What the calculator does, what it needs, and where its limits are
What it is for
The calculator deals with aqueous degreasing in surface finishing. It does
not say how many minutes a part has to spend in the bath. It answers the
question that actually gets asked on the shop floor:
The supplier specifies 60 degrees, 3 per cent and 120 seconds. The plant is running
50 degrees, 2 per cent and 90 seconds. Will the part still be free enough of
grease?
That is why each row in the block “Specification against actual” has two values, the specification on the left and the actual state on the right, and both have two parts:
Specification
Temperature, concentration and time from the technical data sheet,
and what they apply to: how heavily soiled, and how clean is required.
Actual condition
What the plant is set to, and what is actually coming through: the soil
and the requirement of today's order.
The second part is the more important one. A supplier specification is a promise for
a particular task. The same 60 degrees and 120 seconds are enough for a lightly
oiled sheet before an interim clean, and not for a preserved drawn part before
bonding. Between those two cases lies a factor of
3.6
in cleaning work.
The answer: the residual grease
The main statement is not a percentage, but how far the residual grease sits
above the target value. The reason: percentages on their own cannot be interpreted.
The same amount of work done means, depending on the task, either a slight overshoot
or a multiple of what is permitted. The table shows it.
Work done
Light task
Normal task
Heavy task
100 %
on target
on target
on target
90 %
1.3× over
1.9× over
2.3× over
85 %
1.4× over
2.5× over
3.5× over
50 %
3.2× over
22× over
63× over
Light task: oil film before an interim clean (A = 2.30).
Normal: usual oiling before powder coating (A = 6.21).
Heavy: preserved drawn part before bonding (A = 8.29).
Where the percentage comes from
The work done is a product of ratios, not a sum. For the example above, with the
task unchanged:
Temperature
0.65: ten degrees too cold cost a good third of the effect. This is the
strongest of the three levers.
Concentration
0.84: a third less cleaner costs only 16 %. The weakest lever.
Time
0.75: 90 seconds instead of 120. Time enters directly: three quarters of
the time is three quarters of the effect.
0.65 · 0.84 ·
0.75 = 0.41. And that is
exactly why, on the shop floor, nobody understands what is going on: none of the three
deviations looks dramatic on its own. Together almost
59 per cent is missing, and the
residual grease then sits about 38 times the target value.
Why this works without measurement
The calculator does not have to be calibrated. No measured plant value, no
reference sample, no series of measurements, no figure in mg/m².
The reason is simple: the calculation runs against the specification, and that
is a promise: run it and the parts come out clean. Whether a plant is inherently fast
or slow therefore appears on both sides of the calculation and cancels out. What
remains is only how strongly a factor acts.
The limitation that comes with it: the calculator gives absolute seconds only when the plant
has been calibrated. A figure in seconds without that basis looks precise but is not.
The second catch: the supplier's margin
Calculating against the specification requires assuming that this specification is
just sufficient, that at 60 °C, 3 % and 120 seconds the target value is
reached exactly, not one second sooner. That is certainly untrue: every chemical
supplier builds in a margin, or they would face complaints constantly.
The consequence has a direction, and that is the good news: the calculator always
errs on the safe side. It shows too little cleaning performance, never too much.
So a plant is never released in error. How large the effect is, using the example
from above:
Supplier's margin
Calculator shows
actually
1.0× (none)
about 38 times the target value
about 38 times the target value
1.5×
about 38 times the target value
about 11 times the target value
2.0×
about 38 times the target value
about 3 times the target value
3.0×
about 38 times the target value
at or below the target value
From this follows the most important guide to reading the result:
the multiple is a warning level, not a measurement. What is dependable is the
percentage, which does not rest on this assumption, and the effect stated for each
lever in the case as calculated.
How the traffic light judges
The traffic light therefore does not rate the raw multiple but the percentage against
an assumed supplier margin of 1.5×:
Green
100 % or more: on or above the specification.
Amber
below the specification, but the assumed margin still carries it
(at 1.5× that means from 67 %).
