Note: Descriptions are shown in the official language in which they were submitted.
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FACE WIRE INSTALLATION APPARATUS
BACKGROUND OF THE INVENTION
This invention relates generally to installation of
wire screen on porous filter drums and more particularly
to a device for securing the screen to the drum and for
preventing rotation and skewing of the screen on the drum
during operation. The typical use of circumferential
bands to secure the screen to the drum allows the screen
to "walk" about the drum during operation. This may
result in damaged screens and loss of filter capacity.
The foregoing illustrates limitations known to
exist in present devices and methods. Thus, it is
apparent that it would be advantageous to provide an
alternative directed to overcoming one or more of the
limitations set forth above. Accordingly, a suitable
alternative is provided including features more fully
disclosed hereinafter.
SUMMARY OF THE INVENTION
In one aspect of the present invention this is
accomplished by providing an apparatus for securing and
preventing rotation and skew of a screen on a filter drum
comprising a longitudinal groove on the surface of the
drum; a screen disposed circumferentially about the drum;
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a longitudinal member substantially embedded within a
loop formed of one end of the screen; and the
longitudinal member being secured by a retainer within
the longitudinal groove.
The foregoing and other aspects will become
apparent from the following detailed description of the
invention when considered in conjunction with the
accompanying drawing figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Fig. 1 is a perspective view of a drum filter as
presently known in the art;
Fig. 2 is a perspective view of one method for
securing a screen to a filter drum known in the art;
Fig. 3 is a perspective view of one embodiment
showing a method for securing a screen retaining device
to a filter drum;
Fig. 4 is an end view of the embodiment shown in
Fig. 3 in greater detail;
Fig. 5 shows an end view of an alternative
attachment detail;
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Fig. 6 shows an end view of a second alternative
attachment detail;
Fig. 7 shows an end view of a third alternative
attachment detail;
Fig. 8 shows an end view of a fourth alternative
attachment detail; and
Fig. 9 shows an end view of a fifth preferred
embodiment of an attachment detail according to the
present invention.
DETAILED DESCRIPTION
Referring to Fig. 1, a drum filter generally
designated by the reference numeral 1, is shown. The
drum filter 1 is provided with a cylindrical drum 2 which
has its outer peripheral surface encased in a screen 3 as
generally practiced in the prior art. The screen 3 is
secured to the drum 2 by means of a plurality of
circumferential bands or straps 4. In the prior art, the
longitudinal seams of the screen were generally
overlapped and either wire stitched or welded to secure
the joint.
It should be appreciated that during normal
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operation of the drum filter the drum is rotated through
a liquid/particle suspension during which the liquid is
drawn into the drum by vacuum, pressure, or other means,
the particles being generally collected on the outer
surface of the screen for later removal by a scraper
(generally referred to as a doctor blade). Friction
created between the rotating drum and the liquid/particle
media and the doctor blade tend to displace the screen
relative to the drum during operation. The screens,
therefore, rotate relative to the drum often in a
nonuniform manner creating a skewed condition of the
screen material. In extreme cases this results in damage
to the screens and/or interruption of operation due to
the skewed screen interfering with the mechanical
rotation of the drum by dragging on frame members or the
like. As previously stated, the banding method does not
prevent twisting of the face wire or screen. The method
of installation is also expensive and time-consuming.
One known method of minimizing the relative
rotation of the screen is shown in Fig. 2, wherein a loop
3'' is formed in one end of the screen about a piece of
pipe 10 which is positioned adjacent to a rib or grid 7
on the drum surface 8. The screen is then stretched
around the drum and the other end of the screen 3' is
overlapped over the screen portion containing the loop
and either stitched or welded in place.
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The pipe and loop method may create a protrusion if
used without a further means of securing the pipe. The
protrusion may catch on the take-off doctor and thereby
cause damage to the wire or the machine.
According to the present invention, one method of
securing the screen loop and pipe is shown in Figs. 3 and
4 wherein a hook 15 is secured to the rib or grid 7 which
grips a rod 10 inserted in the loop 3 through a series of
cutouts 9 in the screen loop provided along the length of
the rod. The hooks securely hold the rod lo and the
encircling loop of screen 3' at a position substantially
away from the face of the drum thereby minimizing the
possibility of surface interference.
The compartment formed between the grids 7 and 7',
as seen in Fig. 4, provides an area of unsupported face
screen or wire 3 and the support of the rod by the hooks
is noncontinuous. Accordingly in a first preferred
embodiment of the present invention, as shown in Fig. 5,
a tapered locking channel is formed between a deck
support 16 in a C-formed locking channel 18. The
longitudinal channel 30 is open to the top deck through
the screen access opening 35. The grid top hat 16 snaps
over the grid 7 which in turn is supported from the drum
8 and further reinforced by the diagonal brace 27, best
seen in Fig. 5.
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The deck members 28 and 28' are supported on the
top hat 16 and secured there in part by the cap strip 17
and the C-formed locking channel 18. A spacer 29
compensates for the C-formed locking channel height so
that the deck members 28 and 28' line up. The screen
wire 3 passes over the cap strip 17 and is formed into
the locking channel 30 and then up over the C-formed
locking channel 18. A trapezoidal cross section locking
key 20 is then inserted lengthwise from one end into the
complimentary trapezoidal locking form of the locking
channel 30 from one end.
An installation tool 21, which cooperates with a
bore 22 in the trapezoidal key 20, assists in the
longitudinal insertion. Once the key is in place the
installation tool is removed. The complimentary
trapezoidal forms create a key lock with regard to the
screen wire 3 which prevents its rotation uniformly end
to end on the drum. To remove the screen the locking key
is withdrawn axially in a manner similar to its
insertion. The screen may then be removed from the
locking channel as required.
Fig. 6 shows an alternative key in the form of a
circular cross section key 20'. The key is inserted and
performs in a manner similar to that described for the
Fig. 5 embodiment.
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Fig. 7 shows a third alternative embodiment wherein
a pair of circular cross sectional rods 20b and 20c are
inserted in screen loops 3'' and 3''' thereby securing
both ends of the screen 3 and 3' within the same locking
channel 30. To facilitate tensioning and overlap
welding, a stub piece of screen 31 is provided in
conjunction with the end 3', as shown in Fig. 7.
Fig. 8 shows a fourth alternative embodiment
wherein the loop 3'' is formed over a pipe or rod keeper
20' and wherein the end of the screen 3' is carried over
the locking channel to be secured to the screen wire 3.
Fig. 9 shows a fifth preferred embodiment of the
present invention wherein the screen loop 3' and the
longitudinal insert securing member 20d are retained
within parallel adjacent grids 7 and 7' by a modified top
hat member 16' having one leg 22 bent down at
approximately 45 degree angle to form a displaceable
flexible nip which grabs the screen loop 3' and
longitudinal retainer insert 2Od when it is forced down
between the nip point and grid 7' on installation.
A modified top hat 26 and cap strip 17b provides
support for the deck 28'. The top hat 16' and cap strip
17a provides support for the deck portion 28. As in
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embodiments above, the end 3' of the screening wire is
carried over the screen 3 and secured by stitching or
welding the wire together as previously described.
Removal of the screen is rapidly accomplished by simply
cutting the portion of the screening wire inserted in the
nip between the leg 22 and grid 7' and allowing it to
drop into the gap between the grids 7 and 7' upon
installation of a new screen.
It should be appreciated that this embodiment
provides a very simple and fast means for securely
fastening the screening wire to the deck of the filter
drum. Other similar means of securing the screen end may
now occur to one skilled in the art.
