1. Existing problems
　　high pressure water descalingThe function of the equipment is to thoroughly remove the surface scale of the billet by spraying high-pressure water before rolling, so as to ensure the smooth biting of the billet into the roughing mill and the surface quality of the billet in the subsequent rolling. At present, because there is only one set of nozzles for high-pressure water descaling, the descaling is not complete, mainly because there is a certain amount of iron oxide scale on the two side surfaces of the billet after descaling, which is easy to cause the following problems in the process of reciprocating rolling in the roughing mill:
(1) When the billet bites into the pass of the roughing mill, it slips due to the iron oxide in the head, resulting in steel stacking.
(2) Excessive iron oxide scale is accumulated near the roughing mill, which is easy to cause false detection of automatic detection components, resulting in errors in the automatic control program, and also easy to cause steel stacking.
(3) Due to the existence of iron oxide scale on the surface of the billet, the rolling process is prone to product defects such as pitting and foreign body pressure, resulting in a large number of waste products.
(4) When the roughing mill shaft bites into the rolling piece, its torsional vibration is three times the peak value of its torsional vibration in the case of poor descaling, which seriously shortens the service life of the roughing mill shaft.
Due to the existence of the above problems, it has caused very frequent equipment shutdowns and a large number of product defects, which seriously restricts the smooth production of medium-sized steel mills.
2. Modification of high pressure water descaling system
Working principle of high pressure water descaling before 2.1 reconstruction
As shown in the figure:
1. Suction water tank 2, filter 3, motor 4, high pressure hose 5, accumulator (120L × 3) 6, pressure regulating valve 7, discharge valve 8, check valve 9, high pressure plunger pump
The industrial water reaches the high-pressure plunger pump from the suction water tank through the filter for pressurization, and is delivered to the accumulator through the hose (the maximum working pressure of the accumulator is 16.2Mpa, and the minimum pressure is 12.7Mpa) for pressure maintenance. When the billet passes through the water descaling equipment, the nozzle valve is opened, high-pressure water is sprayed on the billet surface for descaling, and the accumulator is unloaded; after the billet passes, the nozzle valve is closed, the accumulator is loaded, and the next work cycle is waited.
2.2 equipment transformation programme:
In view of the problem that the high-pressure water descaling and removing the iron oxide scale on the billet surface are not complete, the following measures are specifically taken:
(1) Add 1 group of nozzles and use them in parallel with the original 1 group.
(2) Add a group of accumulators and use the newly added nozzles.
(3) The distribution mode of the newly added nozzles is changed. Since the outer edge of the roller has worn off the scale on the lower surface of the rolling mill during the walking of the rolled piece from the heating furnace to the roughing mill roller table, the lower nozzles do not need to be added. If the capacity of one plunger pump cannot meet the work of two groups of nozzles at the same time, another high-pressure pump shall be installed.
The principle after equipment modification is shown as follows:
1. Suction water tank 2, filter 3, motor 4, high pressure hose 5, discharge valve 6, pressure regulating valve 7, accumulator 8, check valve 9, high pressure plunger pump 10, check valve 11, discharge valve 12, accumulator
Add 1 set of accumulator and 1 set of nozzles to be used in parallel with the original, and the two sets of nozzles are controlled separately. When the billet passes through the water descaling equipment, the first group of nozzles spray scale first, and through delay control, the second group of spray scale then spray scale, which is equivalent to a billet for two times descaling; In addition, the distribution position and spray angle of the newly added nozzles are readjusted to solve the problem of poor descaling effect on the side surface of the billet.
Capacity Selection of 2.3 Increasing Accumulator and Capacity Checking of Piston Pump
The accumulator used for high-pressure water descaling is a bladder type accumulator, and the bladder is filled with nitrogen during use. The bladder accumulator has the characteristics of compact structure, light weight, and low inertia. It can absorb rapid pressure changes and pulses. It has good shock absorption and pressure stabilization. It is especially suitable for the pressure caused by the reciprocating action of the plunger pump. pulse. Therefore, the newly added accumulator is still a bladder accumulator.
