Bolted connections Flra Hajdu B 406 hajdflsze hu

Bolted connections Flóra Hajdu B 406 hajdfl@sze. hu

Content • Screw threads • Representation of threads • Screws, bolts, nuts washers • Bolted assemblies • Keeping fasteners tight 2021. 09. Hajdu Flóra

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. 2021. 09. Hajdu Flóra

Screw Threads • A screw thread is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder • The pitch of a thread P is the distance from a point on the thread form to the corresponding point on the next form, measured parallel to the axis • The lead L is the distance threaded part would move parallel to the axis during one complete rotation in relation to a fixed mating part (the distance a screw would enter a threaded hole in one turn). 2021. 09. Hajdu Flóra

Screw Threads 2021. 09. Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra

Thread Representation • Simplified representation 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. 2021. 09. Hajdu Flóra

Thread forms Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 09. Hajdu Flóra

Right-and Left-Hand Threads • • 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. scan 2021. 09. Hajdu Flóra Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design

Left-hand threaded parts 2021. 09. Hajdu Flóra

Single and Multiple Threads • Most screws have single threads. • In single threads, the lead is equal to the pitch • A double thread has two ridges, started 180° apart, in the form of helices, and the lead is twice the pitch. A triple thread has three ridges, started 120° apart, in the form of helices, and the lead is three times the pitch. • Multiple threads are used when fast movement is desired with a minimum number of rotations 2021. 09. Hajdu Flóra

Simplified thread representation • Thread crests are represented by a 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 • Runout threads, also called vanish threads, are shown beyond this line by running the root line at an angle to meet the crest line runout 2021. 09. Hajdu Flóra

Simplified thread representation • Thread crests are represented by a 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 • Runout threads, also called vanish threads, are shown beyond this line by running the root line at an angle to meet the crest line 2021. 09. Hajdu Flóra

Dimensioning threads • The nominal diameter and the length of the thread should be given 2021. 09. Hajdu Flóra

Dimensioning threads - simplifications • The nominal diameter and the length of the thread should be given 2021. 09. Hajdu Flóra

Inch threads • 2021. 09. Hajdu Flóra

Metric threads • Metric threads are grouped into diameter-pitch combinations distinguished from one another by the pitch applied to specific diameters • Coarse-Thread Series This series is intended for use in general engineering work and commercial applications. • Fine-Thread Series The fine-thread series is for general use where a finer thread than the coarse-thread series is desirable. In comparison with a coarse-thread screw, the fine-thread screw is stronger in both tensile and torsional strength and is less likely to loosen under vibration. 2021. 09. Hajdu Flóra

Metric thread designation • 2021. 09. Hajdu Flóra

Fits • The fit of a screw thread is the amount of clearance between the 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 have been established. The number of the tolerance grades reflects the size of the tolerance (1 -10). • Grade 6 tolerances should be used for medium-quality length-of-engagement applications. • <6 are intended for applications involving fine quality and/or short lengths of engagement. • >6 are intended for coarse quality and/or long lengths of engagement. • For external threads: • e (large allowance) • g (small allowance) • h (no allowance) • For internal threads: • G (small allowance) • H (no allowance) 2021. 09. Hajdu Flóra

Threaded fasteners • Fastener selection • Fastener types • Property classes • Bolts and nuts • Washers • Specifying fasteners • Keeping fasteners tight 2021. 09. Hajdu Flóra

Fastener selection • Product selection must begin at the design stage • Machine screws are among the most common fasteners in industry • Easiest to install and remove. • To obtain maximum machine-screw efficiency, thorough knowledge of the properties of both the screw and the materials to be fastened together is required. • For a given application, a designer should know the load that the screw must withstand • Once it has been determined, the size, strength, head shape, and thread type can be selected 2021. 09. Hajdu Flóra

Types of fasteners • Machine Screws: Machine screws have either fine or coarse threads and are available in a variety of heads. They may be used in tapped holes • Cap Screws: threaded fastener that joins two or more parts by passing through a clearance hole in one part and screwing into a tapped hole in the other • Captive Screws: remain attached to the panel or parent material even when the mating part is disengaged. • Tapping Screws: cut or form a mating thread when driven into preformed holes • Bolts: a threaded fastener that passes through clearance holes in assembled parts and threads into a nut. The square and hexagon head are the two most popular designs • Studs: shafts threaded at both ends, and they are used in assemblies. One end of the stud is threaded into one of the parts being assembled; and the other assembly parts, such as washers and covers, are guided over the studs through clearance holes and are held together by means of a nut. 2021. 09. Hajdu Flóra

Types of fasteners Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 09. Hajdu Flóra

Property classes • 2021. 09. Hajdu Flóra

Screw/bolt designation • Hex bolt MSZ EN 24014 -M 20 x 100 -5. 6 -B-Fe/Zn • Name • Reference • Size • Mounted length • Property class • Degree of accuracy • Surface treatment 2021. 09. Hajdu Flóra

Threaded assemblies 2021. 09. Hajdu Flóra

Set screw 2021. 09. Hajdu Flóra

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. 2021. 09. Hajdu Flóra

Types of washers • Flat (plain) Washers: 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 large areaparticularly on soft materials such as aluminum or wood • Conical Washers: 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 thickness of the washer section • Tooth Lock Washers: 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. 2021. 09. Hajdu Flóra

Types of washers Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 09. Hajdu Flóra

Specify fasteners 1. 2. 3. 4. 5. 6. 7. 8. 9. 2021. 09. Type of fastener Thread specifications Fastener length Material Head style Type of driving recess Point type (setscrews only) Property class Finish Hajdu Flóra

Keeping Fasteners Tight • 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 basic locking methods: • free-spinning: include toothed and spring lockwashers and screws and bolts with washerlike heads • prevailing-torque: make use of increased friction between nut and bolt. • chemical locking: is achieved by coating the fastener with an adhesive 2021. 09. Hajdu Flóra

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. 2021. 09. Hajdu Flóra

Locknuts Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 09. Hajdu Flóra

Captive or Self-Retaining Nuts • 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 2021. 09. Hajdu Flóra