DETERMINING STRENGTH OF WOOD FIBERBOARD

Abstract

Wood-fiber insulation board is pressed to a uniform thickness and continuously advanced in a horizontal travel direction on a conveyor prior to subdivision into individual panels. The strength of the wood-fiber insulation board is determined by first pressing with an actuator a contact element downward at an actual pressure on a subregion of the advancing wood-fiber insulation board so as produce an actual deformation of the wood-fiber insulation board of between 1% to 7% of its thickness. Then a force sensor determines the actual pressure applied by the contact element to the board that produces the actual deformation and this the determined pressure and the actual deformation are transmitted to a central processor that extrapolates to a standardized deformation based on the determined pressure and actual deformation.

Claims

1. In the manufacture of wood-fiber insulation board where the board is pressed to a uniform thickness and the pressed board is continuously advanced in a horizontal travel direction on a conveyor prior to subdivision into individual panels, a method of determining the strength of the wood-fiber insulation board comprising the steps of: pressing with an actuator a contact element downward at an actual pressure on a subregion of the advancing wood-fiber insulation board so as produce an actual deformation of the wood-fiber insulation board of between 1% to 7% of its thickness; determining by a force sensor the actual pressure applied by the contact element to the board that produces the actual deformation; transmitting the determined pressure and the actual deformation to a central processor; and with the central processor, extrapolating to a standardized deformation based on the determined pressure and the actual deformation.

2. The method defined in claim 1, wherein the wood-fiber insulation board is vertically compressed by 1.5 to 3% of its thickness by the contact element.

3. The method defined in claim 1, further comprising the step of: detecting a vertical displacement of the contact element by a displacement sensor.

4. The method defined in claim 3, further comprising the step of: transmitting the detected displacement with the pressure and actual deformation to the central processor and, with the central processor, extrapolating to the standard deformation based on the determined pressure, the actual deformation and the detected displacement.

5. The method defined in claim 1, wherein the contact element is a skid having a defined width.

6. The method defined in claim 1, wherein the contact element is a wheel rolled in the direction on the board.

7. The method defined in claim 1, further comprising the step, before pressing the contact element down with the actuator, of: setting the contact element on the board to bear thereon only with its own weight.

8. The method defined in claim 1, further comprising the step of: locating where the contact element compresses the board at a location that can subsequently be cut from the board.

9. The method defined in claim 1, wherein the pressure determination is performed cyclically on the basis of a time interval or a certain production quantity.

10. In the manufacture of wood-fiber insulation board where the board is pressed to a uniform thickness and the pressed board is continuously advanced in a horizontal travel direction on a conveyor prior to subdivision into individual panels, an apparatus for determining the strength of the wood-fiber insulation board, the apparatus comprising: a vertically shiftable contact element; actuator means for pressing the contact element downward at an actual pressure on a subregion of the advancing wood-fiber insulation board so as produce an actual deformation of the wood-fiber insulation board of between 1% to 7% of its thickness; a force sensor for determining the actual pressure applied by the contact element to the board that produces the actual deformation; a central processor; and means for transmitting the determined pressure and the actual deformation to the central processor, the central processor extrapolating to a standardized deformation based on the determined pressure and the actual deformation.

11. The apparatus defined in claim 10, wherein the contact element has a defined width in the range from 100 to 250 mm.

12. The apparatus defined in claim 11, further comprising: a displacement sensor associated with the contact element.

13. The apparatus defined in claim 12, wherein the actual deformation is a predefined depth of penetration of the contact element into the wood-fiber insulation board.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0038] The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

[0039] FIG. 1 is a large-scale schematic side view of an apparatus according to the invention for determining the strength of wood-fiber insulation board;

[0040] FIG. 2 is a view like FIG. 1 of a variation on the system of FIG. 1;

[0041] FIG. 3 is a graph comparing pressure as a function of compressive displacement; and

[0042] FIG. 4 is a schematic small-scale top view of a portion of an installation for manufacturing wood-fiber insulation board.

