Patent Abstract:
A drive for use in the manufacture of cans comprises a hydraulically powered guide pod to which a hold down assembly is attached. The guide pod slides along a guide rod which is fixed in the bodymaker. Forward and rear hydraulic chambers are defined between the pod and the guide rod by means of bushings and a seal. Passage of fluid through ports to and from the hydraulic chambers causes the pod and hold down assembly to move forward and backward. The length of the stroke can be set by the distance between the ports. A rotary valve is used to control the timing of the drive and control flow of hydraulic fluid, which is typically obtained from the bodymaker coolant supply.

Full Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a drive for a hold down assembly for use in the manufacture of cans. In particular, but not exclusively, it relates to a drive for a blank holder which holds a can blank against a redraw die. 
     Hold down mechanisms such as redraw sleeves and blanking punches are known. Typically, a lever is held against cam profiles on the crank. The lever drives a pair of push rods to drive a crosshead which, in turn, actuates a blank holder. This combination of push rods and cam actuation moves the blank holder towards a redraw die to bring the can blank, or cup, to the die. The blank holder presses the base of the cup against a flat face of the die while a punch pushes the cup into the die for redrawing. 
     This type of mechanism is heavy and the rotating mass on the crankshaft presents a severe load to the bodymaker main bearings. This invention seeks to reduce problems associated with this loading. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a hydraulic drive for a hold down apparatus in a can bodymaker, the drive comprising a fixed guide rod; a guide pod surrounding the guide rod, the pod having rear and forward end faces which together define rear and forward hydraulic chambers respectively, the chambers being separated by a seal; a first channel (A) for the passage of hydraulic fluid to and from the rear hydraulic chamber via a return stroke port; a second channel (B) for the passage of hydraulic fluid to and from the forward hydraulic chamber via a forward stroke port; whereby passage of fluid into the forward chamber drives the pod and hold down assembly connected thereto to a forward position and passage of fluid into the rear chamber forces the pod and hold down assembly to return to a back position. 
     By using a hydraulically powered drive, the rotating mass on the bodymaker crankshaft is dramatically reduced since the existing push rods, cam levers, redraw cams and cam followers and air bags to hold the cam followers onto the cams are no longer required. This in turn decreases the size of the bodymaker hydraulic power pack which is required for the push rods, cams and followers in known hold down apparatus. Furthermore, an increase in machine speed is possible due to the reduction in mass and subsequent reduction in system inertia which could lead to increased production. 
     Various knock-on effects are achieved by the use of the hydraulic drive for the hold down assembly, such as a reduction in size of power components, flywheel and other drives etc. and thereby reducing load on the bodymaker main bearings and wear. 
     The rear and forward end faces of the pod may typically be defined by bushings. 
     The hydraulic fluid may be the machine coolant which is typically already available in the factory supply. Although this may require of the order of 60 liters/minute, the bodymaker hydraulic power pack can in fact be reduced in size due to the replacement of several components as noted above. The replacement operation is possible simply by means of a retro-fit. 
     The forward chamber typically comprises a substantially cylindrical portion which tapers radially outwardly at its forward end whereby pressure in the hydraulic chamber is decreased at the forward end. The taper, or chamfer decreases hydraulic pressure at the forward end of the hydraulic chamber since the chamber size is increased at the fluid pressure face but limits fluid requirements in the remainder of the chamber. 
     The hydraulic drive may ideally include check valves for controlling initial acceleration of the guide pod and/or pressure relief valves for the avoidance of pressure spikes. 
     Whilst the hydraulic fluid flow may be controlled by a variety of means, ideally a rotary valve is used. The rotary valve may rotate at a speed which is less than or equal to machine speed, according to the desired machine timing. 
     According to a further aspect of the present invention, there is provided a method of driving a hold down apparatus in a bodymaker, the method comprising: providing a fixed guide rod; connecting the hold down apparatus to a guide pod which surrounds the guide rod and is movable along the guide rod, the pod having rear and forward end faces which define rear and forward hydraulic chambers respectively, the chambers being separated by a seal; supplying hydraulic fluid to and from the rear hydraulic chamber via a return stroke port; supplying hydraulic fluid to and from the forward hydraulic chamber via a forward stroke port; whereby supplying fluid into the forward chamber drives the pod and hold down assembly connected thereto to a forward position and supplying fluid into the rear chamber forces the pod and hold down assembly to return to a back position. 
