Abstract:
A sensor for measuring the distance between two surfaces injects pressurized fluid (e.g., air) between the surfaces. The pressurized fluid passes through two flow restrictors prior to reaching the surfaces to be measured. The fluid pressures between the flow restrictors and between the downstream flow restrictor and the surfaces are compared to yield the distance between the two surfaces. An accurate distance measurement can be obtained even where the surfaces to be measured are located in a hostile environment which would destroy many other types of sensors.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to casting molds or other equipment and in particular to a method and apparatus for monitoring separation distance of two surfaces such as casting molds in a hostile environment such as high heat, smoke, dirt, oil mist, and sprays. 
     A casting mold is used to make various cast articles out of various materials. The casting mold typically includes two or more mold sections, such as for example a lower mold section and an upper mold section. When the lower mold section and the upper mold section are placed together in an abutting relationship, they cooperate to define a mold cavity. The mold cavity is generally in the shape of the cast articles to be produced. When the lower mold section and the upper mold section are placed together, a suitable molten or liquid fill material, such as for example, metal or plastic, is provided to fill the cavity and produce the cast article. Preferably, the fill material does not leak or seep out from the mold cavity as the fill material cools. Once sufficient cooling has occurred, the lower mold section and the upper mold section are separated from each other to enable the cast article to be removed. 
     The fill material used with the casting mold is typically obtained in a solid state, then heated to a liquid or molten state. The fill material may be heated in a furnace or other suitable apparatus. The fill material can leak (spill) from the mold cavity if the lower mold section and the upper mold section do not reach the desired separation or do not otherwise properly close together so as to define a sealed or closed mold cavity chamber. Depending on the particular molding process, it may be desirable for the two surfaces to come in contact (as with permanent metal molds) or to obtain a predetermined separation distance (as with sand molds). 
     Such leaks of the fill material are undesirable and can occur because one or both of the mold sections have become misshapen, misaligned, or do not totally close due to presence of dirt or flash, loss of hydraulic pressure, or inadequate lubrication. The resulting spill or leakage can be devastating to nearby components such as electrical wiring, hydraulic lines, coolant lines, limit switches, etc. Thus, it would be desirous to provide an improved method and apparatus for a casting mold that can be used so as to determine the relative positions of the mold sections before filling with molten metal. 
     SUMMARY OF THE INVENTION 
     This invention relates to a method and apparatus for monitoring a casting mold or other equipment to determine if the mold sections are properly closed in a sealing relationship. In a preferred embodiment, the distance between two surfaces is determined using the flow of pressurized air from a chamber through a first orifice into a pipe and then through a second orifice in one surface toward the other surface. The pressure drop between the chamber and the pipe is measured and quantifies the separation distance. For example, if the surfaces have a large separation distance then the second surface will not restrict the air flow and the pressure measured in the pipe will be approximately atmospheric pressure. As the surfaces approach one another, the pressure measured in the pipe will rise following a curve that can be determined empirically. When the surfaces come in contact, the pressure in the pipe will have risen to the pressure in the pressurized chamber. Thus, a reliable and accurate distance can be measured in extremely high temperature, smoky, or dusty environments. Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a mold monitoring apparatus according to the present invention. 
     FIG. 2 is a schematic of a portion of the mold monitoring apparatus illustrated in FIG.  1 . 
     FIG. 3 is a schematic of a wheel mold monitoring apparatus according to the invention. 
     FIG. 4 is a schematic of an alternate embodiment of a wheel mold monitoring apparatus according to the invention. 
     FIG. 5 is a schematic of an alternate embodiment of a restrictor for use with a mold monitoring apparatus according to the invention. 
     FIG. 6 is a schematic of an alternate embodiment of a restrictor for use with a mold monitoring apparatus according to the invention. 
     FIG. 7 is a schematic showing an alternate embodiment of the mold monitoring apparatus according to the invention. 
