GB2221275A

GB2221275A - Tubes of variable diameter

Info

Publication number: GB2221275A
Application number: GB8818083A
Authority: GB
Inventors: James Stevenson
Original assignee: Foundry & Technical Liaison Li
Current assignee: Foundry & Technical Liaison Li
Priority date: 1988-07-29
Filing date: 1988-07-29
Publication date: 1990-01-31
Anticipated expiration: 2008-07-29
Also published as: GB2221275B; GB8818083D0

Abstract

The cross-sectional area of a tubular conduit (1) having a sliding overlapping seam is varied by applying a radial tensile force by means of two diametrically opposed air rams (6) to two chains (3, 7) which embrace a substantial portion of the circumference of the tube. One chain is positioned (7) below the other (3) and when the chains are tensioned the tube diameter is reduced whilst remaining circular. The invention is of particular use in controlling the cross-sectional area of a venturi passage used in the outlet of a cupola furnace. <IMAGE>

Description

TUBES OF VARIABLE DIAtvlETER This invention relates to a mechanical arrangement for varying the effective diameter of a tubular conduit, and is of particular use in controlling the cross-sectional area of a venturi passage used in the outlet of a cupola furnace, although it can well find use in other fields where a tubular passage of variable area is required.

To minimise pollution it is necessary to maintain the velocity of the hot gases emerging from a chimney stack, and in particular those from a metal-melting furnace. It is found that the velocity depends on the temperature and this in its turn depends on the metal/coke ratio so that although it is possible to choose an outlet venturi with a throat of the correct cross-sectional area for a given set of melting conditions this will not be right for a different melting operation, for example a different alloy. It is also necessary to maintain an aerodynamic shape in the venturi so that the energy input is applied with a minimum of loss to the cleanliness of the gases.

Accordingly it is the aim of the invention to provide a simple and effective way of varying the area of a tubular passage, for example one through which hot flue gases are to pass.

It has been proposed (in a proposal not yet published) to do this by making the tube of sheet metal bent round to form a cylinder with an overlapping joint free to slide and then to apply radial inward pressure at diametrically opposed points, so that the cylinder could be made to contract resiliently, the degree of overlap increasing to reduce the effective circumference. However, this has not proved satisfactory as the inward pressure at localised points was found to distort the tube to an oval shape, with a consequent disturbance of the conditions of flow.

According to the invention we propose that a tube of resiliently flexible material with a sliding overlapping seam should be varied in cross-sectional area by applying tensile forces to one or more flexible members, each of which extends a substantially way around the outside of the tube It would be possible to use a single such member acting in the manner of a tourniquet, but preferably we employ two separate ones, each extending more than half way around the circumference. Then if each is acted on by a force-applying member, for example a fluid-pressure ram, in a radial direction the two members can be diametrically opposed and the lateral forces on the tube balance out.

An example of a variable-area tube for use as a venturi outlet in a chimney of a cupola furnace and operating in accordance with the invention is illustrated in the accompanying drawings, in which: Figure 1 is a side view of it and Figure 2 is a section on the line 2-2 in Figure 1.

The tube illustrated comprises a sheet of stainless steel bent around to form a cylinder 1 with an overlapping sliding joint. It includes a welded-on frusto-conical flange 2 similarly formed. Embracing approximately three-quarters of the circumference of the tube is a roller-link chain 3 of stainless steel which forms a loop of greater circumference than the maximum circumference of the tube 1 and is engaged by a fork end connector 4 on the piston rod 5 of a pneumatic ram 6, the body of which is fixed.

A second chain 7 embraces the tube 1 a short way below the chain 3 and is likewise connected to the piston rod 5 of a second ram 6, diametrically opposite the first in relation to the tube 1.

Lugs 8 welded at spaced points on the outside of the tube support the chains and keep them horizontal without restraining their horizontal movement.

It will be appreciated that when air is admitted to the appropriate ends of the two rams 6 simultaneously the two chains will be pulled in opposite directions and they apply a uniform squeeze to the tube, extending evenly all around it, and so the tube is reduced in diameter whilst remaining a perfect circle.

On release of the pressure the tube will revert to its former size under the action of its own resilience.

The tube may be made capable of adopting only two sizes, i.e. with the rams energised or de-energised, or with appropriate control of the rams it could be continuously variable.

The opposed action of the rams results in no net lateral force on the tube. In a modification there could be more than two chains, the rams being uniformly distributed around the tube.

Instead of pneumatic rams, other force applying means could be used, for example hydraulic rams or electric actuators.

The control is preferably automatic. For example in a furnace installation there may be sensors which sense the temperature of the flue gases and energise the actuators to vary the size of the throat appropriately as required. Alternatively or in addition, there may be sensors which responds to the pressure drop across the venturi and acts automatically to vary the its cross-section so as to maintain the pressure drop substantially constant with varying flow conditions, and thereby to maintain efficient cleaning of the gas.

Claims

1. A tubular conduit for fluids made of resiliently flexible material with a sliding overlapping seam in which the cross-sectional area of the tube can be varied by applying tensile forces to one or more flexible members each of which extends a substantial way around the outside of the tube.

2. A tubular conduit according to claim 1, in which there are two flexible members, each extending more than half way around the circumference of the tube.

3. A tubular conduit according to claim 2, in which the two flexible members are diametrically opposed.

4. A tubular conduit according to any preceding claim, in which a force-applying member acts on each flexible member in a radial direction.

5. A tubular conduit according to claim 4, in which the force-applying member is a fluid-pressure ram.

6. A tubular conduit according to claim 1, in which there are more than two members uniformly distributed around the tube.

7. A tubular conduit according to any preceding claim, in which the tube comprises a steel sheet with a frusto-conical flange.

8. A tubular conduit according to any preceding claim, in which the flexible member comprises a roller link chain forming a loop having sweater circumference than a maximum circumference of the tube.

9. A tubular conduit according to any preceding claim, in which a second flexible member embraces the tube longitudinally spaced from the first flexible member.

10. A tubular conduit according to claim 9, in which lugs are spaced around the exterior of the tube and support the flexible members without restraining their movement in a direction perpendicular to the axis of the tubular conduit.

13. A tubular conduit substantially as described hereinbefore with reference to the accompanying drawings.