First, the principle of the heating furnace
The purpose of the heating is to heat the billet to a uniform, suitable rolling temperature (austenitic structure). After the temperature is raised, the first is to improve the plasticity of the steel, reduce the deformation resistance, and make the steel easy to deform. For example, the deformation resistance of T12 steel at room temperature is about 600Mpa. When heated to 1200°C, the deformation resistance drops to about 30Mpa, which is only one-twentieth of the deformation resistance at room temperature. Steel with suitable heating temperature can be used for rolling, which can reduce the equipment accident caused by wear and impact, improve the productivity and operation rate of the rolling mill, and reduce the rolling energy consumption. Second, heating can improve the internal structure and properties of the billet. The uneven structure and non-metallic inclusions are homogenized by the diffusion of high temperature heating. The heating temperature and uniformity are the marks of the heating quality. When the steel of good quality is heated, it is easy to obtain the finished product with the correct cross-sectional shape and accurate geometrical dimensions.
The heating temperature of the billet includes the surface temperature, the temperature difference along the section, and the temperature difference along the length of the billet. The final heating temperature of the billet in the furnace is specified in consideration of the actual conditions such as the rolling process, the structural characteristics of the mill and the structural characteristics of the furnace. The time required to heat to the specified temperature depends on the size of the billet, the type of steel, the temperature regime employed, and some other conditions.
The billet is heated in the furnace by convection and radiation. The former is the furnace gas flushing the surface of the billet; the latter is the furnace flue and the hot lining radiant heat. Our furnace is controlled in three stages along the length: preheating section, heating section and soaking section. The billet enters the preheating section of the heating furnace, the heat flow gradually increases, the billet reaches the heating section, the heat flow remains basically unchanged, and the billet reaches the soaking section, and the heat flow is gradually reduced. In the soaking section of the billet, the surface temperature of the billet remains basically the same, while the section temperature difference is gradually reduced, and the heat obtained on the surface of the billet is diffused to the inside by heat conduction. The smaller the heat flow to the surface of the slab, the larger the heat receiving area, the smaller the section size of the billet, and the greater the thermal conductivity of the steel, the smaller the cross-section temperature difference. Steel slabs with a large cross section have a longer heating time than steel slabs with a smaller cross section, and alloy steels have a longer heating time than carbon steel.
3. heating defects
Alloy steel cracking: at the beginning of heating (below 700 °C), for high-carbon steel such as high-carbon tool steel, high-manganese steel, bearing steel, high-speed steel, etc., if the heating rate is too fast and the surface temperature suddenly rises, the section If the temperature difference is too large, thermal stress will be generated, resulting in cracks.
Overheating and overheating: If the heating temperature is too high or the residence time is too long at high temperatures, the grain of the steel will grow excessively, the relationship between the grains will be weakened, and the steel will become brittle. This is called overheating. Cracks are generated when the overheated billet is rolled; even if the rolling is not cracked, the mechanical properties of the finished product are not satisfactory. Superheated billets can be saved by normalizing. The overheating develops further, the grains continue to grow, and the grain boundaries appear to oxidize or melt, and often break or crack when rolled, which is called over-burning. Overfired billets are irreparable waste. When the rolling operation suddenly fails to stop rolling, it is prone to overheating or overburning; if the high carbon steel is improperly controlled in temperature, it is easy to cause overheating or overburning.
Oxidation and decarburization of billet: During the heating of the billet, the metal element in the steel reacts with the oxidizing atmosphere in the furnace to produce iron oxide scale (the inner layer of iron oxide scale is iron oxide and the middle layer is ferroferric oxide). The outermost layer is ferric oxide). Decarburization is caused by the carbon element in the steel diffusing to the surface and reacting with the atmosphere in the furnace. Bearing steel, tool steel, spring steel and other steel grades, the decarburization of steel is harmful, the surface of the steel after decarburization does not reach the required hardness during quenching, in addition to the pressure resistance and wear resistance The elasticity is reduced.
