Filterless conveying: controversial, but catching on.

In the mid 1980s, Lyn Depew was an engineer at a captive molding house in Toronto. The shop was running about 1.5 million lb of glass-filled nylon each year, and 10% of that was dusty regrind. Consequently, problems often arose in conveying these materials efficiently. So Depew designed and built himself a better conveying system.

The result was an early prototype of a closed-loop filterless system that eased some of the problems the plant had been experiencing. During four years of in-house use, kinks in the system were ironed out, and in 1988, Depew launched his own company, Filterless Conveying Systems, in Brantford, Ontario, to introduce his new-style hopper loaders to the materials-handling market. In doing so, he joined a handful of other suppliers who had been touting their filterless devices to molders as options that could save energy, reduce maintenance and solve conveying problems.

Initial reception in the marketplace was cool. But recent changes in the kinds of resins being processed, coupled with competitive demands for higher productivity and lower downtime are changing attitudes toward this technology. Suppliers of filterless systems say their central and individual loaders eliminate the task of filter cleaning and replacement while solving many of the conveying troubles that are becoming commonplace with the growing use f automated conveying of powdered resins, thermosets and regrind. Those problems include the generation of airborne dust in the workplace. However, they warn, filterless units can be considerably more expensive than conventional conveying systems and can't handle every application or material. "It's unfair to compare a filterless loader to a $995 hopper loader," says Charles Morgan, product manager for Conair's resin conveying systems. "Filterless is not a direct alternative to the other. But it is a real problem solver for processors trying to convey powders, those having continuous filter-clogging problems, or those trying to address the issue of safety in their plants."

Critics of these systems argue that filterless conveying is simply a current buzzword and that the systems are capable of doing nothing that loaders with fabric or screen-type filters can't do. The concept, they claim, is limited in its applications and is nothing more than a "gimmick being foisted on the industry," in the words of one supplier.

TAKING A SECOND LOOK

Despite these feelings, filterless conveying is getting a serious second look from plastics processors, and is being tried in locations such as Dow Chemical's R&D lab in Bay City, Mich., and at various automotive manufacturing sites across the country. Further evidence that the concept is catching on with an expanding number of processors can be found in suppliers' order books. "We have experienced very rapid growth in the sales of these systems in the last three or four years," says Charles W. Thiele, president of Motan Inc. "I think the reason is that we've removed some maintenance from the process."

That claim of reduced maintenance is probably the most noticeably benefit of filterless conveying. With no filters to be cleaned or replaced, a savings in both man-hours and replacement costs can be instantly realized. Suppliers of these systems tell of users who say they go for months without even opening their hoppers. Some users reportedly estimate that their filterless units--which can sometimes cost two to three times as much as conventional hopper loaders--pay for themselves in less than a year.

Reduced maintenance, proponents say, is a step forward in materials loading technology and one for which processors are constantly crying. "People are always telling me the biggest pain in the neck they have is cleaning a filter 15-20 feet up in the air," says Thomas Rajkovich, president of Comet Automation Systems. "But these systems provide more than just maintenance savings."

Based on technology that creates a series of cyclones inside the hopper, causing the heavier particles to fall down toward the feed throat of a processing machine, while the lighter dust and fines are vacuum transported back to either the source or an external dust collector, these closed-loop systems also improve workplace environments since they don't allow dust to escape into the plant air. The lack of filters also leads to energy savings because with no filter to clog, the pump motor does not have to strain to deliver a steady flow of material.

Furthermore, since filterless systems deliver a clean, consistent stream of material, suppliers say processing advantages can be realized when using them with powdered resins, thermosets and materials heavily loaded with additives or mixed with a healthy dose of regrind. For example, suppliers say that when molding polycarbonate, dust particles allowed to enter a machine's injection unit can degrade to the point where they carbonize and show up as black specks in clear parts. And with materials like those described above becoming more prevalent (as is automated conveying), dust from both the manufacturing and regrinding processes is becoming a more frequent problem.

"There are more additives in plastics than ever before," says Filterless Conveying's Depew, referring especially to the growing use of fillers and reinforcements. "These additives are on the surface of the pellets, and when you regrind the material, the grinder blades are not designed to grind glass or rocks, so after 10 minutes your blades are no longer sharp and you're no longer grinding but pulverizing, producing a lot of dust and fines."

