Surfacing Welding of Oil Drilling Winch Brake Drums on 35CrMo Castings

Literature Overview

This paper by Wan Huijun and colleagues from Nanyang Petroleum Machinery Factory, published in the journal "Welding" in 2005, addresses a long-standing manufacturing challenge in the petroleum drilling equipment industry. The study focuses on the surfacing welding process used to fabricate brake drums for drilling winches, which are critical safety components in drilling operations. The authors describe both the traditional manufacturing route and a redesigned approach that significantly reduces production complexity while improving weldability and structural integrity. The work is particularly valuable because it documents a real engineering problem-solving process involving medium-carbon alloy cast steel (35CrMo), dissimilar material welding, and the interplay between casting rigidity and weld cracking.

Traditional Manufacturing Process and Its Limitations

The conventional manufacturing route for brake drums follows a lengthy and costly sequence: casting, normalizing, rough machining, rivet-welding, stress relief, quenching and tempering, rough machining again, welding of the cooling water cavity, final machining, surface hardening, and assembly. This process involves more than ten distinct operations with multiple transfers between workshops, resulting in high costs and extended manufacturing cycles. The fundamental metallurgical challenge lies in the base material itself. 35CrMo is a medium-carbon alloy steel with a carbon equivalent (CE) typically in the range of 0.45 to 0.55%, which places it in a category with poor weldability according to standard classification schemes.

The high carbon equivalent value means that the material is highly susceptible to cold cracking during welding. The HAZ is prone to hardening during cooling, forming martensite or bainite microstructures with hardness values frequently exceeding 400 HV. When combined with the high residual stresses inherent in thick cast sections, the risk of hydrogen-induced cold cracking becomes significant. Traditional practice requires preheating to temperatures of 250 to 350 degrees Celsius and post-weld heat treatment (PWHT) to relieve residual stresses, which adds considerable energy consumption and cycle time to the manufacturing process.

Furthermore, the dissimilar material welding between the 35CrMo casting and Q235A carbon steel components (connecting plates and cooling water cavity) introduces additional metallurgical complications. The large difference in thermal expansion coefficients and the formation of dilution-sensitive weld metal in the transition zone create conditions that favor cracking, especially given the high structural rigidity of the thick cast section which restricts deformation during welding.

Redesign Approach and Key Technical Solutions

The authors propose a redesigned manufacturing route that fundamentally restructures the fabrication process. The core concept involves using a welded-then-machined approach instead of the traditional cast-then-machined approach. Instead of casting the entire brake drum as a single heavy forging, the redesigned approach uses lighter cast sections for the core body and welds on the required structural features. This reduces the casting weight, minimizes machining allowance, and decreases the number of inter-workshop transfers.

The key technical measures implemented include the following:

The redesigned process route consolidates operations and reduces the number of thermal cycles the material undergoes. By welding the structural features before the final quenching and tempering treatment, the weld metal is brought to a tempered condition along with the base material, ensuring uniform mechanical properties across the entire component.

Engineering Practice Insights and Critical Analysis

From an engineering practice perspective, this case study highlights several important principles in heavy equipment manufacturing. First, the decision to redesign the manufacturing route rather than simply optimize the existing process demonstrates a systems-level engineering approach. The traditional route was not merely inefficient; it was metallurgically problematic because it required welding on a heavily constrained cast section that had already undergone multiple thermal cycles.

The concept of welding before final heat treatment is a well-established principle in heavy fabrication, but its application here is notable because it requires careful planning of the entire manufacturing sequence. The weld metal must be compatible with the quenching and tempering cycle that the base material will subsequently undergo. For 35CrMo, the typical quenching temperature is around 840-860°C with oil quenching, followed by tempering at 560-620°C. The selected welding consumables must retain adequate toughness after exposure to these conditions.

The dissimilar material welding challenge between 35CrMo and Q235A is particularly instructive. The dilution of the weld metal by the higher-carbon base material can lead to a weld metal composition that is harder and more crack-sensitive than either parent material alone. The use of a high-alloy filler metal at the interface, which then transitions to a standard carbon steel filler for subsequent layers, is a practical approach that manages the dilution effect effectively.

This literature is valuable for engineers working on heavy equipment fabrication because it demonstrates that process redesign, rather than process optimization alone, can be the most effective way to solve persistent quality problems. The integration of welding considerations into the overall manufacturing design phase, rather than treating welding as a downstream operation, represents a mature engineering philosophy that should be adopted in modern fabrication shops.