     Preferably, the end faces comprise bushings for covering and/or opening the ports, and the method further comprises: accelerating movement of the pod and hold down apparatus by uncovering a port and increasing fluid flow to and from the respective chamber; or decelerating the machine stroke by covering a port and reducing fluid flow to and from the respective chamber. 
     Preferred embodiments of hydraulic drive will now be described, by way of example only, with reference to the drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial side section of a bodymaker showing hydraulic drive and hold down; 
     FIG. 2 is an enlarged side section of the drive of FIG. 1; 
     FIG. 3 is an enlarged partial side section of an alternative drive; 
     FIG. 4 is an alternative hold down assembly; and 
     FIG. 5 is a side section of the rotary valve of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a side section of a bodymaker front end with a hydraulic drive  1  for actuation of hold down assembly  10 . A rotary valve  20  controls flow of hydraulic fluid as will be described in more detail below. 
     As shown in FIGS. 2 and 3, drive  1  consists of a central guide rod  2  and guide pod  3 , to which the hold down assembly  10  is connected. The pod  3  has an inner portion  12  which may typically be made of steel so that the guide rod  2  bears against this inner sleeve  12 . In order to limit mass and inertia, the pod outer portion  13  is of lighter material, typically aluminium. 
     Annular space between inner sleeve  12 , guide rod  2  and forward and rear bushings  14 ,  15  is separated into forward and rear chambers  6 ,  9  respectively by labrynth seal  11 . Guide rod  2  is fixed in position in the bodymaker so that supply of hydraulic fluid to and from forward and rear chambers  6  and  9  forces the pod  3  to move forwards and backwards along the guide rod  2  according to the pressure of hydraulic fluid in the chambers  6  and  9 . 
     Conduits A and B provide channels for passage of hydraulic fluid between rotary valve  20  and the guide rod  2 . As shown in FIG. 2, channel A leads via port  7  and/or rear cushion jets  8  to rear chamber  9 . Similarly, channel B leads via port  4  and/or forward cushion jets  5  to forward chamber  6 . The operation of the ports and cushion jets is described in more detail below. In the embodiment of FIG. 3, check valves  5 ′,  8 ′ are provided in the forward and rear chambers  6 ,  9  respectively and pressure relief valves  46  are provided in the chamber  43 . The operation of these valves is also described in more detail below. 
     Forward chamber  6  comprises a cylindrical portion  16  which tapers outwardly at its forward end  17  to fluid pressure face  18 . The outward taper is defined by the degree of chamfer at the forward end of sleeve  12 . Although no equivalent change in size is provided for the return stroke chamber  9 , clearly this is possible within the scope of the invention. 
     Referring now to FIGS. 1 and 4, hold down assembly  10  comprises a blank holder  30  for holding a cup  31  against redraw die  32 . In the embodiment shown in FIG. 1, the hold down apparatus includes a spacer  33  and centring ring  34 . This centring ring  34  provides for ready access to change the blank holder without the need for lengthy realignment procedures. A retainer  35  and spring  36  may be used instead of the spacer  33 , as shown in FIG.  3 . 
     FIG. 4 is a side section of a rotary valve  20  which is used to regulate flow of hydraulic fluid in a preferred embodiment of the invention. As can be seen in FIG. 1, valve  20  supplies fluid to drives  1  on both sides of the hold down apparatus  10 . Conduits A and B are in each drive unit are connected to drillings A and B in the rotary valve. 
     Valve  20  is connected to rotor shaft  21  which is driven by the bodymaker main crankshaft and rotates in the direction indicated by the arrow in FIG.  4 . Hydraulic fluid from the bodymaker coolant supply enters the rotary valve via inlet  22  and exits via exhaust  23 . Inlet  22  and exhaust  23  are shown out of position in FIG. 4 for clarity. A central bore  24  in the shaft  21  connects inlet  22  and exhaust  23  to drillings A or B in the valve according to the desired machine timing. The valve  20  is mounted on a manifold  40  which is bolted onto the bed of the machine. 
     Operation of the hydraulic drive of the invention is as follows. Pressurised hydraulic fluid from the bodymaker coolant supply is supplied to the bore  24  of central rotor shaft  21  by the action of an accumulator and pump (not shown). As the central shaft  21  rotates, hydraulic fluid passes from the shaft  21  into drilling A when the rotary valve is in the position shown in FIG.  4 . Drilling A supplies pressurised fluid along channel A to chamber  9  to drive the return stoke of the hold down. 
     In the embodiment shown in FIG. 4, the drillings A and B are offset in order to achieve the desired machine timing. For example, the rotary valve may rotate at half machine speed (set by the crankshaft) in order to limit component wear. 
