[0001] This invention relates to a belt sander for open-work wood panels, of a type which
comprises, carried on a frame, an endless sand belt trained around a plurality of
wheels at least one of which is a driving wheel, said belt having a working run which
extends above and spaced apart from a conveyor table for a panel to be processed,
and at least one pressure member acting on the working run of said sand belt to press
it toward said conveyor table.
[0002] There exists a high demand for wooden structures of the type of open-work panels,
consisting of a frame made up of uprights and cross-pieces interconnected at right
angles to each other such that their grain directions have different orientations.
[0003] The problem encountered is that of sand finishing such uprights and cross-pieces
in an assembled frame state.
[0004] As is well known in this specific field, best sanding is obtained by directing the
cutting movement of the sand belt parallel to the wood fibers, and hence to its grain
direction.
[0005] By converse, with the cutting motion of the sand belt directed obliquely to the wood
fibers, thus cutting across the grain, a poor finish is to be achieved on the panel
which will show scratches not to be easily disguised by subsequent processing.
[0006] It follows that for optimum sand finishing of an open-work wood panel, the cross-pieces
must be sanded separately from the uprights using respective machines with sand belts
arranged to only work on the former or the latter.
[0007] Currently available industrial sanders, even if equipped with plural sand belts having
independently operated pressure members of the shoe type, are designed for sanding
the entire flat surface of the panel either lengthwise or crosswise without taking
into account the direction of lay of the grain of the various elements (cross-pieces
and uprights) which make up the panel frame.
[0008] The breadth of the sand belt area at work on the panel is adjusted by varying the
number of the pressure members acting on the sand belt.
[0009] However, this is a fairly coarse adjustment form, because it is to be carried in
increments which are integer multiples of the size of a single shoe of the pressure
members. This size, albeit relatively small, cannot be reduced below a set minimum
dictated by the physical bulk of the shoes themselves and drive members which activate
them.
[0010] Thus, being unable to provide for a continuous and accurate form of adjusting the
breadth of the sand belt active or working area, separate sanding of the cross-pieces
and uprights has yet to find application on an industrial scale, and it is, therefore,
to be accepted that a good finish of the uprights, for example, should result in a
less- than-good finish of the cross-pieces, and vice versa.
[0011] The problem underlying this invention is that of providing a sander which is designed,
both construction- and function - wise, to obviate such prior shortcomings, that is,
a sander wherein the breadth of the working area of the sand belt in engagement with
a panel to be sanded can be adjusted to a very fine degree, and in the extreme, even
continuously.
[0012] In its broadest terms, the solutÃve idea of the problem, is one of apportioning in
an adjustable manner the pressure member area actively affecting the working run of
the cited sand belt irrespective of the size of the pressure members.
[0013] The above solutive idea is embodied by a machine as indicated, characterised in that
it comprises an insert of a set thickness extending in the same direction as said
sand belt, over a set length, and being guided between said sand belt and said at
least one pressure member, and a means of fitting said insert to an adjustable position
between said sand belt and said at least one pressure member, to bring a section of
the working run of said sand belt closer to said conveyor table and bound a working
area thereof at that section of said belt where said insert is interposed between
it and said at least one pressure member.
[0014] The invention features and advantages will become apparent from the following detailed
description of a preferred embodiment thereof, taken in connection with the accompanying
illustrative, but not limitative, drawings, where:
Figure 1 shows diagrammatically a sander according to the invention, in front elevation;
Figure 2 is an enlarged scale detail view of the machine of Figure 1;
Figure 3 is a perspective view of an open-work wooden panel; and
Figure 4 is an enlarged scale sectional view taken along the line IV-IV of Figure
2.
[0015] With reference to the drawing figures, a sander machine, generally indicated at 1,
comprises a frame 2 of the portal type, a belt conveyor table 3 mounted on vertically
adjustable jacks 4 and having a substantially horizontal work surface 3a which extends
longitudinally through the frame 2, and a sand belt surfacing unit, generally indicated
at 5 which is supported on the frame 2 above the conveyor table 3.
[0016] The unit 5 includes a train of four wheels, indicated at 6a,6b,7a and 7b, having
parallel axes laid in the longitudinal direction of the conveyor table 3.
[0017] The wheels 6a,6b are mounted on the frame 2 on opposed sides of the conveyor 3, and
one of them would be a power driving wheel.
[0018] The wheels 7a,7b are mounted at an intermediate, preferably middle, location between
the wheels 6a,6b, and their distance from the work surface 3a of the conveyor is adjustable.