The oxidation and decarburization processes are carried out simultaneously, and they are all related to the heating conditions (temperature, furnace time, furnace atmosphere, and chemical composition of the billet). In general, oxidation and decarburization are not significant at temperatures below 750 °C. However, the increase is particularly fast when the temperature is higher than 800 °C.
Special attention is paid to the fact that the heating temperature of carbon steel is generally not more than 1300 ° C, which is greater than this temperature. First, the iron oxide scale on the surface of the steel slab will melt (the melting point of pure iron oxide scale is 1377 ~ 1565 ° C, and it will drop to 1300 ~ 1350 when impurities are contained. °C), falling off the surface of the steel, revealing a new surface, and the burning loss increases rapidly. Second, when the heating temperature is greater than 1300 ° C, the billet is likely to be overheated or overheated. More attention should be paid to the maximum heating temperature when producing other steel grades.
After the slab is oxidized and burnt, it will inevitably affect the yield; the thermal conductivity of the scale is very poor, which has an effect on the heating time of the slab; the iron oxide peels off and accumulates in the furnace, and manual cleaning is very difficult and the work is very difficult.
The thermal system involves the fuel entering the furnace, the combustion situation, the elimination of combustion products, and the recovery and utilization of waste heat. The thermal system includes a temperature regime, a furnace pressure system, and a furnace combustion system.
5. the furnace pressure system:
The size and distribution of the furnace pressure in the heating furnace is an important means to adjust the temperature field, control the flame and the atmosphere inside the furnace. It affects the heating speed and heating quality, and also affects the quality of fuel utilization. In particular, the furnace pressure at the discharge section of the furnace is particularly important.
The furnace pressure setting should be about 0~30Pa higher than the atmospheric pressure. If the furnace pressure is too large, the opening parts such as the charging port, the discharge port and the observation hole will fire outward. The result is: (1) the furnace gas loss is increased to increase the heat loss; (2) the harmful gas such as SO2 enters the workshop to pollute the working environment; (3) The furnace wall of the fire location, the nearby steel structure or mechanical equipment is damaged or deformed. Conversely, if the furnace pressure is too low, the absorption of cold air in the workshop will cause (1) the furnace temperature to decrease the fuel consumption; (2) the low temperature air will cause the temperature to be uneven due to the cooling of the billet; (3) the increase of the oxygen content of the furnace gas will increase the burning loss.
6. the burning system:
The basic requirement is to ensure that the fuel burns completely within the furnace range, while the air coefficient α is small. Excess air has a large amount of smoke, and the amount of heat taken away increases; the amount of air is insufficient, and incomplete combustion occurs in the furnace, which also increases heat loss.
7. the operation of the stove
LMMGROUP Heating Furnace is a walking beam regenerative heating furnace, which is a complex mechanized and automated thermal equipment. It consists of a furnace body (stepping system), a transportation facility for blanks, a piping system for conveying various media (blast furnace gas, converter gas, air, nitrogen, compressed air, water, hydraulic oil, lubricant), a fuel combustion facility, Emissions of combustion products and waste heat recovery facilities, control systems for thermal systems, cooling systems for various components, and removal facilities for the formation of scales during heating. Only the production personnel can understand and master the process equipment well, and can maintain and operate correctly. The furnace can have good indicators. The work of the production staff involves: the loading of the billet, the transportation of the billet in the furnace, the billet release, the heating system of the billet and the thermal system of the furnace; the cleaning of the scale; the accidental shutdown; the shutdown after the planned shutdown and maintenance Furnace, etc.
The operation of the furnace mainly pays attention to the following aspects:
The control of the thermal system is usually automatic in the early stages when all regulators are put into operation, and the regulator settings are derived from the process specifications. Manual operation after failure or maintenance of the auto-regulator can be performed manually in the event of an accident or automatic component damage.