No cause for panic, but the margin is used up: the next deviation hits unbraked.
Red
not clean even with that margin.
The margin is a setting and lives in config.php (LIEFERANTENRESERVE). Anyone who knows
their own supplier's commitment enters it there; 1.0 makes the light as strict as the
figures.
The result column
To the right of the inputs (on the phone as a fixed bar at the bottom) the verdict
appears as a coloured card: the percentage, the verdict, the residual grease and one
line saying which lever is missing most. Below it three tabs:
What it comes down to
One bar per lever: temperature, chemistry, time, mechanics and the task.
A full bar means 1.00, as in the specification. The shorter, the bigger the loss.
The bars multiply to the percentage in the card.
Way back
What value a single lever would need to get back to 100 %, and whether that is
feasible. Shown only when something is missing.
Curves
One per lever, with a fixed scale in real units. Only that one value is moved,
the others stay put. The filled dot is today's state, the hollow ring
on the 100 % line the value required, the vertical grey line the
specification and the red-shaded area in the temperature curve the range
barred for the material.
Bars and curves contain no figures other than the contributions next to the inputs.
They are the same calculation, only as a picture.
The way back to the specification
“59 per cent is missing” helps nobody. The calculator therefore works out, for each of
the three levers separately, what value would be needed to get back to 100 %,
with the other two left where they are. For the example:
Via time
217 s instead of 90 s. Feasible, provided the line's cycle allows it.
Via temperature
71.5 °C instead of 50 °C. Possible with unalloyed steel; with aluminium
the calculator reports “above the limit” in red.
Via chemistry
14.9 % instead of 2 %. Arithmetically right, practically nonsense. Nobody
doses like that. That is precisely the point being made.
The assessment next to each route therefore matters more than the figure itself. It
says whether the route is viable. If none is left, the cause belongs to be
removed, not compensated for.
“What if something else goes wrong as well”
The block below the inputs puts a fault on top of the actual condition. Six
areas, each with a row of chips: bath temperature, dosing, impingement, cycle, part,
bath maintenance. One tap selects, a second tap clears.
Only one fault can be chosen per area: a bath cannot be 3 and 20 degrees too
cold at the same time. Across the areas, on the other hand, everything counts together,
and it does so multiplicatively.
With faults selected, a second card appears in the result column and the bars show the
state with faults. The worked examples further down are nothing more than pre-filled
chips: one click sets them, and it becomes immediately visible what the result is made
up of.
The customer sheet
The “Customer sheet” button below the form leads to a page that puts the same result on
one A4 sheet: verdict, percentage, specification against actual, the way back and the
chosen additional faults. Customer, plant, prepared-by and a remark can be entered at the
top; they appear in the header and at the end of the sheet. “Print” opens the browser's
print dialogue; form, menu and footer are left out.
The sheet calculates nothing itself. It takes the values from the address line and
displays them differently; that is why the assumptions and the address for reopening the
case are stated at the bottom. The free-text entries are not stored. To keep the case,
save it in the calculator under “Save as case”.
Access protection
The tools (calculator, slider, customer sheet, saved cases, self-test) can be protected with
access codes; start, guide and formulas always stay open. Each customer gets their own code,
which can be blocked individually. After setup the protection is switched off and is
switched on in the administration once codes exist; it can be switched off there at any
time, the codes are kept.
The administration is reached through the “Administration” link in the footer and is
secured with an administrator password from config.php. If that is not set yet, the page
generates the required lines for config.php from a password you enter. A new code is shown
in clear text exactly once; what is stored is a checksum from which it cannot be recovered.
After five failed attempts, signing in is blocked for ten minutes, doubling with each further
failure. “Stay signed in” lasts 30 days per device and ends on sign-out or when the code is
blocked.
Etching on aluminium
Anyone coating aluminium usually runs the degreasing bath so that it etches at the same
time. There is a separate switch in the form for that case. It stays off until you
need it, and changes nothing while it is off.
