Pharma glass defects - 24. Rocker

Welcome to part 24 of an ongoing series devoted to visual defects that can be observed in pharmaceutical glass vials.  Today I will be briefly discussing the “Rocker” defect.  It is essentially the reverse of the “Concave Bottom” defect covered in part 14 of this series.  Instead of going up too far into the body of the vial (i.e., a Concave Bottom), a Rocker defect is caused by the bottom of the vial projecting out of the vial body (see Footnote 1).  I should also point out the differences between the Rocker and “Bullseye” defects, both of which involve a feature that can protrude beyond the footprint of a vial.  A Bullseye defect is a rounded (or teardrop-shaped), thicker region within the bottom caused by incomplete glass flow during the bottom-forming step of tubular vial conversion.  The Rocker defect is instead characterized by a vial bottom with a relatively uniform thickness that is “ballooning” out from the body, as illustrated in Figure 1.

It’s not too difficult to imagine how the Rocker defect can negatively impact vial performance on a fill-finish line.  Vials with a Rocker defect can wobble and be prone to tipping over, the extent of which depends on the severity.  It is therefore considered a Major A defect if the vial observably rocks and is unstable; otherwise it’s an Acceptable Imperfection.  That sounds simple enough, but actually defining the boundary between Major A and Acceptable Imperfection isn’t necessarily established with a simple dimensional measurement.  Instead, suspected Rocker defects can be compared against the behavior of limit samples placed on a flat surface.  I’ve also heard of some home brewed methods in which the surface holding the vials is struck with a quick blow.  The duration of vial wobbling can then be measured against an arbitrarily determined time that sets the limit between what is acceptable or not.  Just remember that the observation of a wobbling vial does not automatically mean it’s a Rocker defect, and so further investigation is needed.

 Questions or comments? – please leave them below or feel free to directly contact me.

Footnotes

1.        The Rocker defect may also be referred to as a “Convex Bottom” defect.  I assume the Rocker terminology is preferred to help prevent confusion with the Concave Bottom defect.

About the Author

 Matthew Hall is Technical Affairs Director for Corning Pharmaceutical Technologies , a manufacturer of primary glass packaging for parenteral drug products.  Based in upstate New York, Dr. Hall serves as a technical expert supporting business operations, sales, and marketing and educating customers on pharmaceutical glass packaging.  He is a member of the Parenteral Drug Association and the International Society of Pharmaceutical Engineering.