FI89751C - Method and apparatus for making a fiber mat - Google Patents

Description

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Method and apparatus for making a fiber mat

The invention relates to a method for producing a multilayer mineral fiber mat to control the quality of the mat by continuously measuring the width of the primary fiber mat with its fiber distribution.

Mineral wool products are produced e.g. said that the required raw material is melted in a furnace, the mineral melt is continuously extracted from the furnace through an outlet orifice and converted into fibers in a fibrating device, e.g. may consist of a plurality of rotating wheels from which the mineral melt is thrown to form fibers. The thus formed fibers are transported with an air stream from the fibrating device 15 and collected on a conveyor in the form of a so-called. primary mat consisting of a thin layer of fibers, which then, e.g. with the help of a shuttle conveyor, tile is folded into a secondary mat of the desired thickness. At some stage of the preparation, the fibers are added a suitable binder, e.g. a resin which is activated at a final stage of the fiber mat treatment e.g. with heat.

The fiber mat manufactured should, of course, exhibit possible variations in its structure, such as the web produced by weight per unit of length or length, the density of the mat and / or the surface weight. This is achieved, among other things. by constantly keeping the melt flow rate from the furnace outlet opening, by controlling the fibrillator and by regulating various parameters on the fiber treatment web following the fibrillator.

In regulating such a process, parameters are usually measured in the final stage of the process, i.e. parameters on the secondary mat and on the final production and uses such dossa measure the volume J '> to regulate different stages at the beginning of the process via one or more interconnected control devices. However, it can be of central importance in such a process to obtain measurement values 2 f '9 7 51 at a Sei early stage as possible of the process in order to be able to direct the corrective measures at the right place and as quickly as possible. Therefore, measurements should be made already on the thin primary fiber mat before this week to the secondary fiber mat.

Due to the thinness of the primary fiber mat, its unevenness and its Large velocity, it is problematic to carry out measurements on it to determine its properties.

In the F-laying document 77901, a method for making blankets is described by means of a fiber-bearing gas stream. The gas stream passes through an oscillating control channel for even distribution of the fibers on a receiving conveyor. The movement of the control channel with respect to d frequency, shape, amplitude, direction or at least some of these characteristics, the pd base is governed by measurements of the fiber mass per unit area. The intention is thus that the base of the measurement of the fiber mass per unit area regulates the distribution of the fibers to obtain a desired final product.

The actual measurement of the fiber mass per unit area is made in this FI lay-out document 77901 pd the finished blanket dd it comes out of the curing furnace with an absorption measurement of X-rays. The measurement results are then used to control the movement of the control channel via a coupled control device. The measurement is performed such that the radiation medium, US 241, performs a continuous pendulum motion (scanning) across the width of the blanket and the pads opposite the blanket detected absorbance values and their distribution are recorded. Here, therefore, a relatively complicated measurement procedure is used which requires an expensive apparatus and safety measures to protect the personnel from X-rays. In addition, the method is robust due to the pendulum movement of the radiation medium and the detector. U.S. Patent No. 3,987,660 discloses a method for determining the thermal conductivity of inorganic fiber insulation mats by measuring the transmission of visible light through such mats. The measurement is performed on a finished 3 o 7 oc in insulation mat so that the mat is guided between the control plates located at a given distance from each other. These control plates thus determine the exact thickness of the mat during the measurement. The control plates comprise on both sides of the mat of two separate parts so that a gap, where the mat's upper and lower surface is completely exposed, is raised. One or more light sources directed towards the gap are placed on the lower side of the carpet in each container. The container forms an opening at the gap so that the light is directed towards the mat in the gap. On the upper side of the carpet, directly above the light source, the specular transmission is detected, i.e. the amount of light that penetrates straight through the carpet. The obtained measurement values can then be used to regulate the amount of fiber measured to the mat via a feedback link. This is all about the measurement of the final product.

A measurement system according to US patent 3,987,660 is associated with certain disadvantages, in particular a lower sensitivity to variations in the structure of the carpet. Particularly problematic is the measurement method if the carpet is radically changed, e.g. exhibits heels, whereby the detector may become dazzled and the measurement sensitivity suffering. This method is suitable for measuring on relatively homogeneous secondary mats but not for measuring the primary mat; which is considerably thinner than the secondary mat and which moves at a significantly greater speed.

