Why Can’t Tungsten Carbide Rings be Resized?

Currently my fiancé, Matt, and I are in wedding planning mode. The tasks taking up our time these days include cake tasting, color coordinating, menu selections and meetings – a lot of meetings. Anyway, one thing on our to-do list was to purchase Matt’s wedding band. We went to a local store, sized his finger and placed an order for a tungsten carbide ring.  It was that simple, or so we thought. About a month ago I picked the ring up; Matt slipped it on his finger and told me it fit. All was well until last week, when he decided to try his ring on again, only to realize it actually doesn’t fit, and is so big it can slide right off his finger. Then, we remembered his ring couldn’t be resized because it’s made from tungsten carbide. But why is this? I spoke with our metals lead, Alex Wensley, who was able to provide insight on why tungsten carbide rings can’t be resized. Here is what I learned:

It all has to do with the atomic bonding, and how tungsten carbide behaves more like a ceramic than a metal. Pure tungsten is a metal, but many metals can bond with non-metal elements and then become ceramics.  For example: Tungsten with oxygen becomes tungsten oxide, tungsten with nitrogen becomes tungsten nitride, and tungsten with carbon becomes tungsten carbide.  Depending on how the different atoms share their electrons with each other in a ceramic, the atomic bonding is either covalent, or ionic.  Covalent and ionic bonds are stronger than metallic bonds, which means they have higher melting points, are harder, and also less ductile.  Glass, bricks, and gemstones are common ceramics which are very strong and hard, but are also brittle.  When tungsten is forged with carbon and becomes tungsten carbide, it forms covalent bonds and becomes very hard but also brittle.

Tungsten carbide rings can’t be resized for two reasons:  they are too brittle, and their atomic bonding, which forms during sintering, doesn’t bond with additional material.  The process of resizing rings involves cutting them, and adding/removing metal of the same alloy.  Trying to resize a tungsten carbide ring isn’t possible because the ring isn’t flexible, so cutting it is as risky as cutting glass and it could break in an unwanted direction.

Secondly, the rings are formed by a sintering process whereby you put tungsten and carbon powder in a mold and heat them up incredibly hot in a vacuum furnace, and it forms as one solid piece.  Even if you cut the ring, reheating it wouldn’t cause the ring to become more flexible or form sufficient bonds at the area which was cut before/after removing material.  The temperature required to allow the ring to be flexible enough to be forged would be so high that the ring would melt and lose its entire shape.

In the case of an emergency (which we hope you never encounter) a tungsten carbide wedding band can be removed from your finger using a tool like vise-grip pliers. These pliers will apply enough pressure to fracture the ring for safe removal.

So while my fiancé may not have a wedding band, at least we have some answers on why tungsten carbide can’t be resized. When shopping for a wedding band it’s important to take into consideration the pros and cons of what a ring is made from; and ensure you know your ring size as well as the jeweler’s return policy in case of a fit issue. I guess it’s time for us to begin searching for Matt’s (next) wedding band…