The present invention relates to a counter blade for a disc chipper
designed for the chipping of wood, as defined in the introductory part of claim
The production of wood chips for the paper and pulp industry is generally
implemented using disc chippers, in which the wood is chipped by means of blades
mounted in a radial or nearly radial arrangement on a disc . As the disc rotates,
the blades strike against the log under chipping, the opposite side of which leans
against the counter blade. The counter blade is located at the delivery end of
the feed funnel, on the opposite side relative to the direction of motion of the
blade. The wood may be fed into the disc chipper either vertically or horizontally,
and the chipper is accordingly called a horizontal-feed or a vertical-feed chipper.
There are corresponding differences in the positions of the disc and blades in
these different chipper types, but in principle they are identical in operation.
In a disc chipper, the parts subject to wear are the chipping blade
and the counter blade, which receives the log being chipped. For the chips produced
to be suitable for use as fibrous material, the counter blade must meet certain
requirements regarding its condition. The cutting edge of the counter blade, i.e.
the arris receiving the log, must not have an excessive radius of curvature, otherwise
the wood fibres will be broken and the result is low-quality chips containing
In prior art, the counter blade consists of a relatively large and
bulky body that requires plenty of material and is difficult to handle during installation
and maintenance. The wearing part of the counter blade is provided with a hard-metal
coating which needs renewal at times. At present, there are also counter blades
of a lighter construction which are free of the above-mentioned drawbacks. However,
there is still the problem that different parts of the cutting surface of the
counter blade are unevenly worn due to the uneven distribution of the logs. For
this reason, the counter blade cannot be utilized in full.
To achieve an optimal chipping efficiency, the counter blade in a
vertical-feed chipper consists of a horizontal part and another part placed in
a direction slightly differing from the horizontal, so that the blade parts are
at an angle slightly diverging from 180° relative to each other. In a blade construction
like this, the horizontal blade area close to the junction of the parts is subject
to the hardest wear, due to the manner in which the logs are directed in the feed
funnel, and so the wear in this area determines the need for blade replacement.
Therefore, when this small area of the whole effective surface of the blade has
worn out, the whole blade must be replaced. If the counter blade has a hard-metal
coating, renewing the coating means re-coating the whole blade.
The object of the invention is to eliminate the drawbacks referred
to above and to produce a new, more advantageous counter blade construction. According
to the invention, this is achieved in the manner defined in the characterization
part of claim 1. Other preferred embodiments are presented in the subclaims.
The invention allows the counter blade to be effectively utilized
as only the worn part of the blade needs to be replaced. In respect of manufacturing
techniques, the counter blade of the invention is advantageous since it does not
involve any difficult angular structures. By using blade parts of a symmetrical
cross-section, it is possible to provide each blade part with two cutting surfaces.
Also, it is possible to swap the two counter blade pieces to replace the more
worn part with the less worn one.
In the following, the invention is described by the aid of one its
embodiments by referring to the drawings attached, in which
- Fig. 1 presents a cross-section through a vertical-feed chipper, showing the
position of the counter blade,
- Fig. 2 presents the counter blade construction of the invention, and
- Fig. 3 presents a cross-section through the counter blade in Fig. 2 as sectioned
along line A-A.
As illustrated by Fig. 1, a vertical-feed chipper consists of a chipper
frame 1 accommodating a counter blade carrier 2 movable relative to the frame.
At the upper part of the counter blade carrier 2 there is a feed space which, together
with a hollow space communicating with the log conveyor (not shown), forms a gravity
funnel 3. Attached e.g. by means of bolts (not shown) to the counter blade carrier
2 is a counter blade holder 4, placed at the delivery end of the gravity funnel
3. The counter blade piece 5 is attached by means of bolts to a groove 7 provided
in the counter blade holder 4. The surfaces of the counter blade holder 4 and
counter blade piece 5 facing the gravity funnel 3 form a continuous and essentially
even surface allowing the logs to slide over it. The cutting edge of the counter
blade consists of an arris 8 located at the delivery end of the gravity funnel
At the delivery end of the gravity funnel 3, next to the counter
blade carrier 2 provided with the counter blade holder 4 and counter blade 5 there
is a space housing a vertically mounted chipper disc 9 rotating on its shaft.
