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Introduction A fastener is a hardware device that mechanically joins or affixes two or more objects together. They can be made from metals, plastics or composites. Fasteners types: Threaded and non- Threaded.
Thread Definitions Screw Thread: A ridge of uniform section in the form of a helix.
Thread Definitions External Thread: External threads are on the outside of a member. A chamfer on the end of the screw thread makes it easier to engage the nut. Chamfer
Thread Definitions External Thread: An external thread is cut using a die or a lathe.
Thread Definitions Internal Thread: Internal threads are on the inside of a member. An internal thread is cut using a tap.
Thread Definitions Major DIA (D): The largest diameter (For both internal and external threads). Minor DIA (d): The smallest diameter. Depth of thread: (D-d)/2 Pitch DIA (dP): The diameter at which a line cuts the spaces and threads equally.
Thread Definitions Crest: The top surface. Root: The bottom Surface. Side: The surface between the crest and root.
Thread Definitions Pitch (P): The distance from a point on a screw thread to a corresponding point on the next thread (in/Threads). Angle of Thread (A): The angle between the threads.
Thread Definitions Screw Axis: The longitudinal centerline. Lead: The distance a screw thread advances axially in one turn.
Identify the Pitch, Screw Axis and Thread Angle. CrestAxis Pitch Root Thread Depth Minorn Pn Majorn 8 Angle Side
Thread Definitions Right Handed Thread: Advances when turned CW. (Threads are assumed RH unless specified otherwise.) Left Handed Thread: Advances when turned CCW.
Types of Fasteners Removable: This type permits the parts to be readily disconnected without damaging the fastener, e.g. nut and bolt. Semi-permanent: For this type, the parts can be disconnected, but some damage usually occurs to the fastener, e.g. cotter pin Permanent: When this type of fastener is used, the parts will never be disassembled. e.g. rivets and welding
Advantages and disadvantagesof using fastenersAdvantages Easy to install Wide variety of standard parts Reversible up to some extent Operational efficiency and speedDisadvantages loosening Failure under tensile loading Cost is higher than welding.
Typical Designation 1/2” - 13 UNC - 2A – RH/LH Terminology of screw threads Sharp vee threads shown for clarity; the crests and roots are A=external thread actually flattened or rounded (B means internal) during the forming operation. Class of fit (1 is loosest tolerance, 3 is tightest) Thread Series UNC (Unified Coarse); UNF (Unified Fine) Pitch (threads/inch)Nominal Diameter(also shown as decimal orscrew #)
Tightening TorqueIt is typical on engines for boltsto have a specified tightening torque. Why?It results in a quantified preload on the boltsIt ensures that parts never separateMaintains friction (no sliding to shear forces)Insures even distribution of loading prevent warpage of mating parts uniform pressure distribution over seal or gasketPreventsbolt from looseningReduces fatigue effects
Bolt ManufacturingProcesses Forging (upsetting) http://www.youtube.com/watch?v= UIPcEWNFcx0 Rolling a) b) Thread-rolling processes: a) reciprocating flat dies; and b) two-roller dies. Threaded fasteners, such as bolts, are made economically by these processes at high rates of production http://www.youtube.com/watch?v=_azbmSeb PQ0
Manufacturing Processes -continued Turning on screw machines (a) Differences in the diameters of machined and rolled threads. (b) Grain flow in machined and rolled threads. Unlike machining, which cuts through the grains of the metal, rolled threads have improved strength because of cold working and favorable grain flow. http://www.youtube.com/watch?v=0q_q53 wsyHU
Advantages of Cut Threading Few limitations with regard to diameter and thread length. All specifications can be manufactured with cut threads.Disadvantages of Cut Threading Significantly longer labour times means higher costs.Advantages of Roll Threading Significantly shorter labour times means lower costs. Cold working makes threads more resistant to damage during handling. Rolled threads are often smoother due to the burnishing effect of the rolling operation.Disadvantages of Roll Threading The availability of pitch diameter round bar is limited for certain material grades.
Standards of Fastenersoo - Indian Standards-IS German Standards-DIN Japanese Standards-JIS American Standards-ASTM British Standards-BS
Special Fasteners Special Fasteners are manufactured to suit unique customer specifications. These may have to be made available in a variety of surface protection coatings.
oSometimes, fasteners may have to be coated in order to prevent them from corrosion.oThe main industries which need coated fasteners are viz. Oil & Gas Industry; Foodprocessing; and Waste Water Treatment Industry.oThe main types of coatings used these days are:-Fluoropolymer- resin/lubricant blends that offer excellentcorrosion protectionMolybdenum Disulfide- friction reduction for high pressure loadsEpoxy, thermal cure- excellent impact resistance plus corrosionand abrasion protectionInorganic Zinc- corrosion and weathering protection for steelPhenolic- ideal protection in low pH, high temperatureenvironmentsPhosphate- ferrous metal coating for anti galling and minorcorrosion resistancehttp://www.metcoat.com/fastener-coatings.htm
Manufacturing processes mainly include- • annealing • cold forging(nuts rivets sleeves) • inline rolling, • heat treatment, • finishing/coating, • CNC turning, • centre less grinding, • circular thread rolling and other secondary operations • Induction hardening of critical fasteners, use of sophisticated in-line hardening and tempering furnaces with auto-load, pre-wash and post- washers, and the manufacture of special fasteners with very close tolerance are key features of our manufacturing process.
Fastener IndustryChief users :automobiles, aircraft, appliances, agricultural machinery, commercialconstruction, and infrastructure.• The fastener industry in India may be classified into two segments, namely, high tensile and mild steel fasteners, which broadly include nuts, bolts, studs, rivets and screws.• All types of fasteners except high tensile and special type of fasteners are reserved for SSI (Small Scale Industries) Sector.• Total domestic market of fastener industry in India: INR 1500 crore.• The market size of high-tensile fasteners in the country is around Rs 1,100 crore.
Fastener Industry• Automobile industry accounts for 75 % of the total demand of this industry. Consumer durables and railways are the other primary users of the high tensile fasteners.• Mild steel fasteners are primarily manufactured by the unorganised sector, while high tensile fasteners require superior technology and are dominated by companies in the organized sector.• The fastener industry has been delicensed and is eligible for 100 per cent FDI under the automatic route. So there is a scope for growth in the exports.• The automobile, general engineering, consumer durables, railways and auto replacement market account for 95% of the demand of cold forged high tensile fasteners industry in India.
ProblemsProblems that make fastener industry less competent in the global market :1)Poor product standardisation : production has never been streamlined2) Increased input costs : due to indiscriminate hike in raw material costs3) Low labour output (because the fabrication process of most fasteners isintricate and complicated and hence the manpower required has to beskilled and this increases the production cost .4) Investment in manpower : In India the unskilled manpower is huge butthe skilled segment is small.
Scope• There is a regular annual growth in the automobile industry which has affected a proportional growth in the fastener market.• The manufacturing cost of mild steel fasteners (which broadly include nuts, bolts, studs, rivets and screws) is lower than that of customised special purpose fasteners, and tensile fasteners.(but profit margin will be low)• High tensile fasteners are much more profitable but require cutting-edge technology to be competent.• To enter into business of aircraft parts the necessary certifications require 3-5 yrs. and the only way to access the technology is through acquisition of companies.