US3682230A

US3682230A - Rotatable cantilevered shell molding machine

Info

Publication number: US3682230A
Application number: US74424A
Authority: US
Inventors: Warren A Blower; Gilbert J Janke; Edward D Abraham
Original assignee: Sherwin Williams Co
Current assignee: Sherwin Williams Co
Priority date: 1970-09-22
Filing date: 1970-09-22
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08
Also published as: DE2146737A1; CA947926A; FR2107870B1; GB1353233A; FR2107870A1

Abstract

A machine for making shell molds or cores having improved safety, serviceability and maintenance which includes a single large ball bearing supporting the radial, thrust and the moment load of the rotating carriage with a considerable safety factor, the carriage thus projecting in cantilever fashion from the base, the distal end of the carriage being provided with a door, the actuating mechanism being an enclosed rack and gear providing constant torque, the operation of the door and the locking of the door being accomplished by piston-cylinder assemblies at the proximal end of the carriage out of the high temperature zone adjacent the tooling,and a simplified automatic sand feed system utilizing a large rubber ball check valve.

Description

United States Patent Blower et al.

[54] ROTATABLE CANTILEVERED SHELL MOLDING MACHINE [72] Inventors: Warren A. Blower, Bercksville; Gilbert J. Janke, Parma; Edward D. Abraham, Cleveland, all of Ohio 73 Assignee: The Sherwin-Williams Company,

Cleveland, Ohio 22 Filed: Sept. 22, 1970 21 Appl. No.: 74,424

[56] References Cited UNITED STATES PATENTS Shallenberger et al. 164/ l 65 3,184,809 5/ 1965 Stewart 164/ 165 d T u 44 43 [451 Aug. 8, 1972 Primary ExaminerR Spe'ncer Annear Attorney-Oberlin, Maky, Donnelly & Renner i 57' ABSTRACT A machine for making shell molds orcores having improved safety, serviceability and maintenance which includes a single large ball bearing supporting the radia], thrust and the moment load of the rotating carriage with a considerable safety factor, the carriage thus projecting in cantilever fashion from the base, the distal end of the carriage being provided with a door, the actuatingmechanism being an enclosed rack and gear providing constant torque, the operation of the door and the locking of the door being accomplished by piston-cylinder assemblies at the proximal end of the carriage out of the high temperature zone adjacent the tooling,and a simplified automatic sand feed system utilizing a large rubber ball check valve.

18 Claims, 7 Drawing Figures PATENTEDAUG 8l972 3.682.230

SHEET 1 0F 4 ?77\"ENTOR$. WARREN A. BLOWER GILBERT J. JANKE EDWARD 0. ABRAHAM a/azwm zmwgm A TTORNEYS PATENTEDIus aImz SHEET 2 [IF 4 I I I l '1 I I I I I l l INVENTORS. WARRE/V.A. BLOWER G/LBERT J. JAN/(E A r romvevs B EDWARD 0. ABRAHAM (7/214): l/yrz/fy flan"! //y 6 fin/"0L PATENTED U 8 3.682.230

INVENTORS. WARREN A. BLOWER GILBERT J. ,JA/VKE E DWARD D. ABRAHAM A TTORNEYS PATENTEDAus 8 I972 3.682.230

sum u or 4 lea we :75 l- 7 INVENTORS. WARREN A. BLOWER I G/LBERZ .1. JAN/(E EDWARD a ABRAHAM ATTORNEYS ROTATABLE CANTILEVERED SHELL MOLDING MACHINE This invention relates generally as indicated to a shell molding machine and more particularly to a foundry shell machine for making shell molds or cores.

In the shell molding process a foundry sand-resin mix is blown or dumped from a hopper into a patterned box with the patterned surfaces of the box being heated. The box is then inverted to remove excess sand, only that portion of the sand adjacent the heated patterned surface curing sufficiently so that when the excess sand is dumped back into the hopper a hollow or shell mold or core is formed. To accomplish the inversion the pattern together with the hopper is usually inverted or turned upside down and rocking may occur following such inversion to ensure that all excess sand has been removed from the interior of the shell.

I-Ieretofore such machines have been difficult to service and maintain because of the lack of accessibility to the area about the machine. Moreover, a careless operator might get caught between closely adjacent relatively moving parts.

