Note: Descriptions are shown in the official language in which they were submitted.
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FILLER PLUG FOR COIL INSERT
IN CONCRETE SLAB OR PANEL
Background of the Inyention
This invention relates to the handling of cast
concrete slabs, and more particularly, to novel development
in connection with the use of a coil insert or nut member
for embedding in a cast concrete slab or panel to receive
a bolt used to attach detachable hoisting means for lifting
the slab.
In recent years, a form of building construction
referred to as the tilt-up slab method has come into rather
wide usage. In tilt-up slab building, large concrete slabs
are formed either on the floor of the building or on a
level ground surface. The concrete slabs are then lifted
to a vertical position and interconnected to form the walls
¦ of the building.
The attachments to the slabs which are used for
lifting them must be removable after the slabs have been
iifted into place to facilitate the provision of a smooth
surface on the walls of the building. Generally, the
lifting attachments, such as a lifting ring and bolt, are
installed and removed at the building site, and therefore
they are designed to be easily and rapidly installed and
removed in order to save maximum time.
The insert into which the bolt is threaded is
normally permanently embedded in the slab or panel. When the
lifting attachments are removed from the slab, a hole where
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the insert is located remains in the slab and must be filled
~ to provide a smooth outer surface. The insert s~ould therefore
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be small enough to be easily and readily concealed after the
slab has been installed, and yet should be able to sustain
the forces of lifting heavy slabs or panels. Also, it should
not interfere with rapid attaching and detaching of the lifting
means.
The art has for many years used bolts of conventional
types having relatively course threads, including nut headed
bolts for use with a lifting device in which a hoist can be
attached, and also eye bolts which do not require separate
lifting rings. A more recent development in the art is a
split bolt such as shown in Strong patent 3,456,547 or Grayson
patent 3,922,946 which can be rapidly inserted without threaded
into an insert in a slab and then tightened in place by only
a partial revolution.
Such a split bolt comprises a pair of separate
longitudinal segments such as would be formed if a conventional
bolt is split along its axis and then has a portion removed
along the axis from each segment so that when the two segments
are placed together, they can be inserted axially into an
insert sized for threaded reception of the entire bolt. An
axially movable key member or wedge is used to replace the
', removed portions and thereby to spread the two segments into
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' threaded engagement with the insert, and a partial turn of the
bolt will then tighten it securely in place. The bolt is
' 25 remoYed by withdrawing the key, thereby enabling the two seg-
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ments to be brought together out of threaded engagement with
the i~sert for axial withdrawal without rotation.
~` The inserts commonly used with both solid bolts
and split bolts comprise a coil of a plurality of turns of
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heavy wire or rod stock welded to supporting leg members or
the like for locating the coil in proper position in-a poured
concrete slab or panel, commonly by setting the foot portions
of the leg members on the form on which the slab is poured.
Experience has established that there is a practical minimum
number of turns in a coil and threads on a coil bolt which
must be in engagement to assure adequate lifting strength
without causing the coil turns to separate and to release
; the bolt.
A number of alternative means have been used in
the art for this space-establishing purpose, including plugs
of various kinds which serve to prevent access of fluid con-
crete both to the interior of the coil and into a space
immediately adjacent the inner end of the coil, and which
~15 can be burnt out or otherwise removed after the concrete is
set. Among patents showing a plug of special characteristics
for thiSpurpose are Boll et al 2,880,608, Jenkins 3,216,171,
Holt 3,590,538 and Tye 3,742,661. The plugs of all of such
patents, however, offer certain disadvantages from the stand-
point of both cost and simplicity of use, as now briefly
summari~ed.
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Boll et al discloses the use of a filler plug des-
cribed as composed of sponge rubber or some easily compressed
rubber or elastic material allowing the plug to be easily
inserted and to retain itself in place yet to be easily sub-
sequently removable. Boll, however, does not teach how to
insert or remove the plug, and apparently it would have to be
crammed into place and subsequently dug out piecemeal. Each
of the other three patents shows a two-part plug which must be
separately threaded or otherwise fitted in place at opposite
ends of the coil prior to installation, with the outer plug
being removed after the concrete has set but with the inner
plug remaining in place for partial destruction by the coil
, bolt as it is threaded into the insert.