The decisive difference: cleaning knows only one direction, more is better.
Etching has a window. Too little removal leaves the deformation layer in
place, too much costs aluminium, dimensional accuracy and appearance. So there is not
one minimum time but a minimum and a maximum, and they have to overlap with the
cleaning condition.
What to enter
Etching route: alkaline (caustic soda) or acidic with fluoride. pH is part
of the calculation on the acid route only.
Measured removal at the specified settings, in g/m². You already have this
figure: it comes from the QUALICOAT test, where the panel is weighed before and
after the process. It is the only real measured value in the whole
calculator. If the field is still at 1.2, the calculator points out that the
grams are then a guess.
Required minimum removal: QUALICOAT standard 1.0 g/m², SEASIDE 2.0 g/m²,
or your own specification. It applies across all etching steps together.
Upper limit: there is no standard for this. The calculator suggests
3.0 g/m²; where your own ceiling sits is an in-house decision.
Temperature sensitivity of the etching: set to 50 and fine to leave there.
It is the least certain number in the block: the literature scatters widely. If you
have measured removal at two different temperatures, enter your own value.
Removal in further etching steps: if a deoxidising step follows this bath,
its contribution belongs here. This bath then has to do correspondingly less.
What comes out
Three figures, and the third is the real one:
How much this bath removes as it currently runs, with a traffic light: too little,
inside the window, too much.
The etching window in seconds at the temperature and concentration set.
The common range: the span of time in which cleaning and etch removal
both hold. Plus which of the two sets the lower bound. Often it is the etching, and
anyone looking only at cleanliness sees half of it.
The most valuable case is the uncomfortable one: if there is no overlap, the
calculator says so explicitly. At that temperature and that concentration there is no
correct cycle time. You have to change T or c, and no amount of extra cycle time
helps. This situation is practically impossible to spot without calculating, because
the two conditions are normally checked separately.
Three statements you will find only here
Running hotter and shorter does not always win. Cut the time just far enough
that removal stays the same, and cleaning only gains on stubborn soils: clearly with
carbonised oil, while with thin oil it actually gets worse. The calculator states which
case applies for the soil you selected.
An etching bath run too cold loses twice over. The detergent slows down, and on
top of that the etch attack that loosens the soil from underneath weakens. The second
loss does not appear in the usual assessment at all; the calculator subtracts it as
soon as the etching switch is on.
For the etching, the detergent is not the weakest lever but the strongest. For
degreasing the rule is: temperature beats dosage, for every soil type. For etch
removal it is the other way round: concentration enters linearly there. Half the
dosage means half the removal, but only about a quarter less cleaning effect. So
economising on the etchant cuts the etch removal first, and that is what appears in
the test report.
The four statements that come as a surprise
Chemistry is the weakest lever
Halving the dosing costs only about a quarter of the effect (factor 0.75). Saving on
cleaner therefore costs more than expected, and reaching for the dosing pump first
when there is a problem means reaching for the weakest tool available.
The reason: concentration acts roughly as a square root, not in proportion. Twice as
much cleaner buys about 40 % more rate, not 100 %.
Temperature is the strongest lever
Ten degrees below the specification cost about a third of the effect (factor
0.65). Ten degrees are quickly missed on a bath thermometer. With the cleaner, the
same loss would mean going down to a third of the dosing, and everyone would notice
that.
So at the bath it pays to look first at the heating, the lid and the warm-up time
after the weekend, before anyone touches the cleaner.
Ten times the soil costs only a third of the effect
Ten times as much oil on the part gives a factor of 0.67, twice as much oil a
factor of 0.87. The amount of soil enters logarithmically, not
proportionally.
The reason: cleaning always removes a proportion of the soil still present.
The first ninety per cent goes quickly, however thick it was: what takes a long time
is the last one per cent. And the last one per cent is equally far away whether there
was a lot of oil or a little.
Caution: with very thick, closed grease films this no longer holds; there
removal is even at first rather than proportional. More on this under
Formulae.
