THE PATENTS ACT 1970
COMPLETE
SPECIFICATION
SECTION - 10


TITLE
IMPROVED METHOD FOR FABRICATION OF A STATOR
CARRIER OF WINDMILL
APPLICANT
Premier Limited
58, Nariman Bhawan
Nariman Point
Mumbai - 400 021

The following specification particularly describes and ascertains the nature of the invention and the manner in which it is to be performed


Another object of the present invention is to provide a non-destructive testing of the welds carried out over the stator carrier.
Another object of the present invention is to provide separate fabrication and assembly of the top, bottom and side panes of the arm assembly.
An exemplary embodiment of the present invention is to devise preparatory work of Hub assembly and arm assembly before the final assembly.
Another exemplary object of the present invention is to devise a similar preparatory work for assembling and welding of the arm assembly to the Hub assembly.
These together with other objects of the invention, along with the various features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
Fig. 1 illustrates the Stator Carrier Asembly in accordance with the present invention;
Fig. 2 illustrates the Arm Assembly to Hub Assembly in accordance with the present invention;
Fig. 3 is the Closer view Arm Assembly to Hub Assembly in accordance with the present invention;
Fig 4 is the joint design is as shown as sketch in accordance with the present invention;
Fig 5 is the required edge preparation as worked out for the situation of the job in accordance with the present invention;
Fig 6 is the algorithm showing the conventional method in accordance with the present invention;

Fig 7 is the algorithm showing the disclosed method in accordance with the present invention;
DETAILED DESCRIPTION
Since the present disclosure is directed to an improved method for the fabrication of stator carrier, (for example the Enercon design) wherein the fabrication comprises Welding of stator arm involves weld of 1.4 metres length. There are six such arms welded to Hub Assembly to make the major body of Stator Carrier.
The technology used for the purpose of welding herein described is Gas tungsten arc welding (GTAW)r also known as tungsten inert gas (TIG) welding that uses a non consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. No loss of material occurs with the GTAW process. Because the resulting welds have the same chemical integrity as the original base metal or match the base metals more closely, GTAW welds are highly resistant to corrosion and cracking over long time periods, GTAW is the welding procedure of choice for critical welding operations. The other technology used for the said welding of the arms and Hub is the Flux cored arc welding (FCAW) is an electric arc welding process that uses an arc between a continuously fed flux-filled electrode and the weld pool. The process is used with shielded gas from a flux contained within the tubular electrode with or without additional shielding from an externally supplied gas. The FCAW process utilizes the heat of an arc between a continuously fed consumable flux cored electrode and the work. The heat of the arc melts the surface of the base metal and the end of the electrode. The metal melted off the electrode is transferred across the arc to the work piece, where it becomes the deposited weld metal.
The Salient features of the welds used in the present fabrication work are :
Full Penetration Weld
Weld checked by Ultrasonc Testing ( UT)
Maximum UT indication (defect) permitted is < 3mm
Narrow Approach - limited access
Restricted working space
Out - of - position welding
No possibility of examination of root side of weld
Curvature of job - making weld preparation and joint set- up difficult.
The procedure adopted for the present case is a modular form of fabrication that is based on manufacturing the job through sub - assembly construction route.

Only those with considerable expertise in fabrication would dare to take this route. Following are the advantages of the modular form of fabrication method :
Simultaneous work at different locations
Optimum utilization of fixtures and infrastructure.
Easier control of production process leading to better productivity
For conducting the arm assembly construction a separate fixture is provided for the welding of the top, bottom and side panes. The fabrication of the arm assembly is done separately. Similarly the Hub assembly construction is carried out separately in a specially configured fixture.
As discussed earlier, for the complete assembly of the carrier assembly, in the modular form of fabrication process, 1 no. Hub assembly 6 nos. of arm assemblies is provided. The arms are set up against the Hub assembly for the fabrication. The three sides of the job are welded with GTAW process and the bottom sides of the arms are welded with FCAW process. Hereafter the job is turned after and the topsides of the arms are welded. Then, the job is loaded in the positioner and the sides of the arms are welded. After the welding process is completed the non destructive ultrasonic testing is carried out over the welded regions. The parameter for the weld testing is being set. If the portion fails the ultrasonic test then the job is rewelded to pass the test. Thereafter the arms are straightened within dimensions and send for for further operations (machining, drilling etc.).
For conducting the Hub assembly to the arm assembly joint a groove angle is maintained. The joint design is as shown in sketch as mentioned in Fig 4.
Since the procedure adopted for the present case is a modular form of fabrication that is based on manufacturing the job through sub - assembly construction route, certain perparatory arrangements rae required to be fulfilled in the sub-assembly process so that when the job is finally assembeled no difficulty in regard with welding, positioning et. Is faced. A person skilled in the art will be able to analyze the importance for the steps as mentioned below.
PREPARATORY WORK ON HUB ASSEMBLY
Mark arm location on Hub.
Mark Peripheryof arm on Hub.
Grind Hub ring on periphery - A band of 1.5" on both sides of periphery marking.
PREPARATORY WORK ON ARM ASSEMBLIES
Cut arms to size by gas cutting / machining. Prepare bevel by gas cutting / machining.

