With more than 100 years of experience in developing this technology. Metso Outotec has designed, manufactured and installed over 8,000 ball and pebble mills all over the world for a wide range of applications. Some of those applications are grate discharge, peripheral discharge, dry grinding, special length to diameter ratio, high temperature milling oprations and more.
All equipment adheres to the applicable standards set by ASTM, NEMA, AGMA, AWS, and ANSI. Reliable and effective grinding mills includes being safe throughout. When the mills are quoted we make sure to include any and all safety components needed.
Metso Outotec process engineers welcome the opportunity to assist you with circuit and circuit control design as well as start-up, operation, and optimization of the milling plant. Automatic operation saves power, grinding media, and liner wear, while increasing capacity.
To ensure top-of-the-line operation, software can be developed to suit the most complicated circuits and complex ores. Our engineers can specify or supply computer control systems for your sophisticated circuit needs. These controls are feasible for also smaller installations.
Three types of tests are available for mill power determinations. In most cases one of two bench scale tests is adequate. First, a Jar Mill grindability test requires a 5 lb. (2 kg) sample and produces a direct measured specific energy (net Hp-hr/t) to grind from the design feed size to the required product size. The second test, a Bond Work Index determination, results in a specific energy value (net Hp-hr/t) from an empirical formula.
If time permits and the user wishes, grinding circuits are set up and continuous tests are run to simulate plant operation. These tests require two or three days for each ore type and approximately 1,000 pounds of material for each day of testing. Variations in ore hardness or circuit design may require larger samples.
Metso Outotec Premier horizontal grinding mills are customized and optimized grinding solutions built on advanced simulation tools and unmatched expertise. A Metso Outotec Premier horizontal grinding mill is able to meet any projects needs, even if it means creating something novel and unseen before.
Metso Outotec Select horizontal grinding mills are a pre-engineered range of class-leading horizontal grinding mills that were selected by utilizing our industry leading experience and expertise. With developing a pre-engineered package, this eliminates a lot of the time and costs usually spent in the engineering and selection stages.
After the grinding circuit has been brought up to normal operating conditions, the operator must monitor the various process variables and alarms. Most of these variables are monitored in the mill control room, however, the operator is also required to sample and analyse process streams and read local indicators.
The ball mill is susceptible to variations in ore hardness resulting in various grinds at constant throughput, or alternatively, various tonnages at constant grind. The variation in grind is not directly determined. However, a changing cyclone overflow density, at a constant tonnage rate and feed density, would be indicative of changing ore hardness and in that case the tonnage fed to the ball mill should be changed accordingly.
The ore feed rate to the ball mill is controlled by the weightometer located on the mill feed conveyor which can be manually adjusted with in the control room to give a constant weight reading. The signal from the weightometer increases or decreases the belt feeder speed and adjusts the water addition to the ball mill (as a function of the actual weight reading). Both weight control and the proportion of water can be adjusted in the control room.
The water rationing controller must be adjusted programmatically to give the desired ball mill discharge density (normally 60-65% solids). The ball mill discharge density should be checked manually at regular intervals and adjustment made to water ratio controller setpoint to adjust the ball mill discharge density.
The grinding circuit operator must ensure that the ball mill runs properly loaded and gives the correct ore grind. A major practical indication of mill loading is the sound made by the mill. A properly loaded mill will have a deep rhythmic roar, while an under loaded mill will have a metallic rattling type noise and an overloaded mill will be quite silent.
The operator must manually measure the cyclone overflow and underflow densities regularly. An increase in overflowdensity is indicative of softer ore and will soon be accompanied by a lowering of power draw at the mill and a change of sound indicating that the mill is becoming under loaded. To compensate, feed tonnage must be increased. Similarity, a decrease in the cyclone overflow density is indicative of harder ore and this will be accompanied eventually by a coking of the mill. Feed to the ball mill must be reduced.
In the event of an emergency, the mill feed conveyor is shut down individually or by stopping the operating cyclone feed pump. The ball mill must be shut down separately. All equipmentshutdowns are performed locally or from the MCC located in the mill control room.
Am sure your BallMill is considered the finest possible grinding mill available. As such you will find it is designed and constructed according to heavy duty specifications. It is designed along sound engineering principles with quality workmanship and materials used in the construction of the component parts. YourBallMill reflects years of advancement in grinding principles, materials, and manufacturing techniques. It has been designed with both the operators and the erectors viewpoints in mind. Long uninterrupted performance can be expected from it if the instructions covering installation and maintenance of the mill are carried out. You may be familiar with installing mills of other designs and manufacture much lighter in construction. YourBallis heavy and rugged. It should, therefore, be treated accordingly with due respect for its heavier construction.
