Abstract:
A fully integrated drying or heating system utilizes forced air and electrical heaters. A solid cartridge heater is enclosed within a compact air plenum with a circuitous air path arranged within the plenum in heat transfer communication with the heater. The plenums are shaped and configured to be used in banks of plural plenums, with the operating controls and all the components of the air distribution system and air heating system fully integrated into a modular package.

Description:
[0001]    This application is a continuation-in-part of U.S. Ser. No. 09/939,144, filed Aug. 27, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to evaporative drying systems, hereinafter called dryers, more particularly to dryers that are used to dry-solvent based or water-based inks, paints or coatings.  
           [0003]    Traditional dryers dry by projecting heated air and/or radiating heat energy. The most common form of a projected air dryer delivers lightly pressurized preheated air into a distribution plenum, which is then dispersed through a series of slots or circular orifices to the medium being dried. These types of dryers typically rely on large volumes of air to adequately dry, thus consuming substantial amounts of energy and requiring extensive air handling equipment.  
           [0004]    In some of the more recent forced hot air dryers, compressed air is preheated prior to entering the distribution plenum(s). The preheating is typically accomplished by the use of a separate heat plant device such as the common triple pass or inline air heater. Using a heat plant that is separated from the air distribution system introduces inefficiencies of operation; additional equipment and manufacturing costs; and additional equipment. The added equipment can also make the dryer prohibitively large in size for some applications that have limited available space.  
           [0005]    Current dryer systems have their operating controls located remotely from the distribution plenum(s), which increases the complexity of the controls system and the associated costs for the manufacturing and installation of the entire system.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention provides a forced hot air dryer for the printing, painting and coating industries that fully integrate the air handling equipment, heat plant, air flow control and air temperature control into a single compact package. The preferred embodiment utilizes a solid cartridge heater within a specially designed air distribution system to raise the temperature of the forced air just before it discharges. The invention greatly simplifies the complexity, reduces space requirements, and maximizes the energy efficiencies over current drying systems.  
           [0007]    Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The invention will be explained in conjunction with illustrative embodiments shown in the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 is a schematic illustration of a narrow web in-line printing press with multiple color stations.  
         [0010]    [0010]FIG. 2 is a schematic illustration detailing a single color station of the narrow web in-line printing press of FIG. 1.  
         [0011]    [0011]FIG. 3 is an end view of the air distribution system.  
         [0012]    [0012]FIG. 4 is a side view of the air distribution system and solid cartridge heater.  
         [0013]    [0013]FIG. 5 is a cross-sectional view of FIG. 4 with the solid cartridge heater partially removed.  
         [0014]    [0014]FIG. 6 is a side view of the manifold connected to multiple air distribution systems.  
         [0015]    [0015]FIG. 7 is a cross-sectional front view of FIG. 6.  
         [0016]    [0016]FIG. 8 is a schematic illustration of the air flow control system for the dryer.  
         [0017]    [0017]FIG. 9 is a schematic illustration of a variable transformer electrical control system for the dryer.  
         [0018]    [0018]FIG. 10 is a schematic illustration of an electronic control system for the dryer.  
         [0019]    [0019]FIG. 11 is a side view of the assembled control box enclosure.  
         [0020]    [0020]FIG. 12 is a front view of FIG. 11.  
         [0021]    [0021]FIG. 13 is a side view of the assembled dryer.  
         [0022]    [0022]FIG. 14 is a front view of FIG. 13.  
         [0023]    [0023]FIG. 15 is a sectional view of the temperature monitoring means for the dryer.  
         [0024]    [0024]FIG. 16 is a schematic illustration of an alternate air flow control system for the dryer. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.  
         [0026]    Printing, coating, and painting lines have various configurations and methods of operation. Configurations vary in the number of printing decks, method of conveying the product, line speeds, etc., which will all depend on the type of product, process, and application. Products can be conveyed in several different ways such as in the form of a continuous web, sheet, or simply moving the product through via a conveyor.  
         [0027]    More particularly, the flexographic press, illustrated in FIG. 1 is a conventional and well-known type of narrow web printing and/or coating press, hereinafter called narrow web press  11 . The narrow web press  11  typically prints and/or applies coating on a continuous web  1 , hereinafter called web, whereupon the freshly applied inks or coating need to be dried. The web  1  enters the narrow web press from the unwind station  2  and then travels through a series of idler rollers  3  in a serpentine path while passing through multiple print stations  4 .  
         [0028]    [0028]FIG. 2 details an individual printing station of FIG. 1. A print station  4  consists of a transfer roll  5  and plate roll  6  that apply a printed image  37  or coating onto the web as it passes through the print station  4 . After being applied to the web, the printed image  37  or coating moves past the transfer roll and plate roll area, and subsequently enters a drying zone  7  where it will be partially or completely dried before entering the next printing station.  
