Metal Fasteners, Joining, & Adhesives

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.

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.

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.

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.

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.

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. Adhesives do not – Light-gauge materials are often good candidates usually impose heavy loads on materials, such as in for adhesive bonding. riveting, or localized heating, such as in soldering or welding.

Cyanoacrylates (superglue) Epoxies

– Adhesives developed for production situations – Synthetic adhesive made of two components, a liquid resin and the hardener to convert the liquid resin into a solid. requiring instant bonds and immediate handling – Create superior bonds for a wide variety of materials strength, particularly when bonding rubber, including metals, rubber, and plastics. metals and plastics. – Widely used in the automotive industry. – Many cars and light- and heavy-duty trucks feature body panels – These adhesives are especially well-suited for bonded with epoxy adhesives. trim attachment and light assembly. – Excellent environmental and chemical resistance. – They resist the effects of dilute acids, alkalis, solvents, greases, – Cure through reaction with moisture held on the oils, moisture, sunlight and weathering. surface to be bonded. – Flexible cure rates. – Good environmental resistance; therefore, they – Allow great versatility in formulation since amount of hardener can be adjusted to increase work time or decrease set time. offer excellent resistance to weathering and – Low shrinkage and good creep properties. aging.

Urethanes Anaerobics

– Primerless adhesive that is ideal for – Specialty adhesives designed to cure on prepared metals, rubber and fiber metals in the absence of oxygen. reinforced plastics. – Primarily used to anchor threaded joints – Create strong flexible bonds that bring and shafts against breaking free due to vibration. excellent structural integrity to assemblies made of plastic, metal, foams and – Can eliminate the need for lock washers and press fitted metal joints. elastomers. – Often known as "locking compounds.” – Based on synthetic acrylic resins.