Abstract:
A reciprocating mold plate food patty-forming machine is provided that includes a mold plate that reciprocates between a cavity fill position and a patty discharge position. The mold plate is movable beneath a mold cover. A mold cover lifting apparatus is provided as part of the machine and comprises a primary threaded drive that is configured to support and elevate the mold cover and which elevates or lowers upon input of rotary power to raise or lower the mold cover. A motor is operatively connected to the primary threaded drive to input rotary power to the primary threaded drive. A secondary threaded element follows the primary threaded drive and is configured to support the mold cover if the primary threaded drive fails.

Description:
This application claims the benefit of U.S. provisional application Ser. No. 60/503,354, filed Sep. 16, 2003 and U.S. provisional application Ser. No. 60/515,585, filed Oct. 29, 2003. 

   BACKGROUND OF THE INVENTION 
   Use of pre-processed foods, both in homes and in restaurants, has created a demand for high-capacity automated food processing equipment. That demand is particularly evident with respect to hamburgers, molded steaks, fish cakes, and other molded food patties. 
   Food processors utilize high-speed molding machines, such as FORMAX F-6, F-12, F-19, F-26 or F-400 reciprocating mold plate forming machines, available from Formax, Inc. of Mokena, Ill., U.S.A., for supplying patties to the fast food industry. Prior known high-speed molding machines are also described for example in U.S. Pat. Nos. 3,887,964; 4,372,008; 4,356,595; 4,821,376; and 4,996,743 herein incorporated by reference. 
   Food processors frequently need to access the mold plate to change out or replace the mold plate or to clean the apparatus. In order to accomplish this, the mold cover has to be lifted off the mold plate. The mold cover is heavy and located above the machine base. Prior systems have provided automated means to lift the mold cover such as described in U.S. Pat. No. 3,887,964. 
   Although heretofore known FORMAX patty-molding machines have achieved commercial success and wide industry acceptance, the present inventors have recognized that needs exist for a forming machine having an improved mold cover lifting arrangement that results in a quicker, more reliable arrangement for lifting the mold cover. 
   SUMMARY OF THE INVENTION 
   The invention provides an improved mold cover lift system for a reciprocating mold plate type patty-forming machine. To change mold plates and/or to thoroughly clean the machine, the mold cover must be lifted. The system of the invention includes two jacks that utilize jackscrews that are turned by a motor drive. The jack screws turn drive nuts that lift columns that lift the mold plate cover. According to the invention, secondary nuts are applied to the jackscrews, beneath the drive nuts. The secondary nuts limit the downward movement of the mold cover in the unlikely event that the drive nuts fail to limit such movement. 
   According to the preferred embodiment, a reciprocating mold plate food patty-forming machine is provided that includes a mold plate that reciprocates between a cavity fill position and a patty discharge position. The mold plate is movable beneath a mold cover. A mold cover lifting apparatus is provided as part of the machine, and comprises a primary threaded drive that is configured to support and elevate the mold cover and which elevates or lowers upon input of rotary power to raise or lower the mold cover. A motor is operatively connected to the primary threaded drive to input rotary power to the primary threaded drive. A secondary threaded element follows the primary threaded drive and is configured to support the mold cover if the primary threaded drive fails. 
   Preferably, the primary threaded drive comprises a first nut guided for vertical movement without rotation and a threaded rod that is threadedly engaged with said first nut. Rotation of the threaded rod vertically translates the first nut. The motor is operatively connected to the threaded rod to rotate the threaded rod about its axis. The secondary threaded element comprises a second nut also engaged with the threaded rod. The first and second nuts are mutually engagable to translate together on the threaded rod. 
   The lifting apparatus described above can be one of two such lifting apparatus with a common motor. The lifting apparatuses are arranged on opposite lateral sides of the mold cover. 
   A gear train is operatively connected between the motor and the threaded rod of each lifting apparatus. The motor is preferably a hydraulic motor powered by the machine hydraulic system. 