USERS PLEASED

Processors, researchers and even some suppliers who resell these units along with other equipment, say they have gotten good results using filterless loading. "When you look at pneumatic conveying technology, the filterless conveyor is the first step in a long time to take the technology out of the stone age," says Bruce Lowden, general marketing manager for K-Tron Vertech, Pitman, N.J.K-Tron, primarily a manufacturer of blending equipment, is offering specially designed loaders from filterless Conveying as part of a package with its new gravimetric blenders. "People are beginning to realize there is now an option," Lowden says.

Even established manufacturers of conventional hopper loaders and conveying systems, such as Conair Franklin, feel filterless conveying can be very beneficial. "The only good reason for anyone to continue using a filtered loader is if there's a need for filtration at a particular machine," says Conair's Morgan. Otherwise, he says, a filterless central system is probably the processor's best bet.

Conair was a pioneer of filterless technology, developing its Gemini loader in the early 1980s. Designed primarily for conveying powders like PVC resin and unpelletized ABS and polypropylene reactor flake, the Gemini is not truly filterless, in that it uses a remotely located dust collector to trap the dust and fines after they are removed from the process stream. However, its twin-cyclone, two-stage air/material separation hopper and remote, three-phase vacuum pump are certainly components of filterless technology.

"When we designed the Gemini, we figured, why not see if we can get a loader without a filter that can service more than one machine," says Doug Boring, Conair's product engineer for conveying systems and inventor of the Gemini loader. "We knew having someone climb on top of a machine all the time to change filters could be hazardouse."

Boring and Morgan say that while Conair's system is designed primarily for conveying powders, many processors are using it for loading pelletized material because they don't want to be bothered with filter maintenance. In response, Boring says he has built a prototype of a filterless unit designed specifically for pellets. "It looks pretty promising and would probably be in the same price range as standard loaders."

NOT ALL ARE CONVINCED

The excitement that suppliers of filterless systems have for their equipment and its future is not shared across the industry. Those skeptical of filterless conveying's benefits and its market potential say the technology is too costly and, despite suppliers' claims of reduced maintenance, hoppers still have to be wiped clean after color changes, filter or no filter. This, they say, negates much of the claimed maintenance savings. The design of some filterless hoppers also goes against the concept of no maintenance, critics say. Because hoppers used in this process create two or more cyclones to move the fines and coarser material in different directions, a smaller and more narrow chamber is usually built inside the hopper. This area, detractors claim, is virtually impossible to clean.

"I personally am very distrustful of filterless conveying," says Robert Munns, regional sales manager for Whitlock/AEC, Inc., Wood Dale, Ill. "Some of them have no protection on the motor. I think that's dangerous." Munns is referring to the filterless systems' lack of a screen or filter mounted near the pump motor to safeguard it from contamination by fines or dust which could cause premature burnout.

"There is a minimal amount of dust and fines that go through that pump," admits Filterless Conveying's Depew. "But we use a bypass motor with a separate fan to cool its armature. Exhaust air from the loader never gets to the motor." The fan motor, Depew says, is protected by an air-seal bearing to further prevent dust from entering the motor. In an effort to prevent hoppers from overloading and material from heading back toward the pump, many suppliers offer a protective switch on the hopper that shuts down the airflow when the material in the hopper reaches a certain level.

As for the claims that filterless conveying has improved the loading of powders, Munns and other skeptics say a bag filter on a conventional hopper loader has proven very efficient and works just as well as the more expensive filterless units.

One more knock against filterless conveying system is that many lack versatility. "These systems are limited in their applications, and because of that, I don't see them becoming a major issue," says Donald Rainville, president of Universal Dynamics Corp., Woodbridge, Va. "I don't think it's the cost that's going to keep people away," he notes. "People want the flexibility to run anything. Conventional systems give them that, while filterless systems do not."

Yet, Una-Dyn has taken a small plunge into the filterless market, offering a filterless chamber as part of its line of modular hoppers. The units, which Rainville admits are not among his most popular, are designed for use with high-capacity extruders.

Even those who make filterless systems agree that they are not for everyone, and in cases where conventional pelletized materials are being transported, the standard hopper loader with a small motor and screen or cloth filter will work just as well. These standard loaders that have served processors for so many years are far from obsolete, suppliers say. "They're low-cost and they have worked for 20 years," says Richard Hamilton, president of A.C. Hamilton Ltd., Mississauga, Ontario. "They're certainly not going to disappear overnight."

A.C. Hamilton recently entered the filterless conveying market when it bought Stream Industrial Systems, Inc., acquiring one of the first truly filterless systems, developed in the mid-'80s.