Abstract:
A valve assembly is provided for a high-speed phase change ink image producing machine between a first storage reservoir for receiving and holding a first volume of melted ink from a source and a second storage reservoir for holding a second volume of melted ink to be delivered under pressure to a printhead system. The valve assembly includes a passive valve disc movable from the closed position in which said disc abuts a valve seat in sealed contact, and an open position in which said valve disc is supported by an angled surface. An upper portion of the valve disc is unsupported and a flow director surface behind the disc directs fluid flow against the upper portion to assist in closing the valve. The surface characteristics of the valve seat are controlled to improve the “crack” time of the valve disc when opening.

Description:
BACKGROUND 
       [0001]    The following disclosure relates to image producing machines, and more particularly to solid ink machines that use a phase change ink melting and control apparatus. 
         [0002]    In general, phase change ink image producing machines, such as printers, employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops. 
         [0003]    An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 6,905,201, issued on Jun. 14, 2005, to Leighton et al., the disclosure of which is incorporated herein by reference. As disclosed therein, a high-speed phase change ink image producing machine, such as printer  10  shown in  FIG. 1 , includes a frame  11  to which are mounted directly or indirectly all its operating subsystems and components. One of the components is an imaging member  12  that is shown in the form of a drum, but can equally be in the form of a supported endless belt. The imaging member  12  has an imaging surface  14  that is movable in the direction  16 , and on which phase change ink images are formed. 
         [0004]    The high-speed solid ink printer  10  also includes a phase change ink system  20  that has at least one source  22  of a single color phase change ink in solid form. When the printer  10  is a multicolor image producing machine, the ink system  20  includes four sources  22 ,  24 ,  26 ,  28 , representing four different colors CYMK (cyan, yellow, magenta, black) of phase change ink solid pieces, as shown in  FIG. 1 . The phase change ink system  20  also includes a solid phase change ink melting and control assembly or apparatus  100  ( FIG. 2 ) for melting or phase changing the solid form of the phase change ink into a liquid form, and for then supplying the liquid form towards the printhead system  30 . The printhead system  30  includes at least one printhead assembly  32 , or in the case of a high-speed, or high throughput, multicolor image producing machine, four separate printhead assemblies  32 ,  32 ,  36  and  38 , as shown in  FIG. 2 . 
         [0005]    The solid ink image producing printer  10  further includes a substrate supply and handling system, which may, for example, include multiple substrate supply sources  42 ,  44 ,  46 ,  48 . The substrate supply and handling system further includes a substrate treatment system  50  that has a substrate pre-heater  52 , substrate and image heater  52 , and a fusing device  60 . The phase change ink image producing printer  10  as shown may also include an original document feeder  70  that has a document holding tray  72 , document sheet feeding and retrieval devices  72 , and a document exposure and scanning system  76 . 
         [0006]    Operation and control of the various subsystems, components and functions of the machine or printer  10  are performed with the aid of a controller or electronic subsystem (ESS)  80 . The ESS or controller  80  for example is a self-contained, dedicated mini-computer having a central processor unit (CPU)  82 , electronic storage  82 , and a display or user interface (UT)  86 . The ESS or controller  80  for example includes sensor input and control means  88  as well as a pixel placement and control means  89 . In addition the CPU  82  reads, captures, prepares and manages the image data flow between image input sources such as the scanning system  76 , or an online or a work station connection  90 , and the printhead assemblies  32 ,  32 ,  36 ,  38 . As such, the ESS or controller  80  is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the machine&#39;s printing operations. 
         [0007]    In operation, image data for an image to be produced is sent to the controller  80  from either the scanning system  76  or via the online or work station connection  90  for processing and output to the printhead assemblies  32 ,  32 ,  36 ,  38 . Additionally, the controller determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface  86 , and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface  12  thus forming desired images per such image data, and receiving substrates are supplied by anyone of the sources  22 ,  22 ,  26 ,  28  and handled by means  50  in timed registration with image formation on the surface  12 . Finally, the image is transferred within the transfer nip  92 , from the surface  12  onto the receiving substrate for subsequent fusing at fusing device  60 . 
         [0008]    Thus an exemplary high-speed phase change ink image producing machine  10  includes: (a) a control subsystem  80  for controlling operation of all subsystems and components thereof, (b) a movable imaging member  12  having an imaging surface  14 ; (c) a printhead system  30  connected to the control subsystem  80  for ejecting drops of melted molten liquid ink onto the imaging surface  12  to form an image; and (d) a phase change ink system  20  connected to the printhead system  30 . 
