US3012845A - Process for desizing glass fabric - Google Patents

Description

3,012,845 PROCESS FGR DESiZiNG GLASS FABRIC Edwin L. Lotz, Nutley, N.J., assignor to Hess, Goldsmith 8: Company, incorporated, New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 31, 1960, Ser. No. 53,034 7 Claims. (Cl. 8-438) This invention relates to a process for removing size or binder material from an unfinished glass fabric, and particularly to a continuous process for thermally desizing such a fabric. Glass fabrics as the term is employed herein, refers to fabrics knitted, netted or woven in a definite pattern from yarns made up of a number of filaments of glass, as distinguished from a random distribution of filaments as in glass wool.

Before individual glass filaments can be formed into strands and woven or knit, for example, they must be coated with a sizing material which serves as a continuous filament binder and affords a measure of protection to the filaments during weaving or knitting or subsequent textile treatments. The sizing material lubricates the glass filaments and the strands or yarns produced therefrom and allows them to slip over one another without undue abrasion and resulting breakage. The size is usually organic in nature, for example consisting of starch or dextrinized starch, gelatine, a complex amine, and in most instances a lubricant such as mineral, animal or vegetable oil. The size, or binder material as it is sometimes called,

is present on the fibers of the resulting glass fabric to the extent of between about 1 and 4% by weight of the fabric, and must be more or less completely removed from the fabric prior to coloring, when the fabrics are to be used for decorative purposes, or prior to the application of a finish in the case of industrial glass fabrics which are to be used with resins for the production of laminated or coated glass products. it is important that the fabric, particularly industrial fabric, be desized in a manner which reduces the original strength of the greige goods as little as possible. Unfortunately, every commercially acceptable desizing technique does lower strength of the greige goods, but fabric strength is restored to an appreciable extent, by application of a fabric finish, forexample Volan or N .O.L.24, among many others, used in connection with the finishing of industrial fabrics, and finish 140K for decorative fabrics, all of which protect the yarn from self-abrasion.

Accordingly, in the desizing of the glass fabric as little strength as possible should be sacrificed, as much of the size should be removed as possible, that is to an ignition loss of less than 0.1% by weight of the fabric, and prefer ably between about 0.02 and 0.08%, and the desized fabric should be as light in color as possible, preferably exceedingly white. It is entirely possible for two identical desized fabrics to have the same ignition loss and yet one may be a light tan and the other an excellent white as a result of different desizing techniques. The Whiter fabric is preferred for both decorative and industrial purposes.

By far the simplest methods and the ones in current use for desizing glass fabrics are thermal treatments, two of which are characterized by the use of low temperatures and two by temperature sufficiently high to cause burning of the size at or immediately adjacent the sufface of the fabric. According to one low temperature method, referred to as the batch oven process, the glass fabric is rolled up on perforated mandrels and the resulting large rolls are placed in an oven which is maintained at between about 500 and 700 F., and the size is slowly volatilized from the fabric. However, the total time in the oven ranges between about 55 and 80 hours. While the batch oven technique thus consumes a very appreciable amount of time, the desized fabric is white and has an ignition loss of about 0.1%, which is considered quitesatisfactory. However, the tensile strength of the fabric is reduced by about 50%, which is somewhat below the strength reduction desired for industrial purposes.

The other low temperature technique is a continuous treatment at temperatures sufficiently low to prevent burning of the size at the surface of the fabric. However, the

thus treated fabric which retains a very high proportionof its initial tensile strength does so at the expense ofleaving on the heat treated goods a very large portion of the size in the form of a carmelized residue. While thiscontinuous low temperature desizing does not detract greatly from the tensile strength of the greige fabric, retention of strength is attained at the expense of incom-. plete desizing. Not much more than about half of the size is removed and because of the high ignition loss the thus treated fabric is not satisfactory for building glass laminates since the resins employed do not adhere well to the carmelized surface coating.

