GB2109480A - Reducing friction between relatively rotatable members - Google Patents

Abstract

The invention is concerned with a method of sealing against the ingress or egress of fluid across the end of a roller. The roller 256, 258 or 260 has a stub axle 20 received in an open- ended slot 12, 14 or 16 in a stationary wall 10 of the apparatus, a lubricating port 26, 28 or 30 is provided in the wall facing an end face of the roller and there is means for supplying a lubricant under pressure into the port, the relationship between the impedance between the end face of the roller and the wall on the one hand, and the pressure of the lubricant supply on the other hand, being such that the lubricant is able to flow radially outwards over the end face of the roller. In the preferred arrangement the port is kidney shaped and substantially concentric with the roller axis. In fact, the port may subtend a considerable part of a circle providing that its ends do not break out into the slot. The invention is particularly applicable to nip rollers used in drying apparatus for fabric or paper. <IMAGE>

Description

SPECIFICATION Reducing friction between relatively rotatable members This invention, in its primary aspect, is concerned with a roller arrangement used for feeding material in continuous form (e.g. fabric or paper) into or out of a pressure chamber. A typical example of a roller arrangement to which the invention may be applied occurs in a drying chamber, through which the material to be dried is passed continuously. In some arrangements, the interior of the chamber may be at or above atmospheric pressure, but in others, the internal pressure is below atmospheric pressure, the vacuum being used to cause moisture in the material being dried, to evaporate. In either case, it is usual to pass the material to be dried into the chamber through the nip of a pair of feed rollers, and to draw the material out of the chamber through a similar pair of feed rollers.

Wherever material passes into or out of a chamber through a pair of nip rollers, and there is a pressure differential across the rollers (i.e. one side is at a higher pressure than the other) it is necessary to attempt to create a seal between the rollers and the walls of the chamber. Some success has been achieved in this direction by makiny the nip rollers somewhat resilient; by using additional rollers engaging with the nip rollers to absorb the reaction to forces tending to separate the nip rollers and by providing flexible sealing strips engaging on the periphery of the nip rollers or the additional rollers. There remains however the problem of sealing the interface between the ends of each roller and the stationary walls of the chamber at the ends of the roller.

Generally, the roller is made to rub at its ends on the inside of the wall. This produces a reasonably effective seal, but the rubbing raises the temperature of the roller and the wall, and can lead to seizing-up. Besides, if the nip rollers are made of resilient material (e.g. rubber) they sometimes deflect (especially if the pressure differential across the nip rollers is substantial) and this causes one part of each end of a roller to dig into the wall, this being another cause of seizing-up of the roller.

The present invention aims at providing an effective seal at a roller end/wall interface, whilst at the same time cooling the interface and thereby reducing the danger of the roller seizing-up.

Another problem arises, because it is important to be able to fit and remove a roller without dismantling a considerable part of the apparatus.

This is usually achieved by providing stub axles one at each end of the roller and forming an openended slot in the stationary wall at each end of the roller, so that each stub axle can be fitted by sliding it along its associated slot, to sit in what is effectively a cup bearing formed at the bottom of each slot. Means are provided for holding each stub axle at the inner end of its slot, but these means are not relevant to the present invention.

An attempt has been made to lubricate the interface between the end of such a roller and the adjacent wall, by providing an annular groove in the end of the roller and supplying fluid into this groove; but this is ineffective, because part of the groove is always in communication with the slot, and therefore the lubricating fluid simply follows the path of least resistance and flows out through the slot without lubricating the interface.

According to a first aspect of the invention in an arrangement wherein a roller has a stub axle which is received in an open-ended slot in a stationary wall, and the end face of the roller is in close proximity to the wall, a lubricating port is provided in the part of the wall which faces the end face of the roller, there being means for supplying a lubricant under pressure into the port, and the relationship between the impedance between the end face of the roller and the wall on the one hand, and the pressure of the lubricant supply on the other hand, is such that the lubricant is able to flow radially outwards over the end face of the roller. Preferably the port is sealed from the slot.

