Vertical Mills Operations V: Complete Technical Guide

Vertical mills operations is the operating discipline of the vertical roller mill: the machine that grinds the raw material, the coal and today the finished cement of the modern plant: the vertical mill replaced the classic ball mill in most new raw grinding sections because it combines the grinding, the drying and the classifying in one tower: the table, the rollers, the gas, the separator: a complete process in one vessel, and a process that demands a complete operating knowledge: this article is the guided tour of the training module that teaches it.

The Complete Cement Technical Package (931 files including the courses, the books, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes the Vertical Mills Operations training module (version 1.0) among its operator and engineer training materials: the module walks the mill crew through the principle of the bed grinding, the components of the mill, the operating parameters, the start and stop sequences, the troubleshooting and the maintenance of the wear parts: this article presents the map of the module with the real numbers of the trade: the grinding pressures, the temperatures, the vibration limits and the fineness targets.

Why the vertical mill deserves its own module: the mill is the bridge between the quarry and the kiln: its product, the raw meal, must carry the chemistry and the fineness that the kiln expects, at the flow that the kiln demands, day and night: a mill upset is a kiln upset, and the smooth operation of the vertical mill is a condition of the whole plant performance: the module of the package teaches the crew to keep the bridge stable: the bed, the pressure, the gas and the class are the four pillars of the mill operation, and each gets its chapter.

1. The Principle of the Vertical Roller Mill: The Grinding Bed

The vertical roller mill grinds the material on a rotating horizontal table under heavy rollers: the material is fed to the center of the table, the table spins it under the rollers by the centrifugal force, the rollers crush and shear the particles against the table, and the ground material is carried by the air stream to the separator: the essential idea that separates the vertical mill from the ball mill is the grinding bed: the material lies as a layer on the table, a few centimeters thick, and the rollers pass over the bed instead of the material falling between the steel bodies:

• The bed grinding principle: the energy of the rollers is transmitted to the material by the pressure through the bed: the particles are ground by the crushing between the roller and the table through the bed layer, not by the random impacts of the grinding media: the principle gives the vertical mill its efficiency: the grinding work is concentrated and controlled, with the losses of the steel-on-steel grinding mostly absent;
• The advantages of the design: the vertical mill grinds the material to the target fineness in one pass through the integrated classifier, dries the material with the gas of the process in the same vessel, and occupies a fraction of the floor space of the ball mill circuit: the specific power of the raw grinding is typically 20 to 35 percent lower than the equivalent ball mill circuit, a saving of several kilowatt-hours per tonne;
• The family of the machines: the raw mill, the coal mill and the finish mill of the cement: the same principle with the different emphasis: the raw mill runs the gas at the high temperature for the drying, the coal mill must avoid the accumulation of the explosive dust, the cement mill grinds the dry hot clinker with the water injection of the cooling: the module covers the family with the special chapter per service;

The bed is the heart: without the bed there is no grinding, and with the unstable bed the mill vibrates, trips and grinds poorly: half of the operating art of the vertical mill is the art of maintaining the bed: the correct feed rate, the correct pressure, the correct gas flow and the correct dam ring: the module opens with the physics of the bed because every subsequent parameter of the operation is a servant of the bed.

2. The Components of the Mill: The Anatomy of the Machine

The vertical mill is a compact machine whose parts work in the intimate cooperation: the module walks the mill anatomy part by part, with the cross-section of the mill in the training deck:

