WO1998050783A1

WO1998050783A1 - Preparation of a mineral fibre product

Info

Publication number: WO1998050783A1
Application number: PCT/DK1998/000171
Authority: WO
Inventors: Jens RIIS
Original assignee: Rockwool International A/S
Priority date: 1997-05-02
Filing date: 1998-04-30
Publication date: 1998-11-12
Also published as: AU7330898A; HRP980233A2

Abstract

This invention relates to a contactless process for fast determination of one or more properties of a mineral fibre product such as binder content, oil content, silane content, tenside content, shot content and/or density in which process the mineral fibre product is irradiated, where corresponding values for radiation intensity and wavelength in the infrared range are determined for a part of the from said mineral fibre product reflected light, where the said corresponding values are compared to mutually corresponding values of radiation intensity and wavelength for reference samples of known properties, and where the properties of said mineral fibre product are calculated on the basis of the comparison.

Description

Preparation of a mineral fibre product

The present invention relates to a process for determining one or more properties of a mineral fibre product, whereby the mineral fibre product is irradiated, where values for radiation intensity and wavelength are determined for a part of the radiation emanating from the mineral fibre product, and where calculation of the said properties is made on the basis of the interrelated values .

It is often desirable to determine different properties of mineral fibre products, e.g. in connection with monitoring the quality, or in view of adjusting process parameters in the course of the preparation process.

The properties which it is particularly desirable to determine include binder content, oil content, surfactant content, water content, shot content, silane content and density.

Binder is added to mineral fibre products in a concentration typically between 0 and 30 weight-%, preferably less than 10 weight-%, in order to improve the binding between the fibres and make the products dimensionally stable.

Till now, the binder content in mineral fibre products has been determined by a determination of loss of incandescence, whereby the mineral fibre product is weighed, where all organic material is calcined at about 590 °C for at least 10 min, where the mineral fibre product after cooling is weighed again, and where the amount of organic material is determined as the weight difference between 1st and 2nd weighing.

The determination of loss of incandescence provides a measure for all organic material in the mineral fibre product, which m addition to binder also comprises optionally present oil. In order to determine the binder content it is therefore necessary either to know the oil content m advance, or to make a determination of the oil content before the determination of ignition loss.

Oil is added to mineral fibre products m amounts of up to about 2 weight-% m order to make the products water- repellent and in order to reduce dust release.

Determination of the oil content has previously been carried out by washing out the oil from a sample of the mineral fibre product using an organic solvent. The solvent and the washed out oil are collected m a container of known weight. Hereafter the solvent is evaporated, and the container is weighed again. The oil content is determined on the basis of the weight difference between the container and the weight of the samp1e .

Water is used m various stages of the production of mineral fibre products, e.g. for cooling, or as suspension agent for the binder.

The previous process for determining water content is based on weighing a sample of the mineral fibre products before and after drying m a drying oven. The drying takes place at about 105 °C for about 1 1/2 hours.

Shots are small lumps of mineral material which have not been converted into fibres in the spinning process. Shots can typically constitute up to about 30 weight-% of a mineral fibre product .

The determination of shot content has previously been performed by calcining a sample of the mineral fibre product for about 30 mm at about 590 °C, whereafter the sample is shaken and sieved through 2 sieves (0.250 mm and 0.063 mm mesh) for about 30 min. The shot content is determined for each of the two sieved off fractions as the weight of the fraction relative to the starting weight of the sample.

Till now, the density of mineral fibre products has been determined by weighing a sample of known volume and calculating the density as the weight of the sample divided by the volume of the sample.

The determination of the properties described has, as appears from above, hitherto been made by comparatively slow and cumbersome analysis methods.

In reality, the previous analysis methods are so slow that they are unfit for automated control and monitoring of the process, as the dead time, i.e. the time from taking out the sample till the analysis result is available and it is possible to interfere m the process, is too long. Furthermore, m the case of the particular processes it is necessary to handle the product during the preparation of the sample, which affects the product as well as encumbers the analysis.

