William Boroski and Stephen Bastian
A portable EQUOTIP hardness tester was used for these measurements.
The measured Brinell hardness of the wind baffle drive surface was 178,
which corresponds to 1040 in a normalized state. The measured Brinell
hardness of the drive roller surface that contacts the drive surface was
211, which indicates that the roller drive surfaces may have been slightly
work-hardened. The Brinell hardness of the drive roller side faces and
flange is 202 and 192, respectively. Since the Brinell hardness
of 1040 hot-rolled steel in its as-rolled state is 201, it appears that
the roller drive surface is the only part of the roller that may have been
The accuracy of the measurement system is determined by how the measured values are used. When using the hardness values obtained directly from the EQUOTIP readout, the average measurement deviation is 0.5% (+/- 4 units throughout the entire measurement range). However, there is a loss of accuracy when converting the hardness value into static indentation hardness numbers, such as Brinell or Rockwell. The mean conversion deviation ranges from +/-3% to +/15%, depending on the measuring range and the static method used. One reason for the large variation is that there is no clear physical relationship between the various measurement methods. A second reason is that the comparison of hardness values from different scales includes the measuring deviations of each of the methods. For the measurements described in this report, the conversion deviation when converting from the raw hardness values into the Brinell hardness equivalent is +/-7%.
The calibration of the hardness tester was checked and verified before
and after these measurements were made. Calibration was checked against
a standard supplied with the unit. The surface hardness of
the standard was 760 +/- 6. The hardness measured by the tester was
760 for both calibration checks.
The average Brinell hardness for the drive surface and guide roller
surface is given in the following table.
|Guide Roller Surface||
From Machinery's Handbook, Vol. 24, 1040 hot-rolled steel in the normalized
state has a Brinell hardness of 170, and in the as-rolled state has a Brinell
hardness of 201 . Within the accuracy of these measurements, it appears
that the metal ring that provides the drive and guide roller surfaces has
been normalized but not hardened. The Machinery's Handbook defines
normalizing as the process in which an iron-base alloy is heated to a temperature
above the transformation range and subsequently cooled in still air at
room temperature. Carbon-steels are normalized to put the material
into a uniform, unstressed condition such that the material will respond
to further heat treatments. Normalizing is also used to transform
steel into a sufficiently soft state for machining. For low-carbon
steels, normalizing alone is sufficient. For medium and higher carbon
steels, the normalizing process is typically preceeded by an annealing
process. This two-part process is often called double-annealing.
As 1040 is a medium-carbon steel, it is possible that the drive surface
material was double-annealed. However, that fact cannot be ascertained
from these measurements. What is clear is that neither the drive
surface nor the guide surface have been hardened.
The average Brinell hardness for the various roller surfaces is given
in the following table.
|Drive surface||211 +/ 4|
|Front/back face surfaces||
The drive rollers are made from 1045 hot-rolled steel. Brinell hardness numbers were not readily available for 1045, so values for 1040 were used for comparison purposes. The Brinell hardness for 1040 in the as-rolled condition is 201, therefore it appears that the rollers as a whole have not been heat-treated. It appears that the flange is the softest part of the roller, and that the drive surface has either been locally treated or has work-hardened due to contact with the drive surface.
2. Machinery's Handbook, 24th Edition, Industrial Press,
Inc., New York (1992).
Last modified 02/23/99