The purpose of this manual is to assist you in the proper installation and to acquaint you a bit further with the assembly and care of this equipment. We suggest that these instructions be read carefully and reviewed by everyone whenever involved in the actual installation and operation of the mill. In reading these general instructions, you may at times feel that they cover items which are elementary and perhaps not worthy of mention; however in studying hundreds of installations, it has been found that very often minor points are overlooked due to pressure being exerted by outside influences to get the job done in a hurry. The erection phase of this mill is actually no place to attempt cost savings by taking short cuts, or by-passing some of the work. A good installation will pay dividends for many years to come by reduced maintenance cost.With the modern practice of specialized skills and trades, there is often a line drawn between responsibilities of one crew of erectors and another. Actually the responsibility of installation does not cease with the completion of one phase nor does it begin with the starting of another. Perhaps a simple rule to adopt would be DO NOT TAKE ANYTHING FOR GRANTED. This policy of rechecking previously done work will help guarantee each step of the erection and it will carefully coordinate and tie it into subsequent erection work. To clarify or illustrate this point, take the example of concrete workers completing their job and turning it over to the machinist or millwright. The latter group should carefully check the foundation for soundness and correctness prior to starting their work.
Sound planning and good judgement will, to a great extent, be instrumental in avoiding many of the troublesome occurrences especially at the beginning of operations. While it is virtually impossible to anticipate every eventuality, nevertheless it is the intention of this manual to outline a general procedure to follow in erecting the mill, and at the same time, point out some of the pitfalls which should be avoided.
Before starting the erection of the mill, adequate handling facilities should be provided or made available, bearing in mind the weights and proportions of the various parts and sub-assemblies. This information can be ascertained from the drawings and shipping papers.
The gearing, bearings, and other machined surfaces have been coated with a protective compound, and should be cleaned thoroughly with a solvent, such as Chlorothene, (made by Dow Chemical). Judgement should be exercised as to the correct time and place for cleaning the various parts. Do not permit solvents, oil or grease to come in contact with the roughened top surfaces of the concrete foundation where grouting is to be applied; otherwise proper bonding will not result.
After cleaning the various parts, the gear and pinion teeth, trunnion journals and bearings, shafting and such, should be protected against rusting or pitting as well as against damage from falling objects or weld splatter. All burrs should be carefully removed by filing or honing.
Unless otherwise arranged for, the mill has been completely assembled in our shop. Before dismantling, the closely fitted parts were match marked, and it will greatly facilitate field assembly to adhere to these match marks.
The surfaces of all connecting joints or fits, such as shell and head flanges, trunnion flanges, trunnion liner and feeder connecting joints, should be coated with a NON-SETTING elastic compound, such as Quigley O-Seal, or Permatex to insure against leakage and to assist in drawing them up tight. DO NOT USE WHITE LEAD OR GREASE.
Parts which are affected by the hand of the mill are easily identified by referring to the parts list. In general they include the feeder, feed trunnion liner, discharge trunnion liner if it is equipped with a spiral, spiral type helical splitter, and in some cases the pan liners when they are of the spiral type. When both right and left hand mills are being assembled, it is imperative that these parts which involve hand be assembled in the correct mill.
Adequate foundations for any heavy equipment, and in particular grinding mills, are extremely important to assure proper operation. The foundation should preferably be in one piece, that is, with a reinforced slab footing (so called mat) extending under both trunnion bearing foundations as well as the pinion bearing foundation. If possible or practical, it should be extended to include also the motor and drive. With this design, in the event of some movement, the mill and foundation will tend to move as a unit. ANY SLIGHT SETTLING OF FOUNDATIONS WILL CAUSE BEARING AND GEAR MISALIGNMENT, resulting in excessive wear and higher maintenance costs. It has been found that concrete foundations on a weight basis should be at least 1 times the total weight of the grinding mill with its grinding media.
Allowable bearing pressure between concrete footings and the soil upon which the foundation rests should first be considered. The center of pressure must always pass through the center of the footing. Foundations subject to shock should be designed with less unit pressure than foundations for stationary loads. High moisture content in soils reduces the amount of allowable specific pressure that the ground can support. The following figures may be used for preliminary foundation calculations.
Portland cement mixed with sand and aggregate in the proper proportions has come to be standard practice in making concrete. For general reference cement is usually shipped in sacks containing one cubic foot of material. A barrel usually holds 4 cubic feet. Cement will deteriorate with age and will quickly absorb moisture so it should be stored in a dry place. For best results the sand and gravel used should be carefully cleaned free of humus, clay, vegetal matter, etc.
Concrete may be made up in different mixtures having different proportions of sand and aggregate. These are expressed in parts for example a 1:2:4 mixture indicates one bag of cement, 2 cubic feet of sand, and 4 cubic feet of gravel. We recommend a mixture of 1:2:3 for ball mill and rod mill foundations. The proper water to sand ratio should be carefully regulated since excess water increases the shrinkage in the concrete and lends to weaken it even more than a corresponding increase in the aggregate. Between 5 to 8 gallons of water to a sack of cement is usually recommended, the lower amount to be used where higher strength is required or where the concrete will be subject to severe weathering conditions.
Detailed dimensions for the concrete foundation are covered by the foundation plan drawing submitted separately. The drawing also carries special instructions as to the allowance for grouting, steel reinforcements, pier batter, foundation bolts and pipes. During concrete work, care should be taken to prevent concrete entering the pipes, surrounding the foundations bolts, which would limit the positioning of the bolts when erecting the various assemblies. Forms should be adequately constructed and reinforced to prevent swell, particularly where clearance is critical such as at the drive end where the gear should clear the trunnion bearing and pinion bearing piers.
For convenience in maintenance, the mill foundations should be equipped with jacking piers. These will allow the lifting of one end of the mill by use of jacks in the event maintenance must be carried out under these conditions.
