Millwright Level II Power Transmission Review PDF

NAME: __________________________________ Power Transmission Review 180221CDM Millwright Level II Answers are in dark blue – additional info is in bright blue Shafts, Keys, Hubs, and Fits 1. What are the two major stresses imposed on...

NAME: __________________________________ Power Transmission Review 180221CDM Millwright Level II Answers are in dark blue – additional info is in bright blue Shafts, Keys, Hubs, and Fits 1. What are the two major stresses imposed on shafts? Torsion and Bending 2. What is machined on reduced a diameter shaft end to reduce stress concentration at the corner? Fillet/Radius 3. Why are keys used between shafts and hubs? A removable component which provides a positive transmission of power between mating components 4. Describe these keys and their applications: 1. Straight – Rectangular shaped. Boxed or open key seats, removable or fixed hub (clearance or interference fit) 2. Flat – reduced hub diameters, taper sleeve bushings, low-profile hubs 3. Woodruff – Semi circular, used for light loads 4. Tapered – 1/8 per foot taper, not on cast iron - self-holding 5. Gib Head – Tapered key application with head – removed by fox wedges 6. Step – Key seat and keyway are different sizes – repair 7. Offset – similar to step key but where keyways are not centered 8. Saddle – rectangular with concave bottom to match shaft radius, no key seat, light loads, unidirectional temporary/emergency 9. P&W – Rectangular with radiused ends, in a boxed/closed key seat 10.Feather – One of the rectangular shapes above, held in with screws, clearance fit, where danger of falling out during servic 5. How are Woodruff keys sized? Width in 32nds, diameter in 8ths. #3208 would be 1” wide, Ø1” (no such key). Cutters are sized the same. First digit(s) = Thickness in 32nds, Last two digits = Ø in 8ths 6. What is the taper per foot of a Gib Head key? 1/8 per foot (also 1:96 - less common) Page 1 of 11  NAME: __________________________________ 7. Describe how a key should be fitted into a shaft and into a hub. Snug (tap fit) into seat with matched radiused..002” clearance in keyway of hub with.002-,005” clearance on top for set screw burr clearance. 8. Explain how set screws are used to hold a hub in position on a shaft. Where are they placed and how are they tightened? Threaded holes 90° opposed, one over key. Tighten screw over key then tighten other screw. Same size as key up to ½” Above that, ½” screw is sufficient. Screws should be correct length to reach top of hole to provide equal balance on high speed. Screws would be 2 different length as screw over key is shorter. Screws should not extend out of hole. A second set screw may be used as a locking device but should be flat type to prevent damage to drive of bottom screw. Should fill hole but not extend outside of hole. 9. Describe the following fits: 1. Interference Smallest allowable shaft Ø is larger than largest allowable bore Ø 2. Clearance Largest allowable shaft Ø is smaller than smallest allowable bore Ø 3. Transition Tolerance could result in either a clearance or interference fit 10.How would you determine how much a shaft would expand in length due to temperature rise? Use COE formula ∆𝑙 = 𝑙 · 𝐶𝑂𝐸 · ∆𝑡 or ∆Ø = Ø · 𝐶𝑂𝐸 · ∆𝑡 11.How much will a 2” steel bore expand if the hub is heated to 250°F and ambient temperature is 22°C? ∆𝑙 = 2 ·.0000063 · (250°𝐹 − 71.6°𝐹) =.0022” 12.How is shafting different from cold rolled bar stock? Ground finish, close tolerance, +.000 - -.00X, never over nominal size 13. What are the different tolerances on shafting up to 6”? up to 1” +.000” - -.002” up to 2” +.000 - -.003” up to 4” +.000” - -.004” up to 6” +.000” - -.005” 14.How can a worn shaft be repaired? Spray weld Sleeves Arc weld Page 2 of 11  NAME: __________________________________ Epoxies Chroming 15. Why are splined shafts used? Allow axial movement while transmitting power. i.e.: gearbox, drive shaft Couplings 16.What is the purpose of a coupling? To join shafts to provide power transmission from a driving source to a driven machine May also absorb: slight radial or axial misalignment, and vibration 17.Why do we use flexible couplings? To allow for: slight radial or axial misalignment, structural deflections and settlement of machine foundations 18.Where are rubber insert jaw couplings used? To absorb: vibration, noise, slight misalignment, minor end float (axial misalignment) 19.What is critical about rigid couplings and where would they be used? Require perfect alignment. Used where no thermal expansion or change possible. Low cost. 20.What considerations should be made when selecting a coupling? The coupling should be capable of transmitting the rated torque at the required R.P.M. and compensate for any misalignment of the shafts (including thermal offset). Also consider install/removal requirements, ease of maintenance, space (radial & axial), availability of spare parts (standardize), vibration encountered. 