US 3286077 A
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United States Patent 3,286,077 HEAT-ZONED PRESS HEAD David L. Radford and Burlin D. Bates, Salt Lake City, Utah, assignors to McGraw-Edison Company, Elgin, Ill., a corporation of Delaware Filed Nov. 23, 1964, Ser. No. 413,105 7 Claims. (Cl. 219-251) This invention relates to a press head that is divided into heat zones, and has for an object to provide means for controlling the level of heat in each zone independently of the other, thereby providing pressing temperatures at different portions of the head according to the form, thickness and other characteristics of garments or items that are pressed'by said head.
Practically all fabrics have an optimum temperature at which best pressing results are obtained. In some fabrics, this temperature may have a wider range-in others, the range is quite narrow. Since garments made of fabrics having a critical or narrow optimum range may be pressed at some portions through a single layer or lay of fabrics, and at others, through two or more lays, the pressing heat that is applied by presses of conventional design is throughout the pressing surface of the press head. Such a uniform application of pressing heat will not, therefore, press single-lay and multi-lay portions of a garment with equal efliciency. Also, in industrial fields, only one portion of a grament may be pressed in an area of the press substantially less than the full area of the head. As a consequence, the portion of the head of a conventional press, that is not pressing the garment, is nevertheless being heated to the level of heat in the portion that in doing the pressing, resulting in an unnecessary expenditure of power entailing a monetary loss.
Accordingly, another object of the invention is to provide a press head that has individually controlled heat zones which may be set to provide different levels of heat in said zones according to the character, areal extent, form or thickness of different portions of the garment or item that is being pressed.
Another object of the invention is to provide a press head, as characterized above that, after setting of the desired heat level at each zone, maintains each level within a narrow range in response to sensing means for each said zone.
A further object of the invention is to provide a heatzoned press head that, because the same, by pre-selection and sensor control, may be kept in a narrow heat range in each individual zone, enables lowering of the pressing time, since all portions of the garment may now be dried and pressed within a time range suitable to all areas of the garment. In conventional presses, the pressing time must be extended to the time required to press the thickest or wettest areas although other portions have been dried and pressed several seconds sooner.
This invention also has for its objects to provide such means that are positive in operation, convenient in use, easily installed in a working position and easily disconnected therefrom, economical of manufacture, relatively simple, and of general superiority and serviceability.
The above objects of the invention may be realized in a press head that is provided with a complement of heating elements arranged in separate groups and provided over two or more areas or zones of the head, temperature sensitive means provided at or in each said zone and responsive to narrow variations in the level of heat at each respective zone, and electrical control means connecting each complement of heating elements and the temperature sensitive means of each respective area. The control means responds to variations in electrical resistance of the temperature sensitive element to cut the heating element in and out of electrical circuit, accordingly.
3,286,077 Patented Nov. 15, 1966 The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description and which is based on the accompanying drawing. However, said drawing merely shows, and the following description merely describes, one embodiment of the present invention, which is given by way of illustration or example only.
In the drawing, like reference characters designate similar parts in the several views.
FIG. 1 is a top plan view of a heat-zoned press head according to the present invention, combined with diagrammatic illustrations of electrical means to control the level of heat at the individual zones of the head.
FIG. 2 is an end view of said press head.
FIG. 3 is an enlarged and fragmentary sectional view as taken on line 3.-3 of FIG. 1.
FIG. 4 is a view similar to FIG. 3 of an alternative form of sensor-mounting means.
FIG. 5 is a schematic view of control means diagrammatically shown in FIG. 1.
FIG. 6 is a diagrammatic view of a temperature control circuit employing regulation or proportioning of the electrical resistance in the heater elements.
The heat-zoned press head that is illustrated comprises, generally, a pressing platen 5, a complement of heater elements 6 mounted on one zone or area of said platen, another complement of heater elements 7 mounted on another zone or area of said platen, a temperature-sensitive device 8 carried by said one zone or area of the platen 5, a similar device 9 carried by said other zone or area of the platen, control means 10 interconnecting the complement of heater elements 6 and the sensor device 8, and control means 11 similarly interconnecting the elements 7 and the sensor device 9.
The platen 5 is preferably made of sheet aluminum because the same has uniform heat distribution and is preferred over mild steel for this purpose. At a thickness of three-fourths of an inch, the same is suitably rigid and,
while it may be made of a flat sheet, is preferably trans versely convexly bowed, as in FIG. 2. The shape in plan is not material. The one shown in FIG. 1 is typical but may be varied.