It is a principal object of the present invention to provide a foundry shell mold or core machine having improved serviceability, maintenance and safety.

Another principal object is the provision of a shell mole or core machine utilizing a cantilever construction permitting greater accessibility to the job.

A further object is the provision of such machine having an enclosed rack and gear mechanism providing constant torque for operation of the pivotally mounted tooling platen, the lock and swing drives for such platen being at the proximal or journalled end of the carriage supporting the same to avoid the heat in the area of the tooling.

Still another object is the provision of such machine having an improved automatic sand feed system utiliz-' ing a rubber ball check valve and eliminating the need for diaphragm pinch-off valves.

A yet further object is the provision of such machine utilizing a single large ball bearing supporting the radial thrust and moment loads of the rotating carriage with a a substantial safety factor.

It is also, of course, an object to provide such machine of simplified construction for extra rigidity, dependable operation and minimum maintenance.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

In said annexed drawings:

FIG. 1 is a fragmentary vertical section of amachine in accordance with the present invention;

FIG. 2 is an end elevation of the machine as seen from the left or line 2-2 in FIG. 1;

FIG. 3 is an end elevation as seen from the right or line 33 of FIG. 1;

FIG. 4 is an enlarged fragmentary detail view of the lock pin actuating mechanism;

FIG. 5 is a fragmentary'section of such mechanism taken substantially on the line 5-5 of FIG. 4;

FIG. 6 is an enlarged fragmentary section of the rubber ball check valve of the sand feed system; and

FIG. 7 is a schematic pneumatic diagram of the machine showing the automatic sand feed system with the blow and exhaust valves for the reservoir.

Referring first to FIGS. 1 through 3, it will be seen that a machine in accordance with the present invention includes a machine base 10 in the form of an upstanding L including upstanding portion 11 and lower laterally directed portion 12 acting as a stabilizer firmly to support the machine on the floor F. The upstanding portion 11 of the base is in the form of a housing substantially open at the back as indicated at 14. The

side walls

15 and 16 are provided with access windowsas seen at 17. The front of the housing includes a pair of spaced

upstanding plates

18 and 19. The forward plate 19 has access windows 20 and 21 each provided with a cover as seen in FIG. 3 as well as a center access window 22 provided with cover 23. The upper end of the plate 19 terminates in an enlarged opening 25 provided with a cover 26 which has a circular interior opening.

The inner upstanding plate 18 includes an opening 28 through which projects shaft 29 of cone drive gear motor 30. The

walls

18 and 19 are interconnected by

webs

32 and 33 seen in FIG. 2 to form a rigid box section. The rear wall 18 is offset rearwardly as indicated at 34 and is provided just above the offset with a circular opening indicated at 35. Just before the offset two spaced

sprocket shafts

37 and 38 extend between the walls and have sprockets 39. and 40 journalled thereon. Such sprockets are vertically aligned with sprocket 41 mounted on the gear motor shaft 29.

A large diameter turntable ball bearing indicated generally at 43 includes an outer race 44 secured by the plurality of fasteners indicated at 45 to the front of the wall 18 adjacent the opening 35. The inner race 46 is secured by similar fasteners 47 to radially extending flange 48 of rear trunnion frame 49 of the carriage shown generally at 50. The balls of the bearing 43 may be separated in conventional manner by a cage or by individual spacers The bearing 43 is designed to support radial, thrust and moment loads of the carriage with a 25-1 factor of safety. For example, the static capacity of the bearing may be a moment in inch pounds of 4,900,000 while the actual applied load is only 130,000.

The rear trunnion frame 49 of the carriage 50 includes four longitudinally extending sleeves seen at 52 in which are shoulder stopped

tie rods

53, 54, and 56. The

top rods

53 and 56 may be solid while the

bottom rods

54 and 55 are hollow. Each rod is provided with a reduced diameter threaded end seen at 57 projecting through the rear trunnion 49 and such rods are secured in place by nuts 58.

The distal or outer ends of the rods support a fron trunnion frame 60 which has the plus sign opening 61 therein as seen more clearly in FIG. 3. Nuts 62 are secured to the distal or outer ends of the rods beyond the front trunnion frame 60.

