Note: Descriptions are shown in the official language in which they were submitted.
~1663~L
B~CK~OUND OF THE INVENTION
This inYention relHtes to a rotat~hle abrading
deyice, and more particularly, to a ~echanical dev~ce for
- propelling abrasive materials at abrading velocities against
a surface to be treated. Such devices are commonly known as
centrifugal blasting machines or abrasive throwing wheels.
This invention also relates to an assem~ly comprised of a
blade block, a blade and a locking means for locking the
blade in position on the blade ~lock.
Centrifugal blasting machines comprising rotors
or wheels having a plurality of blades installed thereon have
been known in the art for many years. The blades propel an
abrasive material against a work surface. Thus, they are
sometimes re~erred to as throwing blades. Due to the action
of the abrasive material on the throwing blades, the blades
exhibit considerable wear over a period of time. Attempts
have been made to fabricate the blades from abrasion-resistant
alloys. In other cases, special blade configurations have
been employed to minimize the effects of the abrasive material
on the blades.
Notwithstanding these attempts to minimize wear
and extend the life of the throwing blades, periodic blade
removal and replace~ent is necessary. This results in a
loss of valuable operating time. Furthermore, while the
blades must be removable, they must also be held so securely
that they will resist the tremendous centrifugal forces
exerted on them when the wheel is operating.
Several methods have been proposed for securing th~
blades in a removable manner to the throwing wheel. One
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method invol~es securing the ~lades to the front side o~ a
wheel disk~ usuall~ ~y means o~ a b-olt or b~ ~eans of radial
grooves in the wheel, frequently of a dove-tail shape.
Another method employs two wheel disks that are maintained
- in spaced-apart relation. Longitudinal narrow edges o~ the
throwing blades are generally inserted into radial grooves
arranged in opposing surfaces of the two disks. Auxiliary
means, such as bolts, pivotal locking means, eccentrics,
set screws, etc. can be employed to secure the blades against
radial displacement. Examples of these devices can be found
in United States Patent 2,819,562, United States Patent
3,352,064 and United States Patent 3,65~,736. Blade replace-
ment is not always easy because the blades "freeze" or
become jammed in the grooves.
Another arrangement is shown in United States
Patent 3,894,360. In this case, the blades are mounted on
brackets having an angular cross-section, and the brackets,
in turn, are mounted on the throwing wheel. The rear of each
blade is provided with a cast-in insert stud, which is
adapted for insertion through an opening in the angular
bracket. The stud is provided with a slot adapted to receive
a clip, which holds the blade in position on the angular
bracket~ The only securing means in this arrangement is
comprised of the stud and the spring clip. Should either
the stud or spring clip fail, such as by the blade wearing
thin around the area of the stud, the blade will fly off the
wheel.
Another arrangement is shown in United States Patent
3,867,791, the entire disclosure of which is relied upon and
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incorporated herein b~ reference. ~n this case, the throwing
~ blade is secured to the wheel by me~ns o~ a blade block~ which
is mounted on the wheel. E~ch blade ~lock has a first groove
. near an inner end of the block and a second groove near an
- outer end. Each blade includes lugs for insertion in the
grooves. There is a centrally disposed impeller that restricts
the movement of the blades, particularly in a radial direction.
This is accomplished by employing an impeller having a
shoulder that contacts the inner end of the blade. While a
degree of commercial success has been achieved with this device,
the rear of the blade must generally be machined in the area
where it contacts the impeller. This adds to the cost of
the biades. Additionally, it has been found to be rather
difficult to cast the b~ade of the type disclosed in the
patent because of its large cross-sectional area.
In short, there exists a need in the art for
improved means for securing the throwing blades to the wheel
of a centrifugal blasting machine. The throwing blades must
be securely mounted on the throwing disk to prevent movement
of the blades, especially in a radial direction. The blades
must be easily removed and replaced without the need for
special tools. Preferably, the blades should not be
susceptible to "freè~ing" or jamming in position, as is
frequently encountered when the blades are installed in
grooves on the disk of the abrasive blasting machine. When
the blade is installed in the centrifugal blasting machine,
it should be possible to replace the blade without removing
the internal parts of the blast machine, such as the impeller
or control cage conventionally found in such machines. The
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means used for locking the blade in position should be suit-
~ able ~or use with any length and widt~ o~ blade. The assembly
should not require ~achining cmd close tolerances character-
,r istic of prior art devi~ces. For commerical reasons, the
- blade and blade ~lock assembly should be adapted to fit
centri~ugal blasting machines now on the market.