   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, and from the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a patty-forming machine of the present invention; 
       FIG. 1A  is an elevational view of the patty-forming machine of  FIG. 1 ; 
       FIG. 2  is a longitudinal sectional view of the patty-forming machine of  FIG. 1 , with some components and/or panels removed for clarity; 
       FIG. 3  is a sectional view taken generally along line  3 — 3  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 4  is a sectional view taken generally along line  4 — 4  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 5  is a sectional view taken generally along line  5 — 5  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 6  is a sectional view taken generally along line  6 — 6  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 7  is a sectional view taken generally along line  7 — 7  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 8  is a sectional view taken generally along line  8 — 8  of  FIG. 2 , with some components and/or panels removed for clarity; 
       FIG. 9A  is an enlarged fragmentary sectional views taken from  FIG. 2 , showing the machine configuration with the mold plate in a cavity fill position; 
       FIG. 9B  is an enlarged fragmentary sectional views taken from  FIG. 2 , showing the machine configuration with the mold plate in a patty discharge position; 
       FIG. 10  is a fragmentary sectional view taken generally along line  10 — 10  of  FIG. 2 , with portions of the apparatus removed for clarity of depiction, with some components and/or panels removed for clarity; 
       FIG. 11  is an enlarged, fragmentary view taken from the right side of  FIG. 2 ; 
       FIG. 12  is an enlarged, fragmentary, sectional view taken generally along line  12 — 12  of  FIG. 11 , with some components and/or panels removed for clarity; 
       FIG. 13  is an enlarged, fragmentary, sectional view taken generally of along line  13 — 13  of  FIG. 12  showing the drive nut assembly lifting the mold cover, before the secondary nut is engaged to the assembly; and 
       FIG. 14  is an enlarged, fragmentary, sectional view taken generally of along line  13 — 13  of  FIG. 12  showing the drive nut assembly in a lowered position not supporting the mold cover. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   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. 
   General Description of the Apparatus 
   The high-speed food patty molding machine  20  illustrated in the figures comprises a preferred embodiment of the invention. The complete machine is describes in U.S. Ser. No. 10/942,627, filed on the same day as the present application, and herein incorporated by reference. This application also incorporates by reference U.S. application Ser. No. 60/503,354, filed Sep. 16, 2003 and U.S. Provisional Application Ser. No. 60/515,585, filed Oct. 29, 2003. 
   The molding machine  20  includes a machine base  21 , preferably mounted upon a plurality of feet  22 , rollers or wheels. The machine base  21  supports the operating mechanism for machine  20  and can contains hydraulic actuating systems, electrical actuating systems, and most of the machine controls. The machine  20  includes a supply  24  for supplying moldable food material, such as ground beef, fish, or the like, to the processing mechanisms of the machine. 
   A control panel  19 , such as a touch screen control panel, is arranged on a forward end of the apparatus  20  and communicates with a machine controller  23 . 
   As generally illustrated in  FIGS. 2–6 , supply means  24  comprises a large food material storage hopper  25  that opens into the intake of a food pump system  26 . The food pump system  26  includes at least two food pumps  61 ,  62 , described in detail hereinafter, that continuously, or intermittently under a pre-selected control scheme, pump food material, under pressure, into a manifold  27  flow-connected to a cyclically operated molding mechanism  28 . 
   In the operation of machine  20 , a supply of ground beef or other moldable food material is deposited into hopper  25  from overhead. An automated refill device (not shown) can be used to refill the hopper when the supply of food product therein is depleted. The floor of hopper  25  is defined by a conveyor belt  31  of a conveyor  30 . The conveyor belt has a top surface  31   a  for moving the food material longitudinally of the hopper  25  to a hopper forward end  25   a.    
   The food material is moved by supply means  24  into the intake of plunger pumps  61 ,  62  of pumping system  26 . The pumps  61 ,  62  of system  26  operate in overlapping alteration to each other; and at any given time when machine  20  is in operation, at least one of the pumps is forcing food material under pressure into the intake of manifold  27 . 
