Mechanical fasteners

Its all about mechanical fastener.nuts and bolt its design manufacturing.

1. MECHANICAL FASTENERS PREPARED BY AKSHAY KATARIYA…..

2. 21-Feb-2018 2

3. THREAD MANUFACTURING THREAD DESIGNTION TYPES OF BOLT FOUNDATION BOLT BOLT & SCREW CLEARENCES STRENGTH OF BOLT BOLT HEAD MARKING STANDARD BOLT LENGTH BOLT FAILURES CONTENT.. 21-Feb-2018 3

4. 21-Feb-2018 4

5. 21-Feb-2018 5

6. 21-Feb-2018 6

7. 21-Feb-2018 7

8. 21-Feb-2018 8

9. 21-Feb-2018 9

10. A nut is a type of hardware fasteners with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts . A washer is a thin plate typically disk-shaped with a hole that is normally used to distribute the load of a threaded fastener. 21-Feb-2018 10

11. 21-Feb-2018 11

12. 21-Feb-2018 12

13. 21-Feb-2018 13

14. THREAD NOMENCLATURE 21-Feb-2018 14

15. THREAD NOMENCLATURE Crest: It is the outermost portion which joins the two sides of a thread. Root: It is the innermost portion which joins the adjacent sides of a thread. Pitch: It is the distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis e.g. distance between crest to crest or distance between root to root. Lead: It is the distance moved by a nut or bolt in the axial direction in one complete revolution. For single start thread; Lead = Pitch For multi start thread, Lead = n x pitch where n = No. of starts 21-Feb-2018 15

16. THREAD NOMENCLATURE Flank: It is the straight portion of the surface, on either side of the screw thread. Angle of Thread: It is the included angle between the flanks of the thread measured in an axial plane. Helix Angle: Angle that thread makes with plane perpendicular to thread axis. Pitch Diameter: It is the diameter of an imaginary cylinder, the surface of which would pass through the thread at the points where the thread width is equal to the space between the threads. Depth of the thread: It is the distance between the cr e s t and roo t o f a t h r e ad m e a sur e d perpendicular to the axis. 21-Feb-2018 16

17. THREAD NOMENCLATURE SINGLE START THREAD….. Single Start Thread: When only one helix forming the thread run on a surface it is called single start thread. A single start thread consists of a single, continuous helical groove for which the lead is equal to the pitch. Only one starting point is seen in the beginning of the threaded portion. 21-Feb-2018 17

18. THREAD NOMENCLATURE MULTI START THREAD….. Multiple-Start Thread : When two or more helices forming the threads run on a surface it is called Multiple start thread. The lead is equal to (pitch x no. of starts) Two or more than two starting points are seen in the beginning of the threaded portion. 21-Feb-2018 18

19. THREAD FORMS There are main two types of thread are which are, V-thread Square thread V-THREAD British Standard Whitworth Threads (BSW) British association threads (BA) Sellers threads Unified standard threads ISO Metric Threads ISO metric Trapezoidal Threads SQUARE THREADS Square thread Acme thread Knuckle thread Buttress thread 21-Feb-2018 19

20. TYPES OF V-THREAD FORM BRITISH STANDARD WITHWORTH(BSW) Used as a standard thread in Britain Give an effective leak-proof joint due to their fine pitches and form Use d o n b olts, n u ts and s c rew s fo r g eneral purpose fastening. BRITISH ASSOCIATION(BA) Modified form of BSW thread with included angle 47.5 Use d fo r precis ion faste ni n g li k e i n m e c h a n i c al instruments, aircraft construction etc.… 21-Feb-2018 20

21. TYPES OF V-THREAD FORM SELLERS THREAD T h e s e threa d h a ve fl at cre st and roo t and can withstand more rough usage Adopted as a standard form in America Used on fasteners for making adjustment. UNIFIED STANDARD THREAD These threads have been standardized by the ISO and are available in inch and metric series. 21-Feb-2018 21

22. TYPES OF V-THREAD FORM ISO-METRIC THREAD Recommended by Bureau of Indian Standard and adopted as a standard form. ISO-METRIC TRAPEZOIDAL THREAD Standardized by ISO and same to ACME threads. 21-Feb-2018 22

