Planning for mill installations

By Peter Nilsson*
The following article outlines some commonsense steps and pointers which are crucial to this planning process.

Step 1 - Preparing the method statement
All safety aspects, especially how to handle the large components, must be the primary consideration when planning any large mill installation. If you can look through a particular installation job with all its peculiarities and challenges (be it a shell- or trunnion-mounted bearing mill, or a mill on riding rings mounted on the shell) and can clearly envisage how you are going to site rig all the components, you are in effect, mentally forming your method statement which you will have to produce to the engineer at some stage. This, in turn, helps with organising the special equipment you need to take when building the various possible configurations of custom built grinding mills.

Step 2 – Preparing the schedule
Once you have written down your method statement, preparation of the activity schedule is the next task. It is advisable to separate all the different tasks into groups. One method would be to group tasks according to how the various sections of the mill itself are assembled. Once you have an overview of issues like timeline, resources, personnel and tools, you are better prepared to ensure full efficiency with the workforce during the installation.
Another benefit of a well-prepared activity schedule is that it then doubles as a progress report of the job itself during the actual installation.

Step 3 - Selecting the right crew
The tradespeople you select must have heavy fitting experience and be trained in use of all the different technical equipment aspects of the jobs tasks. For example, both the use of laser alignment for the drive train and also ultrasonic bolt micrometers for measuring the elongation of critical fasteners are mandatory standards today.
The people you select for the handling and rigging must have heavy lifting experience and preferably have worked in a similar industry for at least ten years. Hundred tonne section lifts are becoming commonplace these days as processing plants become larger, so there are pitfalls awaiting the inexperienced - graphically documented on some websites.

Step 4 – Selecting the right tools
Selecting the right tools sounds easy enough – but this can be a minefield to the inexperienced.  The list can be mind-boggling – an experienced provider’s ‘toolkit’ can cost $300-400,000. Items in a tool container could include temporary power generator, specially designed lifting equipment, computerised laser alignment equipment, a hydraulic torque multiplier for the large critical fasteners and temporary oil lube systems for floating the mill during construction as the main operational equipment is usually still being installed and without mains power.  
The correct clamping force on structural mill bolts is vital as these bolts are designed to last the lifetime of a mill, so choosing the right tool is crucial. An ultrasonic bolt micrometer, for example, measures the elongation of a bolt much more accurately than the ‘old’ (and, unfortunately, still used) method of just measuring the torque.
Apart from ensuring a supplier has an adequate toolkit, there are other tooling issues to also consider. All rigging equipment and specially designed attachments, for example, must be certified for use and the certification must be up-to-date. Items such as slings must be checked and registered before sending to the project.

Step 5 - Planning your delivery timeline
In order for the installation to flow smoothly, component delivery to site must be such that it arrives to compliment the progress of the installation. This avoids congestions and double handling.
The weights and size of components means crane reach and practicable working space adjacent to the mill installation are usually at a premium.

Some pointers to consider:
Depending on a project’s location - be it the tropics or a dusty desert environment - a lot of large tarpaulins are needed to protect the machined items from rust corrosion or contamination while the machine is being erected. Some large mills take up to 12-14 weeks to build and rust/dust prevention is an ongoing task that has to be monitored through the whole erection of the mill.
During the main mechanical erection it is good practicable sense to involve the operational and maintenance staff as much as you possibly can. Usually the various components are already exposed, thus enabling ‘hands on’ visual explanations. This is important not only for smooth day-to-day operation but also when it comes to choosing long term critical maintenance spares other than commissioning and first 12 month run spares. Site operators and maintenance crews will feel more comfortable with the machine if they are involved from the beginning of the mill erection. It is human nature for people to look after a machine better if the correct operational aspects are understood.
Commissioning is very important for compiling all electrical settings and actual starting reference trend data for monitored components, including the mechanicals. The mill charge is normally increased gradually to full load over some days. The drive train sometimes has to be reset to suit the hot alignment and dynamic conditions experienced by the mill as load is gradually increased. Site mill staff should keep handy and retain copies of all the final full load starting data settings for reference against what were new as built data readings.
“House keeping” on mills is also very important and cannot be overlooked. This is especially the case for those who operate in a wet area and, in the case of SAG mills, usually a messy area. It’s a well-known milling fact that when house keeping has been well maintained, there are far less instrument and mechanical problems.
Care, however, should be taken when hosing down around any bearings. Operators should be made aware of what can and cannot be hosed down.

* Peter Nilsson is currently Installation Manager – Grinding Division for Outotec and is based in their Perth office.
For more information contact tel: +61 (0)2 9984 2500 or email: laura.white@outotec.com