A new solution for cans containing dangerous goods
Antonio Carlos Teixeira Álvares
Antonio Roberto Sene
Silvério Cândido da Cunha
The new regulation in Brazil for the practices recommended by the United Nations for the transportation of dangerous goods, more specifically solvent based paints, has imposed a great challenge for the manufacturers of square cans.
The internationally adopted practices and standards, based on the recommendations issued by United Nations committee of experts in the transportation of dangerous goods, provide definitions and information on the required tests and the code standardization.
Due to its physical-chemical properties, dangerous goods may include substances, originated from several processes, which impose a hazard to human health, public safety or the environment. In order to minimize risk during transportation, the tests require the packaging system to offer greater resistance against impacts and also due to an increase in internal pressure.
The ideal system for the fillers, is restricted to the packaging itself, which would prevent the use of composite packaging. In such case, the free fall of the packaging filled with the product, without any additional protection, is one of the rigorous tests to which the packaging is subjected in order to obtain homologation for the transportation of dangerous goods (figure 1).
Fig 1 – UN Packaging (homologated for the transportation of dangerous goods)
In the case of paints and other solvent-based chemical products, the regulation defines a drop from a height of 1.20 meters . This test is particularly critical for the 18 liter square can, especially when the packaging drops on a corner (figure 2), which may cause the seam (union of the body with the bottom/ring) to break.
Fig 2 – Square can after drop.
The classic solution to this problem is to increase the steel sheet thickness, in combination with reinforcement of the system by means of replacing the conventional double seam (figure 3) with a triple seam (figure 4).
However, the triple seam option, demands investments in new equipment (seamers) and redesign of the productive processes, also increasing the usage of raw material.
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Fig 3 – Double Seam |
Fig 4 – Triple Seam |
Brasilata's technical staff as a consequence has conceived a system to relieve part of stress applied to the seam during impact. The studies led to a solution in which the energy of a drop is absorbed by an increased deformation of the body, thereby reducing stress on the seam.
The greater impact resistance was achieved by a more complex solution, comprising the use of beads on the body which work as energy absorbers. These beads enable greater deformation of the body of the can when subjected to the drop impact, as is the case with bumpers in automobiles. In other words, the resistance of the package to the drop impact was paradoxically achieved by the reduction in the resistance of the body of the can in order to protect its weakest portion. The new technology also allowed the use, in the body of the can, of a steel sheet of reduced thickness ( 0.30 mm ) in comparison to the conventional solution having a triple seam ( 0.34 mm ) (figure 5).
Fig 5 – Beaded can
The company relied on the support of the Federal University of Rio Grande do Sul in the study conducted to determine the ideal profile and number of beads. The use of sawtooth type beads (figure 6) provided the best results for impact and the greatest reduction in stress in the seam region.
Fig 6 – Sawtooth Beads
Said results were obtained through a dynamic non-linear finite element analysis of the drop behavior with different types of profiles and amount of beads, since the problem involves large displacements and permanent deformation of the container. The software Ansys was used to carry out the simulation. A few of the profiles tested can be seen in Figure 7.
Fig 7 – Different profiles subjected to simulation
The geometric models then undergo simulation of a drop (figure8), and the results are then compared to real drops, as seen in Figure 2, to validate and improve the mathematical models used.
Fig 8 – Simulation of a drop for a 18L square container
Due to the fact that it is an innovative technology, Brasilata filed a patent application internationally. As in relation to other new product developments, the company expects to be able to license this solution to manufacturers in other countries and thus perform the appropriate allocation of this intellectual property asset.
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