23. ISO METRIC THREAD THE STANDARD DIMENSION FOR DIFFERENT SIZES OF THREAD ARE GIVEN BELOW, 21-Feb-2018 23

24. TYPES OF SQUARE THREAD FORMS SQUARE THREAD These threads have their flanks at right angles to the axis Offers less resistance to the motion G e ne r ally use d fo r pow er t r ansmission. Ex. lead screw of lathe, screw jack Th e pit ch i s twi c e that o f BSW th r e ad fo r s ame diameter. ACME THREADS Modified form of square threads. The thread angle is 29 , These threads are particularly used in cases where engagements and dis-engagements are frequent e.g. brass valves, lead screw of lathe and bench vices. 21-Feb-2018 24

25. TYPES OF SQUARE THREAD FORMS KNUCKLE THREAD Modified form of square threads Rounded at top and bottom. These threads are used in electric bulbs, bottles, railway couplers etc.… BUTTRESS THREAD Combined form of V-threads and square threads. It co m bin es the low f r ictional r e sist a nc e of square threads and the strength of V-threads Used for power transmission in one direction only like carpenter wise, air plane propellers etc.… 21-Feb-2018 25

26. THREAD MANUFACTURING INTERNAL THREAD Internal thread manufactured by taping tool on milling machine. The tap drill hole is a little bigger than the minor diameter. 21-Feb-2018 26

27. THREAD MANUFACTURING EXTERNAL THREAD External thread are manufactured on lathe or die. 21-Feb-2018 27

28. THREAD DESIGNATION (1) ISO-METRIC DESIGNATION (2) CONVENTIONAL DESIGNATION ISO-METRIC DESIGNATION: The diameter-pitch combination of an ISO metric screw thread is designated by the letter ‘M’ followed by the value of nominal diameter, pitch and thread length in mm. The two values are separated by the sign ‘x’ e.g. M10 X 1.25 X 24 METRIC THREAD NOMINAL DIAMETER(MM) PITCH(MM) THREAD LENGTH(MM) 21-Feb-2018 28

29. CONVENTIONAL REPRESENTATION True projections of threaded portion of a part consists of series of helices and it takes considerable time to draw them, Hence some conventional methods are used to represent the threads. Notes may be given at the bottom of the threads stating the particulars e.g. thread form, pitch , di a m et er , l e f t or ri g h t h an d threads etc. It is generally consist schematic representation and simple representation of external thread, internal thread, v-thread. 21-Feb-2018 29

30. CONVENTIONAL REPRESENTATION EXETERNAL THREAD (SIMPLE REPRESENTATION) The crests of threads are indicated by thick continuous line and the roots are indicated by thin continuous line. In side view, the threaded roots are represented by portion of a circle drawn with a continuous thin line of length approximately three-quarters of the circumference T h e l imit of usef u l l eng t h of sc r e w t h r ead s is represented by a continuous thick line. The length up to which the incomplete threads are formed beyond useful limit is represented by two inclined lines. 21-Feb-2018 30

31. CONVENTIONAL REPRESENTATION INTERNAL THREAD (SIMPLE REPRESENTATION) For internal screw threads, the crests and roots are indicated by hidden lines. In side view, the threaded roots are represented by portion of a circle drawn with a continuous thin line of length approximately three-quarters of the circumference. The limit of useful length of screw threads is represented by hidden line The length up to which the incomplete threads are formed beyond useful limit is represented by two inclined hidden lines. 21-Feb-2018 31

32. CONVENTIONAL REPRESENTATION V-THREAD (SCHEMATIC REPRESENTATION) Th e c r e st s are represe nted by con t i n uou s thin lines extending up to the major diameter. The roots are represented by thick lines extending up to the minor diameter. These lines are drawn inclined with a slope equal to half the pitch as shown in figure, 21-Feb-2018 32

33. THREADS IN ASSEMBLY Figure (a) shows schematic representation of thread assembly. Figure (b) & (c) shows simple representation of thread assembly. 21-Feb-2018 33

