Process

MANUFACTURING PROCESS FOR M.B.C. SLEEPERS

BASIC RAW MATERIALS
The essential raw materials for the manufacture of M.B.C. Sleepers are:-

High Tensile Steel Stranded Wire (H.T.S. Wire) (Confirming to IS: 6006)
High Strength Portland Cement (Confirming to IRS T-40
Spheroidal Graphite Cast Iron Inserts (As per Drg. No. RDSO/T-381)
Graded Stone Chips (B.T. Metal) (Also called Coarse Aggregates)
River Sand (Also Called Fine Aggregates)

Presently, the H.T.S. Wire and the Cement are purchased directly by the manufacturer from Railway approved sources, against the rates fixed by the Railway Board. The Railways supply the SGCI Inserts free of cost. Stone chips and the sand is locally available and is brought to the Factory Site by Trucks.

MANUFACTURING PROCESS
Our factory uses Stress Bench Method for the manufacture of M.B.C. Sleepers. A stress bench is steel structure made of Steel Channel to hold sleeper moulds in a straight line. Each stress bench is about 11.5 Meters long and contains 4 moulds.

First of all the moulds are cleaned and all the moulds are then greased and oiled using Mould Release Oil. Four Inserts are then fixed in each mould, holding them securely in place using steel pins. The H.T.S. Wire,
which has already been previously cut into Steel Stress Bench with Sleeper Moulds
lengths of about 11.7 meters each,
is then reeled through all the four moulds and the bench
end plates. The stress bench is brought to the tensioning bed.
The tensioning is done using Hydraulic Jacks.

The stress bench is now ready for Casting. Meanwhile, when the stress bench is being prepared and tensioned, the batching of the Coarse and the Fine Aggregates is carried out using a microprocessor-based weigh-batcher. After weighing the aggregates, the required quantity of cement is added to the aggregates, and this mix is then put into the mixer drum. The stress bench is now brought to the casting bed. Two high frequency shuttering vibrators are then fixed onto each mould. The mixed concrete is then poured into each mould layer by layer, compacting it with the help of shuttering vibrators.

The stress bench is then put into the steam chambers and the chamber covered with Tarpaulins, where each bench is subjected to steam curing for a period of about 12 Hours. The steam is generated using a coal-fired boiler.

If the required strength has been achieved, the stress bench is taken out of the steam chamber. The mould end plates are then opened, and the H.T.S. Wires cut using welding electrodes. The sleepers are then demoulded from the moulds using demoulding Tackle.

The demoulded sleepers are then put into the water curing tanks Each sleeper is then also checked for its dimensions and surface finish. After checking and marking, the tank is filled with water, whereby the sleepers are subjected to Water curing for a period of 15 days.

TESTING AND DISPATCHING
After the curing is complete, one sleeper is taken out at random from each lot, which is tested for its strength using Static Bending Tests. Based on the strength of the concrete and the sleeper test results, each lot is given its category.
After testing and categorisation, the sleepers are taken out of the curing tanks, and are stacked along the railway siding, from where they are loaded into the Railway wagons or the road lorries/trucks, as the per the requirement.

Casting of sleeper using shuttering vibrators

QUALITY ASSURANCE PLAN ADOPTED BY THE UNIT TO ENSURE QUALITY OF PRODUCTION

Presently, the sleepers are manufactured as per Indian Railway Standard Specification for PSC Concrete Sleepers IRS-T-39, revised in May 1996.
The IRS-T-39 specifies all the quality control measures to be taken while manufacturing concrete sleepers.
The various measures taken by the unit to control the quality are as described below: -

PROCUREMENT OF RAW MATERIALS
Whenever HTS Wire is procured, the prior inspection of the Wire is done jointly by the Assistant Inspecting Engineer (AIE) of the Central railway along with a representative of our factory, at the wire manufacturer's site. Upon arrival, the HTS is stored under covered godown to save from rain and moisture. The HTS Wire is always procured from Railway approved sources.
The cement is always procured from railways approved manufactures. With every consignment of cement, a test certificate, in the format approved by the RDSO, is obtained mentioning all the critical values. Once the cement is received in the factory, all the tests are done in the laboratory, to check its strength and fineness etc. These tests are carried out once every week. It is ensured that the cement is always used on the first received, first used basis.