Adequate foundations for any heavy equipment, and in particular Marcy grinding mills, are extremely important to assure proper operation of that equipment. Any slight settling of foundations will cause bearing and gear misalignment, resulting in excessive wear and higher maintenance costs. It has been found that concrete foundations on a weight basis should be approximately 1 times the total weight of the grinding mill with its grinding media.
Allowable bearing pressure between concrete footings and the soil upon which the foundation rests should first be considered. The center of pressure must always pass through the center of the footing. Foundations subject to shock should be designed with less unit pressures than foundations for stationary loads. High moisture content in soils reduces the amount of allowable pressure that that material can support. The following figures may be used for quick foundation calculations:
Portland cement mixed with sand and aggregate in the proper proportions has come to be standard practice in making concrete. For general reference cement is usually shipped in sacks containing one cubic foot of material. A barrel usually consists of 4 cubic feet. Cement will deteriorate with age and will quickly absorb moisture so it should be stored in a cool, dry place. The sand and gravel used should be carefully cleaned for best results to be sure of minimizing the amount of sedimentation in that material.
Concrete may be made up in different mixtures having different proportions of sand and aggregate. These are expressed in parts for example a 1:2:4 mixture indicates one bag of cement, 2 cubic feet of sand, and 4 cubic feet of gravel. We recommend a mixture of 1:2:3 for ball mill and rod mill foundations. The proper water to sand ratio should be carefully regulated since excess water will tend to weaken the concrete even more than corresponding variations in other material ratios. Between 5 to 8 gallons of water to a sack of cement is usually recommended, the lower amount to be used where higher strength is required or where the concrete will be subject to severe weathering conditions.
We recommend the use of a non-shrinking grout, and preferably of the pre-mixed type, such as Embeco, made by the Master Builders Company of Cleveland, Ohio. Thoroughly clean the top surfaces of the concrete piers, and comply with the instructions of the grouting supplier.
1. Establish vertical and horizontal centerline of mill and pinion shaftagainst the effects of this, we recommend that the trunnion bearing sole plate be crowned so as to be higher at the center line of the mill. This is done by using a higher shim at the center than at the endsand tightening the foundation bolts of both ends.
After all shimming is completed, the sole plate and bases should be grouted in position. Grouting should be well tamped and should completely fill the underside of the sole plate and bases. DO NOT REMOVE THE SHIMS AFTER OR DURING GROUTING. When the grout has hardened sufficiently it is advisable to paint the top surfaces of the concrete so as to protect it against disintegration due to the absorption of oil or grease.
If it is felt that sufficient accuracy in level between trunnion bearing piers cannot be maintained, we recommend that the grouting of the sole plate under the trunnion bearing opposite the gear end be delayed until after the mill is in place. In this way, the adjustment by shimming at this end can be made later to correct for any errors in elevation. Depending on local climatic conditions, two to seven days should he allowed for the grouting to dry and set, before painting or applying further loads to the piers.
Pinion bearings are provided of either the sleeve type or anti-friction type. Twin bearing construction may use either individual sole plates or a cast common sole plate. The unit with a common sole plate is completely assembled in our shop and is ready for installation. Normal inspection and cleaning procedure should be followed. Refer to the parts list for general assembly. These units are to be permanently grouted in position and, therefore, care should be taken to assure correct alignment.
The trunnion bearing assemblies can now be mounted on their sole plates. If the bearings are of the swivel type, a heavy industrial water-proof grease should be applied to the spherical surfaces of both the swivels and the bases. Move the trunnion bearings to their approximate position by adjustment of the set screws provided for this purpose.
In the case of ball mills, all internal wearing parts will pass through the manhole, whereas in the case of open end rod mills they will pass through the discharge trunnion opening. When lining the shell, start with the odd shaped pieces around the manhole opening if manholes are furnished. Rubber shell liner backing should be used with all cast type rod mills shell liners. If the shell liners are of the step type, they should be assembled with the thin portion, or toe, as the leading edge with respect to rotation of the mill.
Lorain liners for the shell are provided with special round head bolts, with a waterproof washer and nut. All other cast type liners for the head and shell are provided with oval head bolts with a cut washer and nuts. Except when water proof washers are used, it is advisable to wrap four or five turns of candle wicking around the shank of the bolt under the cut washer. Dip the candle wicking in white lead. All liner bolt threads should be dipped in graphite and oil before assembly. All liner bolt cuts should be firmly tightened by use of a pipe extension on a wrench, or better yet, by use of a torque wrench. The bolt heads should be driven firmly into the bolt holes with a hammer.
In order to minimise the effect of pulp race, we recommend that the spaces between the ends of the shell liners and the head liners or grates be filled with suitable packing. This packing may be in the form of rubber belting, hose, rope or wood.
If adequate overhead crane facilities are available, the heads can be assembled to the shell with the flange connecting bolts drawn tightly. Furthermore, the liners can be in place, as stated above, and the gear can be mounted, as covered by separate instructions. Then the mill can be taken to its location and set in place in the trunnion bearings.
