FIELD OF INVENTION
The present invention generally relates to development of an apparatus for manufacturing of pre-tensioned helical coils for heat exchangers. This device is for manufacturing of pre-tensioned helical Coil Tube Bundles by winding the tubes in cold condition. This is developed for manufacturing helical coils of multi-start and multi-layered tube bundles with different pitches and with varying diameters of tubes. The same can be used for different bundle diameters also.
BACK GROUND OFTHE INVENTION
In compact heat exchangers, helical coiled tube bundles are used. These tube bundles are made up of helically coiled tubes and have straight portions at the ends to connect with the next bundle through headers or pipes. There will be more than one layer and each layer can have one tube or more than one tube. Coiling of tubes is to be carried out over a shell/mandrel. Coiling of each tube has to be started and terminated at a defined orientation with respect to the base shell, with a specified pitch or lead and number of turns. Figure-1 shows the output of the device developed. For making the helical coil, the device layout is shown in figure-2.
Pre-tensioning of the tubes is required for obtaining the final bundle diameter as required for the heat exchanger design. If the tube is not pre-tensioned, the tube may be loosened on winding and thus results in higher bundle diameter.
Since the helical coil heat exchangers are with multi-start and multi-layered, accurate winding of tubes over the shroud is required. Also the helix angle of the coils is need to be changed for different types of helical heat exchanger. Thus demand for an apparatus emerged for manufacturing the helical coils.

The device has been developed and used for the manufacture of compact heat exchangers with stringent quality requirements. Hot medium will flow through the tubes and cold medium will flow outside the tubes. Desired heat transfer area is being achieved with a shorter length heat exchanger. This invention paved the way for the manufacture of such helical coil heat exchangers.
PRIOR ART
Extensive search has been made and it has been found that no similar patents available in the net.
OBJECTS OF THE INVENTION
The objective of the invention is to manufacture pre-tensioned helical coils for tube bundles in helical coil heat exchangers.
Another object of the invention is to manufacture the helical coil with different bundle diameters by ensuring the tightness of the coil.
Further object of the invention relates to the manufacturing of helical coils with different pitch also.
A still further object of the invention relates to the manufacturing of helical coils in left hand and as well as right hand coiling
SUMMARY OF THE INVENTION
The device has been built, resembling like a lathe with a fixed head stock (1), a movable tailstock (7) and a carriage mounted on a common bed. Chucks (2) are being mounted on both the headstock (1) and tailstock (7). Cross slide (21) of the carriage is mounted with a vertical post, called PTU (Pre-Tension Unit) mounting base (11) having a horizontal base with screw rod arrangement for vertical movement. The shell

(4) is mounted in chuck and the tube (5) is held at front support plate (6) at the start of the coil. The tube (5) is held tightly in the pre-tension unit (10) by using hydraulic cylinders. The required helix angle can be obtained by tilting the pre-tension unit (10). The required pitch and number of turns required is fed as program and finally the tube (5) is held in the end support plate.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure-1 shows the output of the apparatus which is multi-start and multi-layered helical coil.
Figure-2 schematically illustrates the specially developed device with a tube in position. The machine resembling like a Lathe having Bed, Headstock, Headstock side Chuck, Tailstock, Tailstock side chuck and a Carriage with Cross side.
Figure-3 shows the pre-tension mounting base without lathe.
Figure-4 shows the pre-tension unit which is attached to the pre-tension mounting base with bolts.
Figure-5 shows the rollers used for holding the tube and the profile of the rollers.
DETAILED DESCRIPTION
The figure-2 shows the general layout of the coiling apparatus developed for manufacturing helical coils. The device consists of headstock (1), tailstock (7) with handle (8) to adjust for varying length of shell/mandrel (4). Shell/mandrel (4) is held in the chuck (2) available at headstock and tailstock. To accommodate the shell/mandrel of varying length, adjusting wheel (8) can be used. Shell/mandrel (4)