Thus, it is generally desirable to lower the analysis times for determination of the above mentioned properties, and to avoid touching the product in connection with the analysis.

NO 162 889 discloses a process for monitoring binder characteristics of a fibre mat, whereby the amount of binder and/or the extent of hardening of the binder is/are determmable. The process comprises irradiating the fibre mat with IR-light at two different wavelengths and with an X-ray at one wavelength, and determining the trans ittance through the mat at the three different wavelengths. The three wavelengths are selected on the basis of knowledge of at which frequencies the binder and an added hardening indicator absorb/do not absorb, respectively, the radiation, and the properties investigated are calculated on the basis of the ratios between the transmittances at the three frequencies.

In practice, it has turned out to be difficult to obtain satisfactory determinations for the binder content in a mineral fibre web by a process of the above kind, since the transmittance through the mineral fibre web may be difficult to determine sufficiently accurately, unless the web is thin.

Furthermore it is inconvenient to add a separate substance in order to determine the amount of hardened binder.

Thus, it is desirable to provide a process whereby it is possible both to measure on different types of mineral fibre products, and where different properties of the mineral fibre products quickly can be determined.

This and other objects which will appear from the following are obtained by the process according to the invention which is characterized in that the interrelated values for radiation intensity and wavelength are determined for a part of the radiation reflected from the mineral fibre product, that the interrelated values are compared with interrelated values for radiation intensity and wavelength for reference samples of known properties, and that the properties are calculated on the basis of the comparison.

It has turned out that the radiation reflected from a mineral fibre product comprises wavelength ranges within which the interrelated values for radiation intensity and wavelength are characteristic as regards the product properties investigated.

Part of the radiation sent towards the mineral fibre product is absorbed as kinetic energy m the bonds between the atoms and thereby causes the individual atoms to be moved relative to one another. The kind of the individual atoms, inter-bonding and position, greatly influence which frequencies the substance absorbs the radiation. Furthermore, the extent of absorption is a function of the amount of the particular substance.

By determining interrelated values for radiation intensity and wavelength of the radiation reflected from the mineral fibre product, a relative measure for the properties is obtained.

The interrelated values determined for radiation intensity and wavelength can hereafter be compared with interrelated values for radiation intensity and wavelength for reference samples of known properties, and the properties of the sample can be calculated. Such a comparison is preferably made by means of a computer. Thus, a number of different properties can be calculated depending on with which reference data the computer is calibrated.

In practice, the computer is calibrated m that reference samples of known properties are irradiated, and interrelated values for radiation intensity and wavelength for the reflected radiation are determined. The known values for the properties are stored together with the interrelated values for radiation intensity and wavelength for each individual reference sample. As a rule, it applies that the larger the number of reference samples used for the calibration, the better the calibration. In practice, typically 20-100 different reference samples are used for each property for which it is desired to calibrate.

It is preferred that each individual reference sample is subjected to more than one measurement or measurement is performed on several samples having substantially the same properties.

When having a such number of measurements of samples having the same or substantially the same properties, it has proven advantageous that these reference spectra are averaged before used m the calibration. In tnis way the calibration becomes more precise.

Furthermore, it applies that at the calibration reference samples should be used having properties evenly distributed over the entire interval within which it is subsequently desired to be able to determine the properties for an arbitrary mineral fibre product.

Finally, a calibration of background radiation bias is performed by measuring the reflection from an optically uniform standard, e.g. a ceramic tile of A1₂0₃. Hereby it is possible to correct for changes m the intensity and the composition of the radiation from the radiation source or the surroundings .

Preferably the reflection standard has a reflectance at the measured wavelengths equal to or slightly higher than the maximum reflectance of the product to be subject to the measurements m order to exploit the range of measurement optimally.

Furthermore, during calibration and/or measurement it is preferred to perform a baseline correction of the measured data, i.e. to displace or bias-adjust the data according to a reference point m terms of an reflectance intensity at a specific wavelength. It has proven advantageous to select a wavelength for such baseline correction at which wavelength there is little or preferably substantially no change in reflectance as a function of change in the product properties. When determining the properties of a mineral fiber product it has proven particularly advantageous to perform the baseline correction at about 4150 cm^'1.

