GB2055684A

GB2055684A - Fluid operated press

Info

Publication number: GB2055684A
Application number: GB8025237A
Authority: GB
Original assignee: CARNFORTH CONCRETE PRODUCTS LT
Current assignee: CARNFORTH CONCRETE PRODUCTS LT
Priority date: 1979-08-02
Filing date: 1980-08-01
Publication date: 1981-03-11

Abstract

A fluid pressure-operated press comprises a lower platten D which is movable towards and away from an upper fixed crosshead X, the platten being movable by means of a main fluid pressure-operated ram arrangement C and at least one auxiliary ram arrangement A, A'. There will preferably be two auxiliary ram arrangements one on either side of the main ram arrangement, actuation of the auxiliary ram arrangements causing actuation of the main ram arrangement. The main ram arrangement will be supplied with fluid from a variable displacement pump through an entry port H, a pilot operated check and prefill valve E connecting the main ram to a tank. <IMAGE>

Description

SPECIFICATION Fluid pressure-operated presses This invention relates to fluid pressure-operated presses, and particularly but not exclusively, to hydraulically operated presses for use in the production of pressed concrete slabs and similar items.

In conventional hydraulic presses, a lower movable platten is moved towards and away from an upper fixed crosshead during the formation of concrete slabs or the like, by means of a single hydraulically operated ram.

Because only one ram is provided the time taken to bring the ram to its maximum pressure and stroke is relatively lengthy, so that the number of slabs or the like which can be produced in a unit time is limited to the number of times that the ram completes a full cycle in said unit time.

The present invention has as its object the provision of an improved form of press which will, in addition to obviating the disadvantages of known presses, improve the production rate of slabs or the like being produced, and at the same time provide other advantages.

According to the present invention there is provided a fluid pressure-operated press including a lower platten which is capable of being moved vertically relative to an upper crosshead, said platten being movable by means of a main fluid pressure-operated ram arrangement and at least one auxiliary ram arrangement, the actuation of which is adapted to cause actuation of said main ram arrangement.

Preferably, there will be two auxiliary ram arrangements, one on either side of the main ram arrangement and the main ram arrangement and the auxiliary ram arrangement will be hydraulically operated.

The main ram arrangement will be provided with a prefill valve in its entry port, the prefill valve passing hydraulic fluid into a space at the bottom of a cylinder of the main ram arrangement when the auxiliary ram arrangements commence their upward stroke and by so doing create a partial vacuum in said cylinder. The prefill valve is preferably a pilot operated type of check valve.

A variable displacement pump is preferably provided to supply hydraulic fluid to said main ram arrangement.

In order that the invention may be more readily understood, an embodiment thereof will now be described, by way of example, reference being made to the accompanying drawing, the single figure of which is a sectional elevation through a press embodying the invention.

Referring to the drawing, the press comprises an upper fixed crosshead Xwhich is carried on pairs of support columns, one such pair being indicated by reference Yand a lower platten Dwhich carries a mould box L and which is movable vertically up and down relative to the crosshead. The platten D and mould box L are movable relative to the crosshead by a main ram arrangement including a cylinder B and a piston or ram C and two auxiliary ram arrangements A and A 1 located one each side of the main ram arrangement.

The cylinder B is provided with a prefill valve Ewhich allows hydraulic fluid to enter main cylinder B through an entry port F, the cylinder B also being provided with an entry H which is fitted with a non-return valve (not shown), the entry H being for connection to a pressure line direct from a variable displacement pump, not shown. The prefill valve Eis a pilot operated type of check valve.

In operation, when the appropriate signal is given, hydraulic fluid is directed to the annulus side of the auxiliary ram arrangements A and Al so that the platten D and mould box L start to move vertically upwards towards the crosshead X. At the same time, the prefill valve E allows hydraulic fluid to enter the main cylinder Bthrough entry port F, hydraulic fluid being prevented from leaving the main cylinder by the non-return valve fitted to entry H.

It is at this stage, when the initial movement and weight of the platten D is being activated by the auxiliary ram arrangements under pressure, that sufficient oil is present in the main cylinder B for full pressure to be exerted upon the main piston of ram C through an additional volume of oil that is delivered through entry H by means of the variable displacement pump.

Because the prefill valve E, which as stated is a pilot operated type of check valve, provides a vacuum action within the main cylinder B when the main cylinder is exhausted to tank by the return pressure of the auxiliary cylinder A and A 1, hydraulic fluid is permitted to enter quickly through the prefill valve E, directly from the tank (not shown), the prefill valve opening at the same time as the auxiliary ram arrangements A and Al are beginning to raise the platten D.

After the main ram has reached its maximum pressure, a signal is passed to the auxiliary ram arrangements A and A 1, to commence their downward stroke taking with them the platten D and piston or ram C, and at the same time a signal to the prefill check valve opens the valve, so enabling oil to be forced out of the main cylinder through the prefill valve Eand discharged into the storage tank, not shown.

By utilising two auxiliary ram arrangements the speed of upward movement of the platten D towards the crosshead X is greatly increased, so that the time required to bring the main piston or ram Cto its maximum pressure and stroke is decreased.

In addition, the provision of the auxiliary ram arrangements ensures a more even distribution of the maximum pressure. The auxiliary ram arrangements serve as guides or stabilisers for the platten D during its vertical movement both towards and away from the crosshead X, the steadying action of the auxiliary ram arrangemeants A and A 1 and the smoother operation of the main ram B resulting in longer life of a main piston or ram seal G.

The provision of the auxiliary ram arrangements A and A 1 should ensure that less wear takes place in respect of the platten D, and also precludes the possibility of the platten D distorting due to overhang from the main cylinder and ram arrangmenet.

By providing the auxiliary ram arrangements A and Al, the need for a hydraulic accumulator is eliminated, and by using 10Q bar pressure through the auxiliary ram arrangements to raise the platten D and then applying 31 5 bar pressure through the entry Hto the main ram arrangement as well as the auxiliary ram arrangement A and Al so as to give maximum pressure over the entire platten means that a smaller capacity pump can be used to operate the press.

It will be appreciated that more or less than two auxiliary ram arrangements may be used, and that the principles of the invention may equally well be applied to a pneumatically operated press. In addition, the mould box may be in the form of a slide having two moulding sections so that as a section is being discharged and/or filled, the other section may be being used to form a slab.

Claims

1. A fluid pressure-operated press including a lower platten which is capable of being moved vertically relative to an upper crosshead, said platten being movable by means of a main fluid pressure-operated ram arrangement and at least one auxiliary ram arrangement, the actuation of which is adopted to cause actuation of said main ram arrangement.

2. A press according to Claim 1, wherein there are two auxiliary ram arrangements one on either side of the main ram arrangement.

3. A press according to Claim 2, wherein said main ram arrangmenet has a prefill valve in an entry port thereof, said prefill valve being adapted to pass fluid into a space at the bottom of a cylinder of said main ram arrangement when the auxiliary ram arrangements commence their upward stroke.

4. A press according to Claim 3, wherein said prefill valve is a pilot operated check valve.

5. A press according to Claim 1 or any of Claims 2 to 4, wherein said main ram arrangement and said auxiliary ram arrangmenet(s) are hydraulically operated.

6. A press according to Claim 5, wherein a variable displacement pump is provided to supply hydraulic fluid to said main ram arrangement.

7. A fluid pressure-operated press constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.