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Case Study
Robotic Sealing System Helps Increase Production Flexibility

August 28, 2003
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Lamson & Sessions is a leading producer of thermoplastic conduits, enclosures, wiring outlet boxes and accessories for the electrical, construction, consumer, power and communications markets, as well as large-diameter pipe for the wastewater market.

Based in Cleveland, the company manufactures millions of injection-molded PVC electrical wiring boxes and junction boxes per year. To achieve approval from Underwriters Lab and the Canadian Standards Association, each box requires a gasket seal to prevent water intrusion. For more than 20 years, the company used die-cut foam gaskets with adhesive backing to accomplish the sealing operation. With 13 size variations of boxes and an increasing production schedule, the manual application had a number of challenges to be addressed, including the following.

Gaskets are sometimes too thin to properly compress inside the boxes. This prevents proper sealing in situations where box lids are slightly warped or “crowned.”

Field installation of gaskets to lids is time consuming and tedious, especially when creases or other irregularities slow down the process of removing the paper backing from the adhesive strip. This problem is compounded in outside installations during cold weather and the need to remove gloves to install gaskets.

Improperly installed or missing gaskets reduce quality levels and result in customer dissatisfaction.

Costs of the existing die-cut foam gasket system were very significant. These included the high cost of the purchased gasket, inventory/tracking costs for 13 different models, and the labor costs to manually pack the gasket into the junction box.

Robotic Alternative

To eliminate the shortcomings of the manual operation, Lamson & Sessions chose to convert the gasket sealing system from cut foam to a urethane “form in place” (FIP) gasket. Chemque, a leading manufacturer of specialty high-performance polymers, manufactures the material, which is less costly and offers a better seal than cut foam. Lamson & Sessions also evaluated alternative methods to apply the material and determined that robotic automation would provide the flexibility and precision required to meet production demands.

The company selected RADCO Industries, a system integrator in Toledo, OH, to develop an automated system that would uniformly dispense the FIP gasket and maintain the critical seal on the PVC electrical wiring boxes and junction boxes. The solution required consistency, precision and flexibility to accommodate the 13 different gasket sizes.

System Components

The automated dispensing system incorporates a FANUC M-710iB/45 and a FANUC LR Mate 100iB robot. The M-710iB/45 is paired with a two-component meter mix dispensing system with triple servo motor portioning and mix.

The urethane form-in-place gasket on the meter-mix equipment is a two-component catalyzed system delivered in individual 55-gal drums. These drums are adjacent to the machine and deliver the A or B component on demand with air operated drum pumps. The product is delivered to one of two “day tanks” holding approximately 10 gal. The A component is the body of the adhesive. Pressurized air is introduced into the tank and a motor operated paddle mixes the fluid to uniformly distribute the air. This air entrainment is what will give the final gasket its loft and sponginess. The percentage of air entrainment is monitored and controlled, as well as the mixing paddle motor. The B component, which is the catalyst tank, is equipped with desiccant dryers to eliminate harmful moisture.

On demand, each day a tank will deliver product through individual electric pumps to the metering system. This consists of an individual servo-driven precision gear pump for each component. The servo pumps allow each component to be delivered in a precise ration, with an accuracy of approximately 1/100 of a gram. (As a reference, a dollar bill weighs one gram. Cut a dollar bill into 100 pieces, weigh one piece and the result equals the delivery ratio accuracy.) The components, still handled separately, are brought to a servo-controlled mixing head. The two parts are thoroughly mixed and the catalyzation process begins. This mixing head is maintained at an exact temperature to control the reaction time that is accomplished with a chilled or warmed water manifold. The servo mixer also generates internal pressure in the head. A double solenoid operated dispense valve opens as signaled by the robot to deliver air entrained catalyzed product onto the electrical box lid. The dispense rate and volume are controlled through dispense servo motor speed (addressable via the robot control), nozzle diameter and robot speed. All travel and dispense parameters are downloaded and preset when the part number is keyed into the HMI.

The M-710iB/45, equipped with HandingTool application-specific software, handles the dispensing of the FIP gasket. Articulation and precision are key characteristics of the robot, which can handle payloads up to 45 kg. The robot also has an extremely large work envelope without requiring significant floor space.