34. BOLT A cy l indrical pi e c e /jo b wit h a h e ad on one s i d e and threaded length on the other side is called a bolt. Bolts are used to join two or more parts temporarily. The fu n cti o n an d t h e pu r po s e of a bo l t decid e s t h e shape of the bolt. Bolt is used along with nut to tighten two parts. Fo l l o w ing t y p es of bo l ts are g e neral l y us e d in engineering applications: Hexagonal head bolt Square thread bolt Cup thread bolt Cylindrical head T-headed bolt Eye bolt Lifting eye bolt Hook bolt Shackle bolt Head less tapered bolt Counter sank headed bolt 21-Feb-2018 34

35. TYPES OF BOLT… 21-Feb-2018 35

36. TYPES OF BOLT… CYLINDRICAL HEADED BOLT Use d w h e n limited sp a c e i s availa bl e and i t also avoids the use of spanner. The rotation of the bolt is prevented by means of a pin inserted in to the shank just below the head T h e s e b o l ts are com mo n ly use d in b ig end s of connecting rod, eccentrics etc … T-HEADED BOLT This bol t i s m ai n ly use d i n m a ch i n e to o l tables that are provided with T-slots This m akes i t p o s sib l e t o mo u n t j igs and fixtu r es anywhere on the slide by using T-headed bolts Th e ne c k o f the b olt i s mad e squ a r e f i tting in to the slot provided on the slide. 21-Feb-2018 36

37. TYPES OF BOLT… HOOK BOLT This bolt passes through a hole in one part only while the other part is gripped by the hook shaped bolt head It is used where there is no space for making a bolt hole in one of the parts. The square neck prevents the rotation of the bolt. SHACKLE BOLT This b olt i s hav i n g h ead just li k e a for k hav i ng holes to receive a pin. Square neck is usually provided with the head to prevent the rotation . 21-Feb-2018 37

38. FOUNDATION BOLT Foundation bolts are used for fixing machines to their foundation Foundation bolts are made by forging from mild steel or wrought iron rods The bolt size depends up on the size of the machine and the magnitude of the forces that act on them when the machine is in operation For setting the bolts in position, their positions are marked and then suspended in the holes made in the ground Afterwards , cement concrete is filled in the space around bolts On ce c e m e n t c o ncr ete m ixt u r e sets , t h e b o l ts are firmly secured to the ground 21-Feb-2018 38

39. TYPES OF FOUNDATION BOLT Va r i o u s types of foundatio n b olts use d for f i xi ng the heavy machines are as follows: Eye or Hoop foundation bolt Bent or Curved foundation bolt Rag foundation bolt Lewis foundation bolt Cotter foundation bolt Square headed foundation bolt T-headed foundation bolt 21-Feb-2018 39

40. BOLT AND SCREW CLEARENCES Bolts and screws attach one material with a clearance hole to another material with a threaded hole. The size of the clearance hole depends on; the major diameter of the fastener → and the type of fit • normal • close • loose 21-Feb-2018 40

41. BOLT AND SCREW CLEARENCES Other fits found in table given below.. 21-Feb-2018 41

42. BOLT AND SCREW CLEARENCES Sometimes bolt or screw heads need to be flush with the surface . This can be achieved by using either a counter bore or countersink depending on the fasteners head shape. 21-Feb-2018 42

43. BOLT AND SCREW CLEARENCES Counter bores: Counter bores are holes designed to recess bolt or screw heads below the surface of a part. Typically, CH = H + 1/16 (1.5 mm) and C1 = D1 + 1/8 (3 mm) 21-Feb-2018 43

44. BOLT AND SCREW CLEARENCES Countersink: Countersinks are angled holes that are designed to recess screws with angled heads . Typically, C1 = D1 + 1/8 (3 mm) Appendix B gives other counter bore, countersink and shaft clearance holes. 21-Feb-2018 44

45. WHAT IS THE NORMAL FIT CLEARANCE HOLE DIAMETER FOR THE FOLLOWING NOMINAL BOLT SIZES. NOMINAL SIZE CLEARRENCE HOLE ¼ 9/32 ¾ 13/16 21-Feb-2018 45

