4 installation steps, 10 requirements and medium selection of ball mill | fote machinery
Ball mill installation is a must step before it is put into production, which will affect the subsequent use of the ball mill, and even affect the production volume, crushing rate, service life, etc., so the importance of ball mill installation is self-evident.
In addition, the choice of grinding medium is also crucial. In the grinding process, different grinding medium can be used for different materials, models and equipment, which can reduce production costs and improve production efficiency.
There are four chassis should be installed: the front tile base, the rear tile base, the motor chassis and the reducer chassis. During the installation of the chassis, the horizontality and horizontal elevation of the chassis must be checked by a level or level gauge and a steel rule.
At the same time, the width of these wedges should be between 50 and 60 mm; the length should be at least ensured to exceed the centerline of the anchor bolts inside the chassis, and the outside should be exposed to a length of 10 to 50 mm; the slope of the wedge should be between 1:10 and 1:20.
If the actual combined size between the motor cylinder and the hollow shaft is inconsistent with the technical documents of the equipment or the relevant design, the construction may be carried out according to the actual size after obtaining the consent of the relevant unit personnel.
The transverse centerlines of the two main bearing chassis must coincide and allow for a combined error of no more than 0.5 mm. The non-horizontal degree of the main bearing chassis is allowed to differ by 0.1 mm/m, and the error of the non-parallelism is 0.5 mm/m, but the ball mill must be ensured to discharge materials.
Before the installation of the spherical surface of the main bearing, it is necessary to carefully check whether there are blisters, pores, cracks and other defects on the babbitt surface and the spherical surface, and there is no possibility of shrinking the shell in the interval between the hollow shaft and the contact surface of the bushing. phenomenon.
Firstly, before assembling the cylinder and the end cap, check the cylinder to ensure that the ellipse of the cylinder is not larger than 4 of the diameter of the cylinder. And meanwhile, the ovality and surface smoothness of the hollow journal should also be checked.
After the end cap and the cylinder bolt hole are aligned with the positioning pin, put a 1/4 number of bolts and tighten by hand, one-third of which are half tightened, and the concentricity is adjusted within 0.25mm, and then tightened.
Next, the cylinder and end cap assembly are transferred into the main bearing, but the housing must be adjusted to meet the requirements before the cylinder and end cap assembly are installed in the main bearing.
After assembling, the assembled cylinder should be measured and the total length and the length of the center of the two journals are compared with the center distance of the bearing housing to make sure they match with each other, otherwise, the bearing housing or the position of the main base need to be adjusted.
The inner surface of the ball mill cylinder is generally equipped with liners of various shapes that are the main wearing parts of the ball mill, and whose cost is about 2%-3% of the price of the whole product.
Thus, the performance and service life of the lining plate are issues that users are very concerned about, for its performance will directly affect the performance of the ball mill. The following are the 10 requirements for the liner installation.
The greater the density of the grinding medium is, the shorter the grinding time is. In order to increase the grinding effect, the hardness of the grinding medium must be greater than the hardness of the material to be ground.
According to long-term experience, the Mohs hardness of the medium is preferably greater than the hardness of the material to be ground by more than three grades. In addition, the smaller the size of the grinding medium is, the more the contact points it will be.
The loading amount has a direct influence on the grinding efficiency, and the particle size of the grinding medium determines the loading amount of the grinding medium. It must be ensured that when the grinding medium moves in the disperser, the porosity of the medium is not less than 40%.
For different fineness requirements, it is necessary to adjust the ability of the grinding medium to break and grind. The filling rate is high and the grinding ability is strong. On the contrary, the crushing ability is weak. When super fine grinding, the high filling rate is generally adopted.
Grinding medium generally is spherical because other irregularly shaped medium can wear themselves and cause unnecessary contamination. The size of the medium directly affects the grinding efficiency and product fineness.
