Are you embarrassed by your vertical roller mill skills? here's what to do

Vertical roller mill is a kind of milling equipment, and then, in the process of daily use, it is inevitable to encounter faults. So,when you meet its faults,are you embarrassed by your skills,the following are the solutions of common faults.

 

1. Mill vibration

(1) The thickness of the vertical roller mill grinding plate material layer is not properly controlled and the material bed is not stable. If the bed is too thin, it is easy to vibrate;well,it is too thick, which is easy to cause more severe vibration. The factors that affect the thickness of the material layer include the feeding amount, material granularity, air volume, powder selection efficiency and circulating load rate, grinding pressure, height of the retaining ring, grinding temperature, material moisture, water spray amount in the mill, etc., and the vibration trip caused by improper thickness of the material layer.At the moment of tripping, the pressure at the inlet of the vertical grinding mill, the pressure difference in the mill and the current of the main motor will rise rapidly, but there is no obvious change before the vibration stop.

(2) There are large metal and other foreign matters in the vertical roller mill, so this kind of skip stop phenomenon is very obvious, usually all kinds of parameters are normal,well the vertical roller mill suddenly stops.

(3) Equipment failure of roller mill itself.Such as abnormal accumulator pressure imbalance, hydraulic pull rod fracture, vibration measuring element failure, etc.

(4) The pressure difference is not stable. The stability of pressure difference indicates that the input and output materials have reached a dynamic balance and the circulation load is stable. Once the balance is broken, the circulation load changes. Among them, the decrease of pressure difference means that the amount of materials entering the vertical roller mill is lower than the amount of materials leaving the mill, the circulating load is reduced, the thickness of the material bed is gradually thinner, and the vibration value of the mill is increased; well,higher is quite the opposite.

 

2. Low loading pressure are:

(1) The overflow valve of the hydraulic station is improperly adjusted or blocked, resulting in overflow.

(2) The check valve at the oil pump outlet fails or is blocked.

(3) Aging and leakage of oil pump seal.

(4) The hydraulic cylinder is not sealed tightly and has internal leakage.

(5) There is leakage in the joint of the hydraulic pipeline, which is mostly caused by the vibration of the mill.

(6) The oil temperature is too low, resulting in high viscosity, excessive load of the oil pump and low oil pressure. This phenomenon often occurs after a long time of shutdown in winter, which is caused by the failure of the temperature control system in the oil station.

(7) The liquid level is lower than the critical line, and the oil absorption capacity of the oil pump is insufficient, which is usually accompanied by the abnormal sound of the oil pump.

 

3. Hydraulic cylinder rod

(1) Fatigue failure caused by repeated action of tension and shear force. The rod is connected with the piston rod of the hydraulic cylinder in the form of thread, and the fracture of the rod mostly occurs at the root of the thread; the rod stress fatigue damage can be reduced by controlling the stability of the material bed and reducing the wave fluctuation vibration of the grinding roller.

(2) Overload, too much loading pressure. The normal loading pressure of the vertical roller mill is 6-8mpa, and the abnormal state is 5-14mpa, which exceeds the normal working curve of the mill.

(3) The lower limit wire value is adjusted too low. The limit wire can prevent the buffer pressure peak value and reduce the load of hydraulic cylinder and pull rod. If the lower limit wire value is adjusted too low, it will not work. After pressurization, all pressures will act on the hydraulic pull rod except the load on the grinding roller, which may cause the pull rod to break.

(4) The hydraulic cylinder rod joint bearing is locked. It is mainly due to the raw material dust and other sundries blocking the oil path and joint bearing of the hydraulic cylinder rod joint bearing, which makes the hydraulic cylinder rod uneven stress, unable to decompose the pressure peak, resulting in the rod fracture.

4. Abnormal wear of grinding roller and disc 

(1) Changes in abrasiveness of materials, such as the use of steel slag instead of iron ore ingredients, or limestone and other raw materials containing flint, pebbles and other impurities with poor abradability;

(2) The sundries such as metal blocks entering the vertical roller mill may be brought in by raw materials or shed from the inside of the mill;

(3) The nozzle ring air velocity is too fast, the inner circulation is large, and the temperature is too high for a long time;

(4) The material layer is thin, or the powder material is too large, and the vertical roller mill vibration is large. In serious cases, the grinding roller will rub against the plate.

