Time filter

Source Type

Washington, DC, United States

The United States Mint primarily produces circulating coinage for the United States to conduct its trade and commerce. The Mint was created by Congress with the Coinage Act of 1792, and originally placed within the Department of State. Per the terms of the Coinage Act, the first Mint building was in Philadelphia, then the capital of the United States; it was the first building of the Republic raised under the Constitution. Today, the Mint's headquarters are in Washington D.C. which is not a coin producing facility. It operates mint facilities in Philadelphia, Denver, San Francisco, and West Point, New York and a bullion depository at Fort Knox, Kentucky. Official Mints were once also located in Carson City, Nevada, Charlotte, North Carolina, Dahlonega, Georgia, New Orleans, Louisiana, Washington, D.C.; and even in Manila, in the Philippines.The Mint was made an independent agency in 1799. It converted precious metals into standard coin for anyone's account with no seigniorage charge beyond the refining costs. Under the Coinage Act of 1873, the Mint became part of the Department of the Treasury. It was placed under the auspices of the Treasurer of the United States in 1981. Legal tender coins of today are minted solely for the Treasury's account. Wikipedia.

Ying T.,United States Mint
Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2015

During the coining manufacturing, the cut blanks must be annealed to remove strain hardening generated in rolling process. After annealing the blank surfaces were oxidized. To remove this oxide layer, the blanks and the stainless steel balls were mixed together, and rotated in a burnishing machine as shown in figure 1. The reaction rate between the blanks and added chemicals was much higher than that without the burnishing movement. In this presentation, the author tried to build a mathematic model to describe the thermodynamic process. The complex burnishing movement is simplified to a ball sliding on a flat surface, and further simplified to two-ball colliding each other as shown in figure 2. In liquid hydrodynamic lubrication, there is an important assumption for Reynolds equation: the first layer of the liquid molecules absorb on solid surface without any movement. When the fluid flows, the second liquid molecular layer is shearing with the absorbed first layer. The coupling relationship between the absorbed molecules and the surface atoms does not change. Source

Ying T.,United States Mint | Gates R.,U.S. National Institute of Standards and Technology
Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2015

As discussed in the Nanotribology surface thermodynamic model, the reaction rate between the absorbed molecules and surface atoms is increased by the sliding movement due to the high entropy in the system. The reacted products depend on the properties of the molecules applied into the system. A burnishing process for blank cleaning in coining industry is used again to analyze the reacted products generated during the sliding movement. There are two kinds of reactions. In one case, the applied chemicals react with surface to form an ionic molecule, and surface then be removed layer by layer. For example, to remove the oxide layer on coin blanks, citric acid was used in the burnishing solution. In this reaction, the acid reacts with copper oxide layer to form copper citrates. The copper atom loses an electron to become an ion. Then, the copper atom is dissolved into the water. In the other case, the applied chemicals may react with surface to adhere on it. For example, to apply a lubricant layer on blank surface, oleic acid was used in burnishing solution. The oleic acid reacts with copper to form copper oleate, an organic salt layer. Although these two reactions are completely different, the rubbing movement in the burnishing process increases the reaction rate in both cases. For material removal etching reaction, the weight lost was compared with and without burnishing process for the same chemical solution. With the rubbing movement, the weight lost was increased several times in a short burnishing test period compared to that in an immersed case. Source

Ying T.,United States Mint | Gates R.,U.S. National Institute of Standards and Technology
Tribology Transactions

A new method has been developed to lubricate metal coin blanks during the coin production process. The lubricant is formed on the metal surfaces as a monomolecular film during burnishing, which provides an exceptional combination of chemical and tribological environments needed to promote reaction. Laboratory-scale burnishing simulations combined with surface analysis indicated the composition and nature of the films formed. A comparison of reactions on metal surfaces with and without burnishing confirmed the importance of the tribochemical process to the successful lubrication of the blanks. Implementation of this lubrication procedure to production lines has improved the surface quality of the coins and tripled the die life, resulting in considerable cost savings. © 2013 Copyright Taylor and Francis Group, LLC. Source

United States Mint | Date: 2011-11-08

(Based on Use in Commerce) Coinage, namely, United States coinage, numismatic coins, commemorative coins, and monetary coin sets for collecting purposes. Coin albums, coin holders and coin wrappers, namely, coin bags and rolls, and printed educational materials relating to coinage.

United States Mint | Date: 2008-04-29

Monetary coin sets for collecting purposes. Coin albums.

Discover hidden collaborations