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

Introduction Types of Belts: MECH1200 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.

Introduction 2 V-belt was invented by John Gates in 1917. MECH1200 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 Friction

Belt Drive Terminology MECH1200 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

Belt Terminology Effective Tension (Te): Te = T1 – T2 Total Tension: MECH1200 Effective Tension (Te): Te = T1 – T2 Total Tension: Ttotal = T1 + T2 Power: Power HP = 𝑇 𝑒 ×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 33000 Drive Ratio (also called Pulley Ratio): 𝐷𝑟𝑖𝑣𝑒 𝑟𝑎𝑡𝑖𝑜= 𝐷𝑟𝑖𝑣𝑒𝑛 𝑠ℎ𝑒𝑎𝑣𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝐷𝑟𝑖𝑣𝑒𝑟 𝑠ℎ𝑒𝑎𝑣𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

Belt Terminology MECH1200 Belt length: 𝑩𝒆𝒍𝒕 𝒍𝒆𝒏𝒈𝒕𝒉=𝟐𝑪+𝟏.𝟓𝟕 𝑫+𝒅 + 𝑫−𝒅 𝟐 𝟒𝑪 Where: C = center distance D = diameter of large sheave d = diameter of small sheave

Belt Terminology Belt Deflection: MECH1200 𝑡= 𝐶 2 − 𝐷−𝑑 2 2 𝑡= 𝐶 2 − 𝐷−𝑑 2 2 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

Belt Calculations Speed and Torque: MECH1200 Speed and Torque: 𝑆 𝐷𝑉𝑅 𝑆 𝐷𝑉𝑁 = 𝐷 𝐷𝑉𝑁 𝐷 𝐷𝑉𝑅 𝑇 𝐷𝑉𝑁 𝑇 𝐷𝑉𝑅 = 𝐷 𝐷𝑉𝑁 𝐷 𝐷𝑉𝑅 𝑆 𝐷𝑉𝑅 = Driver Speed 𝑆 𝐷𝑉𝑁 = Driven Speed 𝐷 𝐷𝑉𝑅 = Driver Pitch Diameter 𝐷 𝐷𝑉𝑁 = Driven Pitch Diameter 𝑇 𝐷𝑉𝑅 = Driver Torque 𝑇 𝐷𝑉𝑁 = Driven Torque 𝐷 𝐷𝑉𝑅 = Driver Pitch Diameter 𝐷 𝐷𝑉𝑁 = Driven Pitch Diameter 𝑇 𝐷𝑉𝑁 𝑇 𝐷𝑉𝑅 =R 𝑆 𝐷𝑉𝑅 𝑆 𝐷𝑉𝑁 =R

Types of V-Belts MECH1200 Fractional Horsepower V-belts: used for light duty applications below 7.5 Hp. 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”

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’’ MECH1200

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.

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.

Types of V-Belts (continued) MECH1200 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) Banded V-belt: a matched set of V-belts joined together at the top by a permanent band. Double Angle V-Belts: to allow for use in serpentine drives. Identified by a double letter as AA, BB, CC. Open End Belts: for tension adjustment V-Ribbed Belt: has longitudinal ribs, runs smoothly, for high speed applications. Designated by the letters J, L, and M. see figure on page 248. Variable Speed Belt: see page 248-249

Synchronous Belts MECH1200 Also called Timing Belts, positive drive belts, and gear belts. 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: See code on page 256 in the text. 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’’

MECH1200 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’’

Belt Sheaves MECH1200

Sheave Alignment Types of misalignment: Alignment Steps: MECH1200 Types of misalignment: Parallel/Offset Angular 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 w.r.t each other. Use a straight edge to make sure there is contact at 4 points. x x x x

Questions What are the positive drive belts? MECH1200 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.

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

𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑅𝑃𝑀 ×𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒=𝑅𝑃𝑀×0.262×𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 Exercise MECH1200 Drive Sheave 5 HP 1790 RPM 30’’ 10’’ 42’’ Belt What is the belt drive ratio? 𝐷𝑟𝑖𝑣𝑒 𝑟𝑎𝑡𝑖𝑜= 𝐷𝑟𝑖𝑣𝑒𝑛 𝑆ℎ𝑒𝑎𝑣𝑒 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝐷𝑟𝑖𝑣𝑒𝑟 𝑠ℎ𝑒𝑎𝑣𝑒 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 30 10 =3 What is the speed of the driven sheave in RPM? 𝐷𝑟𝑖𝑣𝑒𝑟 𝑆ℎ𝑒𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑 𝐷𝑟𝑖𝑣𝑒𝑛 𝑠ℎ𝑒𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑 =3 ⟹ 𝐷𝑟𝑖𝑣𝑒𝑛 𝑠ℎ𝑒𝑎𝑣𝑒 𝑠𝑝𝑒𝑒𝑑= 1790 3 =597 𝑅𝑃𝑀 What is the sheave velocity 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑅𝑃𝑀 ×𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒=𝑅𝑃𝑀×0.262×𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 ⇒𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑓𝑡/𝑠 =1790×𝜋× 1 𝑓𝑡 12 𝑖𝑛𝑐ℎ ×10 𝑖𝑛𝑐ℎ =4686.2 [𝑓𝑡/𝑠] What is the effective tension (Te )? HP= 𝑇 𝑒 ×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 33,000 ⇒ 𝑇 𝑒 = 𝐻𝑃×33,000 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 5×33,000 4686.2 =35.2 𝑙𝑏 4. What is the length of the belt? belt length=2C+1.57 D+d + 𝐷−𝑑 2 4𝐶 =2×42+1.57 30+10 + 30−10 2 4×42 =149.2 ′′