US2994133A - Web heat treatment and apparatus therefor - Google Patents

Description

Aug. 1, 1961 A. v. ALEXEFF ET AL 2,994,133

WEB HEAT TREATMENT AND APPARATUS THEREFOR 2 Sheets-Sheet 1 Original Filed Sept. 17, 1954 @235 XANDER v AL Msuns 2R8 HPCAARDS A. v. ALEXEFF ET AL 2,994,133

WEB HEAT TREATMENT AND APPARATUS THEREFOR Original Filed Sept. 17, 1954 Aug. 1, 1961 2 Sheets-Sheet 2 FIG. 3

FIG. 4

F G 6 INVENTORS ALEXANDER V. ALEXEFF EDWIN P. HONBURG HOWARD RICHARDS wid rates 2 Claims. (Cl. 3456) The present invention relates to heat treatment of webs and strands and particularly to method and apparatus for attaining very precise and responsive temperature con trol of the treated material. For purposes of this application strands is to be understood to include monofilaments such as nylon, rayon, and glass fiber as well as wires, cords, narrow tapes and tubings, and strips" is to be understood to include strands and also webs such as metal sheet, paper, textiles, films and wide tapes.

In a multitude of present-day continuous or semicontinuous processes for the heat treatment of strip, it is necessary to maintain the treated material within critical temperature limits during the actual heat treating step (usually while also maintaining a certain time of exposure or at least not departing from a certain range of exposure times). Any variables which tend to displace strip temperature across such critical limits must, therefore, be counteracted by adjustment of the rate of heat transfer to the web. Such adjustment is accomplished in a number of ways. For example, oven temperature is varied by increasing or decreasing the output of the burners or heating elements which are the source of the heat. It will be apparent that close strip temperature control under quickly fluctuating control conditions cannot be practically attained with this rudimentary arrangement. Another procedure is to provide a standby supply of heat (i.e., heated air) which can be supplied to the oven or drier on demand. Conversely, an overheated oven may be provided which is cooled to the desired temperature by outside air or other cooling medium, the rate of supply of the cooling medium being varied in response to control requirements to counteract any tendency of the strip to exceed temperature limitations. Thus, a degree of strip temperature control may be attained by responsively and continuously damping into the oven or drier an accumulated heating or cooling medium. However, the inherent waste and expense of this procedure renders it impractical for close temperature control. If a relatively wide temperature range is allowed, damping in of the alternative supply used occurs only relatively infrequently, but for close control damping in of the alternative heating or cooling medium must occur almost continuously, representing a prohibitive heat loss. Another possibility is to vary web speed, but in most production set-ups to continuously vary speed of the processing line is obviously impractical. The variation of web speed is, of course, entirely inapplicable to operations in which time of exposure must be maintained at a given figure or within a narrow range.

The above considerations have limited the possibilities of many strip heat treating processes where the ideal would be to closely approach critical temperature without exceeding it. Commercially attainable end results are compromised by the fact that the ideal is attainable only by the use of prohibitively costly and wasteful methods. For example, in hot stretching of nylon fabric following coating or impregnation, it is desirable to approach as closely as possible the limiting top web temperature at which the fabric will soften and fail or scorch. Conventional hot stretch installations provide 72,994,133 Patented Aug. 1, 1961 elaborate temperature control means for the oven through which the web is to pass. As control conditions vary (the wide variable is usually web speed which, on a continuous line, is adjusted from time to time according to production demand) it is, of course, necessary to vary the oven temperature. Excessive destruction of material during shutdowns, either by overheating or under treatment of portions of the web, must also be avoided. Highly responsive control of web temperature cannot be achieved without completely prohibitive expense due to heat waste and the cost of large auxiliary equipment. Accordingly, compromise is necessary and a considerable margin of safety must be maintained by choosing operating conditions so that the web temperature is well below the critical value which it can stand, despite the desirability of closely approaching this critical value.