In the preferred arrangement, the port is kidney-shaped. It is further preferred that the port is arcuate and substantially concentric with the roller axis. The port may subtend a considerable part of a circle providing that its ends do not break out into the slot.

According to a preferred feature of this aspect of the invention, the part of the wall adjacent to the end face of the roller is cushioned so that it can tilt slightly, to permit small changes in the orientation of the roller end face as would occur on deflection of the roller. In a preferred arrangement, a sheet of rubber or like compressible and resilient material is sandwiched between the wall proper and a wearing surface sheet which actually faces or engages with the end face of the roller. The wearing sheet may be a sheet of polytetrafluoroethylene (P.T.F.E.).

The invention also embraces a method of reducing friction at the interface of two members which have relative rotation, such as the interface between the end face of a roller and an.adjoining stationary wall.

According to a second aspect of the invention, a method of reducing friction at the interface of two members, which have relative rotation, and where the proximity of the two members is such as to provide a substantial impedance to fluid flow between them, comprises the steps of: supplying a gas containing atomised water into the interface; causing the gas to flow radially out of the interface into an atmosphere at a reduced pressure such that the water evaporates, whereby at least some of the latent heat of evaporation is removed from one or both of the members at their interface.

Preferably the gas is air. It is further preferred that the two members are pressed together at the interface whereby the friction between them would cause the temperature of the rubbing parts to approach or even exceed 1 0000 in the absence of the lubricating and cooling effect of the gas (air) and water carried by the gas.

One construction of a feed roller arrangement for a fabric drying apparatus, will now be described by way of example only, with reference to the accompanying drawings. A method of using this apparatus will also be described in accordance with the second aspect of the invention. In the drawing:- Figure 1 is a diagrammatic end view of a roller arrangement at the inlet to a vacuum drying chamber, Figure 2 is an end view of a wall adjacent to the inlet, looking outwards, Figure 3 is an exploded perspective view of the end wall and associated rollers, and Figure 4 is a detail view showing a port arrangement.

In this example, the invention in both its aspects, is applied to a fabric drying apparatus, which includes a drying chamber, which is maintained at a pressure lower than atmospheric pressure, so that drying of the material proceeds by evaporation of the moisture in the material whilst the material is passing through the drying chamber. Apparatus of this kind, is described for example in the specification of United Kingdom Patent Application No.8123999 (BRADSHAW).

Referring now to Figure 1, the fabric which is to be dried is indicated at 250, and part of the drying chamber wall is shown at 252. There is a relatively large opening 254 in the wall of the drying chamber, and two pairs of rollers are provided. An inner pair of rollers 256 and 258 has a nip through which the material to be dried is passed, and these nip rollers 256 and 258 are made of rubber or other deformable and resilient material. At each end, the rollers 256 and 258 are provided with metal end caps 257 and 259 (see Figure 3). The direction of travel from the outside to the inside of the drying chamber is indicated by the arrow in Figure 1. The other pair of rollers 260 and 262 are hard surfaced rollers of somewhat larger diameter than the nip rollers 256 and 258, and these rollers 260 and 262 are mounted in stationary journal bearings.Moreover, the arrangement of the rollers is such, that an imaginary line passing through the axes of the rollers 256 and 260 is inclined at approximately 45 to the horizontal path of the material 250, and likewise the imaginary line passing through the axes of the rollers 258 and 262 is inclined at approximately 45 to the path of the material 250.

The action of the differential pressure between the inside and the outside of the drying chamber is to press the nip rollers 256 and 258 into the gap between the outer rollers 260 and 262, and this presses the rollers 256 and 258 hard on to the outer rollers 260 and 262, deforming them slightly, and at the same time, causes the nip rollers to grip tightly on to the material 250. As a result, although the rollers are still rotatable and allow the material 250 to travel into the drying chamber, they also form an effective seal preventing egress of vapour or gas from the inside of the drying chamber.

