How Railway Sleepers Are Made
Sleeper production at the SGR is of the short line concept. Sleeper are made up-side down and only when they are out of the kiln that they get to be overturned to installation position. Each mould duing casting can hold upto 10 sleepers.
The Standard Gauge Railway Project is use concrete reinforced sleepers as opposed to the steel sleepers used in the old railway. The Chinese standards railway sleepers are made out of steel reinforced concrete. This typically means steel is added during casting to increase overall strength. Concrete sleepers are heavier than their steel counterparts making the track more stable. The section 7 sleeper factory is one of the places where the sleepers are cast for the new track. The factory can produce upto 100+ sleeper per day.
Sleeper production at the SGR is of the short line concept. Sleeper are made up-side down and only when they are out fo the kiln that they get to be overturned to installation position. Each mould during casting can hold upto 10 sleepers in 2 rows of 5 each. Pre-streesed wire is installed into the mould then the concrete is poured. After several hours in the kiln under hot steam, the concrete is cured. The sleepers are then removed and cut into individual sleepers each having a serial number from the mould it was cast in. The following is a step by step production of the railway sleepers.
Preparation of Steel Cabling
In the preparation of railway sleepers, tensioned steel cabling must be inserted into the mould then concrete is poured to increase strength. The first step in the production of the railway sleepers is the preparation of these steel cables. Each sleeper has 8 cables running laterally. The form the ends of the sleepers, flat steel plates are added.
Cleaning and Oiling The Mould
Railway sleepers are made out of moulds which can hold upto 10 sleepers per mould. The moulds have to be first cleaned and oiled evenly to make sure that the sleepers will come off easily at the final step. The oil also helps to produce smooth finish on the surface of the sleeper. From this stage the mould as taken via a conveyor system to the steel section.
Insertion of Steel Reinforcement
The earlier prepared steel wires for reinforcement are now added into the oiled mould and arranged evenly. Since each mould can hold 10 sleepers, the steel runs all the way for 5 sleeper as one unit separated by metal plates.
This is perhaps the most important step. Here a computer controlled hydraulic machine applies tension to the steel cables and locks them under this tension until the curing section. They will remain under tension until the sleeper cures.
Pouring of Concrete
Carefully mixed concrete from the batching plant is added to the mould. This addition is via a movable hopper above the mould. The operator of the hopper has to ensure that the pouring is even.
To ensure that the concrete has uniformly set into the mould, the mould is placed on a bed of vibrators which are timed and apply vibration the mould. This vibration ensures that the concrete has set in properly in-between the steel reinforcement.
A secondary vibration bed vibrates the mould but In this step the sleepers are compacted from the top. A print is added from the steel applying the pressure.
Inspection and Cleaning
From the vibration stage, the mould moves to the inspection where excess concrete is removed from the mould. At this stage, rubber separators are also removed. Once it has undergone visual inspection, it is lifted via a crane and taken into the kiln below.
The curing is done in a sealed kiln with constant steam pressure and controlled temperature and humidity. A high pressured jet of steam and cold water is sprayed on the moulds. After several hours, the mould is lifted out of the kiln and overturned.
Separation of Sleepers
From the kiln chambers, the mould are flipped upside-down and the sleepers fall gently on the conveyor system. At this stage each of the 5 sleepers are still connected as one unit. A a high speed rotating blade that moves back and forth cuts the steel cables separating each to individual sleepers.
Storage and Inspection
All the sleepers from the factory will have to undergo a specific test to guarantee their survival in the outside conditions. Above all a pressure test to see how it will react to the weight of the train. Only after passing this test then they can be taken to the final stage where steel bolds are added to the sleeper for fastening the railway.