In U.S. Patent No. 3,889,916, issued June 17, 197S
to Ilukowicz, a solid plastic protective plug for an insert
' i8 dlsclosed. This insert is configured only for use with edge
inserts which are positioned adjacent a mold wall and, additionally,
~, must be threaded completely into and out of the coil. Insertion
and removal of the insert is therefore time consuming.
Summary of the Invention
It is the major purpose of the present invention to
~i- 25 provide a novel construction of plug for use with coil inserts
-~ which offers significant advantages over all prior art devices
for the same purpose in the way of production cost as well as
ease of both assembly in the coil and removal from the coil
in the slab after the concrete has set.
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The plug of the invention is a hollow member of
elastomeric material open at the end thereof which is inner-
most in the slab and with its outer end closed and provided
with a projecting stem proportioned to extend at least to the
outer surface of the slab. The outer surface of this plug is
threaded for matching engagement with the inner surface of
the coil, and the body of the plug is at least as long as the
full length of the coil bolt to be received in the coil. The
outer surface of the plug may be threaded along its entire
length or, alternatively, may be threaded only adjacent the ends
of the plug with the intervening outer surface being substantially
smooth. This alternative thread configuration eliminates problems
which may result in the completely threaded embodiment from
thread misalignment along the intermediate portion of the plug
surface.
Assembly of the plug of the invention in a coil is
accomplished very easily - by inserting a rod into the plug
through its open end and then forcing the closed end of the
plug through the coil from its lower end. Under these con-
ditions, the plug will elongate, and at the same time contractin cross section sufficiently to be pushed axlally through
the coil to the desired position in whlch it completely fills
the coil with its threaded surface in matching engagement with
I the inner surface of the coil, and with the stem on its closed
j 25 end projecting beyond the top of the coil.
After the slab has set, each coil insert is readily
located by the projection of the stem on its plug to or above
i the slab surface, and the concrete immediately above the coil
is chipped away sufficiently to expose the end of the plug.
The plug stem is then used as a handle to pull the entire
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plug out of the slab. This may be easily accomplished since,
as the stem is pulled, the plug elongates and at the same time
contracts radially sufficiently to be pulled free of the en-
gagement between its threaded surface and the threaded interior
of the coil.
When the coil inserts are used in vertical position
during casting of the slab, each plug will similarly stand
vertically and will limit entry of fluid concrete into its
lower end. Since the thickness of the slab is commonly in the
range of only 4 to 8 inches, the hydraulic pressure head of
the fluid concrete is correspondingly low, and experience has
~ho~n that it is balanced substantially by compression of the
air within each plug after the concrete has not risen more
than a small fraction of an inch inside the plug. Release
of the plug from this concrete is facilitated if the inner
end of the plug is beveled to diverge outwardly, and it may
also be provided with a release coating further facilitating
its ready separation from the concrete as it is pulled out of
the coil. If the coil insert is used horizontally in the end
of a ~lab, the plug of the invention can still be used but
should have its open end closed by a cork or the like which
will remain in the slab after the plug is removed.
Brief DescriPtion of the Drawin~s
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' Fig. 1 is a somewhat diagrammatic view partly in
~j 25 section and showing a fragment of a slab with a coil insert
3i and lifting means in position for use;
'l Fig. 2 is a view partly in section and partly in
-~l elevation of a removable plug in accordance with the invention;
~¦ Fig. 3 is a fragmentary section on the line 3--3
ot llg. 2
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Fig. 4 is a view similar to Fig. 1 showing the coil
insert with the plug in place prior to its removal from the
slab;
Fig. S is a somewhat diagrammatic sectional view
illustrating the insertion of the plug of Fig. 2 into the
coil insert prior to casting of the slab;
Fig. 6 is a view similar to Fig. 1 illustrating the
removal of the plug from the coil insert within the slab;
Fig. 7 is an elevational, with portions broken away
and in section, of an alternative embodiment of the present
invention; and
Fig. 8 is a view, similar to Fig. 4, showing a coil
insert with the alternative plug in place prior to its removal
from the slab.
