The system relating to the invention typically comprises -a first hydraulic cylinder, which is connected, on the first side of the web, to a first air dryer box or the like, for lifting and/or lowering the same, and -a second hydraulic cylinder, which is connected, on the second side of the web, to a second air dryer box or the like, for lowering and/or lifting the same in a direction opposite to the movement of the first air dryer box.

It is known to use hydraulic or pneumatic lifting cylinders in paper web coaters or the like for lifting and/or lowering devices, such as air dryer boxes or hoods, on either side of the web. The lifting cylinders are used for opening the devices, for example, for the duration of maintenance or in connection with start-up, in order to pass the end of the web through the device.

The published international application WO 96/12150 discloses a previously known method for lifting a box fitted above the web by means of hydraulic cylinders. In this case, the hydraulic cylinders are fixed to the ends of the boxes.

As the size, and thus the weight, of the boxes increases, it has even been necessary to use two pneumatic cylinders or hydraulic cylinder systems with machine aggregates. A hydraulic system with a machine aggregate increases the cost of the system.

Generally, it is preferred to use pneumatics rather than hydraulics in lifting. It is in fact possible to use pneumatic lifting cylinders for lifting small dryers. Modern air dryer boxes are, however, so heavy that the pneumatic cylinders required to lift them would be far too large and take up far too much space, having a diameter of e. g. 320 mm. Lifting one pair of boxes usually requires four of these large cylinders, which obviously takes up a lot of space and incurs further costs.

The aim of the present invention is to achieve a new, improved system for lifting and/or lowering pairs of air dryer boxes or the like.

The aim is especially to achieve a system by means of which the actual lifting can be carried out using less force than at present.

To achieve the above aims, the system relating to the invention is characterised by what is disclosed in the characterising part of the first claim presented below.

A typical system relating to the invention for lifting and lowering air dryer boxes or the like in a coater or paper machine comprises a first and second hydraulic cylinder connected to the same closed hydraulic system, one of the cylinders being connected to a first air dryer box above the paper web for lifting the said box, and the other being connected to an air dryer box below the web, for the simultaneous lowering of this box, in order to open the space between the boxes in conjunction with the start-up of the machine, maintenance or corresponding service measure.

In this typical solution the hydraulic oil of the hydraulic cylinders, that is, the medium used in the system, is arranged to flow from the second cylinder, that is the cylinder connected to the lower box, to the first cylinder, that is the cylinder connected to the upper box, when the first, or upper, air dryer box is lifted.

In a solution relating to the invention, the lifting and simultaneous lowering of the air dryer boxes thus takes place by means of interconnected hydraulic cylinders in which the oil passes from one cylinder to the other when one air dryer box is being

lifted and the other lowered. The hydraulic system is dimensioned so that the hydraulic cylinders keep the air dryer boxes in a labile state of equilibrium. The cylinder diameters, that is, the size of the hydraulic cylinders, and the angles of elevation of the boxes are selected so that the boxes will remain as balance as possible at all stages of the lifting. In this way, the air dryer boxes can be lifted or lowered in a controlled manner using very little force, because the cylinder does not actually have to lift, but merely overcome a slight friction factor and bring about the initial acceleration of the movement. The lifting can, therefore, be arranged to take place, e. g. by means of a relatively small pneumatic lifting cylinder, or even manually, if the dryer is light. The pneumatic lifting cylinder can be controlled in a conventional manner known as such.

The invention is described in the following with reference to the appended drawings in which Figure 1 shows diagrammatically a cross-section of a drying section provided with the system relating to the invention, when the air dryer boxes are in the running position; Figure 2 shows a cross-section corresponding to Figure 1, when the boxes of the machine are in the open position for the purpose of maintenance or the like; Figure 3 shows a second solution relating to the invention, as shown in Figure 1, and Figure 4 shows the solution relating to Figure 3 as shown in Figure 2.

Figures 1 and 2 show a cross-section of the drying section 10 of a paper machine or coater, in cross direction to the web 12. Above the web 12 is fitted a first air dryer box 14, such as an airborne web dryer, and below the web another, preferably similar air dryer box 16.

The air dryer boxes 14,16 are arranged to pivot around the supporting points 18,20. In Figure 1, the hydraulic cylinders 22,24 support the boxes so that the sides 26,28 of the boxes which face towards the web 12, are parallel with the plane of the web.

The fluid reservoirs 30,32 of the hydraulic cylinders are interconnected by means of a hose 34, through which oil is able to flow from the fluid reservoir of one hydraulic cylinder to the fluid reservoir of the other hydraulic cylinder. The hose 34 is fitted with a valve 36, by means of which the flow of oil can be regulated in order to control the opening or closing speed of the boxes. The hydraulic cylinders are supported at one end on the frame of the machine, or other support structure not shown in greater detail, by support means 38,40, in such a way as to be partly pivotable around these support means. The piston rods 42,44 of the hydraulic cylinders 22,24 are connected to lugs 46,48 protruding outwards from the boxes 14,16 on the tender side of the machine.

