Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Metal Fasteners, Joining, and Adhesives Fasteners Bolts • Metal assemblies are often held • Threaded shafts that use a together with fasteners, hardware threaded nut to fasten metal devices that mechanically join or together. affix two or more objects together. • Bolts are sized by length and • Assembling with most types of thread. fasteners allows components to be • Bolts are stronger than screws. repeatedly assembled and • Bolts are classified by the type disassembled. of head. • This is important where a product – Stove bolts and machine screws is expected to undergo (actually bolts) are turned with a modifications, repairs, or where it screwdriver. may provide access into an – Hexagonal- and square-head bolts assembly. are held in place with a wrench while the nut is turned to tighten. Project Lead The Way® Copyright 2006 1 Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Types of Bolts Types of Machine Screws – Carriage bolt • Smooth round head & course thread that starts part way down the shaft. – Machine & cap screws • Usually used to attach a wooden part to metal. • Come with a variety of head & thread – Machine bolt types. • Hexagonal head & only partially threaded. • Used for precision fit into thread holes • Used for precision attachment using threads in metal. to secure materials together. – Setscrew – Tap bolt • Made with square heads or no heads. • Similar to a machine bolt but the whole body is threaded. • Typically used for safety reasons to hold a sleeve, collar or gear on a shaft – Stove bolt to prevent relative motion. • Round or flat head with course thread along the whole body. – Thumbscrews • General purpose fastener used when • Has one or two wings or a knurled precision fit is not necessary. head. – Stud bolt • Used where a screw must be turned by • No head and threaded on both ends. hand using the thumb and a finger. • One end is driven into material & the other end is left exposed so that other parts can be fastened to it. Sheet Metal Screws Lag Screw – Short thick screws that are self- – Bolt is a bolt head with a screw body. threading (cut or form their own – Has either a square or hexagonal head. threads as driven into soft metals). – Used in fastening where maximum holding – Used in the economical assembly power is needed (i.e.- holding a vice to to a of sheet metal. work bench). – Threaded all the way down the shank. – Come in a variety of head types depending on application. Project Lead The Way® Copyright 2006 2 Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Nuts Type of Nuts – Type of hardware fastener – Machine screw nut (Hex nut) • Square or hexagonal shaped with fine or with a threaded hole. course thread. – Usually hexagonal to permit – Jam nut (Lock nut) • Thinner than an ordinary nut. tightening with a wrench but • Used as a lock to keep another nut from may also be square, loosening. – Castle nut knurled, winged or • Has slots cut into the top of the nut that otherwise shaped. extend upward making it look like a castle. • A hex nut with a slightly reduced slotted – Along with a bolt, nuts are cylindrical section on one end. designed to capture and • Used with a cotter pin to prevent loosening. – Wing nut fasten objects together. • A nut with two thin flat wings. • Used in place of a regular nut and can be turned with the thumb and forefinger. Washers Type of Washers – Placed under the bolt head – Plain washers • Circular, small flat piece to widen the or the nut for a firmer bearing surface of a bolt head or nut. fasten. • Measured by the diameter of the bolt that fits into it. – Designed to protect the – Lock washer surface under a bolt or nut. • Used to lock a nut or screw in place, prevent it from moving from vibrations. – Used to spread load of a – Helical spring - looks like a coil from a mechanical connection out spring that tightens when applied to prevent movement. over a greater area. – Toothed – has teeth that wedge into bearing surface when applied to prevent movement. Project Lead The Way® Copyright 2006 3 Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Pins Keys – Used to keep pulleys and gears from – Used to hold mechanical parts together moving on shafts. or limit travel of moving parts. – Half the key fits into the keyway (a slot – Cotter pin on the shaft), the other half fits into a slot that is on the pulley or gear. • Made of soft wire. • Placed through a hole in a bolt behind a – Square key castle nut to prevent the nut from • Most commonly used. turning. – Gib-head key – Tapered pin • Toothed key that is useful when you • Used to hold a collar or pulley against a need to