Dimensioning of Tube Mills – Volume 2: Complete Guide

Dimensioning of Tube Mills – Volume 2 continues from the process sizing covered in the first volume and focuses on the mechanical systems that turn the process design into a complete machine. It covers shell and head design, bearings, the main drive, ventilation, lubrication, media handling, foundations and the interfaces with the grinding circuit. Used together, the two volumes connect process requirements with the mechanical and auxiliary systems required for an operating cement mill.

The Complete Cement Technical Package includes 931 cement-industry files covering books, courses, Excel tools and presentations. The $249 one-time package includes both tube-mill dimensioning volumes, together with strength calculations, drive-selection references, ventilation material and worked engineering examples, with instant download access immediately after payment.

This article presents the file in its order: the mechanical dimensioning of the shell, the bearings and the drives, the ventilation, the coupling to the process, the maintenance dimensioning and the example sheets: the reader uses it together with the first volume of the series.

1. The Scope of the Second Dimensioning Volume

The first volume dimensioned the process: the power, the D and the L: the second volume dimensions the machine and its systems:

The mechanical: the shell thickness, the heads, the trunnions, the bearings, the drive: the steel of the mill: the strength of the components under the load of the 300 tons of the charge and the rotation:
The electrical: the motor type, the gearbox, the VSD, the auxiliary power: the kW from the first volume to the components: the starting torque, the power factor, the energy bill:
The ventilation: the mill gas flow, the temperature, the drying, the dust collection: the air of the mill: the flow that carries the product and the heat:
The auxiliary: the lubrication, the cooling, the hydraulic lifting, the hoisting of the media: the systems that keep the mill alive:

The two volumes should be treated as one design sequence. Volume 1 establishes process duty, power, diameter, length, speed and media requirements. Volume 2 uses those outputs to size the drive, shell, bearings, ventilation and supporting systems. This prevents mechanical selections from being made independently of the actual grinding duty.

2. The Shell and the Heads: The Strength of the Drum

The tube of the mill: the steel cylinder that carries the charge and the rotation:

The shell plates: the rolled steel: the typical 35-60 mm (the 4-5 m mills), the high quality structural: the welding of the longitudinal and the circumferential seams: the geometry: the “the drum” 2: the bend:
The loads: the shell carries the weight of the shell, the liners and the charge (the ~300 t): the bending, the torsion, the pressure (the lifting: the gas): the dynamic (the ball impacts): the fatigue: the design stress: the factor of the safety:
The heads and the trunnions: the end closures: the cast steel heads: the trunnions (the hollow journals) support the mill in the bearings and admit the feed and the discharge: the trunnion diameter = the feed opening: the reinforcement: the stress concentration:
The tyres and the supports: the classical cement mills on the trunnion bearings: the modern the slide-shoe (the hydrostatic pads): the supports at the L/4 — the L/3 (the bending minimized): the design: the trunnion: the flat: the sliding: the base frames:

Shell sizing requires a combined check of distributed weight, bending between the supports, drive torque, local stresses around openings and attachments, and fatigue from cyclic loading. Plate thickness and reinforcement should be verified against the selected material, weld details, support arrangement and manufacturer design practice. Fabrication tolerances, weld quality, stress relief where applicable and dimensional inspection are part of the mechanical design basis, not separate afterthoughts.

3. The Bearings: The Trunnion and the Slide-Shoe Systems

The support of the mill: the bearings take the vertical load and the thrust:

The trunnion bearings: the classic: the journal of the trunnion in the white-metal lined bearing: the oil bath/splash: the hydrostatic: the jacking: the temperature watch (the max 55-70°C): the clearance: the self-alignment:
The slide shoes: the modern: the mill shell carries the tyres at the ends: the shoes (the hydrostatic oil pads) under the tyres: the pressure of the 300 t on the pads: the pump, the valve, the oil film: the shoe: the start/stop the low-speed:
The thrust: the axial: the helical drive forces: the axial bearing: the thrust ring: the adjustment: the wear of the “the thrust pads”:
The design numbers: the bearing pressure: the oil: the pump capacity: the cooling: The file: the calculations: the specific pressure (the N/mm²) and the pV: the maximum: the temp: the alarms: the lubrication: the viscosity: the selection: the filter: the tank: the safety of the bearing: the “white metal” the damage: the file: the sensor: the “start from the cold”: the jamming:

Bearing selection starts with the mill’s static and dynamic reactions at each support. The design then checks allowable bearing pressure, oil-film formation, start-up jacking requirements, lubricant viscosity, cooling duty, filtration and temperature limits. For slide-shoe systems, the hydrostatic circuit must maintain a stable film during start, stop and low-speed turning; for trunnion bearings, journal condition, alignment and oil cleanliness are equally critical.

