Note: Descriptions are shown in the official language in which they were submitted.
Z~L
This invention relates to a modified surface finish on
a panelboard or the like. More specifically, this invention
relates to a device and a method for sanding a random contoured
surface with a minimum reduction of material thickness. The
resulting surface is non-slippery.
Panelboard includes plywood flakeboard, waferboard and
particleboard. Waferboard, for instance, is made by compressing
a random or oriented arrangement of wood wafers, with a pre-
determined quantity of resin under controlled conditions of pressure
and temperature. The resulting waferboard has a slippery sur-
: face. Furthermore, the surface is not usually flat but tends to
be randomly contoured due to the uneven arrangement of wafers
within the board. The slippery surface of the waferboard is a
disadvantage when waferboards are stacked one upon another, and -
particularly when the stacks are at an angle, such as when they
are used in the construction of a roof. The slippery surface
allows the waferboards to slide and this may be dangerous if the
stacks of the waferboards are on a roof.
By using a coarse sanding belt, the slippery waferboard
20 surface can be roughened to avoid boards sliding. Many existing ~-
sanding devices use a fixed drum or bar or in some cases a bar
with li?~ited floating action to press the sanding belts against
the surface of the board. Thus, sanding occurs across a flat
plane, and in order to sand the whole of the random contoured
surface of a board, despite thickness variation away from this
plane, the thickness or depth of sanding cut may be as much as
.050 inch. A thinner cut may leave unsanded patches where the ~ .
surface has not been touched by the sanding belt. When a cut of
this depth is removed from a board, overall structural strength
is reduced. Since many product specifications require strength
and thickness to be maintained at certain standards, a thicker
board must therefore be produced initially to allow for the
-- 1 --
''.`,',' ''`', '''~ ' . . .?' ' ': . ' .'
-~- 104Z~Z13
necessary depth of sanding cut.
Some panelboards used in cabinets for television sets,
stereos and other pieces of furniture have a thin outer surface
veneer of a hard wood such as walnut. In many cases this veneer
.
~ has tape applied to the surface during the forming steps.
; Attempts to remove this tape on conventional sanding devices can
cause problems because in some cases the depth of sanding is such
that the surface veneer is reduced to paper thickness or even
removed completely.
Contour sanding machines employed today have utilized
the basic principle of a rigid bar for forcing a sanding belt `
::,,
onto a board surface In some cases the bar has a limited float- -
ing action and consists of several individual pressurized sec- ~ -
.,,., : .. . .
tions across the width of the machine. Each section is, however,
. . . .
in itself still rigid and is, for example, six inches long and
four inches wide. Because of the design of these sanding mach-
ines, particularly with respect to the belt tensioning system
and the existence of high tension where the belt moves over the
bar, considerable force is employed to pressurize each separate
section of the bar In another type of contour sanding machine,
a number of narrow sanding belts are staggered across the width
of the machine However, as in the previous case each sanding ~-
belt is rigid across its width. The result is that the so-called
contour sanding s~ill removes, for example, 010 inch per side.
It is one object of the present invention to provide a
method for removing the slippery surface from a panelboard with
a minimum reduction of its thickness.
A further object of the present invention is to provide
a method for sanding a random contoured surface and remove surface
blemishes or tape adhering to the surface with a minimum reduc- ;
tion of material thickness.
It is another object of the invention to provide a
- 2 - `;
; ~
i "` lO~Z~3
method and a device for sanding a random contoured surface of a
panelboard to roughen the entire surface comparatively evenly ;~
without undue loss of material. -
I have found that these disadvantages may be overcome
and the objects of the present invention may be achieved by a
contour sander having a flexible deformable membrane pressing a
sanding belt against the surface of a board. The flexible mem-
brane is pressed onto an area of the sanding belt by a pressure
maintained substantially constant over the area, thus forcing
the sanding belt to conform to the random contoured surface of
the board. The pressure may be varied, but I have found that,
by using a comparatively large area, only a low pressure is
required, and this removes a layer of approximately .~02 to .005
inch evenly across the entire surface. The thickness of this
removed layer is related to the size of the area of the sanding
belt pressing onto the board, the pressure on this area, and the
- relative speed between the sanding belt and the board surface.
