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Detailed Description of the Welding Process

Sep. 05, 2022

1. Rall Preparation

Check the end of the rail. Mainly check the size of the end rail to be welded , and confirm that the end rail is free from damage, cracks and distortion. If there is damage or crack, it must be removed, and the distortion be straightened. When welding old rails, if there is a low joint or damage at the end of the rail head, the part must be cut off. It is recommended to perform flaw detection within 200mm of the welding face If conditions permit.

 

Rall Preparation

 

2. Rail end face cleaning.

--Use wire brush or wire wheel to clean the ends of the rail. To cleaning the end face and the horizontal of the rail. The length of the vertical cleaning is not less than 200mm, and the surface deposits such as rust and oil are removed.

--If there is metal edge on the rail to be welded, use a grinding wheel to polish at least 50mm from the rail end, level with the rail surface.

--If there is a track bed, the ramp from the bottom of gap will be slotted at least 100 mm to provide space for the sand mould installation.

--Place a rail temperature gauge on the side of the backlight of the rail. If the rail temperature is lower than 15 ℃, the rail shall be dried and heated within 1 m on both sides of the rail to remove the moisture on the rail surface.

 

3. Rail End Aligning

--The rail to be welded is padded, and the support pad distance at the joint as close as possible under the condition of easy operation.

--See the smoothness of the joint from a little distance

--Adjust the size of the rail gap to 26~30mm. Place the steel ruler on the side of the two rails bottom, make sure that the bottom of the two rails are level first. Then put the one-meter straight ruler against the side of the two rail heads, so that the two sections of steel rails are tightly attached to the straight ruler.

--Adjust the amount of camber. Place a meter ruler on the top of the rail, center line, and the weld gap, the height of each end is 1.5~2mm. It must be measured with a sharp-point feeler gauge.

--Check that the rail gap, sharp point, horizontal alignment, and unequal tilt adjustments are made after the first adjustment is completed, until adjustment is no longer needed.

--Mark the both side of welded rail in the fourth rail sleeper bottom and the rail bottom plate, to ensure that the weld size is not shifted.

Need to pay attention to the welding process:

> If the rail end has a low collapse, the low collapse depth is greater than 2mm, length is greater than 20mm, it must be cut before welding.

>If the rail head width is different, the rail waist and rail bottom should be aligned first, gap should be filled with paper card.

>If the height difference between the two ends of the rail joint is less than 3mm, it is recommended to align the rail head, and the height difference is eliminated at the bottom of the rail; if the height difference between the two ends of the rail joint is 3~8mm, it is recommended that the difference in the rail height be half at the bottom , half at the rail head.

 

Rail End Aligning

 

4. Mould clamping & pasting

--The sand mould must be inspected before installation as it is fragile, exclude whether there is defective, damp, crack, make sure the vent, gate and riser are unobstructed.

--To fix the sand mold by the mould clamp in the end face of the rail to be welded, check whether the mould bottom plate is aligned with the center of the weld gap, and ensure that the mould clamp is clamped without deviation.

--After the bottom mold is installed, check if any changes of rail on the straightness. If there is any deviation, please re-adjusted.

--Tear off the cardboard cover on the sand mould top to prevent objects falling into the sand mould.

--The sealing paste should be sealed twice. The first time sealed to the outer groove tightly. The second time is sealed again at the intersection of the rail and the sand mould.

--Put a proper amount of dry sand in the slag tray, place it at the specified position, and connect the slag tray and sand mould with the sealing material.

During the sand mould installation and sealing process, pay attention to the following 4 points: 

>Do not screw the sand clamp too tight, otherwise mould will easily crack.

>The center of the bottom plate is aligned with the center of the weld and cannot be offset.

>The sealing material should in appropriate amount. If too much, is not easy to dry during the preheating process, it will cause welding defects. If it is too little, it will easily cause leakage of molten steel.

>When the weld position is on the curve, place the slag tray on the inside of the curve to prevent slag overflowing.

 

Mould clamping & pasting

 

5. Sand mould welding portion preparation

--Check if there is any damage of crucible before use, whether there is floating sand inside.

--Check if the package of welding portion is damage, and no agglomeration, reconfirm whether the welding portion is match to the rail. Gently rotate the welding portion into the crucible, the welding portion appear conical in the crucible, put high temperature ignitor on the portion top and waiting for welding.

--Cover the crucible with the cap to prevent contamination.

--It should be noted that if there is water in the rail, slag tray or crucible during the preparation, it must be dried first before use.