4. The Drive Train: The Motor, the Gearbox, the Pinion

The power of the first volume arrives at the mill through the drive chain:

The ring gear and the pinion: the big gear (the ring) bolted at the mill shell: the pinion on the output shaft of the reducer: the gear ratio: the 4.6 m mill: the ~150 teeth vs the 20: the module: the speed: the forces: the backlash: the alignment (the critical: the gear life): the measurement: the spray lubricant:
The gearbox: the helical/bevel reducer: the ratio: the input motor speed (the 1500/1000 rpm) to the mill (the 15-26 rpm): the center distance: the torque: the selection from the catalog of the vendors: the “the size”: the duty: the power:
The motor: the synchronous or the asynchronous: the kW: the starting torque: the pinion: the breakaway: the 200% starting: the cycloconverter/VSD: the modern: the synchronous: the efficiency 95+: the power factor correction:
The clutch and the coupling: the air clutch (the soft start: the inching), the torque limiting: the inching drive (the maintenance: the ball changing): The file: the train: the selection: the table: the standard: the 5,600 kW: the pinion: the 2.5 m: the gear: the 8 m: the train: the anchor: the alignment: the vibration: The drive dimensioning the design: the gear: the fatigue: the file: the formulas: the tooth: the 25 teeth: the durability: the load: the factor: the vendor: the “the standard”: the deliver: the complete:

The drive train should be selected from the required mill torque, operating speed, starting duty and service factor. The resulting motor, gearbox, pinion and girth gear must be checked as one system. Gear tooth loading, hardness, face contact, backlash, alignment and lubrication directly affect reliability, so the mechanical calculation and the maintenance tolerances should use the same design basis.

5. The Ventilation of the Mill: The Air, the Heat and the Drying

The mill breathes: the gas flow through the drum: the ventilation serves the transport, the drying and the temperature:

The air flow: the 1.0-1.5 m/s in the mill (the velocity of the gas): the volume flow: the fan: the filter: the vent flow: The flow carries the fines: the product: the “the vent” the residue: the mill dust: the blowing of the cement: The gas flow: the process:
The drying duty: the raw mill: the hot gas (from the kiln/ the hot gas generator) dries the feed: the moisture 4-8% to the <1%: the heat balance: the required: the m³: the temperature: the file: the psychrometric: the heat: the mass: The moisture: the process:
The temperature control: the cement mill: the gypsum dehydration: the 100-120°C limit: the ventilation takes the heat: the water injection (the atomized) cools: the temperature: the feed: the water: The clinker: the temperature: The mill: the residue: the temperature the balance:
The collection: the mill vent to the bag filter: the dust: the vent gas: the fan: the filter: the product: the return: The air: the “the mill dust”: the cement: the returns: The bag: The “the vent” the system: the filter: the sizing: the file: the “the mill fan” the selection: the volume: the pressure: the kWh: the “the system” the curve: the operating: the file:

Mill ventilation is sized from a heat-and-mass balance. Required inputs include feed rate, moisture, inlet gas condition, expected heat losses and target outlet temperature. The calculation should produce the required gas volume, fan duty, filter load and expected dew-point margin. Raw-mill drying and cement-mill cooling are different duties, so they should be checked separately rather than using one generic air-flow value.

6. The Grinding Media Systems: The Charging and the Handling

Beyond the first charge, the media life is a dimensioned system:

The first charge: the volume of the media (volume 1), the tonnes, the delivery, the charging opening: the “the charge”: the ramps: The crane: the ball feeder: the chute: the mill rotation: the distribution:
The make-up (the top-up): the daily/weekly additions: the measured power or the level: the ball: the size: the 90 mm: the top-up: the balls: the wear: the file: the formula: the ball consumption: the kg per ton: the schedule: The “the make-up”: the quality: the mill: the “the level”: the ball: The addition: The formula: the “the total”: the additions: the file: the “the media management” the Excel: the charge, the wear, the top-up:
The sorting (the re-screening): the periodic: the mill emptied: the balls sorted: the worn below the limit: the fresh: the sorting interval: the 6-12 months: the cleaning: the “the media”: the mesh: the separators: The sorting: the classification:
The media and the wear: the ball quality: the hardness: the breakage: The rejects: the broken: the removal: the “the cleaning”: the magnet: The iron: the media: The file: the tables: the ball life: the t: The “the steel” the cost: the media the process: The “the charge” the dimension:

Grinding-media management should be treated as a controlled operating system. The initial charge establishes the designed filling and size distribution; routine top-up compensates for wear; periodic sorting removes undersized or damaged media. Tracking media consumption in kg/t together with mill power, production and product fineness helps distinguish normal wear from an inefficient or badly graded charge.

