Rolled Steel, Wire, Sheet and Wire Rope

§1Stock as a component

The forms steel arrives in — bar, section, plate, sheet, wire, rope — carry their manufacturing history as engineering properties, and the designer inherits both.

Nothing on this page is a finished part, yet every entry behaves like a component with a datasheet written by its process. Rolling elongates the metal’s inclusions and grain into fibre running the length of the product, so strength and especially toughness are directional — the timber pages’ grain, rediscovered in steel. Cold processes (cold rolling, drawing) bank strain-hardening into the stock, raising strength and lowering ductility before any part is cut from it, and leaving residual stresses that machining releases as warp. And the stock’s tolerances, surface and straightness set what finishing the part must buy back — the difference between turning a shaft from bright bar and from black bar is a page of process planning. Reading stock this way pays twice over: choosing the semi-finished form is choosing half the part’s properties and cost before the first chip; and the two woven appearances later in the page — wire as the thread-rolling page’s blank, rope as a complete machine element — show stock graduating into this section’s own subject matter.

§2Rolled sections and plate

Hot and cold rolling make recognisably different products from the same steel — and the table is worth internalising, because the differences are the ones fabrication trips over.

§3Sheet metal and the bend

Sheet is stock you shape by folding, and the fold obeys three laws: the flat pattern is longer than the drawing suggests, the metal springs back, and the fold itself is where stiffness comes from.

First, name sheet in millimetres, not gauge — the gauge ladders differ by material and country, and “16 gauge” has caused more mis-cut blanks than any dimension in the trade. The bend allowance is the flat-pattern arithmetic: bending stretches the outside face and squashes the inside, and the unchanged-length neutral axis sits below mid-thickness (the k-factor, commonly around a third to a half; take k = 0.4 as a stated working value). A 90° bend at r = 2 in t = 2 sheet then consumes BA = (π/2)(2 + 0.4×2) = 4.40 mm of flat length — per bend, summed across the part, and the reason unfolded blanks come from the formula or the CAD unfold, never from adding outside dimensions. Springback is the elastic core reasserting itself when the press releases: every bend opens slightly, so brakes over-bend past the target — more for stronger, springier §2 cold stock. And the fold pays for everything: a flat sheet’s bending stiffness scales with t³, so a flange, hem or rib that moves material away from the neutral plane multiplies stiffness enormously at zero weight — sheet-metal design is the art of buying structure with folds. One inherited rule closes the loop: bend across the grain; a tight bend along §1’s fibre cracks the outside face along the inclusions rolling laid there.

§4Wire

Wire is cold work in its purest bottled form: steel pulled through dies until strain-hardening has been banked as extraordinary strength — the stock behind springs, ropes and every rolled thread.

Each drawing pass squeezes the rod smaller and stronger, and by the fine sizes the accumulation is spectacular: hard-drawn spring and music wire reach tensile strengths ordinary steels never approach, the smallest sizes strongest of all — partly the cold work itself, partly the statistics of flaws in a shrinking cross-section. The price is drawn from the same account: ductility spent, springiness maximal (coiled wire fights its coil — the reason wire ships on reels and arrives with a memory), and a strength that heat undoes, so hard-drawn wire is joined mechanically or with care, never casually welded. Three of this library’s earlier pages stand on wire without saying so. The springs pages’ music-wire coils are §4 verbatim. The thread-rolling page’s blank — drawn to the pitch diameter, rolled in a die stroke — is wire graduating into fasteners by the billion, its drawn accuracy becoming the thread’s accuracy exactly as that page warned. And the next section of this page is wire’s masterpiece: take the strongest form steel offers, admit it cannot be bent at any useful scale — and weave it.

§5Wire rope

A rope is the resolution of a contradiction — enormous tensile strength and easy flexibility in one member — bought by dividing the steel into wires so fine that each bends trivially, and paying the sheave arithmetic forever after.

§6Handling and lifting

Rope in lifting service is governed stock: a stamped working limit, angle arithmetic that quietly steals capacity, and handling rules written by old failures.

The governing number is the safe working load, the certified minimum breaking load divided by the service’s factor — the general-lifting convention of 5:1 turning an MBL of 40 kN into an SWL of 8 kN, with harsher factors for people and hostile duties; SWL is a stamped, certified property of the sling as rigged, never a calculation improvised at the hook. The classic thief is the sling angle: two legs splayed 30° from vertical each carry W/(2 cos 30°) = 0.577 W — more than “half the load” by fifteen per cent — and the theft grows without limit as the legs flatten, which is why rigging charts derate by included angle and why a wide, shallow bridle on a rated pair is the classic quiet overload. The remaining rules each answer §5’s physics: pack every edge the rope crosses, because a sharp corner is the world’s smallest sheave; load hooks in their throats, never their tips; take rope off the reel by unwinding, not looping, or the loop becomes the kink; and store it dry and dressed, since a rope’s core corrodes invisibly from within. Stock, at the end of this page as at its start, rewards being treated as the component it already is.

§7Quick reference

The working core of the page on one card rack.