An object of the invention is to provide close control of strip temperatture during heat treatment, such close control being readily maintained despite rapid fluctuation of control conditions such as strip speed, temperature and humidity of the input side of the strip, ambient air temperature and humidity and any other variables that tend to affect strip temperature during the heat treating step.

Another object of the invention is to make possible a very close control of the amount of stretch of a strip in a continuous or semi-continuous processing operation. In many applications close control of strip temperature is not, in itself, of primary importance, but it is highly desirable that the amount of stretch of the strip be confined within narrow limits. The amount of stretch is generally a function of three variables: strip tension, heating period and strip temperature. The first two of these, strip tension and the time of exposure of the strip,

may be very closely controlled by conventional methods.

Heretofore, however, the third of these variables, strip temperature, has not been subject to such precise control. Accordingly, another object of the invention is to make possible extremely close control of the amount of stretch of a strip on a continuous processing basis through precise control of the several parameters of the amount of stretch.

Another object of the invention is to provide improved means of controlling strip temperature regardless of whether extremely fine control is required.

Another object of the invention is to provide for quick accommodation of desired changes in strip speed without the necessity of varying oven temperature.

Another object of the invention is to resolve, by radical and simple means, certain problems of heat damage or improper treatment of the strip incident to shutdown.

A further object of the invention is to provide for economical temperature control in continuous or semicontinuous processes over an indefinitely broad range of strip speeds by employing gangs of ovens or oven sections which may be by-passed and completely shut down when not required.

These and other objects and advantages of the invention will become apparent from the following description of specific embodiments of the invention. As will be apparent to those familiar with Web or strand processing, specific mechanical, electrical or hydraulic equipment components to be employed in any given installation are a matter of choice within the routine skill of the art. Suitable components in each illustrated embodiment are, therefore, illustrated schematically in the interest of clarity in order that the invention itself may be most concisely and completely disclosed and understood.

In the drawings:

FIGURE 1 illustrates a relatively refined continuous web processing system employing the invention.

FIGURE 2 illustrates a semi-continuous web processing system employing the invention in a somewhat different manner than it is employed in the apparatus shown in FIGURE 1.

FIGURE 3 illurstrates an alternate set-up which may replace the central portion between the lines C-C and D-D of the processing line shown in FIGURE 2.

FIGURE 4 illustrates an alternate set-up which may replace the central portion between the lines AA and B-B of the processing line shown in FIGURE 1.

FIGURES 5 and 6 illustrate alternative oven and dancer arrangements.

FIGURE 1 illustrates a fully continuous web treating installation inwhich the invention is employed. The illustrated installation might be employed for impregnation and coating :1 web of nylon fabric with a plastic which is applied to the fabric in a dipping operation, the web then being heated, dried, and simultaneously stretched under considerable tension. In such hot stretching it is desirable to approach as closely as possible the upper temperature limit at which the fabric will fail or permanently weaken. In the illustration the web is indicated by the reference numeral 10.

The main components of the installation shown in FIGURE 1 comprise a pair of let-0E stands 11 and 12, a splice press 13, a tension establishing drive stand 14, a let-01f accumulator 15, a dip station 16, a first hightension-capacity pull rod stand 17, a vertical drying oven 18, a tension sensing stand 19, a second high-tensioncapacity pull roll stand 20, a wind-up accumulator 21 and a pair of wind-up stands 22 and 23.

The installation may employ in any conventional manner a plurality of variable speed DC. motors as a power and control means for the several web driving members. The power and control system may comprise a motor 28, generator 29, field exciter 30, an overriding or governing speed control rheostat 31, and a plurality of voltage responsive variable speed DC. motors 32, 33, 34, and 35, each of these motors with the exception of the motor 33 being provided with its own subsidiary speed control means such as field voltage rheostats 37, such several control means being responsive to variation in tension at several points in the system as explained below. A speed reducer 36 associated with each of the motors is mechanically linked with one of the processing line components as indicated in FIGURE 1.