         [0009]    In one embodiment, the phase change ink system  20  includes a solid phase change ink melting and control apparatus  100  ( FIG. 2 ), including a pre-melter assembly  200  and a melter assembly  300 . The pre-melter assembly  200  is suitable for controllably supplying solid pieces of phase change ink from the sources  22 ,  22 ,  26 ,  28  to the melter assembly  300  located below the pre-melter assembly  200 , and more particularly to the separate melters  300 A-D. A melted molten liquid ink storage and control assembly  400  is located below the melter assembly  300 . The phase change ink melting and control apparatus  100  is thus suitable for melting solid phase change ink into melted molten liquid ink, and for controlling the melted molten liquid ink. 
         [0010]    In high throughput solid ink systems, the storage and control assembly  400  may incorporate a dual reservoir system, as illustrated in  FIG. 3 , corresponding to each of the individual melters  300 A-D for the various colors implemented in the solid in system. In this system, molten liquid ink is fed from a corresponding melter  300 A-D into an associated primary reservoir  402 , which stores a first volume of melted ink for subsequent use. This reservoir is connected by a conduit or passageway  406  to a secondary reservoir  404 , which stores a second volume of melted liquid ink. The liquid ink is ejected from the secondary reservoir at outlet  410  and typically through a heated routing system to reach a respective printhead or printheads of the printhead assembly  30 . In systems of this type, pressurized air P is provided at port  412  to act on the free surface of the liquid ink in the secondary reservoir to discharge ink into the outlet  410 . The volume of ink in the primary reservoir  402  is typically maintained at atmospheric pressure. 
         [0011]    As shown in  FIG. 3 , the level of the two volumes of ink in the primary and the secondary reservoirs  402 ,  404  is the same under equilibrium conditions. It can be appreciated that after liquid ink has been dispensed under pressure through the outlet  410 , the ink level in the secondary reservoir will drop, as depicted in  FIG. 3 . Once the pressurized air at port  412  ceases, the pressure above the surface of the second volume of ink in the secondary reservoir returns to atmospheric. However, due to the difference in ink height, a fluid pressure differential results between the two reservoirs. This pressure differential causes molten ink to flow from the primary reservoir  402 , through the passageway  406  and into the secondary reservoir  404  until the respective ink heights or levels equilibrate. Thus, a supply of liquid ink is always at the ready within the secondary reservoir  404 , even as new molten ink is directed into the primary reservoir  402 . The supply of ink to be discharged at the printhead assembly is therefore never interrupted, at least as long as the flow of melted ink to the primary reservoir is not interrupted. 
         [0012]    In dual reservoir systems of this type, a one-way valve  408  must be interposed into the passageway  406  between the two reservoirs. The valve  408  is operable to permit flow ink from the primary reservoir to the secondary, but not in the opposite direction. The valve  408  is thus closed when the secondary reservoir is pressurized to discharge molten ink to the printhead assembly. 
         [0013]    The valve  408  in one typical system is mechanically actuated under power, and under control of the control subsystem  80 . Actuated valves of this type are opened and closed in timing with the application and release of pressure to the secondary reservoir. Valves of this type are often costly and occupy significant space within the machine  10 . 
         [0014]    In another type of system, the valve  408  is a ball valve, which operates passively as a function of the pressure differential between the two reservoirs. When the ink level in the secondary reservoir  404  is low, the pressure differential favors the primary reservoir  402 , so the ball valve opens. When the secondary reservoir is pressurized, the differential shifts to favor the secondary reservoir and the fluid pressure pushes the ball valve closed against its seat to prevent ink flowing back into the primary reservoir. Passive ball valves, although generally more economical from a cost and space standpoint, react more slowly than the mechanically actuated valves. The slow reaction times of passive ball valves place a limit on the throughput speed of the storage and control assembly  400 , and therefore a limit on the print speed of the machine  10 . Moreover, the slow closing rate allows more ink to leak past the ball valve before the seal is made, which in turn leads to a decrease in system performance. 
         [0015]    There is therefore a need for a valve system for dual reservoir molten liquid ink systems that is capable of high throughputs, that fits within a limited envelop in the machine and that is cost efficient. 
