Hydraulic press assembly

A hydraulic press having an upper ram-die subassembly is lowered hydraulically toward a mold cavity at a relatively high speed while resting by gravity on lower sets of nuts attached to the lower ends of piston rods. When the upper die comes to rest on the pulverulent material in the cavity, the piston rods continue their downward movement through passageways in the ram. At a predetermined distance sensed by a sensor on a set of upper nuts located on the rods above the ram cooperating with a switch on the ram itself, the ram continues downward at a much slower speed against the material with very high pressure for an initial stroke and then is retracted for additional strokes to "de-air" the powder (optional). Finally, after de-airing, the ram-die combination effects the final forming operation on the powder in the cavity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to forming apparatus operating at high pressure and, 
especially, to hydraulic presses for compressing pulverulent materials or 
the like. 
2. Prior Art 
Presses used to compress ceramic powders into predetermined shapes have 
conventionally involved friction-driven screw rams such as shown in U.S. 
Pat. No. 1,503,619 to Zeh or 1,790,041 to Crossley. U.S. Pat. No. 
3,604,076 to Leonard Brown, et al. is a later form of this type of machine 
in which the ram-upper die combination is hydraulically raised and 
lowered. In it an independent friction-driven, screw-operated mechanism 
performs the preliminary "de-airing" step (optional) as well as exerting 
high pressure compression on the floating ram-die assembly as it rests on 
the pulverulent material. 
The hybrid mechanism of the Brown, et al patent referred to above employed 
hydraulic piston rods passed through flanged portions of the upper die 
assembly, with a set of lower nuts screwed on the rods below the die 
assembly and a set of upper nuts screwed to the ends of the rods above the 
die assembly. As the upper die entered the mold cavity, the die assembly 
rested upon and was supported by the lower set of nuts. When the upper die 
rested upon the powder solely by its weight, the flanges on the ram were 
above, not in contact with, the set of lower nuts. When the 
friction-driven pressure hammer was lowered to force the upper die 
assembly downward with high pressure against the powder, the flanges of 
the ram were forced downward again into contact with the upper surface of 
the lower nuts. Switches on the ram cooperating with switch elements on a 
side vertical member signalled the control console to energize the 
friction disc which rotated the pressure screw to produce the hammering of 
the die assembly for the de-airing or final forming operations. Normally, 
the upper set of nuts were not used in either of these operations. 
U.S. Pat. No. 3,225,410 to Boyer shows a wholly-hydraulically operated 
press wherein there is a ram from which, in a lost-motion relation, an 
upper die subassembly is suspended. That press has piston rods to which 
the ram is fixedly attached to lower the ram-upper die combination at a 
rapid speed into contact with the powder to be compressed. Then a 
hydraulically-operated hammer is made to produce repeated high pressure 
impacts downwardly on the upper die subassembly to de-air and/or produce 
the final compression of the powder to be formed. 
The prior art left something to be desired insofar as its cyclic rate was 
concerned as well as its simplicity and reliability of operation. 
It is therefore among the objects of the present invention to provide a 
hydraulic press with a considerably improved cyclic rate of operation and 
which employs a fast, simple and reliable mechanism. 
BRIEF SUMMARY OF THE INVENTION 
A press or the like has a ram assembly to which a forming member is 
attached. A predetermined number of elongated members pass through 
respective apertures in the ram and, by means of lower stop means fixed to 
their lower ends, solely support the ram during the initial part of its 
descent in a forming cycle. Upper stop means are also affixed to the rods 
above the ram. Means are provided for sensing when the downward movement 
of the ram is arrested as the forming member encounters the material to be 
formed. The sensing means produces a signal when this occurs which is 
communicated to the main power unit. The power unit thereafter 
hydraulically drives the ram downwardly at a slower rate but with much 
greater force than during the initial part of the descent.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIGS. 1-5, the hydraulic press according to the present 
invention is shown generally at the numeral 10. It has at its top a surge 
tank 12 for hydraulic fluid from which hydraulic lines 14 and 15 extend to 
a hydraulic control panel (not shown). It has a main press head 16 which 
is a single casting through which the upper ends of shafts or columns 17 
extend. This casting incorporates a cylinder for the hydraulic fluid that 
drives the piston 19 which is bolted or otherwise connected to the main 
ram 20. 
Piston rods 32 attached to pistons in jack cylinders 30 pass through 
apertures 33 and 35 in the head 16. A vertically movable main ram 20 has 
apertures 20a through which the threaded lower ends of rods 32 pass. Ram 
20 is cast integrally with bearings 21 surrounding shafts 17 and has a 
lower plate 37. Lower nuts 36 are screwed onto the lower ends of the rods 
32 and the ram rests solely by gravity on these nuts through most of its 
descent as it approaches the mold cavity 42a. 