The drying oven 18 may be constructed and arranged so that both entrance and egress of the web occurs through the port 42 during normal operation, the web being guided into and out of the port by the rolls 41. Within the oven the web passes around a dancer roll 40. The dancer roll 40 is mounted for lateral displacement so that it may be shifted up or down in a vertical path within the oven 18 and may furthermore be lowered a sufiicient extent to pass completely or at least partially out through the port 42. For this purpose the ends of the dancer roll 40 may be mounted in blocks which are engaged by an endless cable or chain 43 at either side of the oven. Each cable or chain 43 passes around associated sprockets or sheaves 44, one of which is powered by a reversible motor 45 through a speed reducer 48. It will, of course, be understood that other equivalent mechanism may be employed to shift the dancer roll 40, the choice of the most desirable mechanism being a matter of mechanical expediency in the particular circumstances and conditions.

In this example of the invention, a web temperature detector in the form of a radiation pyrometer 46 is provided to sense web temperature at the output end of web travel through the drying oven. Through a suitable and conventional control potentiometer 47 the motor 45 is controlled in response to sensed temperature so that upon increase in temperature the dancer roll 40 is lowered and upon decrease in temperature the dancer roll 40 is raised.

The overall speed of the processing line shown in FIG- URE 1 is governed by the pull rolls 17. It will be seen that the speed of the motor 33 associated with these pull rolls is governed directly by the overriding control rheostat 31, there being no ancillary variable control for the field voltage in this motor 33. As is conventional, variation of the armature voltage for this motor correspondingly varies armature voltage in the other drive motors 32, 34 and 35 through the common armature voltage line 50.

When the web processing line is running under normal conditions, a relatively low tension is maintained between one of the letoif stands 11 or 12 and the tension-establishing drive stand 14 by simple brake friction on the letolf stand. Between the drive stand 14 and the high-tension capacity pull rolls 17, an intermediate tension is maintained by the normally extended letoff accumulator 15 which has a weight or tension member W exerting a constant force in tension on the festooned web within the accumulator. Shifting of the lower member of the accumulator controls the associated rheostat 37 through a linkage 55. Thus, as the lower member of the accumulator tends to rise, the rheostat is automatically adjusted through linkage 55 to cause the motor 32 to speed up, which, in turn, tends to free the accumulator causing the lower member of the accumulator to move downward. Thus, a feed back or self-governing control maintains a constant length of web between the drive stand 14 and the pull rolls 17.

When the letoff roll of webbing is about to become exhausted, the motor 32 is stopped, by suitable means such as a cut-off switch, causing the web to be locked at the drive stand 14. When this occurs, the lower member of the accumulator 15 proceeds to rise as webbing is pulled along by the pull rolls 17. However, constant tension is maintained by the existence of the weight or tensioning member W. During exhaustion of the letoff accumulator 15, the alternate fresh letolf roll from one of the letofl stands is spliced to the tail of the nearly exhausted web at the splice press 13. Thereupon the web, at the drive stand 14, is unlocked by cutting back into the circuit the motor 32. The lower bar of the letoif accumulator is now in an abnormally high position, and, accordingly, the linkage 55 controls the rheostat 37 so as to call for greatly increased speed of the motor 32. Thus, the accumulator 15 quickly refills, and, as its lower member approaches its normal position, the rheostat is automatically varied through linkage 55 until the speed of the motor 32 is reduced to its normal range, whereupon normal feed back or self-governing control of the motor speed continues within such normal range.

During passage from the drive stand 14 to the pull rolls 17, the webbing is illustrated as being processed at the dip station 16, the webbing being dipped into a coating liquid 56, then passed between scraper bars 57, squeegee rolls 58 and heater bars 59.

