“Having requested the screensroom and mill to obtain optimum performance, it is necessary to monitor the results on a regular basis to ensure the maintenance of the correct results. Millers must familiarize themselves with this routine for ensuring their shift’s performance.”
Ronald Sebastian
Milling Technologist
Mechanical Specialist Consultant
a) Items in the screensroom and mill that require attention to obtain optimum performance
Optimum milling performance refers to items such as output per hour, extraction, quality of final flour such as colour (ash value), water absorption, protein values and moisture control with regard to milling gain or loss. There are several factors that can influence these items, some of which have only a small effect and others that have a greater bearing.
b) Supervision and monitoring of mill performance
Having requested the screensroom and mill to obtain optimum performance, it is necessary to monitor the results on a regular basis to ensure the maintenance of the correct results. This monitoring by following specific routines and procedures are set out in the tables, where the varying degrees of importance as regards final milling results are shown against each item to be monitored or checked as a routine. Millers must therefore familiarize themselves with this routine for ensuring their shift’s performance.
Other items that affect the overall efficient operation of the whole process
In addition to the direct factors that influence optimum mill performance and profitability, consideration must be given to the more ancillary factors that contribute to this.
Consideration must be given to the following:
1) Humidity
2) Accuracy of weighers
3) Exhaust and air movement
4) Mixing of chokes and returned products
5) Losses in packing
6) Weighbridge calibration
7) Any other possible losses
1) Humidity:
The ideal situation in any milling process is to be able to maintain constant humidity (preferably at 60 to 65 % humidity). This can only be achieved by installing an air make up system through which the ambient temperatures and pressure within the mill building can be maintained at a constant level. The cost of this system should ideally be taken into account during the planning stages the mill building.
High humidity has the following effect on the milling process:
i) Inefficient dressing of stocks resulting in:
a) Increased colour. (high ash)
b) Reduced extraction.
c) Reduced output due to chokes.
d) Possible increase in protein loss.
e) fluctuations of the mill feed rate
ii) Increased condensation at certain points in the process, resulting in poor hygiene and chokes in the system.
2) Accuracy of weighers:
Weighing mechanisms can be divided into two categories:
a) Internal and
b) External
Internal weighers refers to the B1; flour; byproducts and screenings scales which are essential for accurate monitoring of the mills performance on a regular basis, (in modern mills, these are directly linked to yield calculators that are capable of giving the miller flow rates and extraction values at a glance instead of having to calculate this on their own) care must be exercised in this case to ensure that the accuracy of these scales is verified at least once quarterly. Any fluctuations in the operation of the weighing equipment will give false information regarding the milling performance and often leads to unnecessary changes being made to the mill equipment.
External weighers are those used to weigh incoming raw materials and outgoing finished products. Inaccuracies with these will lead to stock variances, affecting overall performance, and site losses.
To ensure accuracy in this aspect of the milling process, it is critical that all weighing equipment have the following facilities:
i) A means for accurate check weighing.
ii) A means for accurate balancing.
This being provided for by having a bag off point for a complete tip of the scale to a bag and for regular maintenance.
3) Exhaust and air movement
To avoid an imbalance between the air pressure inside and outside the mill, and the possibility of stock losses and unhygienic conditions caused by escape of dust from machinery, it is essential that the incoming air into the system as a whole, balances the outgoing air from the system. Pneumatic systems provide for the exhausting of the main milling machinery (e.g. plansifters and rollermills). However, in an elevator mill, adequate and efficient exhaust must be applied to minimize atmospheric dust as well as maintaining cool and free flowing dressing of stocks and hygienic conditions throughout the mill.
Losses in dust collection and exhaust to atmosphere may occur should the dust/ air separation mechanisms be incorrectly balanced or maintained. This resulting in loss of product and increased air pollution.
4) Mixing of chokes and returned products
i) Records of all stocks mixed into the system are kept so that accurate stock control is maintained and allowances are made during calculation of extraction.
5) Losses in packing
i) Packing machines must be set within fine tolerances to ensure that packed products are not over or under weight.
ii) Bags must be check-weighed at regular intervals to ensure that weighing equipment is set accurately.
iii) Accurate records of each product packed must be kept to maintain stock control and to identify any possible losses due to errors in loading.
6) Weighbridges
i) Ensure that records of all vehicle tare mass and gross weights are cross checked and maintained.
ii) Check that vehicles are positioned correctly on weighbridges prior to weighing.
7) Other possible losses
• Ensure that efficient security arrangements are maintained on site.
• Correct recording of weight of incoming raw materials and care exercised during recycling operations in the silo.
• Proper recording of all returns to the mills with correct weights of mix-backs from customers.
• Accurate recording of all recons from silo to mill; mill to holding bins; holding bins through mixing and blending plants; mixing plants to bulk or packing facilities; packing bins to warehouses and warehouses to logistics and weighbridges.