         [0029]    As the printed or coated web exits the last printing station  8 , depending on the product, process, and application, a final drying stage  9  may be required. The final drying stage  9  may be comprised of a single or multiple dryers. The final drying stage will evaporate the residual traces of ink solvents from the ink, and/or cure the already substantially dried inks prior to being rewound in the narrow web press rewinder  10 .  
         [0030]    The practice of configuring the combination of the web, unwind, print stations, dryers, and rewind is well known. The particular configuration of these fundamental elements of a printing press can vary greatly between printing technologies and process applications.  
         [0031]    The exemplary embodiments of the invention create means of efficiently transferring heat energy from a solid cartridge heater to the air as the air passes through the air distribution system. The exemplary embodiments of the invention substantially equalize the temperature of the heated air that is projected out of the dryer, across the dryer width.  
         [0032]    The solid cartridge heater is a commercially available device that is typically used to heat solid metal structures for plastic or metal manufacturing processes, and to heat liquids in tanks or pipes. The heating element is an electrical resistance heater that is ultimately powered by a voltage source. Various size solid cartridge heaters can be used that may vary in diameter, length, power level and mounting depending on the process and application. The preferred solid cartridge heater is of cylindrical geometry of approximately ½ inch cylindrical diameter with the cylindrical length of the solid cartridge heater approximately equal to the dryer width. The solid cartridge heater is well described in U.S. Pat. No. 3,970,822, herein incorporated by reference.  
         [0033]    To simply pass air over a solid cartridge heater that is housed within a simple shell plenum such as a common cylindrical or square tube may result in non-optimal operating conditions, including inefficient and uneven transfer of heat energy to the air. The inefficiencies originate from the limited surface area of the solid cartridge heater that is exposed to the passing air as well as unrestricted airflow patterns within the simple shell. The inefficient and uneven heat transfer results in localized hot spots within the solid cartridge heater that can severely reduce the operable life of the solid cartridge heater and can produce greatly varying forced air temperatures across the width of the dryer.  
         [0034]    The exemplary embodiments of this invention incorporate a specially designed air distribution system  13  that is fundamentally comprised of two separate metallic extrusions including the cartridge heat exchanger  14  and air distribution plenum  15  as shown in FIG. 3.  
         [0035]    According to the preferred embodiment, the cartridge heat exchanger  14  is designed with a cylindrical cavity  16  to accept the solid cartridge heater  12  (See FIGS. 4 and 5). The cylindrical diameter of the cylindrical cavity  16  is carefully controlled to minimize the clearance between the outside surface of the solid cartridge heater  17  (See FIG. 5) and the internal surface of the cylindrical cavity  38  in the cartridge heat exchanger  14  to provide better heat transfer and power density of the solid cartridge heater  12 .  
         [0036]    The cartridge heat exchanger  14  has multiple heat fins  18  that extend outwardly from the cylindrical cavity  16 . The outer geometrical profile of the cartridge heat exchanger  14  compliments the internal geometry of the air distribution plenum  15  to create air passages  19 . During operation, the solid cartridge heater  12  is energized by a voltage source. Heat that is generated by the solid cartridge heater is transferred into the cartridge heat exchanger  14  and will migrate outwardly into the heat fins  18 . The heat energy is then transferred to the air moving along the heat fin surfaces  24  as the air moves through the air passages  19 .  
         [0037]    Pressurized air enters the air distribution system  13  through a port that leads into the inlet cavity  20  of the air distribution plenum. Located at the bottom of the inlet cavity  20 , a baffle plate  21  is used to redistribute the air in order to provide a uniform and even air flow along the dryer width as the air exits the inlet cavity  20  through the baffle plate  21 . The baffle plate  21  is fabricated with a pattern of baffle plate orifices  22  that may vary in diameter, spacing, and arrangement across the width and length of the baffle plate  21  to facilitate the desired even and uniform flow. The baffle plate is located and captured by the baffle plate recesses  23  that are incorporated into the inner geometry of the air distribution plenum  15 .  
         [0038]    Once the air passes through the baffle plate  21 , the air moves along the heat fin surfaces  24  as shown in FIG. 3. As the air passes over the surface of the heat fins  1   8 , the air absorbs the heat energy from the heat fins  18  of the cartridge heat exchanger  14  through thermal convection. The circuitous air passages  19  increase the dwell time that the air is in contact with the heat fins  18  thus increasing the convective heat transfer efficiency.  
         [0039]    Engineering thermodynamics holds that heat energy output, Q, is directly proportional to the convective heat transfer coefficient, h, the surface area, A, and the temperature differential, ΔT, where Q=h*A*ΔT. By increasing the heat transfer surface area, the temperature differential between the heater and air can be lowered inversely while maintaining a substantially equivalent heat energy output to the air. The lowered temperature differential allows the solid cartridge heater to operate at lower temperatures, thereby increasing the expected life of the solid cartridge heater.  
