US3508891A - Heat treatment of insulating unwoven products formed of vitreous fibers - Google Patents

Description

Apnl 28, 1970 J. PAYMAL 3,508,891

HEAT TREATMENT OF INSULATING UNWOVEN PRODUCTS FORMED OF VITREOUS FIBERS Filed June 20, 1966 3 Sheets$heet 1 an H. r

TEMPEEH race /A/ "0 I V Lp 0 mo 20:) 500 400 50a 6'00 7544 524 7025 //v "c MENTOR Jsnm P4 YMHL ATTORNEY Apnl 28, 1970 J PAYMAL 3,508,891

HEAT TREATMENT OF INSULATING UNWOVEN PRODUCTS FORMED OF VITREOUS FIBERS Filed June 20, 1966 3 Sheets-Sheet 2 E w k 2%];3 ,0.

TEMPE'EH rues m/ "c lzigz \4 re-M aefl rules /A/ "c a 200 400 6'00 800 mm Tsmpsea rules 0v 3 INVENTOR J54 PA H1444 ATTORNEY United States Patent 3,508,891 HEAT TREATMENT OF INSULATING UNWOVEN PRODUCTS FORMED 0F VITREOUS FIBERS Jean Paymal, Clermont, France, assignor to Compagnie de Saint-Cobain, Neuilly-sur-Seine, France, a corporation of France Filed June 20, 1966, Ser. No. 558,762 Claims priority, application France, July 13, 1965,

Int. Cl. B32b 5/02, C03c 25/00, 25/02 US. Cl. 65-3 9 Claims ABSTRACT OF THE DISCLOSURE Fibrous insulating products are generally manufactured by drawing out a molten substance at high temperature which is divided into filaments and is rapidly cooled. The internal structure of the material thus obtained is different from that which the same material acquires during slow cooling.

This is particularly true of fibers of materials in the vitreous state which, after drawing out, are collected in a continuous mat or wadding constituting an insulating product in the form of panels of felt, or pads. These products generally undergo no further thermal treatment capable of changing their internal structure to any notable degree. They are either adapted to uses without sizing or agglomerated by a heat-hardening resin which requires a heating at a temperature about 200 C., this temperature being too low to change the structural state of the glass being utilized, so that the material is in an unstable state.

It is known that for a given material in the vitreous state, for each temperature there corresponds a definite structural state, and that this state of equilibrium is not attained instantaneously. Obtaining this state of equilibrium requires a certain period of time, a time which is longer as the temperature is lower. The peculiar thermomechanical quality of fibers of material in the vitreous state condition the temperature limit when such are used for purposes of thermal insulation. In fact, the insulating fibrous materials are generally utilized slightly compressed, so that there will not be the slightest space without insulation in the vicinity of the hot wall to be insulated. This compression of the product takes place clearly only to the extent that the product acts as an elastic solid. If the temperature of utilization is too high, the material reaches the plastic zone or state, and the product loses its initial compression.

The process in accordance with the invention consists in subjecting the pad or mat of fibers of materials in the vitreous state, through its entire mass, to the action of a homogeneous heat treatment Which imparts to the fibers a condition approximating a stable state at the high temperatures which the pad or mat is called upon to encounter in use.

It has been determined that the starting temperature of the plastic zone is higher for a material which has been treated in accordance with the invention, corresponding to a condition close to the stable state, than for the same material which is rapidly cooled after the temperature of fiberizing.

According to another characteristic of the invention, particularly desirable results are obtained by bringing the pad of fibers to a temperature which can be near the temperature of annealing, this temperature corresponding to the appearance of the first irregularity of the thermal expansion curve and corresponding to a viscosity close to 2.5 X 10 poises.

Another characteristic of the invention which has been determined, is that a prolonged action of treatment does not lead to obtaining clearly superior results over a treatment for a reduced time period, for example, of the order of one minute.

The process of the invention, therefore, lends itself very well to a continuous execution and procedure, and consequently to the production of a continuous pad capable of experiencing a high temperature before the plastic zone or state sets in.

According to another characteristic of the invention, at the same time as the heat treatment, such as described above, is applied to the mat or wadding, the latter is subjected to a compression. Thus, a mat is obtained whose thickness can be much less than that of a mat which has not undergone compression, and whose thermo-mechanical resistance is improved.

Hereinafter are given examples of procedures for executing the process of the invention which are to be read in conjunction with the accompanying drawings wherein FIGS. 1 to 7 show graphical curves representing the results of tests on the products of the invention to determine their improved thermo-mechanical properties.