• The table: the horizontal grinding table of the diameter 3 to 6 meters in the large raw mills, driven by the gearbox at the speed of 20 to 40 rpm: the table carries the bed, the segments of the wear-resistant liners are replaceable, and the dam ring at the table edge keeps the bed in place;
• The rollers: two to six rollers, typically four, of the diameter up to 2.5 to 3 meters in the large mills: the rollers are free to rotate on their shafts, pressed onto the bed by the hydraulic cylinders and lifted by the same system at the start: the tire of the roller, the wear part, is replaced by the segment or the full tire exchange;
• The grinding pressure system: the hydraulic cylinders, the accumulator and the pump unit press the roller carrier: the grinding pressure is set by the hydraulic pressure, normally 40 to 80 bar at the accumulator, and the relief system protects the mill from the foreign bodies and the metal contamination: the pressure is the throttle of the grinding intensity;
• The gas circuit: the hot gas enters the mill through the nozzle ring at the table periphery, lifts the ground material into the mill body, dries it and carries it to the separator: the gas velocity at the nozzle ring is typically 50 to 90 meters per second, the gate of the rejection of the coarse and the heavy particles;
• The separator: the dynamic classifier at the top of the mill body: the rotating cage separates the fine from the coarse: the fines leave with the gas to the filter, the coarse fall back to the table: the separator speed is the primary fineness control of the mill;

The anatomy lesson of the module is accompanied by the maintenance view: which parts wear, which parts inspect, which seals protect: the gearbox, the guide vanes, the expansion joints, the roll seal: the mill is simple in concept and dense in parts, and the module draws the complete machine so the crew recognizes every component when it speaks through a vibration or a temperature reading.

3. The Grinding Process: The Forces and the Physics of the Bed

Inside the mill, three forces meet on the bed: the centrifugal force of the table, the pressure of the rollers and the drag of the gas: the module explains the balance of the three because the balance is the operation:

• The centrifugal distribution: the feed drops on the table center, the rotation accelerates it outward over the table: the larger and the heavier particles travel to the dam ring, the finer stay inside: the table speed and the feed point geometry determine the path: the mill runs best with the feed delivered to the table center by the chute or the three-way feed arrangement;
• The roller passage: each roller passes over the bed many times per second, the particle is nipped between the roller and the table, crushed and sheared: the pressure of the roller on the bed is transmitted through the layer: too high a pressure grinds the bed down to the metal, too low a pressure lets the coarse particles escape unground;
• The bed thickness: the target bed thickness is typically 20 to 40 millimeters at the roller: the dam ring of 80 to 150 millimeters maintains the layer, and the table speed and the feed regulate it: a too-thin bed produces the mill vibration, a too-thick bed reduces the grinding efficiency and increases the rejects;
• The recirculation of the mill: the coarse material rejected by the separator and the heavy particles rejected by the nozzle ring return to the table: the internal recirculation of a vertical raw mill typically runs at 200 to 400 percent of the fresh feed, and the mill design, the gas velocity and the separator setting decide the loop;

The physics of the module is not academic: the crew that understands the forces can read the mill instruments like a control room: the mill differential pressure rises when the internal load grows, the vibration rises when the bed fails, the rejects rise when the gas velocity drops: the training connects the physics to the panel, and the panel becomes the window on the bed.

4. The Hydraulic System: The Grinding Pressure and Its Control

The hydraulic system is the muscle of the mill: the module devotes a full chapter to its components and its operating logic, because the grinding pressure is the single most direct adjustment of the mill performance:

• The pressure values: the working pressure at the accumulator of the large raw mills is commonly 40 to 80 bar, delivering the grinding force of hundreds of tonnes per roller: the specific grinding pressure at the material is normally 3 to 9 megapascals in the raw mills and up to 10 to 12 in the cement mills: the module gives the curves of the pressure versus the mill throughput and the fineness;
• The accumulator: the nitrogen-filled accumulator is the spring of the system: it absorbs the shock of the hard particles passing the roller and returns the pressure: the nitrogen pre-charge is the parameter checked at the maintenance: a deflated accumulator transmits the shocks to the hydraulic cylinders and the mechanical parts, and the mill vibrates harder;
• The relief and the protection: the hydraulic relief system lifts the roller assembly when a foreign body, a bolt or a piece of the metal passes under the roller: the relief pressure is set above the working pressure: the system protects the machine from the mechanical damage: the module teaches the set-up of the relief, the testing and the logging of the events;
• The start position: at the start the rollers are lifted to the top position by the hydraulics, the table accelerates, the feed starts, and the rollers are lowered gradually onto the bed: the gradual lowering avoids the metal-to-metal impact of the empty bed and the overload of the gearbox: the sequence of the module is exact and must be followed in the field;

The hydraulic chapter of the module includes the troubleshooting of the common failures: the pressure loss, the slow pressure build, the leaking cylinder, the blocked filter: each with the check procedure and the operating response: the mill crew treats the hydraulic unit like the heart of the patient: the pressure gauges, the filter condition and the oil temperature of 35 to 55 degrees are the vital signs of the muscle.

5. The Separator: The Fineness Gate of the Mill

The dynamic separator on top of the vertical mill is the quality gate of the whole grinding section: the module teaches its principle, its settings and its service because the fineness of the product is the contract of the mill:

• The principle: the material carried by the gas enters the separator housing, the rotating cage accelerates the particles, the centrifugal force throws the coarse outward while the gas drag pulls the fine inward: the cut size of the separation is set by the cage speed: faster cage, finer product, lower throughput: the module draws the cut curves of the classifier;
• The fineness targets of the raw meal: the raw meal leaves the mill at 12 to 15 percent residue on the 90 micrometer sieve and 1 to 2 percent on the 200 micrometer, with the moisture below 1 percent: the kiln feed spec of the individual plant decides the exact values, and the separator speed of 40 to 100 rpm equivalent is the main adjustment;
• The rejects and the internal load: the separator returns the coarse to the table: the internal recirculation rises when the cage speed increases and the product gets finer: the mill differential pressure follows the load: the operator balances the separator speed, the feed rate and the gas flow to hold the fineness at the maximum throughput: the optimum point of the operating window is the lesson of the module;
• The service of the separator: the guide vanes wear, the cage teeth wear, the sealing air protects the bearings: the module schedules the inspection of the classifier: the wear of the vanes changes the separation quality and the fineness drifts despite the constant speed: the crew measures the fineness by the sieve analysis at the regular cadence and catches the drift;

The separator of the vertical mill is also the place where the drying meets the classification: the gas velocity at the cage determines the cut, the gas temperature the moisture: the module teaches the combined control: when the gas flow changes for the drying, the fineness control compensates: the quality of the mill product is the visible report card of the crew.

6. The Operating Variables: The Balance Sheet of the Mill

The vertical mill is controlled by a small set of variables and the operator reads them as a balance: the module presents the operating balance of the mill with the typical ranges of the modern raw mill:

• The feed rate: the tonnes per hour through the weigh feeder: the target feed is set by the kiln demand and the mill capability: the module teaches the loading of the mill to the stable maximum, the point where the mill runs smooth and the differential pressure holds its band;
• The mill differential pressure: the pressure difference across the mill body, typically 40 to 80 millibar at the stable operation: it rises with the internal load, the recirculation and the dust load of the gas: the module gives the normal band and the response to the deviation;
• The mill outlet temperature: the raw mill outlet runs 80 to 110 degrees Celsius at the normal operation, controlled by the hot gas valve and the cold gas valve: below 80 the drying suffers and the moisture of the meal rises, above 110 the gas volume and the material handling change: the temperature is the drying control;
• The gas flow and the differential of the separator: the main fan speed regulates the gas volume: the module correlates the fan speed, the nozzle ring velocity and the rejects: the gas flow is the carrier of the product and the quality control of the classification;
• The vibration of the mill: the kiln of the bed health: the vibration sensor on the mill housing or the gearbox reads 1 to 2 millimeters per second at the normal operation, with the alarm at 2.5 to 3.5 and the trip above: the vibration rises when the bed thins, the feed stops or the foreign body passes: the module teaches the responses;

The balance sheet of the mill: the stable mill holds its differential, its temperature, its fineness and its vibration within the narrow bands hour after hour: the module trains the crew to read the deviations early and to react with the correct valve: the vertical mill rewards the patient operator and punishes the reactive one, and the training makes the difference between the two.

7. The Drying and the Gas Circuit: The Mill as the Dryer

The vertical mill grinds and dries at the same time: the hot gas, the kiln exhaust or the hot gas generator, enters the mill, evaporates the moisture of the feed and carries the dried product: the drying duty is a large part of the mill operation and the module covers it thoroughly:

• The heat source: the raw mill of the modern plant uses the kiln exhaust gas at 200 to 400 degrees at the mill inlet, or the dedicated hot gas generator when the kiln is off: the coal mill uses the hot gas of the kiln or the recirculated gas: the module compares the gas sources and their moisture and temperature constraints;
• The evaporation duty: the raw material at 5 to 15 percent moisture must be dried to below 1 percent in the mill: the drying work of the mill is limited by the gas temperature and the gas volume: the wet feed of the rainy season forces the mill outlet temperature down and the throughput down: the module teaches the moisture balance of the mill;
• The temperature constraints: the maximum gas temperature at the raw mill inlet is typically 350 to 400 degrees, limited by the gearbox and the mill internals: the coal mill is limited to about 80 to 100 degrees at the outlet and strictly supervised for the safety: the gas path, the filter and the fan are the last leg of the circuit: the module includes the safety interlocks of the coal grinding;
• The dew point and the condensation: when the gas cools below its dew point in the mill or the filter, the condensation occurs: the dust cakes, the filter bags plug, the mill and the cyclone accumulate the sticky material: the module teaches the prevention: the minimum outlet temperatures, the warming-up of the mill before the feed and the purging cycles;

The gas circuit of the vertical mill connects it to the whole plant: the raw mill uses the kiln gas, the cement mill and the coal mill have their own circuits: the module positions the mill in the plant gas balance and teaches the operating modes: the mill on the kiln gas, the mill on the auxiliary heat, the mill stopped with the gas bypassed: the crew must operate the valves in the right order to protect the filter, the fan and the mill itself.

8. The Vibration and the Protection: The Safety of the Machine

The vertical mill is protected by a ladder of instruments, and the highest rung is the vibration: the module teaches the protection philosophy of the mill because a correct response to the vibration alarm saves the gearbox, the table and the rollers:

• The sources of the vibration: the thin bed, the empty mill, the foreign body, the overfeeding, the unstable gas flow, the mechanical failure: each source has its fingerprint in the vibration signal, its frequency and its pattern: the module teaches the diagnosis of the vibration by the frequency analysis: the low-frequency vibration of the bed, the high-frequency of the bearing failure;
• The response sequence: when the vibration rises above the alarm level: reduce or stop the feed, lift the rollers, and investigate: the module drills the sequence until it is automatic: never let the mill run with the high vibration waiting for the trip: the trip is the last resort that protects the machine but costs the production;
• The interlock and the trip: the mill trips on the high vibration, the high gearbox temperature, the low lubrication pressure, the high motor current: the module lists the trip values and the restart conditions: the restart of the tripped mill follows the cold start sequence with the inspection;
• The metal detection: the feed belt carries a metal detector that rejects the tramp iron before it enters the mill: the module teaches the calibration and the monitoring of the detector because the tramp iron is the most expensive foreign body of the mill;

The protection philosophy of the module is preventive: the mill is protected not only by the interlocks but by the routine: the inspection of the feed quality, the check of the dam ring wear, the monitoring of the vibration trend: the mill that runs smooth for months does not do so by luck: the crew reads the trends, and the module trains exactly that reading: the trend beats the alarm.

