How to adjust the dynamic imbalance of the drying drum in asphalt mixing equipment?

Many factors that cause the displacement of the drying drum

No matter what form of asphalt mixture mixing equipment it is, the drying drum is an indispensable and important component. A normally rotating drying drum is a balanced system in a state of motion. The drum rotates the drying drum through the drive gear ring between the two roller rings. Ideally, the roller rings and the four supporting rollers (or supporting rollers) are in complete surface-to-surface contact. Through this contact, continuous friction drive is generated, and the drum is in a dynamic equilibrium state during movement. Once external factors disrupt this balance, Then, during the movement of the drum, it will generate up and down displacement along the longitudinal axis of the drum body, which may further rub against the feeding box and the exhaust box, or wear out the cooling cover of the drum, etc. The main external factors are as follows.

The first factor is the inner cavity of the drying drum. The inner cavity of the drying drum is divided into three structural zones, namely the receiving zone, the lifting and scattering zone, and the discharging zone. The lifting Angle of the helical linear blades in the receiving area relative to the longitudinal axis of the drum is 45° to 60°. The lifting and scattering area is installed parallel to the axis of the dry drum, and the unloading area is equipped with planar blades at 20° to 30° to the axis of the drum body. During the production process, due to the collision and friction between the aggregates inside the cylinder and the blades, the blades inside the cylinder are damaged or fall off over a long period of time. As a result, the aggregates exert uneven impact forces on the drying cylinder within the rotating cylinder. This uneven impact force disrupts the complete contact between the surfaces of the roller ring and the idler, resulting in momentary point-surface friction. The frictional drive generated by continuous surface-to-surface contact is transformed into that generated by discontinuous surface-to-surface contact. This discontinuous frictional drive causes the drum to shift along the longitudinal axis of the cylinder. This also disrupted the dynamic balance of the drum. Therefore, the blades inside the drying cylinder should be inspected regularly. Those that are severely worn should be replaced with new ones immediately, and those that have come apart from welding should undergo welding treatment. In conclusion, the integrity of the blades inside the cylinder must be maintained.

The second is caused by deformation due to different temperatures. There are mainly the following situations. One of them is caused by improper operation. Under normal circumstances, materials can be added for production only when the temperature of the drying drum reaches 100℃. If materials are not added for production when the temperature reaches 100℃, the drying drum will deform. The second reason is that after the production was stopped, the drum was shut down before its temperature dropped to 40° to 50°, causing the drying drum to deform. The third one is a sudden power outage during the production process. All of the above factors can cause local deformation of the drying drum, and this local deformation can also disrupt the continuous planar contact between the roller ring and the roller. Discontinuous surface friction drive disrupts the dynamic balance state of the drying drum. Therefore, correct operation is of vital importance. For those using grid electricity, close cooperation with the power department is necessary to promptly and accurately convey the power outage time to the mixing plant. For those using generators, proper maintenance of the generator sets is essential to ensure normal power supply demands.

The third issue is that the wear condition of the drying drum was not inspected during the maintenance period. For instance, the drying drum of the LB3000 type mixing equipment produced by Xizhu is equipped with expansion and contraction components to compensate for temperature deformation between the drum body and the drum hoop. This kind of elastic tangential expansion and contraction member is fixed to the cylinder body with bolts. Over time, these bolts will loosen, causing the movement of the roller ring. As a result, discontinuous frictional drive occurs between the roller ring and the roller, thereby disrupting the dynamic balance state of the drying drum. Another situation is that the drying drum has not undergone displacement along the longitudinal axis of the drum body for a long time. That is to say, neither abnormal friction sounds are heard nor obvious friction between the thrust position roller and the ring of the drying drum is found. We also need to be on guard against this situation. It is possible that the ring and the roller are temporarily maintaining frictional drive between each other. Once this temporary maintenance is disrupted, dynamic imbalance of the drying drum will also occur. Therefore, regular inspections are also of vital importance.

Another issue is that during the installation process, if the foundation is not leveled, causing the drum bottom frame to be not on the same horizontal plane, it can also disrupt the dynamic balance state of this drying drum. No matter what factors cause the dynamic imbalance between the tugboat and the roller ring.

2. How to adjust the drying drum

Use a micrometer to measure the distance lengths between the two edges of the roller ring and the corresponding edges of the supporting rollers respectively. Compare the 8 sets of measured data and adjust the differences among them as close or equal as possible. First, loosen the fastening bolts of the tugboat bearing housing and adjust the screw to make the adjustment. This adjustment method is an ideal one. Due to the particularity of the mixing equipment and its special operation, there are too many force majeure factors in this method, making the adjustment rather time-consuming. As analyzed earlier, the dynamic balance state of the drying drum is disrupted by the continuous surface-to-surface friction drive between the roller (support roller) and the ring being transformed into a linear or point-surface friction drive between them. Therefore, in actual adjustment, this point-surface or linear friction drive can be changed to a continuous surface-to-surface friction drive, thereby preventing the drum from shifting along the longitudinal axis of the cylinder. This further maintains the dynamic equilibrium state of the drying drum.

