Controllable Fluids in Pipe Bending

Abstract

A method for shaping partially enclosed structures such as pipes, the method comprising: filling the structure with ERF, applying an electrical field to the ERF to increase its viscosity, shaping the structure, removing the field and removing the ERF from the structure.

Description

This invention relates to bending structures containing fluids whose viscosity is adjustable, such as electro-rheological fluids.

In a common pipe bending method a die is pushed against the tube or pipe by a mechanical force, forcing the pipe to conform to the contours of the die. Lacking internal support in the pipe, this pipe bending process creates some cross sectional reduction in the pipe. The thinner the wall of the pipe, the more deformation of the pipe is seen.

Using rotary-draw or cold form pipe bending machines, a steel plug fits inside the pipe while a moving steel die forms the pipe to the radius of the die. The steel plug, or mandrel, supports the pipe internally to reduce the amount of pipe cross section flattening during pipe bending. After the pipe bending process, the mandrel is extracted from the pipe and if heated, the area is quenched by a water or air spray. With proper tooling, this pipe bending process is capable of producing high quality, tight-radius bends for a wide range of applications including football goalposts, davit arms and pneumatic conveying systems. However such tooling is expensive and requires experience and skill to use correctly and its typical cost is higher than other methods.

Sand-packing and hot-slab forming starts with packing the pipe to be bent with a fine sand, then capping the ends. The pipe is placed in a furnace and heated to a high temperature. After removing it from the furnace, the pipe is secured by one end to a bending slab. The unsecured end of the pipe is pulled against pins in the slab until the bend assumes the desired radius. The sand minimizes cross section collapse and ovality. This is an archaic process, with sand residue often remaining in the internal structure of the pipe and the heat in some case being sufficient to alter the physical structure of the sand causing it to adhere to the pipe surface, however, many pipe bends are still made in this fashion.

There is therefore a need for improved method of shaping pipes.

Electro-rheological fluids (ERFs) are known and are described in our patent application GB 0417587.3. Electro-rheological materials are materials whose rheological properties change when an electric current is applied. Typically the materials behave as fluids in the absence of an electric field. When an electric field/current is applied the materials' viscosity and shear stress at yield increase.

A number of applications have been proposed for electro-rheological fluids. These include use in clutches, brakes, hydraulic valves and dampers for use in applications such as engine mounts, suspension shock absorbers and seat supports. (See for example U.S. Pat. No. 6,105,420).

In accordance with the present invention such fluids can be used for assisting pipe bending. Fluid can be introduced into a pipe and then a current applied to it to increase its viscosity. The pipe is then bent and the fluid will support the pipe during bending. The field can then be removed and the fluid can flow out of the bent pipe.

The field can be applied from electrodes at one end of the pipe to the other (if the pipe is of electrically insulating material) or from a conductor in the interior of the pipe to the pipe itself (if the pipe is electrically conductive).

Using this method pipes of complex shapes can readily be bent in a process similar to sand-bending, but cold. The need for removal of the former or support from the interior of the pipe no longer limits the shaping that can be done.

The invention is especially applicable to the shaping of vehicle exhaust pipes. Such pipes could be formed of a dual skin, with the ERF filling the void between the skins and thus allowing complex bends of both pipes together, or the ERF filling the pipes entirely. Dual skins are used for a multiplicity of roles, from the lowering of thermal inertia of the inner wall, through to external heat and noise insulation. A novel use could be that of heat exchange between the two zones thus defined, from the exhaust in one zone to (e.g.) heating fluid for the interior of the vehicle in the other zone.

According to the present invention there is provided a method for shaping partially enclosed structures such as pipes, the method comprising filling the structure with ERF, applying an electrical field to the ERF to increase its viscosity, shaping the structure, removing the field and removing the ERF from the structure.

Further advantageous features are disclosed in claims 2 to 10.

An example of the present invention will now be described, with reference to the drawings.

