Presentation on theme: "Topics Introduction Terminology Thread Specifications Bolts and Screws"— Presentation transcript:
1Topics Introduction Terminology Thread Specifications Bolts and Screws MECH 1200IntroductionTerminologyThread SpecificationsBolts and ScrewsNuts and Locking DevicesExercise QuestionsNote: Refer to Chapter 6 in the text.
2Introduction There are two thread standards: MECH 1200There are two thread standards:The Unified Screw Thread Standard: Used in the U.S. It is based on a 60o thread angle.Unified National Coarse (UNC) series: this is the most common series. Bolts, screws, and nuts of this series are used for general applications in which a quick assembly is required.Unified National Fine (UNF) series: threads of this series are used for handling high tensile stresses, or when the length of engagement is limited such as screws in thin walls.Unified National Special (UNS) seriesThe International Screw Thread Standard: most common standard, based also on the 60o thread angle.
3TerminologyMECH 1200Thread angle: the angle included between the sides of the thread, The ISO thread angle is 60 degrees.Pitch: the distance between one point on a thread to the corresponding point on the next thread.Number of threads per inchMinor (root) diameterMajor (Outside) diameterLead: the distance a screwthread advances in one revolution.Thread Fit: How tight is the threadengagement. Three classes of fit are used in theunified system, loose, medium, and tight fits.A for external and B for internal fits. (see p. 110)Source: Siemens Technik Akademie Berlin
4Thread Specifications MECH 1200Unified system threads:Example: ¼ - 20 UNC-BX1 indicates a thread with an outer diameter is ¼ inch, with 20 threads per inch, the type of thread is UNC, and a B (internal) fit and a thread length of 1 inch.Metric system threads:Example: M10 ×1.5-6g indicates a Metric thread with an outside diameter of 10 mm and a pitch of 1.5 mm, the fit of the thread is 6g.Bolts and Screws: The two words are used interchangeably, but generally, bolt is used when a nut is required to be used.The shank of a bolt has a diameter that is equal to the major diameter.Source: Siemens Technik Akademie Berlin
5Common Bolts and Screws MECH 1200Carriage Boltused to fasten metal to wood. It has a square body right under the head to keep the wood from turning.Machine Screwused for vehicle body and metal sheetsSheet Metal ScrewSet Screwusually has no head, used to lock pulleys or gears to shaftsSocket Head Screwhas the strongest head style
6Has a reduced shank, used for applications in which shock loads occur. MECH 1200Stud (Standing) Bolthas threads on both ends, screwed permanently in one end and a nut on the other end.Hexagon Through BoltHexagon Fit BoltIf the bolt goes through all parts and is fastened with a nut, then it is called a Through Bolt. When used to fix a part in position against movement it is called a Fit Bolt.Anti-Fatigue BoltHas a reduced shank, used for applications in which shock loads occur.Source of images in this slide: Siemens Technik Akademie Berlin
7NutsMECH 1200Hex nuts: Have a hexagonal shape, and has different gradesCastle Nut: Named so because it looks like a castle, used in applications where heavy vibrations occur, such as on wheels. Can handle light torques.only.Wing nutsCap (Acorn) Nut
8Fastener Locking Devices MECH 1200Screw locking devices are used to keep the nut from getting loose.They can be friction based or non-friction based:Friction based Locking devicesInternal tooth lock washerExternal tooth lock washerSpring lock washerLock washerSafety wiresNon-Friction based Locking devicesSplit pinsNut lock plateTab washer
9Exercise Questions What are the two thread standards? MECH 1200What are the two thread standards?The Unified Screw Thread System and the ISO metric thread standard.Thoroughly describe the bolt given by: ¼ - 28 UNF 2AThe bolt has an outer diameter of ¼ inch and a fine thread of 28 threads per inch (Unified National Fine thread series) and has a medium fit with external thread.Thoroughly describe the thread bolt given by:M10 x 1.25The bolt is metric and its outer diameter is 10 mm and has a pitch of 1.25 mm
10If a thread has 40 threads per inch what is its pitch? MECH 1200If a thread has 40 threads per inch what is its pitch?Pitch = 1 inch / 40 = 0.025Is each of the screw locking devices below friction based or not?YesNoYesNoNo
11What is the component shown in the figure below? MECH 1200What is the component shown in the figure below?Castle Nut: used in applications that require low amount of torque, and where vibrations are common.