Hot Rolled Guide Strips for Kelly Bar Production
Guide strips are small sections welded along the tubes of a kelly bar, and they decide whether the telescopic assembly slides smoothly or binds under load. They have traditionally been produced by hot rolling followed by cold drawing, with the second operation there to reach the tolerance class and lift the mechanical properties. Montanstahl developed a rolling process that reaches both targets on its own, through tight process control and optimised tooling, so the strips now come off the mill ready to use, with fewer steps and shorter lead times.
What a Guide Strip Does Inside a Kelly Bar
Kelly bars are central components of rotary drilling systems, transmitting torque and pull-down force from the rig to the tool at the bottom of the hole. They are built as telescopic steel tubes and have to withstand high mechanical loads throughout deep foundation work, with each section sliding inside the next while the whole assembly is under torsion. Guide strips are welded along the tubes to keep everything aligned, allowing smooth telescopic movement and contributing to the structural stability of the bar. Producing them has conventionally meant hot rolling followed by cold drawing, the additional pass being required to reach tight tolerances and improve mechanical properties. The problem is what that step costs, since it adds production time and expense, and the penalty grows with complex geometries or large volumes, exactly the conditions found in machinery manufacturing where these components are produced in series.
Removing a Pass Without Losing What It Delivered
The project set out four requirements that have to hold together. The guide strips had to be produced by hot rolling alone, with no cold drawing stage, which is the whole point of the exercise. Dimensional tolerances had to stay tight along the full length of the section, not only at the sample ends, because a strip welded onto a tube for several metres transfers any variation straight into the running clearance of the telescopic joint. The mechanical properties requested had to be maintained, since the strip is structurally integrated into the kelly bar and carries load rather than simply guiding. Finally the result had to be a genuinely cost-effective alternative to conventional manufacturing rather than a marginal saving. The difficulty is that cold drawing was doing two jobs at once, calibrating the section and work hardening the material, so a rolling process on its own has to compensate for both.
Application Context
Montanstahl developed a hot rolling process that satisfies the dimensional and the mechanical requirements without cold drawing. The result comes from precise process control and optimised tooling, where roll design, temperature management and pass sequence are set so the section reaches its final dimensions inside the tolerance band directly at the mill, with consistent performance from one production run to the next. Removing the extra stage reduces complexity and cost while preserving the quality and reliability a kelly bar application demands, and customers receive a finished product through fewer steps and with shorter lead times, with no compromise on structural integrity. The strips are produced in heat treatable alloy steels, which allow the mechanical properties to be set by the specified heat treatment. Continuous dimensional checks form part of Montanstahl quality management, and questions on which route suits a given geometry are answered in the technical Q&A.