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June 9, 1964
D. A. CALDERWOOD ETAL
3,135,999
MOLDING APPARATUS FOR GRINDING WHEELS
Filed Nov. 25. 1960
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INVENTORS
DON
BY
JOH
D A. CALDERWOOD
. SZLACHETKA
AQV?/Qk
ATTORNEY
United States Patent O
3,135,999
1
,ce
Patented June 9, 1964
1
2
3,135,999
A further object of this invention is to provide the de
scribed mold assembly which can be directly applied to
MOLDING APPARATUS FOR GRINDING WHEELS
Donald A. Calderwood, Pittsburgh, and John A.
Szlachetlra, Cheswick, Pa., assignors to Armstrong
& White, Cheswick, Pa., a corporation of
Pennsylvania
molding apparatus of the conventional type currently
found in industry.
A still further object of this invention is to provide a
mold assembly which can be adapted to secure hub struc
tures regardless of the normal dimensional tolerances en
countered in the threaded hubs.
Another object of this invention is to provide a hub
This invention relates to improved molding apparatus 10 centering structure which may be utilized in the assembly
Filed Nov. 23, 1960, Ser. No. 71,246
7 Claims. (Cl. 18-36)
for the manufacture of abrasive grinding wheels and the
of metal hub structures in preformed abrasive grinding
like.
Wheels, particularly vitreous wheels.
More speci?cally, the present invention is related to a
These and other objects and advantages of the present
pin-and-sleeve assembly for securing a threaded hub
invention will become apparent from the following de
structure within molding apparatus to assure the produc 15 tailed description in reference to the accompanying draw
tion of abrasive grinding wheels having such threaded
ings in which:
hubs concentrically positioned and having their geometric
FIGURE 1 is a cross-section illustration of a conven
axis maintained normal to the rotating plane of such
tional two-piece molding apparatus for forming abrasive
abrasive grinding wheels.
grinding wheels;
In the usual manufacture of abrasive grinding wheels, 20 FIGURE 2 is a cross-section illustration of a two-piece
metal mold structures are provided with a bottom ele
ment and a correlative upper element which are brought
molding apparatus for forming abrasive wheels according
to the present invention;
together to de?ne a molding cavity having the con?gura
FIGURE 3 is a perspective illustration of a hub-holding
tion of the desired abrasive grinding wheel. Suitable
sleeve according to a preferred embodiment of the present
pulverulent abrasive wheel forming compositions are 25 invention; and
poured into the cavity to form the grinding wheel. Such
FIGURE 4 is a perspective illustration of a sleeve
compositions might include, for example, abrasive solid
engaging pin according to a preferred embodiment of the
present invention along with a pin holder.
particles (sand, carborundum, diamond chips and similar
Referring to FIGURE 1, there is illustrated a conven
hard materials) combined with suitable thermosetting
resinous plastic compositions such as phenolic resins.
tional two-piece molding apparatus as employed in the
Such compositions might be of vitreous character. The
industry at the present time. The apparatus includes a
exact composition forms no part of the present invention,
it being understood that the present invention is con
cerned with the molding apparatus which can be em
ployed with any of these compositions.
Upon the application of heat, or other suitable compo
sition-solidifying conditions, the pulverulent composition
is solidi?ed within the cavity into a solid structure which
bottom element 10 and an upper element 11 which are
correlated so that, when brought together in mating rela
tion, a mold cavity 12 is formed which has the con?gura
35 tion desired in the resultant abrasive grinding wheel. Both
the bottom element 10 and the upper element
formed from metals, usually steel.
Concentrically within the bottom‘ mold element 10 is
is thereafter removed from the molding apparatus and 40 a ?rst bore 13 which receives a pin 14 having an outer
diameter in its lower portion only slightly less than the
used as an abrasive grinding Wheel.
