Re: Square pegs in round holes

From: Mikito Harakiri <>
Date: 24 May 2002 09:08:22 -0700
Message-ID: <>

  • Graham Bellamy <> wrote:
    > > You wrote that "pigment is dependent on other
    > > materials". I don't see it: there is pigment name
    > field
    > > B5 on epoxy screed spreadsheet and that's it.
    > Sureshield - E24, and similar concept with B24,
    > Silkal SL - E23, B22
    > Silkal Screed - E23, B22
    > Silkal Rollcoat - E21, B21

IMHO pigment is an ordinary material (at least it looks so for Sureshield). Pigment TreatmentComponents record is dependent upon resin and seales, but there is a similar dependency for resin with mixing formula at epoxy screed.

> > Let's consider what do you store in Epoxy Screed
> > case:
> >
> > insert into treatments (id, name, area)
> > values (1, 'Epoxy Screed', B7);
> >
> > insert into materials values (name, porousness,
> > thickness, density, cost)
> > values ('Primer',1,1/C17,null,E14)
> Why would you enter a thickness of 1/C17? Maybe you
> meant for this to be density? But even then C17 is
> the application rate of the second sealer layer. Do
> you mean 1/C14?

Sorry, a typo. The rate 1sqm/L means that 1L of material will cover 1sqm with 1mm thickness. If the rate becomes 2sqm/L then it will cover 2sqm area with the same 1L, but the thickness will decrease twice. (Because only half of the amount will be used at each 1 sqm area.) Therefore

thickness = 1/rate

It refers to the same materal (1/C14), of course.  

> > insert into materials values (name, porousness,
> > thickness, density, cost)
> > values ('Resin',1,1,2.1,E15/2.1)

Mistake here as well:

insert into materials values (name, porousness, thickness, density, cost)
values ('Resin',1,null,2.1,E15/2.1)

Unlike primer case, there is no data to calculate thickness of resin as a material. And, moreover, this figure wouldn't be used later, anyway.

> > insert into TreatmentComponents values
> (treatment_id,
> > component_id, volume)
> > values (1,1, B7/C17)
> I don't understand why you are storing a volume
> value here.

For each component we need a total amont of material. The total amount can be measured in L, Kg, or even sqm (for wallpaper, for example). We want use a single unit in order to avoid cases explosion, remember? I've chosen volume, and this is arbitrary choice of course, but I'm trying to demonstrate that we can recalculate TreatmentComponents amount from any units to Liters.

We know material thickness -- C14, not C17, of course, so we just multiply thickness by the area and get the volume!

Note that in that case we use *material* thickness, not the thickness of the *layer* C8. Likewise, when the quantity D14 is calculated, layer thickness C8 is not used as well.  

> > insert into TreatmentComponents values
> (treatment_id,
> > component_id, volume)
> > values ( 1,2, B7/(1+B9) )

I made a mistake here as well. It should be B7*B8/(1+B9)

The required volume is just the area that we want to cover multiplied by the layer thickness. Unlike previous case, resin material doesn't have it's own thickness so that we need to use B8 instead. 1/(1+B9) is the mix factor that is also present in the original spreadsheet.

Now, we can convert all the data from my canonical form back to the original form. Mass of resin is volume by material density. Coating layer thickness B8 is not important for primer and can't be restored back from primer data, but can be restored from resin data. It's a resin volume divided by area. Rate for primer is just an inverse of thickness.

I'm not quite sure if thickness is attribute of material, though. User enters rate on the form as if rate can be different for the same material. For example on one treatment he enters Primer Rate=2sqm/L while on the other Rate=4sqm/L In that case we just move it from Material to TreatmentComponents table. All calculations remain the same. Received on Fri May 24 2002 - 18:08:22 CEST

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