Mill Maintenance Methods

“Maintenance, repair and technical service are significant since they affect lifetime of milling machines and ensure them to work non-stop at desired levels. If regular and good maintenance is not performed, machines cannot work for long years. Predictive maintenance monitors active machines and equipment in order to detect possible breakdowns. Thus, it prevents downtimes for machines because of unplanned maintenance as well as loss of production and unnecessary part replacements. As a result, maintenance time and downtime stemming from breakdowns decrease up to %25-30. It enables eliminating minor flaws before letting them to evolve into more serious problems.”


Prof. Dr. Farhan ALFİN
Eurasia University
Food Engineering Department Head

Long time ago, mills were giving a break for production at weekends and maintenance teams were performing their duties until noon on Mondays to allow the mill to be back into action. Now most mills are active 7 days and 24 hours. The downs for maintenance are now at least every 10 weeks. Maintenance can be defined as all kinds of activities like repairs, replacements, inspections etc. in order to maintain working of buildings and equipment during their desired life expectancy.

Maintenance, repair and technical service are significant since they affect lifetime of milling machines and ensure them to work non-stop at desired levels. If regular and good maintenance is not performed, machines cannot work for long years. Regular maintenance is one of the most important factors that affect product quality. Regular maintenance prevents downtimes for machines because of unplanned maintenance and it enables to decrease costly part replacements and dependency to third party repairers.

Insufficient maintenance results in shutdowns for the mill and causes a decrease in capacity and inadequate production. Accelerated amortizations for machines, increase in mineral oils and product costs are also among results of insufficient maintenance. And the ultimate results may be loss of prestige and bankruptcy because of poor quality products.

Expenditures on maintenance cannot show direct returns, but they are very important for guaranteeing the overall return from the operation. Small amounts of costs for maintenance can prevent the mill from far reaching breakdowns and a huge financial damage. Besides, regular maintenance on machines also decrease spare part and service costs. We can diagnose many problems in the mill at early stages thanks to maintenance. One of the first things to examine when a mill is experiencing poor results is the maintenance.

Adequate maintenance program can be achieved by the use of three different methods: Unscheduled maintenance, preventive maintenance and predictive maintenance (Fig. 1). Management and inspectors, can choose and arrange maintenance systems according to specific needs and local conditions by making use of those methods.

It is also called emergency maintenance, breakdown maintenance or repair maintenance.

Maintenance and repair are performed when machine or equipment fails. As a result, loss of production during repair is high. Defects also can harm other machines or tools.

When performing corrective maintenance; the mill or its equipment is returned to base or original conditions and productivity by replacing parts or materials only after the breakdown.

Because of its disadvantages, unscheduled maintenance is currently not performed unless being essential. Alternatively, scheduled maintenance methods are necessarily performed.

The aim of “Planned” or “Preventive” maintenance is to minimize the need for emergency maintenance. It is performed by either one of the following sub-methods:
• Periodical Maintenance (Preventive Maintenance)
• Predictive Maintenance

A-Periodical Maintenance (Preventive Maintenance) The aim of this method is to prevent components of machines or equipment from failures and to improve their strength before any breakdowns. All components of machines or equipment are regularly monitored and failures or possible failure sources are determined and eliminated.

This method enables to maintain and repair components of machines or equipment at a specific interval. As a result, possibility of breakdown is decreased significantly.

• Expected life time of the equipment increases
• Shutdowns and breakdowns decrease
• Costly shutdowns and breakdowns decrease

But stopping machines and equipment frequently for maintenance causes loss of production and high maintenance costs.

Maintenance periods for machines and equipment at mills can be classified as:
• Daily,
• Weekly,
• Long term.

Maintenance periods for machines and equipment are pre-planned according to the specifications given by the company that installs them.

In order to perform the periodic maintenance, a maintenance schedule consisting of check lists is prepared. The maintenance schedule is prepared and kept by the engineer responsible from the maintenance. But it is performed by mainteFig 1. Maintenance Methods nance technicians.

Periodic maintenance includes four main group of activities for component of equipment:
• cleaning
• adjusting (e.g. belt tension),
• replacing (e.g. oil, filters etc. )
• inspection and examination.
(Please refer sources at the end of the article for further information about necessary factors to take into consideration for periodic maintenance.)

b- Predictive Maintenance
This is a relatively new approach as a result of latest technological developments. This concept was first introduced in Turkey in 1988 by R. Kubilay Köse at Middle East Technical University’s National Machine Design and Manufacturing Congress. He chose to use the term “Kestirimci Bakım” for “Predictive Maintenance”.

When performing predictive maintenance, some of the parameters are measured when machines and equipment are still working. Some measuring devices are used for this. Results are recorded at a specific time interval and results are evaluated according to some statistical methods and tendency analysis. Results show some information about machines and equipment. Changes in those results are tracked and possible defects at machines and equipment may be detected before they actually occur and maintenance can be performed on those machines accurately and adequately. In short, predictive maintenance is based on the performance of the machine.