9. The Start and Stop Procedures: The Sequences of the Mill

The vertical mill is started and stopped in a strict sequence that protects the machine, the filter and the process: the module gives the complete procedural chapters of the start, the stop and the emergency stop:

• The cold start: the auxiliaries first: the lubrication unit, the seal air, the main fan at the low speed, the hot gas valve: then the mill main motor at the no-load, the rollers lifted: the mill purges and warms up, the outlet temperature rises above the dew point: only then the feed starts and the rollers are lowered: the complete sequence takes 15 to 30 minutes and is drilled step by step;
• The warm start: the mill that stopped recently restarts faster: the purging is shorter but the sequence is the same: the module warns against the shortcuts: the warm mill still requires the full protection sequence;
• The normal stop: the feed is reduced and stopped, the mill grinds out the bed material, the rollers lift, the mill runs empty to clean, the gas valves close, the fan slows and stops: the correct stop leaves the mill clean of the material and the filter clean of the cake, ready for the next start;
• The emergency stop: the trip of the mill with the material in the bed: the restart requires the inspection and possibly the manual removal of the caked material: the module teaches the emergency procedure, the reasons for the trips and the prevention: the emergency stop is a cost, and the crew works to avoid it;

The sequences are the discipline of the module: the training deck includes the checklist forms that the crew uses at every start and stop: the checkboxes of the sequence make the operation independent of the memory of the individuals: the module and the package provide the forms, the plant adapts them with its own interlocks, and the crew signs each step: the discipline of the sequence is the insurance of the gearbox.

10. The Troubleshooting: The Common Faults of the Mill

The module contains the troubleshooting matrix of the vertical mill: the symptom, the cause and the remedy for the faults that the mill crew meets in the daily life: the honest list of the classic problems:

• The mill vibration with the full feed: the bed too thin (raise the dam ring or the pressure), the feed interruption, the foreign body, the gas flow collapse, the separator fault: the diagnosis ladder of the module walks from the cheapest check to the invasive inspection;
• The low fineness with the normal speed: the separator vanes worn, the gas velocity changed, the feed moisture high, the recirculation loop disturbed: the fineness drift is caught by the sieve control and the corrective adjustment;
• The high mill differential: the internal load too high, the nozzle ring clogged, the filter bag damaged, the material too moist and the bed thick: the module links the differential to its causes and the operator checks them in the order of the probability;
• The low outlet temperature: the hot gas valve defective, the cold gas ingress, the feed moisture low: the temperature must be restored before the condensation damage: the module teaches the protection actions;
• The gearbox and the lubrication alarms: the oil temperature, the pressure, the filter clog: the module explains the limits of the gearbox, the oil change intervals and the vibration monitoring of the gearbox: the gearbox is the most expensive single part of the mill and the lubrication is its life;

The troubleshooting chapter is built as the field guide: the crew with the module in the control room or the pocket looks up the symptom, reads the cause list and applies the checks in the order: the guide does not replace the experience, it structures it: the module and the experience together turn the mill upsets from the panic into the procedure.

11. The Maintenance of the Wear Parts: The Life of the Mill

The vertical mill wears by design: the table liners, the roller tires, the nozzle ring vanes and the separator parts wear at the predictable rates, and the module teaches the wear management that keeps the mill at the peak:

• The wear parts and their life: the roller tire of the raw mill typically lasts 8,000 to 15,000 hours, the table liner a similar range, the nozzle ring 10,000 to 20,000 hours: the actual life depends on the abrasiveness of the raw material, the quartz content, and the operating discipline: the module gives the wear tables and the measuring methods: the profile measurement of the tire and the table by the templates;
• The wear and the performance: the worn tire flattens and the grinding efficiency falls: the mill needs more pressure, the vibration grows, the fineness drifts: the wear is measured at every shutdown and the replacement is planned before the performance collapses: the module teaches the planning of the shutdowns for the tire and the table replacement;
• The maintenance of the hydraulics and the gearbox: the oil analysis of the gearbox, the filter service, the nitrogen re-charge of the accumulators: the scheduled maintenance of the module follows the operating hours and the calendar, with the inspection checklists per system;
• The sealing air and the seals: the roller seals, the feed chute seal, the separator seal: the sealing air prevents the dust ingress into the bearings: a failed seal kills a bearing in weeks: the module treats the seals as the critical small parts of the mill;

The maintenance chapter closes the operating circle: the crew that operates the mill well extends the wear life, and the maintenance that respects the wear plan protects the operation: the module presents the total productive maintenance view of the vertical mill: the operators clean and inspect, the maintenance rebuilds and replaces, and the plan coordinates the two around the production calendar: the mill is a partnership of the two departments.

12. The Energy and the Specific Power: The Efficiency of the Mill

The vertical mill earned its place in the plant by the energy saving, and the module quantifies the saving honestly:

• The raw grinding: the vertical raw mill consumes typically 12 to 20 kilowatt-hours per tonne of the raw meal against 18 to 25 for the closed circuit ball mill: the saving is achieved by the efficient bed grinding and by the replacement of the separator loop of the ball mill circuit;
• The cement grinding: the vertical finish mill runs at 24 to 35 kilowatt-hours per tonne of the cement against 30 to 42 for the conventional ball mill: the saving is smaller than in the raw grinding because the cement fineness demand and the water injection limit the efficiency: the module compares the two routes with the honest numbers;
• The combined saving: the plant that replaces the raw ball mills with the vertical mills saves several kilowatt-hours per tonne of the raw feed, which for a 5,000 tonne per day plant at the 10,000 hours per year means millions of kilowatt-hours per year: the electrical saving is the payback of the mill investment;
• The price of the saving: the vertical mill demands the higher capital, the stronger fan power per tonne in the drying mode, and the stricter operator discipline: the module teaches the full economic comparison, not the single number: the honest engineer evaluates the total plant impact;

The energy chapter of the module is accompanied by the package spreadsheets that compare the mill alternatives: the energy price, the drying demand, the availability: the engineer runs the numbers of his own plant and reads the conclusion: the vertical mill is the standard for the new raw grinding and increasingly the finish grinding, and the energy arithmetic of the module explains why the industry moved.

13. The Quality of the Product: The Fineness, the Water and the Chemistry

The vertical mill delivers the raw meal that feeds the kiln, and the quality of the meal is the contract of the grinding section: the module teaches the quality parameters and their control:

• The fineness: the residue on the 90 micrometer sieve of 12 to 15 percent and on the 200 of 1 to 2 percent for the raw meal, measured by the sieve or the laser particle analysis: the fineness is held by the separator speed and checked at the hourly or the shift cadence: the module teaches the sampling point, the sampling method and the interpretation;
• The moisture: the raw meal moisture below 1 percent for the kiln: the higher moisture costs the preheater energy and disturbs the kiln: the moisture is controlled by the gas temperature and checked by the loss on ignition method or the moisture meter;
• The chemistry of the meal: the mill does not change the chemistry of the feed, but the mixing in the mill and the silo do: the homogenization of the raw meal in the continuous silo evens the chemistry that the kiln needs: the module positions the mill in the homogenization chain: the quarry variations, the mill blending, the silo averaging;
• The cement quality in the finish mill: the vertical cement mill must hold the Blaine fineness and the particle size distribution of the cement: the steeper particle distribution of the vertical mill product changes the water demand and the strength development: the module teaches the adaptation of the cement formulation and the grinding aid to the vertical mill product;

The quality chapter connects the mill to the customer: the raw meal quality to the kiln, the cement quality to the concrete: the module trains the mill crew to own the quality of their product, not just the tonnage: the mill that delivers the stable fineness, the stable moisture and the stable chemistry is the mill that makes the plant predictable: the training of the module is the training of that ownership.

14. The Safety of the Mill: The Dust, the Heat and the Coal

The vertical mill operates with the dust, the heat and, in the coal mill, the explosive material: the safety chapter of the module is not an appendix: it is the frame of the operation:

• The dust exposure: the cement dust and the raw dust are the occupational hazards: the mill operation limits the dust escape, the seals and the filter contain the dust, and the personnel protection is mandatory: the module covers the hygiene rules of the grinding area;
• The heat and the hot surfaces: the mill body, the gas ducts and the filter operate at the high temperatures: the module teaches the isolation, the hot work permits and the burn prevention: the maintenance access to the mill internals happens only after the cooling below the safe temperature;
• The coal mill safety: the coal mill is the explosion risk zone of the plant: the outlet temperature limited to 80 to 100 degrees, the carbon monoxide monitoring, the inert gas injection systems, the fire detection and the emergency inerting: the module devotes the dedicated chapter to the coal grinding safety because the industry history of the coal mill fires is long;
• The confined spaces: the mill body, the filter and the silo are the confined spaces: the entry permits, the gas testing, the lockout and the rescue plan: the module trains the crew in the confined space discipline that protects the lives;

