A heating method for controlling the thickness of the decarburized layer of heavy rail steel billets during the period waiting for rolling

Abstract

The present invention relates to a heating method for controlling the decarburized layer thickness of heavy rail steel billets during the period of waiting for rolling, including predicting the moment when the billet pauses to be charged into the furnace, controlling the gas flow rate of the heating furnace, predicting the moment when the billet starts to be charged into the furnace, the billet staying in the preheating section during the period of waiting for rolling, no billet in the high-temperature section, predicting the moment when the heating furnace resumes normal production, and resuming production after the period of waiting for rolling ends; according to the roll changing plan of the rolling mill, the equipment maintenance plan and the billet heating system, the present invention predicts the waiting time for rolling, modifies the charging plan in advance, reduces the heating time of the billet in the high-temperature section of the furnace, and solves the problem of the thickening of the decarburized layer caused by the overlong heating time of the billet in the high-temperature section due to waiting for rolling by reasonably arranging the production rhythm of the heating furnace.

Description

Technical Field

[0001] The present invention relates to the technical field of billet surface quality control, and particularly relates to a heating method for controlling the decarburized layer thickness of heavy rail steel billets during the period of waiting for rolling. Background Art

[0002] Due to the high carbon content of heavy rail steel, the heating time, heating temperature, and heating atmosphere during the billet heating process have a relatively serious impact on the oxidation and decarburization of the billet, which will reduce its mechanical properties, hardness, wear resistance, and fatigue strength. In recent years, with the continuous increase in railway vehicle speed and axle load, it is required that the rail has greater stiffness and stronger wear resistance, which puts forward more stringent requirements for the decarburized layer depth of the rail. Current research shows that the main influencing factors for the decarburized layer thickness of billets are heating time, heating temperature, and heating atmosphere. However, if the reheating furnace is in a waiting-for-rolling state such as roll changing of the rolling mill or equipment maintenance, the normal furnace charging arrangement will inevitably lead to too long heating time in the high-temperature section of the billet, resulting in the phenomenon of thickening of the decarburized layer.

[0003] Chinese Patent with Publication No. CN 105483602 B discloses a heating method for reducing the decarburized layer of heavy rails: (1) putting the continuous casting billet into a holding furnace for holding, with the holding temperature being 700 - 800 °C to make the temperature of the continuous casting billet reach 700 - 800 °C; (2) loading the continuous casting billet in step (1) into a walking beam reheating furnace for heating. The walking beam reheating furnace is divided into three heating sections, including a first heating section, a second heating section, and a soaking section. Controlling the temperature in the first heating section of the reheating furnace to be 1020 °C, the air-fuel ratio to be between 0.75 - 0.90, and the heating time to be 40 min; controlling the temperature in the second heating section of the reheating furnace to be between 1220 - 1240 °C, the air-fuel ratio to be between 0.70 - 0.80, and the heating time to be 70 min; controlling the temperature in the soaking section of the reheating furnace to be between 1280 - 1290 °C, the air-fuel ratio to be 1.80, and the heating time to be 30 min. This invention reduces the heating time and reduces the decarburized layer depth of heavy rails by adopting three-stage heating in the walking beam reheating furnace. However, this invention focuses on the heating time and heating temperature of the reheating furnace and does not consider the influence brought by the waiting-for-rolling state of the reheating furnace such as roll changing of the rolling mill or equipment maintenance.

[0004] A Chinese patent with the publication number CN 106521120 A discloses a method for controlling decarburization of bearing steel during heating, which uses a walking beam type reheating furnace with side inlet and side outlet; the fuel is a mixture of high-coke gas; a reducing atmosphere is used for heating to control the depth of the decarburized layer, and a one-fire production process is adopted. The raw material is a GCr15 continuous casting billet. The billet is charged into the furnace, enters the preheating section, the air-fuel ratios of the preheating section, heating section and soaking section are set, and it is observed whether the heating temperature, actual air-fuel ratio and residual oxygen display value meet the requirements, and whether the temperature before the heat exchanger exceeds the limit. If abnormalities occur, manual intervention is carried out; this invention solves the contradiction that one-fire bearing steel requires high-temperature and long-time diffusion heating, making it difficult to control the depth of the decarburized layer; the peeling process is cancelled, and the high requirement index that the decarburized layer does not exceed 0.5%D is met at low cost; this patent improves from the heating atmosphere and heating process, and does not improve the important impacts caused by the standby rolling state of the reheating furnace such as roll changing of the rolling mill and equipment maintenance. Summary of the Invention