SPECIFIC DESCRIPTION OF THE INVENTION

[0043] FIG. 1 shows the apparatus 1 for determining the strength of wood-fiber insulation board 2 that 2 is transported on a conveyor 6, here for example a conveyor belt 15. The view shows part of an installation for manufacturing wood-fiber insulation boards moving in a horizontal travel direction F downstream of a continuous press 18 (FIG. 4) for the raw material scattered onto a molding belt and upstream of a sawing device 19 (FIG. 4) for cutting the final dimensions of the finished wood-fiber insulation boards. For the sake of clarity, the upstream press 18 and the downstream cutting station 19 are part of a basic manufacturing process for wood-fiber insulation boards as described in U.S. Pat. No. 8,394,303 that is herewith incorporated reference. The schematic top view of FIG. 4 shows that the continuous press 18 is followed by the apparatus 1 for determining the compressive strength, after which the wood-fiber insulation board is later broken down into individual rectangular boards by the diagonal saw 19. The apparatus 1 for determining the compressive strength can be moved transverse horizontally transverse to the direction F over the width of the wood-fiber insulation board so that measurements can be taken in different regions spaced along the width of the workpiece board 2.

[0044] The apparatus 1 itself is fastened to a stationary mount 7 above the conveyor belt 15 and above the strand forming the wood-fiber insulation board 2 that is coming out of the continuous press 18 and can also be optionally moved thereon over the width of the wood fiber board 2. In this embodiment, it comprisesas the operative actuator 8at least one pneumatic double-acting cylinder 9 whose front and rear compartments are supplied with compressed air via pressure ports 14 from a reversible pump 20. A piston rod 16 of this pneumatic double-acting cylinder 9 can vertically move and downwardly press a contact element 3 against the wood-fiber insulation board 2. A width of about 100 to 250 mm is recommended for the contact element, although this is not binding for the invention. In the embodiment according to FIG. 1, the contact element 3 is a rotatable disk 4 that bears downward on the wood-fiber insulation board 2 and can be pressed downward by the actuator 8. It is shown in the position in which the wheel 4 is just slightly touching the wood-fiber board (for example, only due by the force 9 of gravity caused by the weight of the piston rod and wheel) and thus establishes the reference value, i.e. the zero position, for measurement of the depth of penetration into the wood-fiber insulation board during compression.

[0045] A displacement sensor 11 and a force sensor 10 are connected to the pneumatic double-acting cylinder 9. Data lines 13 go from these two measuring devices to a central processor 12. The measurement process itself is described in connection with FIG. 3.

[0046] FIG. 2 shows a slight variant of FIG. 1. Here, only one other contact element 3 is provided in the form of a skid 5 so that it therefore has a wider and defined contact surface 17.

[0047] Finally, FIG. 3 explains the measurement process for determining the compressive strength of the wood-fiber insulation board. According to standard EN 826, the pressure value for producing 10% relative deformation is set as the strength value. In the pressure-compressive displacement diagram of FIG. 3, curve A shows that the pressure behaves progressively at first in relation to the compressive displacement s, running approximately linear for a bit, and finally dropping off degressively. The boundaries of the linear area are shown in FIG. 3 by the markings L1 and L2. If one takes the value of a 10% relative deformation of the wood fiber board thickness s(10%) as prescribed by EN 826, then it becomes evident that the pressure associated therewith (shown by a dot) is lower than that which results from the extension of the linearized curve B. According to EN 826, however, the pressure value that is shown above the dot by a cross in the figure is the one that must be determined.

[0048] According to the invention, it was recognized that, in order to determine the linearized curve B arithmetically, the wood-fiber insulation board 2 need only be compressed within the range in which the wood-fiber insulation board behaves elastically. What is needed is the gradient in the area between points L1 and L2. To this end, however, it is sufficient to compress the wood-fiber insulation board preferably 1.5 to 3%, but at least in the compressive displacement range from 1 to 7% of the board thickness and to measure or calculate the force or pressure required for that. The second consideration is to no longer carry out the pressing procedure on a board specimen in the laboratory, but instead to determine the relevant data on the fly during production and, by virtue of the fact that compression is performed only within the elastic range of the wood-fiber insulation board, to not leave behind any markings or impressions that are subsequently visible.

[0049] The data, the compressive displacement, and the required force or required pressure that are preferably detected between 1.5 and 3% compressive displacement are forwarded to a central processor 12 that then extrapolates the point that is marked with a cross in FIG. 3. The compressive strength value of the wood-fiber insulation board can thus be determined in a quick and uncomplicated manner.