remove the key from one side of shaft. the pulley or gear. – Roll pins • Can be removed with a wedge. • Made from sheet steel that is rolled into – Woodruff key a tube. • Semicircular in shape and fits a • Driven into holes slightly larger than a matching semicircular pocket in the standard hole size so they grip tightly shaft. when pounded in. • Key becomes locked in position and cannot be knocked loose due to vibration. Joining Metal Rivets – As with wood, there are many ways of joining metal permanently. – Metal pins that look like bolts with no – The method used will depend on the function of the threads. product, the strength needed and the quality of the product. – Used to hold pieces together permanently. – There are several ways of joining metal permanently. • riveting – Used when fastening metals together that • soldering and brazing • welding are not easily welded, or where welding is – The later two of these techniques rely upon heat. not practical. • With soldering and brazing, the two metals are joined by melting a second metal between them. • With welding, the two metals are melted and fused together. Project Lead The Way® Copyright 2006 4 Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Rivet Characteristics Spot Welding – May be either solid or tubular. – Form of resistance welding done with a spot welder. – Made from different materials such as – High current at a low voltage passes through a spot on two soft steel, aluminum, copper, and brass. pieces of metal (usually sheet metal) for a short period of time. – Come with a variety of different shapes – Resistance to the flow of current through the metal at the spot and heads. causes heat, which melts the metal and makes a spot weld. – Most frequently used to weld metal joints but sometimes – For application, rivets are placed in used to weld sheet metal to small diameter rods or small flat holes, pre-drilled in materials and bars. fastened together. – With solid rivets, the headless head is pounded to form a head. – Hollow rivets are clinched at the headless end with a special riveting tool. Soldering Soft Soldering – Process of fastening two metals together with – Occurs at temperatures below solder, a nonferrous metal that has a lower 800 degrees Fahrenheit. melting point than the parts being joined. – For general work, a solder called – Parts being joined are heated until the solder, rosin core 60-40 (60% tin, 40% lead) is often used. when brought into contact with them, melts and flows between the surfaces. – Solder often comes in a coil of wire 1/16” in diameter but can – When the solder solidifies, it adheres (sticks) come in other pre-cut shapes, tightly and forms a strong bond between the two sizes, and forms. surfaces. – Heat for soft soldering is applied using soldering gun or a soldering copper. Project Lead The Way® Copyright 2006 5 Metal Fasteners, Joining, and Adhesives Introduction to Engineering Design Unit 3 – Lesson 3.3 – Structural Analysis Hard Soldering Brazing – If solder melts above 800 degrees – Hard soldering processing where the filler Fahrenheit, it is called hard soldering. material flows into the joints using capillary – Used where a strong joint is needed or where the parts will be used in greater heat action (the natural tendency of a liquid to be than the melting point of soft solder. drawn in between two close fitting surfaces). – The most widely used hard solders are – Filler material used is brazing rods (60% copper, silver alloy solders that come in ribbons, sheets, wire, or pre-cut pieces of various 40% zinc). shapes and sizes. – Often used in jewelry and art metalwork for joining copper, silver, and gold. – Heat for hard soldering is applied directly with the flame of a torch. Advantages of Using Adhesive Bonding of Metals Adhesives to Join Metals – Process of fastening parts of metal products – Many adhesives easily join dissimilar materials if proper together permanently with non-metallic materials. surface treatments are used. – Adhesively joined structures and products are inherently – Often used as an alternative to mechanical smooth. fasteners. – Exposed surfaces are not defaced, and contours are not disturbed – When using adhesives, the entire joint must be as with other types of fastening systems. – This is important both to function and appearance. given even more consideration than when using – Adhesives are sometimes used with mechanical fasteners mechanical fasteners. for sealing flange joints or holding the parts together while – Unlike a bolt or rivet, an adhesive's properties may change the bond forms. depending on where it is used. – Thin or fragile metal parts can be bonded.