Furthermore, I have found that the finished panelboard has a
non-slippery or frictional surface. When a waferboard is pro-
1 20 cessed on a contour sander of the present invention, the slippery
;~ surface is removed and the surface appearance retains the full
shape of the individual wafers.
The present invention provides a method of finishing a
random contoured surface of a panelboard comprising the steps of
advancing a panelboard in contact with a sanding surface of a
; sanding belt, pressing a flexible membrane with an even pressure
onto a portion of the sanding belt to force the sanding surface
to follow the random contoured surface of the panelboard. In a
preferred embodiment, the flexible membrane is as wide as the
panelboard and has a length in the range of 6 to 24 inches
pressing on the sanding belt, the pressure on the flexible mem-
brane is in the range of approximately 0.25 to 10 lbs. per square
- 3 -
ZZ~3
inch and a relative speed between the sanding belt and the panel-
board is up to approxi~ately 2,000 feet per minute, In another
embodiment, the sanding sur~ace of the belt removes a thickness
of approximately ,002 to .005 inch evenly from the random con-
toured surface of the panelboard. In a further embodiment the ;
flexible membrane is pressed against the sanding belt at a pres-
sure within the range of 0.5 to 4 lbs. per square inch. :
.. . ~ .
The invention also provides a device for finishing a
random contoured surface of a panelboard comprising a sanding
belt, means for advancing the board in contact with the sanding
belt, a fle~ible membrane located adjacent a portion of the sand-
ing belt extending for at least the width of the panelboard,
: .,
pressure means adapted to provide an even pressure on the flexible
membrane to force the sanding belt to conform to the random con-
, . : -,
toured surface of the panelboard.
Other embodiments include an even pressure on the flex-
ible membrane in the range of approximately 0.25 to 10 lbs. per
square inch, a gas acting on the flexible membrane, and means to
I vary the pressure in the gas. In another embodiment the flexible
,20 membrane is in the form of a flexible air bag which extends for
at least the width of the board.
`` In drawings which illustrate embodiments of the invention:
Figure 1 is a schematic elevation showing one embodiment
o$ a contour sander of the present invention.
Figure 2 is a photographic reproduction of a finished
surface of a waferboard according to one embodiment of the present ¦~
invention showing the retention of the full particle shape of the ~-
wafers.
Figure 3 is a photographic reproduction of a finished
surface of a waferboard taken with oblique light to illustrate
the non-slippery surface.
Referring now to the drawings, Figure 1 shows a panel-
- 4 -
'`
- ` 1~)4~213
board 10 passing beneath a contour sander of the present invention.
An endless sanding belt 11 passes between two lower belt travel -
- rollers 12 and 13 and over an upper roller 14. A frame 15 bet-
ween the two lower rollers 12 and 13 supports an air bag 16
which has a flexible membrane 17 pressing against the top inner
surface of the sanding belt 11 so that the sanding belt 11 is
I pushed down onto the panelboard 10 and conforms to the contoured
and variable surface of the panelboard as it passes beneath the
sanding belt 11, The lower rollers 12 and 13 are positioned so
that the belt 11 under the rollers does not contact the surface
of the panelboard. Contact only occurs between the belt 11 and
the surface of the panelboard directly under the flexible mem- ~
brane 17. A stationary flexible anti-friction shield 18 is posi- ~--,
~, tioned between the flexible membrane 17 of the air bag 16 and the
sanding belt 11. This shield 18 is preferably a graphite strip
and is flexible to permit the movement of the belt 11 passing
under the flexible membrane 17 without friction causing heating ¦~
or abrasion that might damage the membrane 17 or the belt 11. ¦
The air bag 16 extends for the full width of the sand-
~20 ing belt 11, and the air pressure against the flexible membrane
17 ensures full contact between the sanding surface of the sand-
ing belt 11 and the surface of the panelboard 10. Tensioning ¦; -
devices (not shown) are connected to each end of the upper roller
lg and ensure there is correct tension in the belt 11 in order
~` to keep it tracking and travelling, and at the same time allow
the belt 11 to be pressured by the flexible membrane 17 so the
:I k-
sanding surface of the belt 11 conforms to the surface of the
panelboard 10. This membrane 17 takes into account contour vari-
ations in the surface of the panelboard in its length and breadth.
