Methods and apparatus for measuring and controlling curing of polymeric materials

Claims

What is claimed is:

1. A method for determining the degree of cure of a traveling carbonaceous polymeric material that has been formed from a plurality of chemical reactants and subjected to a curing process, the method comprising

directing into the traveling material a first infrared radiation from the group thereof adapted to selectively interact with molecular resonance vibrations at frequencies that are characteristic of respective terminal functional groups of atoms involved in reactions that take place in the material during the curing process, so that the material exhibits an absorptivity for the first infrared radiation that varies with the degree of cure of the polymeric material,

also directing into the traveling material a second infrared radiation that is either of the kind that does not exhibit substantial selective interaction with molecular resonance vibrations in the material or of the kind that is adapted to selectively interact with molecular resonance vibrations at a frequency that is characteristic of groups of atoms forming the backbones of the polymeric molecules in the material, so that the material exhibits a relatively constant absorptivity for the second infrared radiation as the curing process progresses,

receiving from the traveling material radiations that have interacted with the material,

producing from the received radiations first and second responses to the first and second radiations,

producing a third response that is indicative of the mass of the polymeric material interacting with the radiations and substantially independent of the variations in the absorptivity of the material for the first infrared radiation which occur as the curing process progresses, and

producing from the first, second and third responses an output response that is a function of the changes in the absorptivity of the material for the first infrared radiation, substantially independent of the amount of the polymeric material interacting with the radiations, and correlated with the degree of cure effected by the curing process.

2. A method as in claim 1 wherein the first infrared radiation is selected from the group adapted to selectively interact with molecular resonance vibrations at respective O--H, N--H and C.dbd.O vibration frequencies.

3. A method as in claim 1 or claim 2 which comprises directing into the traveling material a third infrared radiation of the other kind,

producing from the received radiations a further response to the third infrared radiation, and

producing the third response from the further response and the second response.

4. A method as in claim 3 wherein the third radiation is adapted to selectively interact with molecular resonance vibrations at a C--H stretch vibration frequency.

5. A method as in claim 3 wherein the first, second and third infrared radiations comprise near-infrared overtone bands, the first radiation having wavelengths in the vicinity of 1.50.mu., with either of the second and third radiations having wavelengths in the vicinity of either 1.35.mu. or 1.75.mu..

6. A method as in claim 3 which comprises forming a first mathematical function of the ratio of the first and third responses,

forming a second mathematical function of the ratio of the second and third responses, and

combining the first and second functions to produce the output response.

7. A method as in claim 6 wherein the first and second functions are substantially linear functions.

8. A method as in claim 7 wherein the ratio of the first and second functions is formed in order to produce the output response.

9. A method as in claim 6 wherein the first function is indicative of the number of terminal functional groups present in relation to the number of groups forming the backbones of the molecules, and

wherein the second function is indicative of the number of groups forming the backbones of the molecules that have interacted with the radiations.

10. A method as in claim 1 wherein the carbonaceous polymeric material is used to form a binder coating for the fibers in a mat of glass fibers,

wherein the curing process includes exposing the mat to elevated temperatures, and

wherein the exposed mat is passed through a measuring zone in which the radiations are directed into and received from the mat.

11. A method as in claim 10 which comprises controlling the exposure of the mat to the elevated temperatures in accordance with the output response.

12. A method as in claim 10 wherein the first infrared radiation comprises a near-infrared overtone band adapted to selectively interact with molecular resonance vibrations at one or both of the O--H and N--H vibration frequencies.

13. A method as in claim 12 wherein the first infrared radiation has wavelengths in the vicinity of 1.50.mu., and the second infrared radiation has wavelengths in the vicinity of 1.35.mu. or 1.75.mu..

14. A method as in claim 12 or claim 13 which comprises directing into the mat a third infrared radiation which is different from the second radiation and which lies in a band of wavelengths in the vicinity of 1.35.mu. or 1.75.mu.,

producing from the received radiations a further response to the third infrared radiation, and

producing the third response from the further response and the second response.