Between the pull roll stand 17 and the second pull roll stand 20, a relatively high tension, which may be in the order of several thousand pounds, is maintained in the web by a weight or tensioning spring or other equivalent member W associated with the tension-sensing stand 19. Any tendency of the tension through this portion of the run to fall off or build up causes shifting of the member W, which, in turn, through its associated linkage 51 and rheostat 37, speeds up or slows down the motor 34 until the member W is returned to its initial position.

Relatively low tension is maintained between the pull roll stand 20 and the wind-up stands 22 and 23 by the control associated with the wind-up accumulator 21, this control governing the speed of the wind-up stands and being similar to the control of the drive stand 14 by the letofI accumulator 15, except that the lower member for the wind-up accumulator is normally in raised position. When a wind-up stand is filled, the motor 35 associated with that stand is stopped and the guide rolls 53 are locked together. When this occurs the lower member of the accumulator 21 proceeds to fall as webbing continues to be supplied to it by the pull roll stand 20. Constant tension is maintained between the weight or tensioning member W associated with the wind-up accumulator 21. During fill of the wind-up accumulator, the web is severed on the output side of the rolls 53 and the alternate wind-up stand is threaded with the webbing, the rolls 53 being either manually advanced or being advanced by a small auxiliary motor a slight amount to permit such threading. Thereupon, the guide rolls are unlocked while Simultaneously the motor 35 is cut back into the circuit. The lower member of the wind-up accumulator is now in an abnormally low position and, accordingly, the associated linkage 52 controls the associated rheostat 37 so as to call for greatly increased speed of the motor 35. Thus, the accumulator 21 quickly empties, and as its lower member approaches its normal raised position, the rheostat is automatically varied through linkage 52 until the speed of the motor 35 is reduced to its normal range, whereupon normal feed back of self-governing control of the motor speed continues within such a normal range.

When the line is operating at speed as determined by the overriding control rheostat 31, temperature of the web is sensed by the radiation pyrometer 46. As temperature starts to increase or decrease, the motor 45 is controlled to lower or raise the dancer roll 40. It will be understood that the temperature within the oven 18 may remain almost constant, varying only slightly according to ambient conditions of temperature and humidity. Even such minor changes are compensated for by the control of the motor 45 by the pyrometer 46. Thus, it is possible to continuously operate at a web temperature which approaches very closely critical web temperature. If it be comes desirable to change web speed, the setting of the rheostat 31 is varied. As the changing speed begins to reflect itself in a change in web temperature, the pyrometer 46 automatically causes the motor 45 to change the position of the roll 40 in a direction to overcome the indicated direction of change of web temperature. I

It will be observed that while sensing of the temperature of the web itself approaches the ideal control, there may be other variables which are straight line or other known or determinable functions of webtemperature. Accordingly, it is possible to provide for sensing of such variables rather than providing for direct sensing of web temperature. For example, in some installations Web temperature may very closely follow oven temperature and thus, sensing of the oven temperature may provide for satisfactorily accurate control of web temperature.

It will be apparent to those familiar with web or strand processing techinques and equipment that the electric power and control means may be replaced by conventional mechanical or hydraulic apparatus, and that the specific supports shown may be varied as a matter of expediency to provide for greater range control, more eflicient drives, greater practicality of the circuit under given conditions, or for other purposes, all as is conventional in the art.

In FIGURE 2, a semi-continuous installation embodying the invention is illustrated. This installation may include a let-off stand 111, a splice press 113, a dipping station 116, a high-tension-capacity pull roll stand 117, a vertical drying oven 118, a tension sensing stand 119, a second high-tension-capacity pull roll stand 120, which includes tension sensing elements and a wind-up stand 122. It will be seen that the processing line illustrated in FIGURE 2 is generally similar to that shown in FIG- URE l, with the exception that no accumulators are provided so that change-over of the letoff and wind-up rolls cannot be accomplished without shutting down the line. Relatively low tension from the stand 111 to the stand 117 is maintained by brake friction at the stand 111. Through a tension sensing element 126 and a suitable linkage 124 associated with the stand 120, the motor 127 is controlled to maintain correct tension at the output end of the line.

