Iron ore beneficiation and processing technology

In 1996, the country selected 219.97 million tons of iron ore, accounting for 85.2% of the country's iron ore original ore 25.22 million tons. The iron ore produced iron ore concentrate was 85.857 million tons, of which the key ore processing plant processed 10.961 million tons of ore, and produced iron ore fines of 41.58 million tons, accounting for 48.4% of the national iron concentrate powder production.

a) ore crushing

China's concentrating plants generally use crushing, crushing and fine-breaking three-stage crushing process to break iron ore. The coarse-breaking multi-purpose 1.2m or 1.5m rotary crusher is used in the 2.1m or 2.2m standard conical stone crusher, and the 2.1m or 2.2m short-head cone crusher is used for fine breaking. Through the coarse ore, the blockiness is not more than 1m, and then it is crushed by medium and fine, and sieved into the final product of the ore grain size less than 12mm.

b) Grinding process

Most of China's iron ore grinding process uses two-stage grinding process, and small and medium-sized ore dressing plants use a grinding process. Due to the use of fine screening and re-grinding new processes, in recent years some concentrating plants have changed from two-stage grinding to three-stage grinding. The grinding equipment used is generally small, the largest ball mill is 3.6m×6m, the largest rod mill is 3.2m×4.5m, the largest self-grinding mill is 5.5m×1.8m, and the gravel mill is 2.7m×3.6m.

The classification after grinding is basically a spiral classifier. In order to improve efficiency, some concentrators use hydrocyclones to replace the secondary spiral classifier.

c) Sorting technology

Magnetite ore dressing

It is mainly used to select low-grade "Anshan-style" magnetite. Due to the strong magnetic properties of the ore and good grinding, the domestic magnetic separation plant adopts stage grinding and multi-stage grinding process. For the coarse-grained magnetite, the former (a section of grinding), fine-grained and fine-grained inlays are used. The magnetite uses the latter (two or three stages of grinding). The series of permanent magnetization developed by China has made the magnetic separator realize permanent magnetization. 70 years later, due to the magnetite concentrator in the country to promote a fine sieve and then grinding the new technology, the concentrate grade increased from 62% to about 66%, to achieve the requirements of the Ministry of metallurgical industry proposed concentrate grade of 65%.

4) Sintering pellet technology

Sintering technology is the main means of man-made rich ore in China. In 1996, a total of 196.956 million tons of man-made rich ore were produced, of which 94.859 million tons were key enterprises, accounting for 58.9%, and 63.37 million tons were local state-owned enterprises, accounting for 38.1%.

China has reached a considerable level in the technology of fine concentrate sintering. As early as the early 1950s, Angang successfully changed the acid sinter production method to the alkaline sinter production method on the sintering machine, and solved the problem of fine concentrate sintering in the world with slaked lime or quicklime as the flux.

The equipment level of the sintered pellets has also improved. There are 419 sintering machines in the country with a total area of ​​15522 m2, of which 22 are sintering machines of 130 m2 or higher, with a total area of ​​4107 m2; 197 sets of sintering machines of 24 to 129 m2, with a total area of ​​9387 m2; 200 sets of sintering machines of less than 24m2, with a total area of ​​2028m2. The 300m2 sintering machine put into operation at Maanshan Iron and Steel Plant on February 24th, 1994 is the largest modern sintering machine designed, manufactured and constructed by ourselves in addition to Baosteel.

The main technical and economic indicators for sintering in 1995 were: utilization factor 1.36t/(m2·h), sinter grade 53.00%, sintering machine calendar operation rate 80.94%, sinter qualification rate 84.92%, worker labor productivity 2170t/ (h·a).

Angular contact Ball Bearings

Angular Contact Ball Bearing has high limit rotational speed, they can carry radial load and axial load simultaneously, they can also withstand purely radial load. The axial load carrying capacity depends on the magnitude of contact angle and increases with increasing contact angle.

Structures

1. Non-separable angular contact ball bearings

This inner ring and outer ring of this type of bearings cannot be separated and comprises following structures:

Contact angle α=15°      counter bore on outer ring,7000Ctype

Contact angle α=25°      counter bore on outer ring,7000ACtype

Contact angle α=40°      counter bore on outer ring, 7000B type

2. Four-point contact ball bearings

This type of bearings is separable bearings. Whereof, QJ0000 type has two-piece inner ring and QJF0000 type has two-piece outer ring. Their contact angles are same as 35°.When received no load or pure radial load, the steel balls of the Ball Bearing contact with the four points of the rings. When it is received a pure axial load, the steel balls perform a two-point contact with the ring. In addition, besides the axial load from both directions, this kind of bearing can take torque-load as well.