Also attached to the main ram and depending therefrom is an upper die 
holder 22 to whose lower surface an upper die 22a is attached which is so 
dimensioned as to move snugly into the die cavity 42a formed within the 
mold box 42. The mold box 42 is maintained in position within the mold 
case 24 solely by wedge assemblies 50 indicated generally within the 
ellipse (see FIG. 6). Case 24 is also movable vertically, its bearings 24a 
engaging the columns 17. The mold case 24 is supported on rods 38 which 
pass through holes in the press bed 26 which rests on I-beams 35. The 
lower ends of rods 38 are attached to a slab 41. Piston rods 29 extending 
downwardly from cylinders 28 fixed to the underside of the bed 26 are 
constructed to raise or lower the slab 41 which, in turn, raises or lowers 
the rods 38 to which the mold case 24 is attached at their upper ends. 
There is also a stationary lower mold assembly comprising a lower mold 
support 46 which rests upon the top horizontal surface of the bed 26. At 
the upper end of the support 46 the lower die member 44 is affixed. Member 
44 has a cross-section which is substantially congruous with the 
cross-section of the mold cavity 42a so that when ceramic material 43 is 
placed in the cavity, it cannot escape downward past the lower die. 
An automatic mold cavity filler assembly 40 is located on a horizontal 
extension essentially co-planar with the top of mold case 24. It is 
attached to and operated reciprocally by a piston assembly 40a to which a 
feed box 40b is connected. Box 40b is filled with ceramic "dust" or the 
like so that, at the beginning of a cycle of operation, it can be moved by 
assembly 40a into position over the mold cavity 42a whereupon its contents 
43 are discharged therein. The hydraulically operated apparatus shown at 
60 is made to move the lower die assembly 46 and the mold box laterally 
and to bring in a new die as required. 
For the sake of safety, but not constituting part of this invention, 
several devices are employed. Shown at 23 is a bracket holding a safety 
latch, hydraulically operated, which prevents the ram assembly from 
falling should the hydraulic system develop a fluid leak, for example. A 
similar apparatus 25 prevents dropping of the mold case 24. Element 27 is 
a vertical member which engages a gear reduction unit to prevent unwanted 
vertical movement of the mold case. 
At the beginning of a cycle, the jack cylinders 30 and their associated 
piston rods 32 have been hydraulically actuated by the hydraulic console 
so as to be in their highest position (FIG. 1). The main ram assembly 20 
is also in its highest position, supported by the lifting action of the 
upper surface of lower nuts 36 attached to the ends of rods 32. Safety 
latch 23 is in its safety position. When the mold cavity has been filled 
and the automatic charger 40 is reciprocated outwardly out of the way, 
latch 23 retracts and a pre-fill valve located (but not shown) in tank 12 
opens. This allows hydraulic fluid to continue to flow into the main 
hydraulic cylinder above the piston during the descent of the ram 20. At 
the same time, the control panel mechanism actuates the jack ram cylinders 
30 to move the rods 32 downward, the ram 20 resting upon the nuts 36, at a 
fast speed such as about 600 inches per minute. 
The descent of the main ram assembly 20 continues in this fashion until the 
upper die holder 22 attached to it enters the mold cavity 42a and starts 
to bear down upon the dust 43. Its weight alone will continue to compress 
the dust 43 until the compressed dust resists further downward movement of 
the upper die. When this happens, the rods 32 will nevertheless continue 
their downward descent through the apertures 20a so that the upper 
surfaces of the lower nuts 36 become disengaged from the ram. Continued 
downward movement of the rods 32 causes the lower surfaces of the upper 
nuts 34 to approach the upper surface of the ram 20. Affixed to at least 
one of the upper nuts 34 is a disc or ring 38 of metal which therefore 
approaches the upper surface of the ram. Attached to the end of the ram in 
the vicinity of the disc 38 is a proximity detector or switch 39 that is 
set to respond to the approach of the ring to a predetermined distance 
from it (FIGS. 4 and 5). At this distance, proximity switch 39 signals the 
control panel to close the prefill valve. This shuts off flow of oil into 
the main cylinder which drives the main piston 19 so that the ram 20 can 
immediately thereafter be hydraulically impelled downwardly with 
tremendous force, albeit at a much slower rate. 