       SUMMARY 
       [0016]    According to aspects illustrated herein, there is described a valve assembly disposed between primary and secondary reservoirs of a phase change ink image producing machine. The valve assembly is operable in an open position to control the flow of melted ink from the first storage reservoir to the second storage reservoir and in a closed position to prevent backflow into the first storage reservoir of melted ink being delivered under pressure to the printhead system. In one embodiment, the valve assembly comprises a valve housing defining a valve seat between the first and second reservoirs, an angled surface disposed within the valve housing, and a passive valve disc disposed within the valve housing and movable from the closed position in which the disc abuts the valve seat in sealed contact, and the open position in which the valve disc is supported by the angled surface. In one feature, the angled surface is configured to support only a portion of the valve disc with an upper portion thereof unsupported. The valve housing further defines a flow director surface at the upper portion of the valve disc on the opposite side of the disc from the valve seat. This surface is in fluid communication with the secondary reservoir to direct a flow of melted ink behind the valve disc to help lift the valve disc off the angled surface when moving from the open position to the closed position. 
         [0017]    In another aspect, the valve seat defines a sealing surface having a plurality of micro-channels defined therein to permit fluid flow therethrough when the valve disc abuts the valve seat. The micro-channels thus allows the fluid to equilibrate on either side of the valve disc to thereby improve, or reduce, the “crack” time of the valve disc from the closed position. In another feature, the sealing surface has an average surface roughness of between 0.3 and 1.0 μm and a peak-to-valley ratio of heights of less than 10 μm across the entire sealing surface. This feature improves the valve crack time without sacrificing the sealing capability of the valve disc and valve seat. 
         [0018]    The valve assembly disclosed herein is well-suited for use in a high throughput, high speed phase change ink image producing machine, such as a high speed solid ink printer. The valve assembly provides very fast closing and opening rates with negligible leakage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a vertical schematic of a high-speed phase change ink image producing machine or printer. 
           [0020]      FIG. 2  is a perspective view of a phase change ink melting and control apparatus used in the machine shown in  FIG. 1 . 
           [0021]      FIG. 3  is a schematic of a dual-reservoir molten liquid ink storage and control assembly according to one embodiment disclosed herein. 
           [0022]      FIG. 4  is an enlarged side partial cut-away view of the valve assembly embodiment incorporated into the storage and control assembly shown in  FIG. 3 . 
           [0023]      FIG. 5  is an enlarged diagram of the forces acting on the passive valve disc of the valve assembly shown in  FIGS. 3-4 . 
           [0024]      FIG. 6  is an enlarged perspective view of an insert body of the valve assembly shown in  FIGS. 4-5 . 
           [0025]      FIG. 7  is a graphical representation of the surface profile of one embodiment of the valve disc depicted in  FIG. 5 . 
           [0026]      FIG. 8  is a representation of a microscopic surface map of one embodiment of the valve disc depicted in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    According to one embodiment, the molten liquid ink storage and control assembly  400  includes a valve assembly  408  that incorporates a passive valve disc  420 , as shown in  FIGS. 4-5 . The disc  420  is situated within a valve chamber  421  defined by a valve housing  409  between an outlet  405  of the secondary reservoir  404  and the conduit or passageway  406  that is fluidly coupled to the primary reservoir ( FIG. 3 ). In the orientation shown in solid lines in  FIG. 4 , the valve disc  420  is in its “open” position that permits flow of liquid ink from the primary reservoir to the secondary reservoir. As described above, this open position flow allows equalization of the level or height of the liquid ink between the two reservoirs which occurs due to the difference in pressure head. 
         [0028]    In one embodiment, the valve housing  409  includes an insert body  432  disposed within the valve chamber  421  configured to direct a flow of liquid ink from the secondary reservoir to the outlet  410  when pressure P is applied through port  412  to the surface of the ink within that reservoir, as described above. The insert body can thus define a flow cavity  435  that communicates between the outlet  405  and the outlet  410 . 
         [0029]    The insert body  432  further defines an angled surface  430  against which the valve disc  420  rests in the open position shown in  FIGS. 4-5 . The closed position of the valve disc is shown by the phantom representation of the disc  420 ′ in which the disc is essentially vertically disposed within the valve chamber  421 . More precisely, the valve disc  420 ′ bears against a valve seat or sealing surface  450  defined by the valve housing  409  around the interface with the passageway  406 . It can thus be appreciated that in this “closed” position, the valve disc  420 ′ not only prevents flow of ink out of the primary reservoir, it also prevents ink flow into the primary reservoir. In particular, when the secondary reservoir is pressurized it is highly desirable that substantially all of the liquid ink leaving the secondary reservoir pass directly into the discharge outlet  410  to be fed to the printhead assembly  30 . The fluid pressure of the molten ink forced out of the secondary reservoir  404  holds the valve disc  420  against the sealing surface  450  of the valve assembly  408 . 