     FIG. 8 is a schematic of an alternate embodiment of a wheel mold monitoring apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings there is illustrated in FIGS. 1 and 2 a first embodiment of a mold monitoring apparatus, indicated generally at  12 , in accordance with the present invention. Although this invention is discussed in conjunction with the particular mold monitoring mold apparatus disclosed herein, it will be appreciated that the invention may be used in conjunction with other kinds of mold constructions or with any applications where the separation distance of two closely-separated surfaces needs to be measured in a hostile environment that would degrade or destroy other types of measuring devices. Also, only those portions of the mold monitoring apparatus  12  that are necessary for a complete understanding of this invention will be described. 
     In the illustrated embodiment, the mold monitoring apparatus  12  includes a first transducer  16 , a second transducer  20 , a first restrictor  24  and a second restrictor  28 . The first transducer  16  and the second transducer  20  are preferably both air pressure transducers, though other suitable transducers may be employed in the mold monitoring apparatus  12 . As used herein, the term transducer is understood to include a device that is actuated by a stimulus and supplies power, usually in another form, to a second system. The term transducer is also understood to include a device that responds to a physical stimulus (for example, heat, light, sound, pressure, motion, flow, and the like), and produces a corresponding signal. The first transducer  16  and the second transducer  20  are positioned and operative to receive pressure from a fluid and to produce a first signal and a second signal, respectively. The fluid is preferably air, although it may include any suitable gas or liquid. The first signal and the second signal are preferably electrical signals, although they may include any suitable type of signal. 
     The illustrated first restrictor  24  and the second restrictor  28  are closures having inlet openings  32  and  36 , respectively. The inlet openings  32  and  36  are preferably stepped openings. The illustrated inlet opening  32  is a round hole positioned approximately in the center of the first restrictor  24 . The illustrated inlet opening  36  is a round hole positioned approximately in the center of the second restrictor  28 . The inlet opening  32  defines a first restrictor major dimension C 1 . The major dimension C 1  is understood to be the largest chord that can be drawn at the smallest part of the cross-section of the inlet opening  32 . When the inlet opening  32  is a circle, the major dimension C 1  is the diameter thereof. The inlet opening  36  defines a second restrictor major dimension C 2 . The major dimension C 1  is understood to be the largest chord that can be drawn at the smallest part of the cross-section of the inlet opening  36 . When the second opening  36  is a circle, the major dimension C 2  is a diameter of the inlet opening  36 . Preferably, the area of the inlet opening  32  is approximately equal to the area of the inlet opening  36 . Also, the first restrictor  24  and the second restrictor  28  are preferably removable plates. 
     The illustrated mold monitoring apparatus  12  includes a fluid supply line  60 . The illustrated fluid supply line  60  is a suitable conduit or pipe and includes a first or inlet opening  64  and a second or outlet opening  68 . The illustrated mold monitoring apparatus  12  is positioned to allow the fluid to flow in the fluid supply line  60  from the inlet opening  64  to the outlet opening  68 . The fluid supply line  60  is preferably positioned to allow for fluid communication between the first transducer  16 , the first restrictor  24  and the second transducer  20 , and the second restrictor  28 . 
     The mold monitoring apparatus  12  further includes an air supply unit  72  to supply air to the inlet opening  64  thereof, although the mold monitoring apparatus  12  may employ other suitable sources of supply air. The illustrated mold monitoring apparatus includes an optional filter  76  and an optional dryer  80 . In the illustrated embodiment, the second restrictor  28  is preferably positioned adjacent the outlet opening  68  of the fluid supply line  60 . Alternatively, the second restrictor  28  may be positioned upstream of the outlet opening  68  or at any other suitable location along the path of the fluid supply line  60 . 
     The illustrated mold monitoring apparatus  12  further includes an optional regulator  84  and an optional header  88 . The regulator  84  is preferably an air regulator valve. The regulator  84  is positioned and operative to selectively control the pressure of the fluid in the fluid supply line  60 . The illustrated header  88  defines a chamber in the fluid supply line  60 . The header  88  is positioned and operative as a reservoir to selectively supply the fluid to the first restrictor  24 . 