The larger the diameter is, the larger the product size and the yield are. Conversely, the smaller the particle size is, the smaller the particle size and the the yield are. In actual production, it is generally determined by the feed size and the required product fineness.
Generally speaking, in the continuous grinding process, the size of the grinding medium is distributed regularly. The medium size ratio is directly related to whether the grinding ability can be exerted and how to reduce the wear of the medium.
In the process, it will not always maintain at a fixed medium ratio. So, the method of replenishing large balls is used to restore the grinding of the system. It is difficult for the mill to maintain at a fixed medium ratio for a long time.
In the production process, it is necessary to explore the appropriate ratio according to the type of material and the characteristics of the process, and remove the too small medium in time to reduce the cost.
The wear resistance and chemical stability of the grinding medium are important conditions for measuring the quality of the grinding medium. The non-wearing media needs to be supplemented by the need of abrasion, which not only increases the cost, but more importantly affects the production.
As common grinding equipment, ball mills are widely used in power, chemical, mining, cement and other processing sectors. At present, there are many kinds of ball mills popular in the market, with various functions and different prices.
Therefore, enterprises often face a dazzling situation when purchasing. Generally, when selecting a ball mill, the company must combine the material properties, abrasive requirements, production environment, energy consumption and other factors through scientifically comparing to select the ball mill that is most suitable for its use requirements.
As a leading mining machinery manufacturer and exporter in China, we are always here to provide you with high quality products and better services. Welcome to contact us through one of the following ways or visit our company and factories.
Based on the high quality and complete after-sales service, our products have been exported to more than 120 countries and regions. Fote Machinery has been the choice of more than 200,000 customers.
ball mill - zhongde heavy industries co.,ltd
Solution 1: It should be that some of the lining bolts are not tightly screwed. The solution is that you can judge the ball lining by the sound of the machine, then find the loose bolts and tighten them.
(5) The ball mill rolling bearing has too much or too little grease, and excessively formed rolling elements agitate the grease to generate heat, and the heat is not easily dissipated. If the lubrication is too small, the amount of oil should be increased according to the regulations, which is generally 1/3 to 1/2 of the bearing clearance.
PS: The above problems will be dealt with according to the reasons. Only if the side clearance of the bearing bush is too small, or the bottom contact angle is too large, the grinding cylinder body must be jacked up with a hydraulic jack, and the bearing bush is pulled out from one side of the shaft, and the tile is separately scraped.
Solution 4: adjust the wheel gap according to the specified, so that the two axes are concentric. Tighten the coupling bolts of the coupling symmetrically with the same torque. When the rotor is unbalanced, the ball mill rotor is taken out to find a static balance.
Solution 5: (1) The balance shaft of the ball mill and the reducer, the axis is not in the straight line, the reason is: when the mill is installed with the lining, no secondary grouting is performed, or the anchor bolts after the secondary grouting are not fastened, and the grinding cylinder is rotated by the hoisting machine, so that one end of the grinding cylinder is displaced, and the two axes are not in a straight line. The vibration is generated after the reducer drives the mill. To re-adjust, make the axis of the ball mill and the axis of the reducer on the same plane axis.
(2) The large ball mill is bulky and heavy, causing the foundation to sink; displacement occurs. Monitoring settlement points are set up next to the foundation; observations are made and adjustments are made when there is sinking.
Solution 6: The sound of the normal operation of the ball mill reducer should be even and stable. If the gear has a slight knocking sound, the hoarse friction sound, there is no obvious change during the operation, you can continue to observe, find out the reason, stop the ball mill and deal with it; if the sound is getting louder, you should immediately stop the ball mill for inspection.
please feel free to fill out the form below in detail and you can also send a message to us([email protected])
we will send you latest price within 24 hours.Besides, you can click Chat Online on the right hand side to get quotation online
grate ball mill/grate type ball mill/grate ball milling machine--zhengzhou bobang heavy industry machinery co.,ltd
1. Grate liner, 2. Bearing inner cover, 3. Hollow shaft 4.dustpan shape liner 5.central liner, 6. Rib 7. Wedge block.
The grate ball mill is usually used in the first segment of the two stages, or place of discharging the rough ore.
