Lecture Riveted Joints by molvie imran.pptx

Lecture Riveted Joints by molvie imran.pptx

1. Machine Design – I Code: ME - 216 Credit Hours: 2 Lecture Rivets and Riveted joints Dr. Muhammad Imran Mechanical Engineering Department University of Engineering & Technology Taxila

2. Fasteners /Joints

3. RIVETS & RIVETED JOINTS

4. Rivet Material for rivets Essential qualities of Rivet Methods of Riveting Purpose of Riveting Classification of R ivets or Rivet heads Classification of Riveted joint Terminology of Riveted joint Caulking and Fullering operations Types of Failure and Strength Equations Riveted Joints for Boiler Shell RIVETS & RIVETED JOINTS

5. Rivets are short cylindrical pieces of ductile metal having a head , shank and tail Used to join two or more pieces of sheet metals permanently, plates to rolled sections, rolled section to each other etc… Rivets are used for joining of sheets and plates in bridges, boilers, storage tanks, pressure vessels and ships etc… RIVET

6. MATERIAL FOR RIVETS Rivets made of mild steel are used in most of the applications Rivets used in corrosive atmosphere are made of stainless steel Rivets used for connecting non ferrous metals and soft materials are made of copper, brass, bronze and aluminium alloys Duralumin rivets are used for structural joints made of aluminium alloy section

7. PROPERTIES OF THE RIVETS Rivet should be sound, free from cracks, flaws, burrs, seams, pits and other defects Rivet head should be concentric with axis of the shank Rivet end should be square with respect to the axis

8. Th e pro c e ss o f join i n g t w o o r mor e p l ates by means of rivets is called riveting RIVETING

9. During riveting, rivet head is formed from the tail of the rivet when it is place d in the rivet holes drilled in the plates to be fastened Forming of head may be either by hand tools or by machines In machine riveting, force is applied by means of hydraulic or pneumatic pressure METHODS OF RIVETING

10. METHODS OF RIVETING HAND RIVETING MACHINE RIVETING ON THE BASIS OF TEMPERATURE OF SHANK HOT RIVETING COLD RIVETING METHODS OF RIVETING

11. For fluid tightness in case of Boilers, pressure vessels and ships For strength and rigidity in bridges, trusses, cranes and machinery For strength, rigidity, durability and leakproofness in shiphull PURPOSE OF RIVETING

12. Following types of rivets are used for different work Structural rivets (12 to 45mm dia.): Boiler rivets (12 to 50mm dia.) Small rivets (2 to 10mm dia.) (1 ) Structu r al r i v et s ( 1 2 t o 45 mm di a . ): Us e d for structural work TYPES OF RIVETS Snap Head Pan Head Pan Head with Tapered neck Round countersunk Countersunk Head Head

13. (2) Boiler rivets (12 to 50mm dia.): Used for boiler works TYPES OF RIVETS Snap Head Pan Head Ellipsoidal Pan head 1 Conical Head

14. (2) Small rivets (2 to 10mm dia.): Used for general purposes and are of steel brass or aluminium TYPES OF RIVETS Flat Head Countersunk Head Mushroom Head Round Head 1.75d 0.75d

15. Depending upon the manner of placing the plates, riveted joints are classified in to two types Lap joint and Butt joint Lap joint Butt joint CLASSIFICATION OF RIVETED JOINTS

16. Dep e ndin g up o n n o . o f row s o f rivet s i n a joi n t, riveted joints are divided into two types Single riveted joint and Multiple riveted joint Double riveted Triple riveted Quadruple riveted etc… CLASSIFICATION OF RIVETED JOINTS

17. CLASSIFICATION OF RIVETED JOINTS SINGLE RIVETED LAP JOINT

18. CLASSIFICATION OF RIVETED JOINTS DOUBLE RIVETED LAP JOINT

19. CLASSIFICATION OF RIVETED JOINTS SINGLE RIVETED SINGLE STRAP BUTT JOINT

20. CLASSIFICATION OF RIVETED JOINTS 29 SINGLE RIVETED DOUBLE STRAP BUTT JOINT

21. CLASSIFICATION OF RIVETED JOINTS DOUBLE RIVETED DOUBLE STRAP BUTT JOINT

22. CLASSIFICATION OF RIVETED JOINTS Dep e ndin g upo n arrangem en t o f rivet s in adjacent rows, riveted joints are classified as; Chain riveted joint and Zig-zag riveted joint

23. CLASSIFICATION OF RIVETED JOINTS CHAIN RIVETED JOINT

24. CHAIN RIVETED JOINT

25. ZIG-ZAG RIVETED JOINT

26. ZIG-ZAG RIVETED JOINT

27. LOZENGE RIVETED JOINT

28. Riveted joints may also be classified as; Structural joints and Pressure vessel joints Angle Joint CLASSIFICATION OF RIVETED JOINTS

29. CLASSIFICATION OF RIVETED JOINTS Column and Beam Joint

30. CLASSIFICATION OF RIVETED JOINTS Built up girder

31. TERMINOLOGY OF RIVETED JOINTS R i v e t di a mete r i s rep r e s en t e d b y ‘d ’ a n d plate thickness is represented by ‘t’

32. The thickness of plate (t) The diameter of the shank (or rivet) (d) U sing Unwin’s formula d  6 t Stan d ard dia m eter s o f rivet s a s per B. I .S . are shown in the table TERMINOLOGY OF RIVETED JOINTS

33. LENGTH OF THE SHANK TERMINOLOGY OF RIVETED JOINTS

34. Gaug e l i n e: I t i s a l i n e t h roug h t h e c e n t e r s o f a row of rivets and parallel to the edge of the plate

35. Pitch or longitudinal pitch : (p) It is a the distance from the centre of the rivet to the centre of the next rivet in the same row measured on the gauge line

36. T r ansv e r s e pitc h or back pitch or row pitch ( p t ) I t i s a t h e di s tance betw e en adjacent gauge lines in the same plate.