In the drawings:

FIG. 1 shows a cross section through an unbent pipe; and

FIG. 2 shows a cross-section through a bent pipe;

FIG. 1 shows a pipe 1 with an electro-rheological fluid 5 present inside the pipe to an extent that the fluid completely fills the pipe. Electrode 16 are attached to the pipe and these are connected via cables 14 to a power supply 10, which can apply an electrical field between the electrodes 16 on actuation of switch 12. The power supply could contain a battery as a source of electrical power. When the power supply is turned off the fluid has a random structure and conforms to the inside surface of the pipe.

FIG. 2 shows the power supply turned on. The electro-rheological fluid and the power supply are selected so that the fluid can flow readily when no electrical field is imposed, but so that the fluid becomes substantially rigid when an electrical field is imposed by the power supply. The fluid gives support to the internal structure of the pipe during the bending process. Subsequently the field can be removed, releasing the fluid to allow it to flow out of the pipe.

Electro-rheological fluid generally comprises a carrier liquid in which particles are dispersed. Additives may be included to improve the performance of the liquid. The liquid is a dielectric and could, for example, be an oil. The particles can, for example, be based on silica, zeolites, gum Arabic, formaldehyde polymer, active carbon, poly(acenequinone) radical (PAQR) polymers, polyeurethane polymers or surface treated carbon. When no electrical field is applied the particles are free to move in the fluid and the fluid has a relatively low viscosity. When an electrical field is applied across the fluid the particles take on an ordered structure which resists flow, giving the fluid a relatively high viscosity and a relatively high shear stress at yield. By selection of the materials, the particle loading and any additives, the viscosity of the fluid when no field is applied, and the rheological response of the fluid to the application of a field can be tailored for a desired application.

The electro-rheological fluid and the power supply are selected so that the fluid can flow when no electrical field is imposed, but so that the fluid becomes substantially rigid (e.g. about 90% solid or above 10,000 centistokes) when an electrical field is imposed by the power supply. The viscosity of the fluid when no field is imposed can be selected based on the application, but could be in the range from 10 to 1000 centistokes.

The material with which the pipe is filled before bending behaves as an ERF in that it becomes stiffer in the application of an electric field across it. That material need not be a single fluid, or entirely liquid. It could be formed of a mixture of a material that behaves as an ERF with a material that by itself does not behave as an ERF. It may be a mixture of an ERF with a material (such as sand) that comprises rigid particles. It may be a mixture of an ERF with one or more flexible bodies. The amount of ERF that is required may be reduced by introducing a flexible body such as a plastic hose into the interior of the pipe and filling the pipe by introducing the ERF into the region between the hose and the pipe.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A method for shaping a partially enclosed structure, the method comprising the steps of:

filling the structure with ERF,

applying an electrical field to the ERF to increase its viscosity,

shaping the structure,

removing the field and

removing the ERF from the structure.

2. The method for shaping a partially enclosed structure according to claim 1, wherein the structure is an electrically insulating material and the field is applied from electrodes at one end of the structure to the other.

3. The method for shaping a partially enclosed structure according to claim 1, wherein the structure is electrically conductive and the field is applied from a conductor in the interior of the structure to the structure itself.

4. The method for shaping a partially enclosed structure according to claim 1, wherein the ERF comprises a dielectric.

5. The method for shaping a partially enclosed structure according to claim 4, in which the liquid is wherein the dielectric is an oil.

6. The method for shaping a partially enclosed structure according to claim 1, wherein additives are included in the ERF to improve the performance of a liquid in the ERF.

7. The method for shaping a partially enclosed structure according to claim 1, wherein the ERF comprises particles based on a material selected from the group consisting of silica, zeolites, gum Arabic, formaldehyde polymer, active carbon, poly(acenequinone) radical (PAQR) polymers, polyeurethane polymers and surface treated carbon.

8. The method for shaping a partially enclosed structure according to claim 1, wherein the ERF has a low viscosity when particles in the ERF are free to flow.

9. The method for shaping a partially enclosed structure according to claim 1, wherein the ERF becomes substantially rigid when the electrical field is imposed by a power supply.

10. (canceled)

11. The method for shaping a partially enclosed structure according to claim 1, wherein the structure is a pipe.