Classification and Development of Direct Rolling and Hot Feeding

The real direct rolling is to roll the continuous casting slab sent from the continuous casting machine directly into the final product without any other heating or heating process. However, for many years, most of the production process research and tests for producing high-quality products have reheated or reheated the continuous casting slab before rolling.

Continuous casting slab hot feeding and hot charging and direct rolling technology are new technologies under development, and the specific characteristics are as follows:

Continuous casting slabs are directly rolled without heating or supplemental heating, referred to as CC-FDR, and are classified into 1 type. Under the condition that the surface temperature is above 820 ° C (the core is above 960 ° C), the continuous casting slab is directly sent to the rolling mill without any form of heating and supplemental heating, and without building a heating furnace. The slab has not undergone the γ-α-γ phase transformation recrystallization process before rolling, and the as-cast coarse austenite grains are still retained. The trace elements Nb and V do not have the precipitation and re-dissolution processes in conventional cold-loading furnaces, so they must be developed. A new rolling process to obtain a grain-refined structure.

Continuous cast slab rolling, referred to as CC-DR, is classified into 2 types. The continuous casting slab is directly sent to the rolling mill through the corner heating device during the conveying process without passing through the heating furnace under the conditions above A3 temperature.

Continuous casting slab hot direct rolling, referred to as CC-HDR, is classified into 3 categories. The continuous slab temperature is above A3. The slab does not pass through the heating furnace. During the conveying process, the rollable temperature is reached by supplementary heating and soaking, and it is directly sent to the rolling mill for rolling.

Continuous hot-rolling of continuous casting slabs, referred to as CC-DHCR, is classified into 4 categories. The continuous casting slab temperature is below A3 and above A1, and the casting slab is directly sent to a heating furnace for heating and rolling. Due to the high temperature of hot charging, it is also called red delivery, and the heating furnace acts as a buffer between the continuous caster and the rolling mill.

Continuous hot-rolling of continuous casting slabs, referred to as CC-DHCR, is classified into 4 categories. The continuous casting slab temperature is below A3 and above A1, and the casting slab is directly sent to a heating furnace for heating and rolling. Due to the high temperature of hot charging, it is also called red delivery, and the heating furnace acts as a buffer between the continuous caster and the rolling mill.

The continuous casting slab cold rolling furnace is heated and rolled, referred to as CC-CCR, and is classified into 6 categories. This is the conventional rolling method when there is no hot-feed and hot-fill process.

Solution to Slow Start of Rolling Mill Machine

The speed at which the rolling mill machine is started during operation has a very important effect on the efficient work of the rolling mill. If the starting speed of the rolling mill machine is slow when it is ready for operation, it means that there is a significant deficiency in the performance of the rolling mill equipment, which will affect the working efficiency of the rolling mill. The force between the billet or rolled product and the roll cannot reach good condition.

The rolled piece cannot be fully rolled in the rolling mill. Under this condition, the power consumption of the rolling mill machine is several times higher than usual. If it happens often, the speed of the rolling mill cannot be effectively started, the efficiency of the billet or rolled product will become lower and lower. For steel rolling mill equipment, if it cannot be started quickly and overloaded, the billet rolling speed will be too slow. Here, let me analyze the reasons and solutions for the slow startup speed.

Before starting the rolling mill machine, it is necessary to verify the power of the equipment motor, rolling speed, product specifications, hole technology, etc., ensuring that the amount of billet retransmission does not exceed the bearing capacity of the rolling mill equipment, otherwise the startup speed of the equipment will slow down. We also need to check the rolling mill bearings to see if the bearings are adequately lubricated. If the lubrication is not sufficient, the rolling mill machine's start-up will also slow down or even malfunction.

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Repair Method and Operation Process of Rolling Mill Roll

During the operation of the rolling mill, the roll is easy to be damaged. In order to repair the roll body timely and effectively, it is necessary to judge and analyze from the determination of service life, the identification of crack depth, turning crack and other aspects, so that the rolling mill can return to normal.

Because there is no good method to detect the crack depth of the rolling mill roll, the length of service life can only be judged and determined according to the experience, the type of rolling mill, the type of alloy produced and the roughness of the roll surface. According to the theory, the correct service life should be before the crack depth reaches 3 mm, beyond which the roller surface should be grinded, otherwise it is easy to cause the roller sleeve to burst.