The bladder accumulator works according to the principle of gas law. Therefore, the basic relationship between the pressure and volume of the gas is expressed by the following formula:
　　p1v1n=p2v2n 
Where: p1 and p2-initial gas pressure and final gas pressure;
v1 and v2-initial gas volume and final gas volume;
Under isothermal conditions, that is, the compression and expansion of the gas occurs slowly, and there is sufficient heat dissipation time;
Then n = 1, so p1v1 = p2v2 under isothermal conditions;
Under adiabatic conditions, n is equal to the ratio of the specific heat of the gas at constant pressure to the specific heat of the gas at constant volume. If nitrogen n = 1.4 under adiabatic conditions, p1v11.4 = p2v21.4.
2.3.1 Calculate the capacity and quantity of the new accumulator according to the displacement of the original accumulator
As shown in the figure:
Under the conditions of charging, loading and unloading, the volume of gas in the bladder is v1, v2 and v3 respectively, and vx is the liquid displacement of an accumulator.
The relationship between the gas charging pressure p1 and the minimum working pressure p3 of the accumulator is:
p1 ≤ 0.9p3
The average loading process is 20 seconds, which can be calculated as an isothermal process according to p1 = 0.9 p3:
According to the formula: p1v1 = p2v2
Respectively p1 = 0.9 × p3 = 0.9 × 12.7 = 11.43Mpa
　　p2=16.2Mpa 
v1 = 120L Substituting Formula
Available: v2 = 84.67L
The average unloading time is 3 seconds. This process can be used as an adiabatic process, according to the formula: p2v21.4 = p3v31.4
will respectively
　　p2=16.2Mpa 
　　v2=84.67L 
P3 = 12.7Mpa Substituting into Formula
Available: v3 = 100.74L
Liquid displacement of one accumulator vx = v3-v2 = 100.74-84.67 = 16.07L
The total displacement of the 3 accumulators is V = 3 × vx = 3 × 16.07 = 48.22L
According to the adiabatic power curve, it can be found that the accumulator with a volume of 100 L can best meet the requirement of effective liquid displacement of 16.07 L.
According to the gas law, the same can be obtained:
The actual liquid displacement of 1 accumulator with a volume of 100L is:
vx new = v3-v2 = 13.4 L
Set the displacement of the first group of nozzles and the second group of nozzles to be the same, then the number of new accumulators is:
N = V/vx new = 48.22/13.4=3.6 ≈ 4
2.3.2 Check the capacity of booster pump
At present, there are two three-stage high-pressure plunger pumps for high-pressure water descaling. During normal operation, one is working and one is standby. The rated working pressure is 150kgf/cm2, the maximum pressure is 170kgf/cm2, and the rated flow rate is 350L/min. The two accumulators work simultaneously. The average loading time is 20 seconds, the average unloading time is 3 seconds, and the rolling rhythm (the interval time between two billets for high-pressure water descaling) is 120 seconds, the total displacement of 2 accumulators in each working cycle is:
3vx 4vx new = 3 x 16.07 4 x 13.4 = 101.8L
The displacement of one pump in one working cycle is calculated according to 95% of the output power:
350/60 × 120 × 95% = 665L>>101.8L
In addition, the average loading time of one group of accumulators in one working cycle is 20 seconds, so the loading time of two groups of accumulators working at the same time is:
20 ×(1 400/360)= 42 seconds <<120 seconds
Another 4 accumulators with a capacity of 100 L and the original 1 group of accumulators can fully meet the working requirements by using 1 pump together, so there is no need to install another booster pump.
3. Concluding remarks
After the transformation of the high-pressure water descaling of the roughing mill, the problem of incomplete removal of the iron oxide scale on the surface of the billet is completely solved, the equipment downtime, rolling waste and product surface defects caused by the iron oxide scale are greatly reduced, and the service life of the roughing mill shaft is greatly extended.

                                              

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