     Drilling B in rotary valve  20  communicates with the exhaust  23  to exhaust medium in channel B when drilling A is aligned with channel A as shown. Similarly, drilling A communicates with the exhaust  23  to exhaust medium in channel A. 
     The return stroke of the hold down apparatus occurs when the drilling A of the valve is aligned with channel A as shown in FIG.  4 . The return stroke returns the hold down apparatus to the back position. 
     With reference to FIGS. 1 and 2, passage of fluid from channel A to chamber  9  is blocked by rear bushing  15  but can exit radially outwards into the rear chamber  6  through cushion jets  8 . This ensures a relatively gentle start to movement of the pod  3  and hold down assembly away from the cup  31  in redraw die  32  as pressure builds up in rear chamber  9 . 
     As the pressure increases further in the rear chamber, the movement of the pod  3  causes rear bushing  15  gradually to expose return stroke port  7  and allows fluid to pass through the increasingly exposed port  7 , thereby providing further acceleration of the return stroke until the port is fully open. 
     According to the drive timing (set by the valve  20 ), rotation of the shaft  24  in the valve assembly causes drilling A gradually to close. Meanwhile, movement of the forward bushing  14  causes hydraulic fluid in the forward chamber  6  to exhaust out via channel B. As port  4  is closed by the bushing  14 , movement of the pod is slowed until the trailing edge of the port is closed. This deceleration is controlled further by the provision of forward cushion jets  5  which restrict further exhaust and enhance the cushioning effect at the end of the return stroke. The stroke length is determined by the position of the ports  4  and  7  in the guide rod. 
     As drilling B in the valve assembly opens, pressurised fluid passes from inlet  22  via central bore  24  to conduit B. The forward stroke to drive the hold down assembly forward is then initiated as fluid gradually enters the forward chamber  6  via cushion jets  5 . Acceleration of the forward stroke occurs as forward bushing  14  uncovers forward stroke port  4 . Meanwhile, fluid from rear chamber  9  is exhausted through channel A to exhaust  23  in the rotary valve. Slowing of the forward stroke is achieved in like manner to that of the return stroke as forward bushing covers the port  4  and fluid enters the forward chamber through a reduced area of port  4  and finally only via cushion jets  8 . The cup  31  is then held against the die  32  for redrawing by movement of punch  45  into the cup. 
     It can be seen from FIG. 2 in particular that the forward and rear bushings  14 ,  15  provide for acceleration and deceleration of the pod  3  at each end of the forward and return strokes as the bushings gradually close and/or uncover forward and rear ports  4 ,  7  respectively. 
     In the embodiment of FIG. 3, check valves  5 ′,  8 ′ are provided which are closed on the exhaust stroke but open for the pressure stroke, thereby allowing fluid to chamber  6  or  9  respectively. This dead ends the fluid which is used to stop the guide pod  3  and applies pressure to the face of associated bushing  14  or  15  until the supply groove is uncovered. 
     Pressure relief valves  46  prevent the build up of pressure due to fluid compression in chamber  6  or  9  from reaching the point at which pressure spikes occur. Pressure is thus released via channel  41  and pressure relief valves  46 . 
     The hold down apparatus remains in the forward position as the punch  45  enters cup  31  for redrawing. The cycle then repeats. 
     Any coolant which is forced between the guide rod  2  and the sleeve  16  can be removed by the labrynth seal  11 . Swarf or other debris collects in annuli  42  in the bushings  14  and  15  and exits through passages  41  into chamber  43  in the pod  3  to be passed out via port  44  for processing by the coolant supply. 
     The invention has been described above by way of example only and changes may be made within the scope of the invention as defined by the claims. For example, in the first embodiment shown in FIG. 2, movement of the pod is controlled not only by the bushings moving over the ports but also by the use of cushion jets  5  and/or  8  between the channels and respective hydraulic chambers. These cushion jets are positioned such that even after the bushing closes the ports, communication is still possible via the cushion jet or jets. In the second embodiment of FIG. 3, a system of check valves is used to prevent “dead ending” of fluid which is used to stop the mechanism, and pressure relief valves for the avoidance of pressure spikes. Clearly any combination of cushion jets and check and pressure relief valves may be used. Alternative features in either of the guide rod or guide pod (or both) which provide an enhanced soft start/stop to the movement of the guide pod are also considered to be within the scope of the invention. 
     Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.

Technology Classification (CPC): 1