Keeping horizontal conveyors running safe and strong
July 01, 1998
by Teresa Acklin
A practical guide to maintenance and safety
The horizontal movement of commodities has been going on since before recorded time, and over the years, inventors and designers have come up with many clever machines to help us convey materials horizontally. Today we have an amazing variety of horizontal conveyor types.
The modern grain facility is filled with not one type, but a mixture of them, because each type has its own strengths and weaknesses depending on the conveying tasks to be performed. Though vastly different in form and inner workings, horizontal conveyors all have two important things in common: they must be maintained properly to handle material efficiently, and they can all be dangerous to operate.
Why should we pay all this attention, time and effort to safety and maintenance issues? The number one reason is good old-fashioned money. It just makes good fiscal sense to keep safety and maintenance a high priority for the following reasons:
1. Downtime How much does it cost you per hour if your facility is down? Cost estimates range from U.S.$350 to U.S. $34,000 per hour when a facility goes down. This does not take into consideration the frustration and inconvenience to your customers who can't deliver or receive goods. How do you justify the loss for lack of simple safety and maintenance procedures?
2. Injury, lost time accidents or death How much does it cost when personnel can't work? Training new workers is a huge cost that many companies don't fully consider. Accidents also raise insurance costs, but the trauma of a death or serious injury to a key worker is often far more devastating to a company than the increased insurance premiums. Money is replaceable but people are not. How do you justify the loss for lack of simple safety and maintenance procedures?
3. Jail time There have been several cases in the past few years of business owners and managers being jailed as a result of negligence due to unsafe conditions that have led to serious injuries or death. So you see, it's not just the boss or the insurance company you may have to answer to. It may be the courts, the judge, the police and ultimately your devastated family.
These are deadly serious matters. The machines that help us make our living can be horribly dangerous to work in, on and around. It bears asking the question one more time. How do you justify the loss for lack of simple safety and maintenance procedures? The answer is, you can't.
And even more frightening, with the trend toward bigger and bigger equipment in today's facilities, it is even more important that we pay attention. An average human body takes up about one hectoliter of space, and with equipment that can handle more than 17,000 hectoliters in an hour, whisking away a body would not even make a conveyor break a sweat.
Many major conveyor types and sub-types are used in the grain business. The vast majority of today's applications consist of three types: screw conveyors or augers; drag conveyors, including round bottom, flat bottom/en-masse, tall flight/inclines, and L-path/horizontal and vertical; and belt conveyors, including standard open troughing idlers, enclosed belts and air supported belts.
Screw conveyors or augers have been around for a long time. They consist of a pipe with helical flighting attached. They have a very simple design, are relatively inexpensive and can convey a wide variety of products. Applications are generally limited to small capacities and shorter lengths.
Drag conveyors come in many shapes and sizes and are very versatile. They can be used to convey up to 7.5 meters in length and can carry capacities to 2,200 tonnes per hour. They consist of a rectangular housing and carry the material using a chain with flight bar attachment.
This flight is used to push the load either in an en-masse fashion or it can use a fill depth paddle. These conveyors are best suited for tight spaces or where multiple discharge points and dust-tight operations are needed. They can also be arranged with single or multiple bend sections and can convey on inclines all the way to 90°.
There are four main types of drag conveyors used in grain operations. The round bottom drag conveyor utilizes a standard “U-trough” housing. The flat bottom or en-masse conveyor uses a rectangular box and conveys the full stream of material by pushing only the bottom portion of the stream, thus limiting the incline that material can be conveyed.
The tall flight conveyor solves this problem by increasing the paddle height to match the depth of the material stream. This arrangement can be inclined up to 60°, but also reduces the capacity for a given box size as compared to the en-masse type.
The final drag type is the L-path. Though this type is usually loaded in a horizontal section, it can actually be inclined all the way to vertical.
Belt conveyors are used in countless types of applications in every industry. The main advantage of a belt is the ability to carry large amounts of material great distances. The standard troughing idler belts are quite simple in design, gentle on the material and have relatively low installation, operation and maintenance costs.
