The Invention
The patent, US420099A, granted to William B. Purvis of Philadelphia, Pennsylvania, on January 28, 1890, is for an improvement in paper-bag machines. The invention focuses on a more efficient way to form the bottom of a paper bag using suction devices.
Key Features:
- Suction-Formers: The machine uses a pair of “suction-formers” (F F) that have perforated surfaces. As the paper tube is fed between them, air is sucked through these perforations, drawing the paper and forming the bag’s bottom.
- Enveloping Hood: Purvis’s key innovation is a hood or “enveloping cover” (I) that fits over the suction-formers. This hood is not a solid cover; it has a specific opening in its surface.
- Air-Currents for Precision: The hood’s purpose is to control and direct the flow of air. The opening (J) in the hood allows air to rush in and strike the interior of the paper tube. This action assists the suction-formers in opening and shaping the bag’s end. Purvis notes that while suction is powerful on the top and bottom of the bag, the sides are weaker. The directed air currents from the hood provide extra force to open the sides, particularly for bags with a “bellows side-fold.”
- Directed Air Drafts: The suction from the machine’s fan creates two drafts of air—one toward each end of the formers. The air rushing through the hood’s opening is divided into these two currents, which act on the interior of the bag’s side portions, ensuring the end is fully opened and correctly shaped.
- Optional Features: The patent also mentions that the hood’s opening can be a transverse slit and that tubes or pipes (K K) can be added to introduce precise jets of air to further assist in the process.
Significance of the Invention and Inventor
William B. Purvis was a prolific African American inventor who contributed significantly to various industries. His paper-bag machine patent is a prime example of his ingenuity and focus on improving industrial efficiency.
- Improving Industrial Processes: Paper bag manufacturing was a major industry in the late 19th century. Any invention that could speed up the process or make it more reliable was highly valuable. Purvis’s invention made the bag-forming process more precise, reducing defects and likely increasing the speed of production.
- Contribution to a Key Technology: Paper bags were essential for commerce and daily life. Purvis’s improvements contributed to the mass production of these bags, making them more affordable and widely available. His work, along with other inventors, helped to standardize and automate this important manufacturing process.
- A Prolific and Diverse Inventor: William B. Purvis held numerous patents throughout his life for a wide range of inventions, including machines for making paper bags, a fountain pen, and a globe valve. His broad range of interests and his ability to apply his inventive mind to different fields make him a notable figure in American history. His paper-bag machine patent is just one example of his significant contributions.
