JPS5855214B2 - Combustion control method for heat treatment furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to control of a heat treatment line for steel pipes, and particularly to control of loft charging timing in loft change and timing control of starting change of furnace temperature setting.

Steel pipes have variations in their characteristic values as they are manufactured in a rolling mill, so it is necessary to give them a uniform metallographic structure and physical properties through heat treatment.

In addition, for high-grade steel pipes such as those used in oil country tubular goods, the steel pipes need to be heat treated as specified by standards or specified by the customer.

The present invention provides a continuous steel quenching furnace, a water cooling device, a continuous steel quenching furnace,
In a steel pipe heat treatment line consisting of an air-cooling device and connecting each piece of equipment with a roller table, etc., we aim to improve work efficiency and save energy by controlling the combustion in the furnace and the timing of charging steel pipes into the furnace when the loft is changed. purpose.

The steel pipe conveyance interval time (hereinafter referred to as cycle time) in the above-mentioned steel pipe heat treatment line is determined by the soaking time of the tempering furnace (designated from the heat treatment specifications).

In addition, each of the quenching furnace and tempering 4 has its own time required for changing the furnace temperature.

When changing the loft, the cycle time and set temperature of each furnace will change.

The present invention starts changing the furnace temperature for each zone (heating zone, soaking zone) of each furnace, that is, the quenching furnace and the tempering furnace, at an appropriate timing after passing the final blowing of the front loft, and changes the furnace temperature at the timing when the furnace temperature setting is completed. This is to control so that the leading material of the next loft enters each zone of the furnace.

The present invention determines the completion time for changing each furnace zone from the cycle time of the previous loft and the furnace temperature setting change time of each furnace zone, and determines the combustion furnace zone that will be the bottleneck from the cycle time of the next loft. Determine the time to charge the first material of the next lot into the quenching furnace from the combustion furnace zone, and if changing the furnace temperature in the combustion furnace zone that does not become a bottleneck causes a decrease in the furnace temperature, change the furnace temperature immediately after passing the final blow in the previous loft, and In the case of temperature rise, this combustion control method determines the furnace temperature change start time based on the time when the next loft leading material arrives at each combustion furnace zone.

Here, the zone that is a bottleneck refers to a zone where the time required to change the set temperature of the next loft is longer than other zones.

For this reason, the operation of the entire line must wait for the temperature set point of that zone to be changed.

Depending on the range of changes in furnace temperature and the condition of the furnace equipment, the heating zone may become a bottleneck, or the soaking zone may become a bottleneck.

Here, when the furnace temperature drops, change immediately to save fuel.

On the other hand, in the case of temperature raising, there is a time delay (depending on the time constant of the furnace) from the start of the temperature raising operation until the furnace temperature actually rises, so the temperature is raised in advance.

FIG. 1 is a schematic diagram of a heat treatment line.

The steel pipe is heated to about 800 to 1100°C in a quenching furnace 1 and rapidly cooled in a water cooling device 2.

The rapidly cooled steel pipe is then heated to 450 to 750°C in a tempering furnace 3.
After being heated to a certain degree, the temperature is kept soaked for several tens of minutes, and then it is air cooled in an air cooling device 4.

The quenching furnace and the tempering furnace are usually divided into a heating zone A and a soaking zone B, and the furnace temperature can be set individually.

This will be explained in detail with reference to FIG. A1. A2 is the heating zone of the quenching furnace and tempering furnace, and B, B2 is the soaking zone of the quenching and tempering furnace.

Further, if C is the cycle time of the front loft, which is a water-cooled region, as T1, the time at which the fuel passes through each combustion zone of the quenching furnace and the tempering furnace is determined from the cycle time.

Each band passing time is t. 0 to 103.

Next, the time required to change the furnace temperature setting for the next loft is calculated from the amount of change, and the time is set at time t.

Add the required change time to 0 to toa to obtain t10-113.

tOH: @ Loft passing time lθi: Furnace temperature change amount for each zone gi: Temperature increase/cooling rate of each zone jti: Time t.

The furnace temperature is changed from i and the furnace temperature setting completion time is determined.Then, the quenching furnace charging time T1 for entering each zone at each time t11 is determined.

g.

T1-tll-1 T2・・・・・・・・・・・・・・・
・・・・・・・・・(2) 41: Distance from charging to the quenching furnace to each band e: Steel spacing (constant due to equipment) τ2: Cycle time of next lot T from equation (2).

Let TMAX be the maximum value for determining -T3.

TMAX-MAX(To, T1, T2, T3)・
・・・・・・・・・・・・・・・(3) Let TMAX be the charging time of the first quenching furnace of the next lot.

Next, the time t2i at which the steel pipe charged into the quenching furnace enters each combustion zone at TMAX is determined.

e.

t21=TMAX”−τ・・・・・・・・・
・・・・・・・・・(4)2 Furnace temperature change start time t31 from the time calculated by the above equation (4)
seek.

t in case of temperature drop. Press i to start changing immediately.

The flowchart of the above calculation method is shown in FIG. 3. Processing step A
- Consists of F.

Using the above method, it was possible to easily determine the optimal next loft charging time and furnace temperature change start time when changing lofts in a steel pipe heat treatment line consisting of a quenching furnace and a tempering furnace.

According to the present invention, in a heat treatment line for steel pipes consisting of a quenching furnace, a water cooling device, a tempering furnace, and an air cooling device, the empty furnace time when changing lofts can be minimized, and the heating temperature of the furnace can be increased if necessary. It is possible to delay the onset of heat as much as possible.

If this method is implemented using a computer, it is possible to save energy, save labor, and improve production efficiency.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an overview of a steel pipe heat treatment line.
The figure is an explanatory diagram of the timing of entering and passing through each combustion zone for the final material of the previous loft and the leading material of the next loft when changing lofts. Figure 3 is the timing of charging the leading material of the next lot into the quenching furnace according to the present invention and the furnace of each combustion zone. A flowchart of a method for determining temperature setting change timing is shown. 1...Quenching furnace, 2...Water cooling device, 3
..... Tempering furnace, 4.. Air cooling device, 5.
...Steel pipe.

Claims (1)

[Claims] 1. In a control method for heat treating multiple lots of steel pipes in a steel pipe heat treatment line consisting of at least a quenching furnace and a tempering furnace, The furnace temperature change completion time for each furnace zone from the time required to change the furnace temperature setting (1, 1)
, calculate the latest time (TMAX) of the quenching furnace charging time (T1) for the steel pipe to be heat treated to enter each zone at the time when the furnace temperature change is completed, and The time (t21) at which the steel pipe charged into the furnace enters each zone of each furnace is predicted and calculated, and the time (t3t) at which the furnace temperature change starts for each zone of each furnace is determined. Set the temperature increase time in advance of the time when the steel pipe enters each zone, and when changing the temperature, start decreasing the temperature from the time when the steel pipe enters each zone of each furnace to change the furnace temperature of each zone of each furnace. A combustion control method for a heat treatment furnace, characterized by: