Page 481 - NORTON cutting-off and grinding wheels - industrial

TECHNICALINFORMATION
481
TECHNICAL INFORMATION
UNDERSTANDING THE SPECIFICATION
ABRASIVE GRIT SIZE GRADE STRUCTURE BOND
ALUMINIUM
OXIDE
SILICON
CARBIDE
CERAMIC
ALUMINIUM
OXIDE
COARSE MEDIUM FINE SOFT MEDIUM HARD CLOSED OPEN
A 37C SGB 12 30 80 E I Q 5 10 VS
19A 39C 3SG 16 36 90 F J R 11 VXP
25A 5SG 20 46 100 G K S 12 VXPM
38A 1TGP 24 54 120 H L T VTECH
40A 60 M
57A 70 N
86A O
IPA 60 EH 17 VTX
XH 20
ES5 60 80 J L VX
K
BONDED ABRASIVES
TECHNICAL INFORMATION
WHAT IS A GRINDING WHEEL?
A grinding wheel is a precision tool with thousands
of cutting points. It consists of abrasive grains held
in a matrix of bond and separated by pores. The
abrasive grains are the cutting points while the
purpose of the bond is to hold the individual grains
together. The pores (hollow spaces between
adjacent abrasive grains and the bond) serve to
provide clearance for coolant penetration and metal
chips removed in the grinding process.
When the wheel is rotated at grinding speed and
applied to the workpiece, the abrasive grains cut the
material that is being ground, removing the material
in small chips.
Under the action of the forces imposed during
grinding the abrasive cutting points are worn flat,
resulting in the points becoming blunt. This causes
an increase in friction, and a build up of heat.
The increase in grinding forces causes either the
abrasive to fracture, exposing new cutting edges,
or fractures the bond bridges holding the abrasive
grains. In the latter case fresh abrasive grains are
exposed to cut the workpiece.
In normal vitrified grinding applications the wheel
has to be dressed.
By varying the properties of the abrasive, the type
of bond, the make-up of the wheel, it is possible
to produce grinding wheels with a vast range of
different grinding characteristics.
ABRASIVES
Modern synthetic abrasives allow accurate control
over the physical properties and form of the
abrasive grain. This helps to ensure that grinding
wheels can be manufactured with consistent cutting
properties.
Norton offers a comprehensive selection of
abrasive types to provide a wide range of specific
grinding characteristics. This is necessary
for maximum efficiency in the large variety of
operations demanded by the industry today.
Abrasive Grain Size
The grain or grit size is most important in
determining a wheel’s ability to achieve the required
surface finish and remove stock. The size is
designated by a number which increases as grain
size decreases.
For example 10 grit has a median size of about
2,0mm and 60 grit 0,25mm.
Standard sizes are used in all Norton wheels as
specified in the European Standards laid down by
FEPA.
An ideal grinding abrasive has the ability to stay
sharp with minimum point dulling, and when dulling
begins it fractures revealing new sharp cutting
edges. Abrasive grains used in the manufacture of
bonded abrasives come in three main categories.