The Problem
Kimberly-Clark 2 (KC2) Team Members: Jack Brooks, David Sterner,
Byron Dupler, James Milner, Jonathan DavisThe KC2 team was tasked with investigating, researching, and developing a valid mechanical contactor alternative Kimberly-Clark. The Kimberly-Clark Intrepid Team at Chester, PA plant has set a goal of increased productivity within their paper towel converting lines. An obstacle to this goal is a reliability issue with the application of their mechanical contactors. These contactors are operating at cycle rates of 20 cycles/min. The increased productivity goal would increase the cycle rates to 30cycles/minute. To operate at greatest efficiency the production lines are designed to be operated 24 hours a day, seven days a week, 52 weeks a year. Under worst case circumstances, the relay contacts would cycle over 15 million times annually. The KC2 Team has determined the current mechanical contactors have a lifetime of 10 million cycles. Under this scenario, the resulting MTBF (mean time between failure) is less than one year. This failure rate is unacceptable.
The scope of the project is to investigate alternatives and develope a solution to replace the mechanical contactors used in two applications on the production line. The first application is as a motor starter to control 3-phase motors. These motors control an application called an accumulator. The purpose of the accumulator is to provide a synchronization and buffer zone between the front-end towel production side of the line and the downstream packaging side of the line. The second application uses the mechanical contactors to control heater elements. These heater elements are used to seal the individual plastic wrapping on the paper towel product.
Key Problems:
1.) Life cycle < 1 year
2.) Device failure halts production
3.) Cycle Rate limitations
| Specifications | |||||||||
Accumulator- (motors)
Contactor being utilized for both motors: Allen-Bradley 509-BOD-A2D NEMA SIZE 1 = $289.43* * Prices as quoted by the Allen-Bradley Webstore. All parts have a 2 day lead time. |
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Wrapmatic- (heaters) heaters: 84 ohm resistive elements running from a 3-phase stepdown transformer at 380V. Contactor being utilized for heaters: Allen-Bradley 509-AOD B NEMA SIZE 0 = $226.51* Allen-Bradley 509-BOD B NEMA SIZE 1 = $258.46* * Prices as quoted by the Allen-Bradley Webstore. All parts have a 2 day lead time. |
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| Design Critera |
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The Solution
The KC2 solution has been designated the SSR-1.
The design is centered around a Continental Industries RSAA-660-30-3D0 Solid-State Relay (SSR) rated at 600VAC at 30A with 90-280VAC
controls. Solid-state relays have no moving parts and thusly don't wear out as fast as their electromechanical siblings.
SSR's have the capacity to switch very fast, even to inductive loads like motors. They are fast enough in this case to easily meet
the 30 cycles/min. of the design contraints. The downside of SSR's is that they fail in the "on" state and they generate a lot of heat. The SSR-1 has been designed with a aluminum housed 120VAC fan mounted directly to the SSR heatsink to combat the current derating that occurs at high temperatures.
The information provided by Continental Industries makes it very clear that fast-blow fuses are required to protect SSR and that circuit breakers and overload relays don't react fast enough. Based on those conditions, KC2 decided to use Littelfuse KLK030 30A fast-blow fuses because of their small footprint and their ready availablity.
The aluminum adapter plate was custom designed by KC2 to accomidate all of the required components of the SSR-1 and still maintain the same footprint and mounting positions as the current Allen-Bradley mechanical contactor. This allows for quick and easy installation as the mounting hardware is already in place.
A power resistor has been placed in parallel with the inputs controls of the SSR to bypass the leakage current that comes from the triac outputs of the controler. Without the power resistor, the leakage current through the controlling triac is large enough to drive the SSR into it's "on" state involuntarily.
The cost of a SSR-1 is lower than that of the current mechanical contactors minus the labor required to produce the custom adapter plate and assembly the product. The custom adapter plate takes approximately 2 hours to produce.
The SSR-1 is strictly a prototype and should be treated as such. It is recommended that future revisions of SSR-1 include seperate terminals for the SSR contol inputs wires and a clear plastic shield over the fuse and fuseholders.
| Performance Features |
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Data Sheets
Allen-Bradley 509 Series Mechanical Contactors
Continental Industries RSAA-660-30-3D0
Littelfuse KLK030
Littelfuse L60030M-3C
NMB Technologies 2412PS-12W-B30-A00
Vishay Dale RH-25 1K