Flóra Hajdu

1. Boltedconnections Flóra Hajdu B406 hajdfl@sze.hu

2. Content • Screwthreads • Representation of threads • Screws, bolts, nutswashers • Boltedassemblies • Keepingfastenerstight Hajdu Flóra

3. Fasteners • Fastening devices are essential in the construction of manufactured products, in the machines and devices used in manufacturing processes, and in the construction of all types of buildings. • 2 basic kinds of fasteners: • Permanent:rivets, welds • removable fasteners: bolts, screws, studs, nuts, pins, rings, and keys • As industry progressed, fastening devices became standardized • reduces the cost of parts • reduces paperwork • simplifies inventory and quality control. Hajdu Flóra

4. ScrewThreads • A screw thread is a ridge of uniform section in the form of a helixon the external or internal surface of a cylinder • The pitch of a thread P is the distance from a point on thethread form to the corresponding point on the next form, measured parallel to the axis • The lead L is thedistance the threaded part would move parallel to the axis during one complete rotation in relation to a fixed mating part (thedistance a screw would enter a threaded hole in one turn). Hajdu Flóra

5. ScrewThreads • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

6. ThreadRepresentation • Simplifiedrepresentation should be used whenever it will clearly portray the requirements. • Detailed representation is used to show the detail of a screw thread, especially for dimensioning in enlarged views, layouts, and assemblies. • The schematic representation is nearly as effective as the detailed representation and is much easier to draw when board drafting is used. Hajdu Flóra

7. Threadforms • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

8. Right-and Left-HandThreads • Unless designated otherwise, threads are assumed to be right-hand. • For some special applications, such as turnbuckles, left-hand • threads are required. • When such a thread is necessary, the letters LH are added after the thread designation. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan Hajdu Flóra

9. Left-handthreadedparts Hajdu Flóra

10. Single and MultipleThreads • Most screws have single threads. • In single threads, the lead is equal to the pitch • A doublethread has two ridges, started 180° apart, in the form ofhelices, and the lead is twice the pitch. A triple thread hasthree ridges, started 120° apart, in the form of helices, andthe lead is three times the pitch. • Multiple threads are usedwhen fast movement is desired with a minimum numberof rotations Hajdu Flóra

11. Simplifiedthreadrepresentation • Thread crestsare represented bya thick outline and the thread roots by a thin line • The end of the full-form thread is indicated by a thick line across the part • Runoutthreads, also called vanish threads, are shown beyondthis line by running the root line at an angle to meet thecrest line Hajdu Flóra

12. Simplifiedthreadrepresentation • Thread crestsare represented bya thick outline and the thread roots by a thin line • The end of the full-form thread is indicated by a thick line across the part • Runoutthreads, also called vanish threads, are shown beyondthis line by running the root line at an angle to meet thecrest line Hajdu Flóra

13. Dimensioningthreads • The nominaldiameter and thelength of thethreadshould be given Hajdu Flóra

14. Dimensioningthreads • The nominaldiameter and thelength of thethreadshould be given Hajdu Flóra

15. Inch threads • The number of threads per inch is set for different diameters in what is called a thread series. • UNC: coarsethreadseries • UNF: fine-threadseries • UNEF: extra-finethreadseries • Three classes of external thread (classes 1A, 2A, and 3A)and three classes of internal thread (classes 1B, 2B, and 3B)are available. • These classes differ in the amount of allowances and tolerances provided in each class • Externalthread: .250-20 UNC-2A, ASME Bl.l • Internalthread: .500-20 UNF-2B (21), ASME Bl.l Hajdu Flóra

16. Metricthreads • Metric threads are grouped into diameter-pitch combinationsdistinguished from one another by the pitch applied to specific diameters • Coarse-Thread Series This series is intended for use ingeneral engineering work and commercial applications. • Fine-Thread Series The fine-thread series is for generaluse where a finer thread than the coarse-thread series isdesirable. In comparison with a coarse-thread screw, the finethread screw is stronger in both tensile and torsional strengthand is less likely to loosen under vibration. Hajdu Flóra

17. Metricthreaddesignation • M16x2P1LH-7g6g-S • Threadfrom • Nominaldiameter • Lead(L); • Pitch(P); • Left-handedorrighthanded • Tolerances • Tolerancegrade of thepitchdiameter • Tolerancegrade of thecreastdiameter (externalthread: major diameter, internalthread: minor diameter) • Screwmountinglength (S,L,N) Hajdu Flóra

18. Fits • The fit of a screw thread is the amount of clearance betweenthe internal and external threads when they are assembled. • For each of the two main thread elements-pitch diameter and crest diameter-a number of tolerance grades havebeen established. The number of the tolerance grades reflectsthe size of the tolerance (1-10). • Grade 6 tolerances should be used for medium-qualitylength-of-engagement applications. • <6 are intended for applications involving finequality and/or short lengths of engagement. • >6 are intended for coarse quality and/or longlengths of engagement. • For external threads: • e (large allowance) • g (small allowance) • h (no allowance) • For internal threads: • G (smallallowance) • H (no allowance) Hajdu Flóra

19. Threadedfasteners • Fastenerselection • Fastenertypes • Propertyclasses • Bolts and nuts • Washers • Specifyingfasteners • Keepingfastenerstight Hajdu Flóra

20. Fastenerselection • product selection mustbegin at the design stage • Machine screws are among the most common fastenersin industry • Easiesttoinstall and remove. • To obtain maximum machine-screw efficiency, thorough knowledge of the properties of both the screw and thematerials to be fastened together is required. • For a given application, a designer should know the loadthat the screw must withstand • Once ithas beendetermined, the size, strength, head shape, and thread typecan be selected Hajdu Flóra