SU~ARY OF l~E INVEN~ION
This invention aids in fulfilling these needs in
the art by providing, in combination, a blade block adapted for
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mounting on an abrasive throwing wheel. A blade is supported
by and detachably connected to the blade block. The blade has
an inner end, an outer end, a forward surface and a rear
surface. Cooperating engagement means are provided on the
blade block and the blade for permitting inward movement of
the blade ~hile preventing substantial outward movement thereof
relative to the blade block. An abutment means on the blade
block acts as a bearing or driving surface for the blade. The
abutment surface is located outwardly o the engagement means
and usually contacts the rear surface of the blade. The
abutment means substantially prevents rearward movement of the
blade without obstructing its forward movement. Locking means
substantially prevents inward movement of the blade relative to
the blade block in order to prevent disengagement of the
cooperating engagement means.
In accordance with one broad aspect, the invention
relates to a rotatable centrifugal abrasive throwing device
comprising a driven wheel; a plurality of circumferentially
spaced blade blocks on said wheel; a plurality of radially
extending blades, each of said blades secured to said wheel
by one of said blade blocks, each of said blades having a front
surface, a rear surface, an inner end, and an outer end; a
central opening in said driven wheel; a hollow, vaned, driven
impeller mounted in said central opening rotatable with said
wheel; a stationary control cage around said impeller, said
control cage having an opening therein for the passage of
abrasive material from said impeller onto said blades; and
means for feeding particulate, abrasive material to said
impeller; the improvement wherein each of said blades has a
first opening on said rear surface proximate said inner end and
a second opening on said rear surface opposite and spaced from
said first opening and proximate said outer end, said openings
ii6~
being cavities opposing each other and formed in protrusions
on the rear of said blade; each of said blade blocks has a
rigid projecting means adapted for. insertion in said first
opening on the rear of said blade~ an abutment means adapted
to contact the rear of said blade, and an opening intermediate
said lug mP~ns and said abutment means; and locking means for
insertion in said second opening i.n the rear of said blade and
for insertion in said opening in said blade block, to thereby
lock said blade in position on said wheel.
In accordance with another aspect, t~le invention
provides the combination of a blade block for mounting on an
abrasive throwing wheel with a blade for mounting on said blade
block, said blade having a front surface, a rear surface, an
. .
inner end and an outer end; wherein said blade has a first
opening on said rear surface proximate said inner end and a
second opening on said rear surface spaced from said first
opening and proximate said outer end, said openings being
cavities opposing each other and formed in protrusions on the
rear of said blade; wherein said blade block has rigid lug
means for engagement in said first opening on the rear of
said blade, and said blade block also has abutment means that
functions as a bearing surface for contacting the rear of said
blade and thereby rendering support to said blade when said
blade is in motion on said wheel, and an opening intermediate
said lug means and said abutment means; and deformable,
resilient locking means for inser-tion in said second opening
in the rear of said blade and for insertion in said opening in
said blade block to thereby lock said blade in position on said
blade block and restrict disengagement of said lug from said
first opening.
In accordance with a further aspect, the invention
relates to a rotatable centrifugal abrasive throwing device
:
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comprising a driven wheel; a plurality of circum~erentially
spaced blade blocks on said wheel; a plurality o~ radially
extending blades, each of said blades secured to said wheel by
one of said blade block~, each of said blades having a front
surface, a rear surface, an inner end and an outer end; a
central opening in said driven wheel; a hollow, vaned, driven
impeller mounted in said central opening rotatable with said
wheel; a stationary control cage around said impeller, said
control cage ha~ing an opening therein ~or the passage of
abrasive material from said impeller onto said blades; and
means for-feeding particulate, abrasive material to said
impeller; wherein each of sa d blades has a first openLng on
said rear surface proximate said inner end and a second opening
- on said rear surface spaced from said first opening and
proximate said outer end, said openings being cavities opposing
each other and formed in protrusions on the rear of said blades;
wherein each of said blade blocks has rigid lug means for
engagement in said first opening on the rear of a bladel and
each of said blade blocks also has abutment means that
functions as a bearing surface ~or contacting the rear of a blade
and thereby rendering support to said blade when said blade is
in motion on said wheel, and an opening intermediate said lug
means and said abutment means; and deformable, resilient locking
means for insertion in said second opening in the rear of a blade
and for insertion in said opening in the corresponding blade
block to thereby lock said blade in position on said blade block
and restr.ict disengagement of said lug from said first opening.
