Joliet Westside Wastewater Treatment Plant - Bar Screen
THE SITUATION
Mention ‘cast iron’ and thoughts of a tough material come to mind...unless you are referring to the chain Harold Harty previously used for his rake and bar screen. “The chain stretched,” said Harold, Operations Superintendent for the City of Joliet Westside Wastewater Treatment Plant. High concentrations of ammonia, hydrogen sulfide and other chemical components create extremely corrosive conditions, which over time attack cast iron, weakening it. “That bar screen is 50 feet deep, so the rake chain is pulling a lot of weight,” Harold commented. If his maintenance staff did not catch the stretch and adjust the chain tension every week, the chain would jump the sprockets. “Then we’d have a real mess,” remembers Harold. With few options to cast iron, Harold resigned himself to replacing the cast iron chain generally every three years with substantial maintenance required in between replacements.
Make it stand out
One of Joliet’s 50-foot tall vertical bar screens
THE SOLUTION
In 2004, Mike Humcke of Environmental Resources, Inc. came to Harold with a new development: the first ever cast stainless steel chain. As a maintenance engineer, a 30-year wastewater industry veteran, and an inventor by nature, Mike had first-hand experience with the problems presented by cast iron, and he determined to resolve them. Working with a metallurgist and a casting specialist, Mike and his team were able to cast aerospace-grade stainless steel into a line of products for wastewater equipment called DuraMax.
The chain that Mike showed Harold was not only stronger than any other chain material available, but the chain’s alloy composition provided superior hardness and corrosion resistance compared to similar chains made from cast iron. The combined effects of chain design, material alloy, and manufacturing process produced a chain life exceeding 20 years. Mike was so confident in the chain that he offered Harold a 10year full replacement guarantee. Harold so welcomed the opportunity to end years of expensive equipment replacement, labor intensive service outages and equipment failure, that he installed DuraMax on both of his chain and rake bar screens.
Now, in 2010, Harold comments, “I can’t say enough good about it. The chain takes care of itself. I haven’t had to replace or repair it once since it was installed. I really don’t have to think about it.” He liked it so much, Harold is using the chain on his other treatment equipment, such as bucket grit collectors, with equal success.
RESULTS
Equipment
- Cast iron scraper chain corroded and weakened; had to be replaced every 3 years making it expensive to own and operate
- Cast iron chain has no guarantee, so always a cost to replace when it broke
- Chain has worked fine with no need for replacement
- Paid for itself in 3 years, saves Joliet money in economically tough times
- Design life of 20 years means the chain will pay for itself almost seven times over
- Standard 10-year guarantee gives peace of mind
Man Hours
- Man hours needed per year for chain overhaul = 240
- Man hours needed per year for chain maintenance = 24
- 264 total man hours needed per year for cast iron chain repair and maintenance
- Joliet has saved an average of 264 man hours every year since 2004 (1,590 man hours and counting)
- With time-consuming chain repair activity eliminated, plant operates at heavy capacity even though budget cuts have forced staff reductions
Maintenance
- Weakened chain stretched; required weekly adjustment which increased maintenance cost
- Some chain links would need to be replaced, resulting in maintenance cost and equipment downtime
- Reduced cost by eliminating:
- Need for weekly chain tension adjustments (adjusted now just 1× per year)
- Need to replace chain
- Need to fix chain
Operations
Operations would be routinely interrupted to re-route water to allow for maintenance, repair, or replacement.
Equipment runs with only minimal maintenance needed, requiring no interruption of operations.