If on the other hand the handling facilities are limited it is recommended that the bare shell and heads be assembled together in a slightly higher position than normal. After the flange bolts are tightened, the mill proper should be lowered into position. Other intermediate methods may be used, depending on local conditions.
In any event, just prior to the lowering of the mill into the bearings the trunnion journal and bushing and bases should be thoroughly cleaned and greased. Care should be taken not to foul the teeth in the gear or pinion. Trunnion bearing caps should be immediately installed, although not necessarily tightened, to prevent dirt settling on the trunnions. The gear should be at least tentatively covered for protection.
IMPORTANT. Unless the millwright or operator is familiar with this type of seal, there is a tendency to assume that the oil seal is too long because of its appearance when held firmly around the trunnion. It is not the function of the brass oil seal band to provide tension for effective sealing. This is accomplished by the garter spring which is provided with the oil seal.
Assemble the oil seal with the spring in place, and with the split at the top. Encircle the oil seal with the band, keeping the blocks on the side of the bearing at or near the horizontal center line so that when in place they will fit between the two dowel pins on the bearing, which are used to prevent rotation of the seal.
Moderately tighten up the cap screws at the blocks, pulling them together to thus hold the seal with its spring in place. If the blocks cannot be pulled snuggly together, then the oil seal may be cut accordingly. Oil the trunnion surface and slide the entire seal assembly back into place against the shoulder of the bearing and finish tightening. Install the retainer ring and splash ring as shown.
In most cases the trunnion liners are already mounted in the trunnions of the mills. If not, they should be assembled with attention being given to match marks or in some cases to dowel pins which are used to locate the trunnion liners in their proper relation to other parts.
If a scoop feeder, combination drum scoop feeder or drum feeder is supplied with the mill, it should be mounted on the extended flange of the feed trunnion liner, matching the dowel pin with its respective hole. The dowel pin arrangement is provided only where there is a spiral in the feed trunnion liner. This matching is important as it fixes the relationship between the discharge from the scoop and the internal spiral of the trunnion liner. Tighten the bolts attaching the feeder to the trunnion liner evenly, all around the circle, seating the feeder tightly and squarely on its bevelled seat. Check the bolts holding the lips and other bolts that may require tightening. The beveled seat design is used primarily where a feeder is provided for the trunnion to trunnion liner connection, and the trunnion liner to feeder connection. When a feeder is not used these connecting joints are usually provided by a simple cylindrical or male and female joint.
If a spout feeder is to be used, it is generally supplied by the user, and should be mounted independently of the mill. The spout should project inside the feed trunnion liner, but must not touch the liner or spiral.
Ordinarily the feed box for a scoop tender is designed and supplied by the user. The feed box should be so constructed that it has at least 6 clearance on both sides and at the bottom of the scoop. This clearance is measured from the outside of the feed scoop.
The feed box may be constructed of 2 wood, but more often is made of 3/16 or plate steel reinforced with angles. In the larger size mills, the lower portion is sometimes made of concrete. Necessary openings should be provided for the original feed and the sand returns from the classifiers when in closed circuit.
A plate steel gear guard is furnished with the mill for safety in operation and to protect the gear and pinion from dirt or grit. As soon as the gear and pinion have been cleaned and coated with the proper lubricant, the gear guard should be assembled and set on its foundation.
Most Rod Mills are provided with a discharge housing mechanism mounted independently of the mill. This unit consists of the housing proper, plug door, plug shaft, arm, and various hinge pins and pivot and lock pins. The door mechanism is extra heavy throughout and is subject to adjustment as regard location. Place the housing proper on the foundation, level with steel shims and tighten the foundation bolts. The various parts may now be assembled to the housing proper and the door plug can be swung into place, securing it with the necessary lock pins.
After the mill has been completely assembled and aligned, the door mechanism centered and adjusted, and all clearances checked, the housing base can be grouted. The unit should be so located both vertically and horizontally so as to provide a uniform annular opening between the discharge plug door and the head liners.
In some cases because of space limitation, economy reasons, etc., the mill is not equipped with separate discharge housing. In such a case, the open end low discharge principal is accomplished by means of the same size opening through the discharge trunnion but with the plug door attached to lugs on the head liner segments or lugs on the discharge trunnion liner proper. In still other cases, it is sometimes effected by means of an arm holding the plug and mounted on a cross member which is attached to the bell of the discharge trunnion liner. In such cases as those, a light weight sheet steel discharge housing is supplied by the user to accommodate the local plant layout in conjunction with the discharge launder.
TRUNNION BEARING LUBRICATION. For the larger mills with trunnion bearings provided with oil seals, we recommend flood oil lubrication. This can be accomplished by a centralized system for two or more mills, or by an individual system for each mill. We recommend the individual system for each mill, except where six or more mills are involved, or when economy reasons may dictate otherwise.
In any event oil flow to each trunnion bearing should be between 3 to 5 gallons per minute. The oil should be adequately filtered and heaters may be used to maintain a temperature which will provide proper filtration and maintain the necessary viscosity for adequate flow. The lines leading from the filter to the bearing should be of copper tubing or pickled piping. The drain line leading from the bearings to the storage or sump tank should be of adequate size for proper flow, and they should be set at a minimum slope of per foot, perferably per foot. Avoid unnecessary elbows and fittings wherever possible. Avoid bends which create traps and which might accumulate impurities. All lines should be thoroughly cleaned and flushed with a solvent, and then blown free with air, before oil is added.
