SE466294B - Method for autogenous milling of mineral material, and rotating drum mill for autogenous wet milling - Google Patents

Abstract

In a method for autogenous milling of mineral material in a mill with a screen wall, permitting removal of at least three different fractions without the need for a screen wall divided into sections, and thus increased milling material conversion and milling capacity, use is made of screen openings 8 made in the screen wall 7 and a mixed fraction containing all the material fractions with a particle size less than or equal to the largest openings 8 in the screen wall is passed through these openings 8, the mixed fraction is divided in a fractioning device 13 into at least three different material fractions, at least one fine fraction is at all times removed from the fractioning device 13, as well as a coarse fraction and an intermediate fraction, and these two latter fractions are kept separate to permit, when necessary, diversion 38 of the coarse fraction as milling bodies for subsequent milling stages, but are brought together when there is no such need for milling bodies, and together they are led to a device for disintegration to subcritical size in order thereafter to be returned to the mill 1 for renewed milling. <IMAGE>

Description

466 294 2 10 15 20 25 30 35 40 enables autogenous grinding with grinding bodies from the material itself, due to the fact that such material rapidly decomposes into particles or pieces that are not pre-ground but too small to act as grinding bodies in a primary grinding after- following grinding steps or grinder.

By "over-competent" is meant such material as forms one surplus of matter critical, ie heavily ground fractions. Increasing over-competence results in the mill's grinding space being gradually filled critical fractions with rapidly decreasing grinding capacity as a result.

In the said Swedish patent, examples are given of a technology which significantly improves autogenous grinding even of materials with much pronounced over-competence. However, this known technology provides for some intermediate skills and especially those that are pronounced heterogeneous, unnecessarily high construction and operating costs dependent that in these cases one uses, so to speak, "greater force than the need demands ".

The object of the present invention is that in the case of autogenous wet grinding of a suitable mineral material in a primary mill enable the removal of both a primarily pre-ground product and a supercritical fraction for its decomposition into one in the circuit intermediate device to subcritical particle size for return of this latter fraction, and also enable one from the critical fraction can selectively in a controlled amount separate a fraction for the formation of malcharge in a following grinding steps, eg in a primary grinding subsequent secondary pepper painting step.

The objects of these inventions are achieved by the present method and device have those specified in the claims the characteristics. With the method and device according to this finning is given the opportunity to with an extremely simple device master the problems that arise from autogenous grinding of competent material. At the same time as the primary grinding step controlled over to a technically / economically favorable position, obtained also an adjustable outlet of secondary millstone or malcharge to a subsequent, secondary grinding step. bodies such as Some mineral materials can sometimes contain undisturbed rock and then especially those defined here as critical fractions. Also in this case the device is suitable for withdrawal of certain fractions that can proceed over a specific separation 10 15 20 25 30 35 40 3 0 466 294 device for separation of undamaged rock.

In the following, the present invention is described in more detail with reference to the accompanying drawings, in which Fig. 1 shows an axial section through a device according to the present invention finning in its basic design, fig_§ shows a flow chart for a 2-stage autogenous grinding plant, in which the present invention is included as an essential characteristic part, fig_§ shows an axial section through a modified embodiment of the device according to Fig. 1 and Fig. 2 shows an axial section through an alternative design which is particularly suitable for materials such as is predominantly competent.

In the drawings, 1 denotes an autogenous wet grinding intended drum mill, which can but does not have to be a primary mill in a several autogenous grinding steps comprising grinding plant. This mill 1 comprises one around its substantially horizontal longitudinal shaft rotating, a grinding space 2 enclosing mill drum 3, as on i known manner is internally provided with lining and lifter of wear material, such as abrasive rubber, even if not shown on the drawing the ings.

Inside the mill jacket 3 is spaced from it by an output opening end 4 and hollow discharge pin 5 provided end end 6 arranged a screen wall 7 with distributed over its entire surface, walking, through- slit-shaped, preferably rectangular openings 8 with a largest transverse dimension that allows the discharge of mixed goods from the grinding space 2 with a maximum grain or piece size as normal corresponds to the upper or largest piece size for bulk goods which belongs to the class of supercritical size and which is intended to can be used as malcharge or grinding bodies in a subsequent autogenous secondary mill 23 (Fig. 2). From the grinding chamber 2 through the sieve the mixed openings of the wall openings 8 thus contain fractions of fine, ie primarily pre-ground, intermediate and bulk goods. Furthermore, the openings 8 of the screen wall are so arranged applies to size, number and location, that the mill l below normal operation is always brought to maintain the desired pulp level and charge composition in the grinding room 2.