It will be understood that this platen, by means of a steel or aluminum cover plate 15 welded to the longitudinal margins of the platen as at 16, may be carried by a yolk, arm, or other part of a pressing machine so as to be movable toward and from a buck on which a garment or other fabric item may be spread to be pressed by the concave lower face 17 of said platen. The platen-buck disposition may be horizontal, but any other disposition thereof may be used.
The heater elements 6 may comprise conventional strip heaters, or Calrod type heaters, such as used on the burners or ranges or other electrical heating appliances. The same may be mounted on the platen as by means of a conductive mastic or cement 18 that is trowelled on th outer surface of said platen, and the heater strips applied thereto and clamped in place temporarily until more mastic may be built up along the edges of the strips and the same allowed to dry, after ten to fifteen minutes. Thermon T-63 a product of Thermon Manufacturing Company, Houston, Texas, is exemplary of such a conductive mastic. Thermon T-63 is recommended for continuous operating temperatures up to 1250 F. After the same has air-dried so as to be completely hard in four to eight hours, it provides a conductive bond between the platen 5 and the strips 6 that enables safely obtaining platen heat in the range of 350 to 455", which is the contemplated heat required for pressing all-cotton fabrics, or fabrics comprised of varying proportions of cotton and fortrel polyester, dacron polyester, and nylon. Higher heats may be safely used, if well below the mentioned maximum.
The strip heaters 6 and 7 may be electrically connected, as indicated at 19, in groups thereof in each zone, as shown. It will be clear that current conducted to the heaters 6 will heat the latter and, through the mastic 18 connecting the same to the zone A portion of the platen, will heat said zone. Similarly, zone B may be heated by the heaters 7.
' Due to the direct connection of the strip heaters to the platen along the entire lengths of the strips, the heat conduction to the platen is not only such that provides uniformity of heat in the platen, it also insures substantial accuracy of the platen temperature throughout the area of any of the zones. Practice has demonstrated that the application of heat to a complement of strip heaters 6 or 7 to heat the zone of each said complement at an operating temperature of 455 F., will be accurate within one percent of said temperature, i.e., with 4 F., plus or minus, of the desired temperature of 455 F. A-t 350 F., the one percent variation is plus or minus 35 F.
The temperature-sensitive devices 8 and 9 are similar, and will be called thermistors since they are electrical resistors made of a material whose resistance varies sharply in a known manner with the temperature.
Each thermistor, as best shown in FIG. 3, comprises a male plug member 20 that has a nominal ohmage that will cover a temperature range of 300 to 520 F. The range may be wider, but the same may be adequately covered by a thermistor having a mean or mid point resistance of 1500 to 2000 ohms and having a nominal differential of about twenty ohms or 1%" F.
Each thermistory 8 or 9 also includes a highly heatconductive holder 21 into which the plug member or sensor 20 is fitted in a manner to be subject, as directly as feasible, to the heat of the platen 5. To this end,
said holder 21 is tightly threadedly connected at 22 to theplaten, with the innermost end of the plug element well within the sphere of the heat of the platen, due to the direct conduction between it and the holder, and between the holder and the platen. The .base portion 23 of said holder is thinned out at 24 to insure that the heat energy travels to the work surface area and then to the sensor 20. As shown best in FIG. 4, the thermistor holder 21a may be surrounded by a channel 23a formed in the top of the platen rather than in the base 23 of said holder, as in FIG. 3. The arrow 23b shows that the conduction path of the heat energy that originates in the heaters 6 is around said groove to the work surface area and then to the portion of the platen a that is surrounded by the groove 23a. This arrangement insures that the sensor 20 will sense or respond to the temperature of the pressing surface 17 of the platen, rather than the temperature at the top of the platen 5. Each thermistor 8 or 9 is electrically connected to the complement of strip heaters 6 or 7, as the case may be, by one of the similar control means or 11.
Each said control means comprises a power supply unit 25 that is energized by a sixty-cycle, 110-volt or 220-volt A.C. line 26. Said unit 25 is connected to a D.C. amplifier 27 that has an input line 28 and an output line 29. The former, in control means 10, is connected to the thermistor 8, and in control means 11, is connected to the thermistor 9. The output line 29 of each means 10 or 11 is connected to a control relay 30, and the latter by a line 30a to a heavy-duty relay 31 which, in the means 10, is connected by a line 32 to the strip heaters 6 of zone A, and in the means 11, is
connected by a similar line 32 to the strip heaters 7.