21.Why are shear pins incorporated into couplings and how are the pins chosen? Foremost by their shear strength 22.Describe each of the couplings and where they would be used: 1. Pin & Bushing – High inertia drive to low-inertia driven member. i.e. diesel engine to hydrostatic pump 2. Spacer – Short , removable center section with coupling half on each end, used for ease of maintenance, does not disturb alignment – where shafts are separated by small space 3. Floating shaft – Removable shaft section, coupling half on each end, used through a firewall/bulkhead – where shafts are separated by a large space, maintenance may not affect alignment Page 3 of 11  NAME: __________________________________ 4. Fluid – Turbine and impeller in an enclosed housing. Absorb vibration, smooth starts, overload protection. Slippage at full speed. 5. Dry Fluid – Housing filled with dry shot, centrifugal force packs shot which drives impeller, soft start, no slip at speed. 6. Centrifugal – spring actuated, relied on centrifugal force and weight, provides soft start 23.List the preliminary checks for a coupling alignment. Baseplate – firmly mounted, rigid, clean, no paint, burrs, cracks Driver lower than driven (in most cases) Pipe flanges are parallel and connected Motor feet flat, free of weld spatter, burrs, paint, etc. (same applied to driven unit) Soft feet Bearing condition (also condition of units in general) waste of time to align if units need to be repaired or replaced Coupling and shaft runout 24.Describe the four basic steps of a coupling alignment in order of operation. VA-VO-HA-HO VA – Vertical Angular VO – Vertical Offset (Parallel) HA – Horizontal Angular HO – Horizontal Offset (Parallel) 25.When should pipe connections be made to a pump when aligning shafts? Prior to alignment 26.When would you deliberately misalign two coupled shafts? To compensate for expected thermal expansion differential 27.What are the formulas used for coupling alignment? 𝐷𝑖𝑠𝑡.𝑏𝑒𝑡𝑤𝑒𝑒𝑛 ℎ𝑜𝑙𝑒𝑠 Ø𝑤𝑖𝑝𝑒𝑑 𝑇𝐼𝑅 2 COE 28.Describe the difference between the movable and stationary sides of a coupling alignment. Movable is typically the driver and is shimmed to align with the driven unit which is typically stationary and immovable. Page 4 of 11  NAME: __________________________________ Clutches & Brakes 29.List five methods of actuating mechanical friction clutches. Pneumatic Hydraulic Electric Manual Magnetic Mechanical Torque (overload) 30.What are three classifications of clutches? Mechanical Electromagnetic Magnetic Friction Torque Limiting 31.What is the purpose of a clutch? To enable start and stop of a drive without changing the speed(stopping/starting) the prime mover. Provide soft starts and overload protection 32.How does a brake differ from a clutch? Mounting – Clutch mounts to two shafts – Brake mounts to shaft and is fixed to machine 33.How is the gap set between friction plates and linings? Using feeler gauges, the gap is checked in multiple areas around the friction material, while disengaged, until you have achieved the required gap determined by the manufacturer. 34.Explain the maintenance procedures applicable to friction clutches. Check for oil leaking onto the friction clutches Check for cracks or damage to the friction material Check for dust build up and clean If the friction material is attached with rivets, once the rivet heads are exposed the friction material must be replaced (before the heads of the rivets grind into the non friction surface) 35.What criteria are considered in selecting a clutch? Frequency of operation (heat, wear) Horsepower (torque) Page 5 of 11  NAME: __________________________________ Operating R.P.M. 36.Describe the operation of an electrically operated clutch. Uses a solenoid to engage the clutch 37.Describe the operation of a pneumatically operated brake. A pneumatic bladder, piston, device acts to reduce air gap between linings and drum or disc and create friction. Aid in removing heat from brake. Or a pneumatic cylinder is used to actuate the brake usually through a series of linkages built into the brake. 38.Describe the operation of a magnetic clutch. Electricity may be used to generate a magnetic field which acts on the clutch half to drive the other half. Some generate their own electric current, such as an eddy current clutch, and self regulate. 