         [0040]    At the end of the circuitous air passages  19  the heated air enters one of two orifice chambers  25  located near the bottom of the air distribution plenum  15 . The air distribution plenum walls  26  in the area of the orifice chambers  25  are fashioned to provide a simplified means of manufacturing a series of air release orifices  27  that connect the orifice chamber  25  with the outside of the air distribution system  13 . The air release orifices  27  can be manufactured to project the air either directly away  28  from the air distribution system, canted towards the middle  29  of the air distribution system or outwardly from the middle  30  of the air distribution system. In the preferred embodiment shown in FIG. 3, the canted surfaces are constructed at  45  degrees to the central axis of the air distribution system  13 .  
         [0041]    The air release orifices  27  may vary in diameter, spacing, and arrangement across the width and length of the air distribution system  13 , depending on the process or application. The air release orifices  27  are typically 1 millimeter in diameter or less.  
         [0042]    Solid cartridge heaters are commercially available with variable power densities along the axial length of the solid cartridge heater as well described in U.S. Pat. No. 3,970,822. The variable power densities can be used to counteract hot or cold spots resulting from uneven flow patterns past the solid cartridge heater. The variable power densities can also be used to deliberately create heated and unheated regions along the length of the solid cartridge heater. This allows the dryer system to be very versatile in meeting certain process or application requirements where more or less drying capacity is required in specific intervals or in specific areas along the width of the dryer.  
         [0043]    In the embodiment shown in FIG. 3, two isolated elongated thin recesses  31  are located towards the outside wall of the air distribution plenum  15  to function as thermal insulators between the air passages  19  and the outside of the air distribution plenum  15 . By creating a barrier for heat transfer from the air passages  19  to the outside walls of the air distribution system, the elongated thin recesses  31  improve the overall efficiency of the invention and maintain a reduced external surface temperature of the air distribution system  13 .  
         [0044]    In the embodiment shown in FIG. 4 and  5 , the air distribution system  13  is manufactured with end plates  32  and  33 , and gaskets  34  and  35  to effectively seal off the inlet cavity  20 , air passages  19  and orifice chambers  25  from the outside of the air distribution system  13 . One of the end plates, the heater bulkhead end plate  32  is manufactured with a threaded port  36  to fasten the solid cartridge heater  12 , and to effectively prevent pressurized air from escaping at the juncture of the solid cartridge heater  12  and the heater bulkhead end plate  32 . The threaded port  36  also provides a convenient means of assembling and/or replacing the solid cartridge heater  12 .  
         [0045]    By the means described above, the heat source for the dryer unit has been completely integrated within the air distribution system to result in a very compact package. In this embodiment, the end profile of the air distribution system  13  as shown in FIG. 3 is approximately 2″ by 2″.  
         [0046]    The embodiment described herein is capable of operating the solid cartridge heater at high temperatures while simultaneously maintaining substantially lower external surface temperatures given that air is flowing adequately through the air distribution system. This is important where human interaction can cause bodily injury upon skin contact with the hot surfaces.  
         [0047]    The process of evaporative drying of inks, coatings, and paints is not instantaneous. In many cases the maximum narrow web press line speed is limited by the drying capacity of the dryer system. In the prior art, it is standard dryer design practice to increase drying capacity by adding additional length to the dryer, thus increasing the residence time of the product being dried within the dryer.  
         [0048]    The invention increases drying capacity by: the incremental addition of air distribution systems; redistributing a given number of air distribution systems over a greater dryer length; or a combination of both. It is to be understood that the addition of an air distribution system will also, but not necessarily always, include the addition of an integrated solid cartridge heater.  
         [0049]    [0049]FIGS. 6 and 7 illustrate the means by which the invention incorporates a manifold  39  to accommodate multiple air distribution systems  13 . The manifold  39  used to couple the air distribution systems has a central cavity  40  in the major axis of the manifold that is sized sufficiently to provide adequate air flow to all coupled air distribution systems  13 . The coupling of the air distribution system to the manifold can be achieved through a variety of means including threading, sealant, liquid gasket, crushed-gasket sealing, etc. An exemplary arrangement is an o-ring face seal  41  held at the joining surfaces of the manifold  39  and the air distribution system(s)  13 . A series of fasteners  43  are used to pre-load the o-ring  41  and to prevent the air distribution system  13  from moving relative to the manifold  39 .  