'
inner diameter of the bore 13. The diiference in diam
It is customary in the grinding wheel industry to supply
eters may be from about 0.001 to about 0.005 inch. The
such abrasive grinding wheels with metal inserts having
upper portion of the pin 14 has a greater diameter which
a threaded hub portion whereby the wheels may be ai?xed
to rotatable shafts for use. The threaded hubs permit 45 is slightly less than the minimum diameter of the threaded
hubs normally encountered in production. The larger
rapid and simple installation and replacement of such
dia'meter upper portion of the pin 14- terminates in a
grinding wheels. Usually the hub portion has a plurality
shoulder 15 at the center of the pin 14 where the smaller
of radially extended ears which are disposed within the
diameter lower portion commences. This shoulder 15
mold cavity and are engulfed and surrounded by the
molding wheel forming composition during the mold ?ll 50 rests upon the upper surface 16 of the bottom mold ele
ment 1%).
ing operation. ;The completed solidi?ed Wheel, thus, has
The internally threaded hub structure is identi?ed by
the hub portion securely retained at its center.
the numeral 17. The structure comprises usually a flat
However, the industry has found di?iculties (1) in
disk 18 having radially extended bent ears 19 which are
maintaining the hub portions at the exact center of the
mold cavity and also has found difficulties (2) in main 55 extended within the mold cavity 12 and which are en
gulfed and surrounded by the abrasive wheel forming
taining the hub structure with the axis of the threaded
composition which is subsequently poured into the mold
hub normal to the plane of the abrasive wheel. Where
cavity 12.
the hub portion is not concentric, the resulting wheel,
Secured at the center of the ?at disk 18 is a tubular hub
when mounted upon a shaft, will rotate eccentrically and
will be of little value until the eccentricity has been elim 60 v20 usually having a roughened outer surface and a
threaded bore 21. In the manufacture of the threaded
inated through Wear. Where the axis of the hub structure
bore 21, there is an appreciable variation in the inner di
is not normal to the plane of the abrasive grinding wheel,
ameter which is observed in most threading operations.
the resulting wheel, when mounted upon a shaft, will
The actual inner diameter of the threaded bore 21 may
wobble and will never be of value. Such abrasive grind
ing wheels must be discarded.
65 vary 0.010 inch or more from the desired dimension.
The principal object of the present invention is to pro
vide a mold assembly for the manufacture of abrasive
The pin 14 has its upper portion of such diameter that
the minimum diameter of the threaded bore 21 may be
readilyaccommodated. Thus, when hub structures 17
grinding wheels having means for securing the hub por
having greater than the minimum diameter bore are pro
tion of such wheels in a concentric location with respect
to the mold cavity and further for securing the hub por 70 vided~and there is substantial variation in the inner
diameter of the threaded bores 21 from one hub struc
tion so that the axis of the threaded hub will be main
ture to the next one—there is a resulting loose engage
tained normal to the plane of the resulting wheel.
9
a
4
.
ment between the threaded bore 21 and the pin 14. The
looseness permits the hub structure to move into positions
where it is not concentric with the mold cavity 12. The
the tight ?t. The bottom terminus of the sleeve 30 is
tapered to facilitate introduction of the lower portion 32
into the bore 13.
resulting abrasive grinding wheels possess eccentricity.
The upper portion 31 of the sleeve 30 has a normal
diameter which corresponds to the normal diameter of
threaded hubs encountered in production. Thus the hub
17 can be easily ?tted over the upper portion 31 of the
Normally the hub structure 17 rests upon the upper
surface 16 of the bottom mold element 10, and, when
this is so, the geometric axis of the threaded bore 21 is
normal to the rotation plane of the resulting grinding
wheel. However, through continued use, some wear re
sults in the lower portion of the pin 14 and the bore 13
so that the pin 14 may not necessarily ?t tightly and ver
tically. In such cases, it is frequently found that the
geometric axis of the threaded bore 21 is not normal with
the rotation plane of the resulting grinding wheel. Wob
bling wheels are produced in such instances which are
useless.
Further continuing the description of the present mold
ing operations, it will be observed that the upper mold
element 11 has a bore 22 in which a metal cylinder 23 is
slidable. The metal cylinder 23 has a diameter corre
sponding to the outer diameter of the hub 20. The
sleeve 30 within the mold cavity 12. The upper edge of
the sleeve 30 is tapered to facilitate the slippage of the
hub 17 over the upper portion 32.