The known measurement method also has the disadvantage that it does not enable a forwarded control for correcting any detected errors in the carpet, only a reverse feedback, e.g. to vary the amount of fiber to the mat.

According to the invention, the fiber distribution of the thin primary fiber mat is continuously measured over the width of the fiber mat preferably with an optical measurement. The optical measurement is realized with a light source and a light detector located on opposite sides of the primary fiber path, such that the path 47 in i defined by the light detector's measurement sector does not cut the light source's emission surface, ie the measurement sector plane passes the light source's emission surface. By the measurement sector of the light detector is here meant a sector which opens from the detector towards the fiber web such that the entire width of the fiber web is included in the sector. It is of course advantageous that the sector extends across the fiber web but not necessary. It is also advantageous for the sector to extend somewhat beyond the width of the fiber web so that variations in the width of the fiber web can also be detected.

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The detector will thus measure the light scattered in the fiber web, the so-called. forward scattering and not the specular transmission as is the case in US patent 3,987,660.

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The fibers in the primary mat behave in principle like cylinder lenses which, among other things. means that the intensity of the scattered light varies with the scattering angle. However, the intensity maximum of the forward light scattering is reached at narrow scattering angles. The detector should therefore preferably be positioned such that the plane defined by the detector's measuring sector forms a small angle α, with the light source normal without the detector "looking" into the light source. The advantages of this method over the method where the specular transmission is measured are: - Light scattering correlates to the number of fibers in the fiber web.

- Southern dynamic range is obtained if one measures the scattered light than one measures the specular transmitted light.

- No problems with saturation of the detector.

The process according to the invention is fast enough to be used on a high-speed primary fiber mat, whereby the obtained measurement result can advantageously be used for forward and / or reverse process control. The forwarded regulation can be directed e.g. on in 5. r ~ 7 r ·· -> / x 'the speed of the receiver transistors existing after the shuttle conveyor, to control the number of layers folded into secondary fiber mats. The feedback again can be used to control the fiberized amount of mineral fiber raw material, the fiberization conditions, and to control the collection of the fibers into a primary fiber web.

In an advantageous embodiment, background illumination is used in the form of a further light cold on the same side of the path as the detector. Its function is to distinguish the measured heels in the web, respectively, and the impervious web, each of which is detected as total absence of light scattered through the web. When using backlight, a heel in the web was still sensed as the complete absence of light scattering through the web, whereas an impervious (thick) web, p.g.a. a certain reflection from its surface towards the detector, gives a positive result.

In the following, an advantageous embodiment of the invention is described with reference to the accompanying drawing, in which:

Fig. 1 is a principle sketch of a plant for making a fiber mat.

Fig. 2 is a principle sketch of the measuring device according to the invention.

In the principle sketch of Figure 1, the melt is taken from a melting furnace 1 and passed on to a conventional fibrating device 2 where the melt strikes spinning wheels and is further thrown due to the centrifugal force forming fiber.

From the fibrating device 2, the formed fibers are drawn under vacuum to a perforated collection surface which may be a drum or conveyor 3 and form a thin primary fiber mat. From the collection conveyor, the primary fiber feed is passed to a pendulum conveyor 4 which folds the thin 6 µ; 7 £ 1 of the primary fiber mat to a secondary fiber mat of the desired thickness on a belt conveyor 5, which can advantageously run perpendicular to the collection conveyor. From here, the secondary fiber web is passed via conveyors 6, 7 to a hardening furnace 5 8.

In addition, at a suitable site prior to curing, the fibers are added a suitable binder, e.g. a resin which, during the heat treatment in the oven, fixes the fibers to each other to form a mold-stable fiber mat of the desired density and thickness.

The conveyors between the conveying device 2 and the hardening furnace 8 are divided into two speed zones so that the conveyors 3 and 4 in the first speed zone are driven at one speed and the conveyors 5, 6 and 7 in the second speed zone are driven at a different speed. The speed of the conveyors in the first zone is considerably higher than in the second zone.

In the first velocity zone, the primary mat is formed and in the second secondary mat.