37. Diagonal pitch : ( p d ) It is a the distance between the centres of adjacent rivets on adjacent gauge lines in the same plate .

38. M a r gin or Marginal pitch: ( m) It i s t h e di s t a nc e fro m t h e edge o f t h e plate to the entre of the nearest rivet hole .

39. P roportions as per B.I.S .

40. To obtain leak proof joints, the edges of the plates to be joined and the rivet heads are forced to gether by caulking and fullering operations CAULKING AND FULLERING OPERATIONS CAULKING Caulking plate The outer edges of the plates are bevelled These bevelled edges of the plates are caulked Caulking is an operation in which the outer bevelled edges of the plates are hammered and driven-in by a caulking tool The caulking tool is in the form of a blunt edged chisel

41. CAULKING AND FULLERING OPERATIONS Similar to caulking, fullering is also used to produce air tight joints. Unlike the caulking tool, the width of the fullering tool is equal to the width of the bevelled edges of the plates

42. 1 Shear failure of the rivet 2 Tensile failure of the plate between two consecutive rivets 3 Crushing failure of the plate 4 Tearing of the plate in the margin area TYPES OF FAILURE IN RIVETED JOINT

43. Failures of a Riveted Joint A riveted joint may fail in the following ways : Tearing of the plate at an edge . A joint may fail due to tearing of the plate at an edge as shown in Fig. This can be avoided by keeping the margin, m = 1.5 d , where d is the diameter of the rivet hole.

44. Failures of a Riveted Joint 2. Tearing of the plate across a row of rivets . Due to the tensile stresses in the main plates, the main plate or cover plates may tear off across a row of rivets as shown in Fig. In such cases, we consider only one pitch length of the plate, since every rivet is responsible for that much length of the plate only.

45. Failures of a Riveted Joint 2. Tearing of the plate across a row of rivets . The resistance offered by the plate against tearing is known as tearing resistance or tearing strength or tearing value of the plate. Let p = Pitch of the rivets, d = Diameter of the rivet hole, t = Thickness of the plate, and P= Applied tensile stress per pitch length σ t = Permissible tensile stress for the plate material. We know that tearing area per pitch length, A t = ( p – d ) t Tearing resistance or pull required to tear off the plate per pitch length, P t = A t . σ t = ( p – d ) t . σ t Hence, the joint will not fail if

46. 3. Shearing of the rivets . The plates which are connected by the rivets exert tensile stress on the rivets, and if the rivets are unable to resist the stress, they are sheared off as shown in Fig. Failures of a Riveted Joint Single shear Double shear

47. Let, d = Diameter of the rivet hole,  = Safe permissible shear stress for the rivet material, and n = Number of rivets per pitch length. P= Applied tensile stress per pitch length We know that shearing area, A s = / 4 × d 2 ...(In single shear) A s = 2 × / 4 × d 2 ...(Theoretically, in double shear) A s = 1.875 × / 4 × d 2 ...(In double shear, Shearing resistance or pull required to shear off the rivet per pitch length, P s = n × / 4 × d 2 ×  ...(In single shear) P s = n × 2× / 4 × d 2 × ...( In double shear) Hence, the joint will not fail if Failures of a Riveted Joint

48. 4. Crushing of the plate or rivets . Sometimes, the rivets do not actually shear off under the tensile stress, but are crushed as shown in Fig. Failures of a Riveted Joint Due to this, the rivet hole becomes of an oval shape and hence the joint becomes loose. The failure of rivets in such a manner is also known as bearing failure . The area which resists this action is the projected area of the hole or rivet on diametral plane.

49. d = Diameter of the rivet hole, t = Thickness of the plate, σ c = Safe permissible crushing stress for the rivet or plate material, and n = Number of rivets per pitch length under crushing. P= Applied tensile stress per pitch length Failures of a Riveted Joint Crushing area per rivet ( i.e. projected area per rivet), A c = d.t Total crushing area = n.d.t and crushing resistance or pull required to crush the rivet per pitch length, P c = n.d.t . σ c When the crushing resistance ( Pc ) is greater than the applied load ( P ) per pitch length, then this type of failure will occur. The failure in this mode will not occur if

50. Strength of a Riveted Joint The strength of a joint may be defined as the maximum force, which it can transmit, without causing it to fail. P t , P s and P c are the pulls required to tear off the plate, shearing off the rivet and crushing off the rivet. A little consideration will show that if we go on increasing the pull on a riveted joint, it will fail when the least of these three pulls is reached, because a higher value of the other pulls will never reach since the joint has failed, either by tearing off the plate, shearing off the rivet or crushing off the rivet. If the joint is continuous as in case of boilers, the strength is calculated per pitch length . But if the joint is small , the strength is calculated for the whole length of the plate.

51. Efficiency of a Riveted Joint The efficiency of a riveted joint is defined as the ratio of the strength of riveted joint to the strength of the un-riveted or solid plate. We have already discussed that strength of the riveted joint = Least of P t , P s and P c Strength of the un-riveted or solid plate per pitch length, P = p × t × σ t Efficiency of the riveted joint p = Pitch of the rivets, t = Thickness of the plate, and σ t = Permissible tensile stress of the plate material.