, 15 Detailed Description of the Preferred Embodiments
In Fig. 1, the slab 10 contains a coil insert comprising
a coil 11 and supporting legs 12, each of which has~a foot 13
~ resting on the surface of the mold bottom 14. The coil 11 is
- formed of closely spaced turns of heavy wire or rod defining
an internal screw thread surface which will accept the threads
of the coil bolt 15, shown as a split bolt of the construction
disclosed in Grayson patent 3,922,946 issued December 2, 1975
and including a central key or wedge member 16.
The vertical portion of legs 12 are welded to the
turns of coil 11 to secure the adjacent turns together and
thereby to enable the coil to retain the bolt 15 against being
stripped out by the lifting forces which act thereon through
,~ the lift pickup means 17, shown as a piece of angle iron to
which a hoisting cable can be attached at 18, but which may be
of any conventional type such as a lifting ring. Experience
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has established that if the coil comprises at least six turns,
it will be strong enough for normal uses, with coils of larger
diameter being used for slabs of greater thickness. It is
important, however, that the coil engage an intermediate por-
tion of the bolt where the threads are least subject to wearand are of essentially uniform full size, as compared with the
end of the bolt which is subject to greater wear and also likely
to be reduced diameter. It is necessary, therefore, that the
coil interior be free of concrete and have a sufficient number
of turns to engage both the intermediate portion of the bolt
and the end portion below it.
In accordance with the inuention, this purpose is
accomplished by means of a plug 20 of elastomeric material
which is hollow, open at one end, but closed at its opposite
end 21 and provided at its closed end with a solid stem 22 of
substantially smaller diameter. The exterior surface 25 of
the plug 20 is molded with integral threads matching the
interior of the coil 11 in pitch and essential dimensions such
that in the substantially unstressed condition of the plug,
it is slightly larger, e.g. .015-.025 inch, in diameter than
the threaded interior surface of the coil so that when it is
inserted into the coil, its threaded surface 25 will match
and firmly engage the threaded interior surface of the coil.
In addition, a locator lug 26 is molded on the surface 25 in
predetermined spaced relation with its upper end 21 for a
purpose described below. Preferably, the open end of the plug
20 has its inner surface beveled at 28 to diverge outwardly.
Insertion of a plug 20 in a coil 11 could not be
~i effected by threading the coil in place, both because of its
30 larger size in unstressed condition as just described, and -
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also because the torsional stresses resulting from an attempt
to thread it forceably into the smaller interior of the coil
would tend to cause further increase in its diameter. It can
be inserted quickly and easily, however, by means of a rod 30
inserted through its open end and used to force its closed
end 21 through the coil as illustrated in Fig. 5. Under these
conditions, the plug will be forced to elongate and to contract
radially sufficiently to avoid interference with the threaded
interior of the surface of the coil, and the plug can be -
readily pushed through the coil as far as desired. The proper
final position is as shown in Fig. 4, with the closed end 21
projecting sufficiently from the upper end of the coil to be
substantially flush with the upper surface of the slab 10.
Note also that the exposed end portion of the plug is expandable
lS radially with respect to the portion which is confined in coil
11. The coil 11 must extend substantially as low as the lower
end of the plug 20 in order to prevent the plug from being
partially collapsed by the semi-fluid concrete mixture.
The locator lug 26 is used to establish the proper
relation of pl~g 20 in coil ll. The position of lug 26 is
spaced such dlstance away from its upper end of the plug that
if this lug is substantially in engagement with the upper end
33 ( Fig. 1) of the rod or wire which forms coil 11, the closed
end surface of the plug will be properly spaced above the
coil to be flush with the upper surface of the slab 10. The
stem 22 will then pro~ect above the slab to its full length,
typically one inch.
The plug 20 has the dual purpose of preventing access
, to the interior to the coil 11 by concrete which would
contaminate the threaded interior surface of the coil, and
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also of providing the full necessary amount of space within
the slab for reception of the coil bolt 25 in a position firmly
clamping the pick up means 17 against the top of the slab. In
the preferred practice, the lift insert has an overall height
S such that its uppermost end will be a predetermined distance, ~-
commonly 3/8 inch, below the top of the finished slab. The
closed upper end of the plug 20 should accordingly be spaced
sufficiently beyond the upper end of the coil 11 to be flush
with the upper surface of the slab, as is accomplished by means
of lug 26 as already described, and its length is determined
by the size of the ~oil and the corresponding length of the
coil bolt.