A door 64 is hingedly mounted in the opening 61 of the front trunnion frame by means of the hinge pins indicated at 65 and 66 in FIG. 1. Such hinge pins are secured to the door and mounted in the vertically spaced bushings indicated at 67. Thrust bearings are provided surrounding such pins between the door and trunnion at 68 and 69. The latter may, if desired, be a ball thrust bearing.

The bottom pin 66 has secured to it a rack gear 70 between the bushings in the opening provided in the front trunnion. The rack gear is in engagement with a rack on the end of rack gear shaft 71 extending through the hollow tie rod 54. The rack gear shaft is connected to rod 72 of piston-cylinder assembly 73 mounted on the back of rear trunnion frame 49 by the support brackets indicated at 74. When the door is unlocked, extension and retraction of the piston-cylinder assembly 73 will cause the door to swing open and close.

The inside of the door 64 supports a two-part platen indicated generally at 76, such platen including a mounting plate 77 provided with a plurality of parallel T-slots seen at 78 and a gas manifold backup plate 79. The backup plate and the mounting plate form a chamber for conducting gas or other fuel through passages 80 in the mounting plate 77 to which are connected burner tips 81. Mounting blocks 82 may be secured in the desired fashion to the T-slots 78 and are employed to fasten core box half 83 to the platen. The burner tips thus provide direct flame impingement against the core box or tooling. Depending upon the shell mold or core being formed, only the necessary mounting blocks and burner tips need be employed, with those passages 80 not used being plugged.

An opposed core box half 85 is mounted in similar fashion on two-part platen 86 which is in turn mounted on adjustable frame 87. Such frame is provided with four comer sleeves 88 each of which is slidably mounted on the respective tie rod. The frame 87 is provided with a rearwardly projecting adjusting screw bushing 90, the interior of which is threaded on adjusting screw 91 provided with circular handle 92. The screw and handle which may be pinned together are rotatably connected through cap 93 to the rod 94 of pneumatic clamp cylinder 95. Such rod 94 projects through the rear trunnion frame 49 and the clamp cylinder is secured to such frame by the fasteners indicated at 96. The clamp cylinder 95 is situated inside the cylindrical hose reel 97 projecting rearwardly from the trunnion frame 49. t 1

In this manner, the box half 85 may be moved toward and away from the box half 83 to be clamped thereagainst. The box half 83 may be termed the fixed half for clamp purposes although it is mounted on the door 64 to be swung through 90 by the action of the piston-cylinder assembly 73 to facilitate removal of the finished core or mold. When clamped together, the box halves form a cavity shown generally at 98 which includes one or more downwardly directed openings or sprues seen at 99.

Such openings may correspond to similar openings in the blow Accordingly, 101 of sand hopper 102. The sand hopper is supported by

support rods

104 and 105 secured to the tie bars 55 and 54, respectively, by support rod clamps 106 and 107. Secured to and extending between the outer ends of the support rods is support bar 108 to the underside of which is mounted single acting pneumatic cylinder 109. The rod of the cylinder 109 engages the bottom of the hopper as indicated at 110 to urge the same upwardly or toward the box halves 85 and 83 when extended. A cylindrical stop 1 1 1 is secured to the bottom of the hopper and engages the support bar 108 when the rod is retracted. Accordingly when the cylinder 109 is extended, the hopper is clamped against the box halves for introduction of a sand-resin mix into the cavity 98 and a gasket 1 12 is provided to eflect an air seal between the hopper and the box when the cylinder is extended.

Referring now more particularly to FIGS. 2, 3, 4 and 5, the door 64 is locked and unlocked by actuation of piston-cylinder assembly 115, seen in FIG. 2, the rod of which is connected at 1 16 to clevis arm 117 secured to the rearwardly projecting end of lock pin operating shaft 118 which extends through the hollow center of tie rod rod 55. The blind end of such assembly 115 is pivoted to rear trunnion frame 49. The front end 'of the operating shaft in the front trunnion frame 60 is journalled in bearing 120 and has secured thereto by the fastener indicated at 121 laterally projecting operating lever 122. The lever projects through window 123 in the tie rod and the distal end of such lever is provided with a rotatably mounted shoe 124 fitting in a transverse slot on short lock pin 125 which is slidably mounted in

bushings

126 and 127. Extension and retraction of the piston-cylinder assembly 115 will ac- I cordingly cause the short lock pin 125 to move up and down. In FIG. 4, the pin is shown in its extended or lock condition. I

