Claims:We claim:
1) A fixture (100) for welding of tubes (200) comprising:
a pair of jaws (102) of V-shape with an integrally formed hollow cylindrical portion (102(a)) at their center;
a pair of lower plates (106) integrally welded with a pair of vertical plates (110) and a pair of upper plates (108) to form a U-shaped bracket, said pair of lower plates (106) positioned on a platform with a predefined distance in between them and bolted therein;
a mounting plate (104) having angular shape complementary to the V-shape of said pair of jaws (102) and welded on said pair of lower plates (106);
a pair of spindles (112) coupled to a pair of handles (114) at their top portion (112(b)) with a plurality of threads (112(a)) adapted to pass through one threaded hole 108(a) of said pair of upper plates (108) to finally couple to said hollow cylindrical portion (102(a)) of said pair of jaws (102) at their bottom portion (112(c)),

wherein said tubes (200) includes a pair of tubes (200(a) and 200(b)) of same size placed on said mounting plate (104) and adjusted to form a weld position; said pair of handles (114) rotated to bring said pair of jaws (102) in mating contact with said pair of tubes (200(a) and 200(b)) and clamped firmly to maintain said weld position and alignment between said pair of tubes (200(a) and 200(b)) during welding process.

2) The fixture (100) as claimed in claim 1, wherein said pair of handles (114) comprises a hollow hub portion (114(a)) with cylindrical rods (114(b)) extending from either sides of said hollow hub portion (114(a)).

3) The fixture (100) as claimed in claim 1, wherein said pair of lower plates (106) provided with one hole (106(a)) at their one end facilitates in bolting said pair of lower plates (106) to said platform.

4) The fixture (100) as claimed in claim 1, wherein said mounting plate (104) and said pair of jaws (102) are provided with an included angle depending on the diameters of said tubes (200) to be welded.

5) The fixture (100) as claimed in claim 1, wherein said hollow cylindrical portion (102(a)) of said pair of jaws (102) is threaded on its inner diameter.

6) The fixture (100) as claimed in claim 1, wherein said pair of spindles (112) at their bottom portion (112(c)) are threaded.
, Description:DESCRIPTION

FIELD OF THE INVENTION:
The present invention relates to a fixture used in welding operations. Particularly, the present invention relates to a fixture for alignment of tubes in a welding operation.

BACKGROUND OF THE INVENTION:
The function of coils in steam generating units is to absorb heat from the flue gases and add this as sensible heat to the feed water before the water enters the evaporative circuit of the boiler. Typically, the coils of the super heater and reheater superheats the steam by absorbing the heat from the flue gases.

Super heater area is meant to raise the steam temperature above the saturation temperature by absorbing the heat from the flue gas such that the useful energy that can be recovered from the flue gases increases, thus the efficiency of cycle also. Thus, in modern boilers, super heaters and reheater are also used to increase the cycle efficiency economically and attain the designed temperature. The maximum temperature to which steam can be heated is dictated by metallurgy, initial cost and maintenance cost.

Reheaters are used to raise the temperature of steam from which part of energy has been extracted in high pressure turbine. This is another method of increasing the cycle efficiency, which increases with number of stages of reheating.

The coils of the super heaters and reheaters are designed to withstand the steam temperature value of 540 Degree Centigrade. The coil tubes are placed against each other on a stand or platform and butt welding operation is performed on them to achieve circuit of coil tubes of desired length depending on the design specification of the economizers, superheaters or reheaters. Typically, the circuit length of the coil tubes varies in the range of 1000mm to 48000mm.

Apart from welding operation, the desired circuit of the coil tubes depending on the design requirement is achieved through bending the coil tubes in three or four segments by means of a bending machine.

The welding operation to achieve the desired length of the coil tubes can be Metal Inert Gas (MIG), Tungsten Inert Gas (TIG), Flash Butt Welding (FBW) or Induction Pressure Welding (IPW) depending upon the customer requirement, manufacturing capability, flexibility, and cost estimation.

The joining of coil tubes through welding by keeping them on the stand or platform requires skilled operator for proper setting of the coil tubes otherwise there are very high chances of misalignment of the coil tubes, which causes various defects like lack of fillet, incomplete penetrations, weakness of bond strength, chances of formation of vena-contracta and film boiling. These defects may ultimately lead to catastrophic failure of high pressure and high temperature equipment.

The drawbacks of the above mentioned welding operation are as follows:
1) Requires skilled operator
2) The operator needs to put on lot of effort
3) Codes of good practices and safety standards are compromised to a great extent.
4) Number of defective joints in the welded coil tubes may be high.
5) Quality Control and Quality Assurance time is high which ultimately results in high cycle time.

Therefore, there is felt a need for development of a fixture to overcome the drawbacks of the prior art and thereby achieve good quality weld between the coil tubes.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a simple and fool-proof fixture for welding of tubes.

