Presses – Concurrent pressing and conveying – Roll type
Patent
1987-02-12
1988-09-13
Falik, Andrew M.
Presses
Concurrent pressing and conveying
Roll type
100 47, 100 53, 100117, 100170, 137 87, 137115, 137117, B30B 1516
Patent
active
047700947
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a control valve for regulating a pressure ratio between the pressures p.sub.1 and p.sub.2 in two separate pressure systems.
Control valves of the type referred to herein are known from DIN Standard Sheet 24300 dated March 1966, Sheet 3. Page 7, No. 3.2. which describes what is entitled a proportioning pressure relief valve. The control valve serves to maintain a particular pressure ratio value b between two pressures p.sub.1 and p.sub.2.
Separate pressure systems whose pressures are interdependent are found, e.g. in roll presses of paper machines, especially in wet presses (which extract water from the paper web) and/or in smoothers (which smooth the paper web). In these types of roll presses, at least one of the rolls can be a deflection adjusting roll, e.g. what is known as a floating roll. In such cases, there is a problem in regulating and obtaining desired pressures in two separate pressure systems. One pressure system relates to the effective pressure acting on the pistons of the outer hydraulic cylinder pressing the one roll against the other roll. The other pressure concerns the internal pressure in at least one pressure chamber located in the adjustable deflection roll between the rotating roll shell and the stationary "yoke" passing through the shell. Another possible configuration may involve two counteracting internal pressures of two deflection adjusting rolls whose roll shells are pressed together.
In these types of roll presses comprising two separate pressure systems, the problem is to maintain the ratio between the two pressures p.sub.1 and p.sub.2 constant with a high degree of certainty. In particular, in the event of a defect, for example the sudden failure in the supply of control air, a hydraulic pump failure or a line break, the desired ratio between the two pressures p.sub.1 and p.sub.2 must be restored with the minimum possible time delay. In other words, should one of the two pressures change during a dynamic process, the other pressure should also change immediately to maintain the desired ratio at all times. If this is not attained, there is risk of damaging to the rolls or the felt which runs through the roll press together with a paper web. Or the damage may be to the treated paper web itself. Damage of this nature has frequently occurred in the past because it was not possible to maintain the desired pressure ratio with sufficient accuracy in the dynamic operating conditions of the roll press.
Conventional systems use electrically or pneumatically piloted hydraulic valves to produce a reference pressure in the hydraulic pressure chambers. Even if the regulating valves were to operate without delay in response to dynamic changes in the operating conditions, i.e. to increase or decreases in operating pressures, near instantaneous change in the pressures in the various pressure chambers can not be expected because the machine parts are subjected to elastic deformation and specific quantities of oil need to be pumped through the regulating valves before the deformations are produced. For design reasons, it is impossible to always ensure the same time constants for filling or evacuating the hydraulic working volumes resulting from a deformation in both hydraulic systems during loading and relief operations in this type of conventional control model.
This is evident from examining the hydraulic deflection adjusting roll depicted in FIG. 1 of the German laid-open patent application OS No. 33 28 779, taking standard dimensions as a basis. In the event of a pressure change, e.g. by pressing the two rolls together and increasing the pressure from zero to maximum pressure, on the one hand, the side frames not depicted in the Figure are deformed by 2 mm; on the other hand, the yoke 11 of the roll deflects by 30 mm at its center. The pump for the outer hydraulics producing the pressure in the pressure chambers 32 and 33 of the outer contact pressure hydraulics has a flow volume of 40 liters/min. The pistons have 300 mm diameter
REFERENCES:
patent: 4106405 (1978-08-01), Biondetti et al.
patent: 4303091 (1981-12-01), Hertell et al.
patent: 4355655 (1982-10-01), Hertell et al.
patent: 4530371 (1985-07-01), Arav
patent: 4583567 (1986-04-01), Arav
patent: 4597326 (1986-07-01), Tapani
Falik Andrew M.
J. M. Voith GmbH
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