Now referring more particularly to FIG. 3, it will be seen that the door 64 is provided with a long lock pin 130 which when the door is closed will be in vertical alignment with the short lock pin 125. The long lock pin is slidably mounted in

bushings

131 and 132 in bosses on the door and is urged downwardly by compression spring 133 extending between the upper boss and collar 134. A stop collar 135 is also provided on the long locking pin limiting its downward movement. In its upward or lock condition, the long lock pin 130 extends into a bushing or seat 136 in the front trunnion frame 60. It can now be seen that the piston-cylinder assembly will be eflective to lock and unlock the door 64 for swinging movement by the piston-cylinder assembly 73.

When the piston-cylinder assembly 115 is extended, the operating shaft 118 is rotated and the connection between such shaft and the short pin seen in FIGS. 4 and 5 causes the pin 125 to descend until the top thereof is clear of the bottom of the door. The spring 133 automatically causes the long pin to follow to the extent permitted by the stop removing the long pin from the upper socket or seat. When the short pin is thus completely retracted, the door is then free to swing open at the direction of the piston-cylinder assembly 73 through the rack and pinion seen in FIG. 1. An adjustable stop 140 engaging bumper 141 seen in FIG. 3 limits the extent to which the door swings.

It can now be seen that the trunnion carriage 50 which includes: the door 64 on which the platen 76 is mounted; the sliding frame 87 on which the platen 86 is mounted; thedoor actuating and lock mechanisms; the clamp cylinder 95; and the hopper 102, is mounted in cantilever fashion for rotation about a horizontal axis by the large diameter single bearing 43. Rotation of the trunnion carriage in the desired fashion is obtained through the gear motor 30 which drives through sprocket 41 drive chain 143, the position of which is seen more clearly in FIG. 2. The chain 143 extends about the drive sprocket 41 of the gear motor and is pinched between the

idler sprockets

39 and 40 and then extends about the rear trunnion frame 49, being secured thereto by chain anchor block 144. One end of the chain is fixed-to the anchor block while the other end is adjustably connected thereto by chain connector 145 An emergency stop block 146 is mounted on the rear trunnion frame 49 and is positioned to engage spring loaded stops 148 and 149 should the carriage overtravel. Various control devices may be mounted on the rear trunnion frame 49 as seen in FIG. 2. For example, a terminal box may be mounted as indicated at 150 while a manifold may be mounted on bracket 151. Valve 152 is mounted as illustrated. A limit switch cam 153 is provided together with switch actuator rod 154 and mounting plate 155 for a limit switch. All of the control devices are readily accessible through the rear of the machine and do not require operators or maintenance personnel to be exposed to the projecting moving parts of the trunnion carriage while servicing th machine.

Referring now toFIGS. 6 and 7, it will be seen that sand is automatically fet to the hopper 102 through check valve 160 mounted directly on the hopper wall as seen in greater detail in FIG. 6. The valve 160 includes a nipple 161 welded to the hopper wall and a bell coupling 162 is secured to the nipple and a sand hose adapter 163 is internally secured to the bell coupling. The entire valve is surrounded by heat insulating material seen at 164. The bell coupling forms a housing for relatively large diameter rubber ball 165. The ball is precluded from entering the hopper 102 by cross pins 166 and 167 secured transversely in the nipple 161. The valve 160 functions to permit sand to enter the hopper 102 when the latter is not pressurized and further functions to preclude sand from being blown back into the sand feed system when the hopper is pressurized. The ball will seat as indicated in FIG. 6 when the hopper is pressurized.

Sand is fed from reservoir 170 seen in FIG. 7 dropping through Y-

connectors

171 and 172, the latter being provided with air nozzle 173. Air from the plant source may be reduced in pressure by pressure regulator 174 to approximately 30 to 40 p.s.i. and the operator by actuating valve 175 introduces air to the nozzle 173 through check valve 176. When the valve 160 is open, the sand will be blown into the hopper 102.

The hopper is also, of course, provided with the pilot operated blow and exhaust valves seen at 178 and 179, respectively, the latter including a sand filter 180.

