Cam Design

DESIGN OF HELICAL GEAR ON PRO ENGINEER

GEARAGearis arotatingmachine part having cutteeth which mesh with another toothed part to transmittorque. Geared devices can change the speed, torque, and direction of apower source.

HELICAL GEARHelical gears are cylindrical gears whose teeth are not parallel to the axis of rotation. The teeth are angled and appear as a segment of a helix. Helical gears can transmit power between parallel or right angle axes.

Helical gears transmit power between parallel axes

Helical gears transmit power between perpendicular-axis

Types of helical gear

Terms used in Helical Gear1. Helix angle It is a constant angle made by the helices with the axis of rotation. 2. Axial pitch It is the distance, parallel to the axis, between similar faces of adjacent teeth. It is denoted by pc. 3. Normal pitchIt is the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth. It is denoted by pN. Mathematically. Normal pitch, pN = pc cos B

Face Width of Helical Gears

In case of single Helical Gear b =1.15 Pc/ tan= 1.15*m /tan , ( pc = m) Where b = Minimum face width, and m = ModuleIn case of double helical or herringbone gears, the minimum face width is given byb =2.3 Pc/tan= 2.3*m */tan The maximum face width ranges from 20 m to 30 m.In single helical gears, the helix angle ranges from 20 to 35, while for double helical gears, it may be made upto 45.

Strength of Helical GearWT =( o Cv) b. m.y where WT = Tangential tooth load o = Allowable static stressCv = Velocity factorb = Face widthm = Moduley' = Tooth form factor or Lewis factor corresponding to the formative or virtual or equivalent number of teeth The value of velocity factor (Cv) may be taken as follows Cv = 6 /6 +v for peripheral velocities from 5 m / s to 10 m / s. =15/15+v for peripheral velocities from 10 m / s to 20 m / s.= =0.75/0.75+v for peripheral velocities greater than 20 m / s.

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The dynamic tooth load on the helical gears is given byWD = WT +21v ( b cos^2 +WT) cos /(21v b.C cos ^2 +WT)The static tooth load or endurance strength of the tooth is given by WS = e.b. m.y'

NUMERICALA pair of helical gears are to transmit 15 kW. The teeth are 20 stub in diametral. Plane and have a helix angle of 45. The pinion runs at 10 000 r.p.m. and has 80 mm pitch diameter and having shape factor 0.16575 for 20 stub teeth. If the gears are made of cast steel having allowable static strength of 100 Mpa Determine A Suitable Module Face width

Advantages of Helical GearThe angled teeth engage more gradually than do spur gear teeth causing them to run more smoothly and quietlyHelical gears are highly durable and are ideal for high load applications.Helical gears can be used on non parallel and even perpendicular shafts, and can carry higher loads than can spur gears.At any given time their load is distributed over several teeth, resulting in less wear.Can transmit motion and power between either parallel or right angle shafts.

APPlications of HELICAL GEARHelical gears are normally preferred to work under heavy load efficiently.Helical gears are used in fertilizer industries, Printing industries and earth moving industries.Helical gears are also used in steel, Rolling mills, section rolling mills, power and port industries.Helical gears are also used in textile industries, plastic industries, food industries, conveyors, elevators, blowers, compressors, oil industries & cutters.

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