Seal face hardness testing 12.8
The ideal seal face combination is a good grade of carbon/graphite running against a corrosion resistance hard face materials. In another paper I covered the different grades of carbon/graphite, but just what do we mean when we say, “hard face”?
There are a lot of them available that include:
- Several grades of ceramic along with different grades of ni-resist and stellite
- Both tungsten and nickel base tungsten carbide
- Alpha sintered and reaction bonded silicone carbide
In the following paragraphs we’ll be looking at the common methods seal people use to measure the hardness of a seal face and then we will be looking at a chart to learn how to convert from one method to another.
The Moh’s scale is the next one, but I have no illustration to show you. This method compares scratch hardness with ten minerals used as standards. Unlike the other scales mentioned above; in this method the steps are not equal. The difference between #9 and #10 is about as great as the difference between #1 and #9.
The oldest method of testing hardness was to use a hard file on the test piece and see how difficult it is to remove material. One look at the following comparisons and you can learn why this method is seldom used any more, but if you do not have any test equipment it is better than nothing.
Above a number of 350 the standard machining operations of turning, boring, drilling, and tapping become uneconomical. You can compare a Brinell reading to the following file readings :
- 100 Metal removed easily by the file.
- 200 Slightly more pressure needed to remove metal.
- 300 Metal shows resistance to the file.
- 400 Takes more pressure on the file.
- 500 File removes almost no metal.
- 600 Metal cannot be filed.
Mechanical seal faces should read at least 60 on the Rockwell “C” scale. You can consult the following chart to convert this reading to other scales.