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5 <title>Rolling wire-strip calculator: equations</title>
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19 <h1>Rolling wire-strip calculator: equations</h1>
21 <p>The calculations performed by the <a href="rolling.html">rolling
22 wire-strip calculator</a> were derived by examining experimental data.
23 We might not have considered all of the necessary variables. Anyway,
24 here’s how it currently works.
26 <p>Let’s suppose we start with square wire, with side $S$,
27 and we roll it to thickness $t$. Then we find that the
29 \[ w = \sqrt{\frac{S^3}{t}} \,\text{.} \]
30 Rearranging, we find that
31 \[ S = \sqrt[3]{w^2 t} \,\text{.} \]
32 For round wire, we assume that the cross-section area is the important
33 bit, so a round wire with diameter $D$ ought to work as well as
34 square wire with side $S$ if $S^2 = \pi D^2/4$, i.e.,
35 \[ D = \sqrt{\frac{4 S^2}{\pi}} = \frac{2 S}{\sqrt\pi} \,\text{.} \]
36 Volume is conserved, so if the original and final wire lengths
37 are $L$ and $\ell$ respectively, then
38 \[ L S^2 = \ell w t \,\text{,} \]
40 \[ L = \frac{\ell w t}{S^2} \,\text{.} \]
41 Finally, determining the required initial stock length $L_0$ given
42 its side $S_0$ (for square stock) or diameter $D_0$ (for
43 round) again makes use of conservation of volume:
44 \[ L_0 = \frac{S^2 L}{S_0^2} = \frac{4 S^2 L}{\pi D_0^2} \,\text{.} \]
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