[0005] The present invention provides a heating method for controlling the thickness of the decarburized layer of heavy rail steel billets during standby rolling. According to the roll changing plan of the rolling mill, equipment maintenance plan and billet heating system, the standby rolling time is predicted, the charging plan is modified in advance, and the heating time of the billet in the high-temperature section of the furnace is reduced. By reasonably arranging the production rhythm of the reheating furnace, the problem of thickening of the decarburized layer caused by the overlong heating time of the billet in the high-temperature section due to standby rolling of the reheating furnace is solved.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0007] A heating method for controlling the thickness of the decarburized layer of heavy rail steel billets during standby rolling, comprising the following steps:

[0008] 1) Prediction of the moment when billet charging is suspended;

[0009] 2) Control of the gas flow rate of the reheating furnace;

[0010] 3) Prediction of the moment when billet charging starts; during standby rolling, the billet stays in the preheating section and there is no billet in the high-temperature section;

[0011] 4) Prediction of the moment when the reheating furnace resumes normal production;

[0012] 5) Resume production after standby rolling ends.

[0013] Further, the prediction model for the moment when billet charging is suspended is:

[0014]

[0015] where t t is the moment when billet charging is suspended, t d is the planned standby rolling moment, Δt j is the specified heating duration of the billet, Δt iIt is the duration of the i-th confirmed planned change.

[0016] Furthermore, the gas flow control model of the reheating furnace is:

[0017]

[0018] Among them, B is the gas flow during the waiting for rolling period, and B Z is the gas flow during normal production, and Δt is the waiting for rolling duration.

[0019] Furthermore, the prediction model for the starting time of billet charging into the furnace is:

[0020]

[0021] Among them, t k is the starting time of billet charging into the furnace, t t is the pause time of billet charging into the furnace, and Δt y is the heating duration of the billet preheating section.

[0022] Furthermore, the prediction model for the normal production time of the reheating furnace is:

[0023] When Δt > 2Δt j -Δt y , t z = t h -Δt g (4)

[0024] When Δt ≤ 2Δt j -Δt y , the starting time of billet charging into the furnace is for normal production;

[0025] Among them, t z is the normal production time of the reheating furnace, t h is the production resumption time of the production line, and Δt g is the heating duration of the billet high-temperature section.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1) According to the roll changing plan of the rolling mill, the equipment maintenance plan and the billet heating system, predict the waiting for rolling time, modify the charging plan in advance, and reduce the heating time of the billet in the high-temperature section in the furnace;

[0028] 2) By reasonably arranging the production rhythm of the reheating furnace, solve the problem of the thickening of the decarburized layer caused by the overlong heating time of the billet in the high-temperature section due to waiting for rolling of the reheating furnace. Description of the Drawings

[0029] Figure 1 is the control flow chart of the present invention. Detailed Embodiments

[0030] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

[0031] See Figure 1 , which is the control flow chart of the present invention. A heating method for controlling the decarburized layer thickness of heavy rail steel billets during the waiting for rolling period of the present invention includes the following steps:

[0032] 1) Prediction of the moment when the billet loading is suspended: Through the prediction model of the moment when the billet loading is suspended, judge the moment when the billet loading is suspended. After reaching the predicted moment of the model, suspend the billet loading operation;

[0033] According to the roll change plan of the rolling mill, the equipment maintenance plan, and the billet heating system. Predict in advance the moment when the billet loading is suspended to ensure that there is no billet in the high-temperature section of the heating furnace during the waiting for rolling period, and adjust it in time according to the modification of the waiting for rolling plan. The mathematical expression of this model is:

[0034]

[0035] Among them, t t is the moment when the billet loading is suspended, t d is the planned waiting for rolling moment, Δt j is the specified heating duration of the billet, Δt i is the duration of the i-th confirmed plan change, is the cumulative change duration of the multiple confirmed plan change times.

[0036] 2) Control of the gas flow rate in the heating furnace: After suspending the loading, control the gas flow rate according to the gas flow rate control model in the heating furnace. The mathematical expression of this model is:

[0037]

[0038] Among them, B is the gas flow rate during the waiting for rolling period, B Z is the gas flow rate during normal production, and Δt is the waiting for rolling duration.