With the coil insert and plug of the relative dimen-
s~ons noted above, the stem 22 of each plug 20 will extend
above the surface of the slab and will be surrounded by the
concrete fiiling the space immediately above the coil 11 and
its legs 12, but since stem 22 is flexible, it will not inter- -
fere with standard screening operations, but commonly there
will be a thin walled dome of concrete immediately above the
plug, as shown at 35 in Fig. 4. When the concrete has set,
each coll insert is readily located by the projection of its
; associated stem. The concrete dome 35 surrounding the stem
and immediately above the plug is chipped out to expose the
upper end of the plug, and the plug is then easily removed
l 25 by a pulling force applied to its stem 22, as by pliers or
j~ the like indicated on dotted lines 35. As illustrated in
Fig. 6, this will cause the plug to elongate and simultaneously
; to contract radially to a sufficient extent to be readily
pulled out of the slab, leaving the coil open for reception
of a coil bolt.
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As already noted, when the plug of the invention is
used as illustrated in the drawings, it acts with the support
of the surrounding coil like an inverted cup in liquid in that
compression of the air trapped in its interior will limit the
extent to which the fluid concrete can enter its lower end. ~ -
Having in mind that, in general, the lower end of a plug 3.75
inches long will be correspondingly less than four inches
below the top of the slab, the hydraulic pressure head of the
fluid concrete will be correspondingly low, and the level of
the concrete will not rise above the full extent of a beveled
surface 28 which is 3/8 inch in axial extent. Separation of
the plug from this concrete is facilitated by the beveled surface
28, especially if the plug is coated with a release agent such
as f~rm oil. Note also that due to the radial expansion of so
muoh of plug 20 as extends above the end 33 of coil 11, the
concrete surrounding this expanded portion of the plug will be
molded into an internally threaded pattern which is correspondingly
~lightly larger than the threaded interior surface of coil 11,
and which therefore will receive a coil bolt freely and without
;~ 20 interfering with proper engagement of the bolt within the coil,
a~ i8 indicated in dotted lines at 37 in Figs. l and 6.
Reference is now made to Figs. ~ and 8 in which an
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alternative embodiment of the plug of the present invention is
~ ~hown. As seen in Fig. ~, only the outer surface areas of the~ 25 plug body 20 which are adjacent the open and closed ends of
the plug are threaded. The intervening surface area 41 is
substantially smooth. The plug construction shown in Fig. ~
identical in all other respects to that shown in Figs. 1-6.
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` Threading only the end portions of the plug 20 does not sub-
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stantially effect the ability of the plug to engage firmly the
~ interior threaded surface of the coil, as illustrated in Fig. 8
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This for~ of plug construction has a significant
advantage over the piug of Figs. 1-6, however. When inserting --
the plug having its outer surface completely threaded into an
insert coil, it occasionally happens that the axial elongation
of the plug will result in engagement of the coils only at
each end of the plug. The intermediate area may be stretched
slightly such that the interi~r threaded surface of the coil 11
will not mesh properly with the exterior threaded surface of
the plug. Although appearing to be properly seated in the coil,
the plug, so engaged, could not be rotated in order to adjust -
the plug with respect to the end of the coil. By eliminating
these intermediate threads on the exterior surface of the plug,
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; the plug may be rotated slightly to bring lug 26 into proper
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~i position with respect to end 33 of coil 11.
~15 Ordinarily, the plugs of the invention will be
i assembled with coil inserts for shipment as assemblies to
the site of their use, in which case the plugs will be ex-
pendible after one-time use. These plugs can be reused, however,
, ~ particularly by a user who recovers them after each use and
assembles them with new coil inserts. Ordinarily, however, it
~t would not be practical to recover the plugs for return to
the supplier of coil inserts, because the cost of collection
and shipment of used plugs would outweigh their recovery value.
Eyen for one time use, however, the plugs of the invention
25~ offer signific~nt practical advantages over the devices for
the same purpose presently available in the art, in terms of
~-~1 ease of assembly and removal and of assured clear coil interiors
and the necessary additional space in the slab or panel.
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