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Common failure reasons and solutions of roller press

  The roller press has been widely used in various grinding operations since it came into being in the mid-1980s.

  The roller press is composed of two rollers with the same speed and relative rotation.

  The material is discharged from the feed opening above the roller and enters into the gap between the rollers. Under the action of high pressure grinding force, the material is squeezed and the compressed material turns into a compact flat cake full of cracks, which obviously improves the grindability of the material.

  Roller surface wear, bearing damage are common roller press problems, regular maintenance of the roller press to the production of a great help.

  Roll press common problems

  1. Damaged roll surface

  The roller surface of the roller press is made by surfacing several layers of composite metals. The matrix of the roller is made of alloy forging steel. The hardened layer with rockwell hardness >50 is surmounted on the transition layer, and then the harder wear pattern is surmounted on the hardened layer.

  In order to make the life of the roller surface >8000 ~ 10000h, the hardness of the most surface wear pattern can reach 60 ~ 65HRC, so as to improve the wear resistance.

  Reasons for roller surface damage:

  (1) in the process of production operation, the damage of the roller surface is a common phenomenon.

  Its main performance is that the surface of the roller cracks, expanding into cracks, resulting in the surface of the hard wear layer peeling.

  It can be seen from the working condition of roller press that the wear type of roller surface belongs to the typical high stress abrasive wear.

  In the process of abrasive wear, material particles under the action of pressure will cause elastic and plastic deformation of the roller surface, thus forming cyclic compressive stress and tensile stress in different depths of the subsurface layer of the roller surface. When the cyclic stress exceeds the fatigue strength of the roll material, it will cause cracks in the surface layer.

  Under cyclic loading, the plastic deformation of subsurface continues to develop, and cracks will also occur at a certain depth away from the surface, and gradually expand.

  When the crack expands, the material above the crack breaks and breaks off, which is called fatigue wear.

  Therefore, the wear mechanism of rollers is the result of the joint action of high-stress abrasive wear on the roll surface and fatigue wear on the sub-surface of the roll surface.

  (2) in the process of operation, metal sundries or hard materials such as glass will be mixed into the materials of the feeding roller press.

  Under the strong grinding force between two rollers, metal sundries may directly damage the roll surface, resulting in pits or collapse of hard wear-resistant layer on the roll surface.

  Because this hardened layer is very hard, relatively speaking toughness is poor, so the most afraid of hard, resulting in hardened layer crack growth and hardened layer collapse eventually produce roller surface defects.

  If the situation is serious, it will directly affect the life of the roller surface, the increase of defects, directly affect the quality of the cake produced by the roller press and not reach the desired rolling effect.

  (3) manufacturing defects of the equipment itself.

  After the surface of the roller is damaged, treatment methods:

  (1) online repair. In the process of surfacing, welding materials shall be selected according to the materials of rollers and the application occasions. The company USES Beijing guben wear-resistant welding wire.

  (2) offline repair.

  2. Bearing damage of roller press

  The four bearings of the roller press are the key parts of the whole equipment. The grinding force of the crushed materials of the roller press is applied by the hydraulic cylinder to the bearing pedestal to push the roller and driven by the motor to make the roller rotate. This can only be implemented through the bearing.

  Bearing is the key component of roller press, once bearing accident occurs, the roller press will be shut down, resulting in serious consequences.

  The reasons for bearing damage are various:

  (1) manufacturing quality problems of bearing itself;

  (2) may be caused by overload, load aggravation, such as: set working pressure is too high, two rollers speed is not

  With, cake is too thick, liquid couple refueling quantity is not and so on reasons;

  (3) too severe vibration may also cause bearing damage, resulting in a variety of reasons for vibration, such as:

  (1) too much fine powder content in the material (if the particle size below 5mm material content reaches more than 50%);

  (2) into the roller press material is too dense, material forming cake due to the reduction of porosity, the gas can not be discharged through the upper material;

  (3) through the roller press, the roller press inlet is blocked by foreign bodies or stable bin material level low caused by uneven blanking;

  (4) there may be hidden dangers left by improper installation, such as:

  (1) two roll center line is not parallel or parallel but not the same level surface;

  (2) between the two rollers limit block is too thin, idling may cause contact between the two rollers and other reasons;

  (3) when installing, the interference amount of bearing clearance does not meet the required data, that is, 0.25~0.35mm;

  (5) it is possible that both ends of the roll gap deviation is large, and long-term continuous operation.

  The reasons for roll gap deviation are as follows:

  (1) there are problems in the control system, the pressure at both ends, and for a long time can not be adjusted;

  (2) the problem of the material itself, the material into the buffer warehouse, the degree of segregation phenomenon, uneven particle size distribution of the material into the roller press, both ends of the roller force is uneven, roll gap deviation will produce;

  (3) side baffle side failure, material at both ends of the roller through quantity, the unrestricted side through quantity and low pressure;

  (4) the inlet width deviation along the direction of the roller is large or the inlet side is blocked by a foreign body, causing the material through the gap between the two rollers, the two ends of the roller through the amount of unequal;

  (6) poor bearing cooling, poor circulating cooling water or insufficient cooling water may lead to bearing temperature too high and damage;

  (7) for systems lubricated with dry oil, bearing seal failure and insufficient supply of dry oil may result in poor lubrication of the bearing, thus damaging the bearing.

  (8) oil deterioration, oil into ash, resulting in bearing damage.

