PROCESS FOR DETERMINING THE BASIS WEIGHT OF A LOW ATOMIC NUMBER MATERIAL IN A MIXTURE WITH A HIGHER ATOMIC NUMBER MATERIAL

Abstract: The invention relates to an apparatus and a process for determining the relative quantity of a low atomic number ma­ terial in a mixture of the material and a high atomic number ma­ terial. The apparatus comprises a first source (16) for directing a first beam of X rays into the mixture, a second source (20) for directing a second beam of X rays into the mixture, a first and a second detectors (34, 36) for detecting respectively the first and second beams in the absence of the mixture and for detect­ ing respectively the portion of the first and second beams transmitted through the mixture. The apparatus also com­ prises a computer (60) coupled to the first and second detec­ tors to determine, upon the detected beams, the relative quan­ tity of the low atomic number material. Application to the measurement of the concentration of binder material in fiber glass.

Description: BACKGROUND OF THE INVENTION The Field of The Invention The present invention relates to apparatus for measurinq the concentration of binder material in fiberglass. Description of the Prior Art Fiberglass insulation contains glass fibers which are mixed with binder material. The binder material is qenerally composed of hydrocarbon compounds in a water suspension, and the purpose of the binder, when dry is to hole the glass fibers together. In practice, it is often desirable to be able to determine the percentage of binder material in fiberglass. One technique for making such a determination is taught in U.S. Patent 4,363,968 titled "Method and Apparatus for Determining the Binder Content in a Fibrous Mat.* The patent teaches a system including an infrared source located to one side of the fiberglass mat for generating infrared radiation having two wave lengths. A detector is located opposite the source on the other side of the mat to receive the portions of the infrared signals which are transmitted through the mat. Based upon the strengths of the signals received by the detectors, the system determines the concentration of binder in the mat. We have found that systems of the type tauqht in the patent identified above are limited in their usefulness by the extent to which infrared radiation can penetrate fiberglass. It is sometimes desirable to be able to measure fiberglass or other materials which have a basis weight so great that the binder can not be measured by infrared means. Also, as fiberglass is cured, the chemical properties of the binder can change thereby affecting measurements by infrared-type systems. However, it is desirable to be able to measure the concentration of binder without errors due to the degree of cure. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of the preferred embodiment of the present invention shown in partial cross section. OBJECTS OF THE INVENTION An object of the present Invention is to provide a system and process for determining the concentration of binder in fiberglass without the introduction of errors due to the deqree of cure. Another object of the present invention is to provide a system and process for measuring a first material in a second material which has a relatively high basis weight. Further objects and advantages of the invention can be ascertained by reference to the specification and drawings herein which are by way of example only and not in limitation of the invention which is defined by the claims and equivalents thereto. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to t".e figure, the preferred embodiment includes a source housing 10 located to one side of a moving sheet of fiberglass 12. A detector housing 14 is located at the side of the sheet 12 opposite the source housing 10, and both housings 10 and 14 are constructed and arranged to be movable in synchronized fashion across the sheet 12 so that measurements can be made across the sheet. Conventional scanning systems are available to move the housings 10 and 14. The source housing 10 contains a 30 Kilo Volt, tungsten target Bremstralung x-ray source 16 and a gamna ray source 20. The x-ray source 16 generates a beam of x-rays 24, which are absorbed primarily by the silicon (which has a high atomic number relative to the binder) in the fiberglass. The gamma ray source 20 generates a beam of gamma rays 26, having an energy of 59.8 thousand electron volts (KeV) which are absorbed by the silicon in the fiberglass and the binder, which is composed primarily of hyrocarbons having low atomic numbers relative to silicon. For example, the binder can include latex and ureaformaldehyde. The portion of the x-ray beam 24 which passes through the sheet 12 Is designated as beam 30, and the portion of the gamna ray beam 26 which passes through the sheet 12 is designated as 32. The detector housing 14 contains an x-ray detector 34 which is mounted to receive the beam 30, and a gamma ray detector 36 mounted to receive the beam 32. In practice, the detector 34 can be a xenonfilled Ion chamber so that x-rays received by the detector generate a small current in the ion chamber. The detector 36, in practice, can also be xenon-filled. The voltaqe from the detectors 34 and 36 are proportional to the strengths of the beams 30 and 32 received by the detectors. The detectors 34 and 36 are electrically coupled to amplifiers 40 and 42 which generate analog-type electrical signals proportional to the signals from the detectors. The amplifiers 40 and 42 are electrically coupled to voltage-to-frequency converters 44 and 46 which convert the analog signals from the amplifiers into digital signals to be transmitted over lines 50 and 52 to a computer 60. In operation, the system is calibrated before it is utilized to measure binder and fiberglass. The calibration procedure includes operating the system in the absence of the sheet 12 to determine the strengths of the beams 24 and 26 received by the detectors in the absence of the sheet. The signal from the first detector 34 is designated IXO and the signal from the second detector 36 is designated as Tao Thereafter, material is placed in the beams 24 and 26 to insure that the beams do not reach the detectors. The resulting signals from the detector are thus due to background radiation and electronic offset. The background signals are desiqnated as 1B1 and I32, respectively. Based on these values, the following eaualities can be establish end where I1 and I2 are the signals from the first and second detectors when the sheet is placed in the beam: EMI3.1 Therafter, a plurality of samples of fiberglass having different concentrations of binder are analyzed. This data is utilized in a con ventional curve-fitting computer proqram to determine the coefficients, A, B, C and D in the following equation WB s A + B f(R1) + CQ(R2)+Dh(R1, R2). Where WB equals the binder -basis weight, and A, B, C and D are constants determined-by the fitting of the data. The terms f and g are functions of R1 and R2 respectively and h is a function of R1 and R2. The functions f, g and h are chosen according to the particular material being studied. In practice we have found that for fiberglass the functions f and g can be the natural logarithm and h is zero, so that the formula is: WB = A + B ln (R1) + Cln (R2). After the constants A, B,C and Dhave been determined, the system can be operated to measure a continuous sheet of fiberglass moving horizontally as indicated in Figure 1. The computer continuously receives data from the detectors via lines 50 and 52 and determines the basis weight of the binder based on the equations above. In practice, we have found that the embodiment described herein is effective for measurinq the weight of binder in fiberqlass wherein the basis weight of the fiberglass and binder is greater than about 1000 grams per square meter up to about 12,000 grams per square meter. In one test of a fiberglass sheet having a weight of about 5,000 grams per square meter, we have found the constants to be as follows: A = - 400 q/m2 B = 3,000 g/m2 C = 35,000 g/m2 The present invention is applicable not only to measurement of binder in fiberglass but more generally to measurement of a low atomic number material, comprising one or more compounds, mixed with a hiqher atomic number material, comprising one ore more compounds. An example is the measurement of water (which contains relatively low atomic number hydrogen and oxygen) in a mineral base (having relatively high atomic number constituents) as is sometimes used for ceiling tile. tn the case of fiberglass, as another example, the x-ray beam is attenuated by the high atomic number silicon fn the fiberglass, and the gamna ray beam is attenuated by the relatively low atomic number binder as well as by the silicon. We have used our system to measure fiberglass having a binder of phenol and urea-formaldehyde, as an example. It should be understood that it is not necessary that one beam be x-ray and the other gamma ray, but in fact both beams can be either x-ray or gamna ray. However, it is necessary that one beam be of higher energy than the other. In the practice of this invention x-rays and gamma rays have very similar properties. Therefore, the terms "x-ray" and gamma ray" are used interchangeably and "x-ray" means either *x-ray" or gamma ray."