3. Double row angular contact ball bearings

This kind of bearings can accommodate radial loads as well as axial loads acting in both directions; they can also take loading moment. They can restrain the axial displacement from both directions of the shaft or housing; the contact angle is 30° (or 40°)

Permissible tilt angle

There is only a little inclination between the inner ring and outer ring of angular contact bearings, the permissible tilt angle varies according to the internal clearance when the bearings are operating, the bearing dimensions, internal design, force and loading moment received by the bearings. The value of the maximum permissible tilt angle should be able to ensure that no much extra stress to be generated inside the bearings.

The tilt angle existing between the inner ring and outer ring will influence the bearing service life. Meanwhile, the running accuracy is decreased down and noise increased.

Tolerance and clearance

The tolerances of general angular contact bearings are class normal P0, class P5 and P6. Class P4 and P2 are applicable to machine tool spindles and bearing amount in pairs.

Clearance of single row angular contact bearing is decided by the contact angle, which is guaranteed by manufacturing.

Axial clearance of Four-point contact ball bearings is listed in table 1.

Cage material

Generally, the cage of angular contact bearing is pressed cage of steel sheet or brass cage, and it is solid brass cage for two row angular contact bearing.

Dynamic equivalent radial load

Single-row angular contact ball bearings with a contact angle of 15°

Single bearing or bearing in pairs(7000 C.7000 C/DT)

F_a/F_r≤e         P_r=F_r 

F_a/F_r>e          P_r=0.44F_r+YF_a

Back-to-back and face to face arrangements(7000 C/DB.7000 C/DF)

F_a/F_r≤e         P_r=F_r+Y₁F_a       

F_a/F_r>e          P_r=0.72F_r+Y₂F_a    

Single-row angler contact ball bearings with a contact angle of 25°

Single bearing or bearing in pairs(7000 AC.7000 AC/DT)

F_a/F_r≤0.68      P_r=F_r             

F_a/F_r>0.68       P_r=0.41F_r+0.87F_a   

Back-to-back and face to face arrangements(7000 AC/DB.7000 AC/DF)

F_a/F_r≤0.68      P_r=F_r+0.92F_a       

F_a/F_r>0.68       P_r=0.67F_r+1.41F_a    

Single-row angular contact ball bearings with a contact angle of 40°

Single bearing or bearing in pairs (7000 B.7000 B/DT)

F_a/F_r≤1.14      P_r=F_r             

F_a/F_r>1.14       P_r=0.35F_r+0.57F_a   

Back-to-back and face to face arrangements(7000 B/DB.7000 B/DF)

F_a/F_r≤1.14      P_r=F_r+0.55F_a      

F_a/F_r>1.14       P_r=0.57F_r+0.93F_a   

Four point contact ball bearings with a contact angle of 35°

F_a/F_r≤0.95      P_r=F_r+0.66F_a      

F_a/F_r>0.95       P_r=0.6F_r+1.07F_a    

Double-row angular contact ball bearings with a contact angle of 45°

F_a/F_r≤1.34      P_r=F_r+0.47F_a      

F_a/F_r>1.34       P_r=0.54F_r+0.81F_a   

Static equivalent radial load

Single-row angular contact ball bearings with a contact angle of 15°

For single bearing or bearing in pairs(7000 C.7000 C/DT)

P_0r=0.5F_r+0.46F_a   

P_0r<F_r  P_0r=F_r

For back-to-back and face-to-face arrangements (7000 C/DB.7000 C/DF)

P_0r=F_r+0.92F_a

Single-row angular contact ball bearings with contact angle of 25°

For single bearing or bearing in pairs (7000 AC.7000 AC/DT)

P_0r=0.5F_r+0.38F_a  

when P_0r<F_r  let P_0r=F_r

For two bearings in back-to-back and face-to-face arrangements

P_0r=F_r+0.76F_a

Single-row angular contact ball bearings with contact angle of 40°

For single bearing or bearing in pairs

P_0r=0.5F_r+0.26F_a   

when P_0r<F_r  let P_0r=F_r

For two bearings in back-to-back and face-to-face arrangements

P_0r=F_r+0.52F_a

Four point contact ball bearings

P_0r=F_r+0.58F_a

Double-row angular contact ball bearings with contact angle of 45°

P_0r=F_r+0.44F_a

F_r  Actual radial load of the bearing.

F_a   Axial load of the bearing

The values of e .Y .Y₁ .Y₂  see Table 2.

Table 1   Axial internal clearance of four point contact ball bearings

                                        μm

Table 2   Calculate Coefficient

                           Î¼m

Dw is the diameter of the rolling element

Angular Contact Ball Bearing

Machined Cage Angular Contact Ball Bearing,Pressed Cage Angular Contact Ball Bearing,One Row Angular Contact Ball Bearing,Two Row Angular Contact Ball Bearing

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