The Quality of Tantalum Marker Beads

We are a small, sixty year old, family owned and operated company. We have been producing radiographic marker beads since 1986 when we started producing, eighteen karat gold balls, used in the X-Ray treatment of prostate cancer. Our company specializes in the custom manufacture of precision and ultra precision balls. We have built a substantial world wide business by producing high quality balls from difficult to work materials at reasonable cost. Much of this product is balls that are small to very small in diameter.The customers for tantalum radiographic marker beads have themselves established the methodology that we use to guarantee the dimensional and chemical integrity of these balls.

We used tantalum wire for the production of our marker beads that is much larger than actually required for production. This more expensive procedure is employed to be absolutely sure that no foreign material that was left on the surface of the wire from the rolling and drawing processes that preceded our manufacturing remains on the finished balls.

Contamination of the tantalum marker beads by the typical shop environment is avoided in our plants by only using virgin grinding oil, kerosene, and abrasive powder. The tanks and pumps used to mix and dispense the lapping slurry are only used in our tantalum ball production.

In a typical ball manufacturing plant, a central system is used to supply the abrasive slurry to all of their ball lapping machines. In the same way they use a central cleaning system on all balls, while our tantalum cleaning system is autonomous.

Our sphericity tolerance of the tantalum marker beads is typically fifty microinches (this is just a little more than one micrometer). This quality is four times as good as competitive companies. This sphericity is verified in production by making multiple dimensional measurements of the same balls. The common diameter of all of the balls in a given lot of tantalum marker beads is also fifty microinches (this is just a little more than one micrometer). This characteristic is verified by making multiple dimensional measurements of a sample lot of balls.

There is a serious problem when inexperienced producers use a very fine abrasive to polish the very soft, very ductile Tantalum metal balls. This very fine polishing abrasive will literally migrate into the outer surface of the tantalum balls, which causes gross chemical contamination of the metal. For this reason, our tantalum marker beads are finished by lapping with a rolling abrasive which leaves them perfectly clean. This lapping process does not produce a polished surface.

Measuring the absolute diameter of precision tantalum balls, is a serious task. Eliminating all of the uncertainties involved in making the size measurement of tantalum marker beads, is accomplished by specifying, every facet, of exactly how the measurements are performed. The tantalum marker beads are measured between two perfectly flat parallel surfaces (0.000001”) [25 nanometers]. The flat parallel measuring surfaces are made of tungsten carbide that is 94 percent tungsten carbide, with a 6 percent cobalt binder. Tungsten Carbide is used to take advantage of its incredibly high stiffness or Young’s modulus of elasticity. This stiffness is 120,000,000.00 PSI in compression.

The measuring force is standardized at 14 grams. Using this technique, the uncertainties of measuring the diameter of tantalum marker bead is well under ten microinches (0.000010”)[one quarter of a micrometer]. We use a high energy, low frequency, final cleaning process. The liquid cleaning agent we use is kerosene. Any residue of this very simple hydrocarbon can be easily removed in a heated alkaline bath and then a distilled water rinse. The very high mass and small diameter of tantalum marker beads have such high vibration dampening effect that ultrasonic cleaning is not an effective method of cleaning the tantalum marker beads.

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