The latter relays are connected to the AC. input line 26. As will be later more fully described, the coil 31a becomes energized to cause switch 31b to close, thereby energizing line 32, thus heating heaters 7. When the coil 31a is deenergized by the relay 30, the switch 3lb will open, causing line 32 to become deenergized thereby to allow the heating strips 7 to cool.
In explanation of the above and based on amplifierrelay 10 shown in FIG. 5 (a product of Honeywell of Minneapolis, known as Versa-Tran), when the machine is started up and is cold, the relay 30 of the controller 10 or 11 becomes activated. The mercury relay 31 becomes energized because, as shown best in FIG. 5, the same is connected across the terminals 30a, which are make on drop terminals or contacts, which means that this relay will energize on a too cool condition of the press. As a consequence, the thermistor or sensor 8 is too cool. When the press reaches a pre-set temperature, which may be set by conventional means under control of a knob 30b, relay 30 will deenergize, opening the contacts 30a and shutting off power from the 220-volt line to the head or platen 5. When the thermistor starts to cool with the head cooled down, the relay 30 closes, closing the contacts 30a. current value or level is not considered as being too high or too low-it would be off or on with respect to energizing or deenergizing the relay coils.
Each of the above generally-described control means operates in one of two basic ways. One of these ways uses a thermistor as above described. Such a heat-sensitive element 20 has a resistance that is inversely proportional to the temperature that is applied to it and the current flowing to it varies inversely as the resistance. The current flowing through the thermistor is small-in fact, so small that it is insuflicient to actuate the control relay 30 directly. So as to increase the magnitude of the current to a value where it will pull in the relay 30, the D.C. amplifier 27 is provided to provide a D.C. potential at relay 30 high enough to operate it. The relay 30 is actually an intermediate device that, because it is operated by low-value current, cannot of itself send a current to the strip heaters 6 or 7 of magnitude sufficient to cause the same to heat up. However, said control relay 30 is capable of switching on the heavy-duty relay 31 so that the power line 26 is directly connected to the line 32 which feeds current to the banks or complements of strip headers 6 or 7, as the case may be.
Operation rected only to zone A and the related means for control- I ling the temperature of the platen 5 in said zone.
Assume the coil 31a of relay 31 is energized, then the switch 31b would close to eifect a direct connection between the power lines 26 and 32 to the strip heaters 6. This high-potential A.C. will cause the temperature of the heaters 6 to increase, thereby increasing the temperature to which the thermistor 8 is subjected, and to effect a corresponding and inverse decrease in the resistance of the thermistor 8.
Since the D.C. amplifier 27 had been pre-set to the high of a desired control temperature at the platen 5, as this temperature is reached, the amplifier 27 releases the control relay 30, which deenergizes the coil 31a of the heavyduty relay 31 to open switch 31b, cutting the power from line 26 to line 32. Thus, the strip heaters are out of circuit and will cool, allowing the press head 5 to cool also, by convection and radiation.
As the head cools, the low control temperature is reached, causing a corresponding and inverse increase in the resistance of the thermistor 8. As a result, the amplifie-r 27 lets the relay 30 actuate, reenergizingthe coil of relay 31. Now, the circuit to the heaters 6 is reestablished as at the beginning of the operating cycle.
In the above manner, the control means 10 and 11, in response to changes in the resistance of the thermistors 8 and 9, respectively, will maintain the temperatures of In this type of operation, the.
zones A and B, respectively, within the narrow ranges as pre-set.
The means and 11 may comprise Versa-Tran temperature controllers, manufactured by Honeywell of Minneapolis, and, depending on the model that is used, will maintain a temperature at the press head within a nominal differential of about 1.5 F. or about .3 F. when used with thermistors of the character above described.
The above control means 10 and 11 operate in a manner that switches power to the heaters 6 and 7 on and off every few minutes. The thermal inertia of the heat mass (the platen zones) averages out the pulses of heat applied, and the mean temperature remains at a pre-set level.
Another way of controlling the temperature of the zones of head 5 consists in controlling the quantity of the electrical power flowing into the resistance heater elements 6. The same is a proportioning means that operates on a supply and demand principle. If the head is much cooler than the pre-set temperature, the controller supplies a relatively large amount of power to the heaters. As the temperature of the head increases, the controller senses the increase and begins limiting the amount of power to the heaters proportionally to the increase. When the preset temperature is reached, the controller limits the power flow to a heat level-maintaining temperature.
