JPS6143414B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a temperature control method for a continuous heat treatment furnace, and particularly to a temperature control method when preheating an upset portion of a steel pipe using a preheater.

The upset part of a steel pipe has a different heat capacity from the pipe body (center part), so in order to quickly heat the upset part and the pipe body to the same temperature in the heat treatment furnace, the residence time in the heat treatment furnace must be adjusted. Taking this into consideration, a method is used in which the upset portion is heated in advance using a preheater and then placed in a heat treatment furnace.

However, in the case of a continuous tempering furnace for long steel pipes, for example, the quenching equipment in the pre-process, the fixed diameter in the post-process,
Retention time may change depending on the processing capacity of straightening equipment, troubles, etc. In this case, if the heating by the preheater is not adjusted appropriately according to changes in the residence time of the material to be treated, a phenomenon of insufficient preheating or excessive preheating will occur, and the temperature of the material to be treated will become uneven.
As a result, deviations in mechanical test values were occurring. In order to prevent such deviations from mechanical test values, heat treatment can be performed, for example, to lower the processing temperature and extend the furnace residence time in order to absorb variations in furnace residence time. The disadvantage was that the furnace efficiency was significantly reduced.

The present invention was invented in view of the above-mentioned situation, and it calculates the heat treatment capacity from the residence time and heating temperature of the material to be treated in the heat treatment furnace, and heats the upset part to match the heat treatment capacity. The present invention provides a temperature control method for a continuous heat treatment furnace that makes it possible to stabilize quality and improve heat treatment efficiency. Embodiments of the present invention will be described in detail with reference to the drawings as follows.

FIG. 1 is a block diagram of a control system for a continuous heat treatment furnace according to an embodiment of the present invention. In the figure, 10 is a preheater, 20 is a continuous heating furnace, 30 is a control device that controls the preheater 10, 40 is a control device that controls combustion in each stage of the continuous heating furnace, and 50 is a feed rate of the material to be treated, i.e. a control device for controlling beam speed, 6
0 is an arithmetic unit (electronic computer), 70 is a keyboard, 80 is a display, and 90 is a typewriter.

Here, the input data given to the arithmetic device 60 by the keyboard 70 is as follows.

Dimensions (dimensions of the upset part of the steel pipe, dimensions of the pipe body, etc.) Steel type (initial conditions such as composition, quenching method, etc.) Target temperature and range Extraction pitch and extraction schedule Control numbers (serial number, lot number, number of pipes, etc.) Others Needless to say, a table of physical property values, characteristic values, etc. is given and stored in advance.
Physical property values include heat content H (Kcal/Kg), specific gravity ρ
(Kg/m ³ ), thermal conductivity Kd (Kcal/mhr℃), specific heat c
(Kcal/Kg℃), a conversion table between heat content and temperature is required. As a physical property value, the overall heat transfer coefficient φ
cgm, convective heat transfer coefficient αm, etc. are required.

The display 80 displays control contents, instruction contents, etc. The typewriter 90 outputs control results and the like.

An overview of the method according to this embodiment will be described below, and then a detailed description will be given of the method of controlling the temperature of the preheater.

(1) Outline of control method The calculation device 60 determines the heat pattern of each zone of the heat treatment furnace 20 in advance based on input data such as steel pipe dimensions, heating temperature, extraction pitch, physical property values, and characteristic values, and controls the control device 40 and the control method. The devices 50 are each controlled based on the heat pattern, and the heat treatment furnace 2
Each zone of 0 is heated to a predetermined temperature and the material to be treated is transferred.

The temperature of the material to be treated on the extraction side of the heat treatment furnace 20, that is, the target temperature, is determined, and the residence time in the furnace can also be predicted. The amount of heat that can be given to the material to be treated (heat treatment capacity) can also be calculated from the temperature of each zone of the heat treatment furnace and the residence time in the furnace, and this amount of heat can be converted into temperature with a certain relationship. Therefore, from the target temperature and the heating temperature (furnace atmosphere temperature), the temperature of the upset part at a predetermined time (ΔT) before the extraction side of the heat treatment furnace 20 is calculated, and then the temperature of the upset part is calculated. A predetermined time (Δ
T) Find the temperature at the front by inverse calculation, and then find the temperature at the upset part sequentially,
Finally, the temperature of the upset portion at the charging end of the heat treatment furnace 20 is determined. Then, the preheater 10 and the heat treatment furnace 2
The temperature of the upset section on the outlet side of the preheater is determined by taking into account the natural cooling between 0 and 0. Preheater 1
0, the upset part is heated with a heat amount that brings it to the above temperature.

As described above, the heat treatment in the heat treatment furnace and the heat treatment in the preheater are matched to efficiently obtain a uniform tube body temperature.

(2) Preheating machine temperature control method In explaining the method for determining the heating temperature of the preheating machine, we will explain (a) the relationship between the amount of heat input and the temperature of the upset section, and (b) the temperature of the upset section at the charging end of the heat treatment furnace. The explanation will be divided into the sections of calculation and (c) heating temperature in the preheater.

