Maintenance - the often forgotten items
November 01, 2009
by World Grain Staff
Editor’s note: This is the final article in a three-part series that examines maintenance issues in feed mills. The first appeared in the September issue of World Grain and examined maintenance issues related to intake and grinding equipment. The second article appeared in the October issue of World Grain and examined issues related to mixing and pelleting.
Compressed air, steam, general exhaust systems and good practice in maintenance planning matters are items that most maintenance engineers forget about when putting together their wish list for capital expenditures at the start of the fiscal year.
Dry steam in the right volume enables feed millers to deal with the vagaries of several fibrous raw materials that create problems if they aren’t conditioned to the point where their fibrous nature no longer plays havoc with the internal workings of both mill machinery and the animal intestines.
Matching boiler capacity to the job at hand is imperative. Supplying fuel correctly in terms of calorific value and volume is a must, and reducing heat loss from pipes and valves is the third important issue that needs to be addressed.
Insufficient steam will result in droplets of water in acidic form being literally torn off the top boiler water surface. These droplets will create problems in the supply system to the press conditioner. Regular checks on combustion will prove valuable, especially when you receive oil from a range of suppliers. It is surprising how much variance there is between origins of oil. In mills, where there are more than three presses operating, it is quite staggering how fuel costs mount through the year. A check on the outgoing stack will be of interest to all maintenance engineers and of value to some of the more astute ones.
Checking steam traps and valves regularly will also pay dividends. Not only will you be better equipped to control boiler water feed temperature if you know that none of your traps are passing steam, but you will also reduce your fuel costs. Stand next to the hotwell return tank when all the presses are operating, and if you can hear knocking or banging in the tank, you know steam is passing through one or more of the traps. In the last mill I visited, the tank was shaking and vibrating so badly that it had almost broken away from its floor mountings. Needless to say, there were several traps not working correctly.
Additionally, you can tell where lagging is missing on steam piping simply by looking. But the atmosphere is also much warmer, and condensation is often visible where there is excess heat loss.
By taking a walk around the mill when the compressors are running and the mill is stopped, you can quickly pinpoint where compressed air is leaking. By tracking them down and fixing them, you will soon find your compressors running off load more often.
Compressed air can cost a lot of money to produce and you would be foolish to waste it. Using auto-drains on some remote applications often can be a cheap solution rather than returning to a ring main. But when the drain is left open or when the automatic drain chokes and jams, you will be amazed just how much it can cost you — much more than the cost of the pipe work — to return the air back permanently plumbed to the ring main.
Blowing items down with compressed air can be of value, but it must be done safely. Using air tools on the press floor helps protect them from being stolen, and they can be a valuable asset to the press operatives, but it is useful to fit some form of slam-shut valve when compressed air is found escaping.
Keeping mills clean is a constant battle, and hygiene personnel are expensive to employ. Hence, general exhaust systems are being used more widely in feed mills to control dust emissions within the mill. Such systems need maintaining and regular inspection. Installation of appropriate and easily accessible inspection and cleaning doors in general exhaust ducting is essential if dust buildups are to be avoided. The usual maintenance on fans, fan drives and filter cleaning mechanisms applies.
All of these smaller maintenance tasks need to be controlled and scheduled, not just because it is part of a good maintenance scheme but also to demonstrate to outside inspectors that you are maintaining your plant and equipment in such a way that in enables you to produce food for healthy, well-fed animals.
There are a plethora of schemes available for maintenance planning. Some are very good, some are mediocre and some are diabolically inappropriate for use, yet they have been adopted because they fit a financial template, often within an off-the-shelf accounts package.
A good system will generate an asset register that includes everything you want to know about a piece of equipment: when it was made, where and by whom, who the current contact is for spare parts for that machine, and how much it has cost you in spare parts since it was installed. You should also know when it was last worked on, by whom, and when it is planned for its next maintenance shutdown.
This information can be on a small computer package, and there are many out there that will do the job. Invariably, your mill equipment supplier will advise you of a suitable package and can let you have one they recommend at very little cost.
Alternatively, you can derive your own system as many millers have done. Invariably, once the wrinkles and snags are sorted, these "do-it-yourself " schemes get computerized and often end up being run by the person who does the spare parts purchasing. There is a temptation, however, to create a job out of nothing in this situation. If you aren’t careful, the tail wags the dog rather than driving your own maintenance scheme in line with the need of the business and your customer.
Whether you operate on a seasonal "campaign" basis or you have a weekly shutdown for maintenance, the same basic principles apply. You want to get the longest life possible out of your machinery without encountering excessive cost in the power department.
Knowing when to replace equipment parts is critical to a mill’s bottom line. In mills where maintenance is only done every few months, the temptation is to change everything at shutdown time because of the length to the next down period. When replacement is not possible, it is surprising how much longer equipment parts can be left to run, although the one item that should not be "nursed" along is the pellet mill die. When these start to lose output, change them immediately. You might upset one customer who wanted his feed that day, but you will keep many more happy that wouldn’t have received their feed the next day if you had kept trying to persevere with the old die.
Maintenance planning goes hand in hand with budgeting, if done correctly, and is a very good way to control costs. Some of the maintenance programs that can generate work sheets are also related to tonnage throughput, which not only ties your shutdowns to volume but also means that your expense is volume related rather than time related.
If you are using campaign maintenance, then use machinery templates where you limit your maximum expense per machine. You should also spend time shopping around for spare parts knowing that you have a budget to meet and more time available than the volumerelated mill engineer.
While it’s important not to use outside contractors when you can do the work yourself, there is a role for the contract maintenance crew in the campaign mill. When you know what you want to do, have all the parts available, or have them on a sale or return basis, and you do not have or do not want your own maintenance crews hanging around between shutdowns, then it makes sense to bring in maintenance crews when you need them. Doing this will peg your costs down and enable you to predict your expenditure.
The other solution is to let your maintenance crew run the mill between shutdowns. By doing this, you not only optimize your labor, you ensure that the operatives look after your machinery, since they will be the ones to fix anything they break. Cost-effective on all counts, this option works very successfully.
In smaller mills, the drivers also have a role to play with maintenance and they invariably service their own vehicles. The same mindset applies — they drive their vehicles with care knowing they will have to look after them when the time comes for a service. They also make sure the service is done properly.
Jonathan Bradshaw is a consultant to the agribusiness and food processing industries, specializing in project management and bespoke training programs through his company, J.B. Bradshaw Ltd. He has extensive experience in flour and feed milling in Africa, the Americas, Europe and the Caribbean. He may be contacted at firstname.lastname@example.org.
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