When high pressure is exerted, the speed of descent of ram 20 decreases 
first to about 50 inches per minute, achieving pressures up to 2,000 lbs. 
per square inch and then, at 20 inches per minute achieving pressures up 
to 3,800 lbs. per square inch. A preset timer in the hydraulic control 
panel, not shown, determines the period for which the dust is compressed 
at the high pressures. At the end of that period, the pressure is released 
and the stripping of the mold box from the product begins when the 
pressure is reduced to a predetermined level. This level is sensed and the 
hydraulic system is signalled to start to move the mold case 24 mold box 
42 assembly downward by moving piston rods 29 downwardly thereby moving 
rods 39 down also. When the mold case 24 begins to descend, a timer is 
energized which permits the ram 20 to rest on the pressed product for a 
predetermined period at which time the hydraulic system is signalled to 
move the jack ram piston rods 32 up at a fast speed (600 inches per 
minute) whereupon the ram-die subassembly 20, 22 is lifted out of contact 
with the pressed item 43. Meanwhile, the mold case 24 continues to descend 
until its top is approximately level with the bottom of the pressed 
product 43 whereupon the automatic means 40 moves inwardly to push the 
pressed product 43 out of the way. Thereafter, when the mold case 24 has 
again been moved up to the correct level, cavity 42a may again be filled 
at the beginning of the next cycle. 
A variation of the form of the signal producing detection system shown in 
FIGS. 4 and 5 could be easily accomplished by mounting the disc 37 on a 
lower nut 36 instead of on an upper nut. The circuitry in the control 
console (or anywhere else) would be adjusted to respond to the loss of 
proximity as the lower nut continues downwardly after downward motion of 
the ram assembly is arrested by the resistance of the ceramic dust. Of 
course, photoelectric systems or other conventional detecting systems 
could aternatively be used too to measure the slippage between the 
downward movement of the rods 32 with respect to the ram assembly. 
In some pressing operations, "de-airing" of the dust 43 is desired so that 
air is quickly removed from it to obtain maximum possible product density 
and prevent formation of any "air cracks" in the finished product. It is 
known in the art to de-air the powder by subjecting the dust 43 to a 
series of pulses of compression followed by pulses of decompression. It is 
highly desirable that this be accomplished as quickly as possible. In the 
apparatus described, de-airing is accomplished by alternately 
1. lifting the ram 20 by moving the rods 32 upwardly so that the lower nuts 
cause decompression and then 
2. moving the rods downwardly shortly thereafter so that the disc 37 
approaches switch 39 again signalling the console to actuate piston 19 to 
move ram 20 downwardly again. This time, however, the console is so 
programmed that instead of allowing the pressure to build up to 3800 psi 
as in a cycle where no de-airing occurs, it is allowed to attain only 
about 2000 psi or less. When this pressure is sensed, the pressure is 
released until it is in the vicinity of 500 psi whereupon the process is 
repeated and the pressure is allowed to build up again, and so forth, for 
a predetermined number of times. 
By providing this unique system of having the main ram decoupled from the 
main hydraulic drive during its rapid descent toward the workpiece and the 
use of the upper and lower nuts 34, 36 as explained above, it is possible 
to improve significantly the productivity of such apparatus. The use of 
the sensing ring 37 and the proximity switch 39 enables the ram assembly 
to be lowered very fast yet, when the ram rests solely under the influence 
of gravity upon the dust 43, it enables the apparatus to shift from the 
relatively low pressure phase of compression to the very high compression 
phase very rapidly. This is useful both in de-airing and non de-airing 
operation. Whereas existing ceramic presses were capable of producing 
4-41/2 cycles per minute, the present system using the floating ram, 
double nuts, and proximity sensing can increase the rate to 51/2-6 cycles 
per minute. Precentagewise, this is a very great improvement which 
increases production and efficiency considerably. 
While a disc-proximity switch assembly is shown which detects the imminence 
of the relative positions of the ram and the lowering piston rods 32, many 
other types of sensors could also serve alternatively. Photoelectric or 
contact switch systems could be acceptable substitutes. 
Mold Box Assembly 
While not part of the invention claimed herein, there is also shown a novel 
structure for positioning the mold box 42 fixedly within the mold case 24. 
