Belt and pulleys Essay Example

8Belts and Pulleys

Belt and pulleys

Belts and Pulleys

Introduction

. Childs, 2004, 62)Belt drives are very essential in conveying mechanical power from a point to the other. They are mostly found in machines and vehicles. This is mainly because the belt drives tend to have more slippage as opposed to chain drives. Another important aspect to note concerning the pulley that is installed in the belt is not required to be axially aligned (

. Childs, 2004, 62)Pulleys and belts are highly essential for mechanical systems that are required to operate at high speeds. The belt and pulley system is less noisy as opposed to the chain drives. This makes them highly efficient when mechanical power is required to be conveyed over long distances. Belt drives are suitable for mechanical engineering systems that need to run at high speed. They are highly popular in the various mechanical designs that require the reverse drive. There are four types of belts. This includes flat, V-belts, timing, and round belts. V-belts and timing belts are not symmetrical thus they cannot be used for reverse drive systems (

III. MANUFACTURING AND ASSEMBLY

Material ChoicesA.

. Childs, 2004, 62)Aluminum is the most suitable material for the design of pulleys. This is because it is lighter, convenient to carry and assemble, as well as, it require less rigid supports. Aluminum weighs less than half the density of iron. It is also important to note that once aluminum corrodes, it forms a thin layer of aluminum oxide. This thin layer is essential in preventing further corrosion of the metal. It is also a better conductor thus casting of aluminum or heat treatment can be done using various techniques to improve the hardness and strength of the metal (

B. Design and Assembly

. Childs, 2004, 60)The pulleys should be spoked to ensure that there is an economical use of materials, weight, and cost. The efficient rotation of the shafts and pulleys can be attained by mounting them on the shaft and cutting the machine splines out of the pulleys (

Types of Belts

Flat belts

The round or flat bolts are likely to have a surface or two coated with a friction surface. They are relatively quiet and can be used to transmit mechanical power on relatively large center distances. In place of one belt that is wide, a minimum of two round belts are joined, and they operate side by side. These belts van be applied for variable speed drives.

These belts are used to convey mechanical power over short center distances. Several V-belts can be utilized in one pulley. They do not have joints, and they are manufactured in specific lengths.

Timing belts

Childs, 2004, 62). These belts have been proved to transmit mechanical power effectively since they do not slip or stretch when subjected to a load. This is because the pulley is ‘toothed’. As opposed to chain drives, the timing belts are relatively quiet and do not require lubrication. It is important to note that in the case of V-belts, long centre to centre distances are discouraged. This is because the excessive vibration on the slack side is likely to reduce the life of the belts (

Discussion

In the design of the system, V-belts were used as this meant that manufacture of belts was not necessary.

Advantages of V-Belts

They are available off the shelf and they are smooth in starting and operating. Installation is quite easy and they have a long service life. They are also preferred since they allow a range of driven speeds.

Section A

Speed reduction ratio = 2.8:1

Step 2: Input power

T – Torque W – Speed of driver pulley K – Service factor T =? W=800, rpm

C min = 550mm 550 mm < c<1200 T = 119.3 light shock

Step 3 design Power(Pd)

1.1 < k5<1.3 K5 = 1.2 P2 = pi × k5 10,000 × 1.2 = 12,000

Involves choosing and appropriating V-belt type on the basis of the design power

Step 5 (Diameter of driver Pulley)

W1 = 800, W2 = 1/ 2.8 × 800 = 258.7 2+D= C min 2 + D = 550 d= 550- D

2w1 =D w2 d (800) =D (285.7) (550 –D)(800) = D (285.7)

440000 = 1085.7D D = 405.2mm P input 1000 d = 550- 405.2

d = 144.8 mm

d = The diameter of the driving pulley

D= Diameter of the pulley that is driven pulley C=about minimum center distance .w1 & w2 refers to the speed of the pulleys

According to table section c of Mechanical Design =9 inches

Step 6 Calculating the Pitch length

Lp = 2C + ƛ(D+d)/2 + (D-d)2/4C

2(550 )+ ƛ (321.31+228.6 )/2 + (321.31+228.6 ^2)/4(550)

= 2101.2mm=82.60 inch q = 2.9

Step 7 Inside Circumference

Lp = Li – q Li 82.60 -2.9 =79.7 inch Li standard

Step 8 Actual Pitch Length

Lp = Li + q 82.60+2.9 =

C = A + ( A2-B)0.5 A = Lp /4 – ƛ/8(D+D)

2131.06/4 — ƛ/8(321.31 +228.6) = 316.8 mm

B = (D-d)^2 /8 = (321.31-228.6)^2/8 = 1074.39mm

C = 316.8 + ((316.8)^2 – 1074.39)^0.5= 631.8 mm

D-d/ C = 321.31 -228.9/ 631.8 = 0.146 mm

K1 = Correction factor angle of Contact

W – 0.97, v flat – 0.78 K1=0.20+0.97/2=0.58mm

K2 = Correction factor for the belt length K 2 = 0.90

V = wd/2 W = 8 800rpm 800 (2 ƛ).9/2

V = 22619.46 =22619.46 (0.833) =1.884 ft/min

3.34 hp 5.65hp

1000 3.34

2000 5.65

1000 – 1884/ 3.34 – x = 1000-2000/3.34-5.65

-884/3.34-x = -1000/ -2.31 -20.42 = 3.34 –x

P = 4.38 hp X = 4.38 P = 4.38 hp

Pc=Pr*k1*k2=4.38*0.58*0.90=2.28mm

T1/T2=7 Pi=(T1-T2) V

16=(T1-T2) 378 T=16/2268=0.007mm T=7*0.007=0.007

For get the reduction 2.8:1 I need to use 7 belts for N

Belt and pulleys 1

Top of FormReference

CHILDS, P. R. N. (2004). Mechanical design. Oxford, Elsevier Butterworth-Heinemann. http://public.eblib.com/choice/publicfullrecord.aspx?p=288872.

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