The panelboard 10 moves in the direction shown by the arrow in
Figure 1 and the belt 11 moves in the opposite direction to
ensure a maximum surface speed differential between the panel-
_ 5 _
.
.~ .
: `:
~ L2;~.3
board 10 and the sanding belt 11. The depth of sanding on the
panelboard 10 may be varied depending upon the length of contact
,. ~-.,
of the air bag 16 on the sanding belt 11, and hence the sanding
belt 11 on the surface of the panelboard 10, the air pressure
~ within the air bag 15, the belt coarseness, belt tension, and the
; differential speed between the sanding belt 11 and the panelboard
' 1~. 1:'' '
When a panelboard is sanded on a contour sander of the
type shown in Figure 1, the finished surface is non-slippery as
;;10 compared to the panelboard's original surface.
The finished surface of a waferboard seen in Figure 2
highlights the full particle shape of the individual wafers which
, .: '-
indicates that little thickness of material has been removed.
The same surface when seen in oblique light, Figure 3, shows the
;` slippery surface removed.
., 1, - ..
In the case of waferboard a coarse range of sandpaper
is preferred with a range of 80 to 24 grit size. Higher flexible
membrane pressure and belt speeds are generally needed for finer
,, .~
grades of sandpaper. The surface of a waferboard is randomly
contoured, and the sandpaper removes an even layer from this
,~. . .
I surface.
When a panelboard with a thin veneer surface is passed
under a coDtour sander, finer grades of sandpaper are used with ~;
, lower flexible membrane pressures so that little material is
removed, only tape and blemishes adhering to the surface. 1-
I Pressure of the flexible membrane on the sanding belt
may range from approximately 0.25 up to 10 lbs. per square inch
depending on the frictional surface required and the machine
operating conditions. High pressures on the belt in excess of
10 lbs. per square inch tend to remove the surface high spots and ~`
thus do not provide an even thickness removal across the random
...
; contoured surface of the panelboard. A preferred pressure range ~Ij
." .
- 6 -
L3
is 0.5 to 4 lbs. per square inch for processing a panelboard.
In one embodiment a 1 lb. per squars inch pressure acting over
24 inches of panelboard length is equivalent to a 4 lb. per square
inch pressure over ~ inches of panelboard length at the same
belt speed.
In another embodiment 0.5 lbs. per square inch pres-
sure acting over ~4 inches of panelboard length is equivalent to
a 2 lb. per square inch pressure over 6 inches of panelboard
length at the same belt speed.
Panelboards have been processed at speeds up to approxi-
; mately 250 feet per minute on a contour sanding machine, and
belt speeds range up to approximately 1,800 feet per minute
Preferably the belt moves in the opposite direction to the panel-
board to obtain the maximum relative speed between the panelboard
and the belt which is up to approximately 2,000 feet per minute.
In one example, a 24 grit sanding belt was used to
process panelboard. The belt was 103 inches in circumference,
513 inches wide, and was continuously spliced. The graphite
cloth was a ~50 Friction Fighter(T). The flexible membrane was
a vulcanized bag made from a rubber-impregnated cotton duck.
The panelboard 10 was advanced under the sanding belt 11 by means
o~ top and bottom nip rolls which applied a pressure across the
w~dth of the panelboard entering the machine. One of the nip
rolls had a rubber exterior surface to aid in gripping the panel-
board; the other was a steel roll. In one test, the speed of the
panelboard passing through the nip rolls was 70 feet per minute.
Fixed position idler rolls were used to support the panelboard
while passing under the sanding belt and to ensure that the panel-
board retained a flat position during the sanding step.