OPERATION I With the door 64 closed, the clamp cylinder 95 is actuated to assemble the box halves 83 and 85 to form the core or mold box. With the machine in the FIG. 1 position, the hopper cylinder 109 is actuated clamping the hopper against the box halves establishing sealed communication between the hopper and the box halves. The gear motor 30 is now actuated to invest or invert the trunnion carriage 50 swinging the hopper to the position seen at 183 in phantom lines in FIG. 3. At this point, the blow valve 178 may be actuated blowing the sand from the hopper into the cavity 98. This ensures sand contact with the entire cavity wall. The hopper may now be exhausted. The gear motor 30 is again actuated to bring the trunnion carriage back to the position shown in FIG. 1 and excess sand will then drop from the cavity 98 back into the hopper 102. To ensure that all of the excess sand has returned to the hopper, the machine may rock from side-to-side through approximately 45 from vertical as seen by the phantom line position 184 in FIG. 3.-The sand-resin mix contacting the hot cavity wall will cure the resin forming a shell mold or core. That portion of the sand-resin mix which is not cured will then drop back into the'hopper for reuse in the production of the next mold or core. As seen in FIG. 2, the emergency stop block 146 will move to the phantom line position 185 when the trunnion carriage isinverted and during the 45 rocking action will move on one side to the phantom line position 186.

After the excess sand is back in the hopper 102, the pistoncylinder assembly 109 returns the hopper to its down or unclamped position and the clamp cylinder 95 may now be retracted leaving the core or mold in the box half 83. Suitable vibrators or strippers may be provided on the frame 87. The door 64 is now unlocked by actuation of the piston-cylinder assembly and as soon as the long and short lock pins have cleared the door, the piston-cylinder assembly 73 will open the door through the enclosed rack and gear mechanism providing constant torque. The finished sand article will then be swung with the door to be exposed at the front of the machine and the operator may then remove the article again with the assistance of a stripping or ejector mechanism as well as a vibrator if desired. The box pattern surfaces may then be blown off and the cycle repeated with the operator refilling the hopper at any time when it is clamped and vented by actuation of the valve 175.

It can now be seen that there is provided an improved foundry shell mold or core machine having improved serviceability, maintenance and safety.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a roll-over shell molding machine, a rotatable carriage supporting separable tooling platens on horizontally extending tie rods, one separable platen being hingedly mounted to said carriage, and means extending through said tie rods operative to unlock and swing said hingedly mounted platen.

2. A machine as set forth in claim 1, further including a base having an upstanding portion, the carriage at one end being journalled in said upstanding portion for rotation about a horizontal axis, said carriage projecting from said upstanding portion of said base in cantilever fashion.

3. A foundry machine for making shell molds or cores comprising a carriage journalled in and cantilevered from an upstanding base for rotation about a horizontal axis, tooling platens mounted on said carriage for relative movement, a sand hopper adapted to be clamped against the tooling on said platen, and a sand feed mechanism for said hopper including both a rubber ball check valve mounted on said hopper and means to blow sand past said check valve when said hopper is vented.

4. A machine as set forth in claim 2 wherein one of said tie rods includes a longitudinally movable shaft therein with a rock on one end, a pinion engaging said rack on the hinge of said plate, and a piston-cylinder assembly connected to the opposite end of said shaft for swinging said hingedly mounted plate with uniform torque.

5. A machine asset forth in claim 2 wherein one of said tie rods includes a rotatably mounted actuating shaft extending therethrough operative to unlock said hingedly mounted plate for swinging movement.

6. A machine as set forth in claim 5 including spring loaded locking pins linearly movable by rotation of said operating shaft.

7. A machine as set forth in claim 6 including a piston-cylinder assembly at the proximal end-of said tie rod operative to rotate said operating shaft thus to lock and unlock said hingedly mounted plate.

8. A machine as set forth in claim 2 wherein said carriage includes a sand hopper, and means operative to clamp said hopper to such mold box halves.

9. A machine as set forth in claim 8 including chain drive means operative to invert said carriage.

10. A machine as set forth in claim 1 wherein said base is in the shape of an L and includes a horizontally extending bottom portion and an upstanding portion, said carriage projecting from said parallel to said bottom portion.

