Hydraulic platen press

Details Hydraulic platen press Hydraulic platen press

1999-10-18

2001-07-03

Vo, Peter (Department: 3721)

Presses

Reciprocating press construction

Fluid pressure actuation

C100S269140, C100S269080, C100S269100, C072S453060, C072S453080

Reexamination Certificate

active

06253672

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a platen press. More particularly this invention concerns a hydraulically powered multistage platen press.
BACKGROUND OF THE INVENTION
In the production of plywood, chipboard, paneling, and the like a press is used having a pair of main outer platens between which can be sandwiched a plurality of panel workpieces alternating with intermediate platens. A plurality of heavy-duty hydraulic cylinders press one of the outer platens toward the other while the workpieces and intermediate platens are heated to compress and cure the workpieces.
U.S. Pat. No. 5,634,398 describe such a platen press with the actuating cylinders provided underneath the lower platen, the upper platen being fixed. Such an arrangement eliminates the need for double-acting cylinders since the weight of the press can serve to open it. Here there are separate low- and intermediate-pressure accumulators connected in a complex arrangement to different groups of the actuating cylinders.
The main problem with this arrangement is that it is very complex. Furthermore considerable of the nitrogen used as the head above the fluid in the accumulators is lost, in particular from the low-pressure accumulator as gas dissolved in the fluid devolves out as the pressure drops.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved platen press.
Another object is the provision of such an improved platen press which overcomes the above-given disadvantages, that is which is of relatively simple construction and that does not waste hydrogen from the accumulators.
SUMMARY OF THE INVENTION
A press has according to the invention a fixed platen, a movable platen displaceable toward and away from the fixed platen, a plurality of low-pressure cylinders braced against the movable platen and pressurizable to move it toward the fixed platen, and a plurality of medium-pressure cylinders braced against the movable platen and pressurizable to move it toward the fixed platen. A low-pressure accumulator holding a body of hydraulic fluid and a head of nitrogen and a medium-pressure accumulator holding a body of hydraulic fluid and a head of nitrogen are connected via respective conduits with the low- and medium-pressure cylinders. According to the invention a nitrogen supply connects the accumulators above the respective fluid bodies together in a closed system. A controller feeds the fluid therefrom to the respective cylinders. More particularly, the nitrogen supply includes a shunt conduit extending between upper regions of the accumulators and a pump or compressor in the shunt conduit for displacing nitrogen from the low-pressure accumulator to the high-pressure accumulator.
Thus with this system there is no loss of nitrogen at all. The nitrogen that is dissolved in the hydraulic fluid and that devolves out of it when the pressure on the fluid is reduces is recycled back to the accumulator under higher pressure. It is therefore possible to reduce the size of the intermediate-pressure accumulator since the press is not closed only by a first group of cylinders connected with this intermediate-pressure source. The low-pressure cylinders bear continuously on the platen and can serve principally to cancel out its weight.
The medium-pressure cylinders flank the low-pressure cylinders. Thus for example two medium-pressure cylinders at the leading and trailing end of the lower platen can flank four low-pressure cylinders arranged centrally under the lower movable platen.
The control means include a valve in the medium-pressure conduit and a valve and shunt between the low- and medium-pressure conduits. Two-stage valves that open incrementally are used according to the invention.


REFERENCES:
patent: 1891121 (1932-12-01), Thoreson
patent: 2484908 (1949-10-01), Purcell
patent: 2980013 (1961-04-01), Swick et al.
patent: 3343217 (1967-09-01), Daubenberger
patent: 3526188 (1970-09-01), Carlsson
patent: 4157066 (1979-06-01), Pretty
patent: 4492154 (1985-01-01), Rupp et al.
patent: 5379628 (1995-01-01), Pahnke et al.
patent: 5634398 (1997-06-01), McGee et al.
patent: 5690025 (1997-11-01), Hawkins
patent: 5735201 (1998-04-01), Hirao et al.
patent: 5823104 (1998-10-01), Beisel et al.

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