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Materials-handling equipment.

JIT has given a new twist to the old question of whether to "go central" or "go portable."

With Just-In-Time manufacturing forcing molders into shorter runs with frequent material changes, a debate is growing over whether to use central or portable conveying systems. This is the preeminent buying decision on the minds of many processors today.

Traditionally used in applications where machines are dedicated to running a single material and color in very long runs, centralized systems are increasingly finding their way into shops that do nothing but short runs with numerous material and color changes. One reason for this switch is the recent introduction of quick-material-change mechanisms that have greatly expanded the centralized systems' capabilities. But processors who use these QMC systems warn that they may not be for everyone.

"One key now to getting the right equipment is to spend the time up front with your vendors to ensure they understand your application and to get their advice," says William J. Stewart, executive v.p. of Triple S Plastics in Vicksburg, Mich., a custom molder specializing in parts for business equipment and electronics.

Probably the most important consideration is how many presses you have and how many material changes you perform on each machine every day. Pushing a button or flipping a switch on a central-system control panel is an easy and quick way to change the material flowing to a press. Yet some molders prefer to rely on what has worked in the past: shuttling gaylords of material between molding machines as necessary.

"I like having a loader at each individual machine," says a plant manager with 30 years' experience at molding shops in Massachusetts. "It's much easier to change materials that way and you don't have to worry about so many things breaking down."

But with advances in centralized systems, it now takes only minutes to change the material being delivered to a press automatically and by remote control. No more unhooking and hooking up mechanical, electrical, and vacuum/air connections for each material or color change. A centralized system automatically purges its lines. The hopper, usually a small unit at the machine throat, can be wiped clean with a rag. And with just the flip of a switch or a quick disconnect and reconnect of a tube, a different material can be delivered to the press. So many molders who relied on portables for years have chosen to switch.

"The central system is such a far cry better than what we had before," says Mark McCourtney, v.p. of McKechnie Plastic Compounds NA in Minneapolis, a 100,000-sq-ft custom molding shop that makes at least 30 material changes in a 24-hr period. "The system has the ability to handle small batches as well as large ones. We do a lot of short and medium runs and use hundreds of materials in the course of a year. Its versatility is just great."

True, centralized systems cost more initially: One that can deliver two dozen different materials to an equal number of machines costs between $200,000 and $250,000. Individual conveying systems at each press are also less mechanically complex.

On the other side of the economic equation, Stewart of Triple S Plastics says his plant has been using a centralized QMC conveying system for the past year to make 12-16 material changes each day, and "the centralized system greatly improves our uptime, our productivity, and our quality." McCourtney says that after installing his centralized system, he was able to reassign seven workers, filling production areas that were understaffed.

Also, users of centralized systems say that with customers' growing emphasis on quality and contamination-free parts, centralized conveying allows every piece of equipment except a small at-the-throat hopper to be located away from the production floor, ensuring a cleaner molding environment. Many users of these systems say that because one dryer can serve all the presses, the central system is both a space saver and an economic benefit.


Those leery of centralized systems argue against putting all your eggs in one basket. There are too many connections and myriads of wires just waiting to foul up. If the blower goes down, they say, no material moves and production in the entire plant stops.

A supplier of central conveying systems says broken motors are not a realistic problem. "If the motor goes down," he says, "we, and most other suppliers of these systems, provide the user with backup vacuum and drying systems that minimize downtime."

Furthermore, proponents of centralized systems are pleased that they have fewer motors and controllers to worry about than if they had a separate system for each press, and the central approach offers the advantage of central dust collection.


Still, all agree the blower motor, whether it be in a centralized or at-the-machine system, is the key reliability factor in getting material to the process. If it goes down or needs extended maintenance, the machine stands idle, costing you time and money. (For that reason, many processors keep spares on hand.)

So, when buying a conveying system, the type of motor should be a consideration. Some processors feel a brushless motor, either a-c or d-c, is best since it eliminates the risk of burned-out brushes and armatures. Others argue that the higher cost of brushless motors is unnecessary: "As long as you do required maintenance on them and keep a spare motor on hand, you won't have any major problems," one source comments.
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Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Straight Talk on Buying
Author:Monk, Richard
Publication:Plastics Technology
Date:Oct 1, 1992
Previous Article:Resin dryers.
Next Article:Granulators.

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