Thus hubs 17 of minimum diameter in their threaded
bores 21 are securely maintained concentrically Within
the mold cavity 12 by virtue of contraction of the sleeve
30. Hubs 17 having larger than normal bore diameters
are initially free to move somewhat within the mold cav
ity 12.
To accommodate these larger hubs 17, a split pin 37
is provided, more clearly illustrated in FIGURE 4. It
will be observed that the pin 37 had an unslotted portion
38 and a slotted portion 39. The unslotted portion 38 is
press-?tted into a recess 24 within the pin holder 23
function of the metal cylinder 23 is to cover the exposed
end portion of the hub 29 to prevent entry of any abra
sive wheel forming composition into the threaded bore
21. The upper mold element 11 is slipped downwardly
over the metal cylinder 23 when the mold is assembled
(corresponding to the metal cylinder 23 of FIGURE 1).
The unslotted portion 39 extends outwardly from the
pin holder 23 and has a plurality of radial slots 40. A
peripheral groove 41 is provided in the inboard terminus
of the slotted portion 39 to provide suitable resiliency
for use. Occasionally a recess 24 is provided in the metal
is provided, a bore 25 may be provided to facilitate re
for the elements of the slotted portion and further to per
mit the elements of the slotted portion 39 to contract gen
erally radially rather than conically. An axial bore 43
moval of the pin 14 from the metal cylinder 23 when
replacement of the pin 14 of the metal cylinder 23 is
is provided through the slotted portion 39 of the pin 37
to provide additional resiliency of the pin 37.
cylinder 23 to receive the pin 14. When the recess 24
The slotted portion 39 of the pin 37 has a normal
outer diameter slightly greater than the normal inner
diameter of the bore of the sleeve 30. The outer edges
the Wheel hub structure is assured; maintenance of the
of the slotted end portion 39 are tapered to facilitate
geometric axis of the threaded bore of the hub structure
introduction of the pin 37 into the bore of the sleeve
normal to the rotating plane of the abrasive grinding wheel
39. The slotted portion 39 of the pin 37 resiliently urges
is assured.
the upper portion 31 of the sleeve 30 radially outwardly
This is accomplished by providing a radially slotted
until it is in peripheral engagement with the threaded
sleeve element and a mating radially slotted pin element
to replace the usual pin member 14 described in relation 40 bore 21 of the hub 17. Thus the slotted portion 31
of the sleeve 30 expands to engage those threaded bores
to FIGURE 1. The slotted sleeve has a normal outer
21 having larger than normal diameters under the re
diameter corresponding to the normal inner diameter en
silient urging of the slotted portion 39 of the pin 37.
countered in threaded hubs. The slotted pin has a nor
Where threaded bores 21 are of the minimum diameter,
mal outer diameter slightly greater than the normal inner
obviously the upper portion 31 of the sleeve 30 cannot
diameter of the slotted sleeve. Both the slotted sleeve
expand outwardly. In these situations, the slotted por
and the slotted pin are expansible and contractible in
tion 39 of the pin 37 readily resiliently contracts to main
their diameters whereby variations in the diameters of
tain a tight engagement of the meshing elements.
threaded hubs from one to another can be accommodated.
The pin holder 23 has a ?at end surface 42 which
Speci?cally, referring to FIGURE 2, the bottom mold
required.
According to the present invention, concentricity of
element 10 and the upper mold element 11 are un 50 corresponds to the ?at end surface of the hub 17 to
changed from their conventional appearance. Corre
sponding numerals are employed in FIGURE 2 to iden
prevent entry of abrasive Wheel forming compositions
into the threaded bore 21 of the hub 17 during molding
tify corresponding elements already described in reference
operations.
to FIGURE 1.
When the abrasive grinding wheel has solidi?ed, the
mold structure is dismantled by separating the upper
element 11 from the bottom element 10. The pin holder
23 remains with the resulting grinding wheel and is merely
lifted from the hub 20 after the upper mold element 11
has been removed. The pin 30, press-?tted in the pin
holder 23, is removed by lifting the pin holder 23 away
from the hub 20. The abrasive wheel which engulfs and
surrounds the hub structure 17 is thereafter removed from
the bottom mold element 10 along with the sleeve 30.