     The mold monitoring apparatus  12  of the present invention can be employed in a hostile environment indicated in FIG. 1 by dashed line  100 . The term “hostile environment” as used herein is understood to include manufacturing and operator environments that are undesirable for machinery or human exposure. Nonlimiting examples of hostile environments include an environment that is generally characterized by extreme temperatures, for example, temperatures in excess of about 100° F. or temperatures less than about 400° F. degrees; pressures greater than about one atmosphere; the presence of harmful or objectionable gases or odors; the presence of objectionable levels of noise, light or radiation; or any other undesirable environment. The illustrated hostile environment  100  includes the first restrictor  24  and the second restrictor  28 , though need not. 
     In the illustrated embodiment, the mold monitoring apparatus  12  includes a first mold end surface  120  of a first mold half  160  and a second mold end surface  124  of a second mold half  164 . For purposes of clarity, the present invention will be discussed in terms of a two-piece mold system, although the present invention may be practice in other mold environments and is not limited to a two-piece mold system. In the illustrated embodiment, the first mold end surface  120  is preferably a generally flat surface and is positioned generally parallel to the second mold end surface  124 , which is preferably a generally flat surface. The illustrated inlet opening  36  terminates at the first mold end surface  120 . In operation, the first mold end surface  120  and the second mold end surface  124  are selectively movable relative to each other, though one of the first mold end surface  120  the second mold end surface  124  can be stationary. The first mold end surface  120  and the second mold end surface  124  move relative to each other in a manufacturing process or other operation. The inlet opening  36  terminates approximately at the first mold end surface  120 . For the portion of the mold monitoring apparatus  12  shown in FIG. 2, the first mold end surface  120  and the second mold end surface  124  are spaced apart from each other by a fluid or gap  140 . It will be appreciated that the first mold end surface  120  and the second mold end surface  124  are spaced apart by a distance “D” along mold axis “X”. The illustrated axis “X” is oriented approximately perpendicular to the first mold end surface  120  and the second mold end surface  124 . 
     The operation of the mold monitoring apparatus  12  of the present invention will now be discussed. A supply of the fluid, preferably air, is supplied at the inlet  64 . The fluid is preferably under pressure. The fluid desirably flows through the filter  76 , the dryer  80 , the regulator  84 , and the header  88  through the fluid supply line  60  to the first transducer  16 . The first transducer  16  is exposed to the fluid. When the first transducer  16  receives the fluid, the first transducer  16  generates a first signal. The first signal preferably corresponds to the pressure of the fluid supplied to the first transducer  16 . The fluid flows through the inlet opening  32  of the first restrictor  24  to the second transducer  20 . When the second transducer  20  receives the fluid, the second transducer  20  generates a second signal. The second signal preferably corresponds to the pressure of the fluid supplied to the second transducer  20 . The fluid then flows through the inlet opening  36  of the second restrictor  28 . 
     The fluid next flows into the fluid gap  140  when the first mold end surface  120  and the second mold end surface  124  are spaced apart by the distance “D.” When the first mold end surface  120  and the second mold end surface  124  are moved toward one another, the fluid flowing into the fluid gap  140  impinges on the second mold end surface  124 . The fluid flow into the fluid gap  140  completely stops when the first mold end surface  120  and the second mold end surface  124  are positioned substantially in contact. The first mold end surface  120  and the second mold end surface  124  are positioned substantially in contact with each other, thus obstructing flow through the second opening  36 , when the mold sections  160  and  164  are in their closed position (not shown). The relative movements of the first mold end surface  120  and the second mold end surface  124  produces a change in the second signal generated by the second transducer  20 . It will be appreciated that the second mold end surface  124  is an impact surface for the fluid flow into the fluid gap  140 . In operation, the first mold end surface  120  and the second mold end surface  124  move toward one another thus decreasing the distance “D.” It will be appreciated that, as the distance “D” decreases the second signal increases. Likewise, as the distance “D” increases, the second signal decreases. Therefore, the distance “D” and thus the relative positions of the first mold end surface  120  and the second mold end surface  124  can be determined by comparing the first signal generated by the first transducer  16  and the second signal generated by the second transducer  20 . 
