A customer needed to replace a 1950s-era Worthington duplex direct-acting pump — commonly used in O&G and other industries as a low-maintenance, reliable pumping solution.
Replicating a Worthington duplex direct-acting pump
The Conhagen team could have improved the case with streamlined flow passages and low-stress pressure boundaries, but the customer insisted on an exact duplicate. Considering the original case ran for 70 years, it’s no wonder they wanted the same one, but creating an exact duplicate of an ancient part using modern manufacturing methods became a real challenge.
The pump was disassembled in California, and the MEDS team reverse-engineered the case in our Texas facility. A full 3D scan was captured with our GOM ATOS-5 industrial 3D measurement technology. The image was oriented, then sectioned, producing cross-sections within GOM. The sections were imported into Rhino3D modeling software for processing. The solid model and detailed drawings were created in SolidWorks software. A "standard for the exchange of product data file," exported from SolidWorks, was forwarded to the foundry’s mold designer.
The mold designer’s email was short and to the point, "Houston, we have a problem." We intended to use binder jet 3D-printed sand molds to cast the part. We have cast bigger and far more complicated parts in the last year with this foundry process, but those parts were carbon or stainless steel, not cast iron.
A little foundry history: in 2013, binder jet 3D-printed sand began replacing expensive and time-consuming patterns for prototype and low-production run castings. One-off casting’s cost and delivery times plummeted, allowing non-OEMs to replicate cast parts competitively. Ten years later, the 3D-printed mold process has matured and is common in the foundry industry.
However, reproducing a part that is designed to be cast in no-bake sand molds with oven-baked oil sand cores is a challenge for modern binder jet 3D printed sand. The printed sand mold process is terrific for low-cost, quick turnaround, high-fidelity castings but lacks strength for large, mostly hollow castings. Hollow spaces within castings are made by cores that displace the molten metal inside the mold. Not surprisingly, molten metal is hot and dense. The heat breaks down the binding resins while the metal’s density causes strong, buoyant forces on the cores. Sometimes the molds, the cores or both break during the casting process, ruining the casting and costing time and money.
Replicating a Worthington duplex direct-acting pump
The mold designer knew the buoyant forces would break the large cylinder cores. Engineering’s initial solution was to change the material from cast iron to carbon steel and use large holes in the mold to support the cores. We would need to weld carbon steel plates into the core support holes, perform a post-weld heat treat then machine the part to print. The customer did not accept our proposed material change and insisted on cast iron.
The cost and time to produce conventional pattern equipment was prohibitive. We had to make the binder jet, 3D-printed sand method work. After studying the cores and case wall, we decided to print hollow sand cores and then re-enforce the cores with steel bars. Steel bars would prevent the failure of the cores, and the case wall could support them. Of course, steel bars in a mold can cause many other problems during casting, but the foundry knew how to insulate the bars and preheat the mold to minimize the risk. The steel bars protruded through the case wall and actually became part of the casting. The steel bar remnants would eventually be removed, becoming ports for the pump’s piston rods.
The mold and cores were printed in Ohio within two days. The printed components were delivered to Texas overnight. The foundry assembled the mold and poured the casting over two long days. Cool down and knock out took another day. Finally, the casting was delivered to California nine days after the mold designer discovered the problem. Ultimately, the replacement case is an exact copy of the original part.
Because of the expertise of Conhagen and the close relationship with the foundry, the replacement pump will give the customer another 70 years of service.
For more information, visit conhagen.com.