In the principle sketch of Fig. 2, the measuring device according to the invention is shown from the side. A first light source 9 is positioned beneath the primary fiber mat preferably at a location in the gap between two conveyors so that the light directly reaches the lower surface of the primary fiber mat. A detector 10, which is preferably a semiconductor camera, is positioned on the opposite side of the primary fiber mat so that the plane defined by the detector's measuring sector does not intersect the emission surface e of the light source 9. the first light source 9. The detector 10 will rarely measure it. forward scattering around the winkein α.

In order to guarantee a certain minimum light level for the detector 10 and to enable a distinction between sensed heels and impervious mat, a second light source 11 is placed on the same. side of the primary fiber mat as the detector.

The camera 10 measures the brightness at a number of points, for example 1024 distributed in a line over the entire width of the fiber web. Measurement data is then transmitted to a conventional microcomputer M in the form of 8 bit pixels at a speed of 120 Mbits / s. In the microcomputer, measurement data is preprocessed by a transputer processor card T, whose computing capacity amounts to about 1 million measuring points per second.

On the basis of the brightness measured in these 1024 points, the weight profile and variation profile of the primary fiber webs are calculated at certain intervals, for example 0.5s, 5s and 1 min. Further information on heels is obtained in the primary fiber web. The position of the primary fiber web 15 on the conveyor and its appearance can also be graphically displayed on the display of the microcomputer. Averages, deviation percentages, and average weights can be obtained at selectable levels, for example 5s, 1min, 10min, 10h, 10h.

This measurement data can then be used to control mineral fiber production with a back-coupled control device R1, i.e. regulating the melt flow rate from the furnace 1 and controlling the fibrating device 2, and controlling the collection 3 so that the quality of the primary fiber web is kept within a predetermined level.

Furthermore, the folding of the thin primary fiber web into the secondary fiber web can be controlled on the basis of these measurement data. This government takes place, for example. with a feed-in control device R2 30 which affects the frequency of the pendulum 4, i.e. the width of the secondary fiber web and the speed of the conveyors 5, 6, 7 i.e.

the thickness of the secondary fiber web.

Optimal detection is obtained when the distance between the fiber web 35 and the camera is greater than the width of the fiber web. The camera's measuring sector is preferably at most 30 °.

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This measurement method is suitable for measuring a primary fiber web, whose speed is less than about 250 m / min. However, the highest measurement accuracy is achieved for speeds less than about 150 m / min.

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A simpler system without extra transputer processor card T is also possible, whereby the microcomputer M performs all calculations. However, this system has a significantly poorer resolution as the microcomputer is too slow to simultaneously receive and process data at the transfer rate of the camera 10.

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Claims (8)

A method of manufacturing a mineral fiber mat comprising forming a multilayer fiber mat from a primary fiber mat, characterized in that the fiber distribution of the primary fiber over the width of the fiber is continuously measured and that one or more parameters affecting the properties of the fiber are controlled based on the measurement result. A method according to claim 1, characterized in that the assembly of the primary fiber mat into a secondary fiber mat of the desired thickness is adjusted on the basis of the fiber distribution measured by the forward-connected control device (R2). 15 Method according to Claim 1 or 2, characterized in that the production of the fibers and / or the assembly of the fibers to form the primary nonwoven is controlled on the basis of the fiber distribution measured by the feedback control device (R1). Method according to one of Claims 1 to 3, characterized in that the fiber distribution is measured optically from the width of the primary nonwoven. 25 A method according to claim 4, characterized in that the optical measurement is a measurement of the light intensity at several points divided by the width of the primary nonwoven. 30 Method according to Claim 5, characterized in that the intensity is measured on the light scattered from the fibers of the mat. Measuring apparatus for use in a method according to any one of claims 1 to 6, comprising a light source and a detector mounted on opposite sides of a non-fibrous V, "· Γ-ί t *" * w, and a processor for processing measurement data, characterized in that the first light source (9) and the detector (10) are mounted on opposite sides of the primary fiber mat so that the plane defined by the measuring sector of the illuminator (10) does not intersect the emission surface (e) of the light source (9). Measuring apparatus according to Claim 7, characterized in that the second light source (11) directed against the primary fiber mat 10 is mounted on the same side of the primary fiber mat as the detector (10).