US PATENTS 7,237,375 B2 and 7,343,730 B2


Cast steel 700 series collector chains and H-series drive chains have been one of the process equipment mainstays in the municipal and industrial water and wastewater treatment, conveyor, and power transmission industries since the early 1900's. For 700 Series Chains (such as CS720S and 730 chains) and H-series chains (such as H78/988 and H82/C9103 chains) are used extensively in process waste solids and bio-solids removal equipment including Rectangular Chain and Scraper Sedimentation Clarifiers, Storm Water Collectors and Clarifiers; for grit, sand and debris removal in chain and flight Grit Collectors, Chain and Bucket Grit Collectors, Grit Elevators, and Grit Classifiers; and for screening and removal of suspended debris, trash and rags in Mechanical Bar Screens, Catenary Bar Screens and Trash Rakes.

Until the early 1970's, all of these chains were only available in cast or fabricated steel. While the cast steel chains have a high initial ultimate strength and application working load, the chains suffer from rapid wear and loss of strength primarily from corrosion-erosion of the link material. Most chain wear (as much as 90%) occurs from atmospheric, chemical and biological induced corrosion, corrosion-abrasion wear (from the interaction of iron oxide fines formed within the chain link components themselves), and corrosion-erosion wear caused by the gradual wearing away of the chain oxide layer during contact with the teeth of the sprockets. Only a portion of chain wear actually results from such things as contact with grit and silica fines in the process streams. The average service life for cast or fabricated steel chains in most water and wastewater equipment applications is often three to five years, or less.


In 1975, Rexnord introduced the first plastic NCS720S chain, and later NH78 and NH82 plastic drive chains, all molded from acetal plastic, in order to eliminate the rapid wear caused by corrosion and oxidation. These chains have significant limitations with regard to ultimate strength and working load. This limits the use of plastic 720S to C&S collector equipment applications 250 feet or less in length. In some cases, the lack of abrasion resistance can also make plastic chains unsuitable for sustained cross collector service in rectangular (C&S) collectors.

Plastic chains are susceptible to attack from ultraviolet radiation and sunlight. They will become brittle in severe cold, suffer tensile failures due to frost or ice build-up, and have a high coefficient of expansion and contraction due to seasonal air temperature variations and changes in ambient water temperature. The higher load requirements for grit collectors, screening equipment and industrial applications are often well above the rated working load of these chains, and these loads may even exceed the ultimate strength of the plastic chains, causing frequent service outages and catastrophic equipment failures. All plastic chain and plastic chain pin materials have little abrasion resistance, which renders standard plastic chains vulnerable to severe attack from grit and sand, and makes them generally unsuitable for sustained headworks and other abrasive equipment service.


In an attempt to reduce the effects of corrosion, and to a lesser extent, the effects of abrasion, and as an alternate to plastic chains, some manufacturers developed fabricated stainless steel chain link designs made from stamped metal, with the parts press fit together. These chain designs are typically manufactured from 400 series stainless steel bars, rounds and/or plate, a cheap, commercial grade of stainless steel that has little or no nickel content, and as a generally low resistance to corrosive compounds. Chains made from 400 stainless steel, while more corrosion resistant than steel chains, often suffer from chloride embrittlement (in pre-chlorinated applications), stress-corrosion fractures, and severe corrosive attack when exposed to a variety of acids, alkalis, hydroxides, sodium and calcium chlorides, sulfide compounds, and gases (including hydrogen sulfide and ammonia) commonly found in water and wastewater treatment and many industrial processes.

Such designs, depending on the grade of stainless steel used, will have significant strength and working load limitations due to the press fit type of assembly. Typically, fabricated stainless steel chains, typically called 715 chains, only have about two-thirds (2/3) of the ultimate strength, and less than 50% of the working load of conventional cast steel chains.

To overcome the strength limitations of press fit chain designs, some manufacturers offer welded chain designs. Welded chains are often made from 304 stainless steel, a good corrosion resistant material, but one that is relatively soft, and has much lower strength and little abrasion resistance. In addition, all welded chains experience carburization of the link material at the weldments, which results in the formation of stress risers and material embrittlement. These factors can contribute to stress corrosion fractures, and limit the ultimate strength and working load capacity of these chains.

Welded and fabricated chains are labor intensive to manufacture, increasing the cost beyond a cost effective level when compared to conventional cast chains. To compensate for the additional cost of manufacturing, many fabricated chain designs utilize substantially smaller chain pin diameters, thinner link sidebars, and less expensive materials. These size and material quality reductions result in reduced ultimate strength, lower working load capacity, shortened service life, and low overall chain quality.



In order to resolve all of the limitations of cast steel, plastic and fabricated chain designs, a new, advanced precision manufacturing method was developed for casting stainless steel alloys into high-strength CS720S, CS715SS, H82 and H78 chain links. DuraMax Cast Stainless Steel Chains combine all of the best features of other cast, fabricated, and plastic chains, and eliminate all of the material limitations and weaknesses. DuraMax Chains have excellent corrosion resistance (approaching that of 316 stainless steel), and a hardness greater than chilled cast iron. They are unitized, one-piece castings, not assembled parts. DuraMax Chains can be assembled by one person and by hand, quickly and easily, without a need for hammers and clamping tools.

DuraMax Chains are specifically designed for high-strength, severe-duty corrosive, and abrasive applications such as Stormwater, Headworks, and Water and Wastewater process equipment applications, including Bar Screens, Catenary Screens, Trash Rakes, Grit Collectors, and Chain and Flight (rectangular) Collectors and Cross Collectors, Paddle-wheel and Turbine Flocculators.

DuraMax Chains are very resistant to attack from a wide range of chemical and biological compounds, including of acids, alkalis, hydroxides, sodium and calcium chlorides, sulfide compounds, and gases (including hydrogen sulfide and ammonia), which makes DuraMax Chains ideally suited for use with equipment in the water, wastewater, agricultural, grain handling, paper mill, chemical, refinery, food processing, and numerous other industries.

DuraMax Chains increase equipment operating efficiency and productivity by keeping equipment in service longer with significantly lower maintenance requirements. Equipment tanks and basins do not have to be stopped, drained, cleaned and taken out of service every few months for tensioning adjustments, or to repair chain and sprocket failures, or to replace worn out chains and sprockets.

DuraMax Chains are a “Green World” Technology, and use up to 25% “post-consumer recycled material” in the manufacturing process. Unlike rusty, worn out chains made from other metals or plastic, the cast stainless steel alloys in DuraMax Chains are fully recyclable at the end of their life-cycle, and have significant value as a recycled material. The long life-span of DuraMax Chains also provides significant material waste reduction, and reduces the waste-tolandfill stream generated by the frequent replacement of low-grade chain and sprocket systems.

DuraMax CS720S/730 and CS715SS class chains meet or exceed all current standards for welded steel and cast steel chains and attachments per American National Standard ASME B29.21M-1996/2003. DuraMax H78/988 and H82/C9103 class chains meet or exceed all national chain engineering standards per ASME B29.11M and B29.14M-2008.

On an evaluated basis, DuraMax Chains will have the lowest cost of ownership versus any other chain product. In most applications, DuraMax Chains and DuraMax Sprockets will provide 20-years of 24/7/365 continuous duty service without repair or replacement, and are furnished with a standard 10-year Full Replacement Warranty.

Copyright © 2012 by Environmental Resources, Inc. and Michael W. Humcke. All rights reserved.