Weigh the whole thing first
The mass balance is the part of a teardown nobody runs and it takes one extra weighing. Gross the unit before anything comes off it, weigh each sorted pile, weigh what goes in the skip, and add them up. On the defaults that is 145 lb gross against 6, 14, 88 and 4 lb of streams plus 28 lb of residue, which is 140 lb accounted and 5 lb — 3.4 percent — that is not anywhere.
Three and a half percent is normal enough to live with. Ten percent is a finding. It means a scale is out, or a stream was weighed wet and sold dry, or a pile was never weighed at all, or material is leaving by a route that is not in the numbers. All of those look identical in a value calculation, which is exactly why the value calculation is the wrong place to look for them.
Where the money actually is
On the defaults, stream 1 is 6 lb of the 145 and earns 15.90 a unit. Stream 3 is 88 lb — sixty percent of the whole unit by weight — and earns 9.68. The small stream is worth more than the big one, and the big one is most of the handling.
Add it up per unit: 36.70 of stream value, less 1.19 of residue disposal, less 16.33 of labour at 35 minutes and 28 an hour, is 19.18 net. Sold whole at 7.5 cents a pound the same unit is 10.88. Separating is ahead by 8.30 a unit, or 99.62 across twelve.
Two numbers that decide it
The break-even labour rate is what an hour would have to cost before the strip stops paying. On the defaults it is 42.23 an hour against the 28 entered, so there is room but not a great deal of it. The break-even time is the same statement from the other end: 52.8 minutes a unit rather than 35.
Both of those are more useful than the profit figure, because they are the numbers that move. Prices move too, but you find out about that at the scale house. Minutes per unit you control, and the first unit always takes twice what the tenth does, which is why the field asks for a time measured after the first one.
What is not in here
Whether the unit is safe to open. Sealed refrigeration circuits, fuel systems, undeployed airbags and pretensioners, gas struts, accumulators, pressure vessels and batteries are all present in things that arrive at yards, and this page has nothing to say about any of them beyond naming them. What applies is a matter for the manufacturer and for your state environmental and occupational safety agencies.
Nor does it know whether a given item may lawfully be sold, by whom, or with what record kept. Scrap dealing is licensed almost everywhere and some items — catalytic converters above all — have rules of their own on top of that. Proof of ownership is a normal part of the transaction.
Questions people ask
Why should I weigh the whole unit before stripping it?
Because it is the only way to know whether the pieces add up. On the defaults, 145 lb gross against 140 lb of weighed streams and residue leaves 5 lb unaccounted, which is 3.4 percent. Without the gross weighing you would never see that number, and a run where it drifts to ten or fifteen percent looks exactly the same in a value calculation as a run where it is zero.
Is it worth stripping scrap rather than selling it whole?
On the defaults yes, by 8.30 a unit, but the margin is thinner than it looks. The break-even labour rate is 42.23 an hour against 28 entered, and the break-even time is 52.8 minutes against 35 actual. Move either one much and it flips. The answer is specific to the unit, the prices that week and how fast the strip goes once it is routine.
Which stream matters most in a teardown?
Usually not the heavy one. On the defaults the 6 lb stream earns 15.90 a unit and the 88 lb stream earns 9.68, so sixty percent of the weight brings in a quarter of the money and takes most of the handling. If a stream earns less per unit than the minutes it costs, leaving it attached is often the better trade even when it feels like throwing money away.
What does the residue cost me?
Whatever your gate rate is, on the weight that leaves as waste. On the defaults 28 lb a unit at 85 a short ton is 1.19 a unit and 14.28 across twelve. It is small here and it is not always small: a unit that is half plastic can turn a teardown that looks profitable on the metal into one that is not, which is why it is a field rather than an assumption.
How accurate does the reject or residue weight need to be?
Accurate enough that the mass balance closes. That is the useful test, and it is self-checking: if the streams, the residue and the gross reconcile to within a couple of percent, the individual figures are probably fine. If they do not, the error is somewhere in that list and no amount of care with the prices will make up for it.