15. A method as in claim 14 which comprises forming a first mathematical function of the ratio of the first and third responses,

forming a second mathematical function of the ratio of the second and third responses, and

combining the first and second functions to produce the output response.

16. A method as in claim 15 wherein the first and second functions are substantially linear functions.

17. A method as in claim 16 wherein the ratio of the first and second functions is formed in order to produce the output response.

18. A method as in claim 15 which comprises

measuring the weight per unit area of the mat passing through the measuring zone, and controlling the rate of travel of the mat in accordance with the weight per unit area measurement,

controlling the rate of application of the binder coating in accordance with the second mathematical function, and

controlling the temperature of the mat during at least a portion of the curing process in accordance with the output response.

19. Apparatus for determining the degree of cure of a traveling carbonaceous polymeric material that has been formed from a plurality of chemical reactants and subjected to a curing process, comprising

means for directing into the traveling material a first infrared radiation from the group thereof adapted to selectively interact with molecular resonance vibrations at frequencies that are characteristic of respective terminal functional groups of atoms involved in reactions that take place in the material during the curing process, so that the material exhibits an absorptivity for the first infrared radiation that varies with the degree of cure of the polymeric material,

means for directing into the traveling material a second infrared radiation that is either of the kind that does not exhibit substantial selective interaction with molecular resonance vibrations in the material or of the kind that is adapted to selectively interact with molecular resonance vibrations at a frequency that is characteristic of groups of atoms forming the backbones of the polymeric molecules in the material, so that the material exhibits a relatively constant absorptivity for the second infrared radiation as the curing process progresses,

means for receiving from the traveling material radiations that have interacted with the material,

means for producing from the received radiations first and second responses to the first and second radiations,

means for producing a third response that is indicative of the mass of the polymeric material interacting with the radiations and substantially independent of the variations in the absorptivity of the material for the first infrared radiation which occur as the curing process progresses, and

means for producing from the first, second and third responses an output response that is a function of the changes in the absorptivity of the material for the first infrared radiation, substantially independent of the amount of the polymeric material interacting with the radiations, and correlated with the degree of cure effected by the curing process.

20. Apparatus as in claim 19 wherein the first infrared radiais selected from the group adapted to selectively interact with molecular resonance vibrations at respective O--H, N--H and C.dbd.O vibration frequencies.

21. Apparatus as in claim 19 or claim 20 which comprises means for directing into the traveling material a third infrared radiation of the other kind,

means for producing from the received radiations a further response to the third infrared radiation, and

means for producing the third response from the further response and the second response.

22. Apparatus as in claim 21 wherein the third radiation is adapted to selectively interact with molecular resonance vibrations at a C--H stretch vibration frequency.

23. Apparatus as in claim 21 wherein the first, second and third infrared radiations comprise near-infrared overtone bands, the first radiation having wavelengths in the vicinity of 1.50.mu., with either of the second and third radiations having wavelengths in the vicinity of either 1.35.mu. or 1.75.mu..

24. Apparatus as in claim 21 which comprises means for forming a first mathematical function of the ratio of the first and third responses,

means for forming a second mathematical function of the ratio of the second and third responses, and

means for combining the first and second functions to produce the output response.

25. Apparatus as in claim 24 wherein the first and second functions are substantially linear functions.

26. Apparatus as in claim 25 wherein the ratio of the first and second functions is formed in order to produce the output response.

27. Apparatus as in claim 24 wherein the first function is indicative of the number of terminal functional groups present in relation to the number of groups forming the backbones of the molecules, and

wherein the second function is indicative of the number of groups forming the backbones of the molecules that have interacted with the radiations.

28. Apparatus as in claim 19 wherein the carbonaceous polymeric material is used to form a binder coating for the fibers in a mat of glass fibers,

wherein the curing process includes exposing the mat to elevated temperatures, and

wherein the exposed mat is passed through a measuring zone in which the radiations are directed into and received from the mat.

29. Apparatus as in claim 28 which comprises means for controlling the exposure of the mat to the elevated temperatures in accordance with the output response.

