METHOD AND DEVICE FOR CUTTING PLASTIC MATERIAI.

The invention relates to a method for cutting plastic material, in particular semi-plastic cellular concrete, comprising of moving at least one wire reciprocally in its lengthwise direction, the longitudinal direction, and also moving the material transversely of the lengthwise direction of the at least one wire, the transversal direction.

The invention also relates to a device for cutting plastic material, in particular semi-plastic cellular concrete, comprising at least one wire and first means for moving the at least one wire reciprocally in its lengthwise direction, the longitudinal direction, and also second means for moving the material transversely of the lengthwise direction of the at least one wire, the transversal direction.

Devices are known for cutting semi-plastic cellular concrete, also referred to as gas concrete. This has been done since the 1950s by means of wires. Cutting wires moving in the lengthwise direction have been used since the 1970s. It was found here that the micrograins (1-100 μm) make their way more readily into the adjacent zone at the position of a moving wire. This implies a considerable reduction in the load on the wires and an improved accuracy of cutting. The bias of the wires can also be increased, this still further enhancing the cutting accuracy. In the mid-1980s cutting machines appeared for semi-plastic cellular concrete in which the cutting wires move at a much higher speed and frequency. This gives an even smoother cut surface, whereby it becomes possible to produce wallpaper-ready blocks, i.e. blocks which can be wallpapered directly without for instance being plastered. Cutting can also take place more quickly. Such a device is described in EP-A-O 280 350. The cut surfaces obtained with the present known devices and methods are however still insufficiently smooth and closed. They still exhibit a large number of (micro-) cracks, whereby they are susceptible to moisture, fungi and dirtying. As a result the chance of

so-called edge crumbling is moreover great, and thus cut and cured cellular concrete blocks generate a large amount of undesirable dust. Nor is it always possible to wallpaper or paint or coat the final blocks or building elements without pretreatment . The precision and reproducibility of the dimensions of the cut blocks or building elements no longer always comply with the current, increasingly strict requirements in respect of accuracy and speed of construction. The continuous accelerations and decelerations and transitions from static to dynamic friction between wires and material cause shocks and vibrations in the material as well as in the components of the device. It is of the greatest importance to minimize these, since wear, the risk of damage, breakage and crack formation thereby decrease. Particularly the resultant forces exerted by the wires on the material must be minimized.

In addition, current known machines cannot be readily modified to different desired sizes of blocks or objects for cutting.

There is therefore a need for an improved solution for cutting plastic material, in particular semi-plastic cellular concrete, with which compared to prior art devices and methods smoother and more closed cut surfaces can be obtained and it is possible to cut more precisely with less wear to components and a smaller chance of breakage of the cutting wires and the material. It must preferably be possible to switch in relatively simple manner to other sizes of cut blocks, building elements or objects. The object of the present invention is to provide such an improved solution.

The invention provides for this purpose a method and a device for cutting plastic material, in particular semi-plastic cellular concrete, comprising of moving at least one wire reciprocally in its lengthwise direction, the longitudinal direction, by means of first means, and also moving the material transversely of the lengthwise direction of the at least one wire, the transversal direction, by means of second means, characterized in that the or each wire is also moved reciprocally in transversal direction by means of third means, this such

that after the cutting a wire passes at least once more over points of a cut surface.

After the cutting the cut surfaces are thus further 'loosened' , compacted and filled, whereby a smooth and closed surface with a minimum number of (micro-) cracks can be formed. As stated, such surfaces are much less susceptible to moisture, fungi and dirtying, and can for instance be wallpapered or coated without pretreatment . More rapid and precise construction is moreover possible with thus cut blocks, the chance of edge crumbling is smaller, and thus cut and cured cellular concrete blocks will generate less dust.

A 'wire' is understood to mean any thin body, for instance a wire, cord, knife or other suitable cutting body, so not necessarily with a round cross-section. The wires (for cutting) moved in longitudinal direction and the wires (for further ''loosening' , compaction and filling) moved in transversal direction are preferably the same wires, which therefore then move reciprocally in both longitudinal and transversal directions . The first means and third means will then generally be formed integrally. This is not essential however. It is thus also possible for instance to have a first wire (for cutting) followed by a second wire (for further 'loosening' , compaction and filling) , or to have for instance a first wire (for cutting and for further 'loosening' , compaction and filling) followed by a second wire {for further 'loosening', compaction and filling) . A further third wire can optionally follow here, and so on. An additional advantage can also be that wires (for cutting, further 'loosening', compaction and filling) are loaded less because they repeatedly move more or less clear of the material, or at least really cut for only a part of the time. The wire or wires are preferably moved such that points of a wire describe an elliptical, preferably circular path. A circular path is mechanically the easiest to realize. With an elliptical form the ratio of the time 'spent' on cutting and the time 'spent' on further 'loosening' , compaction and filling can be varied and optimized. Other movements, wherein points of

a wire describe more complex Lissajous figures, can however also be imposed by varying amplitudes, frequencies and phases.