In order to maintain the furnace for long-term effective use, it should be regularly maintained and pay attention to its use; regularly clean the scale; regularly check the water volume, water temperature and water pressure of the water-cooled components in the furnace.
When the fan fails or suddenly loses power, the supply air will be gradually interrupted. At this time, the air, gas valve and gas main valve on the burner should be quickly turned off.
Oven: The oven is to remove the moisture in the masonry before the production, overhaul or minor repair. Oven time should consider a number of factors. Here are some reference data: before the production of a 150t walking beam heating furnace, it is raised from room temperature to 150 °C for 36 hours before heating, and heated to 350 °C at a heating rate of 15 °C / h for 60 hours; then 15 °C / The heating rate of h is raised to 600 ° C and kept for 48 h; then it is heated to 8000 ° C at a heating rate of 20 ° C / h for 36 h; then heated to 1200 ° C at a heating rate of 20 ° C / h for 36 h. The total oven time is 14 days. The overheated oven is heated to 200 ° C and kept for 4 h; it is heated to 700 ° C at a heating rate of 20 ° C / h and then kept for 4 h; then heated to 1200 ° C at a heating rate of 50 ° C / h for 4 h. The total oven time is 2 days, and the time is prosperous can be extended to 3 days. The small-sized oven was heated to 600 ° C at a heating rate of 25 ° C / h and then kept for 6 h; then heated to 1200 ° C at a heating rate of 50 ° C / h and then kept for 4 h. The total oven time is about 2 days.
Ignition: The gas in front of the furnace must be clear before the gas is passed through the new, rebuilt or long-term decommissioning. In operation, pay attention to the leak of the pipe and its accessories.
The operation of driving the air in the pipe and its accessories to the atmosphere outside the workshop is called venting, which is now expelling the air with nitrogen (or steam) and then driving the nitrogen (or steam) with gas. The venting is carried out in stages, and is from the main pipe to the main pipes to the respective pipes and finally to the gas pipe before the burner. After passing nitrogen gas for a specified period of time and confirming that the replacement is good, the nitrogen gas is stopped, and then the gas is introduced and the nitrogen gas is driven away from the discharge pipe. After this step is completed, the sampling tube at the end of the gas pipe is sampled and subjected to an explosion test. The release valve can be closed and the section is considered to be released. If it is not qualified, it will be driven for a while and an explosive test will be carried out until it is qualified.
The burst test was carried out in a drum having a diameter of 70 to 100 mm and a length of about 300 mm. A small fire group is placed on the ground at a safe location far from the gas site. The cylinder mouth filled with the sample is moved to the fire group, and the cylinder cover is opened to point the sample in the cylinder. When the fire is slow and silent When it is burnt to the bottom of the tube, it is considered to be qualified; if it burns faster after the point, it means there is still some air; after burning, it will burn quickly or produce a popping sound, indicating that the sample is in the explosion range, the latter two cases should be Continue to disperse and make an explosion test again.
When igniting before the burner, first supply air to the burner (the air disc valve opens 20%~30%), then open the gas valve in front of the burner (open 1/3~1/2), use the sturdy cotton yarn Ignition, and then gradually adjust the amount of gas and air. After the gas is sprayed, it is not lit. The gas valve before the burner should be closed immediately, and then the flammable mixture in the furnace is removed and then re-ignited.
Second, the principle of rolling
1.Roller installation and rolling adjustment
Roller installation and rolling adjustment are a core part of completing and establishing a stable rolling process. The purpose of rolling mill adjustment is to ensure the good running condition of the rolling mill and ensure that the rolling process is carried out according to the feasible process system, so as to ensure the rationality of the production process, ensure the product quality, reduce the steel pile accident and increase the rolling mill operating rate.