     When the fill material (not shown) used in conjunction with the mold monitoring apparatus is molten aluminum, the first mold end surface  120  and the second mold end surface  124  are considered to be substantially in contact when separated by the distance “D” of less than about 0.007 inches apart from each other. It will be appreciated that molten aluminum “freezes” or does not flow between the first mold end surface  120  and the second mold end surface  124  when separated by the distance “D” of less than about 0.007 inches. 
     The illustrated mold monitoring apparatus  12  includes a controller  144 , though a controller  144  is not necessary to practice the invention. The controller  144  is preferably operatively connected to the first transducer  16  and the second transducer  20  so as to receive the respective signals generated by each transducer. In the preferred embodiment, the controller  144  is operative to compare the first signal and the second signal to thereby determine the relative positions of the first mold end surface  120  and the second mold end surface  124 . The controller  144  may also be employed to generate a signal representative of the distance “D.” 
     The mold monitoring apparatus  12  of the present invention may be employed in a wide variety of environments. The mold monitoring apparatus  12  may be employed in the hostile environment  100  that is a molding environment, although use of the mold monitoring apparatus  12  is not limited to the molding environment. The illustrated first surface  120  is a surface of the first mold half  160 , and the illustrated second surface  124  is a surface of the second mold half  164 . It will be appreciated that, in operation, the first mold half  160  and the second mold half  164  move relative to each other, thus decreasing the distance “D”. Therefore, the distance and thus the relative positions of the first mold half  160  and the second mold half  164  can be determined by comparing the first signal and the second signal. 
     Knowing the relative positions of the first mold half  160  and the second mold half  164  is useful. The first mold half  160  and the second mold half  164  cooperate to define a mold cavity  180 , portions of which are shown in FIGS. 3 and 4, used to create a cast article  184  shown in FIGS. 3 and 4 from a suitable fill material. Nonlimiting examples of cast articles that can be created in the mold cavity  180  include automotive parts, such as for example, wheels (the cast article  184  shown in FIGS.  3  and  4 ), brake components, suspension components, powertrain components, structural components and the like. A sand core may also be produced in the mold cavity  180 . When the first mold half  160  and the second mold half  164  are in their closed, casting positions, the fill material preferably does not leak from the mold cavity  180 . The fill material, such as metal or plastic is provided to the mold cavity  180  and is allowed to cool. The first mold half  160  and the second mold half  164  can then be separated from each other to produce the cast article. 
     A variety of other embodiments of the first restrictor  24  and the second restrictor  28  are contemplated. The first restrictor  24  and the second restrictor  28  need not be identical to each other. In the preferred embodiment, the first restrictor  24  and the second restrictor  28  are removable plates or fixed plates. The first restrictor  24  and the second restrictor  28  may also be removable disks or fixed disks. Likewise, the first restrictor  24  and the second restrictor  28  may be narrowed portions of the fluid line  60 . 
     A wide variety of embodiments of the mold monitoring apparatus  12  are contemplated. Examples of the mold monitoring apparatus  12  that may be used in the molding environment will be presented. It should be understood that the mold monitoring apparatus  12  may be employed in other environments and can be configured other than as illustrated and discussed. 
     Referring now to FIG. 3, the mold monitoring apparatus  12  of the present invention is illustrated in conjunction with the first mold half  160 , though may also be suitably employed with the second mold half  164 . The illustrated mold monitoring apparatus  12  includes four fluid supply lines  60   a - 60   d  although any suitable number of fluid lines may be employed and positioned as is desired. The illustrated fluid lines  60   a - 60   d  terminate at a respective outlet  68   a - 68   d . The illustrated outlets  68   a - 68   d  are generally round holes, although they may have any suitable shape. The illustrated outlets  68   a - 68   d  are positioned in the first mold end surface  120  of the first mold half  160 . It should be noted that the outlets  68   a - 68   d  are in fluid communication with the second transducer  20  (shown in FIG. 1) via restrictors  28   a - 28   d  having openings  36   a - 36   d . It should be noted that the outlets  68   a - 68   d  may each be in fluid communication with a dedicated second transducer, thereby having the mold monitoring apparatus  12  employ four second transducers, one for each of the outlets  68   a - 68   d.    
     Referring now to FIG. 4, the mold monitoring apparatus  12  is illustrated in conjunction with the first mold half  160 , though it may also be suitably employed with the second mold half  164 . The illustrated mold monitoring apparatus  12  includes the fluid supply line  60 . The fluid supply line  60  is in fluid communication with four branches  168   a - 168   d  although any suitable number of branches may be employed and positioned as desired. The fluid flows from the fluid line  60  into the branches  168   a - 168   d . The illustrated branches  168   a - 168   d  each terminate at its respective outlet  68   a - 68   d . The illustrated outlets  68   a - 68   d  are generally round holes, although they may have any suitable shape. The illustrated outlets  68   a - 68   d  are positioned in the first surface  120  of the first mold half  160 . It should be noted that each outlet  68   a - 68   d  includes the second restrictor  28   a - 28   d  having the second opening  36   a - 36   d.    
     Other embodiments of the restrictor of the invention are contemplated. The restrictor  228  shown in FIG. 5 may be used in lieu of or in conjunction with the first restrictor  24  and/or the second restrictor  28  shown in FIGS. 1 through 4. The restrictor  228  includes an opening  236 . The illustrated opening  236  includes a major dimension C 3 . The illustrated opening  236  also includes a generally rounded downstream portion  240 . The arrow  244  indicates a preferred direction of the fluid flow through the restrictor  228 . 
     The restrictor  328  shown in FIG. 6 may also be used in lieu of or in conjunction with the first restrictor  24  and/or the second restrictor  28  shown in FIGS. 1 through 4. The restrictor  328  includes an opening  336 . The illustrated opening  336  includes a major dimension C 4 . The illustrated opening  336  also includes a generally conical inlet portion  340  in communication with a generally cylindrical portion  344 . The arrow  348  indicates a preferred direction of the fluid flow through the restrictor  328 . 
     Other embodiments of the invention, which position the restrictor differently, are contemplated. FIG. 7 is a schematic showing an alternate embodiment of a mold monitoring apparatus  412  according to the present invention. In the illustrated embodiment, the mold monitoring apparatus  412  includes a first transducer  416 , a second transducer  420 , a first restrictor  424  and a second restrictor  428 . The first transducer  416  and the second transducer  420  are positioned and operative to receive pressure from a fluid and to produce a first signal and a second signal, respectively. The fluid is preferably air, although it may include any suitable gas or liquid. The first signal and the second signal are preferably electrical signals, though they may include any suitable type of signal. 
     The illustrated first restrictor  424  and the second restrictor  428  are closures having inlet openings  432  and  436 , respectively. The inlet openings  432  and  436  are preferably stepped openings. The illustrated inlet opening  432  is a round hole positioned approximately in the center of the first restrictor  424 . The illustrated inlet opening  436  is a round hole positioned approximately in the center of the second restrictor  428 . The inlet opening  432  defines a first restrictor major dimension C 5 . The major dimension C 5  is understood to be the largest chord that can be drawn at the smallest part of the cross-section of the inlet opening  432 . When the inlet opening  432  is a circle, the major dimension C 5  is the diameter thereof. The inlet opening  436  defines a second restrictor major dimension C 6 . The major dimension C 5  is understood to be the largest chord that can be drawn at the smallest part of the cross-section of the inlet opening  436 . When the second opening  436  is a circle, the major dimension C 6  is a diameter of the inlet opening  436 . Preferably, the area of the inlet opening  432  is approximately equal to the area of the inlet opening  436 . Also, the first restrictor  424  and the second restrictor  428  are preferably removable plates. 
     The illustrated mold monitoring apparatus  412  includes a fluid supply line  460 . The illustrated fluid supply line  460  is a suitable conduit or pipe and is positioned to allow the fluid to flow in the fluid supply line  460  in the general direction indicated by the arrow  464 . The fluid supply line  460  is preferably positioned to allow for fluid communication between the first transducer  416 , the first restrictor  424  and the second transducer  420 , and the second restrictor  428 . The mold monitoring apparatus  412  may also include an optional air supply unit, filter, dryer, regulator and header similar to the mold monitoring apparatus  12  shown in FIG.  1 . Likewise, the mold monitoring apparatus  412  may also be employed in a hostile environment in a manner and position similar to that of FIG.  1 . 
     In the illustrated embodiment, the mold monitoring apparatus  412  includes a first line end surface  520  of a first mold half  560  and an impact surface  524  of a second mold half  564 . In the illustrated embodiment, the first line end surface  520  is preferably a generally flat surface and is positioned generally parallel to the impact surface  524 , which is preferably a generally flat surface. The illustrated inlet opening  436  terminates at the first line end surface  520 . In operation, the first line end surface  520  and the impact surface  524  are selectively movable relative to each other, though one of the first line end surface  520  the impact surface  524  can be stationary. The first line end surface  520  and the impact surface  524  move relative to each other in a manufacturing process or other operation. The inlet opening  436  terminates upstream from the first line end surface  520 . 
     For the portion of the mold monitoring apparatus  412  shown in FIG. 7, the first line end surface  520  and the impact surface  524  are spaced apart from each other by a fluid or gap  540 . It will be appreciated that the first line end surface  520  and the impact surface  524  are spaced apart by a distance “E” along mold axis “Y.” The illustrated axis “Y” is oriented approximately perpendicular to the first line end surface  520  and the impact surface  524 . It will also be appreciated that the first mold half  560  and the second mold half  564  are separated by a distance “F.” 
     In a preferred embodiment, the fluid supply line  460  is operatively connected to the first mold half  560  by a bracket  568 . Likewise, the impact surface  524  is operatively connected to the second mold half  564  by a bracket  569 . The brackets  568  and  569  may be integrally formed with the first mold half  560  and second mold half  564 , respectively. Likewise, the brackets  568  and  569  may be connected to the first mold half  560  and second mold half  564  by one or more fasteners  572 . Non-limiting examples of suitable fasteners include bolts, screws, clamps, pins, welds, adhesive and the like. The brackets  568  and  569  preferably include outwardly extending flanges  576  and  577 , respectively. 
     In a preferred embodiment, the flanges  576  and  577  support and position a nozzle  580  and a set arm  584 , respectively. The nozzle  580  is optional and is operatively connected to the fluid supply line  460 . The nozzle  580  is operative to support the second restrictor  428 . The nozzle  580  is preferably an elongated cylinder, although the nozzle  580  may have any suitable shape. The nozzle  580  is preferably rigidly connected to the flange  576  of the bracket  568 . In a preferred embodiment, the nozzle  580  is removable for servicing or for removal of the second restrictor  428 . 
     The set arm  584  is preferably an adjustable bolt. In a preferred embodiment, the set arm  584  includes a head  588  and a shaft  592 . The shaft  592  is selectively moveable within the flange  577  of the bracket  569  to calibrate the distance “E” as desired. A nut  596  may be provided to limit the movement of the set arm  584 . 
     Operation of the mold monitoring apparatus  412  shown in FIGS. 7 and 8 is similar to the operation of the operation of the mold monitoring apparatus  12  shown in FIGS. 1 and 2. The first transducer  416  is exposed to the fluid flowing through the fluid supply line  460 . When the first transducer  416  receives the fluid, the first transducer  416  generates a first signal. The first signal preferably corresponds to the pressure of the fluid supplied to the first transducer  416 . The fluid flows through the inlet opening  432  of the first restrictor  424  to the second transducer  420 . When the second transducer  420  receives the fluid, the second transducer  420  generates a second signal. The second signal preferably corresponds to the pressure of the fluid supplied to the second transducer  420 . The fluid then flows through the inlet opening  436  of the second restrictor  428 . 
