The domain of technology that the invention refers to

In a broader sense, the invention relates to the field of crushing, grinding and chopping machines and devices in general, and actually to mineral raw material (copper, silver, gold, platinum, palladium etc. mineral) processing ball mils.

According to the International Patent Classification, the subject matter of an invention is categorized, i.e. classified and marked with classification symbols B02C 15/08 and B02C 15/10.

Technical problem

The technical problem solved through this invention is the following: how to construction design a mineral raw material chopping ball mill to achieve a favourable granulometric composition, the increase of the specific surface area of a chopped product with optimisation of high specific power and steel consumption, the solution for three important factors in mill's operation being critical rotation speed, filling level of ball filling and specific mill productivity by increasing the mill's diameter, decreasing wear of vital parts and placing bearings on the housing of the mill.

State of the Technology _^

Different constructions of crushers and mills for chopping food products and mineral raw materials are generally known. Chopping devices mostly consist of rough chopping machines such as crushers, and fine chopping machines - mills of different constructions and types with jaw crushers, cones, disc blades, rollers etc. Two directions are formed during a grinding process. Firstly, a classic trend in grinding fine chopped ore (with three-grade chopping), with on^-grade grinding, instead of combination of a rod mill and a ball mill. Secondly, the use of semi-autogenic mills after primary chopping in combination with balls. Each of the said principles is intended for optimal designs in terms of capital and operating costs, based on very large dimensions of mills, i.e mills' capacities. Due to lower specific power consumption of 12% at the minimum in the first case, the invention aims at improving a ball mill construction.

Ball mills with barrel turning around a horizontal axis tightened on journals with bearings are largely used in processing mineral raw materials. The existing ball mills have many disadvantages reflected mostly in mill's constructional characteristics limiting the mill's capacity increase by conditioning the increase of its dimensions, large wear and significant consumption of mechanic and electric power. The method of resolving the said disadvantages shall be discussed below in detail.

It has been accomplished that the bending and straining forces at the newly established angle of the assembly of slide bearings which lean directly on the housing of the mill closer to the centre of gravity has been decreased (7%) compared to a similar design by RAUMA- REPOLA, or (15%) on journals by the world's famous manufacturers (BOLIDEN- ALLIS, MPSI, KRORUP) in terms of the position of bearings

Searching through patent documentation and referring to professional literature in this field has not produced a similar solution of the set technical problem

Presentation of the Essence of the Invention

Chopping mineral raw material is one of the most important technologic operations; therefore it is necessary to perform technologic optimisation for maximum use of the machine and economic optimum to obtain minimal production costs in order to achieve higher value and lower final product price. The modern chopping technology tries to optimise the most important elements of the process, i.e. the type, size and technology of machines' operations, which includes optimisation of installed power and of the mill's capacity, establishing optimal charge composition, of the grinding body in the mill and evaluation of granulometric composition. Establishing installed power of the mill's engine, which also establishes the capacity, is certainly the most delicate technologic problem, because the facility's total capacity depends on correctly dimensionalised mill. In order to calculate the power of the mill's engine correctly, it is necessary to take into account a range of information such as the mill's dimensions and a number of rotations, the mass and the height of the falling ball, the ball filling ratio of the mill, the input largeness of the ore etc.

The whole issue when constructing ^" a new mill is based on a theoretical work with mathematical models and on a practical work, and confirmed in laboratory research as well as in practical realisation, and a significant technologic and construction advantage compared to previous designs has been recognized. When investigating accomplished mill's specific capacities, as well as when consuming electric power per one grinding product unit, it has been concluded that material costs of grinding had been decreased by increasing the mill's diameter with concomitant change of classic positions of bearings on journals of the mill to bearings placed on the housing of the mill, whereby a lower load of the mill by 15% has been achieved, also a lower specific power consumption by 1.49 kWh/t of processed ore compared to classic constructions. An experimental model of the new mill with the diameter D=5.79 m and the length L=8.53 m has been constructed.

This design, compared to former ones with the increase of the mill's diameter, solves three important factors of the mill's operation: the mill's critical rotational speed, the level of ball filling and the mill's specific productivity. This design's advantage is that there are not any limitations to increase the ball mill's diameter (5.5 m and more) because of the decrease of operation efficacy, because relative height of the free falling ball, which depends on a relative number of rotations of the mill, it is not construction limited any more as it used to be in classic mills (5.0 m - n crit. 0.7), but it is (5.79 - n crit. 0.756). In this way a free falling surface area is optimised through kinetic energy of grinding bodies, as a direct relation between the mill's operational efficacy and a relative number of rotations of the mill. The optimal speed of the number of mill's rotations of a new construction has been investigated in experimental trials in a laboratory mill, on a sample of fine crushed ore. It has been measured that the components of bcftis' speed depend on the ball flying time and on position coordinates, and it has been established that by a value increase of 0.734 n. crit. to 0.756 n. crit., the capacity increased by 6- 28%, the specific power consumption decreased by 0.97 to 1.88 kWh/t and circular charges decreased by approximately 20%. In addition, it has been established that a relative height of the free falling ball depended on a relative number of rotations of the mill, on an investigated optimal speed of the number of mill's rotations, as well as on other important characteristics necessary to perform a chopping process which have been discussed in mathematical and physical equations, allowing detailed analysis of the chopping process efficacy, the power efficacy, the pressure force effect intensity, the specific load of impact power, the method of force effect and the power ratio of the useful effect.

