Process of Casting (Samuel E. Thomas, No. 386,941)
The patent by Samuel E. Thomas of Brooklyn, New York, describes an innovative Process of Casting (Patent No. 386,941, 1888). This invention provides a method for permanently uniting the end of a wrought-lead pipe with cast metal (such as a flange) without the need for traditional soldering. Thomas’s primary objective was to create a joint that would not leak, rust, or separate under the stresses of weather and wear. His innovation relies on a chemical and thermal bonding agent—tin—to bridge the gap between two different metal states.
Inventor Background: Samuel E. Thomas
Samuel E. Thomas was an African American inventor and engineer working in the late 19th century, a period defined by rapid advancements in urban plumbing and sanitation. Based in Brooklyn, Thomas specialized in metalworking and casting. His work for Fred. Adee & Co., a prominent plumbing supply firm in New York, focused on solving the “weakest link” in plumbing systems: the point where soft, wrought-lead pipes connected to rigid cast-metal fixtures. By developing a process that fused these materials together, Thomas helped modernize the reliability of water-closet discharges and other high-pressure plumbing systems.
Key Mechanical & Chemical Steps
The process is a precise sequence designed to fuse a soft pipe to a molten casting without destroying the pipe in the process.
1. The Tinning Phase (A)
- The Agent: Before casting, the end of the wrought-lead pipe (A) is dipped into or coated with molten tin.
- Function: Lead and cast iron (or other casting metals) do not naturally bond well. The tin creates a thin film that acts as a coupling agent. This film chills on the pipe, preparing the surface for the heat of the incoming molten metal.
2. The Internal Core (C) (Key Innovation)
- The Problem: Wrought lead has a relatively low melting point. Pouring molten metal directly against it risks melting the pipe entirely, causing it to collapse or lose its shape.
- The Solution: Thomas inserted a core (C) of rigid iron or stone into the pipe before placing it in the mold.
- Function: The core acts as a heat sink and a physical stabilizer. It prevents the pipe from melting away and ensures that the pipe sets in its original form as the casting cools.
3. The Mold Integration (B, d)
- The Wall: The tinned end of the pipe is placed into a mold (B) so that the pipe itself forms part of the wall of the mold-cavity (d).
- The Ingate (b): Molten metal is poured through the ingate (b), surrounding the tinned end of the pipe.
- The Bond: The heat of the molten metal slightly melts the tin film, which then fuses the new casting directly to the wrought lead, creating a single, unified piece of metal.
Improvements Over Traditional Soldering
| Feature | Standard Soldered Joints | Thomas’s Casting Process |
| Leakage | Prone to “seepage” as solder degrades or cracks. | Creates a unified, fused metal joint that is leak-proof. |
| Durability | Joint can separate under “weathering” or thermal expansion. | Bonded at a molecular level; resists separation and wear. |
| Oxidation | Solder can rust or oxidize over time. | Fusion prevents rust and structural weakening at the juncture. |
| Integrity | Soldering heat can warp the lead pipe. | Core (C) maintains the pipe’s internal shape and structural integrity. |
Significance to Engineering and Plumbing
Samuel E. Thomas’s casting process influenced the development of composite metal bonding and industrial plumbing standards.
- Fusion Bonding: This technique is a precursor to modern metallurgical bonding used in high-pressure oil and gas piping, where different alloys must be fused without the use of secondary adhesives or solders.
- Precision Heat Sinking: The use of an internal core to protect a delicate material during a high-heat process is a foundational principle in advanced manufacturing and glass-blowing today.
- Sanitation Infrastructure: By making water-closet (toilet) discharge pipes more reliable, Thomas contributed to the sanitary revolution in 19th-century cities, helping to reduce water damage and improve public health through better-sealed sewer systems.
- Integrated Components: His idea of making the pipe “part of the wall of the mold” is a sophisticated example of insert molding, a process now ubiquitous in plastic and metal manufacturing to create complex, multi-material parts.