         [0030]    In one aspect of the embodiment of the valve assembly  408  disclosed herein, the valve disc  420  is a passive disc, meaning that it moves to and from its open and closed position under the influence of only the liquid ink within the storage and control assembly  400 . Thus, the disc  420  is freely disposed within the valve chamber  421 , with its movement restrained only by the angled surface  430  and the sealing surface  450 . As shown in  FIG. 4 , in the open position the valve disc  420  is disposed at an angle relative to the vertical (as represented by the sealing surface  450 ). It can be seen in comparing the open position of the valve disc  420  to the closed position of the disc  420 ′ (shown in phantom lines), that the lower contact point or edge  422  of the disc moves between the position  422  to the position  422 ′. In order to prevent binding of the disc as it opens and closes, and to allow for tolerances of fit and form, an annular recess  452  may be defined around the sealing surface  450 . This annular recess  452  corresponds to the outer radial extent of the valve disc so the impact on the sealing capability of the disc is minimal. In addition to providing a relief cut-out for movement of the lower contact point  422  from the closed (vertical) to the open (angled) position, the recess  452  also provides a collection area for burrs and sediment precipitating out of the molten ink that could otherwise interfere with the complete sealing of the valve disc. The recess  452  may further help ensure that the valve disc will lift off the sealing surface  450  when the pressure behind the disc (i.e., at the secondary reservoir  404 ) is less than the pressure in the primary reservoir  402 . The circumferential clearance around the outer diameter of the disc is thus a prime contributor for ensuring disc lift off. 
         [0031]    It can be appreciated that the valve disc  420  is moved from the closed position  420 ′ to the open position  420  when the differential pressure between the two reservoirs favors the primary reservoir. As the liquid ink seeks the equilibrium height or level shown in  FIG. 3 , the gravity flow of the molten liquid ink dislodges the valve disc from the sealing surface  450 , causing the disc to pivot on its lower contact point from the position  422 ′ to the position  422 . 
         [0032]    In a high speed printing application, the valve movement must be rapid and without hesitation. In a print cycle, the secondary reservoir will be filled and an ink dose purged from the reservoir in under three seconds. Any hesitation in the opening or closing of the valve will compromise the rate of dosing of liquid ink supplied to the printhead assembly. In prior devices, the necessary opening and closing times for the valve have required the use of mechanical valves. Prior passive valve devices, such as the passive ball valve, react too slowly and allow too much back flow into the primary reservoir to permit high throughput applications. 
         [0033]    The amount of time it takes to refill the secondary reservoir  404  after an ink dose has been discharged—i.e., the “refill rate”—is a function of the time required to open the valve disc—the “opening time”—and the amount of fluidic restriction between the two reservoirs. On the other hand, the second purpose of the valve disc  420 —to prevent backflow into the primary reservoir  402 —is essentially inversely related to these refill rate variables. Thus, the design considerations for preventing backflow include the time required to close the valve and the effectiveness of the seal between the valve disc  420  and the sealing surface  450 . Reducing the fluidic restriction means pivoting the valve disc as far as possible to provide an open channel between the passageway  406  and the secondary reservoir  404 . However, the farther the valve disc pivots to reach the open position means that the sealing face of the disc is exposed to more direct flow from the secondary reservoir that can, in the worst case, prevent the valve disc from lifting off the angled surface  430  and moving to its closed position. 
         [0034]    Similarly, it has been determined that the “opening time” of the valve disc—i.e., the amount of time it takes the disc to dislodge from the valve seat—is a function of the area of contact between disc and sealing surface and the surface characteristics of the valve seat. The surface characteristics of the valve seat determine the physical gap that exists between the valve disc and the sealing surface when the disc is closed. The opening time decreases as either or both the area of contact decreases and the gap increases. On the other hand, the sealing efficiency necessary for optimum backflow prevention is decreased as either or both the area of contact decreases and the gap increases. In other words, sealing efficiency is improved by an increased area of contact and/or a decrease in the gap between the valve disc and the sealing surface. 