Also, tension between stands 117 and 120 is maintained by the feedback control from the tension sensing stand 119 in a manner which will be apparent from the drawings and is in all respects similar to the feedback control to the tension sensing stand 19 in FIGURE 1. In the installation shown in FIGURE 2, positioning of the dancer roll is accomplished by remote control of a motor which, through a speed reducer 148, raises or lowers the dancer roll 140 by a linkage including the sheaves 144, such linkage being similar to the linkage which includes the sheaves 44 in FIGURE 1. The remote control means for the motor 145 is indicated in FIGURE 2 as a reversing switch 147.

In the installation shown in FIGURE 2, the speed of the line as a whole is tied in to the position of the dancer roll 140 through the linkage 146 and armature voltage rheostat 149. Fine web temperature control is not accomplished in the sense that it is attained in the installation shown in FIGURE 1, that is, varying ambient conditions are not accounted for. However, very rapid changes in web speed may be accomplished without disturbing web temperature and while maintaining constant oven temperature.

When it is desired to shut down the line, the dancer roll 140 may be lowered throughout the length of the oven 118, thus progressively decreasing web speed while at all times maintaining proper web temperature. The dancer roll 140 may thereupon be lowered finally through the port and the line may be simultaneously stopped. Thus, in change-over wastage due to improper heat treatment of certain portions of the web is avoided and, at the same time, constant oven temperature can be maintained.

It will be understood that a control set-up similar to that illustrated in FIGURE 2 may be employed on a fully continuous line such as that shown in FIGURE 1. While the control illustrated in FIGURE 2 is not as refined as the control originally described in connection with FIGURE 1, it will nevertheless enable substantial economies to be realized in the oven installation, while still making possible rapid changes in production.

FIGURE 3 illustrates a modification of the equipment shown in FIGURE 2, the portion of the equipment between lines CC and DD in FIGURE 2 being replaced by the apparatus shown in FIGURE 3. The single oven 118 is replaced by a multiple oven or a plurality of ovens 118A, 11813, and 118C, each having its own dancer roll 140A, 14GB, and 140C. Each of these dancer rolls is positioned by control means similar to that associated with the dancer roll 140. Through linkages 146A, 146B, and 146C the position of these dancer rolls controls the heating of series connected armature voltage rheostatsr 149A, 149B, and 149C. As a run commences, the dancer roll 140C is raised in the oven 118C. When the roll 140C has reached its top-most position, the roll 140B is then raised, then in turn the roll 140C. With decreasing speed, the rolls are lowered in reverse sequence from their ovens, the roll 140C being completely withdrawn from its oven upon complete shutdown. In the particular installation shown, it is immaterial which roll is raised or lowered first. It will be apparent, however, that it may be desirable to inter-lock the controls so that raising or lowering of the rolls will have to progress in a definite sequence. It might be desirable to maintain the oven 1180 at temperature, thus at all times maintaining the line in condition to commence or continue operation at one-third of its full speed capacity. The other chambers might be brought to temperature only when higher capacity was called for. FIGURE 4 illustrates a modification of the apparatus shown in FIGURE 1, the specific apparatus shown in FIGURE 4 replacing the portion of FIGURE 1 between the lines AA and B-B. In FIGURE 4, next to the oven 18, is provided a cooling tower 70. The linkage which raises and lowers the dancer roll 40 simultaneously and conversely lowers or raises a dancer roll 71 Within the cooling tower. The control of the position of the dancer roll 40 is manual and is accomplished by the motor 75 acting through a speed reducer 76, the motor being controlled by an on-and-off reversing switch 77. It will be apparent in this example that Web temperature must be varied manually with the control 77. For example, if the armature voltage rheostat 31 is maintained at a constant position and the temperature of the web (or oven) appears to be rising, the operator would control the motor 75 so as to slightly lower the dancer roll 40. This embodiment is relatively unrefined as far as automatic control is concerned. However, it illustrates a method of making temperature change very highly responsive to change in the position of the dancer roll. With lowering of the dancer roll, the length of web exposed in the oven is decreased while simultaneously the length of web exposed in the cooling tower is increased. It may be desirable in some installations to reverse the order of the heat cooling towers, making the cooling tower precede the heating tower. It will be understood that this principle may be employed in any of the previously described automatically controlled installations.