The sleeve 30 is slipped out from the threaded bore 21
and is available for re-use. Mold release pins (not
shown) frequently are provided in the bottom mold
element 10 to facilitate removal of the product grinding
wheel from the bottom mold element 10. Mold release
A sleeve 30, engaged in the bore 13 of the bottom mold
element 10, is more clearly illustrated in FIGURE 3
wherein the upper portion 31 has a greater normal outer
diameter than the lower portion 32. At the central por
tion of the sleeve 30, the upper portion 31 and the lower
portion 32 are separated by a shoulder 33 which normally 60
rests upon the upper surface 16 of the bottom mold ele
ment 10. The inner bore 34 of the sleeve 30 has a con
stant normal diameter. It will be observed that the
sleeve 30 has a plurality of longitudinal slots 35 extend
ing through the lower portion 32 into the upper portion
31. Further longitudinal slots 36 are provided through
the upper portion 31 into the lower portion 32. The
longitudinal slots 35, 36 alternate over the periphery of
pins, for example, might slide vertically upwardly through
the sleeve 30 which, in effect, becomes a slotted collet
70 various bores in the bottom mold element 10 such as the
sleeve.
bore 13.
By virtue of the slotted collet sleeve construction, the
Frequently the bottom element 10 of the mold is fab
lower portion 32 of the sleeve 30 can be contracted in its
ricated in two pieces which can be separated after forma
diameter to provide a tight fit in the bore 13. The nor
tion of the abrasive grinding wheel to facilitate its re
mal outer diameter of the lower portion 32 is slightly
moval from the mold elements.
greater than the inner diameter of the bore 13 to assure
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3,135,999
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said pin having its'slotted portion engaged within the
said sleeve, whereby said sleeve is resiliently engaged
The present structure also may be utilized as hub
‘centering apparatus for concentrically securing metal hubs
in preformed grinding wheels. Vitreous grinding wheels,
over its outer surface with the hub bore and engaged
over its inner surface with the said pin to hold said
hub rigidly in place upon said bottom element.
3. The holding structure of claim 2 wherein the said
pin has an external peripheral groove at its central
portion adjacent to the inboard terminus of its slotted
for example, are fabricated in the desired shapes and
baked at high temperatures in order to fuse the vitreous
components. The temperatures which are employed
would adversely affect any preliminarily installed metal
hub element. Hence, the formed vitreous grinding wheels
portion.
are ?tted with metal hubs by means of suitable adhesives.
The problems of mass concentricity and geometric axis 10
4. The holding structure of claim 2 wherein the said
pin has an axial bore extending through its slotted portion.
normality (with the plane of rotation) of the hub ele
5. The holding structure of claim 2 wherein the upper
edge of said sleeve is tapered and the outer edges of the
slotted portion of said pin are tapered to facilitate in
By means of the present invention, the preformed
abrasive wheel may be centered peripherally in a base 15 troduction of said slotted portion into the bore of said
sleeve.
(such as the bottom mold element 10) and the necessary
6. Centering apparatus comprising a bottom element
metal hub may be accurately centered and positioned by
means of the pin 37 and sleeve 30 assembly until applied
and an upper element, each having a central bore;
a centrally bored element which is centered between
adhesives have set.