A self-lubricating sealing pad 264 presses onto each of the outer rollers 260 and 262, and it is itself connected to the wall 252 of the drying chamber by a flexible sealing member 266.

It will be appreciated, that the seal shown in Figure 1 is duplicated at the material exit from the drying chamber, that is to say the nip rollers are on the inside of the outer rollers 260 and 262.

Although the arrangement illustrated in Figure 1 provides a method of sealing the rollers at the entrance and exit of the drying chamber, along the length of those rollers, there is still the problem of possible leakage of air into the drying chamber at the ends of the rollers. An I arrangement has been devised therefore, for sealing the ends of the rollers, and this is illustrated in Figures 2, 3 and 4.

Part of the drying chamber wall adjacent to the large opening 254, is illustrated at 10 in Figure 3.

This is a substantial metal wall, which is secured to the remainder of the chamber, in a rigid manner, for example by welding, and will be hereinafter referred to as the "wall proper". A series of four open-ended slots 12, 14, 1 6 and 18 is formed in the wall proper 10, and each of the rollers 256, 258, 260 and 262 is formed with a stub axle 20 at each end, each stub axle 20 being able to slide along the length of a corresponding open-ended slot, 1 2, 14, 1 6 or 18. The inner ends of the slots are so located, that when the stub axles 20 are located at the inner ends of their respective slots, the rollers 256, 258, 260 and 262 are in the correct working position illustrated in Figures 1 and 2.Means are provided for locking the stub axles 20 in the working position, but these means need not be described in detail here, because they do not form part of the present invention. Suffice it to say, that each of the rollers can be readily fitted into the apparatus, or removed therefrom, by sliding its stub axles along the open-ended slots appertaining to that roller.

As has already been mentioned, although this provides a simple and effective method of assembly and replacement of the rollers, it does present problems, when attempting to lubricate the end faces of the rollers.

A thin rubber cushion sheet 22 of the same shape as the wall proper 1 0, fits against the inside face of the wall proper, and a thin wearing sheet 24 also of the same shape as the wall proper 10, and made of P.T.F.E., is fitted against the inside face of the rubber cushion sheet 22. The rubber sheet 22, is bonded to both the wall proper, and the wear sheet 24. This arrangement provides an anti-friction surface on the inside of the wall proper, and at the same time, ailows that surface to flex slightly, due to the deformability and resilience of the rubber sheet 22.

The length of each of the rollers 256, 258, 260 and 262, is such that the end faces of those rollers press against the respective wear sheets 24 on the insides of the walls. Moreover, the engagement of the end faces on the wear pieces, is such that if the apparatus were operated, without any lubrication, the friction between the end faces of-the rollers and the wear piece, would be sufficient to generate heat which would raise the temperature of the ends of the rollers, and the temperature of the wear sheet 24, to upwards of or even possibly above 100 C. The fact that the end faces of the rollers press on to the wear sheets, creates an effective seal at each end of each roller, and this seal offers a substantial impedance to the ingress of air into the drying chamber. This of course is desirable.On the other hand, the heat generated by the friction between the end faces and the wear sheet 24 is undesirable, and unless some lubrication method were employed, would almost certainly lead to seizing-up of the rollers. It will be appreciated, that there is something of a dilemma here, between effective sealing on the one hand, and excessive friction on the other hand.

A series of elongated arcuate ports 26, 28, 30 and 32 is formed by cutting a slot of this shape through the P.T.F.E. wear sheet around the inner end of each of the open-ended slots in the wear sheet. Each of the ports 26,28, 30 and 32 is concentric with the axis of its respective roller, when the roller is in the operative position. It will be observed, that each of the ports 26, 28, 30 and 32 is of considerable length, extending through most of a circle, but that the ends of the ports do not break out into the open-ended slots.An inlet port 34 is formed through the wall proper 10, and a corresponding inlet port 35 is formed through the rubber sheet 22, the location of these inlet ports being such, that in the assembled condition, they both register with one end of the corresponding port 26, 28, 30 and 32. A source of air under pressure is connected to each of the inlet ports 34 on the outside of the apparatus.