In the solution relating to the invention, the hydraulic cylinders are thus supported on a fixed structure of the machine. This makes it possible to use small hydraulic cylinders with a working pressure exceeding 100 bar, even 250 bar, in the solution relating to the invention.

Fitted adjacent to the upper hydraulic cylinder 22 is the lifting cylinder 50 which brings about the actual lifting or lowering movement, the said lifting cylinder being fixed at one end, in such a way as to be pivotable, to support means 52, which is fixed to the frame of the machine or other structure. In the case shown in the figure, the piston rod 54 of the lifting cylinder 50 is connected to the same lug 46 as the piston 42 of the hydraulic cylinder 22 of the upper box 14.

In the solution relating to the invention, considerably less force is required to effect lifting than in previous solutions, which means that much smaller pneumatic cylinders can also be used for lifting than before. A typical cylinder 50 diameter is approximately 50-100 mm.

When the arm 54 of the lifting cylinder 50 pushes, that is, lifts the upper box 14 upwards into the open position, the lug 46 pulls the piston of the hydraulic cylinder of the upper box upwards, which causes oil to flow in the hose 34 towards the container, that is, fluid reservoir 30 of this cylinder. At the same time, oil begins to flow from the container, that is, fluid reservoir 32 of the cylinder 24 of the lower

box 16 to the hose 34. As oil flows from the cylinder of the lower box towards the cylinder of the upper box, the piston rod 44 of the lower box cylinder 24 begins by the weight of the lower box to move inwards, thus enabling the lowering, that is, opening of the lower box 16, as shown in Figure 2. The boxes pivot on the supporting points 18,20 on the other, driving side of the machine.

When the upper box 14 has reached its uppermost position, the container, or fluid reservoir 30, of the hydraulic cylinder 22 has in the main filled up with oil, which means that this cylinder will keep the box in the opened position. At the same time, the lower box 16 will have reached its lowest position so that the cylinder 24 piston 44 has moved more or less completely inside the cylinder, and the container, or fluid reservoir 32, has emptied of oil. In this way, the boxes are mainly in balance even when in the open position, and do not attempt to return to the closed position by themselves.

In the open position, the weight of the lower box 16 keeps the cylinder 24 piston 44 pushed inside, not allowing oil to flow freely into its container 32. On the other hand, the container 30 of the hydraulic cylinder 22 of the upper box 14 has filled with oil, which means that the cylinder tends to keep the upper box lifted, that is, in the open position. Cylinders 22 and 24 balance the boxes hydraulically to keep them in their positions at any given time.

The upper box can, however, be lowered by means of the small force produced by the pneumatic cylinder 50, in which case oil begins to flow in a different direction in the hose 34, that is, from the upper cylinder 22 to the lower one 24, and the boxes will close, that is, move towards the web into the position shown in Figure 1.

In the solution shown in the figures, the pneumatic cylinder 50 is thus double- acting, causing the boxes to open and close.

Conventional hose failure valves can be fitted to the system to increase safety. On the other hand, the system can also be fitted with microswitches, which will give an alarm when they identify abnormal movement of the boxes due to leakage.

In the embodiment shown in Figures 1 and 2, the tender side of the upper air dryer box, the airborne web drying box, and the same side, that is tender side, of the lower air dryer box, are connected so as to function together, that is, so that one is lifted and the other lowered.

In Figures 3 and 4 on the other hand, the tender side of the upper air dryer box and the driving side of the lower air dryer box are connected to function together, which means that when the upper box is lifted on the tender side, the lower box is lowered on the driving side. Otherwise the hydraulic systems of the boxes correspond to the system shown in Figures 1 and 2.

A pump may be arranged in conjunction with the hose 34 of the hydraulic system, by means of which the hose/pipes can be filled with oil and by means of which oil leakages can be compensated. A valve may preferably also be connected to the system, by means of which excess fluid formed in the system, e. g. due to thermal expansion, can be discharged into a reserve container.

By means of the system relating to the invention the following advantages, among others, are achieved compared to the prior art: -increased safety in the vicinity of the machine, when the boxes or the like are in balance and can be lifted in a controlled manner; -smaller size of the actual lifting cylinder, and the possibility of using a pneumatic cylinder; -the speed of the lifting stage can be controlled by means of a valve arranged in the hose between the cylinders; -the hydraulic cylinder components may be simpler and more economical than pneumatic lifting cylinders.

The system relating to the invention can be applied in both paper machines and other machines connected on-line or off-line to paper machines. The system is well-suited for use in various finishing machines or conversion machines, such as coaters, calenders, laminating machines, impregnating machines or even printing machines. The system is particularly well-suited for use in paper web handling

machines, but can also be applied to machines handling paperboard, plastic, mental or textile webs.

The invention is not intended to be limited to the solution described by way of examples in the foregoing, but on the contrary, the aim is to be able to apply the invention widely within the scope of the inventive idea specified in the claims presented below. Thus there may be two pairs of hydraulic cylinders per pair of boxes, one on the tender side and the other on the driving side, in which case the pair of boxes can be arranged to open on both sides.