Claims: CLAIMS 1. A process for determining the relative quantity of low atomic number first material mixed with a higher atomic number second material, the process comprising: a) directing a first beam of x-rays and a second beam of x-rays having a higher energy than the first beam into the mixture; b) measuring the portions of the first and second beams transmitted through the mixture; c) measuring the first and second beams in the absence of the mixture; and d) determininq the relative quantity of the low atomic number first material based upon the first and second beams in the absence of the mixture and the measured portions of the first and second beams transmitted through the mixture. 2. A process according to claim 1 wherein the first material consists of one compound. 3. A process according to claim.2 wherein the first material is water and the second material is ceiling tile mineral base. 4. A process accordinq to claim 1 wherein the first material Is a plurality of compounds. 5. A process according to claim 4 wherein the first material is a mixture of phenol and urea-formaldehyde and the second material is fiberglass. 6. A process according to claim 1 wherein the low atomic number material is binder and the high atomic number material is silicon. 7. A process according to claim 6 wherein the first beam is a beam of x-rays and the second beam is a beam of gamma rays. 8. A system for determining the relative quantity of a low atomic number material in a mixture of the material and a high atomic number material, the system comprising: a) first source means for directing a first beam of x-rays into the mixture; b) second source means for directinq a second beam of x-rays into the mixture said second beam having a higher enerqy than the first beam; c) first detector means for detectinq the first beam in the absence of the mixture and for detecting the portion of thè first beam transmitted through the mixture; d) second detector means for detecting the second beam in the absence of the mixture and for detecting the portion of the second beam transmitted through the mixture; and e) computing means coupled to the first and second detector means to determine the relative quantity of the low atomic number material based upon the detected beams. 9. A system according to claim 8 wherein the first source means generates a beam of x-rays and the second source means qenerates a beam of gamma rays. 10. A system according to claim 9 wherein said x-ra,v source means is on one side of the mixture and the first detector is on the opposite side. 11. A system according to claim 9 wherein said gamma ray source means is on one side of the mixture and the second detector is on the opposite side. 12. A system according to claim 6 wherein the computing means is constructed and arranged to determine the relative quantity of the low atomic number material according to the following formula: WB = A + Bf(R1) + Cg(R2) + Dh(R1, R2) where f, g, and h are functions; WB = the basis weiqht of the low atomic number compound; A, B, C andDare constants; EMI7.1 13. A system accordinq to claim 12 wherein the computing means is constructed and arranged to determine the relative quantity of the low atomic number material accordinq to the following formula: WB = A + B In (R1) + Cln (R2)

Inventors: DAHLQUIST, JOHN, HEGLAND, PHILIP M.
Applicants: MEASUREX CORPORATION
Application year: 1984
Main classification: G01N23
IPC codes: G01N23, G01M11