The calculation of a property on the basis of the comparison of the interrelated values determined for radiation intensity and wavelength with the reference values can by the computer be made in a manner known per se, e.g. by linear interpolation, partial least-square method, multiple regression analysis, principal component analysis, or other known mathematical method within the art of spectroscopy or regression analysis. In order to increase the accuracy of determination for a given property, it is expedient that the comparison preferably is made for radiation intensities at the wavelengths at which the differences in radiation intensity as function of the property at issue are particularly marked. Such preferred wavelengths and/or wavelength ranges can be found by mathematical methods or by visual determination.

It is a great advantage of the process according to the invention that the properties of the mineral fibre product can be determined quantitatively with great accuracy. Furthermore it is a great advantage that several properties can be determined quantitatively from the same set of data.

As a consequence of the process according to the invention being based on measuring the radiation reflected from the mineral fibre product, the properties of mineral fibre products of different embodiment, dimensions and/or physical nature can be determined. Thus, it is not decisive which form, thickness or density the product has. Consequently, the process may successfully be used on both very porous and very compact products. Further, it has surprisingly turned out that there are no particular requirements as to the uniformity of the surface from which the reflection is measureα.

A preferred wavelength interval according to the invention comprises the infrared range from 1250 nm to 8000 nm (8000 cm^"1 - 1250 cm^"1) . The range from 1250 to 3700 nm (8000 cm^-1 - 2700 cm^-1) is particularly preferred.

The process according to the invention is particularly suited for determining the binder content m mineral fibre products. If the binder comprises OH-groups, as e.g. m the frequently used phenol formaldehyde resin, it is particularly preferred that the interrelated values determined for radiation intensity and wavelength comprise determinations at wavelengths in the range from 2410 nm to 3570 nm (4150 cm^"1 - 2800 cm^"1) . For other binder types it is preferred that the interrelated values determined for radiation intensity and wavelength comprise determinations at wavelengths m wavelength ranges within which the bonds characteristic for the binder exhibit absorption of radiation.

In practice however, it has surprisingly been found that the best calibration for determining the amount of phenol formaldehyde resin according to the invention is found m the range from 2410 nm to 2985 nm (4150 cm^"1 - 3350 cm^"1) . It is believed to at least partly be due to interference of other substances such as e.g. oil m the range from 2985 nm to 3570 nm (3350 cm^"1 - 2800 cm^"1) . Accordingly it is preferred to perform the measurement m the range from 2410 nm to 2985 nm (4150 cm^"1 - 3350 cm^-1) . The process according to the invention is further well- suited for determining the oil content in a mineral fibre product. By determining the oil content it is particularly preferred that the interrelated values determined for radiation intensity and wavelength comprise determinations at wavelengths in the range from 3225 nm to 3700 nm (3100 cm^"1 - 2700 cm^"1) and/or the range from 6450 nm to 7400 nm (1550 cm^"1 - 1350 cm^"1) .

By the process according to the invention it has also been found possible to determine the content of tensides in mineral fibre products.

It has surprisingly turned out that by the process according to the invention it is also possible to determine the content of shots in mineral fibre products in spite of these being constituted by inorganic material .

When determining shot content, the interrelated values measured for radiation intensity and wavelength preferably comprise determinations at wavelengths in the wavelength range from 1250 nm to 2850 nm (8000 cm^"1 - 3500 cm^"1) .

In the same way and within the same range as stated above it has by the process according to the invention turned out to be possible also to determine the content of silane in mineral fibre products.

Furthermore, it has surprisingly turned out to be possible to determine the density using the process according to the invention. When determining density, the interrelated values determined for radiation intensity and wavelength preferably comprise determinations at wavelengths within the range from 1250 nm to 2850 nm (8000 cm^"1 - 3500 cm^"1) . Other properties, e.g. the water content, the content of clay, Al(OH)₃ and/or Si0₂, of a mineral fibre product can be determined by comparing interrelated values for radiation intensity and wavelength with reference values for mineral fibre products where the properties investigated are known.