In closed loop configuration around the wheels 6a,6b,7b is a belt 8, called the "running"
belt, which forms a supporting and entraining member for a sand belt 10 overlying
it and being, in turn, configurated as a closed loop around the wheels 6a,6b,7a; both
belts, 8 and 10, extend crosswise to the conveyor table 3.
[0019] The sand belt 10 has a working run 10a facing the work surface 3a of the conveyor
table 3, in spaced-apart and parallel relationship therewith.
[0020] A plurality of pressure members 12 are mounted stationary on the frame 2 to confront
the belt 8 at the working run 10a of the sand belt 10.
[0021] Said pressure members 12, which are of substantially conventional type, are each
provided with an actuator 13, such as an air-operated jack, and a shoe 14 driven by
said actuator to press, on activation, the belt 8, and hence the belt 10, toward the
work surface 3a of the conveyor table 3.
[0022] A subframe 15 is rigid with the frame 2 on the inside of the loop formed by the belt
10 and at the working run
10a thereof. The subframe 15 comprises a beam 16 extending in the direction of the
sand belt 10 and provided, as its opposed ends, with respective heads, 17 and 18.
[0023] Each head, 17-18, carries a plurality of idler rollers 20 arranged with their axes
parallel to one another and to form respective curved guides 21 and 22 with facing
concave sides.
[0024] Trained around the guides 21, 22 is a flexible endless belt element 23 having a first
run 24 which extends between the shoes 14 and belt 8, and a second run 25, juxtaposed
to the first and fastened to a slide 27 by means of clamps 26.
[0025] The slide 27 is mounted slidably along a straight runway 28 which is attached, as
by studs 29, to the beam 16 in parallel relationship therewith.
[0026] An endless chain 30 trained around two idler sprockets 31 and 32, respectively, mounted
rotatably on the respective heads 17 and 18, has a cut-off run with its ends attached
to the slide 27 by means of adjusters 34.
[0027] The sprocket 31 is rotatively rigid with a hand-wheel, not shown, accessible from
outside the frame 1.
[0028] Secured on the flexible element 23 is an insert 40 of a set thickness which extends
over a shorter length than the linear extension of said element 23 and slightly longer
length than said runs 24,25 thereof.
[0029] In the example shown, the insert 40 is formed of a plurality of pads 41 in a row,
which are fastened to the flexible element 23, on the outward side of the loop formed
thereby.
[0030] Between the pads 41 and running belt 8, there stretched preferably an anti-friction
belt 42, such as a graphitized cloth belt, with its opposed ends attached to the heads
17 and 18.
[0031] The insert
40 is introduced in between the shoes 14 and anti-friction belt 42 in the opposite
direction to the direction of movement of the sand belt 10 (arrow A in Figure 2).
[0032] In this direction, the foremost shoe in the row at the working run 10a of the belt
10, has a working surface 45 facing said belt and sloping to diverge from the running
belt 8 in the direction of the arrow A.
[0033] That sloping working surface, additionally to forming a lead-in for introducing the
insert into the space between the shoes 14 and antifriction belt 42, defines the start
of a sanding area, indicated at B in Figure 2, in which the belt 10 engages operatively
with a portion of a panel 50, as explained in detail hereinafter.
[0034] The panel 50 comprises, in the example shown in Figure 3, a peripheral frame formed
of a pair of uprights 51 a and 51 b, and a corresponding pair of cross-pieces 52a
and 52b. The uprights and cross-pieces are mutually connected at right angles and
surround a center portion 53 of the panel 50.
[0035] The operation of the machine 1 is the following: the panel 50 is placed on the worksurface
3a of the conveyor table 3 and fed toward the surfacing unit 5 along a perpendicular
direction to the plane of the sheet in Figures 1 and 2. On the conveyor table, the
panel 50 is registered against a straight detent 55 laid along one side of the conveyor
table 3 and shiftable over the surface 3a thereof transversely to the feeding movement
of the panel 50 by means of screw adjustment members 56.
[0036] Thus, the panel 50 is brought to a position below the surfacing unit 5 which is preset
and adjustable relatively to the latter.
[0037] Upstream of the machine 1, the panel 50 has been subject to a surfacing treatment
either over its entire surface or limited to the uprights 51 a, 51 b or the cross-pieces
52a, 52b alone.
