Building (or rebuilding) A Better Materials Handling System
If you're not conveying your resin as efficiently as possible, you're just not ready for prime time. But a successful materials handling system doesn't have to be out of reach. Whether you're starting from scratch or remaking an old workhorse, a few tips from the experts can help you get it right.
October 1, 2012 by Mark Stephen, editor
Just like that killer double-breasted suit probably does with your wardrobe, materials represent your single largest expense as a plastics processor. You didn’t sew the suit yourself just to save a few bucks, so why scrimp on having a reliable resin handling system? The design and installation of a materials handling system can have everything to do with how well it goes on to meet you production goals — and a lot of the same rules apply when it comes to remaking a system that no longer runs efficiently. Whether it’s big and complex or small-scale and simple, the following tips can help you work with your equipment supplier to make, or remake, the system of your dreams.
DESIGNING A NEW SYSTEM
The first step is a no-brainer: Identify all of the materials that you process in your plant and identify where each material comes from. Refer to those silos, bins, and Gaylord boxes as “sources” — and keep in mind that blenders and dryers may also be considered sources if loaders are pulling material away from them. “Make a complete list for each machine in your plant — injection molder, extruder, blow molder, et cetera — and identify them as ‘destinations’,” said Ray Kelly, product manager, material handling for The Conair Group. “In this context, the hopper of a dryer or the material bins on a blender are considered destinations, since the system will be delivering material to them.”
Next, determine the maximum throughput rate for each destination. “The sum of these throughput rates, plus a factor for each 90° bend in the system and the horizontal and vertical distances that material must travel, will give you an indication of how large a vacuum pump will be needed and what diameter the conveying lines should be,” Kelly continued. Your equipment supplier can help perform these calculations, but here’s a quick rule of thumb: “On horizontal runs, we usually calculate one foot per linear foot, but we double that on vertical runs, so that a 10-foot lift is equivalent to a 20-foot horizontal run,” said Bob Crawford, vice president of engineering for Universal Dynamics Inc. “We also add between 15 to 20 feet for each elbow in the system.”
In most cases, the line size will be dictated by the total throughput rate of all the machines on that system pump. “Remember to keep all the conveying lines served by a given pump of the same size, and make sure the line size matches properly with the horsepower of the pump,” Ray Kelly said. “For instance, never put a large 15-hp pump on a small two-inch OD line; the proper size for a 15-hp pump is three-inch OD.”
As with everything else in life, details matter. “Vacuum loader inlet tubes should match the system piping,” said Gary Brock, process and sales engineer for Pelletron Corporation. “Also, make sure existing loader voltages match up properly with the control system.”
Speaking of controls, make sure the controller you choose has the features you need, or that can be added in the future. “Having the latest control system is very important,” said Brian Davis, general manager of Maguire Canada. “A lot of the older controls out there are no longer supported — you can’t get the timers for them because of their age, for example.”
Next, keep material runs as straight as possible and minimize the number of elbows. “Every change in direction in a material handling system increases back pressure, reduces conveying capacity, and can cause material degradation,” said Jeff Tibbetts, regional sales manager for Vortex Valves. “In pneumatic conveying, you want to run either vertical or horizontal, but no 45° angles — even if it adds to the distance, it’s still better to go over to the wall and up with a single elbow.”
A well-planned system also optimizes conveying velocity. “Make sure that the conveying velocity at the material pick-up point is kept as low as possible, preferably between 3,700 and 4,000 feet per minute,” said Ray Kelly. “Material will accelerate over the entire length of the run and if it moves too fast, the material can degrade.” In case you’re wondering what can happen to resins conveyed at the wrong speeds, it isn’t pretty: softer materials like polyethylene can heat up and smear against the walls of the conveying lines; brittle materials like styrene or polycarbonate can break up and create dust and fines that clog the system; and abrasive materials like glass-filled ABS can actually wear away the inside of the conveying lines, eventually causing leaks and failure.
Finally, make sure your vacuum pump is sized for your location. “Power systems that operate at 50 Hz rather than the more conventional 60 Hz can cause the vacuum pump to turn more slowly, actually derating it by about 17 per cent,” Kelly continued. “You’ll need a bigger pump or one that turns at higher rpm in order to compensate.”
REVAMPING AN OLD SYSTEM
Even the best maintained car wears out after awhile — and so too with a resin handling system. When you need an upgrade — either through gradual loss of conveying efficiency or because of plant expansion — there are actually a few right ways to do it, depending on the problem and on your needs. Take an older processing facility that has, slowly and steadily, become inefficient at conveying resin. There are usually one or two main reasons. “In many processing facilities, a succession of plant managers will have installed new conveying lines over the course of decades and the original conveying pipe routing has simply become lost,” said Rob Miller, president of Wittmann Canada Inc. “The end result is a patchwork of pipes of different sizes and diameters, often with a multitude of unused pipes running along the ceiling in almost every direction.” You can probably guess the solution: The superfluous pipes have gotta go. “The goal is to identify what works and to remove what doesn’t, in the course of which we’ve done everything from taking everything down and starting from scratch, to taking one or two of the lines that are there and modifying them slightly,” Miller said.
But don’t assume that dismantled piping represents a previous investment gone for good. “We normally take superfluous pipes down, but we don’t throw them out,” said Brian Davis. “The processor can subsequently use them to expand, or for future replacement of lines and elbows.”
Another big culprit of efficiency loss is a vacuum leak, usually in flexible hoses and around couplings, seals, and valves. The first problem is, they can be bloody hard to detect. “Even the best maintained vacuum conveying system can develop leaks, and it’s often very hard to know because there won’t be a visible clue such as a water puddle,” said Bob Crawford. Second, the problem is often made worse by shoddy repair work. “I’ve seen many, many instances of flex hoses simply being taped to seal a leak,” said Brian Davis. “The processor can tape it all they want but, with vacuum constantly being turned on and off, the glue is going to come loose.”
Often, a revamp of a well-maintained but aging material handling system can mean nothing more than an upgrade of the control system. “Today’s controllers are capable of storing materials databases, and barcode scanning of a Gaylord of material and configuring the system so that material never goes to the wrong machine,” said Rob Miller. “They’re a good, relatively straightforward fix.”
Sometimes there’s a desirable reason to have an underperforming resin conveying system: new business that results in new lines and an increased total throughput rate, resulting in suddenly-insufficient vacuum power. Adding onto the existing material handling system on your own probably isn’t the best idea, though. “Some processors do reasonably good jobs of adding their own conveying lines, but they don’t know all of the nuances,” Brian Davis said. “Expanding even a small-scale raw materials handling system can be very complex, requiring recalculation of throughput, conveying distances, equipment specifications, and more. It’s something the processor should consult their equipment supplier about.”
For either a revamp or an installation, that sounds like good advice for getting the most out of your resin handling and conveying.
The Conair Group (Cranberry Township, Pa.);
Dier International Plastics Inc. (Markham, Ont.);
Industries Laferriere (Mascouche, Que.);
Maguire Canada/Novatec Inc. (Vaughan, Ont.);
Barway Plastic Equipment Inc. (Vaudreuil-Dorian, Que.);
Pelletron Corporation (Lancaster, Pa.);
Universal Dynamics Inc. (Woodbridge, Va.);
Piovan Canada Ltd. (Mississauga, Ont.);
Vortex Canada (Mississauga, Ont.);
(Dorval, Que.); 514-685-0058
Wittmann Canada Inc. (Richmond Hill, Ont.);