley?
A wheel used to transmit power from its rim to the belt
A sheave?
A pulley with a groove that runs around the circumference.
A sprocket?
A pulley with grooves across the rim.
What are the parts of a pulley?
Rim
Web
Hub
What are the 3 types of sheaves?
Web
Block
Arm
When and why are the web and arm sheaves used?
On large pulley’s to reduce the weight
What are the different sheave materials?
Gray cast iron
Steel and ductile iron
Sintered steel
Pressed steel
Aluminum
Plastics
Nylon polycarbonates
How do cylindrical bored hubs transmit power?
They rely on a key
How much contact is needed for a tapered bore hub with no key?
85%
What are the characteristics of power transmission chains?
Provide a positive drive
98% efficient
Compact
Can be used with any distance in between sprockets
Chain length can be easily changed
A number of shafts can be driven from a
single shaft
Inexpensive
Require only small amount of take up
Can operate in hot environments
What are the limitations of chain drives?
Do not slip on overload
Adequate lubrication is hard to achieve
Service life is shorter then gears
What are the two types of chain?
Roller chain
Silent chain
What are chains made of?
Hardened carbon steel (standard)
Stainless steel (corrosion resistance)
Synthetics such as nylon and various plastics (lightweight, corrosion resistance, cheaper then steel)
What are the two types of roller chain?
Pin link
Roller link
When are cotter pins used on connecting links?
80 pitch and larger
When are spring clips used on connecting links?
25 to 60 pitch chains
Why do you not want to use half link?
Weaker then standard links
True or false? Two pitch offset link provides full strength.
True
Where is light duty chain used?
Chain drives where space is restricted
What is the difference between heavy duty chain and standard roller chain?
All dimensions are the same except side plate thickness
Does heavy duty chain have greater load capacity?
No but thicker side plates increase resistance to fatigue
What is heavy duty chain recommended for?
Heavy shock loading and reversing drives
What is multiple strand chain?
Chain with two or more stands. Comes up two 12 strands wide.
Why are multiple strand chains used?
They are used where loads and speeds are to great for single strand chains.
How much stronger is multiple strand chain?
1.7 times stronger than single strand chain
How does pre lubricated chain get lubricated?
In a sinterd bushing chain is used the powdered metal bushing is loaded with lube and when the bushing is under load the it squeezes out the lube.
How much stronger is standard chain than O-ring chain?
5%
What are some advantages of synthetic chain?
Very light - 15 to 20% the weight of steel
No lubrication
All links are master links
Interchanges with steel chain
Noise is greatly reduced
Corrosion resistant
What are some applications for synthetic chain?
Food handling and processing
Computer equipment
Office machines
Instrument drives
Plating and coating equipment
Instrument drives
Electrically conductive equipment
When is double pitched chain used?
Used for long spans, slow to moderate speeds with low horsepower.
Why would you use a roller less chain?
Less expensive, used in light applications
How can you tell if it is roller less chain?
By a 5 on the right hand part of the chain number
When is silent chain used?
High speed drives
Transmitting high horsepower in small space
Precision timing
What are the 3 types of silent chain?
Side guides
Centre guide
Duplex (serpentine drive)
What are the advantages of silent chain?
Smooth
High efficiency
High speed
Lighter bearing load
Load shared by a large number of teeth
Adaptability to any centre distance
Positive drive
Durable
Before working on a chain drive, what must be done?
De-energized and locked out
How do you calculate chain length of the old chain is missing?
Measure drive centre to centre and double it
Count half the teeth on each sprocket add the two numbers together and and multiply by the pitch. (Distance chain wraps around sprocket)
Add sprocket wrap distance to centre distance
Why must sprocket be aligned?
Ensure smooth engagement of chain with sprocket teeth
Reduce wear on the chain and sprockets
Reduce fatigue in the chain
What planes must be the same when aligning chain drives?
Vertical angular and horizontal
How many points must touch on straightedge?
4
How much is the strength reduced when using a slip fitted connecting link?
30 %
What problems are caused from to much tension?
Reduced chain and sprocket life
Overloading of bearings
inadequate lubrication in the pin and bushing
What problems do to little tension cause?
Chain whip and vibration
Chain rubs opposite chain
Chain can wrap on one of the sprockets and bind
How much sag on slow to medium speed drives?
4 - 6 %
How much sag for high speed, reversing, or impulse drives?
2 - 3 %
How much slack for vertical drives?
2 - 3%
What benefits are from keeping machines and surround areas clean
Service life of chain is longer
Inspections are easier
Repair and service work is much more efficient on a clean machine
What is the most important factor to reduce chain wear?
Lubrication
What are the benefits of of well lubricated chain?
Resists wear at the pin joint
Flushes away foreign materials
Lubricates chain to sprocket contact surfaces
Prevents rust and corrosion
Dissipates heat
Cushions impact loads
What are the three methods of chain lubrication?
Manual or drip feed - low speed drives
Bath - 1500 feet per minute
Forced - heavy loads and high speeds
When should normal chain be inspected?
After first 100 hours then every 500 hours
Drives subjected to shock loads or severe conditions should be inspected more frequently
If a chain is elongated by _____ it should be replaced?
3 %
When do you replace a sprocket?
Roughness or binding when chain engages
Teeth thinned down
Teeth hooked at the tips.
What are causes of bushing failure?
Overload
To small of sprockets
Imperfect form on the sprocket teeth
Badly worn or oversized gullet on the sprocket teeth
To prevent roller failure you can?
Reduce speed or load
Or use
Multiple strand chain with smaller links
What is pitch?
Centre of pin to centre of pin
When ordering sprockets what information do you need to give?
Chain pitch
Chain type
Number of strands
Hub style
What are the 4 types of sprockets?
A - flat plate style
B - hub on one side
C - hub on both sides
D - split sprocket
What are some advantages of a keyless adapter hub?
High durability against reversing and shock loading
Convenient, accurate and secure axial positioning
No reduction in shaft strength
No kit to fit
Capacity of handling high torque without long keys and extended hubs
Ideal centre distance for chain drive is how many pitches?
30 - 50