30. Apparatus as in claim 28 wherein the first infrared radiation comprises a near-infrared overtone band adapted to selectively interact with molecular resonance vibrations at one or both of the O--H and N--H vibration frequencies.

31. Apparatus as in claim 30 wherein the first infrared radiation has wavelengths in the vicinity of 1.50.mu., and the second infrared radiation has wavelengths in the vicinity of 1.35.mu. or 1.75.mu..

32. Apparatus as in claim 30 or claim 31 which comprises means for directing into the mat a third infrared radiation which is different from the second radiation and which lies in a band of wavelengths in the vicinity of 1.35.mu. or 1.75.mu.,

means for producing from the received radiations a further response to the third infrared radiation, and

means for producing the third response from the further response and the second response.

33. Apparatus as in claim 32 which comprises means for forming a first mathematical function of the ratio of the first and third responses,

means for forming a second mathematical function of the ratio of the second and third responses, and

means for combining the first and second functions to produce the output response.

34. Apparatus as in claim 33 wherein the first and second functions are substantially linear functions.

35. Apparatus as in claim 34 comprising means for forming the ratio of the first and second functions in order to produce the output response.

36. Apparatus as in claim 33 which comprises

means for measuring the weight per unit area of the mat passing through the measuring zone, and means for controlling the rate of travel of the mat in accordance with the weight per unit area measurement,

means for controlling the rate of application of the binder coating in accordance with the second mathematical function,

and

means for controlling the temperature of the mat during at least a portion of the curing process in accordance with the output response.

37. A method as in claim 1 which comprises producing from the first and second responses a fourth response that is indicative of the mass of the polymeric material interacting with the radiations but which is dependent on the variations in the absorptivity of the material for the first infrared radiation that occur as the curing process progresses, and

utilizing the fourth response and the third response to produce the output response.

38. A method as in claim 37 wherein the fourth response is compensated for the radiation path length extension effects of radiation scattering.

39. A method as in claim 38 wherein the third response is similarly compensated for the effects of scattering.

40. A method as in claim 38 which comprises directing into the material further radiations having a mode of interaction with the material which is different from that of the infrared radiations,

detecting the further radiations that have interacted with the material to produce an additional response, and

using the additional response to effect the scattering compensation.

41. A method as in claim 40 wherein the further radiations are x rays or gamma rays.

42. A method as in claim 39 which comprises directing into the material further radiations having a mode of interaction with the material which is different from that of the infrared radiations,

detecting the further radiations that have interacted with the material to produce an additional response, and

using the additional response to effect scattering compensation of both the third and fourth responses.

43. A method as in claim 42 wherein the further radiations are x rays or gamma rays, and

the third and fourth responses are similarly compensated.

44. A method as in claim 10 which comprises producing from the first and second responses a fourth response that is indicative of the mass of the polymeric binder material interacting with the radiations but which is dependent on the variations in the absorptivity of the binder material for the first infrared radiation that occur as the curing proces progresses, and

utilizing the fourth response and the third response to produce the output response.

45. A method as in claim 44 wherein the fourth response is compensated for the radiation path length extension effects of radiation scattering by the binder-coated glass fibers.

46. A method as in claim 45 wherein the third response is similarly compensated for the effects of the scattering.

47. A method as in claim 46 which comprises directing x rays or gamma rays into the mat of glass fibers,

detecting the x rays or gamma rays that have interacted with the mat of glass fibers to produce an additional response, and

using the additional response to effect scattering compensation of both the third and fourth responses.

48. A method as in claim 47 wherein the additional response is additionally used to compensate the third and fourth responses for the infrared spectral effects of the glass in the fibers of the mat.

49. Apparatus as in claim 19 which comprises means for producing from the first and second responses a fourth response that is indicative of the mass of the polymeric material interacting with the radiations but which is dependent on the variations in the absorptivity of the material for the first infrared radiation that occur as the curing process progresses, and

means for utilizing the fourth response and the third response to produce the output response.

50. Apparatus as in claim 49 comprising means for compensating the fourth response for the radiation path length extension effects of radiation scattering.