Continuous high temperature desizing is referred to in the art as Coronizing. In one such process the glass fabric to be desized is passed in open width through a vertically or horizontally disposed furnace and subjected;

to temperatures between about 1100 and'1500" E, with atmospheric conditions Within the furnace being such as to cause rapid burning of the size with a blue flame in a band across the fabric at or just above the fabric surface and very near the point of entry of the fabric into the furnace. This continuous high temperature technique is described in Klug U.S. Patent No. 2,633,428 and in Waggoner U.S., Patent No. 2,845,364, and is widely used in desizing glass fabrics to be used for decorative purposes where hand and yarn set are the ultimate aim, and retention of original tensile strength is not so important. While the ignition loss of the finished fabric is about 0.1% and the fabric is very white, the tensile strength is very low, being only about from 30 to 60% of that of the greige goods. Fabrics desized by this technique thus do not exhibit the strength desired for industrial use s. v

A second high temperature desizing process is described, in Merrill R. May US. Patent No. 2,970,934, dated February 7, 1961. According to that process a length of the fabric in open width is continuously passed through a furnace or thermal treating zone which ismaintained at a substantially lower temperature, namely between about 900 and 1050" F. This lower temperature is sufficient to cause ignition and burning of the size on the surfaceof the fabric, but the process differs from that of Klug-and Waggoner in control of the atmosphere within the treating zone so that burning occurs at a point just inside the exit or discharge opening of the furnace, and such burning is with a yellow flame, as distinguished from the much hotter blue flame. The May process also produces a de-, sized glass fabric with an ignition loss of about 0.1%, but the tensile strength of the desized fabric is between about 70 and of that of the greige goods. Thedesized fabric is a light amber or off white material.

It is an object of the present invention to provide a continuous high temperature desizing process which will produce a desized glass fabric having a strength greater than that attained by the high temperature blue flame method, and a fabric which is much whiter and has a lower ignition loss than that produced by the May process.

These and other characteristics which are highly desirable in desized decorative or industrial glass fabrics are achieved in accordance with the present invention by heating a continuously advancing length of sized unfinished glass fabric to a temperature sufficiently high to volatilize the size from the fabric, and in fact to cause ignition of the size under certain conditions, and maintaining the fabric at such temperature for a time sufficient to volatilize a major portion of the size, preferably in excess of 75% by weight of the size originally present on the fabric, while so diffusing the volatilized size as to prevent i-gnition and burning of the same adjacent the fabric, and then raising the temperature of the partly desized fabric to a temperature sufficiently high to set the fibers thereof, sometimes referred to as setting the weave, and maintaining the fabric at this elevated temperature to achieve the desired weave set and to volatilize substantially all of the sides remaining on the fabric, while preventing ignition andburning of the volatilized size during raising of the temperature and while the fabric is maintained at the higher or setting temperature. It is indeed surprising that the present process wherein continuous desizing is carried out at temperatures capable of igniting and burning the size on or immediately adjacent the fabric is capable of producing a superior desized fabric product without ignition and burning of the size.

In an attempt to find an improved technique for continuouslydesizing glass fabrics and to examine the desirability of a vertical rnufiie furnace for carrying out the process, I first examined the basic concepts of high temperature desizing. Through infrared absorption tests it was established that at a temperature of about 1480 F., glass fabric absorbs a maximum of thermal energy, and one would suppose that the radiating walls of a continuous desizing furnace should be maintained at this temperature. Accordingly, a series of tests were carried out with a variety of fabrics at desizing temperatures of about 1480 F. While the size was very efiiciently re moved from the fabric, the strength of the fabrics, as measured by the Mullen burst test after various periods of exposure, deteriorated very rapidly, reaching a practical or'useful minimum after five seconds exposure. After 14 seconds the glass exhibited Mullen. At 1360 F. Mullen strength fell off rapidly up to about 20 seconds after which the strength remained constant. At 1300 F. a somewhat higher minimum was reached after 30 sec onds, while at 1200 F. minimum Mullen strength was achieved after about 50 seconds exposure. In all of these tests thesize burned was a bright blue flame adjacent the fabric shortly after the material entered the furnace. While the results of'these tests definitely indicate that the ideal surface radiating temperature may be about 1480 F., at this temperature there is extreme physical damage to the fabric if it is allowed to remain at that temperature for even 5 seconds. Maximum Coronizing temperatures in current use are between 1200 and about 1480" F.

