From sectional cutting inside inspection, the surface is not smooth, it occurs in the central triangle area of the rail waist and the rail bottom.
Analysis why it will happened?
-Preheating time is too long, with overheating phenomenon because of high temperature in part area, especially in rail waist.
- Offset installation of preheating gun or sand mold.
-Large welding gap.
How to prevent?
-Appropriate preheating time, do not burn the rail end.
-Good control flame length between 12~15mm.
-The preheating gun is installed in the center of the rail gap.
-The rail gap must between 25~28mm.
Analysis why it will happened?
-Incomplete cleaning of rails
-Thermit portion is wet
-Sand mould is web
-Too much luting sand, or too wet.
- Low Preheat temperature.
How to prevent?
-cleaning of both ends of the rail to be welded thoroughly.
-Strictly prevent the welding material from getting wet.
-The sealing paste should not be too wet or used too much.
-Rail preheating temperature needs to reach 700~900℃.
Analysis why it will happened?
-The cleaning of the rail surface is incompletely, there are containing metal oxide and iron oxide slag.
-Weld gap is too large, or "running out of sand mould"
-The calming time is not enough, when reaction is not completed before pouring and the slag is not completely separated from the molten steel.
How to prevent?
- Cleaning of both ends of the rail to be welded thoroughly.
- The rail gap must between 25~28mm.
- Carefully check the crucible not damage before use, put the crucible in the centre of sand mould.
Analysis why it will happened?
-The welding gap moves position during the welding process, large tensile stress existed.
- Premature unpacking makes the weld head acting force too fast.
- Premature shearing process makes the welding head acting force too fast.
- External hammering is received when solidification is not completed during the cooling process
- The rail shrinks before completing solidification during the cooling process.
How to prevent?
-In the whole welding process DO NOT stepping, knocking, prying to be welded rail.
-Unpacking sand mould and shearing according to process requirements.
-Strictly prohibited to remove the rail equipment when weld head temperature higher than 600 ℃.
-Big shrink according to the temperature, rail tensioner can be used to maintain the size of the rail gap.
Analysis why it will happened?
-The cleaning of the rail surface is incompletely, there are containing oxide scab.
-Preheating temperature is too low, aluminum hot steel is not enough to melt the rail head.
-Rail gap is too small, the capacity of aluminum hot steel liquid within the weld is small and fails to fully melt the rail head.
How to prevent?
- Cleaning of both ends of the rail to be welded thoroughly.
-The preheating temperature shall up to 700~900℃.
-Appropriate welding gap between 25~28mm.
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