over which the tube (5) is to be wound / coiled is being fed through a pr-tension unit (10). The tube (5) is held at the front support plate (6) at start of coiling. The pre-tension unit (10) is used to give sufficient tension for the tube to wind it tightly and it is mounted on a vertical slide, called pre-tension mounting base (11) which in turn mounted on the cross slide (21). It has provision for manually tilting to set the helix angle of the coil. By loosening the bolts (13) shown in figure-2, and tilting the pre-tension mounting base (11), the required helix angle can be obtained.
The figure-3 shows the pre-tension mounting base (11). Depending upon the diameter of the shell, the height of the pre-tensioning unit (10) can be set using the handle (12).
While adjusting the height, the pre-tension unit (10) will move along the screw rod (18). The height set can be noted with the help of graduated scale (17) available at the pre-tension base (11) as shown in figure-3. Thus, the tube (5) is held in front support plate (6). The winding is done over the shell with required helix angle and finally the tube is held in rear support plate (3).
The pre-tension load is applied over the tube (5) with the help of hydraulic cylinders (9) as shown in figure-4. The pre-tension unit (10) is bolted to the pre-tension mounting base (11) with the help of bolts (16). The hydraulic cylinder (9) is connected to hydraulic unit (not shown) is used for applying necessary load over the tube (5) while winding. The tube (5) is held between the top roller assembly (14) and bottom roller assembly (15). With hydraulic cylinder (9), the top roller assembly (14) will move and clamp the tube (5) with the bottom roller assembly (15) as shown in figure-4. The profile (20) of the rollers (19) should match with tube (5) which is used for winding as shown in figure-5.

With the use of controlled motors, rotation of the headstock chuck (2) and linear movement of the cross slide (21) are synchronized and desired pitch / lead is being obtained. Direction of motion of the cross slide (21) is also being set depending upon Right Hand coiling or Left hand Coiling.
By tilting the pre-tension mounting base (11), the required helix angle can be maintained. Thus the device is capable of winding the tubes in multi-start, and multi-layers ie. One or more numbers of tubes in one layer and one layer over the other.
The height of the pre-tension mounting base (11) can be increased for manufacturing different diameter bundles. While adjusting the height, pre-tension unit (10) will move along the screw rod (18). The height can be noted with graduated scale (17). Thus is capable of manufacturing different multi-layered tube bundles.
The pre-tension mounting base (11) can be tilted in required angle thus capable of producing tube bundles with “Right hand helix and Left hand helix”. The carriage (21) will move horizontally in line with rotation of chuck (2).
With the help of pre-tension unit (10) the pre-tension load can be applied to the tube during winding thus the device is capable of manufacturing the bundles without any looseness and with close dimensional controls. The hydraulic cylinders (9) are used for applying load over the tube. The top roller assembly (14) and bottom roller assembly (15) will clamp the tube (5) between the rollers (19), thus applying pre-tension load to the tube (5) while winding. The profile (20) of the roller should match with the outside diameter of the tube (5). Thus by changing the profile (20) of the roller (19), different diameter tube or any shape can be like round, square, rectangle etc can be coiled by using this device.

We claim
1. An apparatus for manufacturing pre-tensioned helical coils for heat exchangers
comprising:-
- a mandrel /shell (4) held between head stock (1) and tailstock (7) by
chucks (2, 2);
- an adjusting wheel (8) provided on backside of the tailstock (7) for adjusting the varying length of the mandrel (4);
- a pre-tension unit (10) disposed on a mounting base (11) for imparting tension to tube (5) which is held at front support plate (6) at the start of coiling;
- the said mounting base (11) in turn mounted on a cross slide (21) while the winding is done over the mandrel/shell (4) and finally the tube (5) end is clamped at rear end of support plate (3), wherein the tension of the tube (5) is all along maintained by pre-tension unit (10).

2. The apparatus as claimed in claim 1, wherein the pre-tension unit (10) is made to slide vertically in the mounting base (11).
3. The apparatus as claimed in claim 1, wherein the mounting base (11) has a provision for tilting at required angle by loosening/tightening bolt (13).

4. The apparatus as claimed in claim 1, wherein the arrangement has provision for height adjustment and tilting for winding of tubes in multi-start, or multi-layer, right hand helix or left hand helix.
5. The apparatus as claimed in claim 1, wherein the height of the pre-tension unit (10) is adjusted by moving the pre-tension unit (10) along a screw rod (18).
6. The apparatus as claimed in claim 1, wherein the load is applied to the tube (5) with the help of hydraulic cylinder (9) when the tube is held in the space (20) of roller (19) between the top roller assembly (14) and bottom roller assembly (15).