There have been significant improvements in the suggested mill construction in terms of wear decrease in the process of ore chopping by grinding, since it is well known that the cost price of replacement of used metal from work areas of grinding bodies, of coverings and of diaphragms is a substantial part of grinding costs and of concentration costs in total.

. ₅ * The suggested mill consists of horizontally placed cylindrical journal rotatble over five assemblies of slide bearings tightened to the stand. The mill is geared through an electric motor, and bearings are lubricated and ore is wetted through special devices. A large gear wheel to connect to air connector and to the engine is tightened to the housing. Steel balls and mineral raw material are inserted through an inlet, and the mineral raw material comes out through an outlet after the grinding process. Slide bearings are lubricated by pressured oil and cooled by water. All necessary measuring, control and regulation devices and installations have been mounted within the mill.

Brief description of figures in the drawings

^* The invention is described in detail in an example of carrying out of the invention shown in the drawings where:

Figure 1 - shows a vertical section of the mill according to the invention, and Figure 2 - shows a cross section A-A from Figure 1. Detailed description of the invention

The construction consists of three components, as follows: ring wideness with angular supports for a newly established position of the assembly of slide bearings to the housing of the ball mill, with the world's largest dimensions (5.79 m x 8.53 m) and the hour capacity of 420 t/h in one-grade grinding, with a specially designed stand for the assembly of slide bearings and for a lubricating system, as well as the mill's total mass balance, which is obtained by precise measurement of the mill's weight ±1.5 t, by transformation of the pressure force into electric signals of 0-20 mA.

The mill consists of horizontally placed cylindrical journal 1 the interior of which is cohered with steel coverings and placed near the centre of gravity through an electric motor πMtable over two assemblies of 2 slide bearings, each consisting of five segmental bearings with a slide insert, tightened to the stand 17. The mill is fed with ore and steel balls are inserted at the inlet socket 3, and the mill is discharged through a grid at the outlet socket 4 that has a protective box for the outlet sieve. The mill feeder allows continuous feeding of the mill and is always leaned on the mill's socket through an air absorber. The mill is sealed with the mill's inlet face 10 on the front side, and with the mill's outlet face 11 on the backside. Slide bearings are lubricated through a device 12 having an oil reservoir 15, which contains two gear pumps 13 with an engine to produce low pressure, and two piston pumps 14 with an engine to produce high pressure. Ore is wetted through a water dozer 16. A large gear wheel 5 is tightened broadways to the housing 1 ^" with a shielci in seals that is coupled with a drive gear wheel 6, with spherical roller bearings, to transfer power through the air connector 7 from the engine 8. The gear wheel 5 is lubricated with grease through a spray system. The mill is geared through the electric motor with a three-fold belt drive where the rotation moment is transferred to an inlet shaft of a two- grade gear reducer with cylindrical gears. A gear sprocket wheel is at the inlet shaft of the reducer. The rotation moment is transferred to the very mill through the sprocket wheel, the chj|in and the driven sprocket wheel. Rotation moments and the mill's power have been investigated in different operational conditions using corresponding measurement stripes for dynamic investigations. The suggested design has the lowest value of rotation moment of 26,958.90 kpm compared to other ones, equivalent to the power of 4850 kW. A RAUMA- REPOLA mill has 28,846.82 kpm and 5200 kW. Power load in Boliden AlHs, MPSI and KRUPP mills is 30,999.74 kpm and 5,577 kW, respectively, for the same mill dimensions. Therefore, this design ensures lower specific power consumption by 1,880 kWh/t as a final result. The newly established angle of the assembly of 2 main bearings of the mill is so adjusted that the mill drive operates in both directions; this helps to use mill coverings more completely by 20%, i.e. specific mill coverings consumption is decreased by 14 g/t of processed ore. In addition to that, it is possible to change the mill speed by ± 5% by using only a gear wheel with a larger number of cogs without the adjustment of the stand and of the underlying plates, as well as without dislocation of the mill. This is especially important in conditions of harder ore processing so the hour capacity does not drop by min. 10%. Control of the mill mass ensures its operation in optimal conditions which have a significant influence on a prolonged lifetime of the mill's propelling power drive, as well as on a increased effective operation time of the mill (95.3- 97.4%) compared to other construction designs (88.0-94.0%). Unlike different construction designs in mills by the best known manufacturers (RAUMA-REPOLA, Boliden-Allis, MPSI, KRRUP), having 0.01 mm thick oil film on main bearings, the oil film in this design is 0.2 mm thick, which is more favourable from the aspect of slide bearing damage by the presence of solid particles brought from the outside, which are found in halls for grinding and categorisation process. The newly established angle - position of the assembly of 2 slide bearings, has contributed to a reduction of the mill stand, which decreases investment compared to other designs for these building facilities. Electric motor operates in a constantly favourable mode of 60-80% in operation conditions with mill's weight measurement and continuous addition of balls info the mill depending on the mill's load.