46. GRIP OF FASTENER The thread length of inch-series bolts, where d is the nominal diameter, is 𝐿𝑇 =2 𝑑 + 0.25", 𝑓𝑜𝑟 𝐿 ≤ 6“ =2 𝑑 + 0.50", 𝑓𝑜𝑟 𝐿 > 6" For metric bolts it is 𝐿𝑇 = 2 𝑑 + 6𝑚𝑚 , 𝑓𝑜𝑟 𝐿 ≤ 125𝑚𝑚 =2 𝑑 + 12𝑚𝑚, 𝑓𝑜𝑟 125𝑚𝑚 < 𝐿 > 200𝑚𝑚 =2 𝑑 + 25𝑚𝑚, 𝑓𝑜𝑟 𝐿 > 200𝑚𝑚 The ideal bolt length is one in which only one or two threads project from the nut after it is tightened. During tightening, the 1st thread of the nut tends to take the entire load But yielding occurs & load is eventually divided over about 3 nut threads. The grip l of a connection is the total thickness of the clamped material. Due to a few threads taking the load, 𝑙 ≠ 𝐿𝑇 21-Feb-2018 46

47. FASTENER AND GRIP LENGTH 21-Feb-2018 47

48. NUT AND WASHER DIMENSION 21-Feb-2018 48

49. Twisting the nut stretches the bolt to produce the clamping force. This clamping force is called the pretension or bolt preload . Since the members are being clamped together, the clamping force that produces tension in the bolt induces compression in the members . The spring rate is the ratio between the force applied to the member and the deflection produced by that force. (𝐹 = 𝑘 b Δ 𝑙 ⇒ 𝑘 𝑏 =(F/ Δ l)=( Ea Δ l / (l Δ l) =( Ea /l) Stiffness of bolt or screw clamped zero consist Unthreaded portion Kd =(Ad*E)/ Ld b) Threaded portion Kt =(At*E)/Lt c) Two spring in series (1/Kb)=(1/ Kd )+(1/ Kt ) STIFFNESS OF THE BOLT 21-Feb-2018 49

50. Since the members are being clamped together, the clamping force that produces tension in the bolt induces compression in the members. Clamped members also act like springs in series The spring rate of the members being joint by the fastener is, Where E is the modulus of elasticity of the material of the members. In this formula we assume all the members being jointed are of the same material If one of the members is a soft gasket, its stiffness relative to the other members is usually so small that for all practical purposes the others can be neglected and only the gasket stiffness used . STIFFNESS OF THE JOINT 21-Feb-2018 50

51. The proof load is the maximum load (force) that a bolt can withstand without acquiring a permanent set. The proof strength S p is the ratio of proof load and tensile-stress area. In the specification standards for bolts, the strength is specified by stating SAE or ASTM minimum quantities, the minimum proof strength, or minimum proof load, and the minimum tensile strength. Min proof load is load at which 1% fasteners fail. 99% fasteners exceed it The bolt grades are numbered according to the tensile strengths. The grade of the nut should be the grade of the bolt. Refer to Tables 8-9, 8-10 and 8-11 for minimum strength of steel bolts ASTM threads are shorter because ASTM deals mostly with structures; structural connections are generally loaded in shear, and the decreased thread length provides more unthreaded shank area (remember 𝐴 𝑑 > 𝐴 𝑡 ). STRENGTH OF BOLT 21-Feb-2018 51

52. The bolt grades are numbered according to the tensile strengths. Grades are printed (grades or some geometric code) along with manufacturer logo on the bolt head. Unmarked bolts should be avoided as they may be unstandardized. BOLT HEAD MARKING 21-Feb-2018 52

53. BOLT HEAD MARKING 21-Feb-2018 53

54. BOLT HEAD MARKING 21-Feb-2018 54

55. STANDARD BOLT LENGTH 21-Feb-2018 55

56. 21-Feb-2018 56 BOLT FAILURES Shear loaded joints are handled the same for rivets, bolts, and pins Several failure modes are possible (a) Joint loaded in shear (b) Bending of bolt or members (c) Shear of bolt (d) Tensile failure of members (e) Bearing stress on bolt or members (f) Shear tear-out (g) Tensile tear-out

57. 21-Feb-2018 57