To ensure maximum time saving and production, it is
preferable that each panelboard be butted to the adjacent panel-
board. Thus, the sanding belt is in continuous operation and
~ . i ".
O~Z13
this assures that an even layer of material is removed from all
the panelboard including the leading and trailing edges. In
another embodiment, the upper roller was tensioned by two three-
inch pneumatic cylinders, one at each end. One of the two lower
~ rollers was driven The two lower rollers were located in line
'~; : ,.
horizontally at a centre-to-centre distance of 36 inches Each ;
lower roller was faced by 60 durometer neoprene rubber and was
9~ inches in diameter. The lower rollers were supported in
bearings fixed rigidly to the main rectangular framework con- ;;
structed ~rom 8 inch structural steel channels. The plane of the
framework was effectively the horizontal base of the triangular ;
configuration. The driven roller for the sanding belt was
powered by a 20 h.p. motor via a V-belt pulley reduction system
to give a sanding belt speed of 1,200 feet per minute which could
be increased up to 1,800 feet per minute.
The three rollers each had a 52 inch width to permit
the use of a 51~ inch wide sanding belt. This, in turn, permitted
contour sanding of edge-untrimmed or edge-trimmed panelboards up
to 50 inches in width.
In the example described, an air bag was located bet-
ween the two lower rollers. The bag was 24 inches long by 51
inches wide, the same width as the sanding belt. Thus, the flex-
ible membrane, being the side of the bag directly above the belt,
pressed the portion of the sanding belt downwards over 24 inches.
,~ Full contact was, therefore, maintained between the sanding belt
i and the panelboard for a length of 24 inches across the width of
the panelboard. The air bag was contained by a hold-down plate
located within and forming part of the main framework The depth
.: .
of the air bag was approximately 4 inches when inflated. This
4 inch depth was sufficient to permit upward flexure of the sand-
ing belt in response to contour variation in the panelboard sur
face with negligible change in bag air pressure. Negligible ~ ~ ~
. .
` - 8 - ~
4~13
changes therefore occurred in the horsepower demand for driving
either the belt or the panelboard due to contour variation, The ,
4 inch depth of bag permitted 1/4" to 3/4" thick panelboards to
be sanded without variation in the height of the idler rolls,
A graphite cloth was located and fixed in between the
stationary air bag and the moving sanding belt by a clamping bar
attached to the main framework, The cloth covered the whole con-
~; tact area between belt and bag so that no abrasion or wear occurred
to the air bag. When the air bag was deflated, the tension in
the sanding belt raised the sanding belt off the surface of the
; ,
panelboard to the level of the lower bel~ rollers. Panelboards ~'
could thus be passed through the machine without being sanded
merely by releasing the pressure in the air bag, An air connec-
tion to the air bag enabled the pressure to be varied at will from
a compressed air supply. Furthermore, the vertical location of
the sanding unit was set using spacing bloc~s relative to the
transporting conveyor idler rolls. In this way, panelboards of
different nominal thicknesses, such as 1/4, 3/8, 7/16, 1/2 inch,
etc., could all be treated by the same machine by merely allowing
the sanding belt to deflect downwards until it touches the panel-
board surface. Sanding dust was removed from the machine by
means of vacuum exhaust funnels located close to the contact and
release points between the belt and the panelboard.
In one particular test run, the operating conditions
were as follows:
Panelboard feed speed (ft./min.) - 70 to 90.
Sanding belt speed (ft./min.) - 1200 to 1800.
' Sanding belt tension roll pressure (lbs./sq. in.) -
60 to 80. ~-
Air bag pressure (lbs./sq. in.) - 0.9 to 1.2.
Air bag size - 24" by board width.
Starting up the machine the sanding belt drive was
switched on after pressurizing the sanding belt tensioning roll
and air bag and with a panelboard in position. This ensured good
_ 9 _
.' . ~,.
