ITI Mechanic Auto Body Repair (AITT Theory) flashcards

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

Fire class B

Flammable liquids such as paint, thinner and solvent. Never use water on this class - it spreads the fire; use foam, CO2 or dry powder instead.

Isocyanate exposure hazard

Hardeners in 2K paints and clearcoats can cause occupational asthma. Spraying requires an air-fed full-face respirator and booth extraction, not a paper dust mask.

SDS Section 8

Exposure controls and personal protection. It lists the occupational exposure limits, respiratory protection, glove type and ventilation requirements for the chemical.

Planishing hammer

A flat-faced body hammer used with a dolly held behind the panel to flatten and stretch metal, smoothing a repair after rough bumping.

Aviation snip colour code

Green means right cut, red means left cut and yellow means straight cut. They cut sheet to about 1.2 mm and must not be used on wire or rod.

File card

A stiff brush with short wire bristles used to clean metal filings from the teeth of a body file, keeping it cutting cleanly and preventing scratches.

Vernier caliper least count

The smallest reading the tool can resolve, usually 0.02 mm on a metric caliper. It equals one main scale division minus one vernier division.

Tram gauge

A bar with two adjustable pointed arms used to measure point-to-point distances such as door-aperture diagonals; equal diagonals show the opening is square.

Datum point

An OEM-specified reference hole or mark on the underbody, listed on the body dimension chart, from which structural measurements are taken during alignment.

Bend allowance

The length of the neutral axis within the bend zone, calculated as (pi/180) x angle x (R + K x T), and added to the flat pattern length.

Springback

The elastic recovery of metal after the bending force is removed. Higher-strength steel and larger radius-to-thickness ratios produce more springback, so the part is overbent.

High-strength steel heat rule

Boron and high-strength low-alloy body steels must not be heated above about 200 degrees Celsius when straightening, because heat destroys the temper and crash performance.

Plug weld

A weld made by filling a hole drilled or punched in the outer panel so it fuses to the panel behind, used where a squeeze spot welder cannot reach.

Metal fume fever

A flu-like illness caused by inhaling zinc oxide fume when welding galvanized steel. Grind the coating back and use forced ventilation or an air-fed helmet.

Backstep welding

A distortion-control technique in which short welds are made in reverse order along a seam, so each new weld finishes at the start of the previous one.

Diamond damage

Collision misalignment where one side of the body is pushed rearward, making the two diagonals of a door aperture unequal; corrected by opposing pulls.

Sectioning

Replacing part of a structural panel at an OEM-specified cut location using the specified backing insert, weld type and corrosion protection to restore original strength.

Crumple zone

A deliberately weakened section of the front or rear structure that deforms progressively in a crash to absorb energy and protect the passenger cell.

Off-dolly bumping

A panel-beating technique where the dolly is held away from the strike, on the far side of the panel, so the metal is stretched to raise a low area.

Heat shrinking

Heating a small spot of stretched steel to dull cherry red and quenching it with a wet rag or shrinking hammer to contract the metal and remove an oil-can.

Feather edge

A long taper, typically 25 to 50 mm, sanded into the edge of old paint around a repair so the new finish shows no step or ring.

Thermoplastic panel

A plastic that softens when heated and can be hot-air welded, such as PP, PE, ABS, PC or TPO, unlike a thermoset which chars instead.

MEKP catalyst ratio

For polyester resin, MEKP hardener is added at about 1 to 2 percent by weight. Excess catalyst causes a hot, brittle cure that can crack or discolour the laminate.

GRP bevel ratio

Damage in glass-reinforced plastic is ground back at about a 12:1 taper so each new layer of mat overlaps the old and the repair regains full strength.

HVLP spray gun

A high-volume low-pressure gun that atomises paint at about 10 psi at the cap, giving higher transfer efficiency and less overspray than a conventional gun.

Flash-off time

The wait between coats, usually 5 to 15 minutes, allowing solvent to escape. Painting too soon traps solvent and causes popping or blushing.

Fisheye defect

Small circular craters in a paint film caused by oil, silicone or water contamination on the panel or in the air line; the surface must be cleaned and air filtered.

Laminated windshield

Two glass sheets bonded to a polyvinyl butyral interlayer; it cracks in a spider-web pattern and stays in the frame, which is why it is used for windscreens.

Safe drive-away time

The minimum curing period after bonding a windscreen with urethane adhesive before the vehicle may be driven, typically one to three hours depending on the product.

Parasitic draw

Current drawn from the battery when all systems are switched off and modules have slept; more than about 50 mA indicates a fault that can flatten the battery.

CAN bus termination

Two 120-ohm resistors fitted at the ends of the bus; measured across CAN-H and CAN-L with the bus asleep, the reading should be about 60 ohms.

Betterment charge

An amount charged when a repair leaves the vehicle better than before the loss, such as a new panel or a new tyre replacing a worn one.