From the above it can be seen that the fabric is very appreciably degraded at these high Coronizing tempera tures. In tests carried out at the lower temperatures of 1300 and 1350 F., with the size being permitted to burn on the surface of the fabric with a light blue flame, a medium weight casement fabric, designated Style 841, weighing 4.3 ounces per square yard, constructed of warp and fill yarns comprising 150 single end continuous filaments of a diameter between 0.0002 and 0.0027 in., when coated with 140K finish exhibited a Mullen bursting strength of only about 88 to 120. While the color and the ignition loss of the fabrics thus cleaned were acceptable,'the strength was not up to an acceptable level.

Proceeding on the assumption that the elevated temperatures and also the flame were responsible for the low finished Mullen strength, a series of tests were carried out on Style 841 fabric with the furnace maintained at 1200-1250 F. under conditions which prevented the vaporized size from burning adjacent the moving fabric. In these tests the fabric was exposed to the aforementioned temperature for times of 7.3, 10.8 and 15 seconds. The cleaned fabric coated with 140K finish exhibited Mullen strengths of 116, 105 and 100, respectively. In each case the fabric was at least as white or whiter than when desizing was carried out at 1350" F. with an exposure time of up to about 5 seconds with the vaporized size burning adjacent the fabric with a high blue-yellow flame, which fabric exhibited a finished Mullen of only 88.

4 5' While these tests showed that lower temperature and elimination of the flame produced better results, they-,- also established that in the absence of a flame it is possible to have prolonged exposure of the fabric at 1250 F. without substantial further reduction in physical properties.

Tests on another typical decorative fabric, Style 802, a light weight leno weave weighing only 2.03 oz./ sq. yd., substantiated the above observations that once the size is properly removed, the elevated temperature can be sustained for additional periods without significantly decreasing the physical properties of the goods. Style 802 was exposed in a pilot furnace having three temperature zones maintained at 1100, 1260 and 1400 F. for a total of about 7.5 seconds. Subsequent runs were at exposure times of 12 and 1.5 seconds. Unfinished Mullen strengths were 34, 33 and 31 lbs/sq. in;, respectively.

The above tests were all carried out in a pilot vertical muffle furnace 6 feet in length, and in the runs at 1200-1250 F. considerable difficulty was encountered while endeavoring to pass the fabric through the furnace without ignition and burning of the size at the surface of the fabric. Furthermore, in these tests, as in the prior art, particularly as evidenced by the Klug and Waggoner patents, the fabric at ambient or room temperature was introduced in open width directly into the furnace maintained at Coronizing temperatures somewhere between 1100 and 1500" F., usually between about 1350 and 1480 F. The fabric is thus subjected to a very great thermal shock, it being raised from atmospheric temperature to in excess of say about 1250 F. in the space of but a few seconds. Under such conditions the size volatilizes so rapidly, particularly at temperatures in the upper portion of the range above specified, that it is exceedingly difi'icult to avoid ignition. Accordingly, it was decided to carry out desizing under conditions whereby the fabric is gradually raised to the temperatures necessary to assure proper setting of the fibers or weave setting, usually about 1250-1350 F., while also avoiding ignition and burning of the size in the furnace.

The vertical pilot unit was modified to provide three two-foot sections or zones which were maintained at progressively higher temperatures. The fabric was introduced at the top of the furnace in which the first zone was maintained not above about 1100 F., the second or middle zone at between about 1100 F. and about 1280 F. and the third or bottom zone at a temperature above 1280 and up to 1350 F. When operating in this fashion, astoundingly improved results both as regards the desized fabric whiteness and the finished Mullen strength were. realized, as described hereinafter.