.` ' ` ,
lC)~ZZ~3
tracking. The panelboard feed nip rolls were then started and
feeding continued with panelboards butted together,
Panelboards processed in this test run removed a thick-
ness layer of approximately .002 to .005 inch evenly right across .:
the surface of the panelboards, This variation in thickness re-
moved depended on the panelboard feed speed and the pressure of
the air bag forcing downwards onto the sanding belt, If the pres- .
sure was at the low side of the range and the panelboard feed
speed was at the high side of the range, then the minimum thick-
ness of material was removed from the panelboard, If the pres- ~.
sure was at the high side of the range and the panelboard feed ~ ~:
speed was at the low side of the range, then the maximum thickness
of material was removed.
Results of a series of tests with varying factors are
shown in the following table.
''` ' '~' -
:` ' ~ ':
~'; ' ' ''
,,,'' ;'
-- 1 0
,
04;2'~3
r( N tS) ~ d~
) ~ ~ ~ N N N C~
e.~ e
.. , a ~ P~ ~
~ p, V ~ C;~ S~ ~ N
a
:, ~ a~
.. ~ h .~ :.
m e ~ ~ ' ' o O
.,,,.,,,, . v~ ~ ., ,
. ~ ' 'C ~l ;;
.. ~ ~
.. ~ ~ I CJ
., o ~
) ~ tR
~ o~
' ' ' $
~ ~ :
C) ~ o s~ .,~
l o ..
:' R ",
I) ~ ~ O O O O O ~
m 4 ~ ~ ~ ~ o
':` ' U~ ,~
,~, ~1
., a) ~ ~ .,~
.~. O ~ ~ d' 00 o o o
q~ . ;:
bD~ Oo N 1.
.j 111 1:~ N ~\ ~ I I ~:
,1 ~O o _i C'' '''' '
, j
f~a"~ f~f~
'" E-~ ` ` :
~ ID42'Z~3 -
In the first test, mutliple passes of the panelboard
were made under a stationary belt, and in the second test multiple
passes of the panelboard were made under a moving belt The
remaining tests were all a single pass of a panelboard under a
moving belt. The thickness of the layer removed during the test
was only measured for test run number 4.
Sample panelboards made in these tests were used on a
simulated roof rafter system that had a 5/12 slope. The panel-
boards were evaluated against unsanded spruce plywood sheets and
found to have at least as high a coefficient of friction
Although an air bag has been described in this particu-
lar embodiment, it will be clear to those skilled in the art that
a flexible membrane is required adjacent the sanding belt. The
flexible membrane is joined at its sides to a box or frame, and
has above it a pressure maintained substantially constant over
the area of the membrane to push downwards and thus, in effect,
act as an air bag. The pressure medium which has been described ~ .
in the embodiment as air could be any suitable liquid, gas or
combination thereof, provided the flexible membrane has the abil-
~20 ity to force the sanding belt to follow the contour of the panel-
board and provide a substantially constant pressure on the panel-
board surface over the entire area of the membrane. For instance, --
in the case of a horizontal top sander, the membrane could form
the bottom of a tankcontaining liquid, with the top of the tank
open to atmospheric pressure. Alternatively, a system employing ~ -
a series of small weights side by side or a system of pressurized
rollers or levers could also be used to apply a constant pressure
to the membrane.
The contour sander described in the example and shown
in Figure 1 defines a unit having a sanding head for one horizontal
surface, so that to treat both sides of a panelboard, it is
necessary to turn the panelboard over after the first pass and
- 12 - - -
'
422~3
carry out a second sanding pass. Other embodiments are provided
to treat both sides ofapanelboard in one pass Such a unit
includes twin sanding heads which, in the case of a horizontal
;~ sander, treat the top and bottom surface o~a panelboard at the
;, ~ ,.
same time. Another unit includes twin vertical sanding heads
which allows the panelboard to be passed through in the vertical
position so both sides are treated at the same time. Other
changes may be made to the device which will become apparent to
those skilled in the art without departing from the scope oi the ~ -
present invention.
'
!
;~
,.
. .
'~
"
--
.: .
,',~'~
".:
: - 13 ~
'~': "
