Since the early ’80s, when stainless steel pumps were introduced to the pump market, stainless steel products have faced slow acceptance to date. Comparing the structure of the manufacturing process to that of the traditional cast iron or bronze pumps and parts, the quality, construction, and durability of stainless steel manufacturing faced controversy.
During the early ’80s and due to several inceptions of environmental regulations, stainless steel pumps were introduced to the pump market as a viable environmental solution and cost effective option. Since then, stainless steel products have faced slow acceptance to date. Comparing the structure of the manufacturing process to that of the traditional cast iron or bronze pumps and parts, the quality, construction, and durability of stainless steel manufacturing faced controversy.
Several manufacturing processes exist for the production of stainless steel pumps with validity in each. Primarily, stainless steel pumps are manufactured using a stamping process. EBARA Corporation, Japan, has developed a proprietary manufacturing bulge form process that eliminates most of the imperfections that occur during the stamping and welding process.
In 1991, the corporation’s directive was to develop an environmentally friendly manufacturing process that would produce high quality pump products at a reasonable cost. The use of stainless steel offered unmatched corrosion and erosion resistance in dewatering, effluent and sewage, potable water, and commercial applications. However, developing a new line of cast stainless steel pumps would not achieve the cost or environmental impact that the corporation anticipated and deemed to fit the market needs.
Using sheet stainless steel appeared to be the most viable option, but the standard technology of stamped stainless had inherent flaws. Further, this process was in direct conflict with the company’s program objectives.
Standard technology was to stamp form stainless components and assemble – which requires extensive welding. The traditional process of stamping stainless steel creates stress problems that reduce component integrity. Further, stamping causes stresses along bends as well as irregular wall thickness of the material. These weak spots can cause premature failure of a pump. Additionally, stamping does not allow the creation of a volute in the case. In place of a volute, a diffuser is required to direct the discharge flow. Using a diffuser further reduces the pump efficiency.
To combat the negative aspects of stamped stainless steel technology, EBARA Corporation developed state-of-the-art bulge forming processes. Bulge forming is a cold forging process utilizing a series of six high pressure, 16,000 psi, hydraulic presses. Through a series of progressive dies the stainless steel blank is formed into the final configuration. Forging the metal in steps allows the material to flow into position rather than cause stress by a single sharp blow that occurs in the stamping process. The bulge forming process produces uniform wall thickness throughout the pump components. It allows for the formation of a volute as an integral part of the pump case for increased efficiencies. Smoother surfaces are produced which achieve lower noise levels and lower velocities creating less component strain and longer life.
Ultimately, the formation of complete components drastically reduces the number of welds required in construction and eliminates the associated potential problems created by stamping.
EBARA’s CAD and CAM systems are used in controlling the design and manufacturing process including the bulge forming operation additionally assuring dimensional and component integrity. As a final step, the completed component undergoes a heat treating and pacivation process to relieve stress and provide chemical compatibility in any weld areas.
Pressure bulge formed stainless pumps have proven to be far more structurally sound than stamped stainless and cast iron pumps, especially where corrosion resistance is a key factor. The resulting pumps offer high quality, precise dimensions, increased efficiencies, lighter weights, greater strength, and optimal value.
Established in 1980, EBARA’s Italia plant, located in Cles, Italy manufactures all of the company’s stainless steel pumps. The Italia plant is equipped with state-of-the-art computer controlled pressure forming and processing equipment that now produces more than 55,000 pumps per month. The stainless steel product line includes a line of submersible sump/effluent pumps from 1/3 hp to 11/2 hp, 2-in. handling submersible sewage pumps, end suction centrifugal pumps from 3/4 hp to 15 hp, and vertical multistage pumps from 1/2 hp to 25 hp. These stainless products are sold worldwide through the company’s dedicated sales and service divisions.