Engipress - Pre-Stressed Monoblock Concrete Sleepers for the Indian Railways

Engipress Industries Limited, a leading manufacturer of concrete sleepers in India, is a 25-year-old public limited company.

The company is an ISO 9001 accredited RDSO approved supplier of pre-stressed concrete sleepers (ties) to the Indian railways. The various types of sleepers produced include sleepers for: main lines, 1 in 8 ½ and 1 in 12 turnouts, 1 in 8 ½ scissors crossovers, derailing switches, level crossings, rail expansion joints, bridge approaches and guard rails.

Engipress has also supplied sleepers for the prestigious Delhi Metro Rail Corporation (DMRC) project. The existing capacity of the plant is about 17,500 sleepers per month. To date, the company has supplied about 2 million sleepers to the Indian railways. Its manufacturing unit is based at Banmor, District Morena, in the state of Madhya Pradesh.

STRESS BENCH ON ROLLER SYSTEM - A PROVEN METHOD OF MAKING CONCRETE SLEEPERS

Sleepers are manufactured using the Short Stress Bench method. A stress bench is a steel structure made of steel channel, which holds sleeper moulds in a straight line. Each stress bench is about 11.5m-long and contains four moulds.

In the 'stress bench on roller' system, the stress benches move on steel rollers and the whole system resembles a merry-go-round. This method is advantageous over the long line method as the length of the shed required is much less, reducing capital cost to a large extent. Moreover, a single mould can be used twice in one day, if two systems shift-work.

MANUFACTURING CONCRETE SLEEPERS USING THE STEAM CURING METHOD

The Steam Concrete Curing system of sleeper manufacturing achieves the early release strength of concrete. Another big advantage of this system is the flexibility of switching from one type of sleeper to other type, e.g. from main line to turnout sleepers, in a very short time, which makes this system highly adaptable for manufacturing different types of sleepers in the same unit.

Concrete sleepers, which are pre-tensioned type, are made using 3mm x 3-ply stranded High Tensile Steel (HTS) wire. The rope-like structure of HTS wire helps to develop a high bonding strength between steel and concrete.

PRE-STRESSED MONOBLOCK CONCRETE SLEEPERS - THE PRODUCTION PROCESS

First of all, the moulds are cleaned, greased and oiled using mould release oil. The next step involves fixing the mould end plates using nuts and bolts. The HTS wire is then reeled through all four moulds as well as the bench end plates. The stress bench is brought to the tensioning bed. The tensioning is carried out using hydraulic jacks.

The stress bench is then brought to the casting bed. Two high-frequency shuttering vibrators are fixed onto each mould. The mixed concrete is 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, where each bench is subjected to steam curing for a period of about 12 hours.

If the required strength has been achieved, the stress bench is taken out of the steam chamber. The end plate bolts are loosened, transferring the stresses to the concrete. The mould end plates are opened, and the HTS wires are cut using welding electrodes. The individual sleepers are then loosened using a tackle. The sleepers are de-moulded from the moulds using de-moulding tackle. The de-moulded sleepers are put into sleeper-carrying trolleys.

After the curing is complete, one sleeper is taken out at random from each lot and is tested for its strength using static bending tests. After testing, the sleepers are taken out of the curing tanks and are stacked along the railway siding, from where they are loaded into railway wagons or road lorries / trucks, as per the requirement.