The grate ball mill is roughly composed of the cylinder, cylinder liner,big gear ring, discharging grate,and ore feeding device. Except there is a discharging grate plate installed at the discharging end, all the other is similar with the overflow ball mill. The grate ball mill discharging cover head and grate plate have the structure as the drawing: grate liner, bearing inner cover, hollow shaft, dustpan liner, central liner, rib and wedge block.
In the head cover of the hollow shaft of the discharging end, it has bearing inner cover and discharging grate installed and the later is made from central liner, grate liner and dustpan liner etc. There are eight radial rib casted on the inner wall of the head cover, which divide the head cover into 8 fan rooms. There installed the dustpan liner inside each fan shape room, with the bolt fixed on the end cover. Finally the grate plate are installed on each fan room shaped by the dustpan liner. The grate liner has two kinds of structure: one is the group formed by two pcs, pressed by the wedge block, which get fixed tightly on head cover with the bolt getting through the rib. The central part are supported by the central liner to prevent them from declining and dropping off. The other kind is get two pcs into one block, fixing with bolt directly. The central liner is star shape, formed by two block, tightened on the rib with the bolt.The hole on the grate liner is arranged at inclining direction. The wideth of the hole is getting bigger gradually to the discharging end, which can prevent the slurry from regorging and rough granularity from blocking. The slurry flow into the fan shape room through the hole on the grate plate from the lower part of the discharging end, and get passed up to the upper part along the cylinder rotating and discharged off the hole path. The hollow shaft neck has the grinding proof inner cover, with one end made of trumpet shape blade to lead the slurry to flow out of the mill.As the slurry in this kind of mill is discharged through the grate plate, it is called the grate ball mill.
The characteristics of the grate ball mill:
1. The fast discharging speed, and high production capacity( 20~30% higher than overflow type, and so does power saving )
2. Less overgrinding phenomena--discharging at the lower horizontal level. Less slurry stored inside. And easy to discharge the grinded fine particles in time.
3. Much ball loading- not only big ball but also small ball, for the grate fence. Having the good grinding condition.
4. The complicated structure than overflow---multi grate fence, taking certain room and reducing the effective volume.
The grinded material are carried by the discharging grate plate in the grate ball mill, which has the compelling function, and fast discharging speed. The slurry level in the discharging end is lower than that of the lowest mother line level in the discharged shaft neck, so it is called the ore low level discharging. The mill has height difference from the material input end to the output end, and the slurry get through the mill with faster speed, discharging the grinded particles in time. As little slurry stored in the grate type ball mill and blocked by the grate plate, the mill can load more balls, easy to load the small ball. When the steel ball dropping off, the striking function lessened by the slurry resistence will be less. These causes make the production capacity and efficiency is higher than that of the overflow mill, with rough granularity finished product and not easy to get overcrushing.
Grinding Media Weightt
Copyright Zhengzhou Bobang Heavy Industry Machinery Co.,Ltd.
E-mail : [email protected] Tel0086- 86656957 Address No.11 West Construction Road, Zhongyuan District,Zhengzhou City,Henan Province, China
ball mill frequent problems and solutions
Solution: in the work process of ball mill, if there is frequent and loud clack sound in ball mill, it may be because the screw bolts loosen. To solve this problem, operators should found out the loosen screw bolts and tighten them.
ball mill maintenance & installation procedure
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.
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.
the magic of bolting for a grinding mill assembly - metso outotec
From a distance, a grinding mill may not be an impressive piece of machinery. At first glance, all it seems to do is turn and turn at a constant speed. However, grinding mills play a critical role in minerals processing, with large mills often processing over $1 million worth of ore per day. With grinding equipment operating around the clock, any revenues lost due to a mechanical failure are lost forever and can severely impact a mines bottom line.