   The manifold  27  comprises a path for feeding the food material, still under relatively high pressure, into the molding mechanism  28 . Molding mechanism  28  operates on a cyclic basis, first sliding a multi-cavity mold plate  32  into a receiving position over manifold  27  ( FIG. 9A ) and then away from the manifold to a discharge position ( FIG. 9F ) aligned with a series of knock out plungers such as knock out cups  33 . When the mold plate  32  is at its discharge position, knock out cups  33  are driven downwardly as indicated by  33 A in  FIG. 2 , discharging hamburgers or other molded patties from machine  20 . The molded patties are deposited onto a conveyor  29  ( FIG. 1A ), to be transported away from the apparatus  20 . 
   Food Supply System 
   The food supply means  24  and associated hopper  25  are illustrated in  FIGS. 2–6 . As seen, the conveyor belt  31  spans completely across the bottom of hopper  25 , around an end of idler roller or pulley  35  and drive roller or pulley  36 , the lower portion of the belt being engaged by a tensioning roller  37 . In some cases the tensioning roller  37  may not be necessary, and can be eliminated. A drum motor (not visible) is provided within the drive roller  36  for rotating the drive roller. 
   The forward end  25   a  of hopper  25  communicates with a vertical pump  38  having an outlet  39  at least partly open into a pump intake manifold chamber  41 . A vertically oriented frame  42  extends above hopper  25  adjacent the right-hand side of the outlet  39 . A motor housing  40  is mounted on top of the frame  42 . A support plate  43  is affixed to the upper portion of frame  42  extending over the outlet  39  in hopper  25 . The frame comprises four vertical tie rods  44   a  surrounded by spacers  44   b  ( FIG. 5 ). 
   As shown in  FIG. 5 , the vertical pump  38  comprises two feed screw motors  45 ,  46  that drive feed screws  51 ,  52 . The two electrical feed screw motors  45 ,  46  are mounted on the support plate  43 , within the motor housing  40 . Motor  45  drives the feed screw  51  that extends partly through opening  39  in alignment with a pump plunger  66  of the pump  61 . Motor  46  drives the feed screw  52  located at the opposite side of hopper  25  from feed screw  51 , and aligned with another pump plunger  68  of the pump  62 . 
   A level sensing mechanism  53  is located at the outlet end of hopper  25  comprising an elongated sensing element  54 . As the moldable food material is moved forwardly in the hopper  25 , it may accumulate to a level in which it engages the sensing element  54 . When this occurs, a signal is generated to interrupt the drive for the roller  36  of conveyor  31 . In this manner the accumulation of food material at the forward end  25   a  of hopper  25  is maintained at an advantageous level. 
   When machine  20  is in operation, the feed screw motor  45  is energized whenever plunger  66  is withdrawn to the position shown in  FIG. 2 , so that feed screw  51  supplies meat from hopper  25  downwardly through outlet  39  into one side of the intake  41  of the food pumping system  26 . Similarly, motor  46  actuates the feed screws  52  to feed meat to the other side of intake  41  whenever plunger  68  of the pump  62  is withdrawn. In each instance, the feed screw motors  45 ,  46  are timed to shut off shortly after the plunger is fully retracted, avoiding excessive agitation of the meat. As the supply of food material in the outlet  39  is depleted, the conveyor belt  31  continuously moves food forwardly in the hopper and into position to be engaged by the feed screws  51 ,  52 . If the level of meat at the outlet  39  becomes excessive, conveyor  31  is stopped, as described above, until the supply at the hopper outlet is again depleted. 
   The wall of the outlet  39  immediately below conveyor drive rollers  36  comprises a belt wiper plate  57  that continuously engages the surface of the conveyor belt  31  to prevent leakage of the food material  38  from the hopper at this point. 
