GB2294749A - Tumble drying apparatus - Google Patents

Abstract

A tumble drying apparatus comprises two or more tumbling drums 7, 8 rotatable in respective chambers 3, 4a heater 28 for supplying heated air to one of the drums 7 and a fan 27 for drawing cooling air into the other drum 8 and a door 11 permitting transfer of material to be dried from the first drum to the second drum. Preferably the drum are juxtaposed and substantially coaxial and the arrangement is such that air is first circulated to the second chamber 2 so that it becomes heated by material therein and is then further heated by heater 28, and passed to the first chamber 3 by fan 27. The invention is particularly applicable to industrial tumble drying machines for dust control mats and the like. A conveyor belt or chute (18. Figure 2) may be used to transfer material from one drum to the other. <IMAGE>

Description

TUMBLE DRYING APPARATUS This invention relates to tumble drying apparatus, particularly though not exclusively industrial tumble drying machines. As is well known, tumble drying machines are used to remove water or other liquids from materials, usually after specific treatments which make them wet e.g. washing in washing machines.

Tumble drying machines usually comprise a drum which is rotated about an axis which may be substantially horizontal or tilted. Heated air is passed through the drum, the rotational speed of the drum being such that the materials being dried are tumbled in the heated air flow which evaporates and removes the water or other liquid. In domestic tumble drying machines the air is generally heated electrically but in industrial tumble drying machines, the air is usually heated by either a steam heat exchanger or by combusting gas in the air flow. The air is exhausted through a lint screen before being vented to the atmosphere. It is possible to place a (further) heat exchanger downstream of the lint screen to recover waste heat.

The materials to be dried are usually fibrous at least in part and may include dust control mats, mops, textile materials such as workwear, linen and sheets, and the like. The drying of these materials normally involves a two stage process comprising a set period in which heat is applied, determined either by time or temperature, and then a cool down period in which the heater is turned off and cool air only is passed through the drum to cool the materials. The cool down period is again determined either by time or temperature.

In some cases the cool down part of the process can be as long as the heating period. This is especially true for dust control mats in which the rubber backing can contain sufficient heat to require an extended cool down period. Dust control mats are normally manufactured from synthetic pile yarns with a substantial rubber backing. During the heating period much of the energy input is used to heat the rubber and during the cool down period the heat energy remaining in the rubber will enable further drying of the mat, particularly the pile.

One of the drawbacks of this process is that during the cool down period the entire machine is also cooled down which in itself is undesirable but has previously been considered to be a necessary side effect. Besides increasing energy consumption this also wastes production time and capacity since the machine cannot be simultaneously used for hot air treatment.

The present invention aims to overcome or mitigate these disadvantages by making use of a separate chamber to carry out the cool down process.

According to one aspect of the invention, there is provided tumble drying apparatus having distinct drums for respectively hot drying and cooling material to be dried.

According to another aspect of the invention, there is provided tumble drying apparatus comprising two or more tumbling drums rotatable in respective chambers, means for supplying heated air to one of the drums and cooling air to another of the drums and means permitting transfer of materials to be dried from the first drum to the second drum. It should be noted that with this arrangement the second drum does not need to have a heating device, lint screens and associated controls etc. Another advantage of this arrangement is that the 'hot' part of the apparatus remains hot and there is no energy used in heating the drum and its chamber with every cycle since the working temperature is maintained. The drums and their respective chambers can be part of the same tumble drying machine or can be in distinct or separate tumble drying machine units.

The air circulation arrangement is preferably such that the air entering the heater is taken from the outlet of the cooling drum chamber thereby taking the waste heat from the cooling chamber and recycling it. With such an arrangement there is no need for lint capture at the exit of the cooling chamber as the air is carried through to the heating chamber which is normally equipped with a lint screen.

Two embodiments of the invention will now be described by way of example with reference to the drawings in which: Fig. 1 is a diagrammatic vertical sectional view of a tumble drying apparatus according to the invention; and Fig. 2 is a view similar to Fig. 1 of a modified apparatus.

Fig. 1 shows a tumble drying machine in which an outer shell or housing 1 provides a cylindrical space 2 divided in a substantially airtight manner into a hot chamber 3 and a cool chamber 4. The chambers 3 and 4 contain respective coaxial rotary drums 7, 8 which may be perforated in conventional manner and which are rotatable about a horizontal axis by a drive arrangement which is not shown but which may comprise fixed axis support and drive rollers arranged around its periphery in conventional manner. Their ends are annular and provide upstream and downstream ports 10, 11.

A loading door 13 on chamber 3 provides access to the upstream port 10 of the drum 7 and unloading door 14 on chamber 4 provides access to the downstream port 11 of drum 8. A slidable transfer door 15 is provided on the dividing wall (not shown) between the chambers 3, 4 and can be withdrawn to provide communication between the downstream port of drum 7 and the upstream port of drum 8.