Some prior art structures had a mold box comprising a fixed rear beam, a 
front beam and two intermediate transverse side beams with bolts passing 
inwardly through the front and rear beams to threaded passageways in the 
side beams. Such prior art structures has many disadvantages. In the first 
place, they were keyed to the mold case, thus requiring considerable 
machining. In the second place, the nature of their construction required 
removal of at least one of the beams to enable insertion of the lower die 
horizontally, an operation which was time consuming as it required removal 
of numerous bolts and also could be difficult and awkward. Finally, and 
most importantly, when the mold box was assembled within the mold case and 
subjected to the extremely high pressures produced by the downward 
movement of the upper ram-die assembly, the vertical pressure acting upon 
the ceramic material produced resultant intense outward pressures on the 
walls of the mold box. This caused them to be pushed outwardly and to 
bulge so that the mold box did not maintain the requisite geometric 
integrity in the mold cavity. Since it is necessary to maintain very small 
tolerances in the mold cavity, the useful life of the mold box was 
considerably shortened. So-called "fins" on the pressed product caused by 
the yielding walls of the mold box significantly reduced the press's 
productivity. If the mold's tolerances were so upset by the pressure 
strains as to be unusable, fabrication of new mold boxes entailed 
considerable additional expense. 
In accordance with this construction, there is provided a key-less wedging 
mechanism 50, indicated within the broken line oval of FIG. 1 and also 
shown in FIGS. 2, 3, 6 and 7. This mechanism locks a one piece mold box 42 
within the mold case 24 in such a way that it will withstand the 
tremendous pressures exerted by the ram 20 and the upper die 22. 
Furthermore, its construction enables the mold box to be fitted within the 
mold case 24 from below. Its simplicity enables the insertion or removal 
time of the mold box to be cut from say, a conventional 5 hour period, to 
11/2 hours. This results in higher productivity because of less down time. 
Two wedge assemblies 50a, 50b are shown in FIGS. 1, 2, 3, 6 and 7 holding a 
mold box 42. Wedge assembly 50a is positioned in the left (short) side 
wall position as shown in FIG. 1. Another one, 50b is installed in the 
front wall portion shown on the right in FIG. 2. The two wedge assemblies 
are essentially identical except that 50b is much longer so it requires a 
greater number of horizontal and vertical bolts to fix it in position. 
A downwardly and outwardly tapering wedge 57 is fastened by machine screws 
58 which pass through holes 57b into threaded apertures formed in case 24. 
These screws also pass through apertures (not shown) in a key 49 disposed 
within a horizontal channel defined by facing horizontal grooves 24a and 
57d formed in the mold case 24 and wedge 57 respectively. An upwardly 
tapering wedge 56 having vertical slots 56a is movable essentially 
vertically with respect to wedge 57 thereby changing the horizontal 
location of its untapered vertical surface. 
The two angled surfaces of wedges 56 and 57 are brought into contact with 
one another so that the hollowed-out, partially conical portions 56b in 
wedge 56 face respective hollowed-out portions 57e in wedge 57. Smaller, 
partially tubular vertical grooves 52a lead from the bottom of wedge 57 to 
portions 57e. Similar, partially-tubular, angled grooves or passageways 
52b connect portions 57e with one another. Vertical inlet grease 
passageways 56c are formed in wedge 56 having upper terminal openings in 
the inclined surfaces of wedge 56. 
Vertical bolts 51 have associated washers 48 and pass upwardly, first 
through hollowed-out portions 56b in the movable inner wedge 56, then 
through hollowed-out portions 57e in wedge 57, then through vertical 
threaded apertures 57a communicating with portions 57e and finally into 
the hole 24b in mold case 24. 
As may be seen from FIGS. 1, 2 and 6, a spacer plate or member 54 having an 
upper shoulder 54a and a projecting ledge 54c is also assembled to the 
wedge assembly 50a in this particular construction. It has counterbored 
apertures 54b drilled horizontally through which, via slots 56a, shoulder 
bolts 55 pass. Bolts 55 also pass through slots 56a and terminate with 
their threaded ends screwed into threaded apertues 57e in the fixed outer 
wedge 57. These spacer members 54 are not essential in all forms of novel 
construction, but are useful to enable a standard press to accommodate 
mold boxes of different outer dimensions. 
Shown in FIG. 3 from above are three dust-protective and/or wear plates 
53a, 53b and 53c. Plates 53b and 53c are inset onto the top of the press 
bed opposite one another. Plate 53a is placed on one short side covering 
the wedge assembly 50a and is in the path of the reciprocating dust box 
(FIG. 2, 40b) which fills the mold cavity 42a with ceramic material 43 at 
the beginning of each cycle of operation. Since ceramic dust is abrasive 
and consists of very fine particles, plate 53a is a replaceable member 
made of abrasion-resistant steel that enables the top of the mold case 24 
to be kept level with the top of the mold box 42. It also helps keep the 
dust from infiltrating downward into the spaces in wedge assembly 50a. 
Plates 53b and 53c are disposed along the long front and back sides of the 
mold case 24, the plate 53c serving only a wear-protection function. Plate 
53b is also abrasion-resistant, but serves additionally to prevent dust 
infiltration downward into wedge assembly 50b below it.