Update on sieves

Following the visit to the Barley Mow noticed at reference 1, I returned recently to take a further look at the aggregate sorting sieves.

Sieves which are often used in a sequence. First two inch, to recover the large stones, then one inch to recover those between one and two inches, then half an inch to recover those between half an inch and an inch - and so on. For the purposes of analyzing black top, the stuff you make most road surfaces out of, the sieves would be put into a stack, largest at the top, smallest at the bottom. The blacktop sample would go in at the top, the stack would be filled with a colourless solvent (toluene) and the whole mounted on a shaker. After some standard interval of time, the aggregate would be sorted into its constituent sizes and the amount of bitumen could be computed from the black fluid you drained out of the bottom.

Now I had thought, without having inspected any such sieves for a long time, that these large sieves where made by cutting square holes in a sheet of bronze, say 1mm thick.

But while this may sometimes be the case, it was clearly not the case here. Rather, they were made of very stiff wire, say 1mm diameter, wire which had been bent into a wave, with wavelength say 2cm. One then wove the wires into a square grid by counting waves, as can be seen in the snap above.

Now if you are indeed weaving, the under and over business means that there must be an issue with odd and even. Something to be pondered about when dozing in the afternoon heat to come. With BH threatening temperatures into the low thirties today and getting worse as we go into the weekend.

Next problem. How does this play when you want a sieve with apertures some small fraction of a millimetre, needed when you are grading sands and silts? Do you do the same trick of bending the wires into some very short wave, or is there some new trick?

They have got some of these sieves at the testing museum in Southwark Street, noticed at reference 2, so perhaps a special return visit is indicated.

PS: my memory is that looking through one of these very fine sieves is rather like looking through a peculiar sort of glass. They appear to be transparent, the packing of the wires making up the mesh being too close for the retinas to resolve.

References

Reference 1: https://psmv5.blogspot.com/2022/04/barley-mowed.html.

Reference 2: https://psmv5.blogspot.com/2021/11/facts-not-opinions.html.