  In order to prevent bearing damage, the following aspects should be done:

  (1) strictly control bearing quality when buying bearings;

  (2) ensure the normal and effective operation of the control system;

  (3) when the roller press starts feeding, it first adds a certain pressure. When the material stretches the roller press to a certain seam, it then starts to increase the pressure to the working pressure. In this way, the moving amount of the moving roller is not from the minimum to the maximum, which can effectively reduce vibration.

  (4) bearing installation,  (1) must strictly control the interference of bearing clearance;

                                         (2) to ensure that the two roll center line is parallel and in the same horizontal plane;

  For different specifications of the roller press, block thickness should be different.

  In the author's opinion, it should be based on the principle that the two roller surfaces do not rub against each other when the roller press is idling. Generally speaking, it is advisable to use 18-30mm.

  (5) in terms of working pressure, theoretically, the optimal effective range is 30-150mpa, and the effect is shown in the figure (shown by the curve). However, considering the current situation of our company's equipment, it is advisable not to exceed 50MPa.

  (6) in terms of materials, the content of fine powder should be minimized, and the particle content of 20-25mm should be above 60%;

  (7) take measures to control roll gap deviation as far as possible, such as adding feeder on top of stable bin, adding overflow box inside and adding isolation board inside bin;

  (8) ensure that the passing amount of materials can be adjusted freely;

  (9) strengthen smooth management and site management.

  Standard equipment management and good environment are necessary to ensure the normal operation of the lubrication system.

  3. Roller shaft and reducer hollow shaft are pulled

  The power of the roller press is transmitted to the roller by the motor through the reducer, and the roller and reducer are fixed by the locking plate.

  The locking plate is a kind of keyless coupling device which realizes load transfer by tightening the pressure and friction force generated by the high strength bolts.

  In order to ensure a certain torque and axial load value, it must be tightened according to the specified tightening torque.

  When installing the roller press, if the screws are not tightened according to the data required by the locking disc, it may cause the roller press shaft and the reducer hollow shaft to slide, causing the roller press shaft and reducer hollow shaft to pull.

  Once the roller press shaft is pulled, the repair method generally adopts thermal spraying and cold welding.

  4, hydraulic cylinder leakage

  Cause analysis:

  (1) there are defects in the design. The contact surface between the cylinder body of the hydraulic cylinder and the press plate is flat. This structure cannot automatically adjust the center.

  And because of the weight of the cylinder itself, leading to the movement of the cylinder, the cylinder and the cylinder liner two semicircle arc friction degree is different, resulting in the hydraulic cylinder oil leakage.

  (2) poor environmental sanitation on site. Dust enters the joint surface of cylinder body and cylinder liner, causing seal ring wear and hydraulic cylinder oil leakage.

  (3) high working pressure will affect the sealing effect of the sealing ring.

  (4) hydraulic cylinder cylinder itself has quality problems, machining accuracy is not high, there is a convex point, so that it and the cylinder can not be a good fit.

  Improvement methods:

  (1) the front end of the hydraulic cylinder is equipped with a spherical structure. When the axis of the hydraulic cylinder and the surface of the bearing seat are not perpendicular due to the movement of the bearing seat, the outer sphere rotates in the inner sphere, thus eliminating the radial force that may be generated on the cylinder rod.

  (2) add one or two new seals at the front end of the cylinder liner, and the seals are oil seals;

  Connect the oil return port with the oil tank or other containers by hose to ensure that the joint part is intact and does not leak.

  With the above improvement measures, when the hydraulic oil produces internal leakage, the leaked hydraulic oil will reach the matching part of the plunger and the cylinder liner through the seal on the plunger, but because there is a seal on the front end of the cylinder liner, and the pressure of the oil here is close to zero, so the oil will not leak from the front end of the cylinder liner.

  When there is a lot of oil collected, it will be introduced into the oil tank or other containers through the return port through the hose, so as to avoid oil leakage.

  (3) add canvas soft joint at the front of the hydraulic cylinder to protect the leaking cylinder rod outside, which can effectively prevent dust from entering into the cylinder body;

  In a word, strictly abide by the relevant operating procedures during maintenance, and maintain environmental sanitation in operation is very necessary for the protection of equipment.

  5. Side baffle leakage

  The gap between the side baffle of the roller press and the end face of the roller is not well adjusted. The gap is often enlarged due to wear and other reasons, resulting in material leakage.

  In order for the roller press to ensure supersaturated feed, the baffle must have a good sealing effect.

  Generally, under the condition of no friction with the end face, the closer the end face of baffle and roller is, the better.

  Therefore, to solve the problem of material leakage, we must do the following:

  (1) the baffle must be parallel to the end faces of the rollers, and the end faces of the two rollers must be flush;

  (2) since the side baffle is installed on the feeding mechanism, the correct position of the feeding mechanism must be ensured, otherwise the position of the baffle will be changed;

  (3) the side baffle shall be adjusted at any time after wear, and the gap between the baffle and the end face can be adjusted by using the lower lead screw.

  6. The roller ends are far away from each other

  The causes and preventive measures of this problem have been described before, so it is unnecessary to elaborate here.

  In short, roller press as a kind of material pre-crushing equipment, with its remarkable energy-saving effect, with the development of automatic control technology and material science progress, in the modern cement industry has been more and more widely used, but in

  Some problems exposed in the application still need to be further explored and solved.

  The opinions stated in this article are only some experiences in the application. I would like to take this opportunity to communicate with my colleagues to promote the better application of roller press in the cement industry.

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