The screen wall 7 tightly surrounds one with the rotation of the drum shaft coaxial, in the direction from the grinding space 2 and into the end end discharge opening 4 and pin 5 projecting capsule 9, suitably in shape of a truncated cone with the base lying in the plane of the screen wall.

Like the screen wall 7, the end end 6 of the drum is on its own towards the grinding space 2 466 294 4 10 15 20 25 30 35 40 turned side provided with radial and / or substantially radial lifter 10 of wear material, eg wear rubber. Gable wall lifter 10 operates in one of the end wall 6 and the screen wall 7 limited, circumferential space ll for receiving through the openings 8 discharged mixed goods, which through the care of the end wall lifter 10 is lifted and brought towards the center of the end wall, where the mixed set of the outside of the capsule acting as deflection means 12 is led in in the outlet opening 4 and pin 5 of the end wall and to another the discharge end of the mill drum coaxially connected, co-rotating fractionation device 13.

This device 13 comprises a coarse screen drum 14 and a this coaxially surrounding fine screen drum 15, which is tightly connected to the end end 6 of the mill drum and extends coaxially past it inner discharge end 16 of the coarse sieve drum or ends inside or in line with the same with its discharge end 17. The coarse screen drum 14 may suitably have the same diameter as end outlet opening 4 and constitute a direct continuation of the end pin discharge pin 5 or be tightly connected to this.

With this fractionation device 13 according to the present invention, a very advantageous process technical function is obtained which can be briefly described as follows. It through the sieve openings 8 discharged goods / water mixture are subjected a fractionation and pulp separation in the device 13, wherein the mixed product fed into this is fractionated and divided into a maximum of four product types, namely; 1) one to the outside of the grinding circuit classification device 22 (fig. 2) walking, primary ground product consisting of the finest freight fraction including essentially all water; 2) a fraction overlying the later product, whose largest particle size is smaller than grinding critical size; 3) a fraction containing grinding-critical sizes up to the minimum grit size for a malcharge required in a primary grinding step subsequent, secondary pepper grinding step; 4) a pebble fraction, which in accordance with this invention can be mixed with the foregoing critical fractional and is specifically treated in the manner described in it the following, on the one hand, can be controllably controlled to secondary mill 23 as malcharge.

The device 13 is a fractionation device and is early designed as a transport device for transporting the 10 15 20 25 30 35 40 5 4 466 294 different fractions from the fractionation device 13 to resp subsequent treatment steps. The primary of the fractionation device screen drum 14 is divided into a first zone 18 with screen openings l8a, which allows materials of subcritical size to pass to the coarse screen drum 14 surrounding the fine screen drum 15 which is provided with sight openings l5a and l5b, and a second zone 19 with sieve openings l9a, the size of which is adapted to the lower one the fractional limit of the millstone in the secondary milling stage malcharge. All solids, including substantially all water, which pass through the sieve openings l5a and l5b, which usually has a dimension of the order of 5-15 mm as the minimum width, collected in a socket 20, after which it is pumped by means of a pump 21 or transported in another way to the external cluster of the device 22, from which the plus fraction returns to mill 1, while the minus fraction is transported as input material. rial to the secondary grinding stage 23 or alternatively led past this milling step to a cyclone following this step 24 via one in an outlet line 25 from the secondary grinding station. get arranged pump 26.

The coarse screen drum 14 is internally provided with transport means in the form of helically extending carriers 27 for transport of incoming goods from the opening 4 and outwards and with the aid of these carriers is thus discharged from the coarse sieve drum -14 the fraction that consists of pebbles size and is led with help of a deflection device 38 in a fixed amount to the secondary 23 to form its malcharge, the remainder being or the excess of this fraction is brought together by exodus of the deflection device 38 to the dashed position in Fig. 1, with it the grinding critical fraction that has passed through the sieve opening laaa, in order to be subjected to degradation together, thirdly wet mechanical, to subcritical size, for example in a crusher 28, after which it is returned to the mill 1 by means of a pump 29 or other suitable transport device 30.