In accordance with yet another aspect, the invention
provides the com~)ination of a blade block for mounting on an
abrasive throwing wheel with a blade for mounting on said blade
block, said blade having a front surface, a rear surface, an
inner end and an outer end; wherein said blade has a first :
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opening on said rear surface proximate said inner end and a
second opening on said rear surface spaced from said first
opening and proximate said outer e:nd, said openings being
cavities opposing each other and formed in protrusions on the
rear of said blade; wherein said blade block has rigid lug
means for engagement in said first opening on ~he rear of said
blade, and said blade block also has abutment means that
functions as a bearing surface for contacting the rear of said
blade and thereby rendering suppor-t to said blade when said
blade is in motion on said wheel, and an opening intermediate
said lug means and saîd abutment means; and deformable, resilient
locking means for insertion in said second opening in the rear
of said blade and for insertion in said opening in said blade
block to thereb~ lock said blade in position on said blade
block and restrict disengagement of said lug from said first
opening; whereby said blade is removable from said blade
block by moving said blade longitudinally to compress said
resilient locking means sufficiently for said rigid lug means
to disengage said first opening.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be more fully understood from the
detailed description which follows and by reference to the
accompanying drawings which depict the blade block, throwing
blade and locking means of ~his invention and a centrifugal
blasting machine according to this invention, and detailed views
of its various parts. In the drawings:
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6~
1' FIGURE l is a plan view of a throwing wheel having a
2I blade block and throwing blade installed thereon;
3~ FIGURE 2 is a view of a preferred configuration for a
4'l blade block;
6'l FIGURES 3 and 5 are views of a preferred configuration
61l for a throwing blade; and
F~GURE 4 is a detail view of the central portion of a
8,l centrifugal blasting machine according to this invention.
9l,i DETAILED DESCRIPTION OF THE INVENTION
101i
llil Referring to Figure l, there is depicted a wheel or disk
12!l generally designated as 1. The wheel has a plurality of holes
3 ~! 2 uniformly spaced circumferentially therein. Holes 2 are
14l,l adapted for the insertion of bolts employed to secure blade
blocks, such as blade block 4, to the wheel 1. Preferably, the
6'1 wheel 1 has an opening 3 centrally disposed therein and of a
17jl size sufficient to accommodate a portion of an impeller, which
18l' is described hereinafter. Shown in FIGURE 1 are blade block 4
19 Il' and blade 5 in a typical position on the wheel 1. The blade
20!lblock 4 and blade 5 will be described in greater detail here-
21 !¦ inafter. Also shown in FIGURE 1 is locking means 33, which
22 ¦ locks the blade 5 in position on the blade block 4. Lockin~
231¦ means 33 is a locking spring described in greater detail herein-
24 11 after.
25!l The portion of the device depicted in FIGURE 1 is
26 ~ adapted for rotation in a clockwise direction. The blade 5
7 Ishown in Fi.gure is curved in the direction of rotation.
28 Other blade configurations can be employed. For example, a sub-
29 stantially straight blade or blade having a different curvature
would be satisfactory.
31
321 - 8 -
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Referring to FIGURE 2, there is depi¢ted a bottom
~ vie~ of a pre~erred blade block e~ployed in the device oE this
invention~ The ~lade ~lock generally designated as 4 has two
; drilled and tapped holes 6 and 5' therein. Blade block 4 can
~- be secured to wheel 1 by inserting bolts through holes 2 in
wheel 1 into holes 6 and 6' in blade block 4. slade block
4 has an inner end 8 and an outer end 9. A lug 10 is provided
on the blade block proximate the inner end 8. Blade block 4
is also provided with a surface 7 located outwardly of the
lug 10. Surface 7 acts as an abutment means adapted to
contact the rear of the blade. This abutment means acts as
a bearing surface for the outward portion of the blade as the
blade is rotating with the wheel in a clockwise direction.
Proximate the outer end 9 and intermediate surface 7 and lug
10 there are provided drilled holes 11 and 11', which are
adapted to receive the legs of the locking spring 33 described
hereinafter.
