Density Testing 1

[nbryan]

When performing a density test in accordance with ASTM D 2937, the ASTM requires a drive cylinder volume reported
to the nearest 0.01 cubic inches. What would this convert
to in cubic feet? I am concerned about significant figures
in relation to calculating a final unit weight.

 

[Ron]

The tolerance for volume of a drive cylinder is +/- 1.0 percent of the average volume. You may "calibrate" your cylinders by the following:

For each cylinder selected to represent a shipment or "lot" of cylinders, measure the inside diameter to the nearest 0.010 inches at four equally spaced locations at the cutting edge of the cylinder. Do not measure at the seams if using welded tubes. Calculate the average of these readings.

Measure the height to the nearest 0.010 inches at four equally spaced locations around the cylinder. Calculate the average of these readings.

Using the average diameter and height, calculate the volume to the nearest 0.01 cubic inches.

To obtain the mold factor, if cubic feet is desired, divide the number of cubic inches by 1728. (Report to four decimal places)

The mold factors may then be averaged to obtain a standard.

If more than one cylinder sampled, does not fall within 1% of the standard mold factor or volume , then that standard may be used for all cylinders in the shipment.

If all cylinders sampled, except for 1, do not fall within 1% of the standard, then either return the shipment or calculate individual mold factors for each cylinder.

Determine the mass for each cylinder to the nearest 1.0
gram.

This procedure should be used for new cylinders. If you want to re-check old cylinders, first be sure that they are in good condition, not bent, have no significant "dings" in the cutting edges, and are round.

You may cross-check your volume results by putting a cylinder on a piece of glass, then use hot wax to seal the bottom of the cylinder to the glass (put wax on outside only). Weigh the assembly to nearest 0.01g. Fill the cylinder with water and with the miniscus of the water above the edge of the drive cylinder, place another piece of glass (pre-weighed to same accuracy) on the top of the drive cylinder to achieve a flat water surface. Dry any water spillage from the assembly and re-weigh the assembly. Subtract the "hardware" weights, leaving only the water weight. Assuming this is done at somewhere near 70 degrees F, then compute the absolute volume of the water from its weight and density.

Ron

 

[nbryan]

After much debate and review of the ASTM, I am convinced that it should be six decimal places and not four.
This is very important in computer program applications.
An example conversion would be as follows:
53.56 cubic inches converts to roughly 0.03099537 cubic feet.

Now, to convert cubic feet back to cubic inches and get the same degree of accuracy, I would use 0.030995 divided by 1728 (rounded to 0.01 cubic inches) which would yield 53.56 cubic inches which is reported to the accuracy as required.
Using less than six decimal places as Ron had suggested would not give accuracy to the nearest 0.01 cubic inches in the above conversion.