Sunday, September 25, 2011

Report of Summer Training at BHEL Insulators Plant Jagdishpur, Amethi, Uttar Pardesh


This report is just a brief summary of our detailed training at BHEL Insulators Plant  Jagdishpur. I hope this will help you in making the report.

PRODUCTION OF DISC NSULATORS

Internal structure of disc insulator


         TECHNICAL CHARACTERISTICS:

Rating                      :    45 kN to 210 kN EMS

Creapage Distance   :    192mm to 380mm

Locking Device       :     R / W Type in PB / SS

Glaze Color              :     Brown / Grey

Applications             :    Transmission Lines from 11 kV to765 kV AC & 500 kV   

                                      and 800 kV HVDC, Substations

PROCESS FLOW CHART OF DISC INSULATOR MANUFACTURING:




·         Jiggering                :       Forming Process

·         Finishing                :       Dimensional control & Surface smoothening to enhance

·         Extrusion               :       Filter press cakes to Blanks Glaze adherence

·         Drying                    :      Removal Moisture to < 1%

·         Inspection              :       Segregation of defective insulators

·         Glazing                   :      Application of glaze ( Brown/ Grey )

·         Firing                      :      Tunnel kilns / batch Kilns

·         Inspection               :      Segregation of defective insulators

·         Hydraulic Testing   :      Weed out defective insulators at Head portion

·         Thermal Test           :     Withstand thermal shock

·         Assembly                :     Joining of Metal parts ( Cap and Pin) with Cement

·         Curing                     :     Hardening / Strengthening of cement

·         Final Test                :     Mechanical Test ( At 40% of rated ) and High voltage ,

  High  Frequency Test      

·         Packing and Dispatch

SLIP HOUSE:

The slip house performs the following operations. All these materials are used in different quantities for different type of insulators that are manufactured and demanded by the customers.

 The raw materials required for manufacturing the insulators are:

 

FIRST CHAEGE:

·         Quartz

·         Feldspar(stone powder)

·         Pyrophillite

·         River pebbles

·         Bikaner clay

·         Felsites

·         Alumina

 

SECOND CHARGE: These are different type of clay.

·         Than clay

·          Ellure clay

·          Ball clay

·         Chaibasa clay

·          Japan ball(J.B.)clay 

·         China clay


WHEREHOUSE:

The production in the BHEL runs 365 days, and it is a continuous process. Here raw materials are tested before manufacturing the insulators so that raw materials obtained from places satisfies their requirements.

 

CRUSHING PLANT:

Above said materials other than clay are available in the stone form. Crushing plant is used to crush these raw materials into powder form and also it is used to powder the rejected ones for recycling.

 

WEIGHTINGS:

 The raw materials are required to be mixed in different composition. Therefore weighment of raw material is done. Different raw materials from the storage bins are collected and weighed according to the percentage composition given by the E&D and according to the ball mill capacity to be charged. Then the weighing card is attached to the lot.

 CHARGING:

It is a preproduction section. Before the actual production starts the raw materials have to undergo a certain specific process. In the slip house the raw materials are got from the material management department. These raw materials are mixed into certain composition according to customer need then these are fed to ball mills.

 

BALLMILL:

Above said materials other than clay are available in the stone form. Crushing plant is used to crush these raw materials into powder form and also it is used to powder the rejected ones for recycling. The raw materials are required to be mixed in different composition. Therefore weighment of raw material is done.

 Weighted raw materials including clay are mixed with sufficient water i.e. 50% of raw materials and 50% water and grinding in the ball mills for duration of (17+3) hours; it is a continuous process round the clock. In the first phase of charging feldspar and quartz is mixed with water for 17 hour, after that clay is mixed for next 3 hours. The materials obtained in the ball milling process are called slip or ceramic slurry.

 

RIVER-PEBBLE CHARGING:

For initial charging of river pebble in the ballmill after rolling large ,medium and small pebbles are collected as per standard samples and weighted as per specification number(PPSL: 0100 R-2 )and pebbles are charged as per the quantity specified.

The raw materials are loaded per composition into "ball-mills". In ball -mills  'river -pebble' are put as grinding   -media. When ball -mill is operated the grinding media and raw material produced the file paste called 'slip'. The ceramic slurry got from the ball mill is fed to the vibrator screens to check for the correct accumulation throughout the materials and also to remove solid particles. Then the material will be having too less impurities and then goes for filter press to extract water by pressing that ceramic body with high pressure This slip is the input for the 'filter- presses to produced the 'cake'. This cake is output of slip -house and serves as input for manufacturing Jiggering.

 

PREPARATION OF FIRST CHARGE BODYSLIP:

 Weighed quantity of first charged raw materials is charged into the ball mill by attaching a cone to its hole from the charging hole on the platform. The pebbles are cleaned with water before charging and then specified quantity of water is charged into the ball mill. Generally charging takes 1-2 hours and ball mill runs 14-16 hour.