In preference n (n ≥ 2} groups of a (m ≥ 1) wires are moved with mutual phase differences, preferably always of 2π/n. This results in a reduction of the resultant forces exerted by the wires on the material, and less drive power is necessary. The reciprocating movements of groups of wires can herein also be in opposite direction to those of other groups. In the case of elliptical or circular movements half of the wires can for instance make a rotating movement in opposite direction to the movement of the other half. The momentary resultant forces exerted by the wires on the material will thus be much smaller than in the case of a synchronous and identical movement of the wires, also because the transitions from static to dynamic friction (and vice versa) between wires and material now always take place per group and are thereby spread over time. This results in fewer shocks and vibrations in the material and components, and in less load on the material and components, thereby reducing the risk of breakage and crack formation.

Wires are preferably tilted reciprocally in a plane in transversal direction by means of fourth means. The wires (for cutting) are thus loaded less because only a part of the material is being cut at any time and, with a sufficiently great tilting speed and tilting frequency, to an even greater extent a wire is temporarily always moving more or less clear of the material, or at least really cuts for only a part of the time. It thus also becomes possible to cut larger blocks or objects. Furthermore, at a sufficiently great tilting speed and tilting frequency, the number of times that a wire (for further ^loosening' , compaction and filling) passes over a point of a cut surface will also increase, this resulting in an even better further 'loosening', compaction and filling of the cut surfaces.

The device can also comprise synchronization means, for instance for moving both outer ends of a wire in synchronous and identical manner, or for moving groups

of wires synchronously with fixed mutual phase differences. By using for instance electric servomotors or hydraulic motors and coupling these electronically or hydraulically it becomes possible to drive the wires or groups of wires synchronously without mechanical couplings and gearboxes. A cutting machine can thus be readily modified to other sizes of blocks or objects for cutting. This will become more apparent in the following description of a preferred embodiment of the invention. The device can further comprise hydraulic means, such as a hydraulic motor or a hydraulic coupling. Using hydraulic drive means a much greater drive power per unit of volume can be achieved, so that the required, generally very great forces can be provided using relatively small drive means.

The invention will now be elucidated with reference to the drawings of a random exemplary embodiment, to which the invention is not limited. In the drawings: figure 1 shows a front view of a preferred embodiment of a device according to the invention; figure 2 shows three side views of the device of figure 1; and figure 3 shows an exemplary embodiment of the movement of wires according to the invention. A device 1 according to the invention comprises a fixed first frame 2 in which a second frame 3 is arranged tiltably. Arranged in the second frame 3 are an upper bridge 4a and a lower bridge 4b on which in turn an upper shaft 5a and a lower shaft 5b are respectively mounted. Shafts 5a, 5b are provided with eccentrics to which wires 6 are fastened. Tilting of second frame 3 takes place in the embodiment shown here by means of eccentrics 7, but can also take place for instance by means of hydraulic cylinders. Adjustment of the distance between shafts 5a, 5b and tensioning of wires 6 takes place in the embodiment shown here by means of hydraulic cylinders 8, although other known technical solutions are also available for this purpose. A semi-plastic piece of cellular concrete 9 for cutting can be guided through device 1 at a determined rate of speed v.

The essence of the invention is that a wire makes a transversal movement with a compacting and filling action. By causing the wires to move out of phase and/or in opposite directions the forces are distributed better in space and time. This results in a reduction of undesirable shocks and vibrations.

Wires 6 are divided into a number of groups, these groups being driven with phase differences distributed uniformly relative to each other. Each point of wires 6 makes a circular movement, although half the wires 6' make a circular movement in opposite direction to the movement of the other wires 6" . The momentary resultant forces exerted by wires 6 on material 9 will thus be minimal, and the shocks and vibrations in material 9 and the components of device 1 will be reduced to a minimum. Furthermore, less drive power is thus necessary on shafts 5a, 5b than in the case of in-phase driving.

By tilting all the wires only a part of material 9 is being cut at any time. The load on wires 6 hereby decreases. With a sufficiently great tilting speed and tilting frequency each wire 6 moreover moves clear of material 9 even more frequently. It thus becomes possible to cut a larger piece of material 9. And, with a sufficiently great tilting speed and tilting frequency, the number of times a wire 6 passes over a point of a cut surface will also increase, resulting in and even better ^loosening' , compaction and filling of the cut surfaces. If the wires are tilted, each point of a wire will of course make a composite movement relative to material 9 consisting of the rotating movement and the tilting movement.

Device 1 also comprises synchronization means for causing shafts 5a, 5b to rotate in synchronous and identical manner. Electric servomotors with exactly the same rotation speeds can for instance be used for this purpose, or hydraulic motors coupled electronically or hydraulically, whereby it becomes possible to drive the groups of wires 6 synchronously without mechanical couplings and gearboxes between the two shafts 5a, 5b. Device 1 can thus be readily modified to other sizes of blocks or objects for cutting by changing the distance between bridges 4a, 4b by means of hydraulic cylinders 8. With driving by means of hydraulic motors a much greater drive power per unit of volume can be achieved, so that the required great moments of force can be produced using relatively small drive means.