The safety teaching of the module follows the industry practice of the permit systems and the risk assessment: the crew that operates the vertical mill by the safety rules returns to the families every day, and the plant that respects the coal mill safety avoids the fires that make the industry headlines: the module treats the safety not as the constraint of the operation but as the condition of the operation.

15. The Frequently Asked Questions

What is the biggest difference between the vertical mill and the ball mill operation?

The grinding principle: the ball mill grinds by the impact of the falling steel media, the vertical mill grinds by the pressure of the rollers on the bed of material: the vertical mill integrates the drying and the classification in one machine, uses 20 to 35 percent less energy in the raw grinding, and is controlled by the gas flow, the separator speed and the grinding pressure instead of the media charge: the ball mill is simpler mechanically and the vertical mill is simpler in the system.

Why does the vertical mill vibrate and how does the operator stop it?

The vibration is the bed alarm: the mill vibrates when the bed is too thin or the feed is unstable: the operator first checks the feed, then the grinding pressure, then the gas flow: the standard response is to reduce the feed or to lift the rollers until the bed rebuilds: the persistent vibration with the full feed points to the mechanical damage, the foreign body or the separator problem, and the mill is stopped for the inspection.

What is the ideal bed thickness of the vertical mill?

The operating bed under the rollers is typically 20 to 40 millimeters: it is maintained by the dam ring height (commonly 80 to 150 millimeters) and the table speed: the bed thickness is not measured directly in the running mill, it is read through the vibration, the mill differential and the rejects, and the module trains the reading of the indirect indicators.

How is the fineness of the raw meal controlled on the vertical mill?

Primarily by the separator cage speed: faster cage, finer meal, lower throughput: secondarily by the gas flow, the guide vane setting and the feed moisture: the fineness is verified by the hourly sieve analysis at 90 and 200 micrometers, and the separator speed is trimmed to hold the target at the maximum stable throughput.

Can the vertical mill grind the cement as well as the raw material?

Yes: the vertical cement mills operate worldwide, at 24 to 35 kilowatt-hours per tonne against 30 to 42 for the ball mill: the finish grinding with the vertical mill demands the attention to the water injection for the cooling, the narrower particle size distribution and the adjustment of the cement formulation and the grinding aid: the module covers the cement grinding as a separate chapter with its own operating windows.

How often is the roller tire replaced?

The roller tire life of the raw mill is typically 8,000 to 15,000 operating hours, depending on the abrasiveness of the feed: the tire profile is measured at each maintenance stop and the replacement is planned when the wear approaches the limit: the module gives the wear measurement procedures and the planning tables of the replacement work.

16. Conclusion

Vertical mills operations is the complete discipline of the machine that grinds the modern plant: the bed grinding principle, the anatomy of the table and the rollers, the hydraulic pressure of 40 to 80 bar, the separator fineness gate, the gas circuit of the drying, the vibration protection, the start and stop sequences, the troubleshooting, the wear management and the safety of the coal mill: the module of the package trains the crew in all of them with the real numbers of the trade, and this article has walked the reader through the same map: the vertical mill is the bridge of the plant, and the operations training is the bridge of the crew.

The Vertical Mills Operations module (version 1.0) is one file of the Complete Cement Technical Package (931 files: courses, books, Excel tools and presentations: $249.99 one-time, instant download, lifetime access): the package carries the vertical mill training deck, the associated mill calculation tools and the complete plant documentation: the engineer who masters the vertical mill masters a large share of the plant: buy the package, open the module, and run the mill with the discipline of the numbers.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.