Why deviations multiply
Each fault acts on what the previous one left over, which is why the factors are
multiplied and not added up. Ten degrees too cold (0.65), a forgotten top-up (0.89) and
half-blocked nozzles (0.89) together give 0.52. Almost half is missing, although
none of the three faults would stand out on its own.
On the shop floor people usually look for the one big mistake. Often there are
three small ones.
Terms
Specification
Temperature, concentration and dwell time from the cleaner's technical data sheet. If
it gives a range (“50–70 °C, 2–4 %”), the middle belongs in the form, not the
lower end. The lower end is already the limit and leaves no margin.
Where there is no data sheet, the condition that is known to have produced clean
parts will do. The calculation then runs against “back when it worked”.
Actual condition
What is really set today, measured, not read off the setpoint controller. The
most common mistake when filling the form in: top and bottom hold the same figures,
because that is what the controller displays, and the result is, predictably, 100 %.
For the concentration that means: titrate. A bath that has not been topped up
for three weeks is rarely where the dosing system claims it is.
Mechanics: the process type
The mechanics row carries a process selection on both sides: still immersion, circulated immersion,
immersion with part movement, spray, high-pressure spray, directed high pressure.
Left, the process the specification applies to. Right, the process actually run.
Why two fields and not one: a technical data sheet usually gives not one
specification but two: “immersion 3–5 %, 60–70 °C, 5–10 min · spray 1–2 %,
50–60 °C, 60–120 s”. The specification is therefore tied to a process type. Running
the immersion specification in a spray washer, or the other way round, moves a lever
without anyone noticing.
How much: a specification written for spraying, run in a still immersion bath,
costs between 40 and 75 % of the effect depending on the type of grease, more than
ten degrees too cold. Baked-on oil suffers most, light oil least: the more stubborn
the soil, the more it depends on flow.
With both fields on the same step the mechanics cancels out and changes nothing.
That is the normal case: usually the process run is the one the specification was
written for.
Nothing has to be measured for this. No absolute value ever enters the
formula, only the ratio of the two steps. Stating which process is meant is
therefore enough.
Mechanics also acts as a fault: blocked nozzles, halved pump pressure. Those
are under “What if something else goes wrong as well” and are combined with the
process type.
Ultrasound is deliberately not on the list. It works through cavitation, not
flow, and it has a threshold: below it little happens, above it a great deal. Treated
as a flow factor it would produce a number that looks precise and is not.
Soil and substrate
The type of grease changes how strongly the levers act: with baked-on oil,
temperature pulls far harder than with a light cutting fluid; with polishing paste,
flow counts for more. That is why the result changes as soon as the type is switched,
even when nothing else has been touched.
The amount and the requirement, by contrast, are in the two drop-down
lists above. They do not change the sensitivity, but how much work there is to do in
the first place.
The substrate does not enter the calculation. It only supplies the
limits: maximum temperature and pH window. The “way back” is measured against those:
72 degrees is no problem for steel and component damage for aluminium.
The two fields under “Absolute times”
Right at the bottom of the calculator, collapsed, there are two inputs. They affect
the two time tiles below them and nothing else. They do not change the result
above: neither the residual grease nor the percentage.
k₀: the cleaning rate at the specification
Unit 1/min. It says how fast the grease decreases when exactly the supplier's
specification is run. k₀ = 2.3 /min means: after one minute a tenth of the
grease is still there.
Where the value comes from: from the technical data sheet or from the chemical
supplier's application engineer, or from your own trial. For the trial, take a
process that is known to work and look for the shortest time at which it still
passes. If the part is already clean after half the time and the full time is
measured, the plant is credited with a value twice as poor as the truth.
How it acts: inversely proportional to the time. Twice k₀, half the time.
k₀
calculated
with safety factor
0.5 /min
1,351 s
1,891 s
1.0 /min
675 s
946 s
2.3 /min
294 s
411 s
4.6 /min
147 s
206 s
Example: specification 60 °C / 3.0 % / 120 s, run at
50 °C / 2.0 % / 90 s, usual oiling before powder coating, safety factor 1.4.
