This paper aims to solve the problem of high oxidation and burning rate of slabs in the coil production line of Xinjin Steel Rolling Mill (average 1.65%) through in-depth on-site investigation by the QC team, and tackles the problem from multiple dimensions such as process optimization, equipment transformation, operation standardization and personnel training.
Through comprehensive measures such as adjusting the air-fuel ratio of the heating furnace, shortening the time of slabs in the furnace, strengthening the standardization of steel burning workers, introducing advanced combustion technology and decentralized reversing system, the oxidation and burning rate was finally reduced to 1.57%, achieving direct economic benefits of 3.41 million yuan, while improving the yield rate and strip surface quality, providing a systematic solution for similar problems in the industry.
Oxidation loss is the weight loss caused by metal oxidation on the surface of the slab during the steel rolling process, which directly affects the yield rate and production cost. The average oxidation loss rate of slabs at Xinjin Steel Rolling Mill from May to September 2024 was 1.65%, which is lower than the advanced level of the industry (1.50%), and leads to problems such as increased slag cleaning frequency and fluctuations in strip surface quality. To this end, the QC team carried out special research with “people, machines, materials, methods, environment, and measurement” as the entry point, aiming to reduce the oxidation loss rate to below 1.60% and form standardized operating specifications.
Current situation analysis and goal setting
Current situation analysis and goal setting
The slab oxidation and burning data from May to September 2024 are shown in the following table:
Goal Setting
Based on the industry benchmark (1.50%) and the historical best level (1.61%), the research target is set as: oxidation burnout rate ≤1.60%, and is broken down into key control links:
① Control of oxidation atmosphere in the furnace: air-fuel ratio optimized to 0.5-0.7;
② Slab in furnace time: shortened to less than 90 minutes;
③ Operation standardization: unify the three-shift operation standards to reduce the impact of human factors.
Cause analysis and identification of key issues
The oxidizing atmosphere in the furnace is strong: the air-fuel ratio is set too high (0.8), resulting in excessive oxygen content in the furnace;
The slab stays in the furnace for a long time: the gas pressure is insufficient, and the actual time in the furnace is 120-180 minutes, far exceeding the process requirement (90 minutes).
Identification of key issues
① Strong oxidizing atmosphere in the furnace: the air-fuel ratio is set too high (0.8), resulting in excessive oxygen content in the furnace;
② The slab is in the furnace for a long time: the gas pressure is insufficient, and the actual time in the furnace is 120-180 minutes, far exceeding the process requirements (90 minutes).
③The three shifts have different operating techniques: the level of steel workers is uneven, resulting in fluctuations in furnace temperature control.
④The traditional burner has low combustion efficiency: the traditional burner has a combustion efficiency of 85%, serious gas waste, and high slab oxidation and burning loss.
⑤Poor flexibility of the centralized reversing system: large heat loss, incomplete combustion leads to secondary oxidation of the slab.
Comprehensive consumption reduction measures and implementation
measure:
① Adjust the air-fuel ratio of the heating section: reduce the first stage from 0.8 to 0.7, and stabilize the equalization section to 0.5;
② Optimize temperature control: increase the temperature of the equalization section by 10℃, and reduce the temperature of the second stage by 10℃.
Effect: The air-fuel ratio of the equalization section is reduced by 37.5%, and the oxidation burn rate is reduced from 1.65% to 1.62%; the oxidation reaction is suppressed by a weak reducing atmosphere to reduce metal loss.
Shorten the slab time in the furnace
measure:
① Strengthen gas pressure monitoring: pressure ≥10Kpa, flow ≥140,000 m³/h during double furnace production;
② Promote the “high temperature fast burning” process: reduce the high temperature residence time of the slab.
Effect: The slab time in the furnace is shortened from 150 minutes to 90 minutes, and the oxidation loss rate is reduced to 1.57%; thermal efficiency is increased by 15%, and gas consumption is reduced by 8%.
See the improvement of pyrotechnics operation level
Problem: The operating techniques of the three shifts vary greatly, resulting in fluctuations in furnace temperature control.
measure:
① Formulate the “Standardized Operation Manual for Steel Burners” to clarify the temperature rise curve and air-fuel ratio adjustment rules;
② Carry out monthly skill training and assessment, focusing on strengthening the ability to control weak reducing atmosphere;
③ Implement the “master-apprentice” system to ensure experience inheritance.
Effect: The consistency of three-shift operation increased by 90%, and the furnace temperature fluctuation range was reduced from ±20℃ to ±5℃; the fluctuation of oxidation loss rate decreased by 0.03%, and the process stability was significantly enhanced.
Heating furnace burner modification
Problem: Traditional burners have low combustion efficiency and serious gas waste.
measure:
① Introducing Shanghai Jiade Company’s high-efficiency burner to optimize the gas-air mixing ratio;
② Installing an intelligent combustion control system to adjust combustion parameters in real time.
Effect: The combustion efficiency increased from 85% to 93%, and the gas unit consumption decreased by 12%; carbon monoxide emissions decreased by 30%, and secondary oxidation caused by incomplete combustion was reduced.
Application of decentralized commutation technology
Problem: The centralized switching system has poor flexibility and high heat loss.
measure:
① Adopt Shanghai Jiade’s decentralized reversing technology to achieve independent control of the burner;
② Dynamically adjust the reversing frequency based on furnace temperature and pressure.
Effect:
The switching response time is shortened by 50%, and the furnace temperature uniformity is improved by 10%;
The amount of iron oxide scale generated is reduced by 8%, and the surface quality qualification rate of slabs is increased by 2%.
Effect verification and economic benefits
Oxidation burn comparison
Oxidation burn comparison
Solidification and promotion of measures
Process standardization: Revise the “Operational Procedures for Heating Furnace Heating Process”, add new technical specifications such as burner control and decentralized reversing;
Training and supervision: Regularly organize steel burning worker skill competitions, and the technical department conducts monthly spot checks on process implementation;
Technology promotion: Promote decentralized reversing technology in the No. 2 heating furnace of Xinjin Group, and plan to expand it to the entire production line.
Conclusion and Outlook
Through multi-dimensional technical research, the oxidation and burning rate of Xinjin Steel Rolling Mill has been reduced to 1.57%, with an annual comprehensive benefit of 3.41 million yuan. Future plans:
① Develop an intelligent combustion control system to achieve dynamic optimization of the air-fuel ratio;
② Study the surface pretreatment technology of slabs to reduce the initial amount of iron oxide scale;
③ Build a full-process data monitoring platform to achieve real-time warning of oxidation and burning.
Technological innovation is the core driving force for high-quality development. Through systematic improvements, Xinjin Steel Rolling Mill has not only solved production problems, but also provided a practical model for green manufacturing in the industry.