         [0050]    The control of the preferred embodiment of the invention involves control of air flow and control of electrical power to the solid cartridge heater. The preferred embodiment of the invention provides a means for operators of the invention to vary both the temperature of the air and flow of the air to dry the product. This variability is necessary because products that can be processed on the narrow web press have broad ranges of thermal yield characteristics, and excessive temperature and airflow conditions can detrimentally affected fragile product structures.  
         [0051]    An exemplary embodiment of the invention utilizes a simple and inexpensive control system for the dryer system.  
         [0052]    The volume of air moving through an air conveying medium such as tubing or piping, hereinafter referred to as pipe, is dependent on the geometry of the pipe and the inlet pressure of air moving into the pipe. Variations in inlet pressure, pipe diameter, or pipe length can have a significant affect on the volume of air flowing through the pipe. It is difficult to reliably control the air flow through a pipe system by controlling the pipe system&#39;s inlet pressure if the characteristic of the downstream pipe system are unknown or if the pipe geometry can change arbitrarily. This is the inherent difficulty of utilizing a centralized or remotely located flow control system to control flow in a widely distributed air distribution system. Such systems will typically rely on remote sensing of pressure and/or flow and therefore adjust the pipe system&#39;s inlet pressure accordingly. It is one advantage of the invention to overcome the undesirable effects noted above.  
         [0053]    It is foreseen that multiple drying systems will be integrated into a narrow web press; therefore, it is an advantage of the invention that a repeatable control of air flow is possible by using a common air flow setting for each respective dryer system. According to the exemplary embodiment of the invention, by maintaining consistent pipe geometry in each dryer system, air flow through the air distribution system can be reasonably predicted and adequately controlled by controlling the inlet pressure into the dryer system.  
         [0054]    As illustrated in FIG. 8, the air flow control system is achieved by the use of an air flow regulator  42  which is a relatively inexpensive, minimally complicated, and commercially available device. Pressurized air  44  is supplied to the air flow regulator  42  which controls the output pressure of the air flow discharging from the air flow regulator  42 . The air flow regulator pressure is substantially equivalent to the inlet pressure of the pipe. The volume of air flowing out of the air flow regulator  42 , and thus through the dryer system, can be modified by changing the settings of the air flow regulator  42 .  
         [0055]    The solid cartridge heater is an electrical device with an electrical resistance, R, that generates thermal power, P, from electrical current, I, by Ohm&#39;s Law (P=I 2 R). Note the electrical current is also related to the electrical voltage, V, by Ohm&#39;s Law (I=V/R) therefore (P=V 2 /R). The electrical resistance of the solid cartridge heater is dependent on the operating temperature of the solid cartridge heater typically varying the electrical resistance of the solid cartridge heater by a margin of approximately 10%. The electrical resistance increases with the operating temperature of the solid cartridge heater. For the purpose of the following description, the electrical resistance of the solid cartridge heater will be treated as a constant value, R.  
         [0056]    The amount of electrical power consumed by the solid cartridge heater is directly related to the thermal power delivered to the heated air flow that is discharging from the air distribution system. By controlling the electrical power and volume of air flow, the temperature of the air flow can be controlled.  
         [0057]    A relatively simple scheme for controlling the power to the solid cartridge heater is to control the voltage to the solid cartridge heater. FIG. 9 illustrates a voltage controller based on a mechanically adjustable variable transformer, hereinafter referred to as the variable transformer  45 . The variable transformer  45  is a commercially available device.  
         [0058]    The variable transformer  45  allows simple adjustment of the output coil of the variable transformer  45  thus effecting the voltage output ratio of the variable transformer  45 . The variable transformer  45  is typically manually adjusted to supply a constant output voltage at the desired voltage amplitude. The output voltage from the variable transformer  45  serves as the supply voltage for the solid cartridge heater  12 . In this fashion a constant supply voltage is applied to the solid cartridge heater  12 . Also as shown in FIG. 9 multiple solid cartridge heaters  12  can be connected in parallel across the supply voltage.  
         [0059]    Adjusting the output voltage to one-half of the maximum output voltage will produce one-fourth the power produced at the maximum output voltage as can be determined from Ohm&#39;s Law (¼*P max =((½)*V max ) 2 /R). The variable transformer is an elegant means of adjusting the output power of the heater and the respective drying capacity of the dryer.  
         [0060]    One advantage of using the variable transformer control system is the low cost and low complexity.  
         [0061]    A further advantage of using the variable transformer control system is the ability to energize the solid cartridge heater(s) at a fraction of their rated power continuously, even without air flow through the air distribution system. This provides a convenient and more economical means of pre-heating the dryers by avoiding the consumption of pressurized air.  
