Primary & Secondary Descaling Technology for Plate Mills & Plate Steckel Mills

Achieving high-quality plate surfaces is a complex task influenced by various factors, particularly as the steel plate surface changes under different atmospheric conditions during hot rolling. To meet the surface quality requirements of end-use markets, high-pressure water hydraulic steel plate descaling is a well-established technology used in both Plate mills and Plate Steckel mills. The current challenge is to achieve these quality goals while reducing energy consumption, optimizing water use, and improving system availability for both new installations and customized modernizations.

Plate mills and Plate Steckel mills produce a wide range of rolled products, each with specific process requirements. A key component of steel plate descaling technology from Primetals Technologies is to design each part of the process to address these challenges, building on established technology.

The Core Principles of Plate Descaling Include

• Maximizing surface quality and system efficiency by using systems that automatically optimize according to the product being rolled
• Optimizing descaling energy, which involves a combination of impact pressure and impingement rate: essentially, how hard and for how long
• Delivering descaling hydraulic power in a manner that minimizes both capital and operational costs while optimizing energy consumption for various process requirements
• Promoting equipment longevity by using optimized header designs to avoid excessive operating pressures
• Ensuring ease of maintenance is integrated into the system design

The optimal combination of nozzle geometry and operating pressure can achieve the best surface quality while minimizing water consumption. Primetals Technologies has successfully utilized nozzle stand-off distances of less than 120 mm for primary descaling. In terms of cost versus benefit, this approach is the most effective for enhancing scale removal. This success is based on ensuring that the combination of impact pressure and water impingement provides the correct balance of thermal contraction and mechanical detachment of the oxide layer, delivering the desired performance. Variable-height primary descaling headers are controlled according to slab thickness to maintain a constant standoff distance and consistent performance.

The Nozzle Tip Stand-Off distance is Crucial for Improving Surface Quality. This is Achieved by

• Maintaining the nozzle angle (rake) for systems with variable heights
• Protecting the nozzle from heat and mechanical damage at each descaler
• Carefully selecting system pressure, which complements optimized stand-off distances
• Using nozzle evaluation techniques to establish baseline performance

Descaling System Sized for the Process

The sizing of the descaling system and selection of pumps are critical steps that follow the optimization of nozzle geometry and header design. This sequence is essential for delivering a future-ready solution.

Descaling System Solutions

For wide plate mills with high throughput, centrifugal pump systems are preferred. Accumulators are used to allow pumps to be sized based on average flow rather than peak demand, making the installation more cost-effective and efficient. Pumps can be equipped with fixed or variable speeds to conserve energy and extend their longevity. For narrow mills, smaller delivery piston-type pumps, possibly with optional accumulator systems, can be advantageous. Both centrifugal and piston pump solutions can be offered as direct-pumped systems without accumulators if this is considered a cost-effective and technically appropriate solution. A piston pump solution offers high operating efficiency both on and off-load. These pumps are capable of operating at variable pressures, providing a flexible and energy-efficient solution, particularly beneficial for lower mill throughputs.

Smart Variable Speed Descaling Solutions for Centrifugal Pumps

Variable speed technology is available either through a variable speed motor or a fixed speed motor driving a fluid coupling. Both options allow for pump control by varying pressure and flow rate. This ability to adjust pump speed can result in a return on investment in less than two years.

Smart Descaling System Design for Low Maintenance

High-Pressure Water Systems

High-pressure water hydraulic descaling is inherently aggressive, pushing equipment to its limits. Therefore, descaling systems by Primetals Technologies include standard features designed to reduce both the frequency and duration of maintenance tasks.

Pump Solutions

Centrifugal pump descaling systems are typically constructed in two basic forms: split-case or barrel type. For plate mills and plate Steckel mills, Primetals Technologies recommends barrel-type construction.

Key Advantages Include

• The ability to completely replace pump internals in situ using an exchangeable cartridge
• The pump is driven, and optimal RPM is achieved via a speed-up gearbox. This design requires fewer pump stages, reduces shaft deflection, and enhances longevity.
• Critical areas are constructed from stainless steel to combat erosion from high-pressure water.

Piston pumps offer:

• Ease of maintenance, requiring only basic training and hand tools
• The ability to take a small portion of the pump capacity out of service while keeping the rest of the system operational
• Cost-effective spare parts solutions with low lead times
• Low connected electrical load at startup through the use of cascade control and off-load starting

Valve Solutions

The extensive use of cartridge valves constructed in stainless steel manifold blocks ensures a long-term, leak-free solution.

Header Solutions

Primary descaling nozzles are accessible without entering the confined area of the descaler. The top header can be raised to a maintenance position above the enclosure, while the bottom header can be moved sideways to a secondary maintenance position.

Descaling Upgrades for An Existing Plant

Primetals Technologies can audit the current processes and develop a tailored solution to meet both present and future needs, focusing on:

• Surface quality
• Efficient energy and water usage
• Enhanced system availability