The relatively low-tech hodge-podge of parts-handling auxiliaries rarely arouses much passionate discussion. Yet those molders who rely on conveyors, sprue separators and box fillers know that the various models all have their pros and cons. When the talk turns to buying such equipment, shopping tips nearly always focus on maintenance, reliability and cost. In the end, though, making the "best" equipment choices really comes down to individual needs.
And among those needs, diversity rules. The sheer variety of molders' products and specialized handling requirements has fostered an equal variety of opinions on the things that add up to quality equipment. "Everything is relative to the products you're running," notes production manager Curt Roberts of Multi Technology, a specialty molder of biomedical and research products in Salt Lake City. Most molders simply rate a piece of equipment by how well it works with their particular products.
As for cost, it seems to take a back seat to the other issues. In fact, many molders think about cost only after establishing that a piece of equipment works well for their application. "Cost isn't the most important thing for us, though low cost is always a real asset," says Dan Lock, auxiliary technology manager at Wheaton Injection Molding, a major packaging producer in Millville, N.J.
CONVEYOR BUYING TIPS
Conveyors, as the most ubiquitous sort of parts handler, tend to draw plenty of comment. And reliability surfaces as the one trait coveted above all else by those who buy them. A reliable conveyor should require little in the way of preventive maintenance. It mustn't let parts hang up and get damaged or let them escape onto the floor.
Lock, who has been buying auxiliary equipment for 21 years, says several factors help in the reliability department. "Always watch the clearance between the belt and side-rails," he says. Too much space for a given part will cause hang-ups or part loss. He also advocates so-called "endless belts," because fewer joints or cleats cuts down on the number of maintenance problems waiting to happen. Lock also recommends adjustable-angle conveyors because these can minimize "parts leakage" by meeting up more precisely with the press and other downstream equipment.
Bill Washburn, molding engineer at medical molder Becton-Dickinson in Canaan, Conn., adds drive selection as another way to reduce maintenance. His company has moved away from the typical chain-driven conveyors in favor of what it considers to be a more reliable timing-belt arrangement. And without the chain drive, he doesn't need to worry about grease contamination of critical medical parts.
Washburn also pays attention to the conveyor frame's contribution to good belt tracking. "You need a rugged, firm frame to maintain tracking," he says. The best frame material, however, remains a matter of debate. Washburn says extruded aluminum combines high strength with light weight. Some other molders avoid aluminum frames. "We can't use aluminum in our business because it can turn the parts black," claims Wheaton's Lock. Instead, he prefers painted steel. And at Erie Plastics, a custom molder in Corry, Pa., molding manager Dennis Bogert says, "We pretty much stay with steel." He feels that threads can pull out of holes tapped in aluminum frames.
Another factor, versatility, enters the picture for buyers who plan to move their new conveyors around the plant floor. At Erie Plastics, Bogert requires conveyors to be "flexible from press to press." So they must be fully adjustable for both height and angle, and they also must ride on casters.
Of course, shuffling conveyors around also makes weight a consideration. "We move everything," notes Washburn, so lightweight aluminum construction comes in handy. "Lighter weight conveyors on casters are preferred," agrees Roberts of Multi Technology.
Lock notes that Wheaton, with its 100 presses of many makes and sizes, also has a tremendous need for versatility. As a result, he specifies variable-speed drives as one way to suit a conveyor to multiple jobs. When it comes to casters, however, Lock feels they let the conveyor move around too easily, compromising its stability. For that reason, he says, "We lift the conveyors off the casters if they have them."
Last, some users consider a conveyor's influence on maintaining part quality. To protect fragile parts, Becton-Dickinson's Washburn employs conveyors with drop chutes to soften their fall. "It's easier on the product and stops them from bouncing on the floor," he says.
Washburn adds that enclosed belts prevent contamination. Likewise at Multi Technology, special hinged doors and clear conveyor enclosures stop contamination without blocking the view. That way, an operator can free any stuck parts or inspect for quality.
SEPARATING GOOD FROM BAD
All the same factors that go into buying a conveyor apply to parts separators and box fillers, but these units have their own particular considerations as well. When buying this type of auxiliary equipment, think footprint, says Erie's Bogert. "We're limited on the amount of floor space so we look for equipment that won't take up too much," he explains.
For parts/runner separators, molders advocate whatever works best for the application. For Multi Technology's Roberts, a good separator simply "does what its specified to do--separates without any loss." He favors gap separation for his company's needs but acknowledges that others might benefit from finger separation.
FILL 'ER UP
As for box fillers, consider counting accuracy. According to Erie's Bogert, "We've found the basic thing is the quality of the scale." He also scrutinizes the method by which empty boxes go on the scale. With some systems, the box drops onto the scale platform. Bogert says that approach lengthens cycle times because the system has to wait for the resulting vibration to subside. Now he buys only box fillers with a flat belt conveyor that keeps the next box on the same level as the scale platform.
Finally, as with any type of equipment, the suppliers need to responsive. "They have to be easy to deal with," Wheaton's Lock notes, "especially when you're in a bind."
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|Title Annotation:||Straight Talk on Buying; conveyors|
|Author:||Ogando, Joseph A.|
|Date:||Oct 1, 1992|
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