The Vacuum Decay Method (VDM) is a well-established non-destructive technology used to check the seal of a hermetically sealed container, without compromising the packaging or its contents in any way.
This technology, referred to in American Standard Testing Method ASTM F2338 “Standard Test Method for Non-Destructive Detection of Leaks in Packages” has been applied for decades in the pharmaceutical and food and beverage industries. It is one of the first non-destructive techniques developed for seal analysis of plastic, glass or metal containers.
Bonfiglioli Engineering is proficient in the creation and installation of machines using the Vacuum Decay Method, and the company’s R&D manager, engineer Davide Formenti, spoke to us about the characteristics of this technology and its possible industrial applications.
How Vacuum Decay Method works
The VDM technology uses a vacuum to identify leaks in a sealed container. Unlike destructive methods, this technique does not damage the container or the product inside it, and therefore allows distribution of all analysed samples, once the correct seal of the packaging has been verified.
The technology in Bonfiglioli utilizes a rotating carousel with various test stations that receive the products to be tested directly from the production line. If the test reveals leaks, the analysed products are diverted to a parallel line. Otherwise, they return to the production line to continue to the end of it.
- Each test unit in the carousel consists of a testing chamber, i.e. an environment in which the sample is temporarily enclosed with a certain vacuum level based on the type of product to be tested, up to a maximum of -980 millibars / 20 absolute millibars. Different vacuum levels can be applied depending on the product to be tested. Once the sample to be analysed has undergone these conditions, a certain time interval (transient time) is allowed for the pressure to stabilise, then two pressure value readings are taken, one at the end of the stabilisation phase and one a few seconds later. If the difference between the two values is greater than the physiological threshold—determined during machine set-up—the container has a leak and therefore does not meet the expected standards.
This technique is also used to identify the presence of macro holes (responsible for macro losses) in the packaging, which are identified already by the first pressure value reading. If the data is too low with respect to the expected values, the container is certainly compromised, and a second measurement is not necessary.
Developments of the Vacuum Decay Method
VDM is a consolidated and reliable technique that has been used in the industrial sector for many years. The technology has gradually improved over time, however, with improvements in the possibility to integrate the process directly into the line and the speed of analysis, it is currently possible to perform up to a 1000 tests per minute, although performance in this sense varies greatly depending on the size of the sample to be analysed.
Another area in which the method has been developed significantly is process stabilisation, since it is now possible to create test chambers with a shape very similar to that of the container to be tested. This offers more reliable and accurate results by minimising the volume of the chamber. The development of increasingly sophisticated software for setting also contributes to achieving the same result, making it possible to identify in an increasingly precise way the range of pressure change that can be considered physiological.
Machines for VDM are also increasingly customised from a mechanical viewpoint: Bonfiglioli analyses each type of packaging to be tested in order to develop the most suitable mechanism for handling the product and introducing it in the chamber.
VDM machine potential and performance
Each VDM machine at Bonfiglioli Engineering is custom-built, taking into consideration the requirements of the client, starting from the characteristics of the product to be analysed. Once the equipment has been developed and built, it is tested and subjected to the Factory Acceptance Test (supplier’s automation acceptance). This lets the clients verify its proper operation according to the specifications requested and perform various tests on different types of products to be analysed in the factory. Finally, once the machine is judged to be suitable, it is installed in the plant, where a Site Acceptance Test (customer’s automation acceptance) is performed. Once the final check has been passed, the machine is ready to be operated.
It is recommended that VDM equipment undergo regular preventative maintenance to ensure consistent accurate testing results over the lifetime of the equipment. Maintenance—also carried out by Bonfiglioli Engineering technicians—identifies every possible problem in time and prevents ageing of the mechanical parts, which are physiologically subject to wear.
If, at any point of the product life cycle, the client needs to upgrade its packaging control system, an upgrade of the machine can be carried out, to improve its performance significantly. Today, with over 5000 installations worldwide, upgrading, repairing and reformatting machines is fundamental and already in operation, while focusing on developing and installing new equipment.
Bonfiglioli Engineering is committed to providing the most accurate and technically advanced VDM testing solutions that meet the needs of the industry today and in the future.
We are not just a machine manufacturer. We are your trusted partner for packaging integrity testing and analysis through feasibility studies, technical expertise, validation packages, product handling and custom-built solutions.