In FIGURE 3 there is depicted a preferred blade
employed in the device of this invention. The blade, generally
designated as 5, comprises an unobstructed, continuous, smooth
surface 12 for throwing abrasive. Surface 12 is the front
surface of the blade. The blade also has a rear surface 13,
an outer end 14 and!an inner end 15. The blade 5 has a first
opening 16 near its inner end 15. Intermediate the outer end
14 and the inner end 15 of blade 5 is a second opening 17 on
the rear surface 13 of the blade. It will be apparent from
FIGURES 3 and 6 that the openings 16 and 17 are cavities
facing each other and ~ormed in protrusions on the rear
surface 13 of the blade. Opening 16 is adapted fox engage-
ment with the rigid lug 10 on blade block 4. The wall 17'
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of cayit~ 17 is adapted to contact t~e abu~lent means 7 on
blade block 4 and to shi~Id the locking ~eans from stray
abrasiye. Cavit~`17 recei-ves
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11~9~631
1l a portion of the locking spring described hereinafter. It will
2I be evident from FIGURE 5 that the wall 17' of cavity 17 is
3! cut away slightly to facilitate insertion of the locking spring
4,, 33 shown in FIGURE 1.
5'1l Referring next to FIGURE 4, there is depicted a detailed
6'1 view of the central portion of a blasting machine of this inven-
71l tion. The wheel 1 has mounted ther~on throwing blades 5 by
8'' means of blade blocks 4. The inner ends 15 o~ the blades 5
9,l define a central opening 18. Inserted in the opening 18 is a
lo, hollow, vaned impeller 19 having a bolt hole 20 therein. Sur-
~1~ rounding the impeller 19 is a control cage 21 having an opening
12, (not shown) therein for the passage of abrasive material from the
13t! impeller 19 onto the blades 5. The device also includes means
14jl for feeding particulate, abrasive material to the impeller. This
15,; feeding means is shown in FIGURE 4 as a feed spout 22. A cage
16,, retainer 23 and cage adaptor 24 secure the control cage 21 within
17i'l the blasting machine in a conventional manner.
18j, The wheel 1 is driven by a motor (not shown) having a
l9j' motor shaft 25. A hub 26 is mounted on shaft 25 by means of a
20!' conventional center tapered-lock bushing (not shown). The hub
21ll 26 includes bolt holes shown as 27. The wheel 1 is installed
22 ', on the hu~ 26, and bolt hole 27 on the hub is aligned with a
23 ~bolt hole 2 on the wheel. Blade blocks 4 are then installed so thc t
24 Iholes 6 and 6' in the blade b,lock are aligned with holes 2 in
25 Ithe wheel 1. The blade blocks 4 can then be bolted to the
261~hub -wheel assembly.
27¦1 Blades 5 are installed on the blade block 4. The
281 impeller 19 is inserted in the central opening 18. Pre~erably,
2~ ¦a wheel 1 having an opening 3 is employed, and the impeller 19
80 ¦projects at least partially into this opening as shown in
31 I
32~ - 10 -
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63~
FIGURE 4. The impeller 19 pre~erabl~ has a slot cast into
- its face, which interfaces with ~ pilot hole mach~ned in the
vertical surface ~38 of the hub 26 to thereb~ center the
impeller 19 within the wheel 1 and the opening 3. A pin can
be inserted ~n the hub pilot. The pin projects from the face
of the hub 2~d aligns w~th the slo~ cast into the impeller 19.
This pin not only aligns the impeller slot with the hub pilot,
but also provides a positive means of driving the impeller
with the hub-wheel assembly. The pilot holes and pin are
not shown in the FIGURES. To complete the assembly, a bolt
8 is inserted through opening 20 in impeller 19 and into a
threaded opening 29 in motor shaft 25. A hub seal and
retainer 30 can be installed in a conventional manner.
The blade and blade block of this invention are
particularly advantageous because they can be used with
commercially available centrifugal blasting machines. For
instance, the device of this invention can be employed with
an impeller of the type described in United States Patent
3,867,791 and as also described in FIGURE 4 herein, wherein
the impeller retards movement of the blades radially inwardly.
As shown in FIGURE 4, a shoulder 31 projects above the
surface _ of wheel 1 onto which the blade block and blade
are mounted. Of course, it will be understood that other
impeller configurations can be employed in the device of this
invention. With new machines, it is preferred that a space
be provided between the rear of the blade and the impeller
because machining of the rear surface of the blade is thereby
made unnecessary.
