You're in the DC and everything's buzzing along, and then suddenly ... it isn't. A motor stops working. A belt rips. Now, the entire conveyor system is at a standstill.
Unplanned-for downtime is a huge productivity buster. But often it's completely preventable. Here are a few good habits that can make all the difference.WALK ON BY
When it comes to keeping things moving in the DC, there's no substitute for doing a regular walkthrough of the conveyor system.
As for how "regular" these walkthroughs should be, the inspections can be daily or even weekly, depending on the number of hours the system is in use, how critical a particular area of the system is, and the type of operation. "If it's a high-speed sortation system, you probably can justify looking at it on a daily basis. The cost of looking it over is very, very minimal, compared to having it go down," says Boyce Bonham, director of integrated systems and controls for Hytrol.
Think about when you conduct the inspection, too. Often, maintenance technicians will come in early to do a walkthrough before the start of a crucial high-volume shift. "The problem is, if there's an issue, they don't have time to take care of it before (the system) goes into production," Bonham warns. If techs do the walkthrough at the end of a high-throughput shift, they have time to resolve any problems before the next high-volume shift comes around. During the walkthrough, check that equipment is lubricated and look for things like belt wear and ripped, misaligned, or nontracking belts, advises Bonham. Also keep an eye out for torn or unraveling belt lacings, and make sure that all system components are aligned.
"If something is close to going wrong, you can typically detect it," says Tim Kraus, product management manager for Intelligrated. "For example, a pile of dust on the floor that wasn't there last week would certainly be a good indicator that something is not right (like a belt rubbing against something inside the machine)." That belt could eventually tear or break or overload the system motor so that it can no longer run, he explains. "If you notice (a problem) early, you usually have time to get the component replaced before it causes unexpected downtime," he says. Check belt tension as well. Loose, slipping belts can wear quickly, and they can also cause wear on the machinery. Overtensioned belts put an excessive load on mechanical parts like bearings, which can shorten their life. The proper tension range depends on the type of belt and the application; follow the manufacturer's or systems integrator's instructions for your particular system.
During the walkthrough, don't just look for problems; listen too. A sound that's out of the ordinary could be another indicator of a problem, such as bearings that are starting to fail.
Thermal imaging guns can also be used to detect problems that could ultimately lead to equipment failures. The guns are used to take the temperature of certain components, like gearboxes and control cabinets. If the temperature starts to rise, it could be a sign that the component is working harder than it should be and is at risk of failure. Heat imaging is a task that would likely be done monthly or annually.MAINTAIN THE SYSTEM
An effective but often overlooked way to prevent downtime and make sure the work flows smoothly is to simply follow the preventive maintenance schedules recommended by the manufacturer or systems integrator. "Those are all designed around eliminating the chance for unexpected downtime," says Kraus.
That means adhering to schedules for upkeep such as lubrication of bearings and other moving parts—and making sure to use the correct type of lubrication as well. When bearings fail, 80 percent of the time it has something to do with either lubrication or dirt or dust in the bearings, says Jim Madsen, product manager, Dodge Spherical Roller Bearings, at Baldor Electric Co. So it's not only important to follow the manufacturer's lubrication recommendations, but to avoid contamination as well.
That means keeping the working area as clean as possible when replacing bearings. Better yet, choose bearings that are pregreased and sealed at the factory. These don't need any assembly in the field. "They slide right on the shaft, without (exposing) the rolling elements to a dusty, dirty environment," Madsen explains. When opting for a prelubricated product, he cautions, make sure it's the correct type of seal for your application. That way, you'll get the longest service life from your bearings. Some seals are specifically designed for use in systems that operate at high speeds and temperatures, while others are better suited to slower-speed operations.KEEP HOUSE
A big part of good maintenance is cleaning.
This may sound obvious, but it's a precept that's often neglected, according to the experts. "Especially if you get into the handling of food, beverage, wine, spirits, things of that nature, cleanliness is, a lot of times, not dealt with properly," Bonham says. "People ignore it." But spilled product can cause serious downtime and costly repairs, particularly with sorters. If something spills, "stop the sorter and tend to it immediately," says Bonham. It will probably take five or 10 minutes to clean it up, but if left untreated, that sticky substance could cause an outage that takes 30 minutes or an hour to repair. "The cost of cleaning is really very low," Bonham points out.