 

PREPARATION OF SECOND CHARGE BODY SLIP:

 Weighed quantity of second charge is charged into the ball mill with required quantity of water after preparation of first charge body slip and the ball mill is run for specified time. Then the slip is discharged into the mixing tank and is agitated continuously.

 

BLUNGING RETURNS SLIP:

 Scrap and water returned by the process is charged into the blunger in specified proportions to get required specific gravity of the slip. Then it is blunged to achieve homogeneous slip.

 

VIBROSCREENING – SEPERATION/DEMAGNITIZATION:

Here the slurry is transferred to the tank from the ball mill to remove the unwanted materials like threads of the plastic bags in which the raw materials are stored, wooden pieces through vibration and electromagnetic separation. This tank is called discharge tank.

 

SLIP AGITATING:

After screening, the ceramic slurry is transferred to another specially built bank called top tanks. From this it passed through two vibratory screens which will be rotating continuously to avoid accumulation of raw materials at the bottom and after on top. Then the mixture is fed to Ferro Filter for removing the iron particles. Finally the fresh slip is collected in the fresh tank or storage tank.

 

 

PREPARATION OF CAKE:

The slip from the initial tank is pumped into the press using plunger pump and then adequate pressure is applied to turn it into a cake. Here the slip house work is complete.

 

FILTER PRESSING – DEWATERING:

It is dewatering process. In this process 80% of the water is removed from the slip so as to convert the slip into cake form using nylon clothes. In this process high pressure is applied by compressing them from both sides.

 

PUGGING:

It is a de-airing operation under vacuum. The cakes are filled into pug mills to remove air bubbles present in the cakes. In the pug mill homogenous mixing of cakes takes place. The product which comes out after pugging process is called as blanks. Blanks are extruded from the pug mills in the cylindrical form of different sizes for different types of insulators. In this process the moisture content is reduced up to 22%. Cylindrical Blanks are shaped conically by pre shaping machine to facilitate Proper compaction during forming process.

 

JIGGERING – FORMING OF DISC INSULATORS:

The input for Jiggering station is cake produced by slip -house. The cake are fed into 'pug-mill', which under vacuum homogenous Cake in cylindrical form, which is cut automatically in required length (as per product), called pugs. These pugs are fed into Jiggering machines, which at first go impart initial shape of insulator shells. The secondary or final die gives the final shape shell. These green stage shells are dried in CD (chain-dryer). After drying these shells are taken out of modes and send for finishing.

Pre-shaping blanks are placed into Moulds which inner side has lining of plaster of paris and shaped on Automatic Jiggering Machine. To avoid sticking between The Die and the mould, a mixture of Kerosene oil and Coconut oil is used as Lubricant.

Aluminum Bronze Dies machined and carefully profile finished are used to Shape the insulators. Profile shaped by the Die will not be disturbed further. Insulators are ensured for defects free. Mould will have Aluminum outer Casing for strength and lining of Plaster of Paris – porous material with water absorbing property which facilitates to separate the insulators some time after Forming Jiggering.

 

DRYING:

Insulator after forming are dried In Chain Dryers at 30 to 35 degree centigrade for about 2 to 3 hours to facilitate separation of Insulator from the mould easily.

The different drying steps are as follows:

 

CHAIN DRYER:

These dries are used for drying the disc insulators. After this process the insulators will be having less than 15% moisture.

 

 

BLANK DRYER:

For hollow insulator and solid core insulator the blanks produced by pug mills are directly fed to these blank driers. For making the hollow insulators and solid core insulators the hardness of blanks is very much necessary. Therefore blanks are dried to see that the moisture content is less than 15%.

 

MOULD RELEASING OF DISC INSULATORS:

Insulators are separated from moulds over Aluminum Ring which supports Green Insulator and helps in handling the Insulators at further stages. Insulator are loaded gently to the Racks and moved to Humidity controlled storage chambers to attain leather hard condition (stored for 10 to 12 hours at ~ 60% Humidity).

 

OIL INSPECTION:

After the disc insulators are dried from chain dryer, they will go for finishing operation. Those processes give a perfect shape for the product and then the visual and oil inspection is carried out for the quality of the product.

 

FINISHING:

The article is placed on the rotating wheel and adequate layer of mass is removed without affecting die formation. Dimensional control & Surface smoothening to enhance Glaze adherence .Insulators of specified Hardness (Moisture content) finished for Specified Dimensions like-Head diameter Head diameter and Thickness are the most critical dimensions being maintained stringently.

 

INSPECTION- SEGREGATION OF DEFECTIVE INSULATORS:

Insulators are inspected for different Defects. Originated due to stresses induced during forming, mould releasing, and handling, based on the Position helps in analysis and initiating corrective steps at previous stages.


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