[0039] 3) Prediction of the moment when the billet starts to be loaded: Through the prediction model of the moment when the billet starts to be loaded, judge the moment when the billet loading starts. When reaching the predicted moment of the model, start the loading operation;

[0040] According to the waiting for rolling duration and the heating duration of the billet preheating section, predict the moment when the billet loading starts. When the first billet reaches the head of the preheating section, stop loading the steel to realize the billet staying in the preheating section during the waiting for rolling period, avoid the overlong heating time in the high-temperature section from increasing the decarburized layer thickness, and at the same time avoid the waste of fuel caused by the empty burning of the heating furnace. The mathematical expression of this model is:

[0041]

[0042] Among them, tk is the starting time for charging the billet into the furnace, \(t\). t is the pause time for charging the billet into the furnace, \(\Delta t\). y The heating duration of the billet in the preheating section.

[0043] 4) Prediction of the normal production time of the heating furnace: Through the normal production time prediction model of the heating furnace, judge the normal production time of the heating furnace, and the heating furnace starts normal production at the predicted time of the model;

[0044] In order to immediately meet the rolling requirements after resuming production, the heating furnace needs to start normal production in advance. The gas flow rate is adjusted to the normal production flow rate. The billets staying in the preheating section should be heated and run to the discharge furnace door before the production line resumes production to meet the rolling requirements. The mathematical expression of this model is:

[0045] When \(\Delta t>2\Delta t\) j -\(\Delta t\) y then \(t\) z \(=t\) h -\(\Delta t\) g (8)

[0046] When \(\Delta t\leq2\Delta t\) j -\(\Delta t\) y then the billet starts to be charged into the furnace at the normal production time;

[0047] where \(t\) z is the normal production time of the heating furnace, \(t\) h is the time when the production line resumes production, \(\Delta t\) g is the heating duration of the billet in the high-temperature section.

[0048] 5) Resume production after the end of waiting for rolling: According to the above production arrangement, when the waiting time for rolling ends and the production line is ready to resume production, the temperature of the billet has met the rolling requirements.

[0049]

Example 1

[0050] The planned waiting time for rolling \(t\) d starts at 10:00. The specified heating duration of the billet \(\Delta t\) j is 160 min. The subsequent equipment maintenance plan changes, delaying \(\Delta t\) i by 30 min. The planned stop time for charging the heating furnace is delayed by 30 min. According to the billet pause charging time prediction model, the billet pause charging time \(t\) t can be obtained as follows:

[0051]

[0052] where \(t\) t is the billet pause charging time, \(t\) d is the planned waiting time for rolling, \(\Delta t\) j is the specified heating duration of the billet, \(\Delta t\)i is the duration of the i-th confirmed plan change.

[0053] When the moment of suspending the charging of the billet reaches 7:50, the reheating furnace stops charging and enters the idle rolling period. During the idle rolling period, there is no billet in the high-temperature section, and the gas flow rate is reduced in a timely manner to reduce gas consumption. The normal production gas flow rate B Z is 12000 m 3 / h, the idle rolling duration Δt is 1 h. According to the gas flow control model of the reheating furnace, the gas flow rate B during the idle rolling period should be adjusted to:

[0054] B = 0.7×B Z = 8400 m 3 / h (10)

[0055] where B is the gas flow rate during the idle rolling period, and B Z is the gas flow rate during normal production, and Δt is the idle rolling duration.

[0056] According to the idle rolling duration and the heating duration of the billet in the preheating section, predict the starting moment of billet charging. When the first billet reaches the head of the preheating section, stop charging the steel to enable the billet to stay in the preheating section during the idle rolling period, avoid the overlong heating time in the high-temperature section from increasing the decarburized layer thickness, and at the same time avoid fuel waste caused by the idle firing of the reheating furnace. The specified heating duration of the billet Δt j is 160 min, and the idle rolling duration Δt is 1 h. According to the billet charging start moment prediction model, the billet charging start moment is obtained as:

[0057] t k = t t +Δt = 8:50 (11)

[0058] where t k is the billet charging start moment, t t is the billet suspension charging moment, and Δt y is the heating duration of the billet in the preheating section.

[0059] Since the idle rolling duration is less than the specified heating duration of the billet, no prediction is required and normal production can be carried out.

