“Power requirements in mills is one of the highest of all operational costs, and it is pertinent that all equipment used, is run at optimum capacity to avoid underutilization and wastage. Planned maintenance and regular inspection of all equipment in the plant is the key to optimizing fixed costs. Replacement of major components means more capital expenditure, resulting in lower margins at the end of the day. it is more profitable to have the specialists contract for the maintenance and upkeep of these machines.”

Ronald D. SEBASTIAN - Milling Technologist and Mechanical Specialist Consultant, Morning Star Milling Corporation- Johannesburg

Optimization of fixed expenses in a milling operation has many aspects to look into prior to the actual conversion of the grain into products sought by the end users. All of the following processes functionality and efficiency will depend on the commitment of the millers, their assistants and the engineering department of the mill.

Power requirements in mills is one of the highest of all operational costs, and it is pertinent that all equipment used, is run at optimum capacity to avoid underutilization and wastage. The electrical engineering team has to regularly inspect and correct any anomalies in the transformer banks, capacitor banks and MCB’s, thereby ensuring that there are no unnecessary interruptions during normal operations. MCC’s have to be inspected regularly during which time the electricians must check and ensure that all connections to and from the circuit breakers and overloads are tightened to avoid shorts and failures during normal operations.

Most mills around the world are allocated power off the local power grid, that has to be consumed by the mill or a levy is imposed by the supplier. It is therefore extremely important for the miller to ensure that when the facilities are operational, that they operate at design capacity or better always, and that the parameters set out by management for target moisture content of conditioned wheat as well as quality parameters for milled products are met. This is only achievable if all plant and equipment are maintained and adjusted correctly.

At intake, we ensure that the capacity of the equipment is fully utilized and that down time is reduced to the minimum. The maintenance team ensures that all equipment is serviced at the required intervals and that any piece that is suspect, is repaired or replaced timeously, avoiding breakdowns during operation.

Lubrication of bearings and inspection of the condition of mixing screw conveyors, chain conveyors and elevators helps keep the facility operation at optimum design capacity always. The operator has to ensure that intake capacity is maintained throughout the receiving period.

SILO STORAGE CAPACITY MUST BE FULLY UTILIZED Silo storage capacity must be fully utilized as well. In order to achieve this, the operator adjusts all pre-cleaning equipment (drum sieves; aspirators and separators, where installed) to ensure that all or as much of the impurities are removed at all times. Scales and other monitoring, dosing, and measuring equipment has to be fully functional at all times. All wearing components are inspected and replaced when necessary. This prevents breakdowns and lost time as well as ensuring the accuracy of the equipment.

In the screens room, the miller must adjust all the cleaning equipment to remove the impurities, ensuring that only clean wheat is conditioned (impurities in conditioned wheat can result in blockages in the discharge spouting as well as erratic moisture and flow rate to the mill). Lying times and consistent flow through the screens room ensures that the desired B1 moisture content is maintained throughout the run. Here too, maintenance plays an important role in ensuring functionality of equipment at all times.

In the mill, it is critical that all fluted rolls are thoroughly inspected for wear and that the roll disposition is correct during roll changes. It is the millers’ duty to ensure that roll scratchings are done every time the mill is stopped for maintenance. This ensures that when the mill is operating, the required break releases are achieved. Where there is more than one roll stand being used for each break passage, the miller must correctly balance the feed over all the roller mills involved, thus ensuring that there is always even distribution of the stocks to the equipment following each stage in the process.

Smooth rolls are inspected and replaced regularly when there are signs of wear. (having in-house re-fluting and re-surfacing equipment are an advantage to any mill). Proper and thorough millers’ maintenance on roller mills ensures that there are no blockages in the flow of feed through the feed gates and that the feed is spread across the entire width of the roll. Maintenance and adjustment of brushes and roll scrapers help preserve the life of the roll surfaces and ensure that grinding on the various stages is maintained at correct levels.

Plansifter maintenance by the millers and correct replacement of holed and torn sieves helps with correct distribution of stock to purifiers and lower break and reduction rolls, and proper separation of flour from every stream.

Broken and holed sieves cause contamination of stocks and out of spec production, which result in more rework in the mixing and blending plants as well as returns by customers, which could result in loss of customers. This can impact on the profitability of the plant and reworking of the returns through the mill.

Lubrication of bearings of the sifters helps prevent breakdowns and keeps the machine functioning well. Inspection and replacement of drive belts keep the machine running at the correct speed at all times, and avoids breakdowns and stoppages due to chokes.

Purifier maintenance and inspection to ensure proper separation and distribution of stocks through the following processes. Proper functioning of brushes and turning devices ensure that sieves are kept clean at all times. Mechanical inspection and replacement of wearing components at regular intervals ensure that the machine functions to design specification at all times.

Filter maintenance and regular replacement of blinded filters will ensure that there always enough general exhaust to equipment and that the pneumatics of the mill are functioning to requirements, preventing chokes that require rework and delays as well as product contamination in this manner.

Airlock inspection and lubrication ensure that there is no blockages and stock being sucked into the filter, causing filter blockages and loss of pneumatic lift.Regular inspection and oil changes to blowers ensure that there is always sufficient transport air for milled products to be transferred to the mill bins. This also keeps the blowers working at controlled temperatures without generation too much heat that can impact on the flour moisture content.

All other supplementary equipment such as impact detachers, drum detachers, bran finishers are inspected and maintained at regular intervals and any repairs due are carried out as required.

All milled product holding bins to be completely emptied; cleaned and inspected at regular intervals and records maintained to prevent/ avoid 1) infestation of products, as well as 2) mixing of different products that can result in cross-contamination and rework.

Mixers in the plant are inspected, cleaned and sanitized on a monthly basis, during which time the bearings are lubricated, geared motor oil level checked and topped up if necessary. All dosing scales are checked for accuracy and any anomalies rectified.

Packing bins are cleaned weekly to prevent infestation and mixing of finished products, bin top filters are cleaned and sleeves replaced if necessary, fans are inspected and serviced during cleaning procedures.

Packing lines stopped regularly for maintenance and repairs where necessary. All wearing components are replaced when necessary. The accuracy of all packing scales and dosing equipment has to be checked regularly to avoid over weights which are a loss to the company and underweights which can result in returns and loss of customers. Truck scales and weighbridges have to be checked regularly and calibrated annually to avoid under and overweights leaving the plant.

Ultimately, planned maintenance and regular inspection of all equipment in the plant is the key to optimizing fixed costs.

Wheat quality inspection on arrival at the plant ensures that production parameters can be achieved during normal runs without too many adjustments being made to the mill. Housekeeping in the plant is critical for the miller to be able to identify and correct leaks I spouting, sifter sleeves as well as air leaks, compressors are maintained regularly, in which case, it is more profitable to have the specialists contract for the maintenance and upkeep of these machines.

This basically covers everything that operations should be taking care of to keep fixed costs at a manageable level and generate savings. Replacement of major components means more capital expenditure, resulting in lower margins at the end of the day.