Two more things: k₀ applies to the type of grease it was measured with: a
value from a light cutting fluid does not carry over to drawing compound. And it
applies to this specification: change the specified temperature above and the
meaning of k₀ changes with it, because the reference point is always the
specification.
Safety factor: the margin on the time
A pure number without a unit, usually 1.4. It lengthens the calculated time
by 40 %.
Why it is needed: the equation works with one value for the soil and
one for the rate. In reality both scatter: the soil with tool life, part
position and standing time, the rate with bath age, batch size and position in the
basket. Designing exactly to the calculated time builds a plant in which about
half the parts miss the target value, regardless of how large the scatter is.
Safety factor
time designed for
when it makes sense
1.0
294 s
for comparison only, not for design
1.2
352 s
well-controlled, consistent process
1.4
411 s
value from experience at usual scatter
1.8
529 s
uncertain k₀ or expensive scrap
Etch removal
How much aluminium the bath removes, in grams per square metre. Determined by
weighing: weigh the test panel (AA6060 or AA6063), run it through the process,
strip it, weigh it again. QUALICOAT requires at least 1.0 g/m² across all etching
steps together, and 2.0 g/m² for SEASIDE.
It is the only quantity in the whole calculator that is actually measured in the
shop, which is why the etching part works in real grams and not only in ratios.
Etching window
The span of time in which removal is neither too small nor too large. The word is
not a standard term: "process window" would be the usual one; here it is short for
"the time window in which etch removal is right". Unlike
cleaning, there are two limits here: below the first the deformation
layer stays in place, above the second you pay for aluminium without gaining
quality.
Loosening from underneath (etch attack)
The etch attack dissolves the metal underneath the soil. Whatever sits on top
loses its grip, regardless of what the detergent does. That is a mechanical effect,
not a chemical one, so the calculator counts it towards mechanics.
Practical consequence: if the bath gets colder you lose twice. The detergent slows
down, and the undercutting weakens.
Free hydrogen fluoride
In acid etching the attacking species is not the fluoride ion but undissociated
hydrogen fluoride. Hydrofluoric acid is a weak acid. How much of it is free depends
on pH alone: 94 % at pH 2, 60 % at pH 3, only 13 % at pH 4.
Hence the rule "the lower the pH, the better", and its limit: below pH 2 almost
everything is active already, and going lower gains next to nothing.
Where the calculator does not reach
It knows no thresholds. The melting point of a grease, the cavitation
threshold in ultrasound, an optimum concentration. These are jumps, not curves. With
waxes and drawing compounds five degrees can decide between good parts and scrap.
Degreasing only. Salts, scale and biofilm follow different mechanisms and are
therefore not offered: salts simply dissolve, scale needs a pickle, biofilm is treated
with a biocide.
Particulate cleanliness to VDA 19.1 / ISO 16232 is not calculated. There the
particle count per size class matters, usually with a largest-particle limit. Neither
can be reconciled with a mass in mg/m².
The age of the soil is missing. Dried-on or oxidised oil behaves quite
differently from fresh oil. In many plants the time parts stand between machining and
cleaning is the single largest source of scattered results.
The pH value only comes along as a substrate limit, not as a lever. With
alkaline cleaners its effect is contained silently in the concentration.
Immersion and withdrawal are missing. In laboratory trials a large part of
the removal fell to the moment when the bath surface travels across the part. Dipping
several times can therefore be more effective than dwelling longer.
Water hardness, foam and the choice of cleaner do not appear.
A result above 100 % is not a permission. It says that more work is being
done than necessary, not that the part will take the temperature or that the bath
will last longer.
And the most important sentence to close on: the characteristic values stored for each
type of soil are guide values. They reliably reproduce which lever acts more
strongly than which. That is what the calculator is built for. For a design with
money riding on it, the plant belongs calibrated and a cleaning trial belongs run.