         [0035]    In the past, this trade-off has been unmanageable in the high throughput environment. However, the embodiment of the valve assembly  400  disclosed herein is able to achieve rapid opening and closing times, rapid re-filling of the secondary reservoir and efficient sealing to prevent unwanted backflow, in the environment of a high speed printing application. Improving fluid flow during refill is accomplished without sacrificing the valve closing time by features in the port geometry at the interface between the primary and secondary reservoirs. 
         [0036]    In the illustrated embodiment, the valve disc  420  rests at an angle established by the angled surface  430  defined by the insert body  432 . The angle of the valve disc is preferably between 5 and 15 degrees. A preferred angle is 11 degrees, which has been found to provide an optimum balance between fluid flow from the passageway  406  to the reservoir  404  and the fluidic forces that act to close the disc. In order to maximize the fluid flow into the secondary reservoir, the upper end  424  of the valve disc  420  overlaps at least a portion of the outlet  405  of the secondary reservoir. In this position, the pressurized flow of ink from the secondary reservoir may tend to hold the valve disc in its open position. 
         [0037]    Referring to  FIG. 6 , it can be seen that in the preferred embodiment the insert body  432  may be integrated into a mounting plate  433  along with other insert bodies corresponding to the multiple melters  300 A-D. The mounting plate  433  thus facilitates engagement and removal of the insert bodies, and the corresponding angled surfaces  430 , with the valve housing  409 , such as to permit cleaning of the valve assembly  408 . In addition, the insert bodies  432  may be preferably cylindrical in configuration to correspond to cylindrical valve chambers  421 . A close fit may be established between the insert bodies and the corresponding cylindrical valve chamber, and a gasket or other sealing member may be interposed between the mounting plate  433  and the valve housing  409  to maintain a fluid-tight seal. 
         [0038]    In a further feature of the valve assembly  408 , each insert body  432  defines a flow director surface  434 , as shown in  FIGS. 4-6 . The surface  434  is generally aligned with the outlet  405  of the reservoir and is curved to direct fluid flow against the back of the valve disc at the upper portion  424 . As shown in  FIG. 4 , the upper portion  424  of the disc is at least partially interposed between the surface  434  and the outlet  405  in the open position, so that some of the fluid discharged from the secondary reservoir will be directed by the flow director surface  434  behind the upper portion  424  of the disc to produce a direct fluid force tending to close the valve disc, as depicted in  FIG. 5 . The flow director surface  434  is sized so that the unsupported upper portion  424  corresponds generally to a chord segment of the valve disc that is less than about 10% of the surface area of the disc. However, the area of this upper portion  424  may be adjusted based on the anticipated magnitude of the direct fluid force channeled by the flow director surface  434  to the back of the disc. In other words, if the pressure P is greater, a smaller area of the disc may be exposed to the flow director surface  434 , since the direct fluid force and the drag force (see below) will be greater. 
         [0039]    Of course, once the valve disc  420  has lifted off the angled surface  430  the pressurized fluid flow will bear against more of the entire back face of the disc, pushing it toward the valve seat surface  450 . Furthermore, the resistance of the outlet  410  to the printhead assembly creates a local area of higher pressure which also acts on the back face of the valve disc to help close the valve. The passive valve disc  420  is arranged within the valve chamber  421  to pivot about the lower contact point or edge  422  when moving between the open and closed positions. In order to facilitate rapid movement of the valve disc to the closed position once it has lifted off the angled surface  430 , the insert body  432  may be configured so that a lower portion  436  of the insert body is closely adjacent the valve seat surface  450 . In particular, the gap between this lower portion  436  and the sealing surface  450  is minimized so that the movement of the lower contact point  422  is confined to pivoting. Minimizing the gap thus prevents excessive movement of the disc which could cause binding. In a specific embodiment, this gap between the lower portion  436  and the sealing surface  450  is less than twice the thickness of the valve disc  420 , and preferably about 1½ times the disc thickness. Contact between the lower portion  436  and the valve disc may further act as a fulcrum as the valve disc pivots towards the closed position. 
