Tamil Nadu HSE First Year Basic Mechanical Engineering flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cast iron carbon range

Cast iron contains roughly 2 to 4 percent carbon. It is brittle in tension but strong in compression and damps vibration, so it suits machine beds, housings and engine blocks.

Mild steel properties

Mild steel has about 0.15 to 0.30 percent carbon, giving good ductility, weldability and machinability with moderate strength. It is the standard material for shafts, keys, bolts and general fabrication.

Annealing purpose

Annealing heats steel above the critical temperature and cools it very slowly, usually in the furnace. It softens the metal, relieves internal stress and improves machinability after welding or cold working.

File grade meaning

File grade describes tooth coarseness: rough, bastard, second cut and smooth. A smooth file has fine teeth and removes the least metal per stroke, so it is used for final finishing.

Hacksaw blade selection

Blade pitch is chosen by section thickness. Coarse 14 or 18 teeth per inch suits thick solid sections, while fine 24 or 32 teeth per inch suits thin tube and sheet where coarse teeth would snag.

Centre punch use

A centre punch makes a small conical dot at a scribed intersection so a drill starts without wandering. It is held vertically and struck once, after the layout line is marked.

Tap drill size rule

For metric threads the tapping drill diameter equals the major diameter minus the pitch. For M10 with 1.5 mm pitch, the drill is 8.5 mm, giving about 75 percent thread engagement.

Reamer rotation direction

A hand reamer must always be rotated clockwise, in the cutting direction, and never reversed. Reversing dulls the cutting edges and can score the finished hole surface.

Interference fit

In an interference fit the shaft is larger than the hole before assembly, so the parts must be pressed or shrunk together. The resulting elastic grip transmits torque without keys.

Bend allowance purpose

Bend allowance is the length of the neutral axis within the bend arc. Adding it to the flat pattern dimensions gives the correct blank size before folding sheet metal.

Grooved seam

A grooved seam is a double-locked joint formed by hooking two folded edges and locking them with a seam setter. It is strong and is used on buckets, ducts and boxes.

Sheet metal gauge numbering

Sheet metal gauge numbers run opposite to thickness: a higher gauge number indicates a thinner sheet. Standard wire gauge tables convert gauge number to millimetres for selection.

Mortise and tenon joint

The mortise and tenon joint inserts a projecting tenon into a matching rectangular mortise. It resists racking and is standard for door frames, tables and chair construction in carpentry.

Kiln seasoning

Kiln seasoning dries timber in a heated, humidity-controlled chamber. It is much faster than air seasoning and produces a controlled final moisture content with fewer drying defects.

Rip saw versus cross-cut saw

A rip saw has chisel-like teeth and cuts along the grain, while a cross-cut saw has knife-like teeth and cuts across the grain. Using the wrong saw tears the fibres.

Upsetting in smithy

Upsetting increases the cross-section of a bar by hammering its hot end along the axis. It is used to form bolt heads, collars and thick shoulders on forged parts.

Forging temperature colour

Steel is forged in the orange to yellow range, roughly 1000 to 1200 degrees Celsius. White heat risks burning the metal, and forging below the critical range may cause cracking.

Swage block use

A swage block is a heavy block with grooves and shaped holes. It supports hot work while forming curves, rounds and hexagons with fullers or hammers in the smithy.

Riser in casting

A riser, or feeder, is a reservoir of liquid metal connected to the mould cavity. It feeds the casting during solidification to prevent shrinkage cavities in the final part.

Green sand moulding

Green sand is a moist mixture of silica sand, clay binder and water. It must be permeable, refractory, cohesive and collapsible, and is the most common moulding material in foundries.

Shrinkage allowance in patterns

Patterns are made larger than the finished casting to compensate for metal contraction on cooling. Typical values are about 10 mm per metre for cast iron and 16 mm per metre for aluminium.

DC straight polarity

In DC straight polarity the electrode is negative and the work is positive. More heat is generated at the work, giving deeper penetration, so it suits thicker plates in arc welding.

Carburising flame

A carburising oxy-acetylene flame has excess acetylene and shows three zones with a feathery inner cone. It is used for high carbon steel and hard surfacing to avoid oxidation.

Spot welding heating

Resistance spot welding passes a heavy current through clamped sheets for a short time. Heat generated by I squared R at the contact interface forms a small fused nugget.

Lathe cutting speed formula

Cutting speed in metres per minute equals pi times diameter in millimetres times spindle speed in rpm, divided by 1000. It is used to set the correct rpm for a workpiece diameter.

Climb milling

In climb, or down, milling the cutter rotates in the feed direction, so chip thickness starts at maximum. It gives better surface finish but needs a backlash eliminator on the table.

Shaper quick-return mechanism

The shaper uses a slotted link and crank to give the ram a slow cutting stroke and a faster return stroke. The clapper box lifts the tool on return to avoid rubbing.

Belt drive velocity ratio

For a belt drive the velocity ratio equals driver speed divided by driven speed, which also equals driven pulley diameter divided by driver pulley diameter when belt thickness is equal.

Worm and worm wheel

A worm and worm wheel transmits motion between shafts at right angles with a large speed reduction. The drive is compact and can be self-locking when the lead angle is small.

Slider-crank mechanism

The slider-crank mechanism converts rotary motion of a crank into reciprocating motion of a slider. It is the basis of piston engines, reciprocating pumps and compressors.

Vernier calliper least count

Least count equals one main scale division minus one vernier division. A common metric calliper with 50 vernier divisions over 49 main divisions reads to 0.02 mm.

Micrometer least count

Micrometer least count equals screw pitch divided by thimble divisions. With a 0.5 mm pitch and 50 thimble divisions, each division represents 0.01 mm of spindle movement.