In FIGURE 1, there is shown a locking spring
generally designated as 33. It is comprised of a deformable,
.
i6~
resilient ~ire 34 bent to foxm two subc,tantiall~ parallel
leg members 35. As s~own, the terminal portion of each
leg ~ember 35
=
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:
1 bent over to form a hook. This arrangement is advantageous
2~lbecause the portion 37 of the hook forming leg 35' can be bent
3 closer to or farther away fro~ the portion 38 to assure that
4l` leg 35 fits snugly into hole 11 in blade block 4. The cor-
5~' responding portions of the parallel leg can be similarly ad-
6'ljusted to assure that the leg fits snugly in hole 11'. Of course,
7i other configurations can be employed. The locking spring 33
8l, is also provided with a projection 36, the center line of which
9l is substantially parallel to center lines through the longitudinal
o¦~ portions of each of the leg members. The projection 36 is
adapted for insertion in cavity 17 on the rear of blade 15.
12 i (See FIGURES 1 and 3).
13~l With reference to FIGURE 1, it will ~e readily apparent
l~lj that the blade block and blade assembly can easily be mounted on
~ wheel 1. Once the blade block 4 has been mounted on wheel 1
~6~1by means of bolts inserted through holes 2 on the wheel and
17i' into holes 6 and 6' in -the blade block (See FIGURE 2), the
8 ¦ locking spring 33 can be installed in blade block 4 by inserting
19 1! the parallel legs into the holes 11 and 11', respectively? of
20¦1blade block 4. The projection 36 on locking spring`33 will then
21¦i extend beyond the adjacent surfaces of the blade hlock 4.
22¦~ Blade S is then located in position so that lug 10 on hlade
23¦!block 4 fits into cavity 16 on the rear of the blade~ The outer
24 ¦1 end 14 of blade 5 can then be rotated counterclockwise until
2~1 abutment 7 contacts the exterior wall 17' of cavity 17. Projec-
26~ tion 36 (see FIGURE 1) can be depressed until it clears the cut-
27 out portion of the wall 17' (see FIGURE 5), and then allowed to
28 snap back into its normal position or until the projection 36
29 fits into t:he cavity 17 on the rear of blade 5. The greater the
80 ¦ distance bel:ween the parallel legs, the eesier it will be to
32 I - 12 -
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3~L
deflect the projection 36 to a suEficient extent to pass
_ throu~h the cut awa~ portion o~ the wa11~17~. When the blade
5 has been ~ssem~led to ~lade block 4 ~ means of the locking
spring 33, the lug 10 substant;ally prevents outward movement
_ of blade 5, but does not prevent inward movement of the blade.
Locking spring -33 will ordinarily be in compression. This
forces blade 5 in an outward direction and assures that the
lug 10 on blade block 4 fits snugly against the surfaces
forming cavity 16 on the rear of the blade. This also aids
in keeping the blade properly oriented on the wheel, e.g.
the blade does not cock out of position. It will be under-
stood, however, that locking spring 33 can be under substan-
tially no stress in its installed position, since the
centrifugal force exerted on blade 5 as wheel 1 rotates
will cause the blade ~o move outwardly to a point where lug
- 10 restricts further outward movement of the blade thereby
holding the blade in place. Thus, even if the locking means
fails during operation of the blast wheel, the blade will
remain in place until the wheel stops rotating. Also, lug
10 and cavity 16 are provided with clearance fit so that they
substantially prevent movement of the blade in an upward
direction ~i.e., away from the wheel~. In any case, the
locking means substjantially prevents inward movement of the
blade with respect to the blade block and holds the blade
in position on the wheel when the wheel is not in motion.
With reference to FIGURE 1, the significance of the
abutment means 7 provided on blade block 4 can also be
appreciated. It is shown located outwardly of the cooperating
engagement means comprised of the lug 10 and cavity 16. The
abutment means serves as a bearing surface or driving surface
- 13
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for the blade since the rear sur~ace o~ the blade con-~acts
the abubment means~7. Thus, the abutment means is located
so as to su~stantiall~ prevent backward mo~ement o the blade
as the wheel rotates at high speed in a clockw-ise direckion.
As shown in FI~URE 1, it is pre~erred that the abutment means
contact the rear of the blade nearer the outer end than the
inner end of the blade in order to minimi~e the cantilevered
portion of the blade beyond the abutment means.