By measuring the radiation intensity of the reflected light over a larger wavelength interval it has turned out to be possible to determine more than one property on the basis of one and the same measured data. In order to obtain determination of multiple properties, the only requirement is that appropriate calibration is carried out in respect of each property. Calibration samples can be used for calibrating for more than one property, e.g. the reflection spectrum of one sample can be correlated with both the binder content, density, shot content and so forth for the sample.

Thus, by a particularly preferred embodiment of the process according to the invention it is possible to determine two or more of the properties stated in the introduction on the basis of the same set of interrelated values for radiation intensity and wavelength. It is particularly preferred to determine both binder content and shot content from values which preferably comprise determinations at wavelengths in the wavelength range from 1250 nm to 3570 nm (8000 cm^"1 - 2800 cm^"1) .

In view of the capacity of the measuring equipment or the speed of the calculation of the properties, the number of determinations for the interrelated values determined for radiation intensity and wavelength can be limited to a few characteristic wavelengths.

The irradiation of the mineral fibre product can take place using various types of radiation sources. Preferred radiation sources for use according to the invention include preferably wide-spectrum light sources, such as incandescent lamps, halogen lamps, Nernst filaments, globars (SiC) , etc. The radiation source is preferab_y directed directly towards the product, e.g. by means of a reflector. The radiation emitted from the radiation source must comprise the wavelengths for which it _s desired to determine the interrelated values for radiation intensity and wavelength. In connection with the present invention it is particularly preferred to use a halogen lamp as radiation source.

It has turned out that it is possible to obtain better measuring results if the light source is provided with direct voltage instead of alternating voltage. By using direct voltage it is possible to reduce the number of determinations necessary for obtaining a sufficiently good signal/noise signal, i.e. reducing the number of current wave-periods for which the measurements otherwise must be eaned. Accordingly the measuring time can be decreased considerably and the determination of the desired values relating to the relevant properties of tne mineral fibre product is facilitated as well as quickened.

The light source preferably has a brightness of the same order of magnitude as a 200-300 w halogen lamp. One or more independent light sources can be used.

For determining the radiation reflected from the mineral fibre product, various types of measuring equipment can be used. Basically, the measuring equipment comprises a wavelength selector enabling the selection of a comparatively narrow wavelength range, and a detector capable of intercepting the radiation intensity m the selected range and retransmitting it m an expedient form, preferably as an electric signal.

As wavelength selector, any kind of useful wavelength selector can be employed, as e.g. describeα m "Fundamentals of analytical chemistry", 4th edition, D.A. Skoog et al, CBS College Publishing, 1986, including interference filters or prisms.

As detector, any kind of useful detector can be employed e.g., as also described m the above book, including thermocouples, bolometers or pyroelectπc cells.

The measuring apparatus may e.g. comprise an interferometer, as described m Modern Spectroscopy 2. ed., J. Michael Hollas, Wiley 1992. As detector m connection with interferometers, as a rule termocouples are used. The voltage signals intercepted from the detector are retransmitted to a computer m which the mterferogram received can be further processed. In the case of interferometers, the light is measured m the length domain rather than m the frequency domain. Consequently, the mterferogram received is usually Fourier transformed into a spectrum m the frequency domain. The method is thus also designated FTIR-spectroscopy (Fourier Transform Infra Red Spectroscopy) .

Measurement may be performed at almost any temperature of the product. However, as temperature fluctuations induce bias to the measurements, it is preferred to perform the measurements at a point where the product has a relatively uniform temperature profile over time.

According to a preferred embodiment according to the invention the product is thermostated at the point of measurement. This may be performed using either heating or cooling. Preferably the product is chilled by blowing or sucking ambient air through the product. By thermostating the product even more reliable determinations of the product properties may be performed.