 

Sand mould welding portion preparation

 

6. Preheating

--Before preheating, adjust the distance 47~53mm between the bottom of heating nozzle and the top surface of the rail. At the same time, the center line of preheating device base is aligned with the center line of the rail, preheating nozzle is vertically downward in the center of the weld gap.

--Open the gas cylinder, adjust the gas pressure, ignite the preheating device and adjust the flame, the oxygen valve opens to the end, flame core length is 20~25mm.

--Place the preheating device on the preheating device bracket, record the preheating time.

--Pay attention to the position of the preheating device during the preheating process, to ensure that the flames on the sides of the sand mold are unobstructed and the height is the same. In the windless weather, the flame height from the risers on both sides is 45~55mm.

--By adjusting the mixing ratio of oxygen and combustible gas in the preheating device, Uniform preheating of the rail end face, when the entire end surface of the rail is brightly red when the naked eye is observed, the preheating device is taken out and the heating is stopped. According to the rail type and the quality of the air source, the preheating time can be adjusted. Usually, the preheating time of 60kg/m rail is 5~6min, 75kg/m rail is 6~8min.

--After the preheating is finished, the gas valve is alternately closed to prevent tempering.

--Prepare the plugging rod during the preheating process

Pay attention to the following 2 points during the preheating process:

>The distance between the gas bottle and the oxygen cylinder is not less than 5m, and the distance between the gas cylinder and the flame is not less than 10m.

>During the welding process, it is forbidden to stamp on the air pipe to ensure safe and smooth of gas. Wire cable, air pipe should be away from flame and high temperature operation area.

 

Preheating

 

7. Ignition and pouring

--After the preheating is completed, remove the preheating device. Put in the diverter plug.

--Place the filled crucible on the sand mould, insert the high-temperature match into the welding portion at a 45-degree angle. Insert the depth to 1/3 (about 25 mm)  ignition the welding portion.

--After the portion is ignited, cover the crucible and take the plug standing aside waiting for pouring. The time from the end of preheating to the ignition of the portion should not exceed 30 seconds.

--From flame appearance to shrinking is the reaction time, 8 to 15 seconds usually. When the molten steel appears at the bottom of the crucible, it is the pouring time, after reaction is completed to produce the molten steel called calm time , usually 6 to 18 seconds.

--1 minute to remove the crucible after the end of the pouring , and the slag should be removed after the slag is solidified.

--Record the reaction time and calm time after ignition.

Pay attention to the following 4 points during the pouring process:

>Before ignition, the flammable materials should be evacuated from the work area, free flow personnel are strictly prohibited to close the area. Do not use a preheating device to ignite the portion directly.

>Do not moving rails during welding.

>Crucible and sand mould after pouring shall not be directly touched by hand to prevent burns.

>During the joint cooling, one shot crucible, sand mould and reaction slag should be placed outside of working area to prevent accidents during the operation process.

 

Ignition and pouring

 

8. Demoulding & Shearing

--6'30" after the pouring, remove the sand clamp and sealing material on both sides of the weld. Place the rail shear machine on the rail after cleaning, shearing the extra metal in 8’30’’ after pouring completed. Finally, place the extra metal into the abandoned crucible. The large risers on both sides are swayed apart by the riser separation sleeve, and the small riser is bent so that it does not affect hot grinding in the subsequent step.

--The demoulding & shearing time can be adjusted according to the actual situation.

Pay attention to the following 3 points in demoulding & shearing

>Early removal will affect the quality of welded joint. In contrast, late demoulding will make the shearing process more difficult.

>If the rail temperature is lower than 15℃, apply a heat shield for 10 minutes.

> 15 minutes after pouring, the rail aligning device can be removed.

 

Demoulding & Shearing

 

9. Grinding

--After the shearing is completed, it can be hot polished immediately. Grinding force can not be too large. After the hot grinding is completed, arching value should be greater than the specified value of 1-1.5 mm to prevent low joints after cooling.

--Cold-grinding will start after the joint temperature is cooled to ambient temperature, during the grinding process, the flatness should be checked several times, to prevent the flatness of the rail head exceeding the standard.

 

Grinding

 

10. Cleaning after welding

--cleaning the waste, scrap steel, sand mould etc. after the welding, buried or took to the designated place when leaving. It is strictly forbidden to discard in the turnout or along the railway, it is easily causes accidents.

--If the rail temperature is lower than 15℃, the welding head should be kept warm for 10 minutes after welding.

--After the welding is finished, when the joint temperature is higher than 300 °C, it is strictly forbidden to release the train.

--Fill in the welding record truthfully.

 

Cleaning after welding

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