Wet grinding in a ball mill is the most valuable way of chopping small crushed mineral raw material till its necessary limit largeness that has ever been invented. It consists of rubbing a thinner layer of material between hard surface areas moving tangently against each other and making a sufficiently high pressure to enable cracking and grinding grains of the material. The surface areas of grinding bodies must be very large in order to reach a high grinding capacity, and this is achieved by a large number of relatively small balls (φ 78).

The ball mill consists of a cylindrical part with large dimensions, 5.790 x 8.530 m, which has been constructed to rotate-around its imaginary horizontal axis. The mill cylinder is filled with grinding bodies up to 35-40% of its volume. The material to be ground passes in the form of a current through the mass of grinding bodies rotating together with the mill; this material streams axially, and the very grain moves through the mill due to the force of gravity and o the forced flow produced by continuous streaming of new unground material. The shell is made of steel tin with a round cross cutting and a cylindrical vertical cutting. The ratio of the shell length to^Jthe diameter is 1.48:1. The mill with a horizontal axis lies on two assemblies of segmental beSrings, which are tightened at supports. Hollow axes allow the material to. pass through, and a hollow axis to allow the material to pass through has a larger diameter in order to achieve streaming by gravity.

Grinding mineral raw material in a ball mill is performed using grinding bodies that are moving. Coverings protect the interior of the mill's steel shell. The coverings are made of alloy steel. The aim of the wavy coverings is to help raise the grinding bodies during the mill rotation and to prevent sliding against each other. The covering wave is 140 mm thick and its settled part is 80 mm thick. The mechanical effect of the mill is approximately 8% of total work spent on grinding. The measure of- work spent on- chopping is the relation between a granulometric composition before and after chopping. During a process of releasing minerals from their mutual relation in a ball mill, it is not important only to decrease largeness but to distribute largeness of released mineral grains. Since a flotation concentration requires optimal largeness in order to achieve a satisfying effect in the very operation of flotation concentration.

Assuming that all mills use electric power ranging 7-20 kWh/t in sections for mineral raw materials concentration to achieve necessary grinding fineness in a material of middle hardness for the selected chopping grade, where each grain is specially strained before it is chopped. Also taking into account a chopping process, which is characterised by mechanic power, expressed in three ways: by decreasing dimensions of a solid stage, by making new free surface areas, by changing the number and the largeness of grains, it is shown that the power of the (free) surface area is: 10 ^'5 - 10 ^"4 • J/cm ² . In other words, producing 2800 cm ² /g of the specific surface area requires 2.8 • 10 ^"1 • J/g or 0,1 kWh/t. A relative height of the free falling ball depends on a relative number of rotations of the mill. Since a free falling also defines kinetic energy of grinding bodies, it is a relation between the mill's operation efficacy and the relative number of rσSitions of the mill.

Meaning the following: the most part of the rest of electrical power is spent due to mechanical loads of the mill's weight and a resistance in the propelling power drive. This is why significantly improved construction designs (such as these) have improved the relation between the energy for newly produced surface area and the input power, i.e. power losses for useless work have been reduced. These new designs also reduce operating costs (decreased coverings consumption, longer lifetime of slide bearings and of the propelling power drive), as well as increase the effective time of the mill's operation, which improve the value of the ore grinding process significantly.

The newly established angle - position of the assembly of 2 slide bearings, which lean directly on the housing 1 of the mill, closer to the centre of gravity, in mills with large dimensions and hour capacity, is broadly used in facilities for processing porphyry-type copper ore using standard flotation concentration.

The principal significance of this construction relates to increase of the useful effect grade of|a grinding charge and to increasing effective operations of mills. This is even more important since the recent assessments have established an advantage in value in large mill units. As a result, the tendency to construct larger and larger ore chopping cylindrical mills has been growing recently. The issue of operating costs and effective operation time of cylindrical mills has therefore become more and more important, especially in preparation facilities. These construction designs have shown that mills' efficacy had varied from one machine model to another. Electric power consumption can also be minimised (the newly established angle- position of the assembly of slide bearings) because the mill operates most efficiently in these conditions.

Setting a mathematical equation has allowed a detailed ^" efficacy analysis of the grinding process: the power efficacy, the intensity of pressure force effect, the specific load due to impact power, the impact speed, the method of force effect and power ratio of the useful effect.

Having in mind that copper production in general is a large consumer of electric power and that its consumption is the largest in a chopping stage (over 44% of the total consumption in the mining production or nearly 32% of the entire power consumption in all stages from ore mining tdjϊefined copper production), reduction of electric power consumption by 88 kWh/t using the newly established angle-position of the assembly of main bearings on the mill's housing has a major impact on reducing total costs, especially in production with the capacity of 6,000,000 t/year or more.