Controllable fluids in pipe bending

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.