Continuous Casting General Direction and Topics to Study


This article lists major technical topics on the continuous casting to be studied and understood, in order to qualify for plant operational and maintenance personnel. Topics 1-7 are for the operational personnel, 8-16 for maintenance personnel, and 17-18 are for both.

1. Initial Solidification and Oscillation Mark Formation

(1) Initial solidification at the meniscus is crucial to the surface quality of continuously cast steel. The phenomena that govern initial solidification are explained, with emphasis on how surface quality problems arise.

(2) Each mold oscillation cycle generates a periodic transverse depression called an "oscillation mark" and sometimes also a sub-surface microstructural feature called a "hook". These features usually form due to meniscus overflow and depend on the alloy composition, superheat, fluid flow and level fluctuations, heat transfer to the mold walls, slag properties, and oscillation practice.

2. Functions of Mold Flux

Hydrogen grossly impacts the performance of mold flux.

(1) The mechanism for this change in mold flux performance
(2) Signals and strategies for dealing with hydrogen

3. Sources of Reoxidation and Why to Avoid

To produce high-quality cast products, steel must be protected from reoxidation. Reoxidation can occur in the ladle, at secondary ladle metallurgy operation, and also in the transfer operations from ladle to tundish and tundish to the mold. Various techniques can be used to minimize reoxidation.

4. Caster Secondary Cooling Discussion and Water Treatment

Need an understanding on the variances between hydraulic and two-fluid atomization and on how it applies to everyday production and maintenance personnel.

The nozzle technology and the critical factors that affect spray quality in the steelmaking process need to be understood. From traditional sheet mills to small billet casters, the efficiencies of nozzles should be studied. In addition, there are water treatment-related challenges and needs in continuous caster secondary cooling systems and the potential impacts that secondary water quality can have on the operational and maintenance aspects of a caster.

5. Copper Coatings and Roll Technologies

There are a variety of mold coating options and the roll overlays, base materials, and new roll technologies developed for all types of continuous casting machines.

6. Mold Design, Copper Base Alloys, and Mold Failure Mechanisms

Topics need to be covered include: the advantages/disadvantages of commonly used mold alloys; types of molds, i.e., plate, dogbone, tube; and performance factors, such as cooling, inside geometry, cracking and wear distortion.

7. Strand Solidification

Solidification of the as-cast product starts in the CC mold and continues with the supported section of the cooling machine. The impact of superheat, heat transfer and machine design on cast quality need to be understood.

8. Caster Lubrication and Bearings

Bearings are a critical part of the successful operation of a caster. Proper installation is the first step to ensure that the bearings will last several thousand heats. Lubrication of caster segment bearings is also a critical factor in the successful operation of the segment. The slow speeds, high temperatures, and large volume of water present many demands on the lubricant and preventive maintenance practices. Topics on lubrication principles, grease characteristics and performance tests, modern application of grease, and grease vs. air-oil, etc. should be studied.

9. Segments, Rolls, and Overlay Technologies

Benders, zones and segments are critical to the proper containment and quality of steel. Studies should be focused on design variations for both equipment and rolls, as well as the key elements of component maintenance and alignment. Additionally, roll life can be significantly increased through the use of engineered overlays and base materials. By targeting roll erosion, corrosion, wear and thermal fatigue, the details on the variations of overlay materials, process controls and technologies developed for all types of continuous casting machines, etc. should be covered.

10. Critical Maintenance Issues for Billet and Bloom

These include practical experience issues with casting of blooms and billets in regard to maintenance issues, such as mechanical rigging, molds, etc.

11. Mold and Copper Maintenance Coating Technologies

A variety of mold coating options as well as other factors that, if left unaddressed, can result in unscheduled outages and product quality issues. In particular, issues on slag casting molds, thick to thin slab, need to be addressed.

12. Caster Hydraulics

Hydraulic systems are a key component to the operation of a steel mill caster. Trouble-free operation of the system can be achieved only through understanding the components of the system, proper fluid selection, regular system analysis, and most importantly, proper filtration and contamination control techniques. Study may focus on the basic components of the hydraulic system, types of fluids available (including fire-resistant), system diagnostics (focusing on oil analysis), and filtration/contamination control to extend component life. In addition, the types and styles of cylinders, cylinder failures, preventive maintenance and cylinder reconditioning programming, etc. should also be investigated.

13. Caster Secondary Cooling Discussion and Water Treatment

Caster spray water quality is important in the casting operation. Failure to maintain higher-quality water will lead to cooling losses due to plugged sprays. The loss or reduction of cooling from the secondary cooling system can result in lower casting speeds, unscheduled outages, reduced campaign length and even breakouts.

14. Nozzle Technology

Topics need to understand include: (1) Variances between hydraulic and two-fluid atomization and how it applies to everyday production and maintenance personnel, etc. (2) Nozzle technology and the critical factors that affect spray quality in the steelmaking process; and (3) Efficiencies of nozzles, from traditional sheet mills to small billet casters.

15. Strand Condition Monitoring

There are various benefits derived from systematic caster monitoring. There should be an understanding on types of monitors, components, frequency of use, parameters measured and data retrieval methods. Knowledge should also includes the monitor's effectiveness in measuring important parameters such as roll gap, roll rotation, outer roll alignment and water spray integrity. Additionally, there is a need to detect collapsed bearings, segment misalignment, roll misalignment and bent rolls including the appropriate corrective action, etc. using the measured parameters. Finally, the skills on calibration and maintenance of the monitor are constructive.

16. Predictive Maintenance Diagnostics

Knowledge of basic predictive maintenance tools and their application.

17. Caster Breakout Detection and Prevention

Caster breakouts such as sticking type breakout due poor lubrication in an increased casting speed cause serious damages. Knowledge on the detection and prevention of the Caster Breakouts is needed.

18. Caster Quality Defects and their Potential Causes

The surface and internal quality of continuously cast slabs and billets is intimately linked to the design, operation, and maintenance practices employed in the continuous casting process. Studied issues may cover the impact of these practices on continuous casting defects such as longitudinal cracking, transverse cracking, silvers and lamination defects, internal cracking, and segregation defects.