   Food Pump System 
   The food pump system  26  of molding machine  20  is best illustrated in  FIGS. 2 and 6 . Pump system  26  comprises the two reciprocating food pumps  61 ,  62  mounted on the machine base  21 . The first food pump  61  includes a hydraulic cylinder  64 . The piston in cylinder  64  (not shown) is connected to an elongated piston rod  67 ; the outer end of the elongated piston rod  67  is connected to the large plunger  66 . The plunger  66  is aligned with a first pump cavity  69  formed by a pump cavity enclosure or housing  71  that is divided into two pump chambers. The forward wall  74  of pump cavity  69  has a relatively narrow slot  73  that communicates with the pump manifold  27  as described more fully hereinafter. 
   Preferably the pump housing  71  and the valve manifold  27  are cast or formed as a one piece stainless steel part. 
   The second food pump  62  is essentially similar in construction to pump  61  and comprises a hydraulic cylinder  84 . Cylinder  84  has an elongated piston rod  87  connected to the large plunger  68  that is aligned with a second pump cavity  89  in housing  71 . The forward wall  94  of pump cavity  89  includes a narrow elongated slot  93  communicating with manifold  27 . 
   Advantageously, the plungers  66 ,  68 , and the cavities  69 , 89  have round cross sections for ease of manufacturing and cleaning. 
   In operation, the first pump  61  pumps the moldable food material into manifold  27  and the second pump  62  receives a supply of the moldable food material for a subsequent pumping operation. Pump  61  begins its pumping stroke, and compresses food product in pump cavity  69 , forcing the moldable food material through slot  73  into manifold  27 . As operation of molding machine  20  continues, pump  61  advances plunger  66  to compensate for the removal of food material through manifold  27 . The pump can maintain a constant pressure on the food material in the chamber  69  during the molding cycle, or preferably can provide a pre-selected pressure profile over the molding cycle such as described in U.S. Pat. No. 4,356,595, incorporated herein by reference, or as utilized in currently available FORMAX machines. 
   When plunger  66  is near the end of its permitted range of travel, pump  62  is actuated to advance plunger  68  through pump cavity  89 , compressing the food material in the second pump cavity in preparation for feeding the food material from the cavity into manifold  27 . 
   When the food in the second pump cavity  89  is under adequate pressure, the input to manifold  27  is modified so that subsequent feeding of food product to the manifold is effected from the second pump cavity  89  with continuing advancement of plunger  68  of the second pump  62 . After the manifold intake has been changed over, pump  61  is actuated to withdraw plunger  66  from cavity  69 . 
   Thereafter, when plunger  68  is near the end of its pressure stroke into pump cavity  89 , the changeover process described immediately above is reversed. Pump  61  begins its compression stroke, manifold  27  is changed over for intake from pump  61 , and pump  62  subsequently retracts plunger  68  back to the supply position to allow a refill of pump cavity  89 . This overlapping alternating operation of the two pumps  61 ,  62  continues as long as molding machine  20  is in operation. 
   The pump feed manifold  27 , shown in  FIGS. 2 and 6 , holds a manifold valve cylinder or tube valve  101  fit into an opening  102  in housing  71  immediately beyond the pump cavity walls  74  and  94 . 
   According to the illustrated embodiment, valve cylinder  101  includes two longitudinally displaced intake slots  107  and  108  alignable with the outlet slots  73  and  93 , respectively, in the pump cavity walls  74  and  94 . Slots  107  and  108  are angularly displaced from each other to preclude simultaneous communication between the manifold and both pump cavities  69  and  89 . Cylinder  101  also includes an elongated outlet slot  109 . The valve cylinder outlet slot  109  is generally aligned with a slot  111  (see  FIG. 9A ) in housing  71  that constitutes a feed passage for molding mechanism  28 . 
   One end wall of valve cylinder  101  includes an externally projecting base end  103  that is connected to a drive linkage  104 , in turn connected to the end of the piston rod  105  of a hydraulic actuator cylinder  106  ( FIG. 2 ). 