For distinguishing the material that is allowed to pass through the screen openings 19a from the material passing through the screen 18a in the coarse screen drum 14, the fine screen drum 15 is the plane between the two zones 18 and 19 of the heavy-duty drum is provided with a partition 30 which divides the fine screen drum 15 in two separate zones 32 and 33, the zone 32 containing the sight opening lations 1a and zone 33 the apertures 15b for the primary 466 294 6 10 15 20 25 30 35 40 pre-ground fraction. Inside the zone 32 is the fine screen drum Provided with transport means in the form of helical means carrier 34 for returning it through the screen openings 18a passed the goods that are not allowed to pass through the sieve openings 15a, to the grinding room 2 of the mill via at least one wall-enclosed channel 35, connecting the 32-zone zone of the fine screen drum to the room 2. Through this channel it thus returns by the carriers 34 fed the goods to the grinding space 2 below the part of each turns the mill drum does as said channel 35 is above a horizontal plane through the longitudinal axis 36 of the drum 3.

The fine-sighted drum with 33 designated zones is for obtaining a safe discharge of the critical fraction allowed to pass through the openings 19a in the coarse screen drum 14 and in any case also the millstone fraction, provided with in the opposite direction to the carriers 34 in the zone 32 helically extending transport means in the form of carriers 37. By means of these carriers re from the fractionator 13 discharged the goods are diverted, such as previously mentioned, to a device for, for example, wet mechanical decomposition of this fraction to subcritical size.

As previously mentioned is adjacent to the coarse-sight drum 14 discharge end 16 deflection device 38 arranged, which is formed with a chute 39 and which at 40 is pivotally mounted at a stationary holder for movement not shown in the drawings between a position, i.e. the line in Figs. 1, 3 and 4, in which the deflection device 38 with its chute 39 is on distance from the end of the coarse screen drum and thus allow it out the coarse screen drum 14 discharged the goods to fall into the fine screen drum. flour 15 and by its carrier 37 is discharged from the fractionation device 13, in cases where the fine screen drum 15 extends past the discharge end 16 of the coarse screen drum, or that of the coarse screen drum 14 and the fine sieve drum 15 discharged the goods to be led to the device 28 for further degradation in those cases the fine screen drum has its discharge end 17 aligned with or inside the discharge end 16 of the coarse screen drum, and that in Fig. 1 shows the position in which the deflection device 38 with its gutter 39 diverts it from the coarse screen drum 14 of the carriers 27 discharged fraction, i.e. the millstone fraction, to the subsequent secondary milling step 23, while at the same time the drum discharged the goods is diverted to the device 28 for further further degradation of this freight fraction. 10 15 20 25 30 35 40 7 '466 294 The removal of grinding bodies from the fractionation device 13 to the secondary mill 23 is preferably controlled depending on the secondary the instantaneous grinding body needs of the mill by means of power or weight sensing controls 41, which, when in need of grinding bodies for secondary the mill 23 is present ensures that the deflection device 38 occupies the position shown in Fig. 1 and which reaches such a grinding body need does not exist preferably in conjunction with a counter- corresponding control device 41 for the primary mill 1 that the deflection device 38 is swung out from the position shown in Fig. 1 and thus from the coarse sieve drum 14 included in the fractionator 13 discharge end 16, in which position the millstone fraction is mixed with the critical fraction from the zone 33 of the fine screen drum 15 to together with this is led to said device 28 for external more degradation and return to the starting mill, ie the primary mill 1 in the present case.

With this device according to the present invention is achieved from the point of view of profitability the very advantageous opportunity to ur an autogenous malcharge take maximum amount of critical fractions to together with primarily pre-painted goods and divide and control this withdrawal so that subsequent secondary and / or tertiary mal- steps are always provided with the required or requested amount of bodies at the same time as the problem with known technology with growing surplus of critical goods in the primary mill completely eliminated. One of the features that makes this possible is the one in the mill drum 3 arranged the screen wall 7 which has a possible perforation area equal to the entire circumference of the screen wall reduced by it small part occupied by it for the initiation of from fractionation the device 13 via the channel 35 returned goods in the screen wall center area enclosed the capsule 9.

Fig. 3 shows an embodiment of the present invention as is particularly suitable for homogeneous over-competent material, ie such material which after grinding in the primary mill does not include any larger quantity of the product specified in 2) on page 4 the kind having a largest particle size smaller than that grinding critical size. _ This embodiment differs from that shown in Fig. 1 that the fine screen drum 15 is not divided into any zones but is along its entire length provided with the same carrier 37 as the zone 33 in the embodiment shown in Fig. 1 and which provides discharge of all through the screen openings 18a and 19a in the coarse screen drum 14 466 294 8 10 15 20 25 30 35 40 passed goods with a particle size larger than the finest the largest particle size of the goods fraction from the fractionation 13 and to subsequent decomposition steps 28. At the same method as in the embodiment according to Fig. 1, the fine-grained fraction is discharged or primarily ready-painted goods together with the water through the fine-opening drum sieve openings l5a.

Since no material in this embodiment is intended to or need to be returned directly from the fine screen drum 15 to the grinding space 2 is not required, the return channel 35 which therefore has omitted in Fig. 3. Furthermore, in the embodiment according to the latter figure the sieve openings 18a in the coarse sieve drum 14 have the same size as the sight openings designated by 19a if desired.

In comparison with the fractionation device according to Fig. 1 is thus the number of fractionation steps in the embodiment according to Fig. 3 is reduced. reduced from four to three. Otherwise, this is consistent later embodiment with the embodiment according to Fig. 1.

In the case of autogenous grinding of certain materials, especially those such as characterized by high surface wear and at the same time favorable decay, ie competent material, the device described above and the process does not need to be utilized to its full extent dependent that the goods included in the primary mill are quickly ground down to the desired particle size without particularly high energy consumption and without particularly critical¿fractions being formed in the malcharge. Also in this case, in comparison with the embodiment according to Fig. 1 the number of fractionation steps is reduced from four to three, which allows a simplified embodiment which is shown in more detail in Fig. 4 and which differs from that shown in Fig. 1 in that the flour 15 in this case must extend past the coarse screen drum discharge end 16 and is not divided into any special zones but is instead provided with the same carrier along its entire length 34 as the zone 32 in the embodiment according to Fig. 1. With deflection devices 38 to the position shown by dashed lines thus, the fine screen drum enables conveying means 34 to be returned everything from the heavy-duty drum 14 coming goods to the mill's grinding room 2 via the return channel 35 except the primarily pre-ground the fine goods passing out through the sieve openings of the fine drum 15a and 15b in the same manner as previously described.

Because the material of this design is special intended for does not form any so-called critical fractions that need distinguished from other fractions, the sieve opening of the coarse 10 15 20 25 30 35 40 '- 466 294 18a and 19a be the same as in the embodiment of Fig. 1, but it is also possible to omit the sight openings l9a but in instead allow the screen openings 18a to have a size corresponding to those in Fig. 1 shows the size of the sieve openings 19a, i.e. the lower limit for the millstone fraction, which is thus returned in this embodiment to the mill's grinding room 2 in the cases where the subsequent mill 23 requires addition of grindstone for its grinding function.

In this embodiment, extraction of millstone fractions from the room 2 only conditioned by the need for the gravel in the subsequent grinding step and not in any part of the grinding process in the primary the grinding space 2 of the mill and therefore the number of sieve holes 8 in the sieve wall 7 which allows the passage of the millstone fraction is significantly reduced in comparison with the embodiment according to both Fig. 1 and Fig. 3.

The present invention is not limited to the above described and shown in the drawings but can be modified and modified race in many different ways within the framework of the following claimed invention.

Claims (8)

43: »ON. / 0 O \ hä, |> PATENTKRAV A method for autogenous grinding of mineral material in a rotating mill drum with a screen wall arranged inside the drum at its discharge end, wherein through the screen wall (7) distributed over most of its circumference sieve openings (8) a mixed goods fraction containing all goods fractions with a grain size is discharged less than and equal to the largest openings (8) of the screen wall and the mixed material fraction is divided in a fractionation device (13) into at least three different material fractions, namely a solid material fraction constituting material that can be used as grinding bodies in a subsequent grinding step, a medium coarse material fraction of grinding critical material and a fine fraction constituting pre-ground material in the mill, whereby at least the fine fraction and both the bulk fraction and the intermediate rough fraction are always taken from the fractionation device (13), the two latter fractions being kept separate to allow deflection of coarse fraction if necessary. as grinding bodies for posterity grinding step (23), but is combined when the said need for grinding bodies for the subsequent grinding step does not exist, characterized in that combining both the coarse material fraction and the medium coarse material fraction is led to a device (28) for decomposition to subcritical size and then returned to the mill for re-grinding, to which device (28) the intermediate coarse fraction is also directed when the coarse fraction is deflected as grinding bodies to the subsequent grinding step. Method according to claim 1, characterized in that the removal of the bulk material fraction as grinding bodies from the fractionation device (13) is demand-controlled from subsequent milling steps and that the bulk material fraction taken from the fractionation device (13) is wholly or partly led together with said intermediate coarse fraction to another the mill drum (3) circuit-switched, alternatively detached, crushing plant (28) for crushing these fractions into subcritical material, when there is no need for grinding bodies for the subsequent grinding step 466 294 (23). Method according to claim 1 or 2, characterized in that in the fractionation device (13) separation of two intermediate fractions is effected, namely a coarser and a finer intermediate fraction, the coarser constituting the grinding-critical fraction and thus being diverted from the fractionation device. (l3), while the finer intermediate fraction is returned without action to the mill space (2) of the mill drum. Method according to claim 3, characterized in that the finer intermediate fraction is returned to the grinding space (2) via a reunification channel (35) extending substantially from the fractionation device (13) to the grinding space (2). 5. Device for rotating drum mills for autogenous wet grinding - and of the type which inside a gable provided with a discharge opening has a screen wall separating it from the grinder drum's grinding space, which for most of its extent is provided with screen openings for discharging a mixed goods fraction containing all freight fractions with a grain size less than and equal to the largest openings for discharge of the screen wall also of a bulk material fraction intended as grinding bodies for a subsequent grinding step, and a co-rotating fractionation device connected to said discharge opening for receiving all goods passing through the screen wall screen openings, said fractionation device comprises coaxially arranged screen drums, the inner screen drum (14) of which is provided with screen openings (18a, 19a) which prevent departure of said bulk material fraction, while the outer screen drum (15) of the fractionation device is provided with screen openings (15a) which only allow passage of a finished m all goods comprising fine goods fraction, wherein means (38) are arranged at the discharge end (16) of the inner sieve drum to enable deflection of the bulk goods fraction as grinding bodies to subsequent grinding steps (23), characterized in that the outer sieve drum (Sat) is provided with transport means (37) in the form of carriers for discharging goods which are allowed to pass through the sieve openings of the inner sieve drum except for at least the fine goods fraction from the fractionation device (13), said deflection means (39) also being arranged for bringing it from the two sieve drums (14, 15) discharged the material to a device (28) for degrading this material to subcritical size and returning it to the mill for re-grinding, to which device (28) the discharge end end (17) of the outer screen drum is connected for diverting the later screen drum discharged material to said device during diversion of the bulk material fraction as grinding bodies to efte subsequent grinding steps, and means (29) are provided for returning the material reduced to subcritical size to the mill for re-grinding. Device according to claim 5, characterized in that the inner screen drum (14) is divided into two zones (18, 19) where the zone (19) located closest to the discharge end (16) of the screen drum is provided with screen openings which are larger than the screen openings. (l8a) of the inner zone (18). Device according to claim 5 or 6, characterized in that the outer sight drum (15) is like the inner sight drum (14) divided into two zones (32, 33), the discharge end (17) being closest to the outer sight drum located zone (33) is provided with transport means (37) in the form of carriers for discharging material coming from the corresponding zone of the inner sight drum from the fractionating device (13), while the inner zone (32) of the outer sight drum is provided with transport means (34) in fgrm of carriers for returning intermediate fractions coming from the inner zone (18) of the inner screen drum to the grinding room (2) of the mill via a wall-enclosed return channel (35). Device according to claim 5, 6 or 7, characterized in that the transport means, which are in the form of carriers, have helical extension.