When cutting webs of material, such as webs of paper, plastic (sheeting), laminates of paper, plastic, metal, etc, from a roll or in the form of sheets, with the use of various cutting systems, such as knives, pairs of knives, etc, dust particles are inevitably produced, which mostly consist of particulate fragments of material which are formed when cutting. These dust particles are invisible with the naked eye. This dust formation causes great problems in subsequent handling and working. The dust settles on the surface of the material and makes it more difficult, for instance, to print and causes a con- siderable decrease in quality. In other words, this for- mation of dust gives rise to a significant rate of rejec- tions. It has been found that the formation of dust in- creases when the cutting system is not properly set. This is the case in particular in cutting systems comprising a pair of knives, which in turn consists of a lower knife and an upper knife, which work on a web resting on a sup- port along which the knives are arranged. An erroneous setting of the knives results in a comparatively greater amount of the material being removed than in the case of a correct setting of the knives, which entails an in- crease of the formation of dust, thus making more dust settle on the surface. It would be desirable to minimise the formation of dust, thereby minimising the rate of material rejection.

The present invention solves the above-mentioned problem by means of a process in accordance with the pre-

amble to claim 1, said process having the features stated in claim 1. The problem is also solved by means of a de- vice in accordance with claim 3.

In the process according to the invention, dust formed when cutting is collected in a container, after which the dust content in the container is determined.

The method of determining the dust content in the con- tainer is not critical according to the invention, but any particle determining method may be used. However, a particularly preferred determining method is a photomet- ric method. According to this photometric method, light beams from a light source, for instance a laser, are allowed to hit the container which contains dust par- ticles, the light beams being reflected and made to hit a photo-electronic transducer to generate an electric meas- uring signal. This signal is subsequently fed to, for in- stance, a comparator or a microprocessor for comparison with a limit value and for further processing, respec- tively. Since this method is known to the one skilled in the field of particle measuring, the method will not be described in more detail. Furthermore, a great number of measuring devices for measuring particles are available on the market, and consequently the one skilled in the art can select the measuring device or devices which are suitable in the individual case.

Below, the invention will be described in more de- tail with reference to the accompanying drawing, in which the only Figure schematically shows an embodiment, se- lected by way of example, of the device according to the invention.

With reference to the Figure showing a preferred embodiment of the invention, a plurality of pairs of knives 1 are arranged, and in connection with each pair of knives a vacuum tube 2 is arranged, which is intended to suck in dust when cutting. The dust passes through a collection line 3 to a dust collection container 5.

Valves 4 are arranged for starting and stopping, respec-

tively, the supply of dust. In this connection, it should be noted that the embodiment shown in the drawing is ap- plicable to a system of cutting stations, the flow of dust being optionally started and stopped depending on the measurements which are to be made. Furthermore, it should be noted that measures (not shown) have been taken to remove dust from the container 5 after measuring. With reference once again to the Figure in the drawing, a pho- tometric measurement of the dust content in the container 5 is performed. A light beam source 6, for instance a conventional light emitting diode for generating laser light, is activated and emits beams towards the con- tainer 5, which are reflected to a photo-electronic transducer 7 to produce an electric signal S, which in turn is fed to a comparator to be compared with a limit value or alternatively to a microprocessor, which com- prises software for processing the electric signal. In this manner, the dust content in the container 5 can be registered and it is possible to obtain an indication whether the measured content exceeds a standard limit value. A suitable indicator is arranged to obtain a signal in a visual or auditory manner.

According to one embodiment of the device according to the invention, an air nozzle is arranged adjacent to the vacuum tube. Pressurised air is supplied by this nozzle to the cutting place to reduce the formation of turbulence and improve the absorption of dust. This em- bodiment is particularly advantageous when cutting webs moving at high speed.

According to the invention, it is possible to check and indicate individually the formation of dust at each pair of knives. This checking permits controlling and checking of each cutting operation in the process by means of an indication, for instance on a display con- nected to the microprocessor, of the amount of dust pro- duced by each pair of knives. A content exceeding the limit value immediately indicates that the cutting system

has to be adjusted. By setting the cutting system in a correct manner, a minimal acceptable degree of dust for- mation is obtained. In other words, by establishing the point of time for adjusting the cutting system it is pos- sible to minimise the degree of rejection. This is an im- portant improvement within the field.

Above, the invention has been described with refer- ence to a preferred embodiment, selected by way of ex- ample, but variations and modifications are possible within the scope of the invention. It goes without saying that other measuring methods for determining the dust particle content may be applied, which are based on other principles than photometry.