Moreover, the air supply includes means for creating water droplets in atomised form within the air supply.

In operation, the air under pressure carrying the water droplets in suspension, passes through the inlet ports 34 and 35, and then fills the respective arcuate port 26, 28, 30 or 32. Because of the combined effect of the pressure applied to this supply, and the vacuum within the chamber, the air carrying the water tends to flow radially outwards from the arcuate port across the interface between the end face of the roller, and the inside surface of the wear sheet 24. There may be some slight leakage of this air and water supply to the outside of the drying chamber, but since the greater part of the length of the arcuate port is on the inside of the roller, and moreover there is the suction effect of the vacuum on the inside of the roller, the great majority of the air and water supply will pass inwardly into the drying chamber.

Of course, this flow of air and water across the interface in itself lubricates that interface, and tends to reduce friction. Moreover, as soon as the water carried by the air enters the vacuum chamber, it "flashes off" into water vapour, and the latent heat of evaporation of this water has to be absorbed, mostly from the end of the roller, and the inside of the wear sheet 24. Hence, there is a cooling as well as a lubricating effect on the rubbing surfaces, and this is entirely beneficial to the operation of the rollers.

The forces applied to the rollers 256 and 258 due to the pressure differential across them, can cause those rollers to deflect, and this slightly alters the orientation of their end faces with respect to the walls 10. However, any such change of orientation, is accommodated by compression of the rubber cushion sheet 22. In other words, the wear sheet 24 tends to adopt the same attitude as the end face of each roller in the vicinity of that roller end face.

Claims (13)

1. A roller arrangement wherein a roller has a stub axle which is received in an open-ended slot in a stationary wall, and the end face of the roller is in close proximity to the wall, in which a lubricating port is provided in the part of the wall which faces the end face of the roller, there being means for supplying a lubricant under pressure into the port, and the relationship between the impedance between the end face of the roller and the wall on the one hand and the pressure of the lubricant supply on the other hand, is such that the lubricant is able to flow radially outwards over the end face of the roller.

2. A roller arrangement as claimed in Claim 1, in which the port is sealed from the slot.

3. A roller arrangement as claimed in Claim 2, in which the port is kidney-shaped.

4. A roller arrangement as claimed in Claim 2, in which the port is arcuate and substantially concentric with the roller axis.

5. A roller arrangement as claimed in any one of Claims 1 to 4, in which the port subtends a considerable part of a circle, but its ends do not break out into the slot.

6. A roller arrangement as claimed in any one of Claims 1 to 5, in which the part of the wall adjacent to the end face of the roller is cushioned so that it can tilt slightly to permit small changes in the orientation of the roller end face such as would occur on deflection of the roller.

7. A roller arrangement as claimed in Claim 6, in which a sheet of rubber or like compressible and resilient material is sandwiched between the wall proper and a wearing surface sheet which actually faces or engages with the end face of the roller.

8. A roller arrangement as claimed in Claim 7, in which the wearing sheet is a sheet of polytetrafluoroethylene.

9. A method of reducing friction at the interface of two members, which have relative rotation, and where the proximity of the two members is such as to provide a substantial impedance to fluid flow between them, comprising the steps of: supplying a gas containing atomised water into the interface; causing the gas to flow radially out of the interface into an atmosphere at a reduced pressure such that the water evaporates, whereby at least some of the latent heat of evaporation is removed from one or both the members at their interface.

10. A method of reducing friction as claimed in Claim 9, in which the gas is air.

11. A method of reducing friction as claimed in Claim 9 or Claim 10, in which the two members are pressed together at the interface whereby the friction between them would cause the temperature of the rubbing parts to approach or even exceed 1 OO"C in the absence of the lubricating and cooling effect of the gas and water carried by the gas.

12. A roller arrangement constructed and arranged substantially as herein described with reference to the accompanying drawings.

13. A method of reducing friction substantially as herein described with reference to the accompanying drawings.