LP – welding with long preheating times

Welding involving long preheating times is the most commonly used aluminothermic welding process worldwide. By virtue of various developmental steps, in recent decades preheating time has been reduced from more than 20 minutes to between 4 and 6 minutes. The combination of small portions and lengthy preheating time takes into account all economic and technical requirements for modern track laying. This technique is successfully employed for both high-speed and heavy haul tracks.

Using the original SoWoS and SmW-F techniques, Pandrol GmbH developed the LP technique, which has long since proven its worth. Apart from process stability and reliability, this technique offers the metallurgical advantages of long preheating times for the laying of continuous tracks.


Metallurgical properties

  • Very high level of reliability in terms of elongation at break values
  • Small area affected by heat, as for the SkV / SP process
  • Homogeneous fusion zon
  • Low internal stress thanks to homogeneous elimination of heat centers
  • Rated for all steel qualities; only a suitable portion need be selected

Process characteristics

  • Preheating time ranges from 4 to 6 minutes, depending on the rail profile.
  • Rectangular riser feeder geometry with adequate width makes it easier to center the forms; plus it’s possible to verify at any time that the forms are in the correct position.
  • Thanks to the use of special binders and additives, the high-quality form sand eases the task of working on contours, and ensures high stability for robust worksite use.

Overview of our processes:

  • SkV-P & SP
  • LP
  • LP groove
  • SKS

Paste or sand?

Paste allows for avoidance of the following welding errors:

  • Gas bubbles owing to unduly damp sand
  • Sand inclusions
  • Bubbles from sand inclusions
  • Pores on welding collar beads
  • Leakage Outliers owing to unduly dry sand

Rectangular riser section