11. A foundry machine for making shell molds or cores and the like comprising a carriage, tooling platensmounted on said carriage for relative movement, a base having an upstanding portion, a bearing in said upstanding portion in which one end only of said carriage is joumalled for rotation about a horizontal axis, said carriage projecting in cantilever fashion from said upstanding portion of said base, and a sand hopper I mounted on said cantilevered portion of said carriage.

upstanding portion 7 means to pressurize said hopper to facilitate the blowing of sand into such tooling. v

13. A machine as set forth in claim 12 including a sand feed machine for said hopper including a rubber ball check valve mounted on said hopper, and means to blow sand into said hopper past said check valve when said hopper is vented. I v

14. A machine as set forth in claim 1 1 wherein one of said platens is mounted on a swinging door'at the distal end of said carriage, and means at the proximal end of said carriage operative to unlock said door and open and close said door.

15. A machine as set forth in claim 14 wherein said carriage includes a plurality of horizontally extending tie rods, said last mentioned means extending through at least some of said tie rods to unlock and actuate said door. I

16. A'machine as set forth inv claim 11 including a motor and chain drive operative to rotate said carriage about its horizontal axis.

17. A machine as set forth in claim 11 wherein said tooling platens each include a mounting plate and a gas manifold plate, said mounting plate being provided with a plurality of gas passages interconnecting the gas manifold passages on one side of said mounting plate,

cores and the like comprising a carriage, tooling platens mounted on said carriage for relative movement, one of said platens being mounted on a swinging door at the distal end of said carriage, a base having an upstanding portion, a bearing in said upstanding portion in which one end only of said carriage is joumalled for rotation about a horizontal axis, said carriage pro- 3 5 jecting in cantilever fashion from said upstanding por- 12. A machine as set forth in claim 11 wherein said tion of said base and actuation means located at the proximal end of said carriage and linked to said door

Claims

5. A machine as set forth in claim 2 wherein one of said tie rods includes a rotatably mounted actuating shaft extending therethrough operative to unlock said hingedly mounted plate for swinging movement.

7. A machine as set forth in claim 6 including a piston-cylinder assembly at the proximal end of said tie rod operative to rotate said operating shaft thus to lock and unlock said hingedly mounted plate.

10. A machine as set forth in claim 1 wherein said base is in the shape of an L and includes a horizontally extending bottom portion and an upstanding portion, said carriage projecting from said upstanding portion parallel to said bottom portion.

11. A foundry machine for making shell molds or cores and the like comprising a carriage, tooling platens mounted on said carriage for relative movement, a base having an upstanding portion, a bearing in said upstanding portion in which one end only of said carriage is journalled for rotation about a horizontal axis, said carriage projecting in cantilever fashion from said upstanding portion of said base, and a sand hopper mounted on said cantilevered portion of said carriage.

12. A machine as set forth in claim 11 wherein said carriage includes a sand hopper, means to clamp said hopper against the tooling mounted on said platen, and means to pressurize said hopper to facilitate the blowing of sand into such tooling.

13. A machine as set forth in claim 12 including a sand feed machine for said hopper including a rubber ball check valve mounted on said hopper, and means to blow sand into said hopper past said check valve when said hopper is vented.

14. A machine as set forth in claim 11 wherein one of said platens is mounted on a swinging door at the distal end of said carriage, and means at the proximal end of said carriage operative to unlock said door and open and close said door.

15. A machine as set forth in claim 14 wherein said carriage includes a plurality of horizontally extending tie rods, said last mentioned means extending through at least some of said tie rods to unlock and actUate said door.

16. A machine as set forth in claim 11 including a motor and chain drive operative to rotate said carriage about its horizontal axis.

17. A machine as set forth in claim 11 wherein said tooling platens each include a mounting plate and a gas manifold plate, said mounting plate being provided with a plurality of gas passages interconnecting the gas manifold passages on one side of said mounting plate with burner tips on the opposite side.

18. A foundry machine for making shell molds or cores and the like comprising a carriage, tooling platens mounted on said carriage for relative movement, one of said platens being mounted on a swinging door at the distal end of said carriage, a base having an upstanding portion, a bearing in said upstanding portion in which one end only of said carriage is journalled for rotation about a horizontal axis, said carriage projecting in cantilever fashion from said upstanding portion of said base and actuation means located at the proximal end of said carriage and linked to said door for locking and unlocking said door and for opening and closing the same.