It is advisable to interlock the oil pump motor with the mill motor in such a way that the mill cannot be started until after the oil pump is operating. We recommend the use of a non-adjuslable valve at each bearing to prevent tampering.
When using the drip oil system it is advisable to place wool yarn or waste inside a canvas porous bag to prevent small pieces of the wool being drawn down into the trunnion journal. If brick grease is used, care should be taken in its selection with regard to the range of its effective temperature. In other words, it should be pointed out that brick grease is generally designed for a specific temperature range. Where the bearing temperature does not come up to the minimum temperature rating of the brick grease, the oil will not flow from it, and on the other hand if the temperature of the bearing exceeds the maximum temperature rating of the brick grease, the brick is subject to glazing; therefore, blinding off of the oil. This brick should be trimmed so that it rests freely on the trunnion journal, and does not hang up, or bind on the sides of the grease box.
When replacing the brick grease, remove the old grease completely. Due to the extended running time of brick grease, there is usually an accumulation of impurities and foreign matter on the top surface, which is detrimental to the bearing.
Where anti-friction bearings are supplied, they are adequately sealed for either grease or oil lubrication. If a flood system is used for the trunnion bearings and it is adequately filtered, it can then be used for pinion bearings with the same precautions taken as mentioned above, with a flow of to 1 gallons per minute to each bearing.
These lubricants can be applied by hand, but we highly recommend some type of spray system, whether it be automatic, semi-automatic or manually operated. It has been found that it is best to lubricate gears frequently with small quantities.
Start the lubrication system and run it for about ten minutes, adjusting the oil flow at each bearing. Check all of the bolts and nuts on the mill for tightness and remove all ladders, tools and other obstructions prior to starting the mill.
Before starting the mill, even though it is empty, we recommend that it be jogged one or two revolutions for a check as to clearance of the gear and its guard, splash rings, etc. The trunnion journal should also be checked for uniform oil film and for any evidence of foreign material which might manifest itself through the appearance of scratches on the journal. If there are any scratches, it is very possible that some foreign material such as weld splatter may have been drawn down into the bushing, and can be found imbedded there. These particles should be removed before proceeding further.
If everything is found to be satisfactory, then the mill should be run for ten to fifteen minutes, and stopped. The trunnion bearings should be checked for any undue temperature and the gear grease pattern can be observed for uniformity which would indicate correct alignment.
It should be noted that with an empty mill the reactions and operating characteristics of the bearings and gearing at this point are somewhat different than when operating with a ball or rod charge. Gear noises will be prominent and some vibration will occur due to no load and normal back-lash. Furthermore, it will be found that the mill will continue to rotate for some time after the power is shut off. Safety precautions should therefore he observed, and no work should be done on the mill until it has come to a complete stop.
We have now reached the point where a half ball or rod charge can be added, and the mill run for another six to eight hours, feeding approximately half the anticipated tonnage. The mill should now be stopped, end the gear grease pattern checked, and gear and pinion mesh corrected, if necessary, according to separate instructions.
The full charge of balls or rods can now be added, as well as the full amount of feed, and after a run of about four to six days, ALL BOLTS SHOULD AGAIN BE RETIGHTENED, and the gear and pinion checked again, and adjusted if necessary.
Where starting jacks are provided for the trunnion bearings of the larger sized mills, they should be filled with the same oil that is used for the lubrication of the trunnion bearings. Before starting the mill they should be pumped so as to insure having an oil film between the journal and the bushing.
When relining any part of the mill, clean away all sand from the parts to be relined before putting in the new liners. For the head liners and shell liners you may then proceed in the same manner used at the time of the initial assembly.
Before relining the grate type discharge head, it is advisable to refer to the assembly drawings and the parts list.Because of such limitations as the size of the manhole opening, and for various other reasons, it will be found that the center discharge liner and cone designs vary. The cone may be a separate piece or integral with either the trunnion liner, or the router discharge liner. Furthermore, it will be found in some mills that the center discharge liner is held by bolts through the discharge head, whereas in other cases it depends upon the clamping effect of grates to hold it in position. In any event, the primary thing to remember in assembling the discharge grate head parts is the fact that the grate should be first drawn up tightly towards the center discharge liner by adjusting the grate set screws located at the periphery of the discharge head. This adjustment should be carried out in progressive steps, alternating at about 180 if possible and in such a manner that, the center discharge liner does not become dislodged from its proper position at the center of the mill. These grate set screws should be adjusted with the side clamp bar bolts loosened. After the grates have been completely tightened with the set screws, check for correct and uniform position of each grate section. The side clamp bar bolts may now be lightened, again using an alternate process. This should result in the side clamp bars firmly bearing against the beveled sides of the grates. The side clamp bars should not hear against the lifter liners.
When new pan liners are installed, they should be grouted in position so as to prevent pulp race in the void space between the discharge head and the pan liner. Another good method of preventing this pulp race is the use of the sponge rubber which can be cemented in place.