Large grinding equipment is typically split into multiple segments or cans in order to make their manufacturing and transport to a mine site feasible. For example, a large 40 foot diameter SAG mill without liners weighs in excess of 3.6 million lbs (1.6 million kg), making it impossible to make, ship, or lift this equipment in one piece. Smaller segments can be assembled at the mine site either through field welding or through bolting. At assembly, each part, whether it is big or small must come together perfectly so that the mill can perform as designed.
Bolting has traditionally been the choice of joining multiple mill segments as it is quicker to implement than other methods. It allows for disassembly of components in case of wear and tear (such as when replacing worn trunnions, or damaged gears) and also avoids the need for welding in the field which cannot be as well controlled (in comparison to welding, heat treating, and machining done in a machine shop). Field welding will always cause distortions due to high heat input, which can cause issues during assembly.
Bolting is magical. But it is only magical if designed and executed correctly. The basic principle of bolting is always to ensure metal to metal contact between the mating parts. Why is bolting magical? Imagine you close a spring-loaded umbrella. You are doing work in doing so. When it starts to rain, you push a button on the umbrella, and with very little effort, it opens like magic. This concept is similar to preloading bolts when assembling a mill. When you tighten the bolts, you compress the flanges (i.e. the clamped parts), and when the mill is running, any additional load on the joint will be partially distributed to further stretch the bolt, and partially to relax the joint. With some simplifications, we can mathematically show that the bolt will only see a fraction of the applied load, in the order of 15%. This is because the stiffness of the flanges (which is a function of the clamped area) is much higher than the stiffness of the bolts (which is a function of the bolts cross-sectional area).
These two components (flanges and bolts) are thus connected in parallel and share the load roughly in proportions of 15% (bolts) and 85% (flanges). If the bolt preload is lost for whatever reason, then the bolt starts seeing 100% of the applied load.
Another factor to consider is that bolts need to be preloaded properly such that they perform well under fatigue. In engineering terms, an infinite life is considered as over 10 million stress cycles. A typical medium size grinding mill undergoes over 5 million revolutions per year. A mill, therefore, needs to be designed for infinite life otherwise it could fail within two years. The bolts holding the mill segments together play a critical role and must withstand the high levels of alternating loads placed on them.
Several factors can cause a disruption to the magic. During operation, slurry entering in between flanges and working their way towards the bolts can cause the metal-to-metal contact to cease. Now the additional stiffness of the slurry has been introduced into the equation. The stiffness of the clamped parts will be reduced with the slurry layer, and the bolts will begin to experience much higher loads compared to before. This will most likely cause bolt breakage in the long run and could lead to serious consequences or even catastrophic failure of the mill.
Proper torqueing (calibrating torque wrenches, using elongation as a measure of torque, light lubrication of threads to better control friction, etc) and keeping the clamped parts clean are necessary to fully profit from the magic of bolting. Using hardened washers and re-torqueing bolts after a few days of initial operation are recommended as well.
With bolting and other components that make up the mill, it is often small details in the design or in implementation that make the difference. The design of gear/pinions as well as the oil lubricated bearings can be complex, which requires sophisticated engineering. In addition, the structural design of grinding mills needs to be carefully considered. Design tools such as Finite Element Analysis (FEA) are used to design structural rotating components such as trunnions, heads, and shells. These tools are no different than those used in high-tech automotive and aerospace industries and are used to ensure that the many parts that make up the entire mill come together in the right way. Before embarking on a new mill installation or upgrade project, be sure that you have the right experts in your corner.
Our company helps in prolonging the life of your mills by providing a complete service
to record the load in your bolts and adjust them if necessary, returning your bolts
back to the required tolerances.
Boltprep provides highly skilled and experienced Technicians who are trained to identify
bolted joint issues before they become critical, we initiate corrective actions to
help our customers to implement programs and processes to prevent premature breakdowns.