According to another preferred embodiment of the invention the bias induced by temperature fluctuations is eliminated or limited electronically by measuring the temperature at the point of measurement of wavelength and intensity of reflected radiation and adjusting the measured values and/or the calculated properties according to the measured temperature. Accordingly more reliable determinations of the product properties may be obtained.

It is particularly preferred to perform the measurements at room temperature, e.g. around 15-35 °C, more preferably around 18-30 °C and even more preferably around 20-25 °C. By performing the measurements at room temperature, it is possible to use ambient air for thermostating the product thus facilitating the thermostating process and making it more cost efficient.

Measuring can be performed at several different points on the product, e.g. on the top, bottom, side and/or end surface/surfaces. In a preferred embodiment of the process according to the invention the reflected radiation is measured from the side surface of the mineral fibre product.

In another preferred embodiment of the process according to the invention the reflected radiation is collected from a larger area by means of a convex lens before it is detected.

In a further preferred embodiment of the process according to the invention measuring is performed in several different places of the same product. Hereby it is possible to determine differences in properties in different places of the product. The measurements can be performed in different places by using one or more measuring apparatus, by moving one apparatus in relation to the product or vice versa, or by using movable mirrors or the like.

It has surprisingly turned out that it is possible to obtain a measure for the dominating fibre orientation in a mineral fibre product by determining differences in the interrelated values for radiation intensity and wavelength for light reflected in different directions from one area of the product. The fibre orientation in a mineral fibre product is of great importance to the insulating capacity, since the fibre material insulates better crosswise of the fibre orientation than longitudinally thereto. Thus, it is a further preferred embodiment of the process according to the invention to determine interrelated values for radiation intensity and wavelength of the light which is reflected from one area of the mineral fibre product in two or more directions.

The process according to the invention has further turned out to be useful for determining properties of mineral fibre products in a continuous production process where the product is moving during the determination of the interrelated values for radiation intensity and wavelength.

Based on knowledge of the embodiment, speed and direction of movement of the mineral fibre product in relation the measuring equipment and the time for determining the individual properties of the mineral fibre product, it is possible to calculate differences in properties in different places of the product. It is also possible by means of several measuring apparatus positioned in different places on a production line for mineral fibre products to calculate differences in properties between the products at different stages of the process. Hereby the efficiency of e.g. water evaporation, compression or binder addition can be currently monitored.

It is a particular advantage of the process according to the invention that the determination of the properties is so rapid that the values for the particular properties can be used for adjusting process parameters in connection with the production of the mineral fibre product. Determination of the binder content in a mineral fibre web by the process according to the invention can e.g. be used for automatic adjustment of the addition of binder.

In particular, the advantages of the invention are obtained by determining properties of mineral fibre products which are prepared from man-made mineral fibres, e.g. glass, rock and/or slag fibres, such as those used in plates, sheets, pipes and differently shaped products for thermal insulation, fire-retardant purposes, noise dampening or noise regulation, or for fibre reinforcement of cement and plastic materials or other materials, such as filler, or as growth medium for plants.

The mineral fibre products according to the invention are preferably non-woven.

The invention also relates to an apparatus for carrying out the various embodiments of the process according to the invention and comprising appropriate means for performing the individual steps of the embodiments as disclosed above. Accordingly, the invention relates to an apparatus for determining one or more properties of a mineral fibre product, comprising means for irradiating a mineral fibre product, means for determining interrelated values for radiation intensity and wavelength for a part of the radiation emanating from the mineral fibre product, and means for calculating said properties on the basis of the interrelated values, characterized in that the means for determining the interrelated values for radiation intensity and wavelength are situated so as to detect at least a part of the radiation reflected from the mineral fibre product and that the means for calculating the properties comprise reference data indicative of interrelated values for radiation intensity and wavelength for reference samples of known properties and a processor for calculating the properties of the mineral fibre product by comparing the detected interrelated values for radiation intensity and wavelength for a part of the radiation emanating from the mineral fibre product with the said reference data.

Furthermore the invention relates to the use of the apparatus according to the invention for determining one or more properties of a mineral fibre product.