21. Types of fasteners • MachineScrews: Machine screws have either fine orcoarse threads and are available in a variety of heads. Theymay be used in tapped holes • CapScrews: threaded fastener that joins twoor more parts by passing through a clearance hole in one partand screwing into a tapped hole in the other • CaptiveScrews: remain attached to the panelor parent material even when the mating part is disengaged. • Tapping Screws: cut or form a matingthread when driven into preformed holes • Bolts: a threaded fastener that passes throughclearance holes in assembled parts and threads into a nut. The square and hexagon head are the twomost popular designs • Studs: Studs are shafts threaded at both ends, and they areused in assemblies. One end of the stud is threaded into oneof the parts being assembled; and the other assembly parts,such as washers and covers, are guided over the studs throughclearance holes and are held together by means of a nut. Hajdu Flóra

22. Types of fasteners • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

23. Propertyclasses • The property classes aredesignated by numbers, with increasing numbers generallyrepresenting increasing tensile strengths. • The designationsymbol consists of two parts: • the first numeral isapproximately equal to one-hundredth of the minimum tensilestrength in megapascals (Mpa) • the secondnumeral approximates one-tenth of the ratio expressed as a percentage ofminimum yield strength and minimum tensile strength. • Example • Propertyclass 5.6 Hajdu Flóra

24. Screw/bolt designation • Hex bolt MSZ EN 24014-M20x100-5.6-B-Fe/Zn • Name • Reference • Size • Mountedlength • Propertyclass • Degree of accuracy • Surface treatment Hajdu Flóra

25. Threadedassemblies Hajdu Flóra

26. Threadedassemblies Hajdu Flóra

27. Washers • Washers are one of the most common forms of hardware and perform many varied functions in mechanically fastened assemblies. • span an oversize clearance hole • give better bearing for nuts or screw faces, • distribute loads over a greater area • locking devices for threaded fasteners. • maintain a spring-resistance pressure, • to guard surfaces against marring • provide a seal. Hajdu Flóra

28. Types of washers • Flat (plain)Washers Plain:are used primarily to provide a bearing surface for a nut or a screw head, to cover large clearance holes, and to distribute fastener loads over a • ConicalWashers: are used with screws to effectively add spring take-up to the screw elongation. • Helical Spring Washers: are made of slightly trapezoidal wire formed into a helix of one coil so that the free height is approximately twice the thickness of the washer section • ToothLockWashers: Made of hardened carbon steel, a tooth lock washer has teeth that are twisted or bent out of the plane of the washer face so that sharp cutting edges are presented to both the workpiece and the bearing face of the screw head or nut • Spring Washers: They are made in a great variety of sizes and shapes and are usually selected from a manufacturer's catalog for some specific purpose. • Special-Purpose Washer~ Molded or stamped nonmetallic washers are available in many materials and may be used as seals, as electrical insulators, or for protection of the surface of assembled parts. Hajdu Flóra

29. Types of washers • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

30. Specifyfasteners • Type of fastener • Thread specifications • Fastener length • Material • Head style • Type of driving recess • Point type (setscrews only) • Property class • Finish Hajdu Flóra

31. KeepingFastenersTight • Fasteners are inexpensive, but the cost of installing them can be substantial. Probably the simplest way to cut assembly costs is to make sure that, once installed, fasteners stay tight. • 3 basiclockingmethods: • free-spinning: include toothed and spring lockwashers and screws and bolts with washerlikeheads • prevailing-torque: make use of increased friction between nut and bolt. • chemicallocking: is achieved by coating the fastener with an adhesive Hajdu Flóra

32. Locknuts • A locknut is a nut with special internal means for gripping a threaded fastener to prevent rotation. • prevailing-torque: Prevailing-torque locknuts spin freely for a few turns, and then must be wrenched to final position. The maximum holding and locking power is reached as soon as the threads and the locking feature are engaged. Locking action is maintained until the nut is removed. • free-spinning: Free-spinning locknuts are free to spin on the bolt until seated. Additional tightening locks the nut. • other types: • Jam nuts are thin nuts used under full-sized nuts to develop locking action. • Slotted and castle nuts have slots that receive a cotter pin that passes through a drilled hole in the bolt and thus serves as the locking member. • Single-thread locknuts are spring steel fasteners that can be speedily applied. Locking action is provided by the grip of the thread-engaging prongs and the reaction of the arched base. Hajdu Flóra

33. Locknuts • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

34. CaptiveorSelf-RetainingNuts • Captive or self-retaining nuts provide a permanent, strong, multiple-thread fastener for use on thin materials • They are especially good when there are blind locations, and they can normally be attached without damaging finishes • Plate or anchor nuts: These nuts have mounting lugs that can be riveted, welded, or screwed to the part. • Caged nuts: A spring-steel cage retains a standard nut. The cage snaps into a hole or clips over an edge to hold the nut in position. • Clinch nuts: They are specially designed nuts with pilot collars that are clinched or staked into the parent part through a precut hole. • Self-piercing nuts: These nuts are a form of clinch nut that cuts its own hole. • Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

35. KeepingFastenersTight With 2 nuts Hajdu Flóra

36. KeepingFastenersTight Withspringwasher Hajdu Flóra

37. KeepingFastenersTight Withcastlenut and cotter Hajdu Flóra

38. KeepingFastenersTight Withlockwasher Hajdu Flóra

39. KeepingFastenersTight Withwire Hajdu Flóra

40. Summary • Representation of screws • Boltedconnections • Nextweek: Pins, keys, axial retaining rings

41. ThankYouforYourattention!