Could you explain the most common problems when conducting Rockwell
Here are some of the most common Rockwell hardness testing problems,
along with some tips on what to do if you encounter these types of problems (in
no particular order).
1. Cleanliness of the part
and tester is paramount.
a. Remove and clean the indenter and anvil prior to operation and at shift
b. A small amount of debris can alter the reading by as much as several
2. Non-flat surfaces can
a. Extremely rough or textured surfaces may give inconsistent
readings. Remove any scale, debris, dirt
and oil before testing. Light sanding of both the bottom and top surfaces is necessary before
b. Take into account the curvature of the surface.
c. A correction factor must be added to the hardness reading of small-diameter shapes for Rockwell C, A and D and varies with the apparent hardness
and part diameter. (The correction factor to be added is shown in ASTM E18 Tables 2 and 3.)
3. Surfaces not
perpendicular to the indenter will give false readings.
a. Surfaces should be flat within 2 degrees. Be careful when taking readings on mounted
samples: They must be flat, thick and not flex under load. A microhardness test
may be more appropriate.
4. Readings taken too close to the sample edge will both
damage the indenter and give false readings.
a. Indentations should be no closer than 2½ times the indenter diameter
from the edge. If the metal buckles outward, the indenter is too close to the
edge and the reading is invalid.
Next week we will look at the remaining four problems and tips to
Common Rockwell Hardness Testing Problems
Dan Herring is president of THE HERRING GROUP Inc., which specializes in consulting services (heat treatment and metallurgy) and technical services (industrial education/training and process/equipment assistance). He is also a research associate professor at the Illinois Institute of Technology/Thermal Processing Technology Center. tel: 630-834-3017; e-mail: email@example.com; web: www.heat-treat-doctor.com
Report Abusive Comment