In general, if the crack on the rolling mill roll is open, its depth is deeper than tortoise crack or other microcracks, and the crack width is also larger. Therefore, the longest circumferential crack and the widest crack on the roll surface must be found out correspondingly. Through these cracks, the minimum cutting amount can be determined, and the magnetic particle inspection can be used for crack areas.

In order to ensure the safety, the turning depth of the rolling mill roll needs to add 0.5mm to the crack depth in general, and the roughness of the roll surface after turning shall not be less than 6.3; the surface roughness of the roll surface after grinding shall reach 0.8, which can be compared with the standard block or measured with the roughness detector.


When the defects of the rolling mill roll are turned, magnetic particle inspection shall still be carried out to ensure that all micro-cracks have been eliminated. If there are still micro-cracks, turning is still required. It should be noted that every time the repair is made, the record should be made and kept for the daily backup.

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How to Adjust the Roll Gap?

Adjusting roll hole shape and controlling plate shape are mainly based on rolled products. The rolls are supported and held in a fixed position in the rolling mill. Roller bearings have a large workload and vary widely, so a small coefficient of friction is required.

After determining the products rolled by the rolling mill, the line speed of the rolling mill can be basically confirmed. The hardness of the raw material is measurable. The rolling stock of the rolling mill is determined by changing the plastic deformation size.

How to configure the rolls according to the hole process? Generally, the newly installed rolling mill has a running-in process. During the running-in process, the rolls are run at no load, and the running speed is 50%, 65%, 75%, and 85% in stages. Different rolling mills have different materials and specifications for rolls according to different rolling products.

For example, the continuous casting machine and rolling mill has a daily output of 100 tons and a rolling speed of 15-25 m / s. Rough rolling efficiency accounts for 30% -40%, intermediate rolling efficiency accounts for 50% -60%, and rough rolling efficiency reaches 95%. After the rolling mill is installed, the large and small teeth of the reducer and gearbox need to mesh, the rolling speed is too fast, and the torque is enhanced. After the rolling mill runs normally for 30 consecutive days, stop the rolling mill to check the meshing of the large and small gears. When everything is normal, the rolling speed can be increased.

Under normal circumstances, there is no need to adjust the rolling speed. In the rolling mill, the rolls are constantly worn during operation. In order to maintain the stable operation of the rolling mill when the rolls are under controllable rolling requirements, the rolls must be repaired in time. In severe cases, the rolls need to be replaced.

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Solution to High Temperature of Rolling Mill

In summer, we should pay special attention to the safe operation of the rolling mill in the high-temperature natural environment, improve its maintenance and repair, because the temperature rise is more likely to cause small problems of the rolling mill. First of all, the cooling circulating water of rolling mill roll can not be less, the average temperature is high, and the cooling circulating water volatilizes too fast, which should be added frequently. And check the body of water in time, and if the water body smells smelly, it is necessary to dismantle and replace the cooling circulating water, throw away the sewage, replace the saponification liquid again, and add the water that must be accounted for.

If the rolling mill works for a long time, it will also cause the temperature of the motor to rise, so you have to touch the bearing end cover shell of the motor by hand to see if the temperature is too high. If the temperature is high, it needs to be shut down to reduce the temperature of the motor before it works without overload.

The cycloid reducer is used in the rolling mill, and the installation method is inverted. In high temperature, the temperature rise will occur, which makes the viscosity of the lubricating grease lower and lower, and it will flow into the bearing end cover, resulting in the lack of lubricating grease in the cycloid reducer, leading to the temperature rise of the reducer, and the more severe one will burn the reducer. Therefore, it is necessary to often check whether there is a lack of grease in the reducer to ensure the normal operation of the reducer.

In summer, it is also necessary to check the route of household electrical appliances of rolling mills. The rise of average temperature will accelerate the embrittlement of the route, which is easy to cause short-circuit fault. However, the actual operating staff of the rolling mill shall wear rubber gloves during safe operation, and the temperature of spiral gear after cold rolling is too high, which will burn their hands.