   When the pump  61  is supplying food material under pressure to molding mechanism  28 , actuator cylinder  106  has retracted piston rod  105  to the inner limit of its travel, angularly orienting the manifold valve cylinder  101 . With cylinder  101  in this position, its intake slot  107  is aligned with the outlet slot  73  from pump cavity  69  so that food material is forced under pressure from cavity  69  through the interior of valve cylinder  101  and out of the valve cylinder outlet slot  109  through slot  111  to the molding mechanism  27 . On the other hand, the second intake slot  108  of valve cylinder  101  is displaced from the outlet slot  93  for the second pump cavity  89 . Consequently, the food material forced into the interior of valve cylinder  101  from pump cavity  69  cannot flow back into the other pump cavity  89 . 
   The valve cylinder  101  and corresponding slots or openings can alternately be as described in U.S. Provisional Application 60/571,368, filed May 14, 2004, or U.S. Ser. No. 10/942,754, filed on the same day as the present invention, both herein incorporated by reference. According to these disclosures, rather than a single outlet  109 , two rows of progressively sized outlets, smallest closest to the active pump, are alternately opened to plural openings that replace the single opening  111 . 
   Molding Mechanism 
   As best illustrated in  FIG. 9A , the upper surface of the housing  71  that encloses the pump cavities  69  and  89  and the manifold  27  carries a support plate or wear plate  121  and a fill plate  121   a  that forms a flat, smooth mold plate support surface. The mold support plate  121  and the fill plate  121   a  may be fabricated as two plates as shown or a single plate bolted to or otherwise fixedly mounted upon housing  71 . The fill plate  121   a  includes apertures or slots that form the upper portion of the manifold outlet passage  111 . In the apparatus illustrated, a multi fill orifice type fill plate  121   a  is utilized. A simple slotted fill plate is also encompassed by the invention. 
   Mold plate  32  is supported upon plates  121 ,  121   a . Mold plate  32  includes a plurality of individual mold cavities  126  extending across the width of the mold plate and alignable with the manifold outlet passageway  111 . Although a single row of cavities is shown, it is also encompassed by the invention to provide plural rows of cavities, stacked in aligned columns or in staggered columns. A cover plate  122  is disposed immediately above mold plate  32 , closing off the top of each of the mold cavities  126 . A mold cover casting or housing  123  is mounted upon cover plate  122 . The spacing between cover plate  122  and support plate  121  is maintained equal to the thickness of mold plate  32  by support spacers  124  mounted upon support plate  121 . Cover plate  122  rests upon spacers  124  when the molding mechanism is assembled for operation. Cover plate  122  and mold cover casting  123  are held in place by six mounting bolts, or nuts tightened on studs,  125 . 
   The cover plate  122  can be configured as a breather plate as part of a molding mechanism air-and-fines removal system, such as described in U.S. Ser. No. 10/942,755, and filed on the same day as the present application, and herein incorporated by reference. 
   As best illustrated in  FIGS. 3 and 6  mold plate  32  is connected to drive rods  128  that extend alongside housing  71  and are connected at one end to a transverse bar  129 . The other end of each drive rod  128  is pivotally connected to a connecting link  131  via a coupling plate  131   a  and a pivot connection  131   c , shown in  FIG. 2 . The pivot connection  131   c  can include a bearing (not visible in the figures) surrounding a pin within an apertured end of the connecting link  131 . The pin includes a cap, or carries a threaded nut, on each opposite end to secure the crank arm to the coupling plate  131   a.    
   Each drive rod  128  is carried within a guide tube  132  that is fixed between a wall  134  and a front bearing housing  133 . The connecting links  131  are each pivotally connected to a crank arm  142  via a pin  141  that is journaled by a bearing  141   a  that is fit within an end portion of the connecting link  131 . The pin crank arm  142  is fixed to, and rotates with, a circular guard plate  135 . The pin  141  has a cap, or carries a threaded nut, on each opposite end that axially fixes the connecting link  131  to the crank arm  142  and the circular guard plate  135 . The connecting link  131  also includes a threaded portion  131   b  to finely adjust the connecting link length. 