FIG. 1 is a graph showing the reduction in thickness of a mat as a function of the temperature to which it is subjected, which varies in dilferent samples with the heat treatment imposed upon the mat in the course of its fabrication. The ordinate axis of the graph T:/ T, is the ratio in percent of the final thickness of themat to its initial thickness, and the abscissa axis represents the intensity of heat in the degrees centigrade as the temperature of the mat is increased linearly with time. The curves shown in FIG. 1 are the results of tests on mats formed from fibers of the same glass composition having an annealing temperature of approximately 540 C., and which mats have been subjected to no heat treatment as well as heat treatments for sixty minutes at temperatures of 420 C., 480 C. and 540 C., respectively, in the course of their manufacture.

FIG. 2 is a graph similar to FIG. 1 showing comparative tests on mats formed from fibers of the same glass composition as in FIG. 1, three of which mats corresponding to curves B, C and D" having been heat treated at the same temperature of 540 C. but for different durations, namely, one minute, five minutes and sixty minutes, respectively.

FIGS. 3, 4 and 5 are graphs similar to FIG. 1 showing comparative curves of test results on mats formed from fibers of different vitreous materials, each indicating a higher temperature stability when the mats are subjected to a heat treatment in accordance with the invention in the course of their manufacture. FIG. 3 shows comparative curves for mats formed from a hard glass composition having an annealing point of approximately 660 (3.; FIG. 4, for a windowpane glass composition; and FIG. 5 for a rock wool glass composition.

FIG. 6 is a graph showing the collapse of a fibrous mat which is treated in accordance with the invention, and which is subjected to a substantially uniform high temperature for an extended period of time.

FIG. 7 is a graph similar to FIG. 6, showing comparative curves indicating the diiference in behavior between 3 treated and untreated mats when both are subjected to the same temperature over an extended period of time.

In order to measure the improvement of these thermomechanical characteristics in a practical way, one may proceed as follows:

A sample specimen is cut out of a mat of fibrous material and is placed in an apparatus which imposes on it a definite load, which may be between 50 kg./m. and 200 kg./m. The sample is subjected to a variable temperature, increasingly linearly with time, and the change in thickness of the sample is recorded. The beginning of the sinking or collapse of the product treated takes place at a temperature all the higher corresponding to the higher temperature at which the sample specimen had been subjected during its heat treatment in the course of its fabrication in accordance with the invention.

FIG. 1 represents the loss in thickness of the samples subjected to a load of 100 kg./m. placed in an oven whose temperature rises 5 C. per minute.

These samples consist of fibers manufactured from a glass whose annealing temperature is about 540 C. (glass No. 1).

The curve A of FIG. 1 relates to a raw product such as is usually used, without special treatment; curves B, C and D correspond to the same product after a treatment of 60 minutes at respective temperatures of 420 C., 480 C. and 540 C., respectively. It will be noted that settling occurs at very high temperatures for treated products B, C and D. It is quite diificult to indicate precisely the beginning of settling of the samples. Therefore, one can take as reference datum of the thermomechanical properties, the temperatures corresponding to 5% to 10% of reduction of thickness.

These temperatures are as follows.

TABLE I.GLASS No. 1

Curve A Curve B Curve Curve D before treatment treatment treatment treatment at 420 C. at 480 C. at 540 C.

Temperature corresponding to decrease in thickness 310 465 480 495 Temperature corresponding to decrease in thickness C.) 365 490 512 530 TABLE II Glass N0. 2 (Glass E) hard glass Glass No. 1 soft glass annealing Glass annealing point 540 0. point 660 0.

Temperature 310 C. before treatment, 420

corresponding to 5% 465 C. to 495 0.

decrease in thickness. after treatment.

By utilizing, instead of a soft glass, such as the No. 1 glass above, a hard glass such as glass E, whose annealing point is about 660 C., a gain of only 110 C. is attained over the reference temperature, (Table II), while by the process according to the invention, gains of 155 C. to 185 C. are made on this soft glass which much easier to fabricate.

In order for the process to be truly practical industrially, the length of treatment must be short. In fact, the fibrous mats generally leave the production machines at high speeds, of the order of 10 to 50 meters per minute; and the unit of thermal treatment would attain prohibitive proportions if the time period were of the order of an hour or a half-hour.

It is possible to obtain excellent results with treatments of short duration. FIG. 2 shows comparative curves of specimens heated at 540 C. for different periods of time. Curve A portrays the behavior of a mat which has not been subjected to a heat treatment and corresponds to curve A in FIG. 1. Curve B illustrates the characteristics of a mat which has been heated for one minute, curve C, for five minutes, and curve D for sixty minutes. The decrease in thickness of 5% is obtained at temperatures of 495 C., 470C., and 450 C., respectively, for treatments lasting sixty minutes, five minutes, and one minute (Table III).

The gain is still 140 for a treatment limited to one minute.

An industrial embodiment of the process can be attained easily with the aid of a belt conveyor device permitting continuous treatment. If the mat is thin, it is not necessary to circulate hot air across the mat; if the thickness of the mat is more than a few centimeters, obtaining quickly the temperature at the center of the mat requires a circulation of air across the product.

