WORM GEAR

Presentation on Worm GearPresented by :

SHARFARAZ AHMED (12000713092)SHIVANK KUMAR (12000713093)SHUBHODIP PAL (12000713094)SHUBHAM (12000713095)SHUBHAM ACHARYA (12000713096)SHUBHANKAR SOE (12000713097)SIBARAM KUNDU (12000713098)

MECHANICAL ENGINEERINGB.TECH (7th SEMESTER)Dr. B. C. Roy Engineering College, Durgapur

INTRODUCTIONWorm gears are gears which are widely used for transmitting power at high velocity ratios between non-intersecting shafts that are generally, but not necessarily, at right angles.It can give velocity ratios as high as 300:1 or more.It is mostly used as a speed reducer, which consists of worm and worm wheel or gear.The worm wheel or gear is similar to a helical gear with a face curved to conform to the shape of the worm.

TYPES OF WORMSThere are two types of worms. They are as follows: 1. Cylindrical or straight worm. 2. Cone or double enveloping worm.

TYPES OF WORM GEARSThe important three types of worm gears are given below. 1.Straight face worm gear.

2.Hobbed straight face worm gear.

3.Concave face worm gear.

MATERIALS USED:FOR WORM:CAST IRON ALLOY STEELCAST STEELS CARBON STEELSFOR WORM WHEEL: ALUMINIUMBRASS COPPERPLASTIC

Terms Used Axial pitch: It is also known as linear pitch of a worm. It is the distance measured axially from a point on one thread to the corresponding point on the adjacent point on the worm.Lead: It is the linear distance through which a point on a thread moves ahead in one revolution of the worm.Lead angle: It is the angle between the tangent to the thread helix on the pitch cylinder and the plane normal to the axis of the worm. It is denoted by .

Tooth pressure angle: It is measured in a plane containing the axis of the worm and is equal to one- half the thread profile angle.Normal pitch: It is a distance measured along the normal to the threads between two corresponding points on two adjacent threads of the worm.Helix angle: It is the angle between the tangent to the thread helix on the pitch cylinder and the axis of the worm.Velocity ratio: It is the ratio of speed of worm in r.p.m to the speed of worm gear in r.p.m.

How worm gear works

The worm (screw) continuously rotates and drives the worm wheel (meshed with it). Worm and worm gear form alower pairas they have sliding contact with each other.In a worm gear drive, power is always transmitted from worm to worm wheel. Power cannot be transmitted from worm wheel to worm. This phenomenon is called self-locking. It is highly useful in many applications.Velocity ratio is determined by the number of teeth on worm gear and the number starts on worm. Power transmission decreases with increase in velocity ratio.

Short Animation on working of Worm Gear:

Formula used :

Forces acting on Worm Gear:

Advantages of Worm Drives:

Worm gear drives operate silently and smoothly.They are self-locking.They occupy less space.They have good meshing effectiveness.They can be used for reducing speed and increasing torque.High velocity ratio of the order of 100 can be obtained in a single step

Disadvantages of Worm Drives:

Worm gear materials are expensive.Worm drives have high power losses and low transmission efficiency.They produce a lot of heat.

Applications of Worm Gear Drives:

Gate control mechanismsHoisting machinesAutomobile steering mechanismsLiftsConveyorsPressesSpeed reducer

Areas of further Research and Development specific lubricantsSpecial design for effective lubrication and coolingNew material to accommodate less losses of material in worm wheelDevelopment of specific pair of material for higher transmission capacity and efficiency

References:WikipediaA Textbook of Machine design: R.S khrumi & J.K Guptahttp://mechteacher.com/worm-gear/ScienceDirecthttp://www.youtube.com/watch?v=IYLEUJmVFWohttp://web.iitd.ac.in/~saha/public_html-old/ipromm09loom.pdfhttp://nptel.ac.in/courses/IIT-MADRAS/Machine_Design_II/pdf/2_15.pdf

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