Another object of the present invention is to provide a fixture to minimize weld defects in joining of the tubes.

One more object of the present invention is to perform welding operation on the tubes with semi-skilled operators also.

Still another object of the present invention is to perform welding operation on the tubes in less cycle time.

Further another object of the present invention is to adopt codes of good practices and safety standards.

SUMMARY OF THE INVENTION:
In accordance with the present invention a fixture for welding of tubes is provided, the fixture comprises a pair of jaws, a mounting plate, a pair of lower plates, a pair of upper plates, a pair of vertical plates, a pair of spindles and a pair of handles. The pair of lower plates welded as an integral unit with the pair of vertical plates and the pair of upper plates forms a U-shaped bracket. The pair of lower plates forming a U-shaped bracket are placed on a platform with a predefined distance in between them depending on the length of the tubes to be welded and bolted in position. The pair of spindles are coupled to the pair of handles at their top portion with a plurality of threads adapted to pass through one threaded hole of the pair of upper plates to finally couple to a hollow cylindrical portion of the pair of jaws at their bottom portion. The tubes include a pair of tubes of same size placed on the mounting plate and adjusted to form a weld position. The pair of handles are rotated to bring the pair of jaws in mating contact with the pair of tubes and clamped firmly to maintain the weld position and alignment between the pair of tubes during welding operation.

In an aspect, the mounting plate and the pair of jaws are provided with an included angle depending on the diameters of the tubes to be welded.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a perspective view of a fixture for welding of tubes, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.

Referring to fig 1, in accordance with the present invention, there is provided a fixture 100 for welding of tubes 200 comprising a pair of jaws 102, a mounting plate 104, a pair of lower plates 106, a pair of upper plates 108, a pair of vertical plates 110, a pair of spindles 112 and a pair of handles 114.

The jaws 102 are rectangular blocks typically of V-shape with an included angle varying depending on the size of the tubes 200 to be welded. The jaws 102 are provided with an integrally formed hollow cylindrical portion 102(a) at their center. Typically, the hollow cylindrical portion 102(a) is threaded on its inner diameter.

The mounting plate 104 is of angular shape provided with an included angle complementary to the included angle of the V-shape of the jaws 102.

The lower plates 106 are rectangular plates provided with one hole 106(a) at their one end. The upper plates 108 are rectangular plates provided with one threaded hole 108(a) at their center. The lower plates 106 are welded at the bottom of the vertical plates 110 and extends perpendicularly from the vertical plates 110. The upper plates 108 are welded at the top of the vertical plates 110 and extends perpendicularly from the vertical plates 110. The pair of lower plates 106 welded as an integral unit with the vertical plates 110 and the upper plates 108 forms a U shaped bracket.

The spindles 112 are cylindrical rods provided with a plurality of threads 112(a) in between a top portion 112(b) and a bottom portion 112(c). The bottom portion 112(c) of the spindles 112 are typically threaded and have a diameter less than the inner diameter of the hollow cylindrical portion 102(a) of the jaws 102.

The handles 114 have a hollow hub portion 114(a) with cylindrical rods 114(b) extending from either sides of the hollow hub portion 114(a).

The arrangement and working of the fixture 100 is as follows: The pair of lower plates 106 forming a U-shaped bracket are positioned on a platform with a predefined distance in between them depending on the length of the tubes 200 to be welded. The pair of lower plates 106 are bolted in position to the platform through the hole 106(a). The mounting plate 104 is welded on the pair of lower plates 106. The top portion 112(b) of the pair of spindles 112 is coupled to the hollow hub portion 114(a) of the pair of handles 114 by means of welding or any other means. The spindles 112 with handles 114 coupled to them are inserted into the threaded hole 108(a) of the pair of upper plates 108. The bottom portion 112(c) of the pair of spindles 112 is coupled to the hollow cylindrical portion 102(a) of the jaws 102 by means of threaded configuration or by any other means.
The tubes 200 to be welded includes a pair of tubes (200(a) and 200(b)) having same inner diameter and outer diameter. The pair of tubes (200(a) and 200(b)) are placed on the mounting plate 104 and adjusted by the operator such that the gap between the pair of tubes (200(a) and 200(b)) forms a weld position. The pair of handles 114 are rotated such that the pair of jaws 102 comes in to mating contact with the pair of tubes (200(a) and 200(b)) and clamped firmly therein to maintain the weld position and alignment of the pair of tubes (200(a) and 200(b)) throughout the process of welding.

In an aspect, the pair of jaws 102 and the mounting plate 104 accommodates up to a range of diameters of the tubes 200. In order to accommodate bigger diameter of the tubes 200, the pair of jaws 102 and the mounting plate 104 needs to be changed.

Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.