Dual horizontal axle forced mixer is suitable for mixing dry hard, plastic, fluidity concrete and various mortars. Besides being used as a single machine, it can also be used as a simple mixing station synthesized with the batching unit. It is widely used in construction engineering. Our company has purchased more than ten JS500 double horizontal shaft forced mixers for leasing operation. In the first half of 2002, when the lessee used the mixer, six cases of JS500 double horizontal shaft forced mixer reducer case rupture occurred successively. Cracks are located in the bearing chamber of the output shaft of the reducer. One case of the bottom shell of the reducer box is broken and five cases of the cover are broken. Long downtime maintenance has greatly affected the normal construction of the lessee.

Reasons for Cracking of Reducer Case

After investigation and analysis, it is found that the cause of the cracking of the reducer case is the large overload during the operation of the mixing system, which makes the bearing chamber of the reducer case bear much more support reaction than the design value. Especially, this kind of force is unstable, forming a continuous impact, to a certain extent, it will cause cracking at the bearing chamber of the box, and make the whole box destroyed and scrapped. In the design of double horizontal shaft forced mixer, overload factors have been taken into account, which can generally withstand 10% overload. Therefore, the sudden overload in the operation of the mixing system should not cause damage to the equipment. The reasons for the damage of mixer reducer can be considered from two aspects:

(1) The ability of the mixer itself to withstand overload decreases;

(2) The erroneous behavior in the course of use results in a large overload.

Through the investigation and visit of the users, the causes of the cracking of the reducer case are as follows:

1.1 Excessive clearance between mixing blade and lining plate of mixing tank

After using the mixer for a period of time, the clearance between the mixing blade and the lining plate of the mixing tank gradually increases due to wear and tear, which exceeds the prescribed clearance value. When running, the mixing blade can not scrape the residual concrete on the tank lining board. After long time use, the ash layer is formed on the lining board, which increases the friction resistance between the concrete material and the tank lining board. In addition, when the gap between the two is increased, stones are easy to plug in the mixing system, which leads to the increase of the load of the mixing system. In this way, the mixing system is often overloaded in normal use, and the impact force formed by a large number of stone plugs will affect the reducer until it is destroyed.

1.2 Too Long Water Supply Time

When the hopper of mixer feeds into the mixing tank, because the water supply system can not complete the water supply within the prescribed time, or even there is no water supply, the mixer mixes the dry and semi-dry materials for a long time, which greatly exceeds the requirement that the mixer's dry material mixing duration is not more than 20 seconds specified in the design, resulting in the overload operation of the mixing system, if there are stones. The sub-cassette will cause a large overload of the mixing system and induce the failure of the reducer.

1.3 man-made causes

Man-made factors are various, and often interlace with the problems existing in the equipment itself, which becomes the main cause of equipment damage.

(1) The mixer is equipped with thermal protection device when it leaves the factory. When the mixing system is overloaded, the thermal relay will operate and cut off the power supply. When the field electrician or operator randomly adjusts the limit value of thermal relay, it loses its protective function, creates conditions for large overload of mixer, and also buries hidden dangers for damage of equipment.

(2) The concrete in the mixing tank will harden if the shutdown time is too long. At this time, if the operator forces the equipment to start running, the mixing system will be overloaded. If the concrete in the mixing tank is not unloaded and re-fed, the concrete capacity in the tank will exceed the allowable value, and the mixing system will also be overloaded. Both of them are very easy to build. Damage to mixer.

2 solution

In view of the above situation, we start with equipment and personnel, strengthen the maintenance of equipment and personnel training, fundamentally prevent the occurrence of decelerator case rupture.

2.1 maintenance

In order to ensure the normal use of equipment, it is necessary to strengthen the maintenance of the rental mixer. To this end, on the one hand, the company set up a tour maintenance team to maintain the equipment every half month. Check the mixing system, replace the severely worn mixing blades and lining plates, adjust the clearance value between the mixing blades and the lining plate of the mixing tank to be less than 3 mm (instructions are less than 5 mm), so that the mixing blades can scrape away the residual concrete on the lining plate in time and cleanly, prevent the formation of ash deposit layer, reduce the resistance of the mixing system, and prevent the causes. The gap between stirring blade and liner is too large and the cassette stone produces overload and impact. On the other hand, the water supply system is maintained regularly to prevent leakage of water supply pipelines. Clean the sprinkler hole in the tank and adjust the sprinkler angle in time to ensure that the spray direction of the water flow is directly aligned with the center of the mixing shaft when the water supply time is not more than 16 seconds. When pouring concrete with large volume and multi-machine operation, special personnel should be assigned to manage water source to prevent interruption of water supply, resulting in dry mixing or shutdown of mixing system. In construction, short shutdown time should be used to clean up the concrete attached to the mixing shaft and the inner wall of the tank so as to reduce the resistance of the mixer in normal operation. Immediately after the completion of the work, wash and clean the residual concrete in the mixing tank to prevent the formation of residual layer in the tank lining plate and the mixing shaft. Seal the regulated thermal relay to prevent random movement of personnel, provide overload protection for the mixer, and prevent the occurrence of large-scale and long-term overload of the mixer.

2.2 Strengthen personnel training

Make operation rules of mixer, train operators on site to improve operation level. If there is concrete shutdown time more than 5 minutes in the mixer, or water shortage in the mixing process, the mixer should be shut down in time to release part of the material before starting the mixer operation. In addition, when the leased mixer is permitted, the company can equip operators to operate on site to prevent accidents caused by temporary operators who are not familiar with the operation.

Through the implementation of the above measures, no cracking of the reducer case occurred again, which shows that the above-mentioned method to solve the cracking of the double horizontal shaft forced mixer case is effective.