         [0040]    As reflected in  FIG. 5 , two additional forces act on the valve disc to decrease its closing time. One force is the pressure differential force immediately behind the entire valve disc that arises as the disc begins to move under the direct fluid force. In the preferred embodiment, the angled support surface  430  is annular, as shown in  FIG. 6  so that the greater pressure in the flow cavity  435  behind the valve disc can produce this pressure differential. A second force is a drag force caused by fluid friction as the fluid moves across the forward (or sealing) face of the valve disc. Although this drag force is minimal and brief, it assists the valve closing by decreasing the time it takes the valve disc to lift off the angled surface  430 . (It can be noted that if the open disc is at greater angle this same drag force can work against the valve as the fluid flow bears more directly against the sealing face resisting movement to the closed position.) All three of the forces represented in  FIG. 5  contribute to a rapid closing time for the valve when pressure P is applied to the secondary reservoir. 
         [0041]    With respect to the valve opening time, a further feature of the valve assembly  400  decreases the hesitancy of the valve disc  420 ′ to pull away from the sealing surface  450 , which thereby decreases the valve opening time. In particular, the surface characteristics of the valve seat or sealing surface  450  are tightly controlled. In a specific embodiment, the valve seat has a land width of up to 0.5 mm±0.1 mm for a valve disc having a diameter of 10.0 mm. Furthermore, the sealing surface  450  is machined to have a flatness of less than 10 μm and an average roughness (Ra) value of between 0.3 and 1.0 μm. In addition, the sealing surface is machined to a peak-to-valley (PV) ratio of heights of less than 10 μm across the entire disc sealing surface. The surface profile of a sealing surface in one specific embodiment is depicted in the graph of  FIG. 6 . 
         [0042]    In addition to maintaining these surface characteristics, the manner of machining the sealing surface contributes to its optimized performance. In particular, the surface is machined so that cutter marks from the milling machine serve as “micro-channels” or fluid flow paths through which fluid pressure can equilibrate, thereby reducing the initial opening, or “crack”, time. An exemplary machined surface is shown in the microscopic surface image of  FIG. 7 . It can be seen in this picture that the circular milling pattern creates distinct grooves or micro-channels  460  through which fluid may flow. It can be appreciated that the micro-channels  460  correspond to the PV values in the graph of  FIG. 6 . The PV value in conjunction with the Ra value define the surface characteristics of the sealing surface  450  in terms that permit fluid flow to minimize the valve “crack” time, while preserving sufficient sealing capabilities. In the specific example, it was found that only about 0.3% of the liquid ink in a particular dose leaked past the sealed valve disc  420 ′. On the other hand, the surface characteristics described above allow the exemplary valve to crack open in about 100 msec, and to fully open in less than 500 msec. In a high speed application, the valve disc will typically be closed for only a very short time, on the order of 1.0 sec, before it is required to open again to refill the secondary reservoir. 
         [0043]    In the exemplary embodiment described above, the surface milling machine was operated at a spindle speed of 12000 rpm with an end mill feed speed of 7 in./min. and 450 surface ft./min. It is contemplated that the speed and feed rates of the end mill will be calibrated based on the material of the valve seat and the particular application. In the embodiments described herein, the sealing surface is formed by an end mill. However, other methods of generating the sealing surface, while adhering to the surface characteristics described above, can be used, such as stamping, sanding or etching. This embodiment has been demonstrated to maintain performance to 2.5 million cycles without any noticeable degradation. 
         [0044]    In another aspect of the valve design disclosed herein, the valve seat or sealing surface  450  is preferably formed of a “softer” or less wear-resistant material than the valve disc. Thus, the majority of the wear that occurs will be on the sealing surface, rather than on the valve disc. The effect of this wear is to reduce the surface roughness over time, which has the effect of improving the sealing efficiency of the valve disc. While the opening time will increase, the impact is reduced by the presence of the machining channels or grooves that allow for pressure equilibrium on either side of the valve disc. In a specific embodiment, the valve disc is formed of a stainless steel while the sealing surface is formed of aluminum. 
         [0045]    The valve disc  420  is preferably circular to correspond to a cylindrical valve chamber  421 , an annular valve seat sealing surface  450  and an annular angled surface  430 . However, other configurations for the valve disc are contemplated based on the geometry of the valve assembly within which the disc is disposed. For instance, rather than cylindrical, the components may adopt alternate multi-sided shapes. 
         [0046]    The valve disc is sufficiently thick to avoid bending when moving under pressure between the open and closed positions. On the other hand, the thickness of the valve disc  420  is sufficiently thin to keep the mass of the disc to a minimum, since the mass of the disc will affect how rapidly it can move from one position to another. In a specific embodiment for use in a high speed solid ink printer, the valve disc has a thickness of about 0.3 mm. 
         [0047]    It will be appreciated that various of the above-described features and functions, as well as other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.