The “open” nature of this type however, raises safety and housekeeping issues. The enclosed belt is a relatively new twist that solves those problems by enclosing the belt inside a rectangular housing and uses a “reloading” tail section to capture spills and dust. Air supported belts use a layer of air to float the belt, thus reducing horsepower requirements and completely eliminating the need for trough idlers.
Each piece of conveying equipment is unique, and each manufacturer has its own set of rules by which to maintain the equipment. It would be difficult to include specifics on each make and model used in the industry, so we will focus on general practices and procedures. Your program for your facility obviously must be much more specific.
Many maintenance check items will be generic across all three major types of conveyors. As you or your maintenance staff are inspecting your conveying equipment, always check the following items: Spills is material leaking from anywhere in the system? Shaft seals can be a common source.
Sounds listen for any unusual sounds coming from the conveyor.
Weather tightness Excess moisture is trouble, inside and outside the system.
Rust or corrosion take care of it now (treat like a fire). Treat and paint over immediately.
Sets screws keep them tight. This can be a major problem source.
Inlets and discharges is the material entering and exiting the conveyor properly?
The 2% Rule the conveyor should carry 2% more than the one feeding it, as this prevents system-wide overfills.
Lining inspect all lined areas. Lining is a wear point, so check it out.
Tension this would includes v-belts, conveyor chains and conveyor belting.
Venting if venting is required to relieve pressure, it's a safe bet it's going to clog up.
Bearings, reducers and all drive components these are real hot spots. Make sure oil levels and similar settings follow the manufacturer's specifications.
Here is a short “rule of thumb” list of maintenance reminders to always keep in mind: Noises don't fix themselves.
Tension if it's not tight, it can't run right.
Liners wear, so replace them.
Look inside your equipment, even if you don't think you need to.
If it's broken fix it, before it breaks something else.
Why are the conveyors we use so dangerous? In general, it is because they use heavy components and usually a large enough motor horsepower that they are not going to slow down much if a body part gets caught.
The conveyors we use also run at moderate speeds so they don't look very scary when opened. The other two factors are the relatively large openings that are provided for inspection and the fact that these systems are usually very long, which means the motor cutoff switch can be a great distance from where you are working. Think of a conveyor as a “Body Snatcher.”
As with the maintenance items, many safety checks will be generic across all three major types of conveyors. When working around your conveying equipment, always follow these safety precautions:
Enclosed equipment is safe equipment if there must be an opening, put a grating on it.
Make certain all guarding is in place.
Take off only the covers you need to take off.
Always replace all inspection covers, hatches, and ports.
Safety labeling is a must equipment is considered defective without it.
Lock out power.
Loose clothing, jewelry or ties are not allowed.
Never stand over open equipment while it is running.
Do not stand on top of a running conveyor.
Do not poke anything in the systems to clear jams.
Maintain strict housekeeping rules. Dirty = Dangerous.
Check out safety systems often.
We have concentrated on the equipment, but we all know that none of it matters if we don't have the people side of the equation correct.
There is a big push in this and every other industry I can think of to automate. The reasons are clear. Cut labor costs and improve efficiency. The job market also may force this, as finding qualified and reliable workers may be difficult. Now couple that with the fact that automation has reduced the quantity of people in a facility and the fact that these fewer people need to be of a higher quality because of the broader knowledge required of each person.
This puts a very large emphasis on proper training and worker retention. Why does this enter into the discussion? Because people make your facility go. People find the problems in the equipment. People resolve problems in the equipment.
We do have fancy sensors now that can detect several typical problems in equipment operations. But how do you smell a leaking bearing that is doomed to failure, or feel the vibration from loose flights in a drag conveyor that is about to come off or hear an auger shaft that is bent and impacting the housing? It takes people who are trained in what to look for and are responsible enough to act.
People are the ultimate sensors. We have the ability to see problems, hear problems, smell problems, feel problems and think about the solutions. It doesn't take any time to touch each bearing as you pass it, or to listen to equipment as you're cleaning it or to look for leaks and spills as you're walking through an area. However, what it can save you in the end if a problem is detected early on is significant indeed. Encourage your people to use their senses when working around the equipment and reward their behavior when they do.
FIVE KEY POINTS.
