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Millwright Level 2 > Drives > Flashcards

Drives Flashcards

1
Q

What are some advantages of v-belts?

A

Cheap
Reliable
No lubrication
Absorb shock

Will slip when overloaded to prevent damage

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2
Q

What are the limitations of V-belts?

A

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

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3
Q

What does the tensile member of the belt do?

A

Carry the load

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4
Q

What does the compression section of the belt do?

A

Transmits power between the sheave and tensile members and supports the cords

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5
Q

What does the cover do?

A

Protects the internal parts from wear, weather, and other harmful substances

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6
Q

How does the v belt transmit power?

A

Friction between the sides of the belt and sides of the sheave

and the tensile members from the driver to the driven pulley.

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7
Q

The amount of power a belt can transmit depends on what?

A

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
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8
Q

Describe pitch line?

A

The line that runs through the load carrying zone of the belt where the tensile members are located.

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9
Q

Describe creep?

A

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

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10
Q

What are the factors that friction depends on?

A

The coefficient of friction

The arc of contact

Tension on the belt

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11
Q

What belts are commonly used in single belt drives?

A

A and B

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12
Q

What belts are typically used in multi belt drives?

A

C, D, and E

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13
Q

What are the different types of v-belts?

A

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

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14
Q

What are the advantages of a high capacity V-belt?

A

Compact - allowing for use of smaller diameter sheaves

Higher power capacity

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15
Q

What are the disadvantages of high capacity V-belt?

A

Require higher tension

Higher side wall loading accelerates wear in dusty environments

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16
Q

What are the advantages of classic V belts?

A

Highest tolerance in poor operating conditions

Reliability where maintenance is infrequent

Reliable for unusual drives

Widest selection of belt and sheave sizes

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17
Q

What are the Four variations of the classic belt?

A

Cogged raw edge

Banded

Double v

Fractional horsepower

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18
Q

What are the advantages of Cogged belts ?

A

Greater flexibility, enhanced airflow

Bend around small sheaves

Raw edged belt fits more accurate around sheave

Raw edge belts have higher coefficient of friction

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19
Q

What are the disadvantages of Cogged belts?

A

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

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20
Q

What are the advantages of round belts?

A

Suitable for 1/4 turn drives

Suitable for serpentine drives

Can be joined easily

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21
Q

What are the limitations of round belts?

A

Light duty fractional horsepower

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22
Q

How do you read the RMA (rubber manufacturers association) code?

A

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

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23
Q

What size should your outside tensioner pulley be?

A

At least 1.5 times the diameter of the smaller pulley

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24
Q

What is the advantage of outside pulley?

A

Increases the arc of contact

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25
Where do you position the outside idler pulley?
As close to the smaller sheave as possible on the slack side
26
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
27
What is better, outside idler pulley or inside idler pulley?
Inside if you can maintain adequate arc of contact
28
Using a grooved pulley on an inside idler it provides what?
Better tracking
29
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
30
When would you use a contact idler?
If there is a problem with belt whip(vibration). Check alignment and belt tension first
31
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.
32
Why are automatic take ups preferred?
Provide uniform belt tension
33
When do you recheck the tension of a belt?
During the first 24 to 48 hours Every 8 hours for 24 hours
34
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.
35
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
36
What are the disadvantages of synchronous belts?
No overload protection Expensive Not suitable for shock loads More sensitive to dirt and other contaminants
37
What are synchronous belts not rated for?
Aircraft Lift systems Braking systems
38
What is the arc of contact for synchronous belts?
At least 60 degrees and a minimum of 6 teeth of contact
39
What are the types of synchronous belts?
Trapezoidal tooth Rounded tooth Twin toothed Helical offset
40
What is the proper tension for a flat toothed belt?
Just remove slack from the unloaded span
41
How much tension for a curved tooth belt?
Enough tension to compress the tooth into engagement.
42
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.
43
What is a pulley?
A wheel used to transmit power from its rim to the belt
44
A sheave?
A pulley with a groove that runs around the circumference.
45
A sprocket?
A pulley with grooves across the rim.
46
What are the parts of a pulley?
Rim Web Hub
47
What are the 3 types of sheaves?
Web Block Arm
48
When and why are the web and arm sheaves used?
On large pulley’s to reduce the weight
49
What are the different sheave materials?
Gray cast iron Steel and ductile iron Sintered steel Pressed steel Aluminum Plastics Nylon polycarbonates
50
How do cylindrical bored hubs transmit power?
They rely on a key
51
How much contact is needed for a tapered bore hub with no key?
85%
52
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
53
What are the limitations of chain drives?
Do not slip on overload Adequate lubrication is hard to achieve Service life is shorter then gears
54
What are the two types of chain?
Roller chain Silent chain
55
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)
56
What are the two types of roller chain?
Pin link Roller link
57
When are cotter pins used on connecting links?
80 pitch and larger
58
When are spring clips used on connecting links?
25 to 60 pitch chains
59
Why do you not want to use half link?
Weaker then standard links
60
True or false? Two pitch offset link provides full strength.
True
61
Where is light duty chain used?
Chain drives where space is restricted
62
What is the difference between heavy duty chain and standard roller chain?
All dimensions are the same except side plate thickness
63
Does heavy duty chain have greater load capacity?
No but thicker side plates increase resistance to fatigue
64
What is heavy duty chain recommended for?
Heavy shock loading and reversing drives
65
What is multiple strand chain?
Chain with two or more stands. Comes up two 12 strands wide.
66
Why are multiple strand chains used?
They are used where loads and speeds are to great for single strand chains.
67
How much stronger is multiple strand chain?
1.7 times stronger than single strand chain
68
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.
69
How much stronger is standard chain than O-ring chain?
5%
70
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
71
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
72
When is double pitched chain used?
Used for long spans, slow to moderate speeds with low horsepower.
73
Why would you use a roller less chain?
Less expensive, used in light applications
74
How can you tell if it is roller less chain?
By a 5 on the right hand part of the chain number
75
When is silent chain used?
High speed drives Transmitting high horsepower in small space Precision timing
76
What are the 3 types of silent chain?
Side guides Centre guide Duplex (serpentine drive)
77
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
78
Before working on a chain drive, what must be done?
De-energized and locked out
79
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
80
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
81
What planes must be the same when aligning chain drives?
Vertical angular and horizontal
82
How many points must touch on straightedge?
4
83
How much is the strength reduced when using a slip fitted connecting link?
30 %
84
What problems are caused from to much tension?
Reduced chain and sprocket life Overloading of bearings inadequate lubrication in the pin and bushing
85
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
86
How much sag on slow to medium speed drives?
4 - 6 %
87
How much sag for high speed, reversing, or impulse drives?
2 - 3 %
88
How much slack for vertical drives?
2 - 3%
89
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
90
What is the most important factor to reduce chain wear?
Lubrication
91
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
92
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
93
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
94
If a chain is elongated by _____ it should be replaced?
3 %
95
When do you replace a sprocket?
Roughness or binding when chain engages Teeth thinned down Teeth hooked at the tips.
96
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
97
To prevent roller failure you can?
Reduce speed or load Or use Multiple strand chain with smaller links
98
What is pitch?
Centre of pin to centre of pin
99
When ordering sprockets what information do you need to give?
Chain pitch Chain type Number of strands Hub style
100
What are the 4 types of sprockets?
A - flat plate style B - hub on one side C - hub on both sides D - split sprocket
101
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
102
Ideal centre distance for chain drive is how many pitches?
30 - 50

Millwright Level 2 (15 decks)

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