         [0062]    In using the variable transformer control system as the primary electrical control system, the variable transformer control system lacks a closed-loop temperature control. At a constant output voltage setting a change in the air flow volume will affect the air flow discharge temperature. Thus without an independent temperature sensor monitoring the dryer operating temperature, the operator of this dryer will not have an accurate measure of the effective drying temperature. Furthermore, even with a temperature sensor feedback, a mechanically adjusted variable transformer would be very complex to configure to automatically control to a desired dryer operating temperature.  
         [0063]    In practical operation, depending on the product, process, and application, the air flow settings and the variable transformer settings can be determined through trial and error, and subsequently used as reference settings to reliably reproduce the same dryer conditions in the future on any of the variable transformer controlled dryers on the narrow web press.  
         [0064]    The variable transformer control system provides an effective means for operating the dryer, however the preferred dryer system includes a means to control to a desired dryer operating temperature since an acceptable level of drying is more readily correlated to a dryer temperature.  
         [0065]    The electrical control system illustrated in FIG. 10 uses an electronic controller  47  to modulate the supply voltage  49  to the solid cartridge heater(s)  12  between an energized and de-energized state. In this scheme, the supply voltage  49  to the solid cartridge heater(s)  12  is modulated at either the maximum supply voltage setting or none at all. The amount of thermal power delivered by the dryer system is related to the percentage of time the dryer is energized.  
         [0066]    The electronic controller  47  is a commercially available device that can be obtained in a variety of configurations and with a variety of features. In this preferred embodiment the controller output signal  46  from the electronic controller is a low voltage, low power signal incapable of energizing the solid cartridge heater(s)  12  directly. However, this low voltage, low power controller output signal  46  can be used to activate a secondary device such as a mechanical relay or solid state relay to energize the supply voltage to the solid cartridge heater  12 . In the embodiment shown in FIG. 10, a solid state relay  48  is used to energize the supply voltage  49  to the solid cartridge heater(s)  12  when the solid state relay  48  is commanded by the electronic controller  47  via the controller output signal  46 .  
         [0067]    The electronic controller  47  utilizes an external temperature measurement and compares it to a pre-set temperature as established by the operator of the narrow web press. The pre-set temperature settings depend on the product, process, and application. If the external temperature measurement is lower than the pre-set temperature, the electronic controller  47  commands the solid state relay  48  to energize the supply voltage  49  to the solid cartridge heater(s)  12 . If the external temperature measurement is higher than the pre-set temperature, the electronic controller  47  commands the solid state relay  48  to de-energize the supply voltage  49  to the solid cartridge heater(s)  12 .  
         [0068]    A potential problem of this scheme is that the electronic controller continues to command an energized state of the supply voltage whenever the external temperature measurement is below the pre-set temperature. This condition can exist when the air flow to the dryer system is shut-off either intentionally or mistakenly. Since this control scheme will only supply the maximum supply voltage when energized, the above condition can place the solid cartridge heater(s) at a severe risk of failure from reaching excessive temperatures.  
         [0069]    A solution to this problem is the integration of an electromechanical pressure switch or pressure transducer to monitor the pressure and thus flow of air through the air distribution system. The electromechanical pressure switches and pressure transducers are commercially available devices. In this preferred embodiment, an electro-mechanical pressure switch  50  monitors the air pressure of the air distribution system and allows the controller output signal  46  to activate the solid state relay  48  as long as the system is operating with adequate air pressure. Without adequate air pressure the electro-mechanical pressure switch  50  will electrically ground the solid state relay  48  and ensure the supply voltage  49  is not energized to the solid cartridge heater(s)  12 .  
         [0070]    A temperature sensor  51  is located to monitor the effective temperature of the dryer system, and to provide the external temperature measurement signal to the electronic controller  47 . The temperature sensor  51  can monitor the temperature of the air distribution system&#39;s component; the air within the air distribution system; the air discharging from the air distribution system; a component that is in contact with the product being dried; etc. Depending on the location of the measurement point, the control response of the system and the maximum achievable temperature can vary greatly. To overcome this, the operational control gains of an electronic temperature controller can be adjusted to establish acceptable system controllability.  
         [0071]    A circuit breaker  52  is incorporated as a switch and safety device for the control system of either the variable transformer control system or the electronic control system as shown in FIG. 9 and  10  respectively.  
         [0072]    The above text has described in detail the three basic subsystems of the forced air dryer including the air heating and distribution system, the air flow control system, and the electrical power control system. According to an exemplary embodiment of the invention, the three subsystems are combined into a singular compact unit for ease of integration with the web and into the narrow web press.  
         [0073]    An advantage of this exemplary embodiment of the invention is that by housing all of the air flow and electrical controlling components of the dryer into a control box enclosure the components are isolated from the environment. These components include the electronic temperature controller, air flow regulator, pressure switch, solid state relay, and circuit breaker, all of which have already been described above.  
