Mill End Replacement: For Mills With Slide Shoe Bearings

Mill End Replacement For mills with Slide Shoe Bearings

© Holcim Group Support Ltd 2008

Holcim exclusive property , Do not show externally

Scope Attention !! The following procedure and join design between new mill end and mill shell can only be used if no changes of the roundness and run-out of the remaining mill shell are required. If corrections are necessary, please use the method for kiln section replacement as a guide.

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Mill End Replacement

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Agenda ƒ Introduction ƒ Time constraint ƒ Project definition ƒ Preparation ƒ Cutting the shell ƒ Shell Alignment ƒ The welding techniques   

Description of techniques and conditions Phases for a shell replacement Non Destructive Testing

ƒ Conclusion 3 © Holcim Group Support Ltd 2008

Mill End Replacement

Objectives

To know the key points and options of the project definition To know the work process To know the quality requirement To know the most suitable techniques

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Introduction, Shell section Replacement ƒ Need to be as fast as

possible ƒ Is a very expensive

operation ƒ Is not so common in

the plant

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Mill End Replacement

Time constraint, factors of influence ƒ Time is money ƒ In a mill end replacement, time can be

shortened in different ways : 

Technical solution (see case study)



Proper planning of schedule



Shift and work organization



Welding techniques



Adequate equipment

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Preparation: Planning and CTC ƒ The powerful tool that will help you to reduce the

shutdown time

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Mill End Replacement

Preparation: Time ƒ To save time as much as possible, preparation and

preassembling of the equipment can be done before the mill shut down.

Preparation of roller supports 8 © Holcim Group Support Ltd 2008

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Preparation: Time ƒ Assure that all jobs are done that can be

done before stopping the mill ƒ Make sure all the needed tools are ready ƒ Put the protecting plates to drain the ball

charge in place or close to the mill, if not possible for safety reason

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Preparation: Conclusion ƒ Prepare the needed material for the following phases: 

External drive with friction wheels



Support for lathe tool (supplier)



Hydraulic aggregate and cylinders



Electrical supply (for external drive / welding machines / Hydraulic aggregate)



Iron Cross (stiffener)



Roller support



Welding machines (supplier)



Pulling rods, Screw Block, Tension Block (supplier)



…... 10

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Starting

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Starting ƒ Prior commencing work on the mill, safety locks

must be installed to the power source

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Dropping the ball charge ƒ The area under the mill has to be protected

from the balls with steel and rubber plates Twin hopper

Fill into barrels

Removal

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Accessibility: ƒ To work on the mill, the feed tube and the liners

in the specific sector have to be removed.

Feeder tube (Intake)

liner plates

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External drive: ƒ For lathe work, cutting and welding, the mill

has to be rotated with different speed ƒ It has to be done by an external variable speed

drive (e.g. motor with frequency converter) Speed for lathe work: 20-40m/min Speed for welding: 0.5-1.0m/min

External drive with four friction wheels © Holcim Group Support Ltd 2008

Attention: Make sure the lubrication system is working during rotation !!!!

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Disconnecting of main drive ƒ Support the shaft with rollers ƒ Disconnect coupling between gearbox and shaft

Shaft on wheel support

Disconnected 16

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Cutting the shell: cross bars ƒ Place iron crosses about 100 mm from the cutting area in the

remaining part of the shell to avoid deformation during project

Ø<4.5 8 spokes Ø>4.5 10 spokes

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Mill End Replacement

Axial positioning bearing ƒ For the following lathe work, an axial bearing keeps

the mill in the exact same position

Axial bearing

Support

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Lathe device ƒ To move the tool, two axes are required (radial / axial) ƒ A strong support of the lathe device is essential to

avoid vibrations

Axial

Lathe support reinforcement

Radial

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© Holcim Group Support Ltd 2008

Lathe work installation ƒ During all rotary operations the mill is running in its

original Slide Shoe Bearings Mill Shell

Lathe device

Stiff Platform

Slide Shoe Bearing 20 © Holcim Group Support Ltd 2008

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Lathe work (part 1) The main functions of the lathe work. ƒ Centering and positioning of the new mill end ƒ Keep the same running condition of the mill

(no changes of shell run out) ƒ Proper connection between the two parts ƒ Reduce the thickness which has be gas cut

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© Holcim Group Support Ltd 2008

Lathe work (part 1) ƒ The axial position of the lathe work has to be

according to the new part, that the mill length will not change ƒ The spigot diameter can be calculated after taking

the circumference with a tape measure according new mill end 35 36 (10)

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Mill shell

spigot diameter (according new mill end) © Holcim Group Support Ltd 2008

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Roller support ƒ For cutting, the

Heavy load roller

remaining shell has to be supported by an adjustable roller support ƒ To have the rollers is

convenient, so the position of the cutting tool can be changed if necessary

4 Hydraulic cylinders

ƒ The hydraulic cylinders

to move the rollers, has to be equipped with an mechanical blocking system

Adjustable roller support

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© Holcim Group Support Ltd 2008

Cutting the shell ƒ Automatically gas cutting device with electrical drive Old mill end

