Lubrication – Systems – With lubricant treatment means
Reexamination Certificate
2001-09-25
2002-10-29
Fenstermacher, David (Department: 3682)
Lubrication
Systems
With lubricant treatment means
C162S199000
Reexamination Certificate
active
06471006
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for use in the hydraulic roll control system of a papermaking machine or the like, in which method oil is pumped from a supply tank to points of service, wherein the oil is pumped at least at one low pressure level such as is required for the lubrication of the roll bearings and/or drive gearbox and at least at one high pressure level such as is required for pressure-loaded zones of a roll and in which pressurized system the oil being pumped is filtered and if necessary cooled and in which system the return circulation of oil from the points of service is passed back to the supply tank.
The invention further relates to a multipressure hydraulic roll control system suited for use in a papermaking machine or the like, in which system the oil is arranged to be pumped from a supply tank to the points of service at least at one low pressure level such as is required for the lubrication of the roll bearings and/or drive gearbox and at least at one high pressure level such as is required for the pressure-loaded zones of a roll and in which multipressure system the oil being pumped is filtered and if necessary cooled prior to being passed to the points of service and in which system the return circulation of oil from the points of service is arranged to be passed back to the supply tank.
A plurality of functions are today implemented in papermaking mills with the help of hydraulics. One of the most important hydraulics applications herein is the crown compensation of rolls. Furthermore, e.g., the adoption of long-nip presses in fast-running papermaking machines and the growing favor of covered rolls needing improved cooling circulation has pushed hydraulic roll control systems to dimensions corresponding to those of circulating oil lubrication systems. When implemented using conventional constructions and components, the overall costs of circulating fluid systems have increased steeper than could be anticipated from a linear extrapolation of costs on the basis of nominal pumping capacity required. Another factor urging toward larger systems is the adoption of large-scale hydraulic power supply centers serving a plurality of rolls in common. On new papermaking lines, there may be a great number of crown-compensated rolls, whereby the present convention of providing each roll with a dedicated hydraulic control center is an expensive solution for the system manufacturer and, frequently, for the end user, too. Revamping a mill with larger hydraulic systems is often hampered by the problem of finding sufficient footprint for a single hydraulic fluid supply tank. Hence, a need exists to manage with smaller supply tanks and simultaneously develop the technology and manufacture of larger systems toward higher cost efficiency.
The inception of the method and system according to the invention builds on the state of the art that is first explained by making reference to
FIG. 1
illustrating at a very schematic level the principles of a typical circulating oil lubrication system. In a system of the kind shown herein, the hydraulic oil is taken from a supply tank
50
, wherefrom it is distributed by means of a hydraulic pump
51
a
to lubricated points. The system also includes a standby pump
51
b
and check valves
52
required thereto. From the pump
51
a
, the hydraulic oil is taken advantageously via a two-way valve
53
and further via filters
54
and a cooler
55
to the lubricated points along a feed line denoted by reference numeral
56
. The system pressure is regulated with the help of a bypass flow controlled by means of a two-way valve
57
wherefrom the return flow is directed back to the supply tank
50
along a piping line
58
. The return flow of oil from the system to the supply tank
50
takes place along a return line
59
.
Another example of the state-of-the art systems is shown in
FIG. 2
illustrating a typical hydraulic system of a roll equipped with spray piping. In the conventional system shown in this diagram, an oil tank
60
is divided into two parts, whereby the tank is comprised of a return oil chamber
60
a
and a suction chamber
60
b
. The main reason for this two-compartment division is that as the supply pressure to the valve manifold of controlled-crown rolls is generally about 85 bar typical, coolers used for cooling the oil cannot be mounted directly on the supply lines, because standard-type coolers are specified for a maximum working pressure of about 25 bar. Consequently, the oil is cooled in a separate filtering/cooling circuit into which the oil is passed by a hydraulic pump
61
a
. Next to the pump
61
a
, the circulating oil is passed in a conventional manner through a filter
62
a
. A standby pump is denoted by reference numeral
61
b
and at filter connected thereto by reference numeral
62
b
, while the check valves required are denoted by reference numerals
63
. Next to these, the filtering/cooling circuit is provided with a cooler
64
after which the forward flow
66
to the spray piping is taken with the help of suitable arrangements from a manifold
65
. The manifold
65
is further connected by a line
67
to the suction chamber
60
b
of the oil tank
60
so that the oil can be supplied from the return oil chamber
60
a
to the filtering/cooling circuit and exhausted therefrom back to the suction chamber
60
b
. The oil to be passed to a high-pressure circuit
74
connected to the control valve manifold of the roll is taken from the suction chamber
60
b
via a pump
71
a
and a filter block
73
. In
FIG. 2
, a standby pump of this circuit is denoted by reference numeral
71
b
and the check valves by reference numeral
72
. Respectively, the oil supplied to the roll bearings and the drive gearbox is passed by a pump
81
a via a filter block
83
. In this circuit, a standby pump is denoted by reference numeral
81
b
and the check valves by reference numeral
82
. A return flow pipe back to the oil tank
60
is denoted by reference numeral
68
.
The return oil chamber
60
a
forms about 60% of the overall volume of the tank
60
. The volume of the return oil chamber
60
a
is effectively utilized, e.g., for separating entrained air bubbles from the oil. The suction chamber
60
b
serves only partially as the active volume of the tank
60
, whereby it makes the tank dimensions larger but also functions as an internal manifold of the tank
60
. Because roll control systems frequently need a high cooling power, the flow rate pumped through the filter
62
a
,
62
b
of the filtering/cooling circuit must be equal to the maximum flow rate of oil to be pumped through the actuators. This means that the oil returning from the roll is filtered twice before it is resupplied to the system. Such an almost double-capacity filtering arrangement imposes substantial extra costs on both the system manufacturer as well as the end user operating the system.
Improvements to the conventional system shown in
FIG. 2
have been sought, e.g., from stripping off unnecessary filtering capacity. Still adhering to the elucidation of the state of the art, said approach is depicted in
FIG. 3
illustrating a system comprising a low-pressure circuit
104
and a high-pressure circuit
114
, complemented with a cooling circuit in which oil is taken by a hydraulic pump
91
from the return oil chamber
90
a
of supply tank
90
and passed via a cooler
93
and a check valve
92
along a return flow line
94
back to the suction chamber
90
b
of the tank. This arrangement omits the filtering circulation of FIG.
2
and hence has only the cooling circuit. However, all oil being pumped to the roll is filtered immediately after pumps
101
a
,
101
b
,
111
a
and
111
b
. Of these, pumps
101
b
and
111
b
serve as standby pumps.
At large flow rates, the most advantageous technique of implementing run-time replacement of filters has constituted a parallel connection of multiple filters in which the filters can be replaced one at a time. In
FIG. 3
, the filter banks are denoted by reference numerals
103
Hulkkonen Matti
Lahtinen Juha
Salavamäki Esa
Fenstermacher David
Lathrop & Clark LLP
Metso Paper Inc.
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