In order to achieve the above objectives, the mill adjustment work should first re-confirm the rolls, guides and frames provided for the roll inspection section, implement the online replacement and installation of the above components, and complete the on-line pre-adjustment of the rolling mill. In the rolling process, according to the quality situation, the adjustment workers judge the cause of the accident in the production accident in time, formulate a reasonable adjustment plan and adjust and implement it. Adjustment should ensure the accuracy of the geometry and geometrical dimensions of the rolling stock, ensure the micro-tension control of the rolling mill and the tension-free control of the looper to ensure the normal continuous rolling process.
The completion of the rolling process is divided into three steps: firstly, the replacement of the rolling mill is completed or the replacement of the rolls is carried out; then the rolling mill is pre-adjusted; the final rolling mill starts normal rolling and the on-line rolling mill is adjusted.
2.Rolling mill online replacement and installation
Before changing the roll, it is necessary to check whether the upper roll is the roll of the changed number, rolling type and specification; the slides, the flat head of the roll and the inner hole of the sleeve should be scrubbed, and the clean grease should be applied after being cleaned. After the preparation is completed, the rack work can be replaced according to the roll change plan. The working steps are as follows:
Turn off the mill cooling water and remove the inlet and outlet guides. Unscrew the water pipe joint of the upper and lower rollers. Start the hydraulic locking device that opens the rack. Horizontal rack selects “Rack traverse” to advance the frame and move the mill to the extreme position on the operating side. (The vertical rolling mill selects the “rack lifting/lowering” button to lower the frame and lower the rolling mill to the lower limit position.) Pull out the flat headgear bracket wrench fixing pin and pull the bracket wrench to make the frame flat and flat. The hood brackets are separated. Pull the horizontal traverse button of the horizontal rolling mill to retreat the flat hood bracket, the flat hood and the flat head of the roller are disengaged, and move the flat hood bracket to the limit position of the transmission side (pull the vertical rolling mill button to make the flat hood When the bracket rises, the flat head cover and the flat head of the roll are disengaged, the flat head cover bracket is raised to the limit position of the transmission side, and then the “frame traverse” button is pulled to traverse the vertical rolling mill to the outer limit position). Use the crane to lift the frame from the rolling line. Put the new roller frame as a whole on the sliding roller, and rotate the roller with the skid bar to make the flat head of the roller and the position of the rotating shaft flat head cover. After confirming that the rolling mill frame is aligned with the rolling line, pull the horizontal traverse button of the horizontal rolling mill to traverse the flat hood bracket to the operating side (pull the vertical traverse button of the vertical rolling mill to make the frame retreat Move the stand mill to the inner limit position. Then pull the “Rack Lift/Drop” button of the stand mill to lower the flat head cover bracket). Put the flat head of the roller into the flat head cover of the drive shaft until it reaches the limit position. Start the locking device to lock the frame and connect the water pipe connector. Install the guide. And the rolling mill is rolled, and the guide is fine-tuned.
3.Method of replacing the groove
Each pair of rolls is engraved with a plurality of grooves, and the new groove is replaced after the tonnage specified in the production process specification (or the groove is damaged). Its operation method is as follows:
Loosen the outlet and inlet guides, traverse to the new groove, and tighten the alignment after the center;
Refer to the original hole height and the values
Adjust the position of the cooling water pipe so that the cooling water can be accurately poured on the new rolling groove;
The traverse rolling mill causes the new rolling groove to exit the rolling line position;
The new groove uses a hand grinder to remove rust and roughen the surface to prevent the rolling stock from slipping.
4. trial rolling after changing slots
Under normal circumstances, due to the large section of the rough-rolled rolling stock, the rolling speed is low, and there is little steel pile accident. Generally, the small steel is not tested, but is directly rolled. In the case of medium-rolling or finish-rolling, in order to prevent the slippage or the adjustment from being irregular, the speed is not matched and the pile is caused by the steel. Therefore, the small steel should be tested.