51. Apparatus as in claim 50 comprising means for similarly compensating the third response for the effects of scattering.

52. Apparatus as in claim 50 which comprises means for directing into the material further radiations having a mode of interaction with the material which is different from that of the infrared radiations,

means for detecting the further radiations that have interacted with the material to produce an additional response, and

means for using the additional response to effect the scattering compensation.

53. Apparatus as in claim 52 wherein the further radiations are x rays or gamma rays.

54. Apparatus as in claim 51 which comprises means for directing into the material further radiations having a mode of interaction with the material which is different from that of the infrared radiations,

means for detecting the further radiations that have interacted with the material to produce an additional response, and

means for using the additional response to effect scattering compensation of both the third and fourth responses.

55. Apparatus as in claim 54 wherein the further radiations are x rays or gamma rays, and

the third and fourth responses are similarly compensated.

56. Apparatus as in claim 28 which comprises means for producing from the first and second responses a fourth response that is indicative of the mass of the polymeric binder material interacting with the radiations but which is dependent on the variations in the absorptivity of the binder material for the first infrared radiation that occur as the curing process progresses, and

means for utilizing the fourth response and the third response to produce the output response.

57. Apparatus as in claim 56 comprising means for compensating the fourth response for the radiation path length extension effects of radiation scattering.

58. Apparatus as in claim 57 comprising means for similarly compensating the third response for the effects of the scattering.

59. Apparatus as in claim 58 which comprises means for directing x rays or gamma rays into the mat of glass fibers,

means for detecting the x rays or gamma rays that have interacted with the mat of glass fibers to produce an additional response, and

means for using the additional response to effect scattering compensation of both the third and fourth responses.

60. Apparatus as in claim 59 comprising means for utilizing the additional response to compensate the third and fourth responses for the infrared spectral effects of the glass in the fibers of the mat.

TECHNICAL FIELD

This invention relates to methods and apparatus for measuring and controlling the degree of cure of carbonaceous polymeric materials that are formed from a plurality of chemical reactants and passed through a curing process, from which they issue as a traveling product or intermediate in a continuous or semi-continuous form. More particularly the invention relates to methods and apparatus for performing the measurements by directing into the traveling material infrared radiations at multiple wavelengths, detecting radiations that have been transmitted or reflected by the material, and computing the degree of cure in a substantially instantaneous, continuous and non-destructive manner from instrument responses to the detected radiations.

The availability of instrumentation which functions or is constructed in accordance with the invention permits immediate manual or automatic feedback control of one or more of the process parameters that affect the degree of cure, thus enabling the manufacture of a product or intermediate in an optimized state of polymerization and with the probability of substantial raw material savings and/or energy savings.

While the methods and apparatus of the invention are applicable to the manufacture of many different polymeric material products, the invention is herein described and illustrated in an embodiment for measuring and/or controlling the degree of cure of the binder resin applied to a mat of glass fibers, to be used, for example, in building insulation products.

BACKGROUND ART

Synthetic resins and natural polymeric compounds are used in the production of a great many materials and discrete items whose manufacture includes a curing stage. The manufactured material or item may consist of the polymerized material itself, or the polymerized material may be used as a binder to hold together various layers or aggregates of other materials which in combination with the binder can impart to the finished product its desired properties.

The desired properties are often significantly affected by the degree of polymerization of the resin compound. The affected properties typically include the flexibility and toughness of plastics, or the stiffness, abrasion and impact resistance of laminated sheets.

In various manufacturing processes, the degree of polymerization has been controlled by regulating one or more process parameters such as concentration, residence time, temperature and catalysis. Various instruments have been used to determine heat liberation, viscosity, density and electrical conductivity. Spectroscopic instruments of the gas chromatographic and nuclear magnetic resonance type have been very useful. Laboratory determinations of molecular weights are commonly performed as a quality control measure.

An article by Crandall, E. W. and Jagtap, A. N., entitled "The Near-Infrared Spectra of Polymers", Journal of Applied Polymer Science, Vol. 21, pp. 449-454 (1977) and its bibliography have indicated that near-infrared spectroscopy can be useful in the identification of resins and polymers and in following the course of polymerization and giving some indication of the state of cure. Polymers were melted and pressed between glass plates to give a transparent film, or they were dissolved and their spectra in solution were run against the spectrum of the pure solvent. It was observed that in various polymers the process of curing (with heat) affected the relative intensities of the overtone bands of carbonyl (C.dbd.O), amino and amide N--H and alcoholic O--H. The overtone bands of alkyl and aryl C--H were also observed along with certain C--H combination bands. The intensities of various bands were set forth by way of comparison with that of the C--H stretch band whose fundamental vibration lies at 3.3-3.5 .mu.m in the middle-infrared and whose first overtone appears at 1.7 .mu.m in the near-infrared.

Two of the carbonaceous polymeric materials discussed by Crandall et al are phenol-formaldehyde and urea-formaldehyde resins, which are commonly utilized, inter alia, as binders in glass fiber mats, say, for building insulation. In the manufacture of these mats, typically glass fiber is spun from molten glass and is sprayed with uncured binder compound as the fiber is being showered onto a moving chain conveyor. The conveyor carries the resulting glass fiber blanket through curing ovens wherein the polymeric binder material is exposed to elevated temperatures for an appropriate time period to complete the curing of the binder. After its exit from the ovens, the mat or blanket is cooled by a stream of air from a fan, and certain of its properties may be measured, typically with radiation gauges.

The mass per unit area of the traveling mat has been measured, with various degrees of success, using beta ray gauges, gamma ray or x-ray gauges, or infrared radiation gauges using combinations of wavelengths. The resulting measurements have been used to automatically control the speed of the chain conveyor, thereby determining the amount of coated glass fibers deposited while a section of the conveyor moves through the felting chamber, with the objective of maintaining the weight per unit area of the mat constant along its length.

Various attempts have been made to measure the mass of the binder material per se, for example by taking advantage of the fact that glass is substantially transparent to certain optical (e.g., infrared) and x-ray wavelengths that are significantly attenuated by the binder materials. The objective of this measurement is to be able to control the mass of the binder by regulating the amount or the dilution of the spray material applied.

The degree of cure has been measured in laboratories, for example, by free phenol determination or molecular weight determination. On the basis of their experience with laboratory-analyzed samples, line operators typically make a visual estimate of the degree of cure by inspection of the "color" of the mat, and adjust the oven temperature accordingly. However, as an indicator of cure, color has been shown objectively to be misleading in many cases, as well as subjective. Moreover, color changes do not exhibit high sensitivity except when the mat is already over-cured (burnt).

The degree of cure of the binder is believed to have considerable economic significance, since it affects the property of the glass fiber mat which is termed "recovery". The manufactured mat is usually compressed into rolls or bales for shipment and storage, and "recovery" is the extent to which the mat is able to spring back to its original thickness when the compression is relieved. Recovery is also related to the ability of the mat to maintain its shape and thickness for long periods of time in use as insulation and for other purposes. Hence, if the binder has an optimum degree of cure, a mat with a desired thickness and insulation value in service can be manufactured from a smaller amount of glass fiber and binder. The avoidance of overcuring can also result in lower energy costs during manufacture.

The properties of recovery and resistance to sag and deterioration in service seem to be dependent on an adequate degree of polymerization. There is evidence, on the other hand, that overcuring results in depolymerization as well as other deleterious effects.

It follows that there has been a need for a method and apparatus which provides an instantaneous, substantially continuous and non-destructive indication of the degree of cure of certain traveling polymeric materials.

DISCLOSURE OF INVENTION

In accordance with this invention, there are provided methods and apparatus for determining the degree of cure of a traveling carbonaceous polymeric material that has been formed from a plurality of chemical reactants and subjected to a curing process, comprising combinations of method steps and apparatus elements for directing into the traveling material a first infrared radiation from the group thereof adapted to selectively interact with molecular resonance vibrations at frequencies that are characteristic of respective terminal functional groups of atoms involved in reactions that take place in the material during the curing process, so that the material exhibits an absorptivity for the first infrared radiation that varies with the degree of cure of the polymeric material, also directing into the traveling material a second infrared radiation that is either of the kind that does not exhibit substantial selective interaction with molecular resonance vibrations in the material or of the kind that is adapted to selectively interact with molecular resonance vibrations at a frequency that is characteristic of groups of atoms forming the backbones of the polymeric molecules in the material, receiving from the traveling material radiations that have interacted with the material; producing from the received radiations first and second responses to the first and second radiations; producing a third response that is indicative of the mass of the polymeric material interacting with the radiations, and substantially independent of the variations in the absorptivity of the material for the first infrared radiation which occur as the curing process progresses, and producing from the first, second and third responses an output response that is correlated with the degree of cure effected by the curing process.

Typically the first infrared radiation is selected from the group adapted to selectively interact with molecular resonance vibrations at respective O--H, N--H and C.dbd.O vibration frequencies.

Method steps and apparatus elements may be provided for directing into the traveling material a third infrared radiation of the other kind, producing from the received radiations a further response to the third infrared radiation, and producing the third response from the further response and the second response.

The third radiation may be adapted to selectively interact with molecular resonance vibrations at a C--H stretch vibration frequency.

The first infrared radiation may comprise the near-infrared overtone band having wavelengths in the vicinity of 1.50.mu., whereas either of the second and third infrared radiations may have wavelengths in the vicinity of either 1.35.mu. or 1.75.mu..

A first mathematical function of the ratio of the first and third responses may be formed, together with a second mathematical function of the ratio of the second and third responses, and the first and second functions may be combined to produce the output response.

The first and second functions may be substantially linear functions. The ratio of the first and second functions may be formed in order to produce the output response.

The first function may be indicative of the number of terminal functional groups present in relation to the number of groups forming the backbones of the molecules, and the second function may be indicative of the number of groups forming the backbones of the molecules that have interacted with the radiations.

The first and second responses may be used to produce a fourth response that is indicative of the mass of the polymeric material interacting with the radiations but which is dependent on the variations in the absorptivity of the material for the first infrared radiation that occur as the curing process progresses, and the fourth response and the third response may be utilized to produce the output response.

The fourth response may be compensated for the radiation path length extension effects of scattering. The third response may be similarly compensated.

Method steps and apparatus elements may be provided for directing into the material further radiations having a mode of interaction that is different from that of the infrared radiations; these further radiations that have interacted with the material may be detected to produce an additional response, and the additional response may be used to effect the scattering compensation. The further radiations may be x rays or gamma rays.

The carbonaceous polymeric material may be used to form a binder coating for the fibers in a mat of glass fibers; the curing process may include exposing the mat to elevated temperatures, and the exposed mat may be passed through a measuring zone in which the radiations are directed into and received from the mat.

The exposure of the mat to the elevated temperatures may be controlled in accordance with the output responses.

The first infrared radiation may comprise a near-infrared overtone band adapted to selectively interact with molecular resonance vibrations at one or both of the O--H and N--H vibration frequencies.

Method steps and apparatus elements may be provided for measuring the weight per unit area of the mat passing through the measuring zone, and controlling the rate of travel of the mat in accordance with the weight per unit area measurement; controlling the rate of application of the binder coating in accordance with the second mathematical function, and controlling the temperature of the mat during at least a portion of the curing process in accordance with the output response.

The objects of this invention are to provide methods and apparatus for accurately and reliably measuring the degree of cure of traveling carbonaceous polymeric materials in a substantially instantaneous, continuous and non-destructive manner; to provide such methods and apparatus which make possible automatic feedback control of curing processes so as to maintain constant a desired degree of polymerization of the material; to provide such methods and apparatus that are useable when the polymeric material has been applied as a binder or coating for other materials, and to provide an improved measuring and controlling system for a glass fiber manufacturing process including binder cure control.

Other objects and advantages of the invention will become apparent in the following detailed description of some best modes for carrying out the invention, taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing of a process for producing a mat of glass fibers that are coated with a controlled amount of a carbonaceous polymeric binder material and cured to an optimum degree of polymerization of the binder by a method and apparatus according to the invention.

FIG. 2 is a schematic showing, including a quasi-section on the line 2--2 of FIG. 1, of an apparatus for automatically determining the degree of cure and binder weight of the polymeric coating material.

FIG. 3 is an enlarged and more detailed schematic showing of a portion of FIG. 2.

FIG. 4 is a graph depicting near-infrared absorption spectra of a particular carbonaceous polymeric material in four different stages of cure.

FIG. 5 is a graph depicting near-infrared reflection spectra of a particular carbonaceous polymeric material in four different stages of cure.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, molten glass from a melter 10 flows into a forehearth 12 that supplies a stream 14 of melted glass to a centrifugal spinner 16. Filaments 18 of glass ejected from the spinner 16 are directed downwardly and partially solidified by air streams from jets as at 20. The filaments 18 descend through a felting chamber 22 and are collected on a traveling conveyor chain 24. Air suction through the conveyor 24, depicted by arrows 26, aids the formation of a fiber blanket 28 on the conveyor.

The filaments 18 are sprayed, during their descent through the felting chamber 22, with a binder spray ejected through a plurality of spray nozzles as at 30. The binder spray comprises a carbonaceous polymeric material that has been formed from a plurality of chemical reactants 32. Typically the reactants 32 comprise the components of phenol-formaldehyde and urea-formaldehyde that are mixed in a suitable material former 34 and supplied to an injection pump 36. Pump 36 pressure-feeds the spray nozzle 30 through a header 38 and distributor pipes as at 40. As a result of the foregoing process, the blanket 28 comprises a mat of glass fibers that have a binder coating of uncured carbonaceous polymeric material.

The polymeric binder material is subjected to a curing process which is completed by transporting the blanket 28 through ovens as at 42 and 44 on the conveyor 24. The conveyor moves to the right in FIG. 1, as indicated by the arrow 46. In the ovens 42 and 44, the mat of glass fibers is exposed to elevated temperatures for a time period appropriate to effect the cure of the polymeric material that forms the binder coating on the fibers.

In due time the cured glass fiber mat 48 emerges from the last oven 44 and is cooled by a current of air (indicated by arrows at 50 and 52) from a fan (not shown). The mat 48 is picked up by other conveyors indicated generally at 54 whose movement is synchronized with the operation of a shear 56 and a windup 58 that forms somewhat compressed rolls of the glass fiber mat for shipment or storage.

The filamentary glass 18 is commonly ejected from the spinner 16 at a substantially constant rate (mass per unit time) and hence the weight (mass per unit area) of the cured mat 48 depends on the rate of travel of the chain conveyor 24 as set by a conveyor speed control 60. The cured and cooled mat is commonly measured in a measuring zone 62 wherein there is located a gamma-ray or x-ray gauge having a radiation source unit 64 and a radiation detector unit 66. Radiations emitted from the source unit 64 pass through the mat 48 and are attenuated by absorption in the mat in accordance with its mass per unit area. The unabsorbed radiation is detected in the detector unit 66 to produce a detector signal that is processed by conventional means not shown to produce a response, represented by a line 68, that is utilized by the speed control unit 60 to control the speed of conveyor 24. The objective of this feedback control is to maintain the weight of the mat 48 nominally constant along its length at a desired value.

The weight (mass per unit area) of the polymeric binder material contained in the cured mat 48 is controlled by a sprayer control device 70. Device 70 may regulate the volume per unit time of the spray material fed by the pump 36 to the spray nozzles 30, or it may control the dilution of the spray material.

The degree of polymerization, or degree of cure, of the carbonaceous polymeric binder material is determined by the temperature in the ovens as at 42 and 44. The temperature of one or more of the ovens may be controlled by a temperature control unit 72. As previously noted above, the line operator commonly observes the "color" of the mat 48 issuing from the last oven 44 and manually adjusts the set-point of the temperature control unit 72 accordingly.

The apparatus so far described