2.6　Operation Key Points forCritical Working Procedure

The sleeper is produced by mechanical production line.The production line in the sleeper production yard is composed of concrete pouring device，formwork conveying equipment，automatic hydraulic formwork overturning device，automatic curing device，concrete batching and conveying device.The key equipment（tooling）required for sleeper production mainly refers to sleeper production formwork，batching plant and feeding equipment.The corresponding formwork turnover using and concrete pouring serve are the critical working procedures.

2.6.1　Key points of sleeper formwork application

1.Formwork is the key factor to ensure precise sleeper size，which must be produced by capable manufacturer to meet the high precision and high quality requirement for sleeper production.

2.The precision machined steel formwork shall be adopted，whose structure shall be of adequate strength，rigidity and stability，and shall ensure the precise shape and dimension for all parts of the sleepers and the correct position for the embedded parts.

3.Prior to initial using of the formwork，the appearance and dimension of the formwork shall be inspection，and the defective formwork can not be used.During normal application of the formwork，the formwork shall be periodically detected，it shall be repaired immediately once transformation is detected，only qualified formwork can be used.

2.6.2　Concrete pouring

1.Basic requirement：concrete strength grade shall be C60，and the percentage of cement in concrete should not be over 500 kg/m3.In preparing concrete mixture，the measuring error for water，cement and admixture shall not be over 1％，and the weighing error for coarse and fine aggregate shall not be over 2％.

2.Concrete adopts hopper to evenly charge and continuously output material.The concrete batching speed shall coordinate with concrete pouring speed，to avoid the concrete slump loss for unpoured concrete owing to pouring work suspended for unexpected reasons.The concrete slump shall be controlled within 20～30 mm in winter time，and within 30～50 mm in summer time，the entering formwork temperature shall be controlled within 5～30℃.

3.If concrete surface is even without bleeding，no sinking，and no bubble，which means the concrete has been vibrated compacted.The vibrating time shall be strictly controlled，over-vibration is inappropriate.The pouring in layers can effectively eliminate bubbles.The formwork shall be monitored in concrete pouring，to try to avoid mortar blocking plate loosening and mortar leakage.

4.Upon completion of concrete pouring，the electric trowel shall be used to plaster it manually，to ensure the smooth bottom sleeper.