Application of Tubular Wire Submerged Arc Surfacing to Nonwoven Fabric Industry Hot Rolls

Literature Overview and Background

This paper, published in 1998 by Pang Ming and Fu Wenlong from the Shanghai Textile Machinery Research Institute and Shanghai Dayang Welding Technology Engineering Company, addresses a niche but practically significant application: the use of tubular wire submerged arc surfacing (SAW) technology to repair hot rolls used in nonwoven fabric production equipment. The authors note that tubular wire SAW surfacing is already a mature technology in the steel industry for manufacturing and repairing hardfacing components and rolling mills, and they propose transferring this technology to the textile machinery sector. The target application is the restoration of worn hot rolls in nonwoven fabric lines, with the stated objectives of reducing roll replacement costs, improving surface quality, and extending service life.

Core Technical Points

Tubular Wire SAW Surfacing Fundamentals

Tubular wire surfacing welding utilizes hollow tubular electrodes filled with flux or alloy powder, which distinguishes it from solid wire SAW in several key aspects. The tubular geometry provides a self-shielded or semi-shielded arc with higher arc energy density, enabling deeper penetration and better dilution control. The internal flux or alloy content allows for precise chemical composition adjustment of the deposited layer without requiring external flux supply, which simplifies the process setup and improves deposition efficiency.

Parameter	Typical Range for Tubular Wire SAW Surfacing
Arc voltage	28–38 V
Welding current	350–600 A
Travel speed	250–600 mm/min
Wire diameter	1.6–3.2 mm
Single-pass deposition rate	8–25 kg/h
Typical overlay thickness per pass	1.5–3.0 mm

Application to Nonwoven Fabric Hot Rolls

Hot rolls in nonwoven fabric lines operate under conditions of moderate temperature (typically 150–250°C depending on the polymer being processed), continuous contact with molten polymer, and mechanical wear from fabric friction. The primary failure modes are surface wear, thermal fatigue cracking, and polymer adhesion buildup. The authors argue that a properly designed surfacing layer can address all three failure modes simultaneously.

The key design considerations for the surfacing layer on these rolls include:

Hardness requirement: The overlay hardness should exceed 350 HV to resist abrasive wear from the fabric surface and any embedded abrasive particles.
Thermal stability: The coating must maintain its hardness at operating temperatures without significant softening, which requires a carbide-based or martensitic microstructure with secondary phase stabilization.
Surface finish: The roll surface roughness after surfacing must be controlled to Ra ≤ 1.6 μm to ensure proper fabric web formation and prevent surface defects in the nonwoven product.
Bond strength: The metallurgical bond between the base roll steel (typically low-carbon or low-alloy steel) and the overlay must withstand thermal cycling without delamination.

Process Considerations

The application of tubular wire SAW to nonwoven fabric hot rolls requires careful process planning. The authors suggest the following approach:

Surface preparation: Complete removal of the worn layer by grinding or machining to expose sound base material. Preheating to 250–350°C is recommended to reduce hydrogen absorption and minimize residual stress in the base metal.
Underlay pass: A transition layer of austenitic or nickel-based alloy may be required to reduce dilution and improve bond strength when surfacing hardfacing alloys onto low-carbon steel substrate.
Overlay passes: Multiple passes of the hardfacing alloy are applied to achieve the required thickness (typically 2–5 mm total overlay). Each pass is deposited with overlapping to ensure uniform coverage.
Post-weld treatment: Controlled cooling or stress-relief annealing at 550–650°C for 1–2 hours to reduce residual stresses. Final grinding to achieve the required dimensional accuracy and surface finish.

Engineering Practice Integration

From a practical standpoint, this paper represents an early example of technology transfer between industries. The nonwoven fabric industry in the late 1990s was experiencing rapid growth in China, and the cost of replacing hot rolls was becoming a significant operational expense. By applying proven steel industry surfacing technology to textile machinery, the authors demonstrated a cost-effective repair strategy.

However, several practical challenges must be acknowledged:

Geometric constraints: Hot rolls have cylindrical geometry with relatively small diameters (commonly 200–500 mm), which requires specialized welding fixtures and potentially multi-position SAW equipment.
Dimensional tolerance: After surfacing, the roll must be re-ground to precise dimensional tolerances (typically ±0.05 mm for diameter), which requires sufficient overlay thickness to allow for post-weld machining.
Production downtime: The repair process must be scheduled to minimize production line downtime, which favors the relatively high deposition rate of tubular wire SAW over manual processes.

The authors also note that the improved surface quality achieved through surfacing can reduce polymer adhesion, which translates to fewer fabric defects and reduced cleaning frequency. This represents a secondary benefit beyond the primary objective of wear life extension.

Key Questions and Reflections

Several questions arise from this paper that merit further investigation. First, the paper does not provide detailed metallurgical characterization of the overlay microstructure or specific hardness profiles. For engineering application, quantitative data on microhardness distribution, phase composition, and wear test results would be essential for process qualification.

Second, the long-term performance of the surfacing layer under thermal cycling conditions is not thoroughly addressed. Hot rolls in nonwoven fabric lines experience repeated heating and cooling cycles, and the overlay must resist thermal fatigue cracking. The residual stress state of the multi-pass overlay is critical in this regard.

Third, the paper could benefit from a cost-benefit analysis comparing the surfacing repair approach with full roll replacement. Such analysis would include material costs, labor costs, downtime costs, and the number of service cycles achieved, providing a clear economic justification for the technology.

Study Insights and Implications

This paper, while brief, illustrates an important principle in welding engineering: mature technologies developed for one industry can often be adapted to serve other industries with different but analogous requirements. The tubular wire SAW process, refined over decades in steel rolling mill applications, offers a ready-made solution for hot roll repair in the textile sector. The key lies in understanding the specific failure mechanisms of the target application and selecting the appropriate alloy composition and process parameters.

For practicing engineers, this paper serves as a reminder that technology transfer requires careful adaptation rather than simple copying. The process parameters, alloy selection, and post-weld treatment must all be tailored to the specific operating conditions of the nonwoven fabric hot rolls. The paper's value lies in establishing the feasibility of this approach and opening a path for more detailed engineering development in subsequent work.