Inspection of FIG. 6 will show that, in the present control circuit, as explained in connection with FIGS. 1 and 5, the selenium control rectifier 40 replaces the relay 31 previously described. In this case, two selenium control rectifiers 41 and 42 are combined in a device known as Triarc (a product of General Electric Co.), connected, as shown, in an inverse parallel network with a common gate terminal 43. Two separate selenium control rectifiers (SCR) may be used as a triggering means, but the same is more complex than the Triarc compound rectifier device.
In the circuit illustrated in FIG. 6, the thermistor 8 senses the temperature of the heated surface 17 of the head 5. If this surface is relatively colder than a desired temperature, the amplifier and triggering circuitry of device 10 or 11 fires the rectifier unit 40 at the beginning of each half-cycle, thereby keeping the power level high and causing a temperature increase in the head 5.
As the temperature approaches the pre-set temperature, the device 10 or 11 fires the rectifier unit 40 progressively later (due to resistance changes in the thermistor 8) during the half-cycle, thereby lowering the input level. In this manner, the current flow or level is proportioned according to the demand of the preset temperature.
It will be clear that a feature of the control means employing Triarc or SCR is the complete and graduated control maintained because the power, in effect, is turned off and on one hundred twenty times a second, instead of every one or more minutes under relay control.
While two zones have been shown and described, more than that number may be used, if desired.
While the foregoing has illustrated and described what is now contemplated to be the best mode of carrying out the invention, the construction is, of course, subject to modification without departing from the spirit and scope of the invention. Therefore, it is not desired to restrict the invention to the particular form of construction illustrated and described, but to cover all modifications that may fall within the scope of the appended claims.
Having thus described this invention, what is claimed and desired to be secured by Letters Patent is:
1. A heat-zoned press head comprising:
(a) a metal pressing platen,
(b) at least two complements of heater elements, each arranged over different areal or zonal portions of the platen,
(c) heat-conductive mastic directly and fixedly connecting each heater element of both said complements to the surface of the platen opposite to the pressing surface thereof for conducting the heat of said elements directly to the platen,
(d) means to individually heat said complements of heater elements,
(e) a temperature-sensitive device having direct physical contact with the platen within the areal or zonal portion in which each complement of heater elements is located, and
(f) individual control means for each complement of heater elements detached and located remotely from the platen and responsive to each temperature-sensitive device, and electrically connected between each complement of heater elements and temperaturesensitive device.
2. A heat-zoned press head according to claim 1 in which each control means is adapted to be preset to maintain the temperatures of each respective complement of heaters in a range between 650 and 455 F.
3. A heat-zoned press head according to claim 1 in which each control means is adapted to be preset to provide a temperature range of 350 to 455 F. in each respective complement of heaters and the areas of the platen over which the respective complements of heaters are arranged.
4. A heat-zoned press head according to claim 1 in which each means to heat the heater elements includes an electric circuit to energize the respective heater elements, and the temperature-sensitive devices each comprise a thermistor em bodying an electrical resistance connected in said circuit and varying in its resistance according to the level of heat conducted thereto by the platen around the thermistor.
5. A heat-zoned press head according to claim 4 in which the thermistors are of the type that have decreased electrical resistance as the same are subjected to increasing temperatures, and the control means connected to each thermistor becomes energized, when the resistance of the latter lowers to a predetermined level, to open the heater circuit.
6. A heat-zoned press head according to claim 4 in which each control means includes selenium control rectifier means in the heater-energizing circuit that, in response to changes in the resistance of the thermistor, proportions the current flow accordingly.
7. A heat-zoned press head according to claim 4 in which each control means includes selenium control rectifier means in the heater-energizing circuit that, in response to changes in the resistance of the thermistor, proportions the current flow accordingly, the rectifier means comprising two selenium control rectifiers in inverse parallel network, with a common gate.
References Cited by the Examiner UNITED STATES PATENTS 2,162,589 6/1939 Rich 236-7 2,248,676 7/1941 Jensen 21925 2,415,275 2/1947 Bruckman 219243 X 2,623,976 12/1952 Miles 219504 2,701,926 2/ 1955 Meyer 219243 X 2,758,150 8/1956 Zargarpur 174-84 2,840,679 6/1958 Hart 219519 X 2,912,557 11/1959 Michaelis 219505 X 2,970,394 2/ 1961 Brumbaugh 219251 X 3,114,819 12/1963 Woodling 219252 X 3,148,269 9/ 1964 Van Hartesveldt et al. 219243 RICHARD M. WOOD, Primary Examiner.
C. L. ALBRITTON, Assistant Examiner.