Cotter joints

you will be able to improve you knowledge about cotter joints. i think after study this section you will know how to design cotter joints.

1. MACHINE Design presentation – 3 Cotter joints D.M.Gamage Institute of technology University of moratuwa Sri lanka

2. 1. What is a cotter joints A cotter is a flag wedge shaped piece of steel. Cotter joint uses one or two cotters to connect two rods rigidly transmitting forces and motion, with no rotation of the rods

3. 2. Types of cotter joints Socket and spigot cotter joint. Sleeve and cotter joints. Gib and cotter joints .

4. Socket and spigot cotter joint . In a socket and spigot cotter joints, one end of the rods is provided with a socket type of end and the other end of the rod is inserted into a socket the end of the rod which goes in to a socket is also called spigot .a rectangular hole is made in the socket and spigot

5. A cotter is then driven tightly through a hole in order to make the temporary connection between the two rods the load is usually acting axially but it changes its direction Hence the cotter must be design to carry both the tensile and compressive load is taken up by the collar on the spigot.

6. Sleeve and cotter joints. Sleeve and cotter joint is a type of joint used to typically connect two similar coaxial cylindrical rods it contains a sleeve and two wedge shaped tapered cotters appropriate slots are cut in the sleeve and in the cylindrical rods the cotters are assembled in to these slots.

7. Gib and cotter joints. There are 3 type of gib and cotter joints Gib and cotter joints COTTER WITHOUT GIB COTTER WITH ONE GIB COTTER WITH TWO GIB

8. COTTER WITH ONE GIB When one gib is used the cotter with one side tapered is provided and the gib is always on the outer slide. COTTER WITH TWO GIB When two gibs are used the cotter with both slide tapered is provided.

9. Cotter without gibs When the cotter alone is driven the friction between its ends. The inside of the slots in the strap tends to cause the slides of the strap to spread outwards. More ever gibes provide a larger bearing surface for the cotter to slide on due to increase holding power.

10. 3. Application of cotter joints Connection of the piston rod with the cross heads. Connection of a valve rod to its stem. Joining of tail rod with piston rod of a wet air pump. Connecting two halves of fly wheel.

11. 4.Advantages of cotter joints Cotter joints can be easily made, and the parts always occupy exactly the same relative positions after reassembly The joints can be used to connect similar pipes tubes. It is quite rigid and can take both tensile and compressive loads.

12. 5.Disadvantages of cotter joints Rectangular rods and dissimilar cylindrical rods cannot be connected usingthis joints. The sleeve and cotter joints which cannot connect cylindrical members undergo rotation.

13. 6. Failure of a Cotter Joint

14. DESIGNING OF ROD Designing of rod we should consider FALIURE OF ROD IN TENSION FALIURE OF ROD FALIURE OF ROD OR COTTER IN CRUSHING FALIURE OF ROD’S END IN SHEAR

15. Tension failure of the rods at diameter d Assume that the rod end, socket end and the cotter are made of the same material P is the tensile force on the joint C, t , and are the permissible tensile, shearing and crushing stresses respectively Internal resistance to tearing = external applied load d 2 t = P  

16. FALIURE OF ROD OR COTTER IN CRUSHING d 1 t c = p  

17. FALIURE OF ROD’S END IN SHEAR 2 a d 1 = P  

18. Designing of spigot Failure of spigot in tension across the slot Failure of spigot failure of spigot collar in crushing Failure of spigot collar in shearing

19. Tension failure of the spigot across the slot ( d 1 2 – d 1 t ) t = P Inner diameter of the socket, d 1 can be obtained when the thickness of the cotter, t , is known  

20. Failure of spigot collar in crushing Cotter joint may be used for transmitting compressive load also This compressive load is transmitted through the collar (whereas the tensile load is transmitted through the cotter) (d 1 2 – d 2 2 ) c = P  

21. Failure of spigot collar in shearing d 1 t 1 = P Thickness of the collar, t 1 can be calculated  

22. Designing of socket failure of socket in tension across the slot Failure of socket failure of socket collar in crushing failure of socket end in shearing

23. failure of socket in tension across the slot P = {( D 1 2 - d 1 2 ) - ( D 1 - d 1 )t } c   The outer diameter of the socket, D 1 , can be obtained

24. failure of socket collar in crushing (D 1 – d 1 ) t c = P  

25. failure of socket end in shearing 2 c (D – d 1 ) = P  

26. Designing of cotter Shear failure of the Cotter 2 b t = P The width of the cotter b can be obtained Taper of the cotter To ensure that the cotter does not work back, the taper should not exceed 1 in 24  

27. Bending of cotter Since the distribution of pressure on the crushing surface is unknown, the bending moment cannot be accurately estimated Pressure distribution is assumed to be as shown in the figure t = =  

28. t h a n k y o u