     The fluid next flows into the fluid gap  540  when the first line end surface  520  and the impact surface  524  are spaced apart by the distance D. When the first line end surface  520  and the impact surface  524  are moved toward one another, the fluid flowing into the fluid gap  540  impinges on the impact surface  524 . The fluid flow into the fluid gap  540  completely stops when the first line end surface  520  and the impact surface  524  are positioned substantially in contact, thus obstructing flow through the second opening  436 . 
     The relative movements of the first line end surface  520  and the impact surface  524  produces a change in the second signal generated by the second transducer  420 . It will be appreciated that the impact surface  524  is an impact surface for the fluid flow into the fluid gap  540 . In operation, the first line end surface  520  and the impact surface  524  move toward one another thus decreasing the distance “E”. It will be appreciated that, as the distance “E” decreases the second signal increases. Likewise, as the distance “E” increases, the second signal decreases. Therefore, the distance “E” and thus the relative positions of the first line end surface  520  and the impact surface  524  can be determined by comparing the first signal generated by the first transducer  416  and the second signal generated by the second transducer  420 . 
     The illustrated mold monitoring apparatus  412  includes a controller  544 , though a controller  544  is not necessary to practice the invention. The controller  544  is preferably operatively connected to the first transducer  416  and the second transducer  420  so as to receive the respective signals generated by each transducer. In the preferred embodiment, the controller  544  is operative to compare the first signal and the second signal to thereby determine the relative positions of the first line end surface  520  and the impact surface  524 . The controller  544  may also be employed to generate a signal representative of the distance “E.” The mold monitoring apparatus  412  of the present invention may be employed in a wide variety of environments. The mold monitoring apparatus  412  may be employed in a hostile environment similar to the hostile environment  100  (shown in FIG. 1) that is a molding environment, although use of the mold monitoring apparatus  412  is not limited to the molding environment. 
     Referring now to FIG. 8, the mold monitoring apparatus  412  of the present invention is illustrated in conjunction with the first mold half  560 . The first mold half  560  includes the mold cavity  180  (shown also in FIGS. 3 and 4) which contains the cast article  184 . The illustrated mold monitoring apparatus  412  includes four fluid supply lines  460   a - 460   d  although any suitable number of fluid lines may be employed and positioned as is desired. The illustrated fluid lines  460   a - 460   d  terminate at the respective nozzles  580   a - 580   d . The flanges  576   a - 576   d  support the nozzles  580   a - 580   d  and the second restrictors  428   a - 428   d . The nozzles  580   a - 580   d  support the second restrictors  428   a - 428   d  having openings  436   a - 436   d . It should be noted that the openings  436   a - 436   d  are in fluid communication with the second transducer  420  (shown in FIG.  7 ). It should be noted that the openings  436   a - 436   d  may each be in fluid communication with a dedicated second transducer, thereby having the mold monitoring apparatus  412  employ four of the second transducers, one for each of the openings  436   a - 436   d.    
     The first mold half  560  and the second mold half  564  cooperate to define a mold cavity  180 , portions of which are shown in FIGS. 3 and 4, used to create a cast article  184  shown in FIGS. 3 and 4 from a suitable fill material. Nonlimiting examples of cast articles that can be created in the mold cavity  180  include automotive parts, such as for example, wheels (shown in FIGS.  7  and  8 ), brake components, suspension components, powertrain components, structural components and the like. A sand core may also be produced in the mold cavity  180 . When the first mold half  560  and the second mold half  564  are in their closed, casting positions, the fill material preferably does not leak from the mold cavity  180 . The fill material, such as metal or plastic is provided to the mold cavity  180  and is allowed to cool. The first mold half  560  and the second mold half  564  can then be separated from each other to produce the cast article. 
     The principle and mode of operation of this invention have been described in its preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.