In the following the invention is described in more detail, reference being made to the drawing in which

Fig. 1 illustrates a schematic measuring set-up for measuring reflected IR-radiation.

Fig. 2 illustrates a schematic measuring apparatus with convex lens.

fig. 3 illustrates a schematic measuring set-up for measuring on 2 surfaces of the mineral fibre product. Fig. 4 illustrates a schematic measuring set-up for measuring light emanating in two directions from the same point.

Fig. 1 shows a top view of a mineral fibre product 1 and a cross-section of an IR-measuring apparatus 2. The IR- measuring apparatus comprises a monochromator 3 and a detector 4 which records radiation intensities at different wavelengths of the light reflected from the side surface of the mineral fibre product, as indicated by two dotted lines. The values measured are retransmitted to a computer, not shown. The incident radiation on the mineral fibre product is indicated as a light cone by two dotted lines, and comes from a halogen lamp 5 being supplied with direct voltage from a direct voltage source 6.

Fig. 2 shows a cross-section of a mineral fibre product 1 and an IR-measuring apparatus 2, which by means of a convex lens 7 intercepts the radiation from the entire thickness of the mineral fibre product, as indicated by dotted lines. The incident radiation on the mineral fibre product comes from a wide-spectrum light source, not shown.

Fig. 3 shows a cross-section of a mineral fibre product 1 and an IR-measuring apparatus 2, which via an inclined, rotatable mirror 8 and the stationary, inclined mirrors 9 is capable of intercepting the light from both the bottom and the top surface of the mineral fibre product. The paths of the reflected radiation are indicated by dotted lines. The incident radiation on the mineral fibre product comes from a wide-spectrum light source, not shown.

Fig. 4 shows a measuring set-up for measuring radiation emanating from two different directions from a point on a mineral fibre product 1. The IR-measuring apparatus 2 intercepts the radiation via the inclined, rotatable mirror 10 and the stationary, inclined mirrors 11. The path of the reflected radiation is indicated by dotted lines. The incident radiation on the mineral fibre product comes from a wide-spectrum radiation source, not shown.

In the following the invention is described in more detail by way of examples.

Example 1:

This example describes a measuring set-up for carrying out the process according to the invention in a production of mineral fibre products.

For determining the properties of a moving mineral fibre web on a conveyor band, a commercially available interferometer is positioned at a distance of about 50 cm from the place on the conveyor band where the mineral fibre web will pass. The apparatus is positioned in such a way that the apparatus will be able to measure reflected light from one of the side surfaces of the web. A strong light source in the form of a 250 w halogen lamp connected to a direct voltage source is positioned at a distance of about 40 cm from the place on the conveyor band where the mineral fibre web will pass, and in such a way that the area of the side surface of the mineral fibre web from which reflected radiation is to be intercepted by the IR-measuring apparatus is irradiated.

The IR-measuring apparatus is provided with a convex lens capable of collecting the radiation emitted in the entire height of the mineral fibre web prior to being intercepted by the apparatus . The IR-measuring apparatus is coupled to a computer which by means of a program is capable of collecting and processing the IR-data measured. The measuring apparatus is connected to the current and heated for about 4 hours before it is calibrated or used for measuring.

To compensate for temperature variations in the mineral fibre web, a pyrometer is positioned at a suitable distance from the place on the conveyor, where the mineral fibre web pass. The pyrometer is positioned in such a way that the pyrometer will be able to measure the radiated heat (i.e. the temperature) from the area of the mineral fibre web, in which the IR-measurement takes place .

Example 2:

This example is substantially identical with subject matter of example 1 except for the compensation for temperature variations in the mineral fibre web is performed by means of a suction and/or blowing device placed in the vicinity of, but not in, the area of the mineral fibre web in which the IR-measurement takes place. The suction and/or blowing device is placed so that an optionally thermostated and/or temperature controlled airflow induced by the device will pass through the mineral fibre web, thus stabilizing the temperature of the web, at the place where the IR- measurement takes place.