   The crank arms  142  are each driven by a right angle gear box  136  via a “T” gear box  137  having one input that is driven by a precise position controlled motor  138  and two outputs to the gearboxes  136 . The “T” gear box  137  and the right angle gear boxes  136  are configured such that the crank arms  142  rotate in opposite directions at the same rotary speed. 
   The precise position controlled motor can be a 6–7.5 HP totally enclosed fan cooled servo motor. The servo motor is provided with two modules: a power amplifier that drives the servo motor, and a servo controller that communicates precise position information to the machine controller. 
   The controller  23  and the servo motor  138  are preferably configured such that the servo motor rotates in an opposite rotary direction every cycle, i.e., clockwise during one cycle, counterclockwise the next cycle, clockwise the next cycle, etc. 
   A bearing housing  143  is supported on each gearbox  136  and includes a rotary bearing  143   a  therein to journal an output shaft  136   a  of the gear box  136 . The output shaft  136   a  is fixed to the crank arm  142  by a clamp arrangement formed by legs of the crank arm  142  that surround the output shaft and have fasteners that draw the legs together to clamp the output shaft between the legs (not shown), and a longitudinal key (not shown) fit into a keyway  136   b  on the output shaft and a corresponding keyway in the crank arm  142  (not shown). 
   A tie bar  139  is connected between the rods  128  to ensure a parallel reciprocation of the rods  128 . As the crank arms  142  rotate in opposite rotational directions, the outward centrifugal force caused by the rotation of the crank arms  142  and the eccentric weight of the attached links  131  cancels, and separation force is taken up by tension in the tie bar  139 . 
   One circular guard plate  135  is fastened on top of each crank arm  142 . The pin  141  can act as a shear pin. If the mold plate should strike a hard obstruction, the shear pin can shear by force of the crank arm  142 . The guard plate  135  prevents an end of the link  131  from dropping into the path of the crank arm  142 . 
   During a molding operation, the molding mechanism  28  is assembled as shown in  FIGS. 2 and 9A , with cover plate  122  tightly clamped onto spacers  124 . 
   The knockout cups  33  are driven by a knockout drive mechanism as described in U.S. Ser. No.10/943,809, filed on the same day as the present application, and herein incorporated by reference. 
   In each cycle of operation, knockout cups  33  are first withdrawn to the elevated position as shown in  FIG. 9B . The drive for mold plate  32  then slides the mold plate from the full extended position to the mold filling position illustrated in  FIGS. 2 and 9A , with the mold cavities  126  aligned with passageway  111 . 
   During most of each cycle of operation of mold plate  32 , the knockout mechanism remains in the elevated position, shown in  FIG. 9B , with knockout cups  33  clear of mold plate  32 . When mold plate  32  reaches its extended discharge position as shown in  FIG. 9B  the knockout cups  33  are driven downward to discharge the patties from the mold cavities. 
   The discharged patties may be picked up by the conveyor  29  or may be accumulated in a stacker. If desired, the discharged patties may be interleaved with paper, by an appropriate paper interleaving device. Such a device is disclosed in U.S. Pat. No. 3,952,478, or U.S. Ser. No. 60/540,022, filed on Jan. 27, 2004, and herein incorporated by reference. In fact, machine  20  may be used with a wide variety of secondary equipment, including steak folders, bird rollers, and other such equipment. 
   Mold Cover Lift System 
   During mold plate change or to clean the apparatus, it is necessary to lift the mold housing or mold cover  123  from above the mold plate  32 . The bolts  125  are removed as a first step for lifting of the housing  123 . 