(a) Relationship between the amount of heat input and the temperature of the upset part; The following relationship holds true between the amount of heat input Q _t and the temperature θ _t of the upset part.

Q _t =4.88φ _rgt {(θ _g +273/100) ⁴ −(θ
_t +273/100) ⁴ } + α _t (θ _g −θ _t ) (1) However, φ _rgt : radiant heat absorption rate θ _g : ambient temperature (°C) α _t : convective heat transfer coefficient. It is assumed that φ _cgt and α _t include terms (coefficients) depending on the shape of the pipe.

The increase in heat content ΔH _t (Kcal/Kg) is determined by the following formula.

ΔH _t =D _t・ΔT・Q _t /ρT _t (D _t −T _t )(2) However, ΔT: Calculation timing, e.g. 10 seconds D _t : Diameter of the upset part (m) T _t : Thickness of the upset part (m) ρ: Specific gravity (Kg/m ³ ). Note that although the above-mentioned upset part indicates the top part, the same applies to the bottom part, and the related dimensions may be interchanged. The shapes of the top part T and bottom part B of the upset part are shown in FIG.

Therefore, the heat content of the upset part H _t (i) at time t _i and the increase in heat content during the division time ΔT are expressed as ΔH
_t (i), the heat content of the upset portion H _t (i+1) at time t _i +1 is determined by the following equation.

H _t (i+1)=H _t (i)+ΔH _t (i) (3) And the temperature of the upset part θ _t (i+1) is given as θ _t (i+1)=f(H _t (i+1)) (4) , is determined as a function of the upset heat content H _t (i+1). The relationship between H _t and θ _t may be made into a table and stored in a ROM or the like in advance.

(b) Calculating the temperature of the upset part at the charging end of the heat treatment furnace Since the residence time in the furnace can be predicted, the temperature in the upset part from the extraction end to the charging end is determined by inverse calculation using this residence time. This calculation follows the steps below.

First, the inverse calculation is performed using the above equations (1) to (4) with ΔT=constant (here, 10 seconds). For example, as shown in FIG. 3, since the target temperature θ _i is known, θ _i −1 at a time ΔT before the target temperature θ i is determined. Needless to say, the furnace temperature is based on a predetermined heat pattern. Next, from θ _i −1 to Δ
Find θ _i −2 before T time. In this way, the temperature of the upset portion is determined one after another, and finally the temperature θ _c at the charging end of the heat treatment furnace 20 is determined.

(c) Heating temperature in the preheater The heating temperature in the preheater and the initial temperature θ _e at the time of charging into the furnace have the following relationship in consideration of natural heat radiation.

θ _e = θ _f (θ _p −θ _f ) e ^-mtc (5) However, θ _f : Atmospheric temperature (°C) θ _p : Preheating temperature (°C) t _c : Time from preheater exit side to furnace charging (Hr) m=αS/CW α; heat transfer coefficient S; surface area (m ² ) W; weight (Kg) C; average specific heat (Kcal/Kg°C).

Therefore, since θ _e is calculated by calculation in the above (b), the preheating temperature θ _p is calculated using the above equation (5). Therefore, the preheater 10 heats the upset portion of the material to be treated at this θ _e .

The experimental results of the above examples are shown in FIG. In the figure, θ _n is the tube body temperature, θ _t is the temperature of the upset portion without preheating, and θ _t ′ is the temperature of the upset portion with preheating as in the above embodiment. If preheating is not performed, 20 minutes of residence time is required for the tube body temperature to match the temperature of the upset section, but if the above-mentioned preheating is performed, it takes 15 minutes. Heat treatment efficiency is improved by reducing residence time by 25%. In addition, in this experimental example, the tube body is 60.3φ x 4.83t (thickness), and the upset part is 75φ.
×14t (wall thickness), furnace temperature is 950℃.

As is clear from the above explanation, according to the method of the present invention, the heat treatment in the heat treatment furnace and the heat treatment in the preheater are matched, the heating in the preheater is appropriate, and quality is stabilized. It has become possible to improve heat treatment efficiency and heat treatment efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a control system for a continuous heat treatment furnace according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of an upset tube, and Fig. 3 is an illustration of a method of calculating the temperature of the upset section at the furnace charging end. The explanatory diagram, FIG. 4, is a characteristic diagram of the experimental results of the above embodiment. 10... Preheater, 20... Continuous heating furnace, 30, 4
0, 50...control device, 60...computing device, 70...keyboard, 80...display, 90...typewriter.

Claims (1)

[Claims] 1 In the heat treatment of upset steel pipes, the upset of the steel pipe at the charging end necessary to obtain the target temperature on the extraction side of the heat treatment furnace is based on the heat treatment capacity determined from the temperature of the heat treatment furnace and the residence time of the material to be treated. The heating temperature required for the preheater is calculated using this temperature and the natural cooling between the preheater and the furnace charging end, and the upset part is heated by the preheater at the heating temperature. A method for controlling the temperature of a continuous heat treatment furnace, characterized in that: