Show deschi description ati on of the new marcy ball mill by F E MARCY there will be published shortly in the proceedings roce edings of the american institute of ining hining engineers an article which will de rote te considerable space to the theory and practice of ball and pebble mills so in this short hort article I 1 will mention more of the tactical rac and actual operations of the results obtained from the marcy ball mill first the mill is designed and built to successfully take the product of the blake I 1 r gyratory crusher say 4 in to 2 in in li ameter and with one simple operation I 1 nd ind with one ball mill produces a non se 1 chive product of say 10 20 40 or 80 mesh ill of the product passing the meshes given above ove by nonselective non selective I 1 mean a product n which the mineral has not been subjected 0 o a classifying action that is has not I 1 een over crushed as compared with the sangue angue this makes a desirable concentrate g product and equally good for amalgams pion 1 and flotation 1 I 1 it is difficult to explain to the ordinary operator Pe who is used to the graded crushing rushing how the rock can be broken sue suc salt sait lake city manager of the mine supply company cess fully and economically from the larger size to the finest product in one operation in the first place steel balls have a gravity of nearly three times that of the ordinary rock while with pebble mills the gravity of the pebbles is practically the same and consequently it is the Eur survival vival of the fittest whichever is the softest succumbs to the other it is not difficult for 4 in and 5 in steel balls to crush 4 in n and 5 in pieces of rock and do it with a large tonnage we find that the ball mill will take 1 in feed and successfully reduce it all to pass 12 mesh by one operation and 60 to 70 per cent of the product will pass a 48 mesh screen now then if it is desired to crush to GO 60 mesh we separate the plus 60 from the minus 60 either by callow screens or drag classifiers and return the oversize to the mill but before doing so in order to get the best efficiency we increase the size of feed going to the mill that is raising it from 1 in to 3 in or 4 in thus the coarse rock entering the mill is covered with the oversize and while it is being broken much crushing J is s being done by the rock itself between the balls so that in order to obtain the highest efficiency and produce fine product it is important and a nd to obtain the greatest economy essential that the mill be fed with coarse feed the grinding dimensions of these mills that we have developed are as follows ane 4 foot diameter mill varies in length from 2 feet to 4 feet the 6 foot diameter varies in length from 3 feet to 5 feet the 8 foot diameter mill varies in length from 4 feet feel to 6 feet and the capacities of these mills vary from one ton per hour up to thirty six tons per hour of course as the grind grinding ng becomes finer the capacities are reduced in order to make the dimensions simple we call a mill that is 8 feet in diameter and 5 feet in length a no 85 and the same with the different sizes the results of my experiments which commenced in november 1912 have been that we have six of these mills of various types in operation and are now building ten no 85 mills for one of the large copper companies having a daily capacity each of tons taking 3 in to 4 in feed and crushing it to pass a 10 mesh screen 30 that as to the crushing efficiency of the ball mill as compared with the dry work in cement practice these mills of the there it is discharged through the with the pulp line W cwi wwi W and with the with the feed there water entering tile the mill K 0 0 0 0 6 00 0 wa 0 0 a 0 W wa figure no I 1 same dimensions have greater capacity by three or four times the general scheme of the mill and tile the principle are briefly as follows the feed is delivered to the mill in the ordinary way the liners are made in sections suitable to pass through the manhole fitted with the minimum number of bolts preferring the use of large size and less in number in order to avoid leaks the circumferential ferent ial liners are of the standard krupp type that is they are laid like shingles and with the upper holes slotted liners can be easily removed without any wedging ledgin action due to material getting in between them the discharge end of the mill is fitted with a grate covering over the entire end this grate is made in segments each segment made up of grizzley bar sections securely bolted together the whole being held in place against the radial ribs or lifters by bolts passing through tile the head of tile the mill these ribs or lifters are 3 in to 15 in in width depending upon the service required in the operation of the mill fig 1 tile the pulp line is indicated by WW as compared with WW W W of a mill that is operating with only a central discharge the integrity of this water line WW is maintained by the action of the lifters which has the effect of a pump in other words as the material is ground out it passes the grate and from is a difference in head between that of its entering the mill and the discharge of the pulp through the grate consequently there aerial is carried through quickly thus thu w we have rid the mill of tile the slushy mass and I 1 have caused the slime and the fines to tn migrate faster than the coarse particles I 1 have successfully made a grate of steel having an opening of a sixteenth of an inch thus I 1 am able to produce a minus millus 12 mesh product which carries app roxi 1 5 per cent on 20 this mill takes a feed as great as three inches and reduces it to a quarter an eighth or a sixteenth opening depending upon chatis what is required this I 1 call the coarse mill the energy available for crushing by steel balls in a ball mill is three to four times that of flints all other conditions re equal with the lowering 0 of L the pulp or water level in the mill leaving the other conditions equal the pulp resistance is of less effect and each crushing unit is enabled to deliver its energy with less friction loss while the ratio between steel ana flints is somewhat reduced the capacity cf the mill is increased right here are the limitations of flint pebbles they do not stand up under the falling conditions without the retardation of the pulp but crack and break up absorbing energy reducing effective capacity and increasing pebble costs while the large ton mills are extremely interesting to the large oper operator alor the smaller sizes are particularly adapted to the needs of the small property owner as they have great efficiency and simplicity when operating either for concentration flotation or any of the fine grinding processes many small properties cannot be t 5 3 4 7 9 10 I 1 0 L u 3 AZ zose 0 W r 7 1 IV co figure no 2 is a sluicing action of the water due to a difference of head ie between 17 and D and consequently the slime and the th e fine f 1 n e ma operated by the standard methods due to the first cost of the P plants ants and the saving that is made by the ordinary methods 00 U sulphide ores flotation will undoubtedly do what cyanide has done for gold and with cheap chushi crushing ng it at is the day of the poor POOI man As an illustration of a small mill I 1 men tion the pulaski mineral co at ketchum EId idaho aho operating an amalgamation and concentration cent cent ration plant with a capacity of thirty five tons per day with flow sheet as shown in fig 2 1 grizzley A 2 bla blake e crusher ia 3 shaking feeder 4 4 ft 3 ball mill 5 elevator 75 cy 3 eight hundred ton mill taking 3 inch feed and crushing to pass 10 mesh screen 6 callow screen for minus 40 mesh product 7 four plates 8 V box classifier 9 8 ft callow tank and two 6 G ft wilfley tables the total horse power in motors is 35 len en in full operation and when the usher is not in operation 25 in motors this mill was designed by the general igi ligi company and was built and t in operation in about thirty days after e material was on the ground they prose e to operate summer and winter and as located in a cold country it was feces ry FY to build a tight and warm building ie e total cost of this plant erected and ady dy for operation including excavation v building motors transform f in fact everything complete was a tie le less than in many places with this type of crushing unit it is not necessary to build heavy buildings but light in construction sufficient to take the wind and snow load for the very small mill it would seem best to determine the efficiency of the milling and the practical metallurgy as determined by the net returns and then finish the building and the outer structures afterwards with flotation and cheap crushing these are certainly the days for the small operator as compared with the expensive equipment and buildings low extraction and often failure |