   A mold housing lift mechanism  800  is mounted inside the machine base  21  and extends upward to the housing  123 . The lift mechanism includes two jacks  802 ,  804  shown in  FIGS. 8 and 10 . The jacks are operatively connected to right angle drives  808 ,  810 , which are operatively connected to a T type right angle drive  814 , via drive shafts  818 ,  820  and respective couplings  823 ,  824 ,  826 ,  828 ,  830 . The right angle drive  814  is driven into rotation by a hydraulic motor  836 . 
   The jack  802  is described below with the understanding that the jack  804  is identically configured and functions identically, in tandem, as the jack  802 . 
   As shown in  FIGS. 8 ,  11  and  12  the drive  808  turns a threaded rod or jackscrew  842  that drives a nut drive assembly  844  vertically. The jack screw  872  is journaled for rotation at a top end by a guide  845 . The jack screw  842  and guide  845  can include a bearing therebetween for smooth journaled rotation of the jackscrew. The drive assembly  844  is operatively connected to a lift column  850  via a bracket  851  which is vertically driven with the drive nut assembly. The columns  850  of the jacks  802 ,  804 , are fixed to the housing  123  by bolts  856 ,  858 . The columns  850  are hollow and can also serve as wire and tube conduits. 
   As shown in  FIGS. 11–14 , the bracket  851  is clamped onto a bottom of column  850 . The bracket  851  rests on a drive nut  870  that is driven by the drive rod  842 . A limit plate  862  is fastened to the drive nut  870  by spacers  867  and fasteners  866 . A collar  874  is fastened to the bottom of the drive nut  870  with fasteners  875 . 
   The drive nut  870  has inside threads engaged to the outside threads of the drive rod  842 . A secondary nut  882  is threaded onto the jackscrews  842  beneath the drive nut  870 . 
   Proximity target, magnetic plate  892  is fastened to a mounting plate  894  which is fastened to the bracket  851  by fasteners  900 . A proximity sensor  908  is mounted within the machine base  21  along the vertical path of the magnetic plate  892  and set at a maximum acceptable. The magnetic plate  892  sets an acceptable vertical range for a mold cover operating elevation. If the mold cover is elevated beyond this range, the sensor  908  will be below the magnetic plate  892  and will so signal the machine controller which will prevent operation of the machine. 
   A further proximity target  904  is fastened to a lateral side of the bracket  851 . Proximity sensor  910  is mounted at an elevated position within the machine base along the vertical path of the target  904  and signals a pre-determined raised maximum height of the mold cover casting for a mold plate change out procedure. The proximity sensor  910  signals the machine controller to stop the motor  836  at that point. 
   The collar  874  has internal protruding pins  878 , surrounding the jackscrew  842  and a secondary nut  882 . The secondary nut includes notches  886  for receiving the pins  878 . During normal lifting operation, the pins will be engaged to, or will engage, the secondary nut  882  as shown in  FIG. 14 . The secondary nut  882  ceases to rotate freely with the jackscrew  842  and thereafter travels with the assembly  844  up and down on the jackscrew  842 . The secondary nut  882  provides backup support for the drive nut  870  in the unlikely event that the drive nut fails to support the bracket  851 . 
   As shown in  FIG. 13 , before engagement with the pins of the drive nut assembly  844 , the secondary nut  882  is free to rotate with the jackscrew  842  between the nut  870  and the pins  878 . Once the pins  878  are relatively elevated with respect to the nut  882  to engage the notches  886  the secondary nut moves vertically with the assembly  844 . If the drive nut  870  fails during lifting, the secondary nut  882  is in a position to support the drive nut assembly and bracket  851 , but will not function to lift the nut assembly  844 . If the jackscrew is turned, the secondary nut  882  will rise to the point until it disengages from the pins  878  and then turn substantially freely with the rotating jackscrew  842 . 
     FIG. 14  illustrates the assembly with the mold cover lowered and the nut  870  lowered a further amount with the plate  862  contacting, or adjacent to, the bracket  851 . Thus, the nut assembly  844  can completely disengage from the bracket  851 . 
   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.