[0038] To only sand, for example, the cross-pieces 52a, 52b, the detent 55 would be positioned
such that the trailing end of the working area B in the direction of the arrow A is
brought to coincide with the line of joint between said cross-pieces and the upright
51 a.
[0039] To merely sand the cross-pieces 52a, 52b, the working area B should be adjusted to
have the same dimension as the cross-pieces.
[0040] To this aim, through its respective handwheel, the sprocket 3
1 is turned, thereby the chain 30 is pulled to provide a like displacement of the slide
27 on the runway 28. Along with the slide 27, the flexible belt element 23 is also
shifted by an equal amount whose runs 24 and 25 would be respectively released and
taken up (or vice versa) according to the direction of movement of said slide 27.
[0041] lf, for example, the slide 27 is moved in the direction of the arrow A in Figure
2, a progressive introduction of the insert 40 into the space between the shoes 14
and belt 8 is obtained, thereby the breadth of the sanding area B is increased. Thus,
the element 23 functions also a means of introducing the insert 40 to an adjustable
position between the sand belt 10 and pressure members 12. The sanding area will be
bounded by a start position B, which is fixed relatively to the frame 2 and defined
by the working surface 45 of the leading shoe 14, and an end position B, which is
variable and corresponds substantially to the position of the end of the insert 40
between the shoes 14 and anti- friction belt 42.
[0042] The net effect is one of apportioning the area of the pressure member affecting the
area B, of the end sanding in an adjustable manner.
[0043] In sanding the cross-piece 52b, for example, the plurality of pressure members 12
would be lowered as a whole toward the conveyor table 3, but only some of them, specifically
those overlying the insert 40, would become active on the belt 10 to confine its sanding
area B.
[0044] On moving the shoes 14 of all the pressure members 12 away from the conveyor table
3, the sand belt 10 is disengaged from the cross-piece 52b, and the panel 50 is quickly
fed forward on said conveyor table to position the cross-piece 52a below the working
run 10a of the belt 10, thereafter the aforesaid operations are performed in like
sequence.
[0045] Thus, the sander of this invention solves the problem set forth and achieves a number
of advantages, among which great constructional simplicity, just as high reliability
in operation, and a degree of accuracy within the sanding area B on the order of one
millimeter.
1. A belt sander comprising, supported on a frame (2), a sand belt (10) trained in
closed loop configuration around a plurality of wheels (6a,6b,7a) at least one of
which is a driving wheel, said belt (10) having a working run(10a) extending above
and spaced apart from a conveyor table(3) for a panel to be processed, at least one
pressure member (12) acting on the working run (10a) of said sand belt(10) to press
it toward said conveyor table(3), characterised in that it comprises an insert (40)
of a set thickness extending in the same direction as said sand belt(10) over a set
length and being guided between said sand belt and said at least one pressure member(12),
and a means(23,27,30) of fitting said insert (40) to an adjustable position between
said sand belt (10) and said at least one pressure member(12) to bring a section of
the working run (10a) of said sand belt (10) closer to said conveyor table and bound
a working area(B) thereof at that section of said belt (10) where said insert (40)
is interposed between it and said at least one pressure member(12).
2. A belt sander according to Claim 1, characterised in that said insert (40) is flexible;
and said means comprises a flexible belt element(23) whereto said insert (40) is attached,
said flexible belt element (23) extending in the same direction as said belt (10)
and between said belt (10) and said at least one pressure member (12).
3. A belt sander according to Claim 2, characterised in that it comprises a subframe
(15) rigid with said frame (2) within the loop formed by said belt(10) and extending
in the same direction as said belt(10) above said at least one pressure member(12),
a curved guide (20,21) at each end of said subframe (15), and a slide(27) supported
slidably on said subframe (15) and movable adjustably thereon, said flexible belt
element (23) being mounted in a closed loop configuration around said subframe(15)
and said curved guides (20, 21) with a first run (24) thereof extending between said
sand belt(10) and said at least one pressure member(12) and with a second run(25)
thereof attached to said slide(27), said insert (40) including a plurality of pads(41)
affixed to the outward side of the loop formed by said flexible belt element (23)
and arranged in a row.
4. A belt sander according to Claim 1, characterised in that said insert (40) has
a longitudinal dimension substantially equal to the distance spanned by said pressure
members (12) in the longitudinal direction of said sand belt(10).
5. A belt sander according to Claim 3, characterised in that said insert (40) has
a shorter longitudinal dimension than the longitudinal dimension of said flexible
belt element (23)