Figure 5-4.--Standard marking system for grinding wheels (except diamond).
the wheel. Since different grinding jobs require different
up steel castings. Silicon carbide (designated by the
abrasives, you should learn this identification system
letter C in station 1) is harder but not as tough as
so you can identify the grinding wheel you need for a
aluminum oxide. It's used mostly to grind nonferrous
given job. The six stations are (1) type of abrasive,
metals and carbide tools. The abrasive in a grinding
(2) grain size, (3) bond grade, (4) structure, (5) type of
wheel makes up about 40 percent of the wheel.
bond, and (6) the manufacturer's record symbol.
2. Grain size: Grain sizes range from 10 to 500.
Figure 5-4 shows the six stations that identify nearly
The size is determined by the size of mesh of a sieve
all abrasives except diamond, which we'll explain in
through which the grains can pass. Grain size is rated
later paragraphs. Follow the stations in the figure
as follows: coarse: 10, 12, 14, 16, 18, 20, 24;
from left to right as you read an explanation of each
medium: 30, 36, 46, 54, 60; fine: 70, 80, 90, 100, 120,
station in the following paragraphs:
150, 180; and very fine: 220, 240, 280, 320, 400, 500,
1. Type of abrasive: There are two types of
600. Fine grain wheels are preferred to grind hard
abrasives: natural and manufactured. Natural
materials-they have more cutting edges and will cut
abrasives, such as emery, corundum, and diamond,
faster than coarse grain wheels. Coarse grain wheels
are used only in honing stones and in special types of
are generally preferred to remove metal quickly from
grinding wheels. The common manufactured
abrasives are aluminum oxide and silicon carbide.
They have superior qualities and are more economical
3. Bond grade (hardness): The bond grade runs
than natural abrasives. Aluminum oxide (designated
from A to Z, (soft to hard). It's a measure of the
by the letter A in station 1) is used to grind steel and
bond's ability to hold the abrasive grains in the wheel.
steel alloys and for heavy duty work such as to clean
A grade of soft or hard does not mean that the bond or