Thus, in accordance with the process of the present invention, the fabric is continuously introduced into a first zone maintained'at a temperature sufficiently high to fairly rapidly volatilize the size, preferably above 800 F. but not above about 1100 F. In this zone the volatilized size is so diffused, preferably with air, that burning which is possible at temperatures between about 800 and 1100 F. is avoided, and then the fabric is introduced into another zone where it is raised to proper weave setting temperatures, i.e. up to about 1400 F. and the remaining size is volatilized, but not permitted to burn adjacent the fabric in this other zone. While it is possible to carry out the present process by first heating the fabric up to about 1100 F. and then subjecting it to temperatures between about 1280 and 1400 F. in a second zone, for example, it is preferred to employ one or more intermediate zones serving to gradually raise the temperature of the fabric to the range 1280-1400 F., thus avoiding the thermal shock which I have found is detrimental to the material.

During initial heating of the fabric at least a major portion of the size thereon is volatilized, and in most instances between about 75 and 95% of the size is removed in this stage. During the initial heating or in the first heating zone the ignition loss of Style 841 greige fabric is preferably reduced about for example from 3.53% to about 0.33%, before the fabric is raised during subsequent heating to above about 1100 F. I have also found that 'with certain of the heavier and bulkier fabrics, for example those weighing above about 6 ounces per square yard, it is more important that a high proportion of the size be removed during this initial heating than with lighter fabrics in order to achieve an excellent white color in the completely desized fabric. For example, with Style 978, a heavy boucl fabric weighing 9.22 ounces per square yard and having an initial ignition loss of 1.91%, unless the ignition loss is reduced to about 0.20% or below during initial heating, a very white product is not obtained. In like manner with Style 95919, another heavy boucl fabric, the ignition loss of about 2.4% is preferably reduced to about 0.15% in the first zone. Thus, in order to achieve a desized fabric of excellent whiteness it can be said that a minimum of about 75% and in some cases about 85 to 95% of the size is removed from the fabric in the first zone or during initial heating.

Burning of the size is avoided in the first zone by sodiifusing the volatilized size as to produce a mixture of size vapor and air too lean to ignite and burn. This diffusion may be most simply effected by providing an adequate draft through at least the first or fabric entering zone of the furnace, A major portion of the diffused volatilized size is desirably removed from the vicinity of the fabric in the first zone, so that only a minor portion of the vapor produced therein may enter the second and any subsequent zones of the furnace. Where the furnace is vertically disposed with the coolest zone at the top and the fabric is passing downward the problem of diffused vapors entering the second or subsequent hotter zones of the furnace does not exist.

Reference may be had to the application of Horace L. Smith, Jr., entitled Muffie Furnace, Serial No. 53,192, filed on even date herewith, for a description and illustrations of a vertical mufiie furnace particularly adapted for carrying out the process of the present invention. The Smith furnace provides a muffie run comprising at least three heat treating zones, each of which are provided with vapor exhausting means.

While the novel desizing process of this invention has thus far been described as the sequential heating of a glass fabric in two or three stages or thermal treating zones, the process may be carried out in a muffle furnace comprising but a single zone maintained at incrementally increased temperatures over its entire length, it being essential only that the fabric be subjected to gradually increasing temperatures and that a major portion of the size be removed below about 1100 F. For example, in a vertical muffie with sized fabric entering at the lower end the base ofthe furnace might be maintained at 900 F., but a foot or two above the base the temperature of the muffle may be 1000 F. and so on to the exit end of the muffie which might be maintained at 1400 F. In most instances it will be simpler from the point of view of furnace control to carry out the process in a mufile having three sections the first maintained between about 800 and 1100 F., the second between about -0 and 1280 F., and the third from about 1280 to 1400 F. The temperature differential between adjacent zones is not sufficient to adversely affect the fabric.

It is essential to the present process that a major portion of the size be removed below about 1100 F. and that ignition and burning of the size be avoided throughout the process. In the apparatus set forth in the aforementioned Smith application no auxiliary means such as a fan need be provided for avoiding ignition in the second or third treating zones, although in some instances it may be desirable to provide an independent draft in the zone subsequent to the initial heating zone to prevent ignition therein. In the Smith furnace, a major portion of the diffused size vapor is removed from the mufiie at the head of the first zone so that the draft to the second zone plus the size vaporized therein does not produce an ignitible mixture in the second zone.