In addition, the M-710iB/45 offers floor, invert, wall, shelf and angle mounting to accommodate a variety of installation variations, making it possible for users to have better access to unusual work pieces. The flexibility of the robot’s design allows it to flip over and work behind itself. A 70-kg variation, the M-710iB/70, is available for higher payload applications. Both models offer a compact body and six axes of motion.

Once the FIP gasket is dispensed, a five-axis, a 100iB robot equipped with a quick-change vacuum end-of-arm tool transfers the electrical boxes to an infrared curing oven. The robot’s small size and extensive capabilities allow it to easily handle the parts without disturbing the integrity of the dispensed gasket. This automated process helps the customer achieve quality standards that could not be met manually or with hard automation.

RADCO Industries designed and built the curing oven with an automatic stainless steel link belt conveyor. The 20 KW, infrared oven cures parts at 160 degrees F and 100 percent humidity. Watlow’s 1120 radiant heater panels provide heat control for curing.

RADCO system also specified a Camco three-station indexing dial system to provide a load station, gasket dispense station and auto unload station.

How the System Works

An operator manually loads parts into the indexing dial system that has a dedicated master plate to locate each set of tooling. The tooling is made of UHMW polyethylene, a tough material with a chemical-resistant surface. As parts are loaded, the system assigns and stores a unique signal for each of the 13 box sizes. Once tooling location is complete, the table indexes to begin the dispensing operation. A light curtain prevents operator intrusion until each job is complete.

The robot dispenses a bead of urethane foam around each part to form the FIP gasket. Bead rates depend on the mix of the material, the speed of the robot, and the size and features of each part, such as corners and a “ramped blend” that occurs at the start and finish of each gasket. Dispense rates vary from 3 inch/sec for the smallest part to 6 inch/sec for the larger parts. The foam gaskets typically take three minutes to gel.

Upon completion of all of the gaskets, the M-710iB/45 stops and the table indexes to the unload position where the LR Mate 100iB transfers parts to the curing oven conveyor. The robot picks from one to six parts depending on weight and dispense cycle time. The curing oven conveyor has a variable-speed drive to maximize throughput regardless of the amount of parts being unloaded.

All three stations function simultaneously, load-dispense-unload. Unload time is always less than dispense time, which makes throughput dependent on dispense speed. Average processing time is four seconds per part.

The curing oven reaches the correct temperature and humidity level before dispensing begins. A Simpson temperature indicator, which is tied into the control system, signals the robot to begin dispensing when the oven is ready. Automatic temperature gauging helps streamline the entire process.

Finished products exit the curing oven into completion storage bins, sorted and prepared for shipment.

The Results

Payback for the system is estimated to be 12 months. RADCO engineers credit pre-planning and conceptual design during the quoting stage to the system’s success and quick return on investment. RADCO also performed extensive testing of the adhesive and the infrared/moisture curing mechanisms. The curing was a crucial part of the system engineering since no one had previously taken freshly dispensed foamed urethane gaskets and dropped the parts into bulk storage bins.

The customer has realized several key benefits as a result of the new robotic system.

• Sizeable cost savings with the elimination of the previous cut foam gaskets.

• Consistent and reliable automated process significantly increases product quality.

• Flexibility to handle additional parts in the future.

According to George Foos, senior project engineer at Lamson & Sessions, the entire project was a success. “From initial construction to final testing, RADCO Industries accommodated our ‘on the fly’ changes. The changes proved to be painless and really enhanced the functionality and user friendliness of the system.

“The system is well-conceived and innovative. It’s highly durable, as in ‘built like a tank.’ I’m sure this system will be running production 20 years from now,” he added.

For more information:

Lamson & Sessions is a leading domestic producer of thermoplastic conduit, enclosures, wiring outlet boxes and accessories for the electrical, construction, consumer, power and communications markets, and large-diameter pipe for the wastewater market. For more information, contact Lamson & Sessions at www.lamson-sessions.com.

RADCO, a member of FANUC Robotics’ integrator network, is a 41-year-old turnkey systems house specializing in custom designed and built equipment for a range of applications, including assembly, adhesive and gasket dispense, pressure decay and helium mass spec leak testing, CNC and indexing dial machining systems, and electrical integration. For more information, contact Jim Paul at RADCO Industries at 800-283-0792 or visit www.radcoindustries.com.

FANUC Robotics America Inc. designs, engineers, and manufactures robots and robotic systems for a range of industries and applications. For more information, visit www.fanucrobotics.com or call 800-47-ROBOT.

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