[0060] According to the above production arrangement, when the maintenance ends at 11:30 and the production line is ready to resume production, the billet has run to the discharge furnace door and the temperature has met the rolling requirements, and the steel can be discharged at any time.

[0061]

Example 2

[0062] The planned idle rolling moment t d is for maintenance to start at 8:00, and the specified heating duration of the billet Δt j is 160 min. According to the billet suspension charging moment prediction model, the billet suspension charging moment can be obtained as:

[0063]

[0064] When the time reaches 5:20, the charging of the reheating furnace stops and enters the waiting-for-rolling period. During the waiting-for-rolling period, there is no billet in the high-temperature section, and the gas flow rate should be reduced in a timely manner to reduce gas consumption. The normal production gas flow rate B Z is 12000 m 3 / h, the waiting-for-rolling duration Δt is 4 h. According to the gas flow control model of the reheating furnace, the gas flow rate B should be adjusted to:

[0065] B = 0.5×B Z = 6000 m 3 / h (13)

[0066] According to the waiting-for-rolling duration and the heating duration of the billet preheating section, predict the starting time of billet charging. When the first billet reaches the head of the preheating section, stop charging steel, so that the billet stays in the preheating section during the waiting-for-rolling period, avoiding too long heating time in the high-temperature section to increase the thickness of the decarburized layer, and at the same time avoiding fuel waste caused by the reheating furnace running idle. The specified heating duration of the billet Δt j is 160 min, the waiting-for-rolling duration Δt is 4 h, and the heating duration of the billet preheating section Δt y is 60 min. According to the billet charging starting time prediction model, the billet charging starting time is obtained, which is less than the specified heating duration of the billet Δt j 160 min, Δt > 2Δt j -Δt y The billet charging starting time obtained according to the billet charging starting time prediction model is:

[0067] t k = t t +Δt j = 8:00

[0068] In order to immediately meet the rolling requirements after resuming production, the reheating furnace starts normal production in advance, the gas flow rate is adjusted to the normal production flow rate, and the billets staying in the preheating section are heated and run to the discharge furnace door before the production line resumes production. It is known that the heating duration of the billet in the high-temperature section Δt g is 100 min, and the production line resumption production time t h is 12:00, which satisfies Δt > 2Δt j -Δt y According to the normal production time prediction model of the reheating furnace, the normal production time of the reheating furnace can be obtained as:

[0069] t z = t h -Δt g = 10:20 (14)

[0070] Among them, t zAt the normal production time of the heating furnace, t h At the time when the production line resumes production, Δt g is the heating duration of the high-temperature section of the billet.

[0071] According to the above production arrangement, when the production line is ready to resume production at 12:00, the billet has reached the discharge furnace door, the rolling requirements have been met, and the temperature has met the rolling needs, and the steel can be discharged at any time.

[0072] The above embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are all conventional methods unless otherwise specified.

Claims

1. A heating method for controlling the thickness of the decarburized layer of heavy rail steel billets during the period waiting for rolling, characterized in that, Including the following steps: 1) Prediction of the moment when the billet pauses being charged into the furnace; The prediction model for the moment when the billet pauses being charged into the furnace is: （1） Among them, is the moment when the billet pauses being charged into the furnace, is the moment when rolling is planned to be suspended, is the specified heating duration of the billet, is the duration of the i-th confirmed plan change; 2) Control of the gas flow rate in the heating furnace; The control model for the gas flow rate in the heating furnace is: （2） Among them, B is the gas flow rate during the period of waiting for rolling, is the gas flow rate during normal production, is the duration of waiting for rolling; 3) Prediction of the moment when the billet starts being charged into the furnace; During the rolling suspension period, the billet stays in the preheating section and there is no billet in the high-temperature section; The prediction model for the moment when the billet starts being charged into the furnace is: （3） Among them, is the moment when the billet starts to be charged into the furnace, is the moment when the billet charging is paused, heating duration of the billet preheating section; 4) Prediction of the moment when the heating furnace resumes normal production; The prediction model for the moment when the heating furnace resumes normal production is: When then (4) When the billet starts to be charged into the furnace, normal production begins; Among them, is the normal production time of the heating furnace, is the production line resumption time, is the heating duration of the high-temperature section of the billet; 5) Resume production after the end of rolling suspension.

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