When three zones are employed, the second zone provides a very gradual transition to the temperatures above about 1280" F. necessary to effect proper weave setting and fiber relaxation, which impart a desirable feel and hand to the desized fabric. In the second and third zones the size remaining on the fabric is substantially completely volatilized and the desized fabric has an ignition loss between about 0.02 and 0.08%. The desized fabric is exceedingly white.

The first zone, maintained at temperatures up to about 1100 F. results in a substantially lower rate of volatilization of the size than occurs in conventional Coronizing process, a rate sufiiciently low that combustion does not take place with a normal air draft which would support combustion at higher temperatures. In pilot plant operations and also in a commercial installation employing the present process it has not been necessary to employ a forced draft in the first or fabric entering zone to avoid ignition and combustion of the size therein. Yet, I have found that at temperatures appreciably above 1100 F. in the first zone, i.e. 1250 F. and upward normally employed in Coronizing,'burning of the size occurs regardless of the'manner in which the draft is'controlled.

The tests reported in the following Tables I-III are illustrative, of the present process, but are not intended to limit the scope of the invention, neither do they necessarily present optimum operating condition for a commercial installation. Each test wascarried out in-a six foot vertical pilot mufile furnace, either withall of the furnace maintained at the indicated temperature or divided into two or three sections of equal length as indicated by the temperatures and dwell times reported. In

Table l [Casement fabric style 841-4.3 ozJsq. yd. Warp and fill ECDE 1/0 1Z] Mullen Bursting rength Temp. Dwell Ignition (1b.,lsq. in.) Run F.) Time T oss Color (See) (Percent) Un- Finished finished (140K) Greige (untreated) 3. 53 1 1,020 7. 35 0. 13 Dark Tan. 2 1, 070 4 1, 350 4 0. 04 Fair White.

1, 350 4 0.08 103 182 Excellent White. 1,020 7. 35 5 1,275 7 1, 350 7 0.07 50 D0. Present Standard 0. 04-0. 08 40 125 Fair White.

Product (Coronlzed with Flame).

7 some instances the fabric was introduced at the top and sometimes at the bottom, but always to the zone of lowest temperature. The direction of fabric travel was found to have no effect upon the characteristics or prope'rties of the desized goods. In every case, unless otherwise specified, desizing was effected without ignition and burning of the size in the fabric treating muflle.

In run 1, which is not the complete process of this invention, the fabric was subjected to a temperature 1020 F. for 7.35 seconds. While a desized fabric exhibiting substantial strength was produced, its dark tan color was not acceptable. In run 2, where the fabric was subjected volatilization of size from this medium weight Style 841" casement fabric was about the same at temperatures of;

1050 and 1275 F. On the basis of this information and 1 the data of Table I, a commercial thermal desizing furnace, as described in the Smith application, having three foot sections or treating zones, and capable of desizing Style 841 fabric at the rate of 60 yards per minute is being operated with the first section at 1000" F., the second section at 1200 F. and the third section at 1350" F., with a dwell time in each section of about 7 seconds.

Table II reports tests conducted with heavier fabrics, namely boucl Styles 95919 and 978.

Table II [Bonel fabric style 05919-799 ozjsq. yd. Warp ECDE 150 l/O IZ: Fill RX 43 Ratine] Mullen Bursting trength Temp. Dwell Ignition (lb./sq. in.) Run 7 F.) Time loss Color (See) (Percent) Un- Finished finished (140K) Greige Goods (Un- 2. 41 480 treate Present Standard 0. 04-. 08 102 Fair White.

Product (Coronlzed with Flame).

""""""""""" 1,275 Good White.

1, 350 Fair White. 1,040 3 1,275

1, 350 Excellent White.

[Bouel fabric Style 978-9.22 oz./sq. yd. Warp ECD 450 2/2: Fill RX 31E Ratine] Greige Goods 1. 133

Present Standard 0.0%.08 90 Fair White.

Product (Coronized with Flame). p

"""""""""""" 1, 350 9. 7 0.17 55 105 Excellent White.

to temperatures of 1070 and 1350 F. for 4 seconds each a fairly white product was obtained which was substantially stronger than the present standard material. Good results were also obtained in run 3, but the whitest fabric was obtained in runs 4 and 5, with run 4 being equivalent to 4 seconds at 1070 F. and 8 seconds at 1350 F. It is significant to note that runs 4 and 5 both produced a superior white, as compared to the standard product, and also gave an increased strength of about 46% and about 24%, respectively, over the material cleaned in the "standard fashion.