Alternatively an iris-style barrier or a flap door can be used. The outer shell 1 is hinged at its downstream end for pivoting around a horizontal axis at 20 and has a hydraulic or pneumatic tilting cylinder 21 at its upstream end such that its extension tilts the shell 1 in the desired direction. The hinge 20 and cylinder 21 can be interchanged in which case the cylinder 21 is retracted to tilt the shell 1 in the desired direction. Also, the tilting arrangement can be arranged to lower the downstream end of the shell 1 as well as raise the upstream end.

Cold air enters chamber 4 through line 25 and leaves it through line 26. This flow is induced by a fan 27 in line 26.

Downstream of the fan 27 is a heater 28 of conventional type which further heats the air (it will already have been heated by the material in drum 8 which is being cooled). Line 26 supplies the hot air to chamber 3 where it heats and dries the material in the drum 7. It leaves chamber 3 by a line 30 in which there is a lint filter 31. In operation, the air flow will be stopped when it is desired to load material into or unload material from the drums 7, 8 or to transfer material between them. While loading of drum 7 or unloading of drum 8 can be carried out manually, these operations are facilitated by operation of the tilting cylinder 21. However such operation is essential for transferring material from drum 7 to drum 8. This transfer is facilitated by maintaining rotation of drum 7.

In the Fig. 2 arrangement, chambers 3, 4 are part of separate shell units la and Ib (in this case separate machines) and the transfer door 15 is replaced by respective unloading and loading doors 15a and 15b which are operated substantially simultaneously.

A chute or conveyor belt 18 interconnects the doors 15a, 15b. The chamber 3 is desirably positioned at a higher level than chamber 4 to facilitate transfer. The Fig. 2 arrangement permits standard machines to be used with little or no structural modification; note that the drum openings and doors should be symmetrical with respect to the horizontal rotary axis.

A typical operating cycle for the Fig. 1 machine starting with a fully loaded machine is as follows. At the completion of the drying period the machine is tilted and the unloading door 14 opened to unload the cooled material, the unloading door 14 is then closed and the transfer door 15 is opened allowing the hot material to transfer from chamber 3 to chamber 4. Once the transfer is complete the transfer door 15 is closed and the loading door 13 opened to accept the next load which is usually fed via a chute or conveyor belt. It is normal during loading and unloading for the drums 7, 8 to be rotated but the fan 27 and heater 28 to be turned off. The machine is returned to the normal horizontal position for running.

The Fig. 2 modification is operated in an analogous manner.

The apparatus just described is especially suitable for use with batch tunnel washing machines where a continuous series of batches of work is produced which needs to be dried at the same rate. Typically, batch tunnel washing machines are capable of producing batches every 2t-5 minutes. A typical cycle for tumble drying dust control mats is between 5 and 10 minutes depending on mat type and system efficiency. In normal circumstances two tumble drying machines working in parallel will be required to cope with the throughput which in turn requires complex loading and transfer equipment to hold and move the work between machines. The apparatus described above operates in series and can as much as double tumble drying capacity so reducing the need to have two conventional tumble drying machines for each batch tunnel washing machine.

Claims (11)

1. A tumble drying apparatus comprising two or more tumbling drums rotatable in respective chambers, means for supplying heated air to one of the drums and cooling air to another of the drums and means permitting transfer of material to be dried from the first drum to the second drum.

2. Apparatus according to claim 1 in the form of a tumble drying machine wherein the drums are juxtaposed and substantially coaxial.

3. A machine according to claim 2 wherein each of the drums has an axial upstream loading port and an axial downstream unloading port, the respective drum chambers being closed off from each other by a transfer door which can be opened to permit communication between the downstream port of the first drum and the upstream port of the second drum, wherein the first chamber has an upstream loading door and the second chamber has a downstream loading door.

4. A machine according to claim 3 wherein the means permitting material transfer also comprises means for tilting the drums so that the material in the first drum can be transferred to the second drum by gravity and by the rotary motion of the first drum.

5. Apparatus according to claim 1 wherein the chambers are in separate machine units.

6. Apparatus according to claim 5, wherein each of the drums has an axial upstream loading port and an axial downstream unloading port, the chambers having a door corresponding to each port, the downstream door of the first chamber and the upstream door of the second chamber being interconnected by material transferring means in the form of a conveyor or chute.

7. A machine according to claim 6 wherein the means permitting material transfer also includes means for tilting at least the first drum to facilitate discharge of material from the downstream port.

8. Apparatus according to any preceding claim wherein the arrangement is such that air is first circulated to the second chamber so that it becomes heated by material therein and is then further heated and passed to the first chamber.

9. Tumble drying apparatus having distinct drums for respectively hot drying and cooling material to be dried.

10. A tumble drying machine substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the drawings.

11. A method of tumble drying material in which there is used apparatus according to any preceding claim and in which heated air is supplied to one drum and cooling air is supplied to another drum.