39.Describe a toothed clutch. Often a manual clutch used to connect or disconnect parts that are stopped or rotating at the same speed. 40.Describe a torque limiting clutch and where it might be used. This clutch will slip if an overload situation exists. This will protect from further damage if a “Jam up” occurs. I.e. high speed packaging machinery, conveyors. 41.Describe the operation of a centrifugal clutch. When does it become positively engaged? Centrifugal force act against a spring and forces a weighted lining outward to create friction. Once the RPM of the rotating shaft provides enough centrifugal force that the friction shoes are force out to engage the inside of the outer hub of the clutch. 42.Why are friction linings softer than their mating pressure plates? So they can wear first. They are replaceable. 43.What might cause a brake to overheat? Overloading Undersized brake Dust build up Oil on the friction plates Excessive force applied Repeated operation/usage 44.What are the advantages of multi-disc clutches? Can be stacked to increase surface area without increasing diametral space Page 6 of 11  NAME: __________________________________ Belt Drives 45.Explain the steps in installation of new V-belts. Reduce the center-to-center distance Install the new belt Tension to “new” belt setting halfway between shafts Recheck tension after 12-24 hours of service 46.What is the arc of contact on a V-belt sheave and how is it determined? it is the area of contact between belt and pulley surfaces dependent on pulley diameter, center-to-center distance and if a take up device is used. 47.Where is the pitch line of a V-belt located? Situated about 1/3 of the thickness of the belt from the top surface 48.What are the differenced between a B50 and 5L530 belt? Cross section of the belt 49.Name 3 V-belt classifications and one size of each. 3V, 5V and 8V 50.Explain how sheave alignment is performed. With straight edge touching on 4 points 51.What must be ensured when installing belts on a multi-belt drive? Shafts are parallel and square and belts are matched 52.Describe how to check belt tension. With belt tensioning tool 53.Where are linked V-belts used? For emergency repairs difficult installs 54.What is a trade name for a joined belt? 55.What configuration are poly V-belts often used for? Compact drives 56.Explain the code of a timing belt and how to determine the length and width of the belt. First number is pitch length x 10- the code for the pitch of the belt- the belts width x 100 57.Describe the possible causes and resolutions when a belt has been found turned over. Belts have been pried on Misaligned sheaves Insufficient tension Page 7 of 11  NAME: __________________________________ Wrong belt type / cross section Obstruction in groove Belt bottomed out in sheave groove 58.What codes are used for FHP V-belts? 2L, 3L, 4L and 5L - each number = 1/8” of width 59.How should belts be stored? Cool dry place hung on loops 60.Determine the approximate belt length required for a drive with one 5” sheave, one 15” sheave and a center distance of 20”. 71.4 = 71-1/2 or 72” 61.A 3” pulley is used to drive a 10” pulley by V-belt. The 10” pulley shares a shaft with a 4” pulley that is, in turn, driving a 15” pulley by V-belt. Calculate the ratios and output speed of the 15” pulley shaft, given an input of 1750 RPM. 140rpm 62.Explain the use of belt dressing. Used to soften the belt and the stickiness of it help attract dirt to stick to it and embed in the pulley and belt. 63.Describe where the slack side of the belt is on a V-belt drive. Opposite of the drive direction 64.What is used to prevent a timing belt from running off the pulley and when is it employed? Flanges on one pulley both when 8 x center distance than pully diameter and vertical drives. 65.What is the recommended tension when no manufacturer’s specs are available? 1/32 per inch of center distance 66.Why might the bearings in an electric motor driving a V-belt overheat? Excessive belt tension 67.What might be heard on start-up if there is insufficient belt tension? squeal 68.What could cause the bottom of a sheave to become shiny? Worn belt/ sheave 69.What is the advantage of a 3V belt over an ‘A’ belt? High-capacity V belts transmit 3 x the HP 70.On a variable speed drive, which sheave diameter is increased to reduce the output RPM? The driven 71.Why do some belts have ribs across the inside? Increase flexibility and heat dissipation smaller sheaves short center and high speed drives Chain Drives 72.Describe the following parts of a roller chain: Page 8 of 11  NAME: __________________________________ 1. Roller link consists of 2 bushings pressed into 2 link plates with 2 rollers on the bushings 2. Plate link plates that connect the roller links together 3. Master link connects 2 roller links 2-pitches 4. Offset link connect outer and inner roller links 1-pitch 5. 