From information obtained in the series of runs reported in Table I it was determined that the rate of Examination of run 2 shows that the present process produces a fabric of equal whiteness but having a physical strength approximately 100% greater than the standard commercial product. Run 3 produced a far superior White with a physical strength greater than the standard.

It will be noted that substantially longer dwell times are required at the temperatures indicated to remove a substantially lesser quantity of size or hinder material from the heavier, more bulky fabric.

Table III reports the results of tests carried out with a heavy industrial glass fabric, and Table IV the rate of volatilization from that fabric.

Table 111 [Industrial fabric HG639.76 oz./sq. yd. Thickness 0.14 in. Warp and fill: 16 X l il50S 4/2] Tensile Temp Dwell Ignition Run F.) Time loss Unfinished Volan Color (See) (Percent) Warp Fill Warp Fill Greige Goods 2.2 308 279 1,020 7 1 1,280 7 1,350 7 0.06 130 I18 Grey White. 1,020 10 i 2 1, 280 10 1, 350 10 0. 05 103 199 128 Good White. 1,020 15 a 1,280 15 1,350 15 0. 03 79 73 I55 131 Excellent White.

From Table IV it can be seen that the sizing material is very rapidly volatilized from the fabric at 1020" F., but once approximately 90% has been removed equivalent treatments at 1280 and 1350 F. removes the remainder only with very great difficulty. Accordingly, a proper time sequence for a fabric such as PIG-63 is approximately 4 seconds at 1200 F., 8 seconds at 1250" F. and about 15 seconds at 1300 F.

The tests above reported clearly indicated that the time of treatment is not only dependent upon temperature but also upon the weight of the fabric and its weave, whether tight or loose. The quantity of size on the greige goods is of course also an important factor, and it can be seen that one cannot predict the precise treating times required for all of the many fabrics encountered.

As a practical matter, a vertical furnace is preferred to a horizontally disposed muffie since with the former it is possible to have a much longer thermal treating run without imposing undue tensile stress upon the hot fabric or encountering sagging as in a horizontal furnace.

Thus in accordance with the present invention desizing is carried out without a flame and under initial heating conditions, preferably between 800 and 1100 F. such that a major portion of the size, preferably between 75 and about 95%, is volatilized from the fabric and so diffused as to prevent ignition of the same. The fabric is then gradually raised into the range of about 1280-1400 F. for substantially complete volatilization of the size and setting of the weave. By the method of continuous desizing set forth herein a thermally desized fabric can be produced which has a superior finished physical strength, for example, from about 20 to 100% greater, and a much whiter color as compared with comparable materials desized by continuous high temperature techniques employing a flame to remove the size or binder material.

I claim:

1. A process for desizing a sized unfinished glass fabric, which comprises heating an advancing length of said fabric to a temperature sufficiently high to volatilize the size from the fabric, maintaining the fabric at such temperature for a time sufficient to volatilize at least 75% of the size, so diffusing the volatilized size as to prevent ignition and burning of the same adjacent the fabric, raising the temperature of the partly desized fabric to a temperature sufliciently high to set the fibers thereof, and volatilizing substantially all of the remaining size from the fabric while diffusing the volatilized size to prevent ignition and burning of the same in the vicinity of the fabric at the elevated temperature.

2. A process for desizing a sized unfinished glass fabric, which comprises heating an advancinglength of said fabric to a temperature sufficiently high to volatilize the size from the fabric, maintaining the fabric at such temperature for a time sufficient to volatilize at least 75% of the size, so diffusing the volatilized size as to prevent ignition and burning of the same adjacent the fabric, removing volatilized size from the vicinity of the fabric, raising the temperature of the partly desized fabric above about 1100 F. to set the fibers thereof, and volatilizing substantially all of the remaining size from the fabric, while diffusing the volatilized size to prevent ignition and burning of the same adjacent the fabric during-raising of the temperature and while the fabric is at fiber setting temperature.