The common problem with the new tank is that it is difficult to bite the steel and slip after the bite is bitten. In order to smoothly bite into the first steel, the following measures can be taken:
Grinding the groove with a grinding wheel to remove oil and roughen the surface to increase friction;
Appropriately raise the height of the hole of the new tank, generally can be raised 0.5~1mm;
Rolling down the front (upstream) mill of the new tank mill by 3~5%;
Close the groove cooling water to reduce the temperature drop of the rolling head;
After the finishing or middle rolling mill is changed to the groove, it is generally necessary to carry out trial rolling of small steel. The purpose is to confirm whether the roll gap is reasonable, whether the size of the rolled piece meets the requirements; the second is whether there is a problem in the installation and adjustment of the guide; the third is to increase the roughness of the groove and confirm whether there is a problem with the bite of the groove to the rolled piece. .
The sample size can be sampled by the unit’s front flying shears or left behind after the accidental pile of steel. The specifications are the same as those required for the front part of the unit. The sample is placed in a heating furnace and heated to the opening and rolling temperature before the change of the groove. The rolling mill is fed by hand at a “crawling” speed, and the height dimension of the sample is measured with a vernier caliper.
5．rolling mill online adjustment
The main contents of the on-line adjustment of the rolling mill are: axial adjustment of the rolls, radial adjustment of the rolls, roll gap adjustment, installation and adjustment of the guides, measurement and adjustment of the rolled parts, inspection and adjustment of the finished products.
1) Axial adjustment of the roll
Due to the large turning error of the hole type, the poor roller installation can lead to the axial misalignment of the hole type (commonly called the wrong roller). The wrong roller can cause the rolling piece to bend, twist, the rolled piece is not standardized or the ear is generated, causing the groove to wear. Unevenness, unstable rolling, and serious accidents such as scrapping of steel and finished products between racks, so the adjustment must be checked before the rack is installed or when the rolls are adjusted. If the wrong roller is found, it must be adjusted.
2) Adjustment of the roll gap
The adjustment of the roll gap is one of the important parameters of the rolling process. Its setting and adjustment is an important part of the rolling mill operation. Especially the adjustment after the new roll change or groove change is especially important.
Adjustment of roll gap of roughing mill and medium rolling mill: The roll gap of coarse and medium rolling mill is relatively large, and the error of hole type turning is large. Generally, the adjustment should adjust the roll gap value according to the depth of the groove bottom groove. It can be measured with internal calipers. The bounce value of the roll gap is considered in the adjustment. The rough rolling is generally about 1 mm, and the medium rolling is about 0.5 mm. The measured groove bottom depth plus the roll seam bounce is the red blank size of the actual rolled piece.
In the production, the measurement of the size of the rough rolled part can be measured by the external caliper in the movement of the rolling stock. At this time, the measured value has a certain error, and the adjustment work should be measured multiple times.
The size of the rolled piece of the coarse and medium-rolled end frame is also a key value. The size measurement of the rolled piece can be measured by cutting the head or cutting the 1# and 2# flying shears.
3) Adjustment of the finishing roll gap:
There are two ways to adjust the finish roll gap, namely the plug gap and the small round steel indentation method.
The feeler gauge adjustment method is relatively simple, but the roll gap value measured at this time should also consider the bounce of the mill.
The small round steel indentation method uses a softer round steel which is about 3 mm larger than the set roll gap value, and the rolling mill is idling at a “jog” speed, holding a round steel bar, rolling the round steel from the roll gap, and then measuring The thickness of the indentation is compared with the set value of the roll gap and it is adjusted repeatedly until the thickness of the indentation is equal to the set roll gap value.
It is difficult to measure the size of the rolled stock in the production, and the wood printing method is generally used.
Wood burning is a simple and effective means of dynamic inspection of rolling stock. The method is to use a wooden strip to face and directly attach to the moving rolled piece, and then take out the shape of the printed wood to observe the fullness, guide and hole shape of the rolled piece.
4) Alignment of the rolling line
In the production, the rolling lines of each frame are required to be on the same straight line, and the deviation of the rolling line of the frame causes uneven wear of the hole type and damages the guide. The heavy one can directly cause the steel pile accident.