In addition, the roll of the rolling mill shall be cleaned. At the end of daily work and after standby, the roll must be removed. Clean the roller surface with a clean towel and wipe off the air oxide skin adhered on the surface, so as to improve the service life of the roller.

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Rolling Mill Packaging, Transportation and Storage Requirements

We have introduced a lot of knowledge about the use and operation of rolling mills. However, if we want to ensure the normal use of the rolling mill machine, we need to comply with certain requirements for its packaging, transportation, and storage. Now we will introduce this aspect for you, hoping to provide a reference. 

First of all, let's take a look at how to properly pack the rolling mill. In general, since the equipment is shipped in bulk during transportation, it is required to wrap the motor part with a plastic cloth during packaging so as to prevent damage due to moisture. In addition, the shaft head of all exposed parts also needs to be wrapped with plastic cloth to prevent damage and corrosion.

As for other parts of the rolling mill, it is necessary to apply antirust oil in advance to avoid rusting in early summer. Therefore, in the process of transportation, what should we pay attention to? When loading, unloading and hoisting the equipment, it is necessary to operate it carefully and ensure that the rope used has sufficient strength. At the same time, it should be noted that the protruding part of the equipment shall not be damaged during lifting, and it is better to use some soft things for protection.

In the process of transportation, it is necessary to ensure that the rolling mill machine is fixed so as to avoid sloshing, and no strong vibration or impact. During the driving process, the speed should be uniform and the driving should be stable. In addition, we also need to pay attention to some problems when storing the product.

When the rolling mill arrives, we need to remove it from the box and check it carefully. The rolling mill equipment is then placed in a ventilated and dry room to prevent rust damage. If long-term storage is required, it should be cleaned and rust-proofed.

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How to Avoid Accidents in Cold Rolling?

In many steel rolling plants, especially in cold rolling production, accidents are most likely to occur, including operation accidents, equipment accidents, and quality accidents. All those directly affect equipment, quality, and output. So when accidents occur, remedies should be taken immediately.

1. The rolling piece is deviated, which usually occurs when the head is worn or the tail deviates when the belt is worn. It is caused by the uneven thickness of the incoming material, unskillful operation, old-fashioned roll holes, electrical problems, etc. The slight deviation during threading can be eliminated by timely adjusting and screwing down; for serious deviation, it is necessary to cut the strip steel in front of the frame, find out the cause of deviation, and then re-thread the strip; if it is found that the strip tail is deviated during tailing off, it is necessary to stop immediately, and lift the screw-down according to the situation to make the strip steel pass or cut it. When rolling a very thin strip, the roll is easy to be damaged due to deviation, so special attention should be paid.

　　

2. The rolling mill runout. Rolling mill runout usually occurs during high-speed rolling of extremely thin strip. Because of the beating, the thickness of the strip fluctuates, it is easy to break the strip. Therefore, once the rolling mill has obvious beating sound, the rolling speed shall be reduced immediately to eliminate the vibration. There are many reasons for the runout, such as high rolling speed, thin product thickness, low rolling pressure and small deformation of the finished pass, large tension before the strip steel, too good or too bad lubrication, insufficient roughness of the working roll, damage of the supporting roll, sudden change of various rolling parameters, large gap between the roll bearing and the bearing seat, etc. The cause of rolling mill vibration is complex and it is not easy to make a correct judgment. Through careful search and analysis, before the correct conclusion is reached, only the method of limiting rolling speed is used to prevent the occurrence of run out. 

2. The broken strip of rolled piece. There are many reasons for the broken strip of the rolled piece. Generally, it can be concluded as four kinds: defective incoming material, poor weld quality, misoperation, electrical and mechanical failure. In case of strip breaking, stop the mill immediately to reduce the loss. Serious belt breaking not only makes the work roll and even the support roll bond seriously, but also makes the treatment of the waste belt and the extraction of the work roll very difficult after bonding. Moreover, the treatment time is long and the labor intensity is large. After the belt breaking treatment, the equipment shall be inspected. The surface quality of the first coil of steel to be rolled after roll change shall be checked carefully. For the coil with weld, the mark of the weld position shall be accurate and clear. The rolling speed shall be reduced before the weld passes through the rolling mill. The steel coil with defects must be rolled slowly to minimize the occurrence of accidents in cold rolling production.

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