 

5. Blocking the equipment body and its discharge port

(1) The amount of fine powder is small, and the slag is mainly large limestone. The reason is that limestone has poor grindability (such as containing bluestone, chert and cobble), large grinding particle size and small loading pressure.

(2) There is a lot of fine powder in the slag. The main reasons for the phenomenon are: insufficient air volume or too high air temperature of the circulating fan, blocked air inlet, abrasion or improper area of the nozzle ring, resulting in low air speed at the nozzle ring, low retaining ring, excessive feeding amount of the mill, abnormal abrasion of the grinding roller and disc, and decreased grinding efficiency.

 

6. Low mill output

(1) Material impact: if the particle size is too large or too small, the abradability is poor.

(2) Defects of the vertical roller mill itself: such as serious wear of grinding disc and roller, low loading pressure caused by hydraulic system failure, low efficiency of powder separation caused by blade wear, improper adjustment of blade angle, wrong rotation direction of rotor, etc., and large circulation in the vertical roller mill. When the nozzle ring is worn down, the material layer of the disc becomes thick and the amount of slag is large.

(3) Operation impact: for example, the drawing of circulating fan is too small or the air inlet is blocked and not cleaned in time. Vertical roller mill vibration caused by high outlet temperature control, small water spray volume and poor atomization effect.

 

7. Hydraulic system failure

(1) The hydraulic pump starts frequently. The main reasons are: unreasonable pressure setting; leakage of hydraulic cylinder seal or hydraulic system pipeline.

(2) If the loading pressure fails to meet the requirements, the hydraulic pump will continue to operate. Main causes: the setting value of relief valve is too low; the hydraulic cylinder accumulator charging pressure is too low or there is leakage; there are sundries blocking the relief valve or safety valve which causes the valve leakage; the seals or pipe joints of hydraulic cylinder are leaking.

(3) The hydraulic oil temperature is high. Main reasons: low pressure of nitrogen bag in hydraulic cylinder or damage of skin bag lead to failure of energy storage buffer function of nitrogen bag; large vibration of vertical roller mill, frequent action of piston in hydraulic cylinder; large resistance or small diameter of hydraulic pipeline, high pressure and high flow rate of hydraulic oil.

 

8. Lubrication system failure

(1) The main faults of the main motor bearing lubrication system are: the liquid level is too low or too high or even overflowing; the liquid level difference between the front and rear axles is large. The main reason is that the diameter of the throttle valve at the outlet of the lubricating pump is too large and the regulating accuracy is not enough. Solution: install a throttle valve on the oil inlet pipeline of the front and rear bearings of the main motor, and adjust separately.

(2) The main faults of the reducer lubrication system are: the small diameter of the return pipe or the oil tank high level in the lubrication station causes the poor return oil; the low pressure of the high-pressure pump. The main reasons are: the setting value of overflow valve is not appropriate or the overflow is blocked; the cooling water fault causes the oil tank temperature to be high and the viscosity of lubricating oil to drop; the pump head of lubricating pump is blocked, etc.

(3) The main fault of the roller lubrication system is that there is no return oil or the return oil quantity is small. The reason is that the oil return pipeline is not well sealed, the jet pump suction effect is poor, the filter is blocked, etc.

(4) The main faults of dry oil lubrication system are as follows: ① the lubricating point does not produce oil or the oil output is small. The reason is that the viscosity of lubricating grease is too large; there are many impurities in lubricating oil; there is leakage in the overflow valve or safety valve of lubricating pump; ② there is oil leakage at lubricating point or pipeline joint. The main reason is: the oil pressure is too high or the mill vibration causes the joint expansion sleeve or the contact looseness.

 

As a professional manufacturer of grinding mills, Shuguang Heavy Machinery sells a variety of different types of mill equipment, including ball mills, Raymond mills, vertical mills, etc.Welcome to contact us for more details.

 

Factory Address: Longjiang West Road, Shangjie District, Zhengzhou City

Contact number: +86-371-67666660 676667

Mobile phone: 0086 13523465141

After-sales Service Department: 0371-67666667