Struck on a Ballcone burnishing beads?
By Patrick Glassford | Tuesday, 3 September 2019
The following content comes from Patrick Glassford website which no longer exist. To keep this information available to the public and for a perpetuity reason, we reproduced it here.
These coins appear to be struck on Stainless Steel Ballcones.
The 2004 Five cent coin shown above is 1.11 grams and is the same weight as the 3/16 type Ballcone. This coin also attracts a magnet the same way as a Ballcone burnishing bead. The 2004 Twenty Five cent coin shown is 1.21 grams and appears to be the same weight as the 1/4 type Ballcone. This coin also attracts a magnet the same way as a Ballcone burnishing bead.
The image of Stainless Steel Ballcones shown are similar to the type used by the Royal Canadian Mint (RCM) to burnish planchets. They weigh 1.11 grams, are magnetic and enlarged 5x in the image above. Burnishing is a process that involves tumbling the planchets in a large drum with small steel ballcones. This uniformly roughens or dimples the entire surface of the planchet and is fundamental in producing the finest coin possible.
I first noticed these odd ballcones in a display at the RCM in Ottawa in the late 90's. Evidence gathered by observing off centre coins indicated all planchets intended for circulating coins in the RCM have been burnished since about 1992 & 1993. Prior to that only planchets for numismatic issues were burnished. This also includes some foreign coinage for other countries. Coins struck by Canada for other countries are usually distinguishable as higher in quality of appearance that has been achieved in part by burnishing planchets.
Ballcones or Satellites (variously called saturn, sputnik, planet, UFO) are mixed with round steel ball and other steel burnishing media (diagonal, pin, eclipse) to achieve overall cleaning, consistent metal polishing and excellent mirror finish all over the component profile.
Functionality of Ballcones
Steel round ball is the most widely used shape in steel media. However, it is not always versatile, as a sphere cannot access corners. It is also unable to make contact in grooves or recesses if the steel ball diameter is larger than the groove width. In such cases, milky areas become apparent on the component surface where balls are unable to provide polishing action. Steel ballcone and satellite works very well in such areas for providing uniform finishing results. These steel ballcones are also useful for preventing media clogging in the components being polished.
Tolerance
Stringent dimensional controls are maintained and the tolerance on the dimensions are +/-0.25mm or +/-0.01" (250 microns) which are amongst the best in this industry.
Shape
One half of the steel ball-cone is a semi-sphere, the other half is a cone and both are separated by a sloping central flange. The semi-sphere provides rolling action for good luster, the cone accesses holes and grooves and the flange contributes in cleaning and finishing corners, collars and recesses. The overall shape prevents media clogging. A very versatile steel media.
Steel Material
Stainless steel or inox media, 300 series (typically AISI 304) is the one which is most widely used for metal polishing. It has excellent resistance to rust, corrosion and wear and can be used in conjunction with chemically aggressive burnishing compounds, both acidic and alkaline. Stainless steel requires no maintenance or after care during storage, non usage or idle periods. The burnishing performance remains consistent over long periods of time and it does not require replacement as no deterioration in quality takes place. The 300 series stainless steel are austenitic and are unhardenable by heat treatment. However, some work-hardening takes place during the cold-forging process. The media is passivated after final polish.
- NHB BALL & ROLLER LTD.
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