The SGCI/MCI Inserts are supplied free of cost by the Railways. These inserts are always tested by RITES and Test Certificate from RITES accompanies every consignment of Inserts. But in spite of that, some sample inserts are always checked and measured at the factory site for their critical dimensions, before being used in production.

The stone aggregates are procured from the near by crushers. Every week, the aggregates are tested for their grading and size. They are also tested for Flakiness and Elongation Index. If there is any change in the Grading, the mix proportions are adjusted accordingly.

The water used for making and curing concrete is tested once a year by any government approved agency, so that it confirms to IS: 456.

CONCRETE MIX AND CASTING
The concrete produced is of controlled quality. First of all, before the concrete mix is prepared, the quantity of water to be added is ascertained by taking into account the water absorption of the aggregates. The proper grading of the aggregates is ensured. The mixer used by the factory is one of the latest available that uses cyclo-pan drum that ensures positive mixing. The weighing of the aggregates is done using Microprocessor based automatic weigh-batcher.

With every lot, some concrete cubes are cast, which are used to ascertain the strength of the concrete. Every month, a statistical analysis of the cube test results is carried out, to ensure that the results are within the design parameters.
After mixing. It is ensured that the mix is used as early as possible. The mix is poured in layers in the moulds, each layer being compacted by use of high frequency shuttering vibrators.

STRESSING OF HTS WIRES
The HTS wires are stressed using Hydraulic Jacks. It is ensured that equal and uniform load is applied to all the strands. The load applied is read from a dial Guage attached to the tensioning machine. It is counter checked by measuring the elongation of the wires. An auto cut-off switch that is provided in the tensioning machine ensures that the wires are not over-stressed.

CURING OF SLEEPERS
The initial curing of the sleepers is done by steaming at atmospheric pressure. The steaming is done strictly as per the steam curing cycle approved by the RDSO. The temperature of the steam curing chambers is recorded every half hour by hand held mercury thermometers as well as dial type thermometers which are embedded in the steam chambers.

After demoulding, the sleepers are further water cured for 14 days. It is ensured that the sleepers are fully submerged in water and that the water is free of any impurities.

TESTING OF SLEEPERS
After the curing is complete, one sleeper is taken out at random from each lot, which is tested for its strength using Static Bending Tests. The testing is done by the Railway's Inspecting Engineers and Inspectors. Along with the sleepers, three test cubes are also tested for the representative strength of the concrete. Based on the strength of the concrete and the sleeper test results, each lot is given its category. The various tests that are carried out for the sleepers have been described in details under "Details of Facilities available with the manufacturer."

CALIBRATION OF GAUGES AND METERS
All the measuring instruments and gauges are periodically calibrated using Master gauges and proving rings, as per the schedule provided in IRS-T-39. These master gauges and proving rings, in turn, are calibrated by some government approved testing houses.

GENERAL QUALITY CONTROL MEASURES TAKEN
It cannot be denied that the control of quality has to start from the base level, only then complete control of quality can be achieved.
The factory has all the required technical staff, civil engineers, Diploma Holders, ITI certified technicians and electricians, Boiler operators etc. It is ensured that each one of them ensures his contribution towards quality. Even every worker has been taught the importance of quality.

The railways have appointed an Assistant Inspecting Engineer (AIE) and an Inspector of Works (IOW), to ensure that the quality norms are strictly adhered to.
Besides these measures, the RDSO Lucknow, carries out its periodic inspections to ensure that the quality norms are being followed. It would not be out of place to mention here that in the last inspection by the RDSO, the RDSO has observed a great improvement in the working of the factory and they have expressed their satisfaction over the quality of the sleepers being produced.