After the mill is erected, in order to avoid overlooking both obvious and obscure installation details, we recommend the use of a check list. This is particularly recommended for multiple mill installations where it is difficult to control the different phases of installation for each and every mill. Such a check list can be modeled after the following:
No. 1 Connecting Bolts drawn tight. A. Head and Shell flange bolts. B. Gear Connecting, bolts. No. 2 Trunnion studs or bolts drawn up tight. No. 3 Trunnion liner and feeder connecting bolts or studs drawn up tight. No. 4 Feeder lip bolts tightened. No. 5 Liner bolts drawn up tight. No. 6 Gear. A. Concentric B. Backlash C. Runout D. Joint bolts drawn up tight. No. 7 Coupling and Drive alignment and lubrication. No. 8 Bearings and Gearing cleaned and lubricated. No. 9 Lubrication system in working order with automatic devices including alarms and interlocking systems.
We further recommend that during the first thirty to sixty days of operation, particular attention be given to bolt tightness, foundation settlement and condition of the grouting. We suggest any unusual occurrence be recorded so that should trouble develop later there may be a clue which would simplify diagnosing and rectifying the situation.
As a safety precaution, and in many cases in order to comply with local safety regulations, guards should be used to protect the operators and mechanics from contact with moving parts. However, these guards should not be of such a design that will prevent or hinder the close inspection of the vital parts. Frequent inspection should be made at regular intervals with particular attention being given to the condition of the wearing parts in the mill. In this way, you will be better able to anticipate your needs for liners and other parts in time to comply with the current delivery schedules.
When ordering repair or replacement parts for your mill, be sure to identify the parts with the number and description as shown on the repair parts list, and specify the hand and serial number of the mill.
By following the instructions outlined in this manual, mechanical malfunctions will be eliminated. However, inadvertent errors may occur even under, the most careful supervision. With this in mind, it is possible that some difficulties may arise. Whenever any abnormal mechanical reactions are found, invariably they can be attributed to causes which though sometimes obvious are often hidden. We sight herewith the most common problems, with their solutions.
Cause A GROUT DISINTEGRATION. Very often when the grouting is not up to specification the vibration from the mill tends to disintegrate the grouting. In most instances the disintegration starts between the sole plate and the top surface of the grouting near or at the vertical centerline of the mill. As this continues, the weight of the mill causes the sole plate and trunnion bearing base to bend with a resultant pinching action at the side of the bearing near the horizontal center line of the mill. This pinching will cut off and wipe the oil film from the journal and will manifest itself in the same manner as if the lubrication supply had been cut off. If the grout disintegration is limited to about . 050 and does not appear to be progressing further, the situation can be corrected by applying a corresponding amount of shimming between the trunnion bearing base and the sole plate near the centerline of the mill in such a fashion that the trunnion bearing base has been returned to its normal dimensional position. If, on the other hand, the grouting is in excess of . 050 and appears to be progressing further, it is advisable to shut down operations until the sole plate has been re grouted.
Cause B HIGH SPOT ON THE BUSHING. While all BallMill bushings are scraped in the shop to fit either a jig mandrel or the head proper to which it is to be fitted, nevertheless there is a certain amount of seasoning and dimensional change which goes on in the type of metals used. Therefore if high spots are found, the mill should be raised, the bushings removed and rescraped. Bluing may be used to assist in detecting high spots.
Cause C INSUFFICIENT OIL FLOW. Increase the oil supply if it is a flood oil system. If brick grease is used, it is possible that the particular grade of brick may not be applicable to the actual bearing temperature. Refer to the remarks in this manual under the paragraph entitled Lubrication.
Cause E EXCESSIVE RUBBING ON THE SIDE OF THE BUSHING. This comes about due to the improper setting of the bearings in the longitudinal plane. In some cases, particularly on dry grinding or hot clinker grinding mills, the expansion of the mills proper may account for this condition. In any event, it can be remedied by re-adjusting the bearing base on the sole plate longitudinally at the end opposite the drive.
There are many more lubricant suppliers, such as E. F. Houghton and Co. , or Lubriplate Division of Fiske Bros. Refining Co. In making your final selection of lubricants, you should consider the actual plant conditions as well as the standardization of lubricants. New and improved lubricants are being marketed, and we, therefore, suggest that you consult your local suppliers.
There are many different designs and styles of ball mill liners. As with grinding balls local economics and ultimately operating costs determine the best design and material to use. The initial set of liners is rarely the final design selected. Based upon individual experience, mill superintendents develop preferences for liner designs. The following is given as a guideline for the initial set of liners.
For 60 mm (2.5) and smaller top size balls for cast metal liners use double wave liners with the number of lifters to the circle approximately 13.1 D in meters (for D in feet, divide 13.1 D by 3.3). Wave height above the liners from1.5 to 2 times the liner thickness. Rubber liners of the integral molded design follow the cast metal design. If using the replaceable lifter bar design in either metal or rubber the number of lifters should be about 3.3 D in meters (for D in feet* divide 3.3 D by 3.3) with the lifter height above the liners about twice the liner thickness. The use of double wave liners, particularly when using 50 mm (2) or larger balls, may show a loss of 5% or so in the mill power draw until the waves wear in and the balls cannest between the lifters.
