- June 01, 2000, Edward Boyle, Contributing Editor
When your company converts critical materials for manufacturers of electronic circuit boards, product purity is of the utmost concern--and eliminating dust from the production process is key to meeting stringent quality demands. Consequently, eliminating piles of unwanted dust generated from coating procedures posed a major headache for management at the 250,000-sq-ft Pendleton, SC, plant of Isola Laminate Systems.
As Isola process engineer Joe Sangl explains, previous systems that were used to collect trim on three coating lines negatively affected product quality, causing excessive downtime and generating overwhelming disposal problems.
"Our business calls for coating an epoxy-type resin onto a fiberglass woven web," says Sangl, "which has a feathered edge and tends to accumulate resin. As it gets sheeted down into a cut length, we trim away this edge, and a great deal of dust results."
What was needed, Sangl explains, was a system designed not only to pull all the trim away but to remove the piles of dust generated as well. Enter Convair Systems Inc.
Flaking Off into Trouble
In the production process, a liquid-state, epoxy-type resin, comprising raw glass and a catalyst, is applied in a bath onto a woven fiberglass web that is 38-58 in. wide, using a liquid coater from Caratsch (co. no longer in business). A metering roll system assures proper coating weight. The impregnated fiberglass web goes through overhead ovens (also from Caratsch) for drying. The construction is then slit on EMT slitters, where the Convair trim removal system is employed to remove the feathered edges that could prohibit proper lamination when thin copper foil is laminated to the impregnated fiberglass construction. This lamination occurs after the construction is sheeted to 4x7-ft sheets on Maxson equipment.
Sangl notes that feathered edges are a natural consequence of the production process. The resin on the fiberglass that is cured is considered the "B" stage. At this point, the copper is applied.
"What was happening," explains Sangl, "was that the dust would flake off of the feathered edges and would invariably get on the copper. When subjected to pressure during laminating, it would leave an unwanted impression on the surface. The result might mean a broken circuit, short circuit, or open circuit, any of which could initiate a circuit board failure."
Seeking a Complete Solution
This concern caused management to investigate ways to eliminate such problems completely. Sangl notes that while Isola looked at a number of trim removal systems, it found that they were essentially full vacuum technologies, which were designed to pull the trim via vacuum completely outside the building to a compactor.
"The glitch is that it's difficult to maintain an adequate vacuum throughout the entire length of tubing," says Sangl. "Any hole that develops in this piping arrangement can lead to a major clog in the system, often causing much downtime."
The Convair trim removal system, however, pulls the vacuum for a maximum of 20 ft, thereby avoiding wear on the inside of the tubing, Sangl reports. "Fiberglass is very abrasive when pulling a full vacuum; as it passes over elbows in the trim removal system, it inevitably rubs on an edge. However, the Convair system is designed so that once the trim gets past the vacuum on the eductor, it is blown in such a way that it gets centered in the middle of the tubing."
Convair Systems installed its S-7 Model blower, a 7.5-hp unit, with an eductor identified as GM-3. The air separator used, Type DPN-3, features inlets for each of the production lines at the plant. Convair supplied the system with a DCE dust collector to filter residual dust from the conveying air.
Comparison Points Up Benefits
"To make a descriptive comparison, our new unit works much like a shop vacuum, though on a much larger scale," says Sangl. "Not only is it a cleaner, more efficient system, it keeps our cutting blades operating longer, because the amount of pull the vacuum provides helps to tear off the edges better on the trim that is removed. We removed approximately one-half inch on either side of the web."
Sangl adds, "Another point in favor of the new system is that with its flex tubing and wider mouth for suction, it can be positioned perfectly across our varying web widths. The previous system was a solid tube design that could not be moved into position as readily. We did attempt to adapt an eight-inch-wide mouth on top of the vacuum for it to work properly. But, unfortunately, this only served to pull the trim at angles, not straight down. We were back to square one with a great deal of dust to contend with and considerably more clogging."
With the Convair trim removal system, a blower takes removed trim through stainless steel tubing that continues from the building to a collection site outside the plant. At this point, the removed material is channeled into an air separator situated atop a compactor. Trim that goes into this compactor is monitored by a special sensor. Whenever a specified amount is collected, the compactor is cycled, and the material is pushed into the container. The dust that is separated from the rest of the material goes to the dust collection bin that is removed and replaced, on average, once a day.
Heading Off a Wrap
"The situation we faced before this installation was terrible," says Sangl. "We had piles of dust from the edge trim collecting on the floors. What's worse, when we trimmed the edge away, it would frequently wrap around the rolls and even around the cutter blades. This would result in what we call 'a wrap.' When this occurs, we have to shut the equipment down. Scrap is incurred each time. We had an incredible amount of scrap with the former system in place. Now, we've witnessed a reduction of defects related to dust to one-half a percent in the coating area alone, not to mention the great reduction in the number of dents in products produced."
Sangl continues, "In terms of the yield on our overall laminates, we saw a minimum of three-tenths of a percent improvement. This aggregate reduction is noteworthy when you consider that we produce a great deal of material quite rapidly. Last year, we processed some 60 million sq ft of material. These gains were realized almost immediately after we installed the new system. On an annual basis, we probably saved some $250,000. The system has been in operation for about two years now."
Early on, plant management opted to use stainless steel tubing specified by Convair Systems, since the material being produced was so highly abrasive. Holes would appear in theflexible standard steel tubing used originally for three months. Switching to stainless steel tubing solved the problem, Sangl reports.
Problem-solving appears to be routine at Isola Laminate Systems, and Convair Systems has been an important part of that process.
Convair Systems Inc., Elmwood Pk., NJ; 201/797-4909
EMT Intl., Green Bay, WI; 920/468-5475
Maxson Corp., Muncie, IN; 765/284-3304