MEULE ABRASIVE

CBN GRINDING WHEEL

Abrégé anglais

ABSTRACT
A CBN grinding wheel is bonded by a resinous matrix
including active fillers selected from the group consisting
of (1) iron sulfide and an alkali sulfate, (2) potassium
aluminum fluoride, and (3) cryolite.

Revendications

-5-
WHAT IS CLAIMED IS:
1. A resin bonded grinding wheel containing cubic
boron nitride abrasive grits characterized in that the
resinous bonding matrix contains a filler selected from the
group consisting of (1) iron sulfide and an alkali sulfate in
a volume ratio of 1/4 to 4/1, (2) cryolite, (3) potassium
aluminum fluoride, and mixtures thereof, in the amount of 8
to 50% by volume of the abrasive, bond, and filler
combination.
2. A resin bonded grinding wheel containing cubic
boron nitride abrasive grits characterized in that the
resinous bonding matrix contains, as filler, finely divided
iron sulfide and alkali sulfate in a volume ratio of 1/4 to
4/1 in the amount of 8 to 50% by volume of the abrasive,
bond, and filler combination.

Description

33
C~N _~I nING WiiF.F.L Docket RD-1637
FIELD OF THE INVENTION
This invention relates to orqanic bonded grinding
wheels containing cubic boron nitride abrasive and active
fillers.
5 BACKGROUND OF THE INVENTION:
~ o-calle~ active fillers such as metal sulfide and
haloqen salts such as cryolite which have reactivity toward
the material being around have been employed in conventional
aluminum oxide abrasive containing orqanic bonded grinding
10 wheels for manv years.
Such qrindinq aid ~illers have not been used in
qrindinq wheels containing diamond qrits as the abrasive,
because the i~portant use of diamond wheels is in qrinding
carbides, qlass and ceramics, particularly ~for resin bonded
15 wheels) in qrinding hard carbides. Grinding aids suitable
for qrindinq steel, for example, are of no apparent advantage
in carbide qrindinq.
The development of diamond grindinq wheels began in
the 1930's, and, until the late 1960's, diamond was the sole
20 "super" abrasive, much harder than the conventional aluminum
oxide and silicon carbide abrasives. Concurrent with the
development of synthetic diamond bv the hiqh pressure-high
tem~erature method tau~ht in General Electric patents issued
in the 1960's, the hiqh density cubic form of boron nitride
25 (CBN) having a hardness similar to diamond was discovered, by
a~piyin~ hiqh pressur~ to hexagonal ~oron ni~ride at hiqh
temperature and in the presence of a catalyst, as disclosed
in U.S. Patent 2,947,617.
,~

--2--
~ hile not superior to diamond in the grinding of
carbides (e.q. cementecl tunqsten carbide) cubic boron nitride
(CsN) has been Eound to be superior to diamond when ferrous
metals, particularly tool steels are beinq ground. Thus C~N
5 wheels can be superior to diamond wheels in the grinding of
tools which combine hard carbides and steels.
Althouqh C~N wheels have been made and tested by
others, containinq specific qrinding aids, so far as is
known, no commercial use has been made of grindin~ aid
10 fillers in resin bonded C~N wheels.
British Patent 834,351, published in 1960 teaches
the use of metal sulfides together with alkali-metal salts
such as sulfates as fillers in conventional abrasive wheels
for qrindinq alloy steels. While the pat~nt refers to
15 abrasives generally, and lists diamond, such fillers, so far
as is known, have never been commercially employed in diamond
wheels or in CBN wheels.
Gerrnan Patent P2230701, to Winter h Sohn discloses
employinq zinc sulfide with cryolite as a ~rinding aid in
20 stick form to be applied to the workpiece. No suq~estion of
incorporatinq the qrindinq aids in the wheel bond appears in
the patent.
_MMARY OF THE INVENTION
The present invention is the inclusion in CBN
25 orqanic resin bonded wheels of an iron sulfide filler
together with sodium or potassium sulfate. Somewhat inferior
to the iron sulfide/alkali sulfate filler are cryolite, or
potassium aluminum tetrafluoride, or hexafluoride, in the
amount of 8 to 50% bv volume of the qrinding section of the
30 toolO Obviously, combinations of these fillers can be
employed. Such wheels, in dry qrinding of tool steels, or
qrinding of tool steels in combination with cemented
carbides~ show equivalent or better results than the best
prior art wheels usinq hond compositions containing silver
35 and drv film lubricants. Elimination of the need for silver
is a ma~or economic henefit. These wheels also are
advantaqeous in providing qreater freeness of cut and thus
more rapid cut of the workpiece.

()3
--3--
DE'~\ILF.D DE~ CRIP'rION OF THE INVF.NTION
Wheels according to the present invention may be
prepared as followsO
Wheel Pre~aration
An intimate mixture of fillers and the csN abrasive
is prepared. Fillers are those active materials included as
the suh~ect of the application as well as other inert
substances. The mixture is then coated with a liquid pickup
aqent. A finely divided powdered resin is then mixed with
10 the liquid coated abrasive/filler mixture so as to coat the
surfaces of the abrasive and filler particles evenly with
resin. In the usual practice, phenolic novolak resin with
hexamethylene tetramine crosslinking aqent is chosen as the
resin and furfural as the liquid pickup agent.
A typical formulation which illustrates the
invention is:
InqredientPercent bv Volume
CBN 19
K2SO4 20
FeS2 11
.SiC 8
Furfural 2
Resin 38
CaO 2
This mixture is then distributed evenly in a groove
molded or machined around the circumference of a core. The
core is composed of finely divided aluminum powder and resin
which has previously been compressed either cold or hot. The
wheel, which now consists of the core and circumferentially
30 located abrasive section, is hot pressed to melt and fuse the
resin bondinq both the abrasive section and the core.
Pressures to 50 tsi and temperatures from 140 to 200c are
applied to the wheel during a period of one-~uarter to one
hour to form the wheei Subsequent to this operation the
35 wheel may be heated to a temDerature higher than the molding
temperature at at~ospheric pressure to improve grinding
characteristics. Finally, the ~heel is machined to prepare a
product to standard and fixed dimensional specifications.

~8~
f)ther thermosetti.llg resins or e~uival.ents can be
e,lPloyed. The wheels may be straight cyli~drical wheels
(lAl shape), or may be cup wheels as in the example above, or
mav be any other conventional shape.
S The active filler should be present in a total
amount of ~rom 8% to 50% by volume of the qrinding section of
the wheel. The ratio of FeS2 to alkali sulfate may be from
4/1 to 1/4 by volume, but is preferably from 40/60 to ~0/40
by volume. Sodium sulfate may replace all or part of the
10 ~254'