         [0074]    Enclosing the air flow and electrical control components is an advantage of this embodiment since the control box enclosure can be gasket sealed and lightly pressurized to achieve a purged environment within the control box enclosure to prevent ingress of gases and contaminants. The lightly pressurized air is provided as a by-product of the relieving pressure regulator under normal operating conditions.  
         [0075]    Enclosing the air flow and electrical control components is also an advantage of the invention in that all of the controlling components are substantially shielded from incidental debris generated by normal operation of the printing press. The debris includes ink spills, cleaning solvent, lubrication, etc.  
         [0076]    It is also an advantage of the embodiments of the invention that the air flow lines and electrical lines to and from the control box enclosure can be connected and sealed such that the control box enclosure can be sealed and capable of being lightly pressurized.  
         [0077]    It is an advantage of the embodiments of the invention that the operational controls are located such that they are accessible to operators of the narrow web press.  
         [0078]    It is an advantage of the embodiments of the invention that the solid heater cartridge is enclosed within the air distribution system such as to result in acceptably low external surface temperatures of the air distribution system.  
         [0079]    The air distribution system can be advantageously designed to accommodate the maximum web width of the printing press and to provide the desired residence time of the dryer. This is accomplished by appropriate layout of the manifold and air distribution system(s) within the dryer as described in detail earlier in the patent.  
         [0080]    It is well known that drying capacity decreases as the distance between the web and the discharge orifices of the dryer increase. It is also well known that uniform drying will result when the web is held uniformly and at a constant distance from the dryer across both the length and width of the dryer, given that the discharging air flow and temperature are uniform across the same. It is an advantage of the embodiments of invention that the web can be held in the dryer at a close and even distance from the discharging air to achieve proper drying.  
         [0081]    In consideration of retrofitting the dryer onto a narrow web press, the integration of the web support into the dryer will minimize press modifications and dryer design variations with respect to web handling as the web passes through the dryer. The web support that is incorporated into the dryer must provide an even support across both the width and the length of the dryer, such that the web is prevented from being deflected when subjected to the discharging air from the air distribution system(s). It is also an advantage of the embodiments of invention that the web support can be a simple device in that it provides the operator easy access for web threading and dryer cleaning  
         [0082]    It is an advantage of the embodiments of invention that all components and subsystems of the dryer can be housed into a single compact unit that can be mounted in an area where space is limited.  
         [0083]    It is also an advantage of the embodiments of invention that the installation time of the dryer unit can be minimized. By including provisions into the dryer design, only mounting the dryer to the press and connecting to the electrical power and compressed air sources to the dryer can be required for installation.  
         [0084]    The air flow regulator  42 , pressure switch  50 , electronic controller  47 , solid state relay  48 , and circuit breaker  52  can be housed in a dedicated control box enclosure  53 . It is also an advantage of the embodiments of invention to include the control box enclosure  53 , manifold  39 , air distribution systems  13 , and all interconnecting components inside the dryer enclosure  62 .  
         [0085]    As illustrated in FIGS. 11 and 12, an external compressed air supply line is connected to the dryer through a single air supply port  54  on the control box enclosure  53 . The air supply port  54  can be achieved by a number of means including a quick air disconnect, a push-to-connect fitting, a hose barb fitting, threaded pipe fitting, etc. An exemplary means is a push-to-connect fitting, which provides a convenient and tool-less means of connecting and disconnecting the dryer from the external pressurized air supply line.  
         [0086]    The air supply port  54 , which is rigidly joined to the air flow regulator  42 , passes the supply air through the wall of the control box enclosure  53  and into the inlet port of the air flow regulator  42 .  
         [0087]    The air flow regulator  42  is advantageously accessible for manual adjustment by the press operator during normal operation of the dryer. The air flow regulator  42  can be mounted inside the control box enclosure  53  such that the control dial  55  of the air flow regulator  42  passes through an opening in the control box enclosure  53  thus allowing convenient manual adjustment of the air flow in the dryer.  
         [0088]    According to the exemplary embodiment, air flow exiting the outlet port of the air flow regulator  42  passes through a specially designed air flow block  56  which is then connected to an air outlet port  57  mounted to the wall of the control box enclosure  53 . The air flow block  56  can be connected to the air outlet port  57  by tubing. Outside of the control box enclosure, the air outlet port  57  can be connected to the inlet port on the manifold  39  by tubing.  
         [0089]    The air flow block  56  can also provide an air pressure sensing port for the electromechanical pressure switch  50 . The air flow block  56  can also provide holes  58  for mounting the solid state relay  48  firmly against the air flow block  56 . This firm surface contact between the solid state relay  48  and the air flow block  56  can provide a means for heat generated by the solid state relay  48  to be transferred to air passing through the air flow block  56 . The solid state relay  48  advantageously sheds this heat in order to operate safely and reliably, and the transfer of thermal energy to the air is an efficient use of the available thermal energy for the purpose of drying.  