7. The Lubrication Systems: The Oil of the Giant

The lubrication of the mill: the oil films that carry the loads:

The types: the gear lubrication (the spray: the viscosity the gear: the EP), the bearing oil (the hydrodynamic: the ISO VG 220-460), the pinion: the oil: The viscosity: the selection:
The systems: the oil tank, the pumps (the main and the standby), the filters (the duplex: the change), the coolers (the water/oil: the plate), the heaters (the cold start), the return: the instrumentation: the pressure, the temperature, the level, the flow: The alarms: the trips:
The spray gear lubrication: the ring gear: the spray nozzles: the air/oil: the intermittent: The consumption: the lubrication: the gear: the wear: The file: the “the spray” the adjustment: The gear: the flank: the spray: the pattern:
The hydrostatic: the slide shoe: the pumps: the pressure: the film: the jacks: The “the lift”: the start: the rotation: The low speed: The file: the complete: the lube: the schematics: the P&ID: The sensors: the “the mill safe”: The “the oil” the cleanliness: the ISO codes: The filtration: the water: the emulsions: The file: the “the lube”: the dimension: the tank: the pumps: the coolers: The selection: the vendors: The file: the table: the “the duty” the load:

Lubrication-system sizing must account for oil flow, reservoir volume, heat rejection, filtration, start-up conditions and redundancy. Bearing circuits and gear-spray systems have different requirements and should be designed independently. The final P&ID should clearly define duty and standby pumps, filters, coolers, heaters where required, instrumentation, alarms and trip logic. Routine oil analysis is then used to monitor contamination, viscosity and wear debris.

8. The Foundation and the Base Frame: The Mill Meets the Ground

The mill rests on the concrete: the foundation dimensioning:

The loads: the static (the mill, the charge, the bearings), the dynamic (the media impacts, the gear forces, the imbalances), the seismic: The combined: the design: The foundation: The “the block”: the concrete: the rebar: The base:
The base frames: the steel frames: the bearing pedestals: the anchor bolts: the grouting: The level: the alignment: The tolerance: The “the mill”: the torque reaction: The drive: The base: The “the fixed” the end: The expansion: The thermal: The alignment: The file:
The vibration: the isolation: the springs: the dampers: The vibration measurements: The limits: The “the mill”: the vibration: The monitoring: The file: the alarm: the trips: The “the foundation”: the resonance: The design: the frequency: The “the mass”: The file: the calculation: the natural frequency: The avoidance: The resonance:
The civil works: the excavation, the pile caps, the mass concrete, the cracks control: The file: the drawings: the details: The “the foundation” the dimension: The “the pit”: The lubrication: The drains: The “the construction”: The file: the “the foundation” the complete:

Foundation design begins with the actual equipment reactions and the geotechnical report. Static bearing pressure and settlement must be acceptable, but dynamic behavior is equally important because the mill, drive and grinding charge generate cyclic forces. The civil and mechanical teams should therefore coordinate pedestal elevations, anchor-bolt loads, grout details, stiffness and natural frequencies before construction drawings are released.

9. The Process Integration: The Mill in the Flowsheet

The mill dimensioning ends in the flowsheet: the interfaces:

The feed system: the bin, the feeder, the chute, the inlet trunnion: the “the feed” the dimension: the belt: The “the mill feed”: the moisture: The “the inlet”: the spiral: The feed: The “the chute”: the hopper: The “the feed”: the speed:
The discharge: the outlet trunnion: the “the discharge”: the chute: the elevator: the air slide: The “the discharge”: the temperature: The “the product”: the conveying: The “the outlet”: the dust: The “the discharge” the dimension: The “the elevator”: the bucket: The “the air slide”: the aeration: The “the discharge”: the “the return”: the classifier:
The classifier (the separator): the closed circuit: the dimensioning of the separator: the air: The “the wheel”: The “the fines”: The “the oversize”: the return: The “the mill”: the “the loop”: The “the product”: the residue: The “the separator”: the “the mill”: the balance: The “the circuit”: the file: the “the tromp”: the curve: The “the efficiency”: The “the classification”: the dimension: The file: the “the separator” the table:
The sampling and the control: the “the mill”: the sampler: the “the residue”: the “the power”: The control: The “the loop”: the “the feed”: The “the fineness”: the “the separator”: The “the control”: the “the plant”: The “the integration”: The file: the “the P&ID”: The “the flow”: the complete: The “the mill”: the “the flowsheet”: The “the dimension”: the file: the “the integration” the chapter: The complete: the “the cement”: the “the circuit”:

A tube mill must finally be checked as part of the complete grinding circuit. Feed equipment, mill discharge, bucket elevators or air slides, separator return, ventilation and dust collection all impose interface constraints. A consistent material balance and flow diagram are therefore essential: equipment capacities should be checked against both fresh feed and circulating load, not against the mill’s nominal throughput alone.

