Topics

1. MECH1200 Topics • Introduction • Belt Drive Terminology • Types of V-Belts • Synchronous Belts • Belt Sheaves • Please read Chapter 10 in the text.

2. MECH1200 Introduction • Types of Belts: • Flat Belt: Least efficient, thus rarely used as a power drive, but still in use as conveyors. It was commonly used in the 19th century • V-Belt: work by friction, may slip. It was invented in 1917 • Synchronous Belt: has teeth, and does not slip. Most efficient.

3. MECH1200 Introduction 2 • V-belt was invented by John Gates in 1917. • Advantages of belt drives: • Low cost • No lubrication required • Shock resistance • V-belt drive operation depends on: • Tension – tension, ironically, is what helps a belt work but is also what wears it down. • Friction

4. MECH1200 Belt Drive Terminology Driven Sheave (Pulley) Arc of Contact Driver Sheave (Pulley) Belt Tight side T1 Center Distance Slack side T2 Source: Drawing is in the public domain and was taken from Wikimedia Commons, Wikimedia Foundation

5. MECH1200 Belt Terminology Effective Tension (Te) - how hard is the belt pulling, what is the transmission of power? Te = T1 – T2 Total Tension – the tension the belts and shafts must support Ttotal = T1 + T2 Ex: 50# + 10# = 60# Power: Higher speed means less net pull, higher HP means more net pull is needed.

6. MECH1200 Belt Terminology Drive Ratio (also called Pulley Ratio): For example, a 4” diameter 1750 driver (motor sheave) and a 12” driven sheave have a ratio of what? Drive Ratio = == 3:1 Driven RPM = Driver RPM ÷ = 1750 ÷= 583.33 RPM This setup created a speed reduction. Putting the larger sheave on the driver and the smaller on the driven would result in a speed up drive.

7. MECH1200 Belt Terminology Belt length: Where: C = center distance D = diameter of large sheave d = diameter of small sheave

8. MECH1200 Belt Terminology Belt Deflection: t = span length, in inches C = center distance, in inches D = large sheave pitch diameter in inches d = small sheave pitch diameter in inches Calculate the deflection distance by: t/64 = deflection. Deflection distance is always 1/64” per inch of span length. Example: A 32” span length would require a deflection of 32/64 or ½ inch

9. MECH1200 Belt Calculations Speed and Torque: = Driver Speed = Driven Speed = Driver Pitch Diameter = Driven Pitch Diameter = Driver Torque = Driven Torque = Driver Pitch Diameter = Driven Pitch Diameter R R

10. MECH1200 Types of V-Belts Fractional Horsepower V-belts: used for light duty applications below 7.5 HP, i.e. small shop equipment or small garden equipment Classical V-belts: standard v-belts, used in heavy duty applications. Notches may be added to the belt to reduce bending stress. How to identify classical V-belts? • Cross sections are designated as A, B, C, D, and E. • Belt length measured on the circumference is designated numbers following the letter prefix • Notched V-belts are identified by an “X”

11. MECH1200 Classical V-belt dimensions: Prefix width across the top A ½ ’’ B 21/32 ’’ C 7/8 ’’ D 1 ¼ ’’ E 1 ½ ’’ Example 1: A belt has the number A42 what is its top cross sectional width and its inside circumference length? Answer: from the table above, prefix A indicates a top width of ½’’ and a circumference of 42’’

12. MECH1200 Example 2: What are the dimensions of the belt shown in the figure below? Answer: The belt shown above has a top width of ½’’ from the A prefix; and an inside circumference of 58’’. Exercise: Go to the Amatrol trainer after this lecture, and locate this belt, then measure its dimensions and match your measurements to that indicated on it.

13. MECH1200 Example 3: What are the dimensions of the belt shown in the figure below? Answer: The belt shown has a top width of 21/32’’ from the B prefix; and an inside circumference of 36’’. The “X” indicates that it is a notched belt as shown above. Exercise: Locate this belt in the trainer, measure its dimensions and match your measurements to that indicated on it.

14. MECH1200 Types of V-Belts (continued) Narrow Section V-Belts: Also called Wedge belts, cross sections are narrower than the classical belts. Used for high duty applications (up to 500 Hp) – similar ratings to classic, but smaller and compact reduces cost and space requirements. Banded V-belt: a matched set of V-belts joined together at the top by a permanent band – used in applications that are subject to extreme vibration and pulsating. Double Angle V-Belts: to allow for use in serpentine drives (alternator, types of pumps that use one belt for several “pulleys”. Identified by a double letter as AA, BB, CC. Open End Belts: for tension adjustment, allows for quick replacement of belts and requires a fastener clip and tool. V-Ribbed Belt: has longitudinal ribs, runs smoothly, for high speed applications. Designated by the letters J, L, and . Variable Speed Belt: used on drives with adjustable pitch sheaves, higher load carrying capacity and when variable speeds are required https://www.youtube.com/watch?v=O4h-Me5lSOY

15. MECH1200 Synchronous (Timing) Belts • Also called Timing Belts, positive drive belts, and gear belts. • Positive drive means movement without slip such as the case in the linking between the crankshaft an the camshaft in the reciprocating engine. Belts are usually negative (or contain slippage). • Slip is not allowed in synchronous belt drives • If jamming occurs the V-belt will slip, but the synchronous belt will shear off. • Synchronous Belt Dimensions: Five stock pitches found on page 256 in the text. Belt with a part number 400H025 means: the length of the belt is 400 tenths of an inch, or 40 inches. The H means the pitch is ½” and a width of ¼” https://www.youtube.com/watch?v=DKF5dKo_r_Y https://www.youtube.com/watch?v=MFylgsucVFs

16. MECH1200 Example 4: What is the length, pitch, and width of the synchronous belt specified as 200XL025? Answer: length is 200 tenths of inches = 20 inches, XL indicates a pitch of 1/5’’ and the width is 0.25 inch = ¼’’ Example 5: What is the length, pitch, and width of the synchronous belt specified as 500H150? Answer: length is 500 tenths of inches = 50 inches, H indicates a pitch of 1/2’’ and the width is 1.50 inch = 1 ½’’

17. MECH1200 Belt Sheaves Synchronous Sheave Double Groove Sheave Single Groove Sheave

18. MECH1200 Sheave Alignment Types of misalignment: Angular Parallel/Offset Angular & Offset Alignment Steps: • Use a feeler gauge to check bases for “soft foot”. • Use a level to make sure the driver and driven shafts are level with respect to each other. • Use a straight edge to make sure there is contact at 4 points. x x x x

19. MECH1200 Questions • What are the positive drive belts? • The Open end V-belts • A type of the narrow section V-belts • The double angle V-belts • The synchronous belts • Banded V-belts • What is another name for a sheave? Pulley • Which do you think will cause a higher overhung load on the shaft, the V-belt or the timing belt of a similar rating? The V-belt, because it only relies on friction and tension, but the timing belt has teeth on it.

20. MECH1200 4. What is the pulley ratio of the belt drive below? 2.5’’ 8’’ Solution: Drive (Pulley) ratio = 8/2.5 = 3.2

21. MECH1200 Drive Sheave 5 HP 1790 RPM Exercise 30’’ 10’’ 42’’ Belt What is the belt drive ratio? What is the speed of the driven sheave in RPM? What is the sheave velocity What is the effective tension (Te )? 4. What is the length of the belt?