Double-toothed roll crushers have been successfully used for crushing coal ore. Due to hard and large pieces of the limestone, some problems appear during the crusher employment such as the breaking of tooth crow, difficult to repair and replace while the toothed ring has broken, and cracking of the inner ring of bearing for crushing rolls. During the maintenance operation, case-shaped tooth crown and compound toothed ring is applied to replace originals and axial-fixed settings is added to crushing rolls, so as to solve the above problems. Thus, the productivity enhances, and the production costs decrease.
The double toothed roll crusher is a highly efficient and energy saving crushing equipment developed in the international crushing field in the mid to late 1980s. Deya Machinery is one of the earliest companies to produce double roll crusher since 1990. The crushing rolls adopt large tooth shape, small roll diameter, multiple crushing discs and spiral crossed tooth form, which has a strong ability to hold large pieces, less repeated crushing, selective crushing of materials, uniform discharge size, also known as screen crusher.
This model utilizes the characteristics of low bending and shear strength of brittle materials for crushing, low power consumption and large production capacity. The motor drives the reducer through the hydraulic coupling, and the reducer drives the crushing roller to rotate through the toothed coupling. A replaceable tooth crown is fixed on the crushing roller, and a height-adjustable crushing rod is installed under the middle of the two crushing rollers. The material is crushed into products by two toothed rollers rotating relatively and the crushing rod below it.
1. Application in limestone mines
A company in Chongqing built a stone crushing production line with an annual output of 2 million tons in 2014. The primary crushing equipment selects the 2PGC-1370A double-toothed roller crusher produced by Henan Deya Machinery Equipment Co., Ltd. with an installed power of 2×250 kW. The capacity is 1200~2200 t/h, the maximum feeding particle size is 1500 mm, and the discharging particle size is 300 mm. The crushed material is limestone.
Due to a large number of mine slope stripping materials used in the production process, the compressive strength of the ore varies about 8 ~ 12MPa, and the proportion of bulk ore is high, and the working conditions of the double-toothed roller crusher are poor. Therefore, many unexpected problems occurred. Deya Machinery Technical Department now analyzes and summarizes some problems encountered in the use of double-toothed roller crushers for reference by those who use this type of equipment.
2. Problems and solutions
2.1 The tooth crown is easy to break
The tooth crown is equivalent to the teeth of the crusher. Because it is installed on the top of the ring seat of the crushing roller, it is called the tooth crown. The original tooth crown is an arched tooth crown, made of ZG35CrMo, quenched and tempered 230±20 HRB, with both strength and wear resistance. The middle part of the inner side of the two feet of the tooth crown is cut into a key with a height of 10mm and a width of 58.5mm. When installing, align the key of the tooth crown with the key groove of the tooth ring seat and insert it, then put on the tooth crown bolt, tighten it with a power-enhancing wrench (pre-tightening torque 17 500 N m), and lock the nut by welding the locking piece to make the tooth crown. It forms a solid whole with the toothed ring. There are 3 contact surfaces between the tooth crown and the tooth ring. The belly of the tooth crown and the top of the tooth ring seat are arc joint surfaces, which can prevent stress concentration when the force is applied. When the side of the crown is stressed, it swings left and right.
2.1.1 Reason Analysis
(1) The crown bolt is stretched or broken
In the initial stage of use, the mating surfaces are closely matched, and the crowns are rarely loosened, swayed and broken. Although the crown bolt is a high-strength quality bolt, the wear of the contact surface between the nut and the crown causes the false appearance of the crown bolt being loose. The looseness of each mating surface and the frequent impact force will cause the crown bolt to break sometimes. If it is not found in time , the crown is easily damaged or even broken.
(2) The tooth crown is affected by the impact force when the bulk ore is dropped, and the back of the tooth crown is fatigued and fractured
The drop from the discharge end of the apron feeder to the tooth crown of the double-toothed roller crusher is close to 3 m, and the impact force when the large ore falls is large.
(3) Influenced by the high block rate of the ore source
According to the original design requirements of the 2PGC-1370A double-toothed roller crusher, the proportion of large ore with a particle size of more than 800 mm in the supplied raw ore shall not exceed 8%, and the actual production process varies greatly, sometimes exceeding 12%. When the bulk rate is too high, it is also easy to cause damage or breakage of the tooth crown.
The box-type tooth crown is used, which is equivalent to adding two steel plates on both sides of the arcuate tooth crown, which not only strengthens the overall strength of the tooth crown, but also controls the left and right swing of the tooth crown. Except for the bolt holes which require mechanical chip processing, other parts of the box-type crown do not need chip processing.