Maintenance and safety of horizontal conveyors are critical issues and should receive the highest emphasis. The specifics for your equipment must come from the manufacturer, but there are five key points you should keep in mind.
1. Establish an organized program of maintenance and safety. If you have one already, see if it can be enhanced and improved. Simply trying to remember to do critical tasks isn't good enough. You must have a written program that records and cross checks scheduled tasks and procedures. We live in a world filled with distractions, so use a written program or a checklist to perform all of your maintenance and safety functions.
2. You don't need to develop your own maintenance and safety programs from scratch. On the market today are a number of very good preventative maintenance software packages, which lead you through a series of questions and assist in establishing a schedule. These programs will then print out a schedule for hourly, daily, weekly, monthly or annually performed functions. Some can even alert you, alarm clock fashion, when something needs to be done. Many training videos also are available from industry organizations for your workers and visitors to view.
3. Create in your corporate culture an attitude that upholds the fact that maintenance and safety have a positive benefit. It is proven that you can measure the results of a well-established program on the bottom line, but take it further than just the financial balance sheet. There are benefits to worker morale and retention, and let's not forget customer and community respect and loyalty.
4. Communication is the key. You could attend a seminar every day for the next 10 years and establish an incredible storehouse of knowledge and wisdom, but unless you go back to your operation and share it with your people, the knowledge is wasted. Share information with your people and see if you can't spark their interest in helping you with your program.
5. If you don't have the time or the people to create a top-notch maintenance and safety program, then hire it done. Many consultants and experts can be hired for very reasonable fees to do the work for you. These consultants will come into your facility, determine the codes and regulation you must follow, establish the program, train the workers and return on a regular basis to update and monitor the progress. If you don't have the time or you don't consider yourself an expert, then hire one.
Bob Moser is executive vice president of InterSystems, Omaha, Nebraska, U.S. This article is based on his presentation in San Antonio, Texas, U.S., at GEAPS Exchange '98, the annual conference of the Grain Elevator and Processing Society.
Maintenance check items for individual conveyor types
Note: always follow the manufacturer's specifications.
1. Screw conveyors or augers
flighting every 700 hours
2. Drag conveyors
Flight hardware and wear
Gouges in the flights and bent flights
Section joint alignment
Chain and pin and roller condition
Don't run empty as this causes
excess wear, noise and power
Sprocket profiles should be
checked for “hooks” and other
Clean out tail and remove material build-ups.
Inspect return rail/sprockets for proper function or wear.
3. Belt conveyors
belt alignment throughout
inlet skirts Measure belt thickness every 500 hours.
oil leaks on idler bearing
idlers roller surface Lubricate the idlers every 500 hours
idler spool wear – note: end
idlers wear faster than center.
Horizontal conveyors: purchasing considerations
You should look for a number of things when you purchase a conveying system. Initial purchase price is only one part of the cost of owning and operating a conveyor system. Many manufacturers have designed in features that aid maintenance procedure, thus making it easier and less expensive keep the system running safe and strong.
The following considerations are generic across all three major types of conveyors.
Complete specifications horsepower, capacity, speeds, shafts and drive components and references
Contoured interiors to reduce build-up of material inside the system Water-weather-resistant housing
Lots of inspection openings
Easy open inspection, no-tool access, to assure inspections
200% factor v-belt drive or use cog belt type drives Make certain of the operating environment. Do you need x-proof components? Are you sure?
Removable shaft assemblies can save time in a number of ways, and externally mounted bearings are a must to prevent fires inside the equipment.
Split bearings can greatly reduce down time during bearing replacement, and tramp iron magnets are a real life saver in grain facilities.
Purchase all the safety devices you can. These include:
Cover disconnect switches
Bearing temperature monitoring
Motion sensing devices
Electrical overload protection
Drag conveyor purchasers might also want to consider:
Chain break detectors
Slack chain detectors
Divided flow or control fed inlet to prevent overfilling
AR lining in wear areas
Roller chain as opposed to welded types
Product return cups when using multiple discharges
Belt conveyor purchasers might also want to consider:
Belt alignment detectors
Single point lubrication for troughing idlers
Gravity take-ups to maintain constant belt tension