The meaning of the alignment of the rolling line includes both the inlet and outlet guides of the same frame and the alignment of the rolling holes, and the consistency of the entire unit on the rolling line.
During the rack installation process, the positioning of each frame rolling line is usually to select two coordinate points at both ends of the entire rolling line, and the coordinates of each rolling mill are determined by hanging the wire. The center line of the steel wire is coincident with the center of the frame rolling line, and the fixed frame is installed. After the roll change is changed, the following three methods are generally used for the centering of the rolling line:
The rolling line is used as a marking method. The center line coordinates of the rolling line are generally made at the mill base or the arch. During the traverse or installation of the rack, the centerline of the guide is coincident with the mark.
Use the light source to observe the alignment. Typically, a light source is placed at the entrance guide of the previous rack mill, and an observation is made at the exit of the next rack to determine the rolling centerline of the intermediate frame.
Data adjustment method: Calculate the size between the rolling mill and the end of the rolling mill base by the relevant dimensions of the rolling mill, and calculate the dimensional relationship between the centerline of each of the pair of rolls and the rolling line in combination with the size of the rolling line. To measure the adjustment of the rolling line.
5) Adjustment during rolling
The main adjustment process in the rolling process is to check whether the process of the guide, the use of the groove, the speed adjustment and other process systems are reasonable by checking the operation and size of the rolling stock, so as to ensure that no steel pile accidents occur and the qualified products are rolled out. The basis for the adjustment is obtained by means of “observation”, “sampling”, “wood printing” and “strike”.
Observe whether the exit of the rolled piece is “headed up” during the bite-in process between the racks. If there is, the imported rolling guide is installed too low; if the head of the rolled piece has a “down tie” phenomenon, the imported rolling guide can be judged to be installed. Too high. Observe the round rolling of the strip, if there is a torsion phenomenon, it means that the inlet rolling guide wheel gap or the height of the rolling stock is too small.
By sampling the flying shear head (tail) or the broken rolling piece, it can be judged that the wear condition of the groove, the alignment of the guide and the roll gap meet the requirements of the size of the rolled piece, and the judgment can be divided into the following cases:
The width of the roll marks on both sides of the rolled piece is different, indicating that the imported guide is not installed correctly;
The height of the rolled piece is suitable, and the fluctuation of the width dimension is small, indicating that the incoming section size is insufficient or the tension is too large;
Ears, the reasons are manifold. One is that the material is too large, causing the pore shape to be overfilled when entering the next rolling mill. In this case, the section of the rolled piece is relatively full, and the two sides of the rolled piece have ears; the second is that the frame is pressed down. Large, the rolled parts are also bilateral ears, and the height is too small; the third is that the entrance guide is more biased, the performance of the rolling parts on one side of the ear, one side is relatively lacking; the fourth is the entrance guide is too large or damaged, In this case, the rolled section after rolling is irregular, with ears on both sides, and the guide should be replaced in time.
Folding, usually caused by the occurrence of ear or scratch after a certain rack, should be found in time.
Up and down asymmetry (unsuitable ellipticity) caused by a wrong roller or an imported guide.
There are periodic pockmarks, pits and indentations on the rolled parts, which are caused by the “falling meat” and cracks in the rolling groove.
Wood burning is a simple and effective means of dynamic inspection of rolling stock. The method is to directly attach a wooden strip to the position of the roll of the moving red steel, and then take out the image of the printed wood to observe the fullness of the rolled piece, the guide and the use of the roll.