Drive unit With motor Guide wheels

Guide sheet Fit between the wheels

Driving chain Gas cutter

Guide sheet fixation (weld in hole) Mill shell 24

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Cutting the shell ƒ The chain allows moving the gas cutter around

the whole shell without changes

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Cutting the shell ƒ Important is the angle 60° of the cut surface ƒ This is one side of the inner weld prepare

Mill shell

old mill end

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60° gas cutting

Mill center 26 © Holcim Group Support Ltd 2008

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Cutting the shell: automatically ƒ Some tools :

BUG-O Systems

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© Holcim Group Support Ltd 2008

Lift out the mill end ƒ The lifting is done by a mobile crane ƒ Weight of mill end approx. 15 tons Special hook

Old mill end

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Weld prepare ƒ To achieve a high quality of welding, grind away the

combusted cutting surface

Grinding of the gas cut surface 29 © Holcim Group Support Ltd 2008

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Maintain the slide bearings The slide shoes and swivel bearing has to be: ƒ cleaned ƒ Inspected ƒ replaced (if necessary) ƒ Re-greased Slide plate Spherical swivel bearing

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Maintain the swivel bearing ƒ In case of only little wear, the swivel bearings

can be polished by a soft cloth

Outer spherical swivel bearing

Inner spherical swivel bearing

Backside of the bearing shoe

Top of the bearing support 31

© Holcim Group Support Ltd 2008

Mill End Replacement

Lift-in the new mill end ƒ To simplify the alignment afterwards, it is necessary

to fix the hook on the right position. So the holes for the armor plates are approximately in line on both parts. Hole line shell

Force to rotate Hole line mill end

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Join the mill end ƒ The new mill end has to be pulled onto the spigot ƒ Therefore at least eight pulling rods are required,

every 45° around the circumference

Pulling rods

33 © Holcim Group Support Ltd 2008

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Joining the mill end new mill end

mill shell

defined contact surface

2

mill shell

new mill end

60° 34 © Holcim Group Support Ltd 2008

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Pulling Rods ƒ The pulling rods keep the new mill end on the

remaining old mill shell ƒ After tighten the rods, the support rollers can be

removed, so the mill lays again in its original slide shoe bearings Stiffener Cross Pulling Block Pulling Rod (Tube)

Bolt M36

Nut M36 (welded on tube) 35 © Holcim Group Support Ltd 2008

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Run out meassurement ƒ Before start welding, the axial and radial run out

has to be measured

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Inside weld ƒ The inner weld can be done by manual arc-welding ƒ Procedure (Example): Electrode material: Electrode diameter: Preheat temperature: Dehumidification of electrodes:

new mill end

EN 499 3.2mm 100-120°C 2h @ 350°C

mill shell

inside weld (hand weld) © Holcim Group Support Ltd 2008

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Lathe work (part 2) ƒ For the weld outside, the bevel has to be done by

the lathe device ƒ The depth of the chamfer has to remove the root

of the inner weld

lathe work (weld prepare)

mill shell

new mill end

inside weld (hand weld) © Holcim Group Support Ltd 2008

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preheating ƒ The shell has to be preheated to the correct

welding temperature

Propane gas burner 39 © Holcim Group Support Ltd 2008

Mill End Replacement

Outside weld ƒ The outside can be done by an automatic

arc-welding machine ƒ Procedure (Example): Electrode material: Electrode diameter: Preheat temperature: Flux: Dehumidification of flux:

EN 499 4.0mm 100-120°C P240 2h @ 350°C

new mill end

inside weld (hand weld) © Holcim Group Support Ltd 2008

outside weld (arc-welding)

mill shell

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Automatic arc-welding Granulate tank

Wire coil

Wire feeder

Welding nozzle

Arc-welding machine © Holcim Group Support Ltd 2008

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Automatic arc-welding ƒ To get a continuous Granulate tank

Pneum. Ejector

Granulate suction tube © Holcim Group Support Ltd 2008

speed with as less vibrations as possible, it is preferable to mount the welding machine on a scaffolding and let it not run on the shell

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Automatic arc-welding The advantages of the automatic machines are: ƒ Higher efficiency, faster (deposition rate of about

5kg/h instead of 1kg/h by hand) ƒ constant weld thickness and parameters ƒ More

homogenous temperature around the whole weld area

ƒ Less sources of errors

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Automatic arc-welding The disadvantages of the arc welding: ƒ High current requested from the power supply

(approx. 60A @ 3x400V) ƒ Dry

compressed air for recirculation (injector) needed

the

granulate

ƒ The granulate has to be dried in an oven before

welding ƒ Risk of Lack of fusion ƒ Mill has to rotate in a certain speed

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Weld grinding ƒ After removal of the stiffener cross, the weld

inside has to be grinded flat and smooth because of the liner

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Weld Test ƒ To check the the weld, an ultrasonic test has to

be done.(100%)

Ultrasonic weld test © Holcim Group Support Ltd 2008

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Installation of Liners ƒ Take care about a tide fit of the liners (especially in case of single row bolted liners)

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Ball charge ƒ The adequate ball charge

can be filled into the two mill sections

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Restart the Mill ƒ All the safety controls has to work properly ƒ Especially the lubrication aggregate has to

feed the new slide bearings with a sufficient flow rate! ƒ Don’t rotate the mill without feeding material

(damages can cause to balls and liners)

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© Holcim Group Support Ltd 2008

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