Gears And its types

A Brief Description of Gears and its Types for UG Students....

1. Kumaraguru College Of Technology P15CCT104 - INTEGRATED MECHANICAL DESIGN GEARS Presented By, RAGHUL S(17MCC006)

2. Table of Contents Introduction General Nomenclature Types Of Gears Gear Materials Gear Tooth Failure

3. Introduction: A gear is a wheel with teeth that mesh together with other gears. Transmit motion by engaging teeth Two or more meshing gears, working in a sequence, are called a gear train Used to change, Speed Torque Direction

4. General nomenclature

5. Face Width: The Face width of a gear is the length of teeth in an axial plane. Pressure Angle ( α ): Pressure angle is the leaning angle of a gear tooth, an element determining the tooth profile. Whole depth: The distance from the top of the tooth to the root; it is equal to addendum plus dedendum or to working depth plus clearance. Working depth:   Depth of engagement of two gears, that is, the sum of their operating addendums.

6. Pitch circle: A Pitch circle is the curve of intersection of a pitch surface of revolution and a plane of rotation. Outside diameter: Diameter of the gear, measured from the tops of the teeth. Root diameter : Diameter of the gear, measured at the base of the tooth. Clearance: Distance between the root circle of a gear and the addendum circle of its mate.

7. Addendum: Radial distance between the pitch diameter and the outside diameter. Addendum circle: Coincides with the tops of the teeth of a gear and is concentric with the standard pitch circle. Dedendum: Radial distance from the depth of the tooth trough to the pitch surface. Dedendum Circle: The circle touching the bottom of the spaces between the teeth of a gear wheel.

8. Types Of Gear: Spur Gear Helical Gear Bevel Gear Worm Gear Rack And Pinion Herringbone Gear

9. Spur Gear: Most commonly used Gear type. Teeth are parallel to the axis of the gear. Transmit power from one shaft to other parallel shaft.

10. Advantage: Low Cost Ease of manufacture Availability Disadvantage: Only works with mating gear Axis of each gear must be parallel Applications: Washing Machines, Rolling Mills, Marine Engines.

11. Helical gear Teeth are at an angle to the gear axis This gradual arrangement makes helical gear operate much more smoothly and quietly than spur gear Can transmit power between Right angle or Parallel Axis

12. Advantage: Smooth and quiet due to gradual tooth engagements Parallel to perpendicular shaft arrangement Disadvantage: Difficult to Manufacture Cost is High Resulting axial thrust component Applications: Fertilizer industries, Printing industries, earth moving industries, Conveyors, Elevators

13. Bevel Gear: Usefull when the direction of shaft location has to be changed. Mounted on shaft that are 90deg apart, can also be designed to work in other angles. Teeth can be straight, Spiral or Hypoid

14. Advantage: Operate on Shafts intersecting at an Angle. Sliding friction will be low. Disadvantage: Assembled with respective shaft precisely. At high speed it will produce noise. Applications: Textile Machine, Sewing Machine.

15. Worm Gear: Used when large Gear Reduction is needed. Have good intersecting property. Used widely in material Handling and transportation machinery, machine tools etc…

16. Advantage: Higher speed reduction could be secured; speed reduction could be secured up to 300:1 Worm and worm gears operate silently Disadvantage: Manufacturing cost is high as compared with manufacturing cost of bevel gear Worm and worm gear set will have heavy power losses. Efficiency will be low Applications: Tuning Instruments, Lifts/Elevators.

17. Rack And Pinion: Convert Rotational to Linear motion Round Gear – Pinion Flat or Straight Gear – Rack Best example is Car Steering System.

18. Advantage: Rack and pinion gives easier and more compact control over the vehicle Cheap, Compact, Robust. Disadvantage: The rack and pinion can only work with certain levels of friction. Applications: Rack Elevators, Steering.

19. Herringbone Gear: Two helical gears that have been placed side by side. Referred to as “double helical”. No thrust loading on the bearings

20. Advantage : The double helical form balances the inherent thrust forces. Efficient transfer of torque and smooth motion at very high rotational velocities. Disadvantage: High cost due to special gear shaping equipment and special cutting tools . Applications: Used in Heavy Machinery.

21. Gear Materials: Numerous nonferrous alloys, cast irons, powder-metallurgy and plastics are used in the manufacture of gears. Steels - commonly used - high strength-to-weight ratio and low cost. Plastics - cost or weight is a concern - Reduce repair cost.

22. Gear Tooth Failure: Gear failure can occur in various modes. Care has to be taken to avoid such failures Types of Gear Tooth Failure: Scoring Failure Wear Failure Pitting Failure Plastic Flow Tooth Fracture

23. Scoring Failure: Occurs Due to Lubrication failure in Contact region and metal to metal contact. Weldi n g and tearing action resulting from metallic contact removes the metal. Types of Scoring: Initial Scoring Moderate Scoring Destructive Scoring

24. Initial Scoring: Occurs by High spots left by previous machine. Lubrication failure at this point leads to Scoring Scoring stops when temperature, load and speed remains unchanged.

25. Moderate Scoring: Occurs After initial scoring if the load, speed or oil t emperatu r e increases, the scoring will spread over to a larger area. Progresses at tolerable rate.

26. Destructive Scoring: If the load, speed or oil temperature increases appreciabl y , then severe scoring sets in with heavy me t al will occur. Predominant over Pitch line since the lubrication is least at that region.

27. Wear Failure: Wear is a kind of tooth damage whe r e a layers of metal are removed more or less uniformly from the surface. Tooth Thins and get weakened. Cause of gear tooth wear is Adhesive Wear Abrasive Wear Corrosion Wear

28. Adhesive Wear: Hard to detect. Occurs from start since the rate of wear is low. When the load and s peed of o peration a r e more than m ild wear conditions, moderate wear takes place with higher rate. Occurs over long Period.

29. Abrasive Wear: Reason for the failure of open gearing and closed gearing of machine operated in Abrasive materials. Depending on t he size, shape and con c entration of the abrasives the wear will change.

30. Corrosion Wear: Due to the chemical act i on of the lubricating oil or the additives.

31. Pitting Failure: Surface fatigue failu r e of t he gear tooth. Occur due to repeated loading of tooth surface and contact stress. Pit is formed. Impact load resulting from pitting may cause failure. Types of Pitting Initial Pitting Progressive Pitting

32. Initial Pitting: Sm all pits of 25 to 50 μm deep are formed just below the pitch line. the load gets distributed over a larger surface area and stress comes down. Common with medium hard Gears.

33. Progressive Pitting: High load and corrective action of initial pitting leads to Progressive Pitting. Pitting begins on the t ooth flanks near t he line along t he too t h p assing through the pitch point. Very rare in tooth Face.

34. Plastic Flow: Occurs due to sliding action of Gear. Surface deformation Occurs due to yielding of surface. But occurs only in heavy loading Case.

35. Tooth Fracture: Dangerous kind of gear failure leads to disablement of drive and frequently to damage of other components. Occurs over a long a period of time. Tooth failure may result low-cycle fatigue, Repeated cyclic load

36. THANK YOU