Breakage of Refillable Beer Bottles
It was reported that 750 ml refillable beer bottles were breaking in the pasteurizer. The failures consisted of a single crack running radially across the bottom of the bottles as shown in the picture. In order to properly diagnose the cause of the breakage, it was necessary to determine whether the tensile stresses were too high or whether the glass strengths were too low.
Based on the nature and simplicity of the fracture pattern, it was concluded that the bottles failed under the influence of a low-level internal pressure which is consistent with failure in a pasteurizer. The absence of any mirrors at the fracture origins indicated that the failures occurred at very low stress magnitudes. Thus, the breakage was associated with inadequate glass surface strength.
Microscopic examination indicated the presence of cleavage scratches randomly distributed across the center bottom region of the containers as shown in this picture and that one of these scratches was present at the fracture origin. Further measurements revealed that the depths of these scratches ranged from 0.002 inches (0.05 mm) to 0.010 inches (0.25 mm). These values indicated that the cleavage scratches were relatively severe which was consistent with the low glass surface strengths.
A scanning electron microscope (SEM) was used to further examine the cleavage scratches at the fracture origin sites to determine if any metal residues were contained within the scratches that would help to identify the source of the scratches.
No other features were observed within the scratches as shown in in the SEM picture. Thus, the cleavage scratches most likely had been created by contact with another glass surface.
It was concluded that the damage had been created by the consumers during collection and recycling of the bottles. Such damage would have been created during the last recycling; otherwise, due to the severity of the damage and the associated low glass strength, the bottles would have failed during a previous filling.
In order to avoid this problem in the future, more care must be implemented during handling of the bottles in the recycling processes.