Grind bevel to obtain required edge preparation.
The required edge preparation is worked out for the situation of the job as shown in Fig 5 :
Light grind inside surface of arm plates to an extent of about 1/2" from edge.
SET UP ARM ASSEMBLY TO HUB ASSEMBLY
Set up for each arm as per drawing dimensions. The root gaps as mentioned below are maintained during assembly. The Root gaps were worked out considering in-process welding shrinkage. Maintaining these root gaps minimizes grinding work under difficult situation on job at later stages of operation
3.5 - 4.0 mm for sides
4.5 - 5.0 mm for bottom plate
5.0 - 5.5 mm for top plate
PREPARATION FOR WELDING
Tack weld two restraint plates at least 150 mm long at equidistant location on bottom plate
Tack bridge between side plates and Hub ring.
WELDING ARM TO HUB ASSEMBLY
Root and Second Pass are welded only by GTAW process.
Sequence of welding :
Weld root run of arm sides by GTAW process in vertical position (3G) using WPS 003.
Weld vertical welds on opposite sides of arms one after the other
Remove restraint plates of bottom plate of arm
Weld root run on bottom side of arm by GTAW process in flat position (1G ) using WPS 003
Complete welding of bottom side of arm by FCAW process in flat position (1G) using WPS 001
Allow job to cool
Remove job from assembly fixture and load and clamp it in welding fixture.

Weld root run on top side of arm by GTAW process in flat position (1G) using WPS 003
Complete welding of top side of arm by FCAW process in flat position (1G) using WPS 001
Light grind sides to remove high spots and merge ends.
Remove job from welding fixture and load on positioner.
Bring job to vertical position so that side welds are in flat position
Complete welding of sides of arms in flat position ( 1G ) by FCAW process using WPS 001
NON DESTRUCTIVE TESTING ( NDT ) OF WELDS
Ultrasonic Testing is done on welds
Job requirement calls for three angle probes to be used viz. 45° , 60° and 70°.
No indication > 3mm is acceptable.
Any defect should be repaired by welding.
After the fabrication is complete the job is subjected to further operations like drilling, machining etc. after assembly of brake pads and top plates.
Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

We Claim:
1. An improved method for fabrication of a stator carrier of windmill comprising the
steps of:
providing 1 no. Hub assembly and 6 nos. arm assemblies;
setting of the arms to Hub assembly;
performing Gas tungsten arc welding (GTAW) to top three sides and Flux
cored arc welding (FCAW) to bottom sides of arms adopting a specific
sequence of welding steps;
turning the job;
performing welding to top sides of arms;
loading job on positioner;
performing welding to other sides of arms;
performing non destructive testing ( NDT) of welds;
straightening the arms to within dimensions; and
sending for other operations like machining and drilling.
2. An improved method for fabrication of a stator carrier of windmill as claimed in
claim 1 wherein the sequence of the welding comprising the steps of:
welding root run of arm sides by GTAW process in vertical position (3G) using WPS 003;
welding vertical welds on opposite sides of arms one after the other;
removing restraint plates of bottom plate of arm;
welding root run on bottom side of arm by GTAW process in flat position (1G) using WPS 003;
complete welding of bottom side of arm by FCAW process in flat position (1G) using WPS 001;
cooling the job to normal temperature;
removing job from assembly fixture and load and clamp it in welding fixture;
welding root run on top side of arm by GTAW process in flat position (1G) using WPS 003;
complete welding of top side of arm by FCAW process in flat position (1G) using WPS 001;
grinding lightly the sides to remove high spots and merge ends;
removing job from welding fixture and load on positioner;
bringing job to vertical position so that side welds are in flat position;
complete welding of sides of arms in flat position (1G) by FCAW process using WPS 001;

3. An improved method for fabrication of a stator carrier of windmill as
claimed in claim 1 wherein the non-destructive testing (NDT) of welds comprising the
steps of:
ultrasonic Testing on welds using three angle probes viz. 45°, 60° and 70°;
rejecting the samples having defects of more than 3mm;
repairing the defected samples with rewelding.
4. An improved method for fabrication of a stator carrier of windmill as claimed in claim 1 wherein the arm assembly and Hub assemblies are conducted using separate specially configured fixtures.
5. An improved method for fabrication of a stator carrier of windmill as claimed in claim 1 wherein the welding of the top, bottom and side panes and the fabrication of the arm assembly is done separately.
6. An improved method for fabrication of a stator carrier of windmill as claimed in claim 1 wherein for conducting welding of Hub assembly to the arm assembly joint a groove angle is maintained.
7. An improved method for fabrication of a stator carrier of windmill as claimed in claim 1 wherein the preparatory work of Hub assembly before the final assembly comprising the steps of:
marking arm location on Hub;
marking periphery of arm on Hub;
grinding Hub ring on periphery with a band of 1.5 " on both sides of periphery marking.
8. An improved method for fabrication of a stator carrier of windmill as claimed in
claim 1 wherein the preparatory work of arm assembly before the final assembly
comprising the steps of:
cutting arms to size by gas cutting / machining;
preparing of bevel by gas cutting / machining;
grinding the bevel to obtain required edge preparation; preparing the edges of the arms for secure welding;
grinding the inside surface of arm plates lightly to an extent of about Yt" from edge.
9. An improved method for fabrication of a stator carrier of windmill as claimed in
claim 1 wherein the preparatory work of assembling the arm assembly to the Hub
assembly comprising the steps of:

setting up each arm as per drawing dimensions.
maintaining a root gap of (3.5 - 4.0 mm) for sides, (4.5 - 5.0 mm) for bottom plate and (5.0 - 5.5 mm) for top plate
wherein the root gaps are worked out considering in-process welding shrinkage.
10. An improved method for fabrication of a stator carrier of windmill as claimed in claim 1 wherein the preparatory work of welding of the arm assembly to the Hub assembly comprising the steps of:
welding of two restraint plates at least 150 mm long at equidistant location on
bottom plate
tacking of a bridge between side plates and Hub ring.
(Signature of applicant)
11. A fabricated stator carrier of the windmill using the improved method for fabrication of a stator carrier of windmill as claimed in any of the preceding claims.