When liners, and double wave liners in particular, wear with circumferential grooves, slipping of the charge is indicated, and this warns of accelerated wear. When the top size ball is smaller than 50mm (2.5) and mill speed is less than 72% of critical wear resistant cast irons can be used. For other conditions alloyed cast steel is recommended.Rubber liners are well suited to this same area and not onlyreduce operating costs but can reduce noise levels.
Single wave liners are recommended for larger size balls (50mm/2.5 and larger). The number of the lifters to the circle equals approximately 6.6 D in meters (for D in feet, divide 6.6 D by 3.3). The liners are from 50 to 65 mm thick (2 to 2.5) with the waves from 60 to 75 mm (2.5 to 3) above the liners. The replaceable lifter bar design madeof either metal or rubber in about the same design proportions can be used. There could be a loss in power with rubber particularly if the mill speed is faster than about 72% of critical speed, and the ball size is larger than 75 mm. Because of the impacting from the large balls, single wave liners for ball mills are usually made from alloyed steels or special wear-resistant alloyed cast irons. Because of the difficulty of balancing growth and wear with work hardening manganese steel is used infrequently and then with extreme care to allow for growth.
When a grate discharge is used the grates and wear platesare normally perpendicular to the mill axis while the discharge pans conform to the slope of the mill head. The grates and wear plates are normally made from alloy wear resistant cast steel or rubber. They are ribbed to prevent racing and excessive wear. The dischargers and pans are generally made from either wear resistant cast ironor rubber, or wear resistant fabricated steel.Slot plugging can be a problem in grate discharge mills. Whether the grates are made of metal or rubber the slots should have ample relief tapered toward the discharge side. Total angles 7 to 10 degrees (3.5 to 5 degrees per side) are commonly used. Metal grates often havea small lead-in pocket or recess which can fill in with peened metal rather than have the slot peen shut. With the proper combination of metal internals and rubber surfaces, rubber grates have flexibility that tend to make them self cleaning and yet not fail due to flexing.
Except when using rubber liners, the mill surfaces are covered with a protective rubber or plastic material toprotect the surfaces from pulp racing and corrosion. This is done in wet grinding mills. Since dry grinding mills get hot due to heat from grinding generally rubber liners and rubber materials cannot be used.
Shell liners may be furnished of various materials and of several designs. In each case the material used is the best obtainable, resulting in the lowest cost per ton of ore ground. The liner contours are selected for the specific grinding application and take into consideration liner wear, scrap loss, and mill capacity.
Liners cast of Manganese Steel, Ni-Hard, Chrome-moly, or other similar materials may be of the step type, block type, wave type, or the two-piece plate and lifter construction. These are illustrated on the right. During the past years of building ball Mills various other shapes of liners have been tried, such as the pocket type, spiral liners, etc.; in most cases it is found that these special shapes and designs are not justifiable from the standpoint of economics. They involve additional costs which are not generally recovered from an increased efficiency in milling operation.
Lorain Shell Liners consist of high carbon rolled steel plates accurately formed to the mill shell radius. These are held in place by rolled alloy steel heat treated lift bars. This type liner is carefully engineered for the specific grinding application. Variations in lift bar design and liner plate thickness provide this flexibility of design for application.
All shell liners designed for ball mill operations are of such size and shape that they will easily pass through the manhole opening to facilitate relining operations. In rod mill work the design is such that they will easily pass through the large ball open end discharge trunnion.
Where cast liners are used, and especially in rod mill applications, we furnish rubber shell liner backing to help cushion the impact effect of the media within the mill and prevent pulp racing. With the Lorain type of liner such shell liner backing is not required. For special applications where severe corrosive conditions exist a shell liner of special alloys can be furnished and also the interior surface of the shell can be treated to protect such parts from the corrosive conditions.
Head liners are of the segmental type constructed of Manganese Steel, Chrome molybdenum, or Ni-Hard and are designed to pass easily through the manhole opening or discharge opening in the case of rod mills. For ball mill work ribs are cast with the feed head liners to deflect the ball mass and minimize wear on the headliner itself.
Where cast liners are used shell liner bolts and head liner bolts are made of forged steel with an oval head to prevent turning and loosening within the liners. These are held in place with two hex nuts and a cut washer. For wet grinding applications special waterproof washers can be furnished.
Theeffect of liner design upon mill performance appears to have received little attention. Clearly, the main function of the liner is to form a removable surface to the null body, which may be replaced when seriously worn.
It is also clear however, that the metal plates which serve this purpose may have a surface which ranges from smooth in one which carries an intricate pattern of raised bars or sunken depressions. The merits of the various types do not appear, however, to have been studied.
where smooth liners are those which have projections insufficient to give appreciable keying between the liner and the ball charge, whilst lifter liners are those which are so heavily ribbed as to give rise to appreciable interlocking between the balls and the liners.
Various common types of liners are illustrated in Fig. 6.12. Although these liners have various patterns of projections, or depressions, to give an amount of interaction between the liner and the grinding medium, it would be expected that wear would round the edges. It is doubtful whether, after some time in service, the performance of a mill with these liners differs appreciably from that of a mill with a smooth surface. Liners furnished with heavy lifter bars are also sometimes used and in such a case the locking of the ball charge to the shell must be very effective. Nevertheless, although a few vague general statements to the effect that a lifter mill gives a product with different size characteristics to that of a smooth mill have appeared, the point does not appear to have been widely investigated. It is probable, however, that, on the grounds of differences in the size characteristics of the products, there exists no sound reason for the use of lifters in preference to the normal smooth liners.