Example 3:

This example describes a method of calibrating the measuring equipment for carrying out an embodiment of the process according to the invention. The background light is determined by positioning a ceramic tile (A1₂0₃) in the place where the mineral fibre web is irradiated and measured 50 times. The radiation intensity is calculated by averaging, and stored in the computer.

Subsequently, each reference sample is alternately positioned in the place where the mineral fibre web is to be irradiated and measured, whereafter interrelated values for radiation intensity and wavelength for the reference sample are measured and stored. After the measuring, the value for the characteristic property of the reference sample is entered, and the value is stored in the computer together with the interrelated values determined for radiation intensity and wavelength.

The temperature of the sample is optionally measured and/or controlled, e.g. as indicated in the above example 1 or 2, and, if measured, the temperature of the sample is stored in the computer together with the interrelated values determined for radiation intensity and wavelength. Preferably the measured samples has a common and/or at least a known temperature.

For each reference sample the wavelength range from 1250 to 3570 nm (8000 cm^"1 - 2800 cm^"1) is measured with a measurement for each 32nd wave number, and the entire range is measured 20 times, whereafter the computer averages the 20 measuring series in order to equalize random noise.

For the calibration for determining binder content, 30 reference samples are used having differing content of binder in the range from 1.0 weight-% to 5.0 weight-%. For the calibration for determining shot content, 30 reference samples are used having differing content of shots in the range from 20 weight-% to 40 weight-%.

Example 4 :

This example describes an embodiment of the process according to the invention in which a measuring set-up as described in example 1 is used, and for which measuring set-up a calibration is carried out for binder and shot content as described in example 2.

A mineral fibre web having a width of 190 cm, a thickness of 35 cm and moving at a speed of 15 m/min passes through a measuring zone as described in example 1, where the web is illuminated by a halogen lamp, and where reflected IR- light is intercepted and recorded by an IR-measuring apparatus. The temperature of the web is preferably continuously monitored, and optionally controlled and/or measured as indicated in the examples 1 or 2.

The measuring apparatus measures continuously in the wavelength range from 1250 to 3570 nm (8000 cm^-1 - 2800 cm^"1) with a measurement for each 32nd wave number, and the entire range is measured 20 times, whereafter the computer averages the 20 measuring series in order to equalize random noise. The averaged measuring series for the interrelated values for radiation intensity and wave- length and the optionally measured temperature are compared by the computer with interrelated values for radiation intensity and wavelength and the optionally measured temperature for reference samples which are known from the calibrations as carried out in accordance with example 3. Based on the calibrations/ the computer calculates the binder content on the basis of the calibration for binder content, and the shot content is calculated on the basis of the calibration for shot

21 content. The results are stored in a log file and printed on a screen.

The determination of binder content and shot content is carried out continuously, and the results are printed each 10th second, whereby the properties of the mineral fibre web can be monitored. The computer is further provided with a device which gives off a signal if the values determined deviate by more than 0.2 percentage point from a pre-entered set point.

The calibration of the measuring apparatus is checked approx. each week with a reference sample, and post- calibration is performed, if required, as described in example 3.

The background light is determined, and postcalibration is performed for any changes therein approx. each 4th hour by measuring on a ceramic tile (Al₂0₃) as described in example 3.

Example 5.

This example relates to the determination accuracy for the binder content as measured by the process according to the invention compared to as measured by the prior art method.

A mineral fibre product comprising a known binder content of 3.83 weight-% and no further organic matter was split into a number of samples.

At random half of the samples was chosen for analysis by the prior art method involving a determination of loss of incandescence, whereby the mineral fibre samples was weighed, where all organic material was calcined at about 590 °C for around 10 min, where the mineral fibre product after cooling was weighed again, and where the amount of binder was determined as the weight difference between 1st and 2nd weighing. The hole process taking around 45- 60 minutes.

The binder content was determined by the prior art method as 3.83 +/- 0.26 weight-%.

The remaining samples was measured using a setup as illustrated above and calibrated appropriately for determining the binder content.