The adjustment of the finished product size should be carried out according to the above judgment method according to a certain method. Here are a few simple ways to make adjustments:
By measuring the dimensions of the finished product or observing the width of the rolled piece by the method of burning the wood sample, the size of the head, the middle and the tail of the whole rolling piece change to large, medium and small. It should be judged that there is excessive rolling of the steel between the frames. Timely notify the main control station to adjust as soon as possible;
The size of the rolling strip is not changed much, the height is suitable, and the width is small. The front hole and the front hole of the finished product should be adjusted. If the width is out of tolerance, the size of the rolled piece of the whole unit should be adjusted;
In the process of dimension control of each pass rolling, it should be enlarged or reduced at the same time to ensure that it is close to the size of the standard rolling stock, so that the deformation of each pass is evenly distributed, and there is no large deformation of individual passes, and some deformations of the pass. Small phenomenon. The size determination of the intermediate pass rolling stock can be calibrated by trial rolling small steel at the handover. With the wear of the groove, the adjustment of the roll gap in the shift can be carried out by the method of roll gap compensation, thus avoiding the unevenness of the deformation between the passes, and thus making the control of the main control station easy to grasp and adjust the rolling speed. So that the upper and lower can be combined.
It is judged whether the deformation amount of each pass is reasonable by comparing the actual rolling load and the elongation coefficient of the main control table with the theoretical value.
The ovality of the finished product size is not suitable. Check whether the opening of the finished roll hole or the inlet guide is too large.
6) Judgment and adjustment of tension between racks
The effect of tension between the racks on the dimensions of the rolled stock is a very complex plastic mechanics process. For example, in the No. 1 and No. 2 hole types, a tensile steel is generated, that is, a tension is generated between the No. 2 and No. 1 rolling mills, and this tension causes a decrease in the resistance in the rolling direction, thereby increasing the flow of the metal in the rolling direction, and The flow in the width direction is reduced to make the width of the rolled product smaller. On the contrary, the steel stacking process can increase the size of the rolled product in the width direction.
From the above analysis, it can be seen that when the tail of the rolling stock leaves the previous frame, the width becomes larger, indicating that there is tension between the front frame and the frame, because once the tension disappears, the width of the rolling stock of the frame changes. Big. The greater the change in width, the greater the tension, so that the adjuster can determine whether there is tension between the frames by measuring or judging the change in the width dimension of the head and tail of the rolling stock and the width dimension of the intermediate rolling stock. The change in the width dimension of the intermediate rolling stock can be judged by the width of the unrolled portion on both sides of the rolled piece (at the roll gap). There are two ways to use the site: one is to observe with the naked eye, the other is to judge by burning wood, and the latter is suitable for rolling parts of smaller size.
The tension between the racks can be directly judged by the change of the motor load current by the main console. When the rolling piece bites into the first steel, the current value is a. If the current value remains unchanged after the rolling piece bites into the second frame, there is no tension. When the current value changes, such as less than (or greater than) a value , which indicates that there is tensile steel (or stacking steel) in one or two.
After the mill has been confirmed by the height of each rolling stock, the speed of the rolling mill can be used to eliminate the tension on a frame-by-frame basis. Adjusting the tension should start from the first frame and adjust backwards from frame to frame. If the adjustment is started from the last frame, it is possible to adjust the back, and when the first few frames are adjusted, the tension relationship in the back can be destroyed again, causing an accident.
It is possible to increase the speed of the previous one, but the speed of the lifting should be small and progressive. Observe whether the rolling stock of the frame increases in the width direction while increasing the speed. When speeding up, pay attention to observe whether there is a slight riser in the rolling stock between the two frames. The speed has been raised until the width of the rack is up to the required. If the dimensional change of a rolled piece in the width direction is irregular, it may be caused by uneven temperature of the local steel; if there is periodicity, there may be one of the previous passes, one of which has an eccentric rotation of the frame roll, or a hole type The upper part is peeled off, commonly known as “meat meat”, and the periodic incoming material size is inconsistent. The above situation should be dealt with according to specific reasons.
Generally speaking, the main method of adjusting the tension is to adjust the rotation speed of the rolling mill. However, before realizing this process, it must be ensured that the height dimension of each frame rolling part meets the process requirements, and the rotation speed must not be adjusted again. Adjustments at the same time will inevitably lead to adjustment confusion.