The treating procedure applies to all fibrous products having a base of vitreous material. It is suitable to adapt the treating temperatures to the characteristics of the materials. In a general way, for glass, a temperature near the annealing point is selected, slightly lower than this, if the time of treatment can be longslightly higher, in the contrary caseto obtain more rapidly the desired structural evolution or change. This point corresponds to a viscosity of 2.5 10 poises. For mineral fibers, a temperature will be selected corresponding substantially to this viscosity value.

By similar treatments, gains of to 200 in tem perature stability have been obtained on different glasses over those temperatures which cause a 5% decrease in thickness under a load of 100 kg/m. as Table IV indicates, corresponding to the curves shown in FIGS. 3, 4 and 5.

FIG. 3 shows comparative curves E and F. Curve E portrays the behavior of glass No. 2 in Table 11 above, having an annealing point of 660 C. without heat treat ment, and curve F portrays the characteristics of the same glass mat which has undergone a heat treatment.

FIG. 4 shows comparative curves G and H. Curve G (glass No. 3) portrays the behavior of window glass having an annealing point of 550 C., without heat treatment, and curve H portrays the characteristics of the same glass fibers which have undergone a heat treatment.

FIG. 5 shows comparative curves I and J for mats of rock wool formed of lime feldspar minerals. Curve I depicts the behavior of a mat which has not been subjected to a heat treatment while the mat represented by Curve I experienced a heat treatment.

The improvement in temperature stability obtained by the treatment in accordance with the invention is preserved when the products are maintained for a long time at high temperatures. In a realm of temperatures below the annealing point, centered at about 150 C. below this point, there appears a very marked difference between the raw or untreated product and a heat-treated product. The crushing or collapse of a raw product under a given load is greater than that of a treated product. Take, for example, a mat of fibers of glass No. 1, having a mean diameter of 6 microns, which has been heat-treated 2 minutes at 540 C., and having a thickness of 100% under a load of 100 kg./m. As shown by curve K in FIG. 6, when the mat is brought to a temperature of 400 C. it undergoes, by reason of the combination of the effects of the load which is applied to it and of the temperature, a slow decrease in its thickness to a limit value which corresponds, in the case of this experiment, to a thickness of 78%, which is reached after 1000 hours. By continuing to maintain the temperature beyond this time, no further change in thickness was evident. Under the same conditions of load and temperature, a mat of fibers of the same glass No. 1, having the same mean diameter, which has not been subjected to any heat treatment, undergoes a much more rapid collapse at the start of heating. As shown by curve L in FIG. 7, the thickness stabilizes at a value of 62% after the lapse of 257 hours. This final thickness is much less than that of the mat of fibers which has been heat-treated and which is represented by curve M thereabove. The latter corresponds to curve K in FIG. 6, representing the behavior of a treated mat formed of fibers from glass No. l. The curves in FIG. 7 are plotted on a logarithmic scale on the axis of the abscissas.

The two types of tests described above, i.e., tests with progressive elevation of temperature (FIGS. 1 to 5), and tests with uniform temperature (FIGS. 6 and 7), evidence a reduction in thickness of the test samples under the effect of a definite load. Another type of test can be visualized in which the thickness would be maintained constant between two parallel plates and in which the reaction of the sample compressed between these two plates would be measured. The relaxation effect thus experienced by the mat is the same as that which is reproduced in the most ordinary conditions of utilization of insulator panels held between two fixed walls. The temperature may be homogeneous at every point of the samples, or, on the contrary, the temperature may be non-uniform and variable as a function of the distance between the point under consideration and to the confining walls. The latter condition corresponds to the temperature variation which is established naturally in an insulator panel during the performance of its heat-insulating function.

The general form of the relaxation curves thus obtained, representing the variation of the reaction of the product initially compressed between the two walls as a function of time, is substantially similar to that of the preceding curves giving the variation in thickness of the mat under constant load as a function of time. The decrease in reaction on the walls is less in the case of a mat of fibers, which is heat-treated beforehand in accordance with the invention, than in the case of a mat of untreated fibers. This difference in loss of reaction remain small at any moment, in particular, when temperature stabilization is attained.

This different behavior of heat-treated and untreated mats may be explained as follows. In the range of temperatures under contemplation, i.e., about 150 C. below the annealing point of glass, the viscosity of the glass is so high that the plastic deformations of the fibers are :practically nil. The value of the viscosity is in fact of the order of 10 to 10 poises. The raw fibers having a much lower initial viscosity which are subjected to this temperature undergo a deformation or relaxation until the viscosity of equilibrium at temperature T is attained. As this temperature T is relatively low, the change in viscosity is slow, and the result is that a large relaxation or deformation will have time to take place. On the contrary, the fibers which have been previously treated have a higher viscosity, much farther from the value of equilibrium at temperature T; therefore, these fibers during the same time period, will undergo less deformation or relaxation. Finally, the treated pads will maintain a thickness under load greater than the raw mats, or will exert at constant thickness a greater reaction on the walls.

Another very interesting advantage of the process according to the invention concerns the obtaining of a mat of fibers of desired thickness for a given density. At the moment of formation of the mat, generally obtained by suction of the fibrous elements on a belt conveyor, the fibers are lapped one over the other which gives a certain cohesion to the fibrous mat. Depending upon the nature and length of the fibers, a product is obtained having a certain natural density. Often, this density is too low for the mat to have good insulating properties for a small thickness. It is sought, therefore, to increase the density of the mat by calendering or rolling it. This operation of cold rolling brings about a certain decrease in natural thickness of the mat and hence an increase in its density, but it has the disadvantage of breaking a large number of fibers, and this decreases the cohesion and elasticity of the mat. Moreover, the increase in density which can be obtained in this way is quite limited. On the other hand, by applying a heat-treatment according to the invention to a mat which is subjected simultaneously to a reduction in thickness, there is obtained, at a thickness which can be much less than the natural thickness, an undamaged product, which, in addition, is improved from the point-ofview of thermo-mechanical resistance.

The objectives of the instant invention may be realized by proceeding as follows:

The pad or mat of fibers, having, for example, a weight of 2.5 kg. per square meter is obtained with a natural thickness of formation of 25 cm., presenting initially a density of 10 kg./.m. To obtain a more effective insulating product with this pad, a stress of compression capable of reducing its thickness to 4 cm. may be exerted at the start, which will make the density rise to 62 kg./m. But this solution has several disadvantages. The initial product is very cumbersome, it is often difficult to exert at the start the compression necessary for a strong decrease in natural thickness and, finally, a too strong initial reaction of the insulator panel on the walls, due to this application under compression, can sometimes be difficult to maintain. A process according to the invention consists in bringing the pad, within a suitable time, to the temperature selected for treatment, and simultaneously maintaining it at a reduced thickness, slightly under the desired thickness. The time durations and temperatures are such as indicated previously. For the formation of a light pad from fibers of glass No. 1, having a weight of 2.5 kg./m. one may apply, for example 2 minutes of heating at 540 C. at a thickness of about 4 cm., and a pad of the desired density of 60 kg./m. to 65 kg./m. will be obtained for a thickness very little above 4 cm. Without treatment, it would be necesseary to exert a pressure at the start of kg./m. while after treatment, it would suffice to exert at starting a much weaker pressure, of the order of 10 kg./m. to 30 kg./m. according to the value of the excess thickness of the pad, which may amount to only a few percent, this excess thickness being necessary in order for the pad to accommodate itself satisfactorily to the shape of the walls which are to be insulated, so as to leave no empty space where movements of air convection currents might develop which would be harmful to the insulation effect According to one variation of the invention, in order to obtain a mat having a definite thickness and density, there may be added to the fibers, before heat treatment, for example, at the moment the mat is formed, a binding agent resistant to high temperatures, which may be, for example, a mineral binder such as silicate of soda.

The mats and pads obtained by the process in accordance with the invention may be used particularly in every case where an apparatus, such as for example a boiler, oven, etc., is raised to a high temperature and is to be insulated thermally by means of mats or pads subjected to compression in order to form an insulating body without a break in continuity.

I claim:

1. The method of treating a resilient thermal insulating unwoven mat of fibers of vitreous material of substantial thickness with the fibers in freely interlaced condition, which consists of (a) heating the mat uniformly through its entire thickness at a temperature in the vicinity of the annealing temperature, and Well below the softening temperature, of any of the viterous material in the mat, for a short period of time of the order of one to five minutes to increase the heat resistance and stability of the fibers at elevated temperatures while maintaining the integrity of the fibers and their disposition in the mat, and

(b) simultaneously compressing the mat to reduce the thickness thereof in the course of the heating operation to a limited degree, to preserve the resilience and heat-insulating capability of the mat for functioning at higher efficiency.

2. The method set forth in claim 1, wherein the duration of the heating period is approximately one minute.

3. The method set forth in claim 1, wherein the mat of fiber-s of vitreous material comprises a mineral binder for the fibers.

4. The method set forth in claim 3, wherein the mineral binder is sodium silicate.

a density of 60 to 65 kilograms per cubic meter.

8. An article produced by the method set forth in claim 1.

9. An article produced by the method set forth in claim 3.

References Cited UNITED STATES PATENTS 1,899,056 2/1933 Powell 653 3,328,230 6/1967 Levecque et al. 65-9 XR 3,002,857 10/1961 Stalego 117126 S. LEON BASHORE, Primary Examiner S. R. FRIEDMAN, Assistant Examiner

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