20
said bottom element and said upper element;
We claim:
a sleeve having longitudinal radial slots, said sleeve
1. A centering structure for a hub of an abrasive wheel
being partly engaged in the central bore of said base
including:
a bottom element peripherally supporting and de?ning
element;
a pin having radial slots at one end and having its
an abrasive wheel composition;
other end engaged in the central bore of said upper
a correlative upper element cooperating with said bot
element;
tom element;
said centrally bored element being retained between
a ?rst bore in the center of said bottom element and a
said bottom element and said upper element with
second bore in the center of said upper element;
the said sleeve being inserted into the central bore
a sleeve having longitudinal radial slots and having a
thereof so that the outer ‘surface of the said sleeve
?rst normal diameter extending from a ?rst end
is in surface engagement with the said central bore
thereof to a central portion corresponding with the
inner diameter of said ?rst bore and having a second
of said centrally bored element;
the said pin being inserted into the said sleeve, whereby
and larger constant normal diameter extending from
the said centrally bored element is restricted between
said central portion to the other end thereof, the
said central portion comprising a peripheral shoulder 35
the said upper element and the said bottom element
against vertical movement and is restricted by means
on said sleeve;
'
a pin radially slotted at one end and having a normal
of said sleeve against horizontal movement.
7. A hub-centering structure for abrasive wheels in
outer diameter slightly greater than the normal inner
cluding:
diameter of said sleeve;
O
4
a pin holder comprising a cylinder having a bore in
a bottom element peripherally supporting and de?ning
which the unslotted portion of said pin is engaged;
an abrasive wheel .composition;
ment is substantially the same as that described in the
foregoing discussion of wheel molding operations.
said pin holder being engageable within said second
a correlative upper element cooperating with said bot
tom element;
bore of said upper element and having a bottom
surface engageable with the said hub over its normally
exposed surface;
said pin having its slotted portion engaged within the
a ?rst bore in the center of said bottom element and a
45
second bore in the center of said upper element;
a sleeve having a ?rst normal diameter extending from
said sleeve, whereby said sleeve is resiliently en
a ?rst end thereof to a central portion thereof cor
gaged over its outer surface with the hub bore and
engaged over its inner surface with the said pin to
responding with the diameter of said ?rst bore and
having a second and larger normal diameter extend
ing from said central portion to the other end there
hold said hub rigidly in place upon said bottom ele 50
ment.
2. In a mold for an abrasive wheel having an insert
hub structure, said mold having a bottom element and a
of, the said central portion comprising a peripheral
shoulder on said sleeve;
a plurality of spaced ?rst radial slots in said sleeve
correlative upper element, an improved holding structure
for said insert hub comprising
55
a ?rst bore in the center of said bottom element and a
second bore in the center of said upper element,
a sleeve having longitudinal radial slots and having a
?rst constant normal outer diameter extending from
tudinally through said central portion, the said ?rst ra
dial slots alternating with the said second radial slots
a ?rst end thereof to a central portion thereof cor— 60
responding with the inner diameter of said ?rst bore
and having a second and larger constant normal di
ameter extending from said central portion to the
other end thereof, the said central portion compris
65
ing a peripheral shoulder on said sleeve,
a pin radially slotted at one end and having a normal
outer diameter slightly greater than the normal inner
diameter of said sleeve,
a pin holder comprising a cylinder having a bore in
which the unslotted portion of said pin is engaged,
said pin holder being engageable within said second
bore of said upper element and having a bottom
in the said central portion;
_
a pin radially slotted at one end and having a normal
outer diameter slightly greater than the normal di
ameter of the bore of said sleeve;
a pin holder comprising a cylinder having a bore in
i which the unslotted portion of the said pin is en~
eased;
said pin holder being engageable within said second bore
of said upper element and having a bottom surface
engageable with the said hub over its normally ex
posed surface;
said pin having its slotted portion engaged within the
said sleeve, whereby said sleeve is resiliently en
surface engageable with the said hub over its nor
mally exposed surface,
extending from said ?rst end longitudinally through
said central portion, a plurality of spaced second
radial slots extending from said second end longi
75
gaged over its outer surface with the hub bore and
engaged over its inner surface with the said pin to
3,135,999
8
hold the said hub rigid'lzy in place upon said bnttom
element.
References Cited in the ?le of this patent
UNITED STATES PATENTS
1,265,793
Larsen ______________ __ May 14, 1918
1,501,026 '
2,135,380
Guay ________________ __ July 8, 1924
Benge ________________ -_ Nov. 1, 1938
546,977
Germany ____________ __ Mar. 18, 1932
Great Britain ________ .._ Mar. 16, 1933
FOREIGN PATENTS
5
389,253

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