Roll-up Tank Covers Resist Acid Fumes and Splash
When American Chemical & Equipment needed tank covers that could resist fumes and splash from hydrochloric acid, it partnered with its supplier of metal roll-up covers to create a successful solution.
Founded in 1988, American Chemical & Equipment is an international manufacturer and distributor of products for the metal finishing industry. Its equipment division designs and manufactures plating and waste treatment lines that include large tanks. For several years, the company has used Steelflex? Walk-On Duty metal covers to enclose the tops of these tanks. The covers are made by A & A Manufacturing Co., Inc., New Berlin, WI, a specialist in the design and manufacture of protective covers for a wide range of applications throughout industry. (Shown right, roll-up cover for chemical tank is made of two different polymers to resist hydrochloric acid fumes and splash; rollers visible under housing maintain down pressure to keep cover in position.)
For the current application, the standard covers made of steel, stainless steel, and aluminum could not be used because the acid would attack these metals. Chuck Connon, president of American Chemical & Equipment, says that his company defined the concept of using materials that would resist the acidic fumes and then worked closely with A & A to turn the design into finished covers.
Working Together for the Right Design
To accommodate the corrosive application, the design combines polypropylene material for the cover with PVC tubes for the ribs. Instead of the aluminum extrusions normally used as stiffening ribs, the tubes are riveted to the underside of the cover. A shaft inside the end housing is driven by a gearmotor and drive chain. Sprockets on the shaft engage these tubes or ribs to extend and retract the cover, which rolls up into a housing. This requires less space than other methods and is a simple design that improves reliability. Standard Steelflex covers generally incorporate stainless steel sheets that roll up in a similar fashion and are suitable for most other applications. Wiper strips keep the cover under tension and remove any debris before the cover is rolled up. (Shown left, tank cover design incorporates gearmotor drive sprockets that engage the PVC ribs beneath the cover to move it open or closed, and scroll configurations on each end into which the cover retracts.)
American Chemical & Equipment developed the control panel for the cover system and also joined with A & A in refining several safety features, including an emergency stop line and limit switches. A light tower displays green when the cover is moving and red when it is stopped.
To simplify installation, the special covers were built as complete units with a metal frame designed to fit easily over the top of a tank. Similar units can also be built without the frame for installation as an integral part of the tank itself. (Right, safety features include safety line and e-stop, as well as limit switches to control cover motion and signal lights.)
Cover size is determined by the size of the tank, with some Steelflex units already made in lengths up to 20 ft. For longer covers where space is limited for the housing or canister into which the cover retracts, two covers with canisters at opposite ends of the tank may be used. Two sizes of polypropylene covers were made for this application; both are 70 in. long but one is 50 in. wide while the other measures 62 in. wide. Both have been operating reliably for more than a year.
According to Connon, the need for a tank cover is determined by the chemistry of a tank's content and its usage. All covers are corrosion resistant to some degree, and the stainless steel covers can be used in most applications. By using a similar design but substituting appropriate plastic materials, it was possible for the cover to withstand attack by the acidic fumes.
The combined strengths of both companies working in close partnership produced a solution that met a new need for which a sturdy and dependable cover previously hadn't been available.