This method enables to monitor machines or equipment in order to detect possible breakdowns. As a result, unscheduled shutdown of machines and equipment, loss of production and unnecessary part replacements are minimized.

Advantages of Predictive Maintenance
• Expected life time and productivity of equipment increases
• Enables corrective maintenance for critical components.
• Machines that are in good condition are not stopped unnecessarily and this saves time.
• Maintenance time and downtime for machine breakdowns decrease 25-30%. Work-load and labor costs decrease.
• Maintenance costs decrease significantly.
• It is 8-12% more profitable than preventive maintenance.
• More energy saving.
• Prevents minor flaws to become source of bigger problems in time.
• Possibility of significant breakdowns on machines decrease to the lowest level.
• Production loss decreases considerably. Production levels go up by 20-25%
• Breakdowns decrease by 35-45%.

1. Measurement: Critical points to be analyzed and measured are identified. Necessary measurements are performed during working conditions of the machine. Predictive maintenance usually involves non-destructive tests like oil analysis, temperature analysis (infrared thermography measurement), ultrasonic test, vibration measurement and visual inspection.
2. Analysis: Results of measurements are analyzed. The source of the failure is analyzed.
3. Repair: The detected fault is evaluated according to working schedule of the mill and necessary repair works are done.

Engineers in charge of production and maintenance have to be aware of all aspects of maintenance work.

Maintenance team is not only responsible for fixing and repairing breakdowns. They also have to investigate root causes of the problem and prevent similar breakdown or problem from reoccurring.

Maintenance leader maybe a mechanical engineer or another qualified technician who studied engineering or technical disciplines. Maintenance must be performed by well trained personnel who have technical knowledge. This training will also include safety issues and detailed information about special machines.

If we do not have enough personnel that have necessary and adequate technical experience or if we need machines to work more efficient, we have to seek technical support from manufacturer of machine or equipment to perform maintenance. This can be done with service contracts. So that, manufacturers will replace failed parts with original and high quality ones and warrant coverage will continue.

Personnel at the production floor are at the first level of maintenance. Maintenance workers on the spot are the second level of maintenance, and equipment engineers constitute the third level of maintenance.

Predictive maintenance is generally performed by a contracted or expert technician. Predictive maintenance team must be qualified and well trained about cutting edge technology. They must have measurement devices and know how to use them. And they must also know how to analyze data from former measurements and report them properly.

In order to evaluate equipment which maintenance was performed on, maintenance schedule and an inspection schedule are needed. Maintenance schedule has to be planned by maintenance leader in cooperation with management and he/she should complete a number of arrangements before maintenance program takes effect.

Detailed records have to be kept in order to ensure efficient control of materials and labor. Inadequate records cause conflict among departments that are related with the breakdown.

Responsible technicians have to draft a form for each machine and equipment of the mill. The forms have to include following information:
•Name of the machine
•Code of the machine
•Year of production
•Name of manufacturer
•Mechanical drawing
•Power of engines
•Serial number
•List of spare parts
•Supply source

Past maintenance activities and maintenance specifications from manufacturers must also be recorded and loaded into maintenance programs. All catalogues, maintenance and repair manuals, spare part catalogues etc. must be asked from manufacturers. This procedure must be performed for every machine at the plant.

Production manager of the mill must keep records of inspection results and part replacement during repair works. He/she must prepare timetables for preventive maintenance tasks. Maintenance leader must continuously track equipment conditions as part of decision process. This enables to change maintenance programs when it is feasible to do so.

It is important for the mill to have critical spare parts available in stocks against possible failures. Giving order for a spare part and stopping the whole shift will cause important losses for the plant. Millers should not evaluate critical stocks as a financial burden for them.

Spare part inventory of the mill may change according to maintenance activities in the mill. The management should decide on the components and their amount to stock. To do so they evaluate the location of the mill and they compare logistics cost and stock cost. Spare parts inventory must be tracked closely by management of the mill by means of a computer program.

Records should be kept well for a reliable maintenance program. Newly developed software (Computerized Maintenance Management System – CMMS) support record keeping, scheduling and cost control tasks significantly. Many software packages involve various interactive modules that share a common database. Each module is assigned to a specific maintenance task like preventive maintenance, inventory control, work orders, procurement, equipment history, job scheduling, backup schedule, human resources planning, budgeting, cost control etc. Maintenance software are designed to run on desktop or laptop computers.

Some advantages of computer assisted software are:
• Decreasing costs
• Compiling data more efficiently
• Better planning
• Minimizing stoppage costs
• Having better controlling opportunities.

We also suggest you to read our previous article titled "Predictive Maintenance".

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