To facilitate a concise explanation of the adjustment method, first mark and draw a concise schematic diagram of each drag wheel and each adjustment screw of the drying drum. Figure 1 shows the names of some of the components of the drying drum mentioned in this article. Figure 2 is a clear front view of the drive shaft bearing housing where the tugs are connected to each other. Figure 3 is a simple top view of the tugboat, the drive shaft and the bearing housing connected to it. First, mark the four rollers (support rollers) and the connected drive shaft bearing housings as shown in Figure 3. Facing the burner, the left side of the two rollers at the cold material entry end is No. 1 and the right side is No. 2. The two sets of rollers on the left side of the hot aggregate entering the elevator end are No. 3 and on the right side are No. 4. Among them, No. 4 is the roller at the hot aggregate entering the elevator and the connected drive shaft bearing housing. The adjustment rods on the left side of each roller, from the hot aggregate entering the hot end to the cold aggregate entering end, are respectively marked as a, a1, c, c1, e, E1, g and g1, and on the right side are respectively marked as b, b1 and d. d1, f, f1, h and h1. The corresponding bearing housing fastening bolts on the left side are A, A1, C, C1, E, E1, G and G1 in sequence, and on the right side are B, B1, D, D1, F, F1, H and H1 in sequence.

If the drying drum moves upward along the longitudinal axis of the drum (i.e., towards the cold aggregate entry section), practice shows that the No. 3 and No. 4 rollers and the roller ring are driven by unconnected surface friction, that is, instantaneous point-surface or line-surface contact. The adjustment method for this situation is: The fastening bolts A, B, C and D of the bearing seats of No. 3 and No. 4 tugboats remain stationary. Loosen the bolts A1, b1, C1 and D1 of No. 3 and No. 4 tugboats. The adjusting screws a, B, c and d of No. 3 and No. 4 tugboats remain stationary. Loosen the adjusting screws B1 and c1 of No. 3 and No. 4 tugboats. (Mark the number of threads of each loosening screw.) Then, adjust the screws a1 and d1 to the corresponding number of threads, and then tighten the loose fastening bolts A, B, C, and D.

If the drying drum has a downward shift along the longitudinal axis of the cylinder body, the adjustment method is exactly the opposite of the upward shift. That is, loosen the bolts A1, B1, C1, and D1, keep the adjustment screws a, b, c, and d still, loosen the adjustment screws A and d (mark the number of threads of each loosened screw), and then tighten b and c by the corresponding number of threads.

There is another situation, that is, the No. 4 roller is close to the hot aggregate elevator and the place where the hot aggregates in the drying drum enter the hot lift. Therefore, the wear of the No. 4 roller is relatively severe. The No. 4 roller can be adjusted separately to achieve the purpose.

If the drying drum moves upward along the longitudinal axis of the cylinder body, the adjustment method is: Keep No. 1, No. 2 and No. 3 still. Loosen the fastening bolts D and C of No. 4, while keeping the bolts D1 and C1 still. Keep the adjusting screws of c 1 and d1 still. Loosen the adjusting screw of c (mark the number of threads of each loosening screw), then tighten the corresponding number of threads of d screw, and then tighten the bolts D and C.

If the drying drum moves downward along the longitudinal axis of the drum body, the adjustment method is exactly the opposite of that when it moves upward. Keep No. 1, No. 2 and No. 3 still, loosen the fastening bolts D and C of No. 4, while keeping the bolts D and C1 still, and the adjusting screws of c1 and d still. Then loosen the adjusting screw d (mark the number of threads of each loosening screw). Then tighten screw c by the corresponding number of threads, and then fasten bolts D and C.

The above adjustment methods should be carried out until the drum operates smoothly, with upward and downward thrust, the positioning roller not rotating, and no friction sound from the drying drum. Generally, No. 1 and No. 2 do not need to be adjusted. If, after adjusting No. 3 or No. 4, the drying drum has not yet reached a dynamic equilibrium state, that is, there is displacement along the longitudinal axis direction, at this time, No. 1, No. 2, No. 3 and No. 4 should be adjusted respectively. Then, use a micrometer to measure 8 sets of data for each drag wheel and the edge of the roller ring respectively. Then, adjust according to the displacement direction to make these 8 sets of data as basically the same or similar as possible. In conclusion, which adjustment method may enable the drying drum to reach a dynamic equilibrium state in a short period of time? Because before the adjustment, the roller ring and the roller are not in continuous surface-to-surface contact. After the adjustment, it may temporarily achieve continuous surface-to-surface friction drive. If it wears out for a long time, this continuous surface-to-surface friction drive is always at risk of damage. Therefore, it is necessary to observe frequently. Once any abnormality is found, Timely adjustments should be made.