2 pitch offset link riveted pin in center of 2 links - 2 pitches plus 2 masters to link chain 73.Name three common methods of retaining chain links to the pins. Spring clip, cotter pins and spring pins 74.Define the type and pitch of the following chain: 1. #35 3/8 pitch rollerless 2. #40 ½ pitch usual or regular proportions 3. #55 5/8 pitch rollerless 4. #80 H 1 inch pitch usual proportions heavy duty 5. #60-2 ¾ pitch usual Proportions double strand 75.Describe the different types of sprocket hubs. A B C D (draw) 76.How are sprockets identified? By chain size pitch hub type and number of teeth 77.List the advantages of chain drives over belts and gears. 98% efficient long distances 78.When are hardened teeth used on sprockets? Heavy loaded drives 25 teeth or less 79.Describe double pitch chain? Where would it be used and give an example of its code. Links 2x as long slow speed light loads code 2040 (1’ pitch 2 x 40) 80.What is the minimum required wrap and on which sprocket? 120 degree 81.What is the recommended tension for a horizontal drive? 2% or 1/32 /inch center distance 82.What is the advantage of multiple strand chain and smaller pitch on high speed roller chain drives? Smoother and longer live 83.Describe silent chain and on which applications its used? Toothed link-plates riveted together heavier applications take more HP 84.How are chains lubricated? Oil brush oil can, drip cup, oil bath, oil disk, oil stream/(spray) 85.Describe the steps in replacing a roller chain using a spool of new chain. 86.Provide possible causes of a noisy chain drive. Loose chain misaligned worn 87.How are chain drive periodically checked or PM’d? chain tension, wear, sprocket wear, lubrication Page 9 of 11  NAME: __________________________________ Gear Drives 88.Explain the following terms of gears: 1. Addendum 2. Dedendum 3. Pitch Circle 4. Pitch Diameter 5. Diametral Pitch 6. Clearance 7. Face 8. Flank 89.Most gearboxes are reducers. What is a gearbox that increases speed called? overdrive 90.Explain how to find the DP of a damaged gear which is to be replaced. # teeth/ pitch diameter. D.P = #teeth/Pitch diameter or #teeth= D.P. x pitch diameter 91.Describe the following gears and provide an application in which they are employed along with the shaft orientation: 1. Spur 2. Rack & Pinion 3. Internal Spur & Pinion 4. Helical Gears 5. Double Helical or Herringbone 6. Bevel 7. Mitre 8. Worm 9. Hypoid 92.Name 2 gears with a 1:1 ratio. Mitre gears, Rack & Pinion 93.Which gears require an EP additive? Hypoid Worm Gears 94.Explain backlash. Distance between gear teeth on pitch circle 95.Describe helix angle and the difference between right and left helices(helixes). Angle up to 45degrees left or right hand thumb 96.How are gearboxes lubricated and what special consideration should be made for vertical shaft gearboxes? 97.Explain how to set end float of a shaft on a worm and wheel gearbox and then how to adjust to correct gear mesh. Page 10 of 11  NAME: __________________________________ 98.What type of bearings are used in conjunction with helical gears and why? Angular thrust taper roller ball and thrust 99.Provide reasons that a gearbox might run too hot? Overloaded no oil 100. What is the gear ratio of a unit with a 10 tooth gear driving a 24 tooth gear? 101. A 50 tooth worm gear is driven by a two-start worm. What is the reduction ratio? 102. An input gear with 20 teeth is driving a 48 tooth gear on a countershaft. The other end of the countershaft has an 18 tooth gear that is meshed with a 60 tooth gear on the output shaft. What is the overall ratio of the gear train? 103. What would the RPM of the output shaft above be if the input were 100 RPM? 104. Describe the possible wear patterns and their causes on gear teeth. Problem Solving 105. A 12”Ø conveyor drum is driven by a chain drive from a 20:1 gear reducer. There are 25 teeth on the reducer output shaft and it is driving a 60 tooth sprocket on the drive drum. The motor is coupled directly to the input of the reducer and rotates at 1725 RPM. Calculate the speed of the belt conveyor in SFPM. 106. If the reducer above was changes to a 12:1 ratio, what number of teeth would be required on the reducer o maintain the previously calculated speed of the conveyor? Page 11 of 11