The shaft and the power means rotating the disc, which are suitably mounted on
the chipper frame, are not shown and they can be implemented in a manner known
in the art. The chipper disc 9 accommodates several, usually 12 -16 blade bodies
10 provided with cutting blades 11 and mounted on the disc in a manner known in
The logs are brought to the funnel by means of conveyors and directed
into the chipper in a manner known in itself. The blades of the disc 9 cut the
wood into chips of a desired size. The chip length can be determined by adjusting
the distance T between the blades 11 and stoppers provided in the disc. This is
done by moving the blade body 10 so as to obtain a suitable distance T, preferably
approx. 13 mm. To achieve a good chipping efficiency, the distance C between the
blade 11 and the counter blade must be correct, suitably approx. 0.5 mm. The arris
8 forming the cutting edge of the counter blade must not be allowed to be rounded
too much by wear. The radius of curvature must remain below 5 mm to ensure that
the wood fibres are not damaged and that the chips produced-will not contain sawdust.
Fig. 2 depicts the counter blade holder 4 and one of the two counter
blade pieces 5 accommodated by it as seen from the side facing the disc 9. The
holder 4 is provided with a groove 7 for the counter blade pieces 5. The groove
extends over the whole length of the holder and is bent into an angle δ
at a point midway between the ends. The thickness of that part of the holder which
lies above the groove decreases towards the edge so that its surface 16 constitutes
part of the wall of the funnel 3. The counter blade holder 4 is fixed to the counter
blade carrier 2 by means of bolts screwed into holes 12.
The counter blade consists of two identical counter blade pieces
5. Each part has two longitudinal arrises 8 and 8' placed at a distance from each
other and forming the cutting edge of the counter blade. The counter blade piece
has a cross-section symmetrical in relation to plane B-B, which, as shown in Fig.
3, is equally distanced from the arrises 8 and 8' and perpendicular to the normal
connecting the two arrises. When the two counter blade pieces are placed in the
groove 7 in the holder 4, the cutting surface of the counter blade has an elbow
equal to angle δ. The end faces 14 of the counter blade pieces 5 form an
angle α diverging from the straight angle relative to the longitudinal side
of the part 5. Angle α is determined by the angle of the elbow at point 13.
Thus, the parts can be so fitted together that a continuous blade surface 8 is
formed at the upper edge of the counter blade.
In a preferred embodiment of the invention, as illustrated by Fig.
3, each counter blade piece 5 is provided with four parallel arrises 8, 8' 18,
18', each of which is so made that it can act as the cutting edge of the counter
blade. When the piece is in position, two of the arrises always face towards the
chipper disc 9. One of these two arrises acts as the cutting edge. The other two
arrises are essentially on the opposite side of the counter blade piece 5 as seen
in the direction of the shaft of the disc 9. The counter blade piece is symmetrical
in relation to plane B-B. Plane B-B is perpendicular to the normal connecting the
adjacent arrises 8 and 8' forming a cutting edge and correspondingly arrises 18
and 18'. It is located at an equal distance from each arris 8,8' and similarly
from arrises 18 and 18'. Thus, each counter blade piece 5 has altogether four
arrises, each of which can be used as a counter blade surface by turning the piece.
In a preferred embodiment, the lower part of the end face 14 of the
counter blade pieces forms an angle of 180-2α relative to the upper part
of the end face. This renders the horizontal and oblique blade parts interchangeable.
This is practical because the horizontal part of the counter blade is subject
to faster wear than the oblique part, which is due to the fact that the logs under
chipping tend to move horizontally side by side in the feed funnel. The minimum
requirement is that the cutting edges of the two blade pieces 5 should be in contact
with each other. It is possible to place supporting or filling elements between
the lower parts of the counter blade pieces to achieve a continuous overall structure.
It is also possible to provide the counter blade pieces with end faces constituting
parallel planes relative to each other. In this case, a given counter blade piece
can only be used in one position as the end faces of the other part of the counter
blade slant in another direction.
The counter blade pieces 5 are attached to the counter blade holder
4 by means of bolts or equivalent placed in holes 15. The bolts may extend through
the counter blade carrier 2 as shown in Fig. 1. The holes are symetrically laid
out so as to allow the pieces 5 to be mounted in alternative positions and locations
using the same holes and fixing elements. The pieces can be joined by their ends
to each other or to the above-mentioned supporting structures e.g. by means of
Fig. 3 presents a cross-section of the counter blade holder 4 and
counter blade piece 5 as taken along line A-A in Fig. 2. Part 16 of the holder
4 is at an angle β relative to the vertical plane. The counter blade piece
5 is in the groove 7 and has a part 17 shaped in the same angle with the holder
and protruding out of it. The front surface 28 of the counter blade piece is in
a vertical position, so that arris 8 constitutes the cutting edge of the counter
In the above, the invention has been described with reference to
one of its embodiments. However, the invention is not restricted to this embodiment,
but the scope of patent protection may vary within the limits permitted by the