10. The Dimensioning Example of Volume 2: The Complete Machine

The full worked example: the 4.6 x 16 m cement mill from volume 1 receives its machine design:

The shell: the 60 mm: the heads: the trunnion: The bearing: the “the load”: the “the hydrostatic”: the shoes: The “the lube”: the pump: the filter: the cooler: The “the dimension”:
The drive: the 5,600 kW: the motor: the reducer: the pinion: the ring gear: the clutch: the inching: The “the torque”: the “the selection”: The “the gear”: the module: The “the teeth”: The “the alignment”: The “the spray”: The “the dimension”:
The ventilation: the 220,000 m³/h: the 1.2 m/s: the fan: the filter: the temperature: The “the dew point”: The “the water”: the injection: The “the dimension”: the “the fan”: the “the power”:
The auxiliaries: the media: the charging: the make-up: The “the lubrication”: the oil: The “the foundation”: the concrete: The “the anchors”: The “the base”: The “the complete”: the “the machine”: The “the file”: the “the drawing”: the “the spec”: The “the dimension”:

The worked example shows how the process-sizing outputs are carried into a mechanical specification. Required power drives motor and gearbox selection; mill mass and charge define support reactions; geometry and process duty determine ventilation and auxiliary requirements. The result is a coordinated equipment specification that can be used for vendor comparison, technical clarification and tender review.

11. Practical Tube Mill Mechanical Design Check

Confirm the process-sizing outputs from Volume 1: throughput, mill diameter and length, operating speed, media load and required drive power.
Calculate the total operating mass and support reactions using the shell, liners, media and material load.
Check shell, head and trunnion stresses for bending, torsion, fatigue and local reinforcement requirements.
Select the bearing arrangement and verify bearing pressure, oil-film requirements, jacking system, cooling and filtration.
Size the motor, gearbox, pinion and girth gear from operating torque, starting duty and service factor, then define alignment and lubrication limits.
Complete the ventilation heat-and-mass balance and verify fan duty, gas velocity, filter loading and temperature limits.
Check lubrication, media handling, inching drive, instrumentation and maintenance access as complete auxiliary systems.
Verify foundation reactions, anchor loads, settlement and dynamic behavior before releasing the mechanical and civil interface drawings.

12. Frequently Asked Questions on the Tube Mill Dimensioning, Volume 2

Do I need both dimensioning volumes?

Yes, for a complete new-mill design. Volume 1 covers process sizing such as power, diameter, length, speed, media and compartments. Volume 2 takes those outputs into the shell, bearings, drive, ventilation, lubrication and foundation. For a limited retrofit study, only the sections relevant to the modification may be required.

Which components of the drive wear out first?

Wear depends on alignment, lubrication, loading and operating practice. The pinion and girth gear are especially sensitive to poor contact pattern, incorrect backlash and inadequate spray lubrication. Bearings are highly sensitive to oil contamination and loss of film, while clutches and couplings are affected by starting duty. Condition monitoring should therefore combine gear-contact inspection, vibration, temperature and oil analysis.

How do I know the ventilation of my mill is right?

Check both the calculated balance and the operating measurements. Useful indicators include mill inlet and outlet temperature, gas velocity, pressure drop, fan operating point, product temperature, moisture and dust-collection performance. If the mill runs hot, carries insufficient material, shows poor drying or approaches the dew point, the ventilation balance should be reviewed rather than changing fan speed alone.

What is the importance of the inching drive?

The inching drive rotates the mill slowly for inspection, liner work, media handling and accurate positioning. It reduces the need to use the main drive for maintenance movement and gives the maintenance team controlled low-speed rotation. Its torque capacity, interlocks and braking arrangement should be designed for the loaded mill and the intended maintenance procedures.

Can the existing mill be upgraded using these files?

Yes. Existing mills can be reassessed using measured throughput, power, product fineness, circulating load, ventilation, media condition and equipment limits. The same calculations can support studies such as media optimization, ventilation improvements, drive changes or separator upgrades. Retrofit decisions should be based on measured plant data and verified mechanical limits rather than design assumptions alone.

12. Conclusion: The Second Volume Completes the Machine

Volume 2 completes the tube-mill design by connecting the process requirements to the shell, bearings, drive, ventilation, lubrication, foundations and auxiliaries. The key engineering principle is consistency: every mechanical selection should trace back to the same process duty, load case and operating assumptions established during mill sizing.

The Complete Cement Technical Package includes both tube-mill dimensioning volumes together with worksheets, Excel calculators, grinding references, separator material, ventilation references and drive-related documents. The complete 931-file library is offered for $249 as a one-time purchase with instant download access immediately after payment.

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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.