Compared with the arcuate crown, the box-type crown has the characteristics of simple manufacture, low cost and long service life. According to more than 6 years of experience, the average service life of the arched crown is no more than 5 months, and it cannot be repaired after deformation; while the box-shaped crown can be used repeatedly for more than 2 years after the head is worn and repaired by welding.
2.2 The tooth crown is not wear-resistant
The tooth crown is a force-bearing part with a complex structure. Therefore, the quenched and tempered hardness should not be too high. Practice has proved that it should not exceed 250 HRB, otherwise it will be too brittle and easily broken; the quenched and tempered hardness should not be too low, otherwise the strength and wear resistance cannot be guaranteed.
In order to prolong the service life of the tooth crown, the method adopted on site is to prepare small wear-resistant alloy castings, referred to as “tooth tip”. The grinding electrode welds a protective layer on the tooth tip, and the durability of the tooth tip is increased from about 2 months to about 5 months. This method requires the crusher to have a maintenance time of 3 to 5 hours every day, because the welding work is carried out almost every day.
2.3 Ring gear fracture
The gear ring is also an important force-bearing part of the double-toothed roller crusher. During the production process, the proportion of large lumps and ultra-large lumps in the ore source is too high, which causes the gear ring to break at the keyway. If the whole machine is dismantled and overhauled, one is the workload.
Second, the spare parts processing cycle is long, which seriously affects the normal production. The composite tooth crown was designed on site and the damaged tooth crown was successfully repaired. The composite tooth crown is to cast the original tooth ring and tooth crown together, but it is divided into two pieces.
When a gear ring is broken, the two composite tooth crowns can be placed at the original tooth ring position at the same time, and then connected with M36 long bolts, aligned with the keyway position and then slowly tightened, and finally the two composite tooth crowns are connected with J506 welding rod welded together.
From 2015 to 2016, 2 broken tooth rings were successfully repaired by this method. When the head of the composite tooth crown is worn, the high wear-resistant alloy steel casting (tooth tip) is welded to the worn position of the composite tooth ring. The method is simple and practical, and can save a lot of maintenance time and cost.
2.4 The inner ring of the main bearing is easy to crack
2.4.1 Reason Analysis
The main bearing of the crushing roller adopts the spherical roller bearing, the model is 23176CAK/W33, the original SKF imported bearing, the price is high, the service life is not long, the average is 8 months. Later, it was changed to domestic bearings, and the service life was shorter, with an average of 6 months.
Since the tooth crown of the crushing roller is a spiral cross-arrangement of teeth, there are radial loads and axial loads during the working process, and the main bearing supporting the crushing roller is subjected to the combined action of radial force and axial force.
During use, it was found that with the increase of use time, the axial movement of the crushing roller became larger and larger, and the maximum amount could reach 30 mm. The movement speed was very fast, and a clear impact sound was emitted. Shortly after that, the inner and outer rings of the main bearing were fractured, and the main bearing inner ring was fractured.
Deya machinery technical team believes that the main reason for the short service life of the spherical roller bearing is the limited ability of the spherical roller bearing to withstand the axial force due to the large axial force generated in the process of crushing the bulk ore.
The main reason for the 30 mm axial play is not due to bearing wear and increased clearance, but due to the mounting structure of the bearing. One end of the left and right main bearings is a tensioning sleeve, and the other end is a withdrawal sleeve, and the taper direction is the same.
When the crushing roller is moved to the right end by external force, as long as the impact force is large enough, the inner ring of the main bearing is completely likely to be with the tensioning sleeve and the retracting sleeve. The unloading sleeve is disengaged at the same time.
When the main bearing was disassembled and inspected during the overhaul, it was also found that the joint surface of the inner ring of the main bearing and the outer ring of the withdrawal sleeve was obviously worn, indicating that the joint surface of this part had been loose; Wear marks.
Add axial thrust device. The thrust device overcomes the axial movement of the crushing roller, protects the bearing from the impact of axial force, and prolongs the service life of the bearing. After more than 2 years of use, it has been proved that the service life of the domestic bearing has been increased from the original 6 months to about 1 year. The connecting bolts are not broken, serving multiple purposes.
The 2PGC-1370A double-toothed roller crusher produced by Henan Deya Machinery Equipment Co., Ltd. in 2014 has large capacity and high efficiency, but there are still some deficiencies in crushing medium-hardness ore. According to the experience of a customer company in Chongqing, the above-mentioned problems are improved, and this type of crusher is fully capable of producing and processing medium-hardness ores.