Then there's the matter of labels and packing tape. These get stuck to conveyor rollers and sorters. Shoe sorters in particular are vulnerable to malfunction from this quarter; they may become unable to slide. As with spills, it's best to stop the equipment and scrape off any labels or bits of tape that get stuck to the equipment. "If you leave it on there until it gets tangled up in something, then suddenly you've got 30 minutes of downtime with the possibility that components will have to be replaced, (and) that could cost you something," notes Bonham. In addition, pieces of label or cardboard that get stuck in a conveyor can cause belts to go off track. If the belt gets torn up as a result, that's an expensive item to replace.DON'T ABUSE THE EQUIPMENT!
A big no-no: not using the system as intended. One common mistake is overloading the system with items that had been defined as nonconveyable in the sale contract, in what's called an "item master."
Often, people know that certain items are supposed to be handled manually, but manual handling is so much trouble that they put them on the conveyor anyway. "They go ahead and push the limit," Bonham says. "That's abusive to a system." For example, a too-large item may fit on the conveyor when it's traveling in a straight line, but once it hits a curve or a junction, it could jam. "If you're going to do that, you've got to understand there's a cost associated with it. There's a risk involved," Bonham says.
Product jams occur in automated systems for a variety of reasons. Common causes include loose hardware on guardrails or pan guards, and open flaps on cartons. Sometimes, jams are caused by errors in data entry, says Scot Filgis, field engineering manager for Dematic. Someone keys in the wrong dimensions when creating the item master, and as a result, a too-big box gets the OK from the dimensioning system. It gets put into a tote that's not quite big enough to handle it. Things might be fine at first, but when the tote goes up an incline, the product falls out. This can also happen when all of the items fit in the tote or carton but are not arranged well. Some operators refer to this challenge as "the Tetris of picking."
Another no-no: overriding system controls. Conveyor systems typically have sensors that detect when the line is full and can't accept any more items. It may look as if there's still room on the conveyor and you might be tempted to try to squeeze in a few more items, says Kraus. But that's a mistake. The system probably will not have enough time to react and stop sending product down the lane. The result: a pile-up; potential damage to products and equipment; and decreased, instead of increased, productivity.
In other cases, years after a system has been installed, the item master has simply been forgotten. Or inexperienced temps working on the line might route items incorrectly. In either case, the solution is to keep employees trained. If they're on the job long enough, they'll probably learn by experience what's conveyable and what's not. "But you don't want that to come at the cost of unexpected downtime," Kraus says.
Filgis advises companies to develop what he calls an "ownership strategy" for any material handling system. "That strategy should address everything from audits to preventive maintenance and the proper training of technicians to handle breakdowns when they occur," he says. "Make sure ... you have a plan in place for the full amount of time it's going to take to complete the preventive maintenance, based on your operating schedule," he says. Scheduling preventive maintenance by the calendar isn't ideal, he adds. You may be over- or under-maintaining your system. Instead, look at the OEM recommendations and develop a schedule based on the equipment's hours of use.
As an additional preventive measure, a "go/no-go" gauge can be placed at points where people are loading items onto the system. For example, that gauge might be a narrow opening that makes it impossible to put a too-wide item onto the conveyor, even if the conveyor seems wide enough to handle it.
Early warning of a problem can shorten the amount of downtime needed for repairs. Some vendors offer electronic monitoring systems that send technicians a text or e-mail alert when there's a problem, says Filgis of Dematic. These systems can often diagnose the problem so the repair tech knows, say, that a scanner is down and where that broken scanner is, so he or she can bring a replacement to the zone where it's needed.AN OUNCE OF PREVENTION …
So will all these efforts to prevent problems really save money? Sure, although it's difficult to make a generalization about how much. "What exactly that cost (of unexpected downtime) is ... is very specific to the different types of material handling systems that exist. So, that looks different for a high-speed sortation system (than for) a low-speed, simple conveyor system or a highly automated storage-and-retrieval system," says Kraus. But whatever the system, an ounce of prevention is definitely worth a pound of cure.
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