If your contracting company uses torque and is very diligent in the application of
their bolting techniques, you could only end up with a mill which has 50% of the
bolts doing 100% of the work and all this before a single liner or the weight of
the ore and grinding media are introduced.
Bolts by their very nature are designed to undo, from the very moment the load used
to tighten a bolt for the very first time is released, a bolt starts to loosen, it
can loose anywhere from 10-20% of its load in the first 48 hours and thats without
the normal bedding in process.
When your mill goes into production we are able to periodically come back and adjust
your bolts back to the required load needed to keep the joints securely fastened,
these regular checks enables us to look for potential problems and gives you the
opportunity to rectify them before they turn into costly down time.
This is why a re-torque is specified and is usually carried out, (mostly seen on
liner bolts), but what about the bolts holding the mill together?, All to often they
are just overlooked, and the results can be seen above.
When the mill finally goes into operation the structural bolts on mills are exposed
to extreme loads during operation and after a period of time they start to relax
and loosen off further, this can lead in a surprisingly short time to joint leakage
and eventually failure.
Our aim is to educate mill owners and give them a way to stop this happening, we
provide a service where we record the actual load in each and every individual bolt
while the mills are constructed making sure that the mill owners have a record of
the correct load in each bolt, before the mill enters production.
When a mill is commissioned, the construction company should make sure that all the
bolts are tightened to the correct load / torque to keep the flange joint tight and
together during operation.
The mill manufacturer specifies a load which is designed to be the optimum load applied
to the bolts to hold the mill together for its entire life, which can be in excess
of 20 years, some mill manufacturers specify an elongation, unfortunately they usually
specify a torque figure which should in a best case produce the correct elongation,
but rarely does.
If your company has a grinding mill or are going to install a mill in the future,
then the saying above, says it all, unfortunately for all involved, too many companies
don't follow these words.
BOLTPREP Technicians have been called to many sites, to correct problems that shouldnt
have happened. These problems could have been avoided if the mine owners and construction
companies had given bolting the time and respect it deserves.
Our technicians come across broken mill bolts at many sites around the world, to
the operators of the mills it is an almost normal occurrence, but if you have breaking
bolts there is an underlying problem which needs to be fixed.
Broken liner bolts cause the mill to lose ore, the bolt holes become worn leading
to a reduced service life and when new liner bolts are installed there is a greater
chance of the bolts breaking again.
The impact of the grinding media on the liners and the heads of the liner bolts,
leads to bedding in and relaxation of the liner bolts, incorrect tightening techniques,
un-calibrated torque wrenches, inexperienced personnel.
The liners are installed then the bolts are tightened to the required load using
the correct techniques, the mill is then put back in operation. A first re-tightening
(re-torque) of the liner bolts is usually done within 24 hours of production at full
Some companies carry out a second re-tightening approximately 30-40 days later to
confirm all the bolts are tight, depending on the life of the liners a further re-tightening
should be done at approximate 6 monthly intervals.
If you have been doing a tightening regime which is the same or similar to the above
and you are still getting broken bolts, you should consider tightening the liner
bolts using Ultrasonic bolt load verification, to record the correct elongation or
stretch on your bolts.
This process involves taking an unstressed or loose bolt reading on the bolts before
they are tightened, the correct load as specified by the mill and liner bolt manufacturers
is calculated into an elongation length, then the bolts are tightened until the required
elongation is achieved. This technique guarantees that your bolts have been tightened
to the correct load. After the mill is stopped to carry out the first re-torque the
bolt lengths are again measured any bolts which have lost elongation / load are re-tightened
to the required load, again guaranteeing that all bolts are at the correctly tightened.
During further subsequent re-torques the bolts can be measured and adjusted to confirm
correct bolt load. This process overcomes issues associated with torque and stops
bolt breaking due to un-uniform bolt loads. This procedure should be implemented
as the first option to rule out the main culprit of bolt breakage.