Reference to FIGURE 1 will also make it clear that
the blade 5 can be easily removed from blade block 4 for
replacement or servicing. This can be readily accomplished
by depressing the projection 36 on locking spring 33 until
it clears the cut-out portion provided in the wall 17' (see
FIGURE 5) forming cavity 17. A blow on the tip of the blade
with a hammer sufficient for the lug 10 to become dislodged
from cavity 16 will also permit easy removal of the blade if
radial movement of the blade is not impeded by the impeller
or other part of the blasting machine. In either case a new
blade can be readily installed by repeating the procedure
outlined above.
Typically, the centrifugal blasting machine of
this invention will be driven by a belt connected to a motor
or by direct connection to a motor shaft. The latter method
is preferred and is depicted in FIGURE 4. One can employ
either a loc]ced bearing or a floating motor shaf~. The
latter is preferred and can be employed with the impeller
and control cage arrangement disclosed in United States
Patent 3,867,791. Therein a control cage is disclosed,
which does not wrap around the surface of the impeller as is
conventional in the art. The impeller is generally mounted
- 14 -
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on the motor sh~t, and when the impeller an~ motor shaft
- moye in~a,rd ~nd outward, as is com~on w-~th'a motor having a
floating motor shaft, there'is no interference between the
control cage and the impeller.
Conventional impellers can also be employed in
practicing this invention. Likewise, the'pre~erred impeller
described in United States Patent 3,867,7~1 can be employedO
Theréin, it is described that the impeller comprises a
plurality of fingers that extend in a longitudinal direction.
The outermost ends of the fingers are not connected to each
other and openings are thereby formed between the fingers.
The fingers are immediately adjacent the feed spout when the
centrifugal ~lasting machine is assembled. This makes it
possible to feed relatively large quantities of abrasive
material to the impeller. Of course, it will be understood
that conventional impellers in which the fingers are connected
at their outermost ends can also be employed.
- While this invention has been described in connection
with a cen~rifugal blasting machine comprised of a single wheel
disk, it will be understood that two wheel disks maintained in
spaced apart relation can also be employed.
There are a number of advantages associated with
this invention. Fir~st of all, means are provided for rigidly
securing a throwing blade to a blasting wheel. Movement of
the blades in a radial direction or in a rearward direction
is substantia]ly prevented making for a very safe device.
The blades can be removed relatively easily and quickly
replaced. Special assembly and disassembly tools are not ''
required. While the device of this invention can employ
blades inserted in grooves in the throwing wheel, the use of
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i631
such grooVes is not necessary and will ~enerall~ be avoided
- since blades frequently ~ecome wedged or ~ozen in such
grooves. Lost production time is mlni`mizea ~ecause of the
. ease and speed wl~th which blades can be serviced or replaced.
_ It is not necessary to remove any of the ~nternal parts in the
centrifugal blasting machine to replace the blades according to
- 15a - `
.
l~q~;31
ll this invention. It has been found that the blades can be
2l' fabricated using less metal ~han required to fabricate blades
3ll of the type described in United States Patent 3,867,791. The
4ll locking design of this invention can be adapted to any length
61l or width of blade. Because of the close-interace between the
6 li lug on the blade block and the cavity on the rear of the blade, th
~,¦ locking means is much stronger than with prior art devices.
8 il Since the machine tolerances of the parts employed in this in-
gjl vention are not as critical as in prior art devices, the throw-
10,i ing blades do not have to be ground and polished to fi~ in place.
11 Importantly, the blade and blade block of this invention can be
12l' interchanged with the blade and blade block of the type disclosed
13 li, in United States Patent 3,867,791, making this invention oper-
14llable with centrifugal blasting machines commercially available
15,ltoday.
16 ~, A preferred method of installing blades on the blade
i blocks comprises locating blade S in position so that cavity 17
lgi~has encased wire projection 36. The outer end 14 of blade 5
l9l'is then rotated so that rear surface 13 is laying against block pr _
20¦ jection 10. By applying sufficient force downward on blade 5
2~ at 14 to deflect locking means 33. Cavity 16 of blade 5 can then
22¦lbe rota-ted to a position which will accept lug 10 of block 4
23~lwhen force on blade S is released.
24 ¦ i
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26
27
28
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3111 - 16 -
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