         [0090]    The electronic controller  47  is advantageously accessible for manual adjustment by the press operator during normal operation of the dryer. The electronic controller  47  can be mounted inside the control box enclosure  53  such that the temperature display and temperature controller keys are presented outside the control box enclosure  53  thus allowing convenient manual adjustment of the dryer temperature setting.  
         [0091]    The circuit breaker  52  can operate as an electrical safety device and as a switch for energizing the control system of the dryer. The circuit breaker  52  can be mounted such that the switch can be manually switched from outside the dryer.  
         [0092]    The electrical power supply to the dryer can be provided by an electrical cable that penetrates the wall of the control box enclosure  53  utilizing a sealed electrical bushing  59 . The sealed electrical bushing  59  can have the capability to lightly pressurize the internal volume of the control box enclosure  53 .  
         [0093]    The electrical power supply can be connected to the circuit breaker  52  and then distributed internally to the electronic controller  47  and the solid state relay  48 . The control signal from the electronic controller  47  can be connected through the pressure switch  50  and then to the solid state relay  48 . The pressure switch  50  can be mounted to the pressure sensing port of the air flow block  56 . When air flows through the air flow block  56 , air pressure activates the pressure switch  50  and closes the electrical signal path between the electronic controller  47  and the solid state relay  48 .  
         [0094]    The electrical power can be switched on by the solid state relay  48  and then made available for connection to the solid cartridge heaters  12 . The controlled electrical power output to each of the solid cartridge heaters  12  can be achieved by utilizing a sealed electrical bushing  60  for each of the solid cartridge heater power cables  61 . The heater manufacturer can seal the power cables  61  to the end of the solid cartridge heaters  12  as part of the standard design.  
         [0095]    The temperature sensor feedback signal cable can also pass through the control box enclosure wall utilizing a sealed electrical bushing (not shown). The temperature sensor feedback signal is signal-connected to the electronic controller  47 .  
         [0096]    As illustrated in FIG. 13 and  14 , the control box enclosure  53  can be mounted to the dryer enclosure  62 . The manifold  39  and air distribution system(s) assembly can be mounted to the dryer enclosure  62 .  
         [0097]    As shown in FIG. 15, the web can be supported by a slide plate  63 . The slide plate  63  can be of a sheet metal construction, and can be attached to back side of the dryer enclosure  62  by use of a hinge allowing the slide plate  63  to function as a door. Mechanical latches  65  can be located towards the front-side of the dryer enclosure providing a convenient means for the press operator to open the slide plate for manual threading of the web through the dryer during machine set up, or for maintenance access to clean the air distribution systems  13 . The slide plate  63 , hinge, latches  65  and supporting structure of the enclosure can be designed to ensure that when closed, the slide plate  63  provides a firm web support that is positioned approximately ½″ from the discharge orifices of the air distribution system. The mechanisms described above also ensure that the location of the slide plate  63  relative to the air distribution systems  13  is held evenly across the length and width of the dryer.  
         [0098]    Normal operation of the dryer discharges significant volumes of air into the area where the product is being dried. As the product dries, significant volumes of solvent vapor are evaporated into the area where the product is being dried. It is an advantageous that the mixture of discharged air and evaporated solvent vapors are removed. This is achieved by substantially enclosing the area where the product is being dried within a box  66  and then exhausting the internal volume of the box  66 .  
         [0099]    The dryer enclosure  62  and control box enclosure  53  form five of the six sides of the box type construction of the box  66 . The slide plate  63  and web provide the sixth side of the box  66 . It is advantageous that minimal slot openings  67  and  68  are provided for the web to enter and exit the box  66  respectively. An external exhaust system provides the light suction necessary to draw the air and solvent vapors from inside the box  66 , and is connected to an exhaust port  69  located on the dryer enclosure to remove air and solvent vapors from inside the box  66 .  
         [0100]    Mounting holes  70  for attaching the dryer to the narrow web press structure are provided in the back plate  71  of the dryer enclosure  62  of the dryer.  
         [0101]    As briefly discussed earlier in the patent, dryer systems monitor and control a temperature of an element of the dryer system. It is most desirable to measure the actual product temperature of the product being dried since the product temperature is indicative of the level of drying that has been achieved. Historically, the means of measuring the actual product temperature has been very difficult to implement.  
         [0102]    In lieu of measuring the temperature of the product being dried, a common practice has been to measure the temperature of the forced air of the dryer with the general assumption that the product achieves the substantially equivalent temperature of the forced air. Depending on the product, process, and application this assumption may be invalid.  
         [0103]    It is one aspect of the invention that a means is provided that will more accurately represent the actual temperature of the product being dried. FIG. 15 illustrates this embodiment.  