3. A process for desizing a sized unfinished glass fabric, which comprises gradually heating an advancing length of said fabric to a temperature sufficiently high to vo1a tilize the size from the fabric up to about 1100 F., maintaining the fabric at such temperature for a time sufficient to volatilize a major portion of the size, so diffusing the volatilized size as to prevent ignition and burning of the same adjacent the fabric, removing volatilized size from the vicinity of the fabric, gradually raising the temperature of the partly desized fabric sufiiciently to set the fibers thereof and not above about 1400 F., and volatilizing substantially all of the remaining size from the fabric, while diffusing the volatilized size to prevent ignition and burning of the same adjacent the fabric during raising of the temperature and while the fabric is at fiber setting temperature.

4. A process for desizing a sized unfinished glass fabric, which comprises heating an advancing length of said fabric to a temperature between about 800 F. and 1100 F., maintaining the fabric at such temperature for a time sufficient to volatilize between about and of the size, so diffusing the volatilized size as to prevent ignition and burning of the same adjacent the fabric, gradually raising the temperature of the partly desized fabric to between about 1280 F. and 1400 F., and volatilizing substantially all of the remaining size from the fabric, while diffusing the volatilized size to prevent ignition and burning of the same adjacent the fabric during said gradual temperature raising and while the fabric is at said latter temperature.

5. A process for desizing a sized unfinished glass fabric, which comprises continuously introducing an advancing length of said fabric to a treating zone maintained at a temperature between about 800 F. and 1100 F., retaining the fabric in said zone for a time suflicient to volatilize a major portion of the size, so diffusing the volatilized size as to prevent ignition and burning of the same adjacent the advancing fabric, exhausting a major portion of the volatilized size from said zone, subsequently introducing the advancing partially desized fabric to another zone maintained at a temperature between about 1280 F. and 1400 F., and retaining the fabric in said other zone for a period sufficient to volatilize substantially all of the size remaining on the fabric and to set the fibers thereof, while diffusing the volatilized size to prevent ignition and burning of the same adjacent the fabric therein. 1

6. A process for desizing a sized unfinished glass fabric, which comprises continuously introducing an advancing length of said fabric to a treating zone maintained at a temperature between about 800 F. and 1100 F., retaining the fabric in said zone for a time sufficient to volatilize a major portion of the size, so diffusing the volatilized size in said zone as to prevent ignition and burning of the same therein, exhausing a major portion of the volatilized size from said zone, introducing the advancing partially desized fabric to a zone maintained at a temperature between about 1100 F. and 1280 F., volatilizing a major portion of the remaining size therein While diffusing the volatilized size to prevent ignition and burning of the same adjacent the fabric therein, and then introducing the advancing fabric to a zone maintained at a temperature between about 1280 F. and 1400 F. to set the fibers thereof and volatilize any residual size from the fabric.

7. A desized glass fabric product desized by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,845,364 Waggoner July 29, 1958

Claims (1)

1. A PROCESS FOR DESIZING A SIZED UNFINISHED GLASS FABRIC, WHICH COMPRISES HEATING AN ADVANCING LENGTH OF SAID FABRIC TO A TEMPERATURE SUFFICIENTLY HIGH TO VOLATILIZE THE SIZE FROM THE FABRIC, MAINTAINING THE FABRIC AT SUCH TEMPERATURE FOR A TIME SUFFICIENT TO VOLATIZE AT LEAST 75% OF THE SIZE, TO DIFFUSING THE VOLATIZED SIZE AS TO PREVENT IGNITION AND BURNING OF THE SAME ADJACENT THE FABRIC, RAISING THE TEMPERATURE OF THE PARTLY DESIZED FABRIC TO A TEMPERATURE SUFFICIENTLY HIGH TO SET THE FIBERS THEREOF, AND VOLATILIZING SUBSTANTIALLY ALL OF THE REMINING SIZE FROM THE FABRIC WHILE DIFFUSING THE VOLATILIZED SIZE TO PREVENT IGNITION AND BURNING OF THE SAME IN THE VICINITY OF THE FABRIC AT THE ELEVATED TEMPERATURE.