It is possible that, when a material with a low coefficient of friction is milled, the charge might slip on a smooth mill shell, with consequent loss of grinding capacity, and in such a case the use of lifter bars might well be the solution. It has also been suggested by one of the authors, Rose, that the use of lifter bars might eliminate the surging of the charge sometimes encountered in mill operation.
An entirely different conception of the duty of the mill liner underlies the design of the studded liner developed by Usines Emile Henricot of Count St. Etienne. These liners, illustrated in Fig. 6.12 and Fig. 6.13, consist of comparatively thin plate liners with uniformly spaced studs on the working surface; these studs being integral with the plate. Provided the spaces between the studs are not allowed to become choked with tramp-iron, etc., the studs furnish a good key between the shell and the charge which, it is claimed, leads to a greater power consumption and to improved grinding. Furthermore it would appear that the studs impose a definite geometrical arrangement in the outer layer of balls which, in turn, brings about a closer packing, throughout the ball mass, than obtains with conventional types of liner. This effect would also lead to improved performance. Evidence of this effect of the studs upon the packing of the charge appears in Fig. 6.13b, for the balls are clearly seen to lie in rows in the mill instead of in completely random array.
An incidental merit claimed for these liners is that the high bearing pressure between the balls and the studs of the liners leads to work hardening of the studs; with a consequential reduction of the rate of metal wear.
The Henricot liners, which have been discussed in a paper by Belwinkel, appear to be the only attempt so far made to influence the grinding characteristics of a mill by means of correctly designed liners. It would therefore appear that there is some room for development in this direction.
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By this drawing, it is suggested that a typical homemade laboratory rod mill or ball mill might be fabricated from 20 cm (8 inches) diameter schedule-40 type 316 stainless steel pipe and would be about 38 cm (15 inches) long.
The plans show stainless steel grinding rods for this size of mill may be a graduated charge from 25 to 10 mm diameter (1 inch to 1/2 inch) but variations in size are not essential. Some mineral processing laboratories use a 30 cm diameter x 61 cm long (12-inch x 24 inch) rod mill with 30 and 45 mm rods (1 1/4 inch and 1 3/4 inch). A similar but smaller 30 cm x 30 cm (12-inch x 12 inch) laboratory ball mill with 40, 30, 25, and 20 mm balls (1 1/2, 1 1/4, 1 and 3/4 inch) is used for their ball mill work index calculations. Stainless steel is suggested because the abrasion and corrosion will be negligible, it is easy to clean out and there will be no rust to influence the subsequent metallurgical results. However, mild steel or carbon steel test mills and rods or balls may be desirable for certain ores to duplicate plant flotation or leaching practice when soluble iron has a bearing on the metallurgy or the solution used might react with the commercial mill or media.
Other sizes of rod mills or ball mills can be used but it is suggested that, regardless of the choice, the same mill should be used on all ores and for all tests. This will permit continuous comparisons with past research and with known ores.
The 20 x 38 cm laboratory mill mentioned above is suitable for testing 2000 gram lots of most normal specific gravity ores. If the same quantity of sample and pulp density are used for all tests in the same mill, the results obtained when changing the grinding time will be analysed readily since the length of time required to grind the sample is proportional to the work input.
It is impractical or at least extremely difficult to measure the grinding power consumed by laboratory mills directly because of the high proportion of the power which is consumed in drive inefficiencies and fixed load characteristics. Without very sophisticated instruments, it is difficult to tell the difference between a lab mill whichis loaded with steel and pulp or one with steel alone. Fortunately, it is not necessary to measure this power because alternate means to determine the work index are available.
Where there are no previous records of grinding mill power calculations, it may be necessary to consult with a commercial or an associates laboratory personnel to have the initial work index determinations done on your ore in their laboratories and compared with reference ores. A second method is available when an operating grinding mill is processing an ore which can be tested in the laboratory. By producing the same product screen analysis in the laboratory, a direct comparison between the products in the plant and the laboratory permits calculations of relative work performed. Alternately, when your own research staff have established work indices during previous projects, they will have historical data upon which to base their present project. The research team will find that the straight lines shown on log-log plots of the results from the various ores tested will be useful for comparisons.
The amount of grinding required for any project is established by the efficiency or adequacy of the initial and subsequent separating stages. Hence, once the correlation between grind and recovery has been established, the economic power requirements can be estimated. The most suitable method of grinding which might be with steel or autogenously can then be determined.
Rod mills may have been termed fine crushing machines but two directly opposing statements about their operating costs have been made in the earlier days of this century, one frequently heard that it is cheaper to crush than to grind but today, with the tremendous increase in grinding mill sizes and power utilization, it is doubtful that the statement is still true. Since a rod mill will accept a coarser feed than a ball mill, it fits in naturally as the intermediate comminution step. However, rod mills, like crushers, must be operated under controlled conditions to obtain maximum efficiency and are more difficult to operate than ball mills. Thus, the ultimate choice between a rod mill or ball mill for the primary grind may depend on the operators or designers experience as much as the metallurgists research.