         [0104]    A commercially available temperature sensor  51  can be mounted onto the backside of the metallic slide plate  63 , near the end of the metallic slide plate  63  where the web  1  exits the dryer  72 . The temperature of the metallic slide plate  63  in this area will essentially stabilize at the temperature of the web due to the close and constant proximity with the heated web  1 .  
         [0105]    Additional heat loads in the slide plate  63  may be generated due to the friction of the web  1  sliding over the slide plate  63 . The additional heat loads from friction are considered negligible due to the low contact force of the web  1  against the slide plate  63 . To minimize any other interference from the environment to the temperature sensor  51 , insulation  64  is added onto the backside of the slide plate  63  and the temperature sensor  51 . The thermocouple wire leads are then routed back to the input of the dryer&#39;s temperature controller.  
         [0106]    Alternately to this embodiment, the temperature sensor  51  can be located within one of the recesses  31  of one or more of the plenums  15 , mounted to the plenum  15  as shown in FIG. 3. Insulation (not shown) can be added onto the backside of the temperature sensor  51  onto the plenum  15  to minimize any other interference from the environment.  
         [0107]    [0107]FIG. 16 illustrates an alternate embodiment of an air flow control system. In this system  100 , a remote pilot-operated regulator or dome loaded regulator  104  is used to control air flow into the unit or units  13 . A conventional set point regulator  105  is operator controlled to send pilot pressure or set point pressure air to the dome  104   a  of the dome loaded regulator. The regulator  104  sends regulated compressed air to the unit or units  13  that is controlled by the regulator  104  to be equivalent to the operator set point pressure. The regulator is internally sensed, that is, the feedback of the output pressurized air of the regulator is taken from a tap within the regulator, just downstream of the regulator valve element. A feedback line  110  sends the regulated compressed air to a pressure gauge  112  located near the set point regulator  105 . The set point regulator  105  and pressure gauge can be located in a control box  116 . Alternately, all the components shown in FIG. 16 can be located in a common enclosure for the reasons described herein.  
         [0108]    The foregoing illustrative dryer systems can include the following features:  
         [0109]    1. All components and subsystems of the dryer can be combined into a single unit that can be mounted in an area where space is limited.  
         [0110]    2. Provisions have been made to minimize the installation time of the dryer unit so that only mounting the dryer to the press and connecting the dryer to the electrical power and compressed air sources will be required for installation.  
         [0111]    3. An air distribution system maintains cool external surface temperatures while simultaneously integrating the heat source directly into the air distribution system at the immediate vicinity of the discharging forced air.  
         [0112]    4. A control system for both air flow and air temperature is integrated directly with the dryer system so as to provide a convenient means for the operator to make adjustments to either the air flow setting or temperature setting or both at the dryer location. The integration of the control system into the dryer eliminates the need for the operator to make said adjustment(s) from an inconvenient remote location.  
         [0113]    5. The heat source is mounted within the air distribution plenum providing the most efficient means of utilizing the power from the heat source for the purpose of drying. The air is heated just before it is dispersed through the air release orifices onto the web. By combining the heat plant into the air distribution plenum, the unit is very compact, requires fewer parts, and is less expensive to manufacture.  
         [0114]    6. When the dryer system is operated in a gaseous environment, the control box enclosure can be gasket sealed and lightly pressurized to achieve a purged environment within the control box enclosure. The lightly pressurized air is provided as a by-product of the relieving pressure regulator under normal operating conditions.  
         [0115]    7. A slide plate is used to provide even support to the web as the web passes through the dryer. The slide plate has a hinge and latch configuration that allows the press operator a convenient means to rock the slide plate back out of the way for manual threading of the web through the dryer during machine set up, or for maintenance access to clean the air distribution assemblies.  
         [0116]    8. Solid cartridge heaters are available with various power levels in the same cylindrical geometry. A conveniently located bulkhead plate with a threaded port is used to mount the solid cartridge heater in the air distribution system. This provides the press operator with a means to readily change out solid cartridge heaters with different power levels for different processes and application.  
         [0117]    9. The effective drying temperature of the dryer is measured using a temperature sensor that is mounted to a metallic slide plate that is in contact with the web. The temperature of the metallic slide plate essentially stabilizes at the temperature of the web, due to the contact with the web, and will provide the operator with a more accurate measurement of the effective drying temperature of the process. This can greatly reduce set up time and maintain quality on repeat jobs.  
         [0118]    10. Solid cartridge heaters are available with variable power densities along the axial length of the solid cartridge heater. The variable power densities can be used to create hot or cold spots in specific intervals or in specific areas along the width of the dryer to counteract uneven flow patterns past the solid cartridge heater or to meet specific process or application requirements.  
         [0119]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.