Keeping an eye on things.

Keeping an eye on things

Every year, it seems that competition is tougher. Margins are slimmer. Quality requirements are more stringent. This is particularly true in market areas where price is a major element in the market mix. And it usually requires increased automation. The roofing material market is one of these markets. Several years ago, it was a very lucrative market for a limited number of people. However, it quickly changed to one of intense competition. Those who decided to persist in the business have had to make major adjustments. Those who have not are no longer in the business.

One of those who made the commitment to stay is Burke Industries of San Jose, CA. One of the key elements of their being able to compete effectively in the business is a new monitor added to the production line. It has reduced scrap losses, improved machine efficiency and made a significant contribution to the bottom line for this product.

What has Burke done?

Burke's product is called the Burkeline Roofing Membrane. The product, used as a single ply roofing membrane, consists of three layers of material that are calendered together. The top layer consists of 22 mils of a white CSM (chlorosulfonated polyethylene - Hypalon from Du Pont), followed by a 5 mil middle layer of a polyester reinforcing scrim and a bottom layer of 18 mils of a black CSM compound. In the calendering operation, the two rubber layers must be bonded to each other through the scrim layer.

Once calendered and plied together, the calendered sheet passes through a series of cooling drums - and a monitoring system called the "Advisor." The Advisor is an on-line surface inspection monitor produced by Flow Vision, Inc., of Clifton, NJ. This system, originally installed in 1987, inspects the calendered plied sheet for wrinkles, voids and foreign contaminants.

The system consists of a light source, video cameras, monitors and a computerized control panel. It fits into the production line just before the roll windup equipment.

It works in the following manner: As the sheet passes beneath the monitor's solid state charge-coupled device (CCD) cameras, defects are detected across the full 61 inch width of the sheet. The cameras in the system are set linearly across the sheet and scan rapidly, sensing the reflected light off the surface. When the camera detects changes in the light, it provides a signal for defect identification.

Using the system's computer, it is possible to discriminate defects by size and type and send appropriate alarms to the operators. In the case of the Burke system, it has been programmed to detect and to flag wrinkles, voids and foreign matter. When a defect is spotted, several things happen. The signal activates a tape thrower which applies tape in the edge of the sheet, "flagging" the defect location. Simultaneously, it sounds an audible alarm, alerting personnel in the area to a problem.

Internally, the computer displays the exact location of the defect in the control console screen and prints a hardcopy map of the roll. This information is used by inspectors during the rewind inspection of the 2,000 ft. master rolls to locate defects accurately and quickly. With the map and flags, inspectors can find defects quickly and cut them out as the material is wound onto 100 foot rolls for shipment.

What have the benefits been?

According to Burke, the automating flagging and mapping provided by the system have enabled the operating speed of the rewind station to be increased by 25%. The system has also alleviated the problem of human error involved in visual inspection of calendered sheet surfaces for defects. Overall scrap is reported to have been reduced by 80% and consistency of the product supplied to customers has improved dramatically.

With the automatic in-line inspection, operators are free to concentrate on the production process, monitoring temperatures, thicknesses and speeds more effectively. This also is expected to have a positive effect on product quality.

In addition to the labor saving aspects, the system provides permanent documentation of production performance. Reports generated summarize the quality of each roll, noting types and locations of defects. Use of these records allows for process control adjustments to reduce overall product defects.

The bottom line is that the system has enabled Burke to stay competitive in a rapidly expanding, highly competitive market. The system has increased the efficiency of the entire production line by 3-4%, effectively adding an extra day of production with no extra cost.

What about cost?

Cost of any system is made of several factors including basic equipment cost, installation and maintenance costs. Since the price for roofing material is under one dollar per square foot, overall system cost was an important factor. Particularly important in this application was its ability to stand up to plant operating conditions. Downtime on the system could have a very negative effect on overall effectiveness.

Needless to say, this system came through with ease at Burke. The company was able to recover its investment in the system in just over one year. Burke figures that addition of the system has resulted in a net improvement of $70,000 in bottom line salable product.

Based on Burke's experience, it appears that this system could be used to advantage in many other applications involving calendered sheet goods. Detection of defects, reduction of human error and providing documentation of product quality can be very significant advantages. Capability of generating SPC type parameters from the information generated by the system is uncertain. However, even if not currently available, it should be easily added.

It would also seem that the system could be applied to other manufacturing operations. While no information is available on other applications, the principles of the operation could be applied to extrusions and other continuous operations. This certainly appears to be a positive addition to quality monitoring in our industry.

PHOTO : Schematic of calendering operation

PHOTO : Schematic showing sheet construction