While all the above specific examples of the invention have employed similar ovens and similar dancer arrangements, almost unlimited alternatives are possible. In FIGURE 5, for example, is schematically shown a horizontal oven 218 through which a Web or strand 210 is passed. The web is guided by the idlers 211 and 212 outside the oven and by the fixed idler 213 Within the oven. A pair of dancers 240 and 241 are mounted for pivoting movement around a common axis in the manner illustrated in the figure. It will be seen that in the dotted line position the web or strand has a somewhat increased path of travel through the oven. &1ch an arrangement is obviously suitable for only a narrow range of strip speed at a given oven temperature, but within such range this arrangement enables fine strip temperature control to be achieved. If there is a roughly linear or planar heat source 220 within the oven, the arrangement preferably is such that as the web path is lengthened, spacing from the heat source diminishes, the two variables thus affecting web temperature in the same direction.

In FIGURE 6 is shown another example of an oven and dancer arrangement. Here the web 314 is guided by the idlers 311 and 3 12 outside the oven 318 and by the fixed idler 313 Within the oven. A dancer 340 is mounted for reciprocating movement to vary the length of web within the oven in the manner indicated in the drawing.

The above description of the invention should make it apparent that the invention may be embodied in many different specific strip processing set-ups. Disclosure of the invention will suggest to the art many possibilities for specific installations which are tailored to particular conditions and operating requirements. The scope of the in- 8 vention is, therefore, not limittd to details of the embodiments described above, but is to be defined by the claims set forth below. In the claims it is to be understood that the term roll embraces pulleys and sheaves, cylindrical bars and tubes and other equivalent elements.

This application is a divisional application with respect to our copending application Serial No. 456,691, filed September 17,' 1954, now Patent No. 2,837,834, issued JunelO, 1958.

What is claimed is:

1. Strip treating apparatus comprising a heating chamber having heating means combined therewith, input guide means to guide strip material to said heating chamber, output guide means to guide strip material from said heating chamber, other guide means intermediate said input and output guide means and comprising dancer guide means, means for translatably mounting said dancer guide means for translation within said heating chamber and through a continuous range therein to vary the length of strip material within the heating chamber over a continuous range, means to sense the strip tem perature which results from exposure of the strip to heat supplied within said heating chamber by said heating means, and means responsive to said sensing means to actuate said mounting means so as to translate said dancer guide means to vary the length of strip material within the heating chamber as an inverse continuous function of indicated strip temperature.

2.. Strip treating apparatus comprising a heating chamber having heating means combined therewith, input guide means to guide strip material to said heating chamber, output guide means to guide strip material from said heating chamber, other guide means intermediate said input and output guide means and comprising dancer guide means, means for translatably mounting said dancer guide means for translation from without said heating chamber to within said heating chamber and through a continuous range therein to vary the length of strip material within the heating chamber over a continuous range starting from zero, means to sense the strip temperature which results from exposure of the strip to heat supplied within said heating chamber by said heating means, and means responsive to said sensing means to actuate said mounting means so as to translate said dancer guide means to vary the length of strip material within the heating chamber as an inverse continuous function of indicated strip temperature over a continuous range starting from zero.

References Cited in the file of this patent UNITED STATES PATENTS 1,467,106 De Moos Sept. 4, 1923 2,092,657 Smith Sept. 7, 1937 2,501,537 Parkes Mar. 21, 1950 2,872,173 Munker Feb. 3, 1959

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