It was found that by doing 1 measurement (1 scan of the wavelength range) of approximately 5 seconds duration on each sample the binder content was determined as 3.83 +/- 0.38 weight-%. By increasing the measurements to 7 for each sample (about 30 seconds) , the binder content was determined as 3.83 +/- 0.14 weight-%.

As can be seen from these results it is possible by the process according to the invention to determine a property of a mineral fibre product quantitatively and virtually instantaneously at the same or even higher accuracy as by the prior art method.

Example 6.

This example relates to the determination accuracy for total loss of incandescence as measured by the process according to the invention. A setup as disclosed in the previous examples and calibrated appropriately was employed.

A number of samples comprising a known amount of organic matter was measured a number of times by the process according to the invention. The time for each measurement was varied from 3 seconds to 39 seconds corresponding to from 5 to 100 scans of the wavelength range. The deviation of the determined values for loss of incandescence is disclosed in the table below:

Table 1

Claims

C l a i m s :

1. A process for determining one or more properties of a mineral fibre product, wherein the mineral fibre product is irradiated, where interrelated values for radiation intensity and wavelength are determined for a part of the radiation emanating from the mineral fibre product, and where calculation of the said properties is made on the basis of the interrelated values, c h a r a c t e r i z e d in that the interrelated values for radiation intensity and wavelength are determined for a part of the radiation reflected from the mineral fibre product, that the interrelated values are compared with interrelated values for radiation intensity and wavelength for reference samples of known properties, and that the properties are calculated on the basis of the comparison.

2. A process according to claim 1, c h a r a c t e r i z e d in that interrelated values for radiation intensity and wavelength are determined at wavelengths within the range from 1250 to 8000 nm.

3. A process according to claim 1, c h a r a c t e r i z e d in that interrelated values for radiation intensity and wavelength are determined at wavelengths within the range from 1250 nm to 3700 nm.

4. A process according to any of the preceding claims, c h a r a c t e r i z e d in that the binder content, the oil content or the tenside content is calculated.

5. A process according to any of the preceding claims c h a r a c t e r i z e d in that the shot content, the silane content or the density is calculated.

6. A process according to any of the preceding claims, c h a r a c t e r i z e d in that two or more properties are calculated on the basis of the same set of interrelated values for radiation intensity and wavelength.

7. A process according to any of the preceding claims, c h a r a c t e r i z e d in that the mineral fibre product is moving during the determination of the interrelated values for radiation intensity and wavelength.

8. A process according to any of the preceding claims, c h a r a c t e r i z e d in that the mineral fibre web is illuminated by a wide-spectrum light source, such as a halogen lamp.

9. A process according to any of the preceding claims, c h a r a c t e r i z e d in that the light source is supplied with a direct voltage.

10. A process according to any of the preceding claims, c h a r a c t e r i z e d in that interrelated values for radiation intensity and wavelength are determined for the radiation reflected from one area of the mineral fibre product in two or more directions.

11. A process according to claim 10, c h a r a c t e r - i z e d in that the dominating fibre orientation in the area is calculated.

12. Use of the value for a property calculated by the process according to any or the preceding claims for adjusting process parameters in connection with the production of mineral fibre products.

13. An apparatus for determining one or more properties of a mineral fibre product, comprising means for irradiating a mineral fibre product, means for determining interrelated values for radiation intensity and wavelength for a part of the radiation emanating from the mineral fibre product, and means for calculating said properties on the basis of the interrelated values, c h a r a c t e r i z e d in that the means for determining the interrelated values for radiation intensity and wavelength are situated so as to detect at least a part of the radiation reflected from the mineral fibre product and that the means for calculating the properties comprise reference data indicative of interrelated values for radiation intensity and wavelength for reference samples of known properties and a processor for calculating the properties of the mineral fibre product by comparing the detected interrelated values for radiation intensity and wavelength for a part of the radiation emanating from the mineral fibre product with the said reference data.

14. Use of the apparatus according to claim 13 for determining one or more properties of a mineral fibre product .