There are three types of heat tunnels: steam, hot air, and radiant heat. Understanding the specifics of each type of heat-shrink tunnel can help make appropriate decisions about which will partner well with a given application.
Steam tunnels use live steam to provide the energy necessary for the shrink process. They offer the most uniform heat—360° around the package—which means overall even shrinkage of the film. Steam is also the least aggressive heat of the three tunnel types. Steam tunnels are ideal for round, hourglass, and other non-straight sided packages because of gentle, even shrinkage. PET packaging does extremely well in steam tunnels. However, steam tunnels are not suitable for every application. For example, if the packaging line is in a cold environment, steam will not be applicable. Packaging powders and certain other products are also not suitable for steam. Steam is recommended for most, but not all sleeve-label applications, in particular, where the sleeve is applied to a liquid filled container, especially glass. On the other hand, steam tunnels are generally not acceptable for tamper-evident band applications, although steam can be used when the TE band also serves as a label, or where the shrink application is located in a hazardous environment.
Environmental and product assessments are necessary before specifying a steam tunnel, which can also require a separate steam source and equipment to remove excess moisture and condensation from the area near the tunnel.
Hot air tunnels
Hot air tunnels (also known as convective tunnels) are extremely popular due to their ease of use, and the fact that they don’t require anything out of the ordinary to operate, unlike steam tunnels which need a steam source. This technology is an option when the environment is not conducive to steam. Hot air tunnels use forced, hot air to provide the heat energy required to complete the shrink process. The tunnel usually includes a fan of some type to force air through a heat source to achieve a heated air stream. Many tunnels feature a recirculation system to pull the heated air back into the process for greater efficiency. In some cases, industrial hot-air guns are used as the heat source and fan. Hot air can be directed to specific areas of the film that places the heat where and when it is needed in the shrink process, and multi-zone tunnels are often the best choice when the application calls for labels. This allows different temperatures to be used in stages, minimizing distortion. Hot air offers a more aggressive heat than steam, requiring a careful assessment of the packaging material’s heat resistance. Depending on the application, hot air tunnels may have al arger footprint than steam tunnels; this can impact cost of ownership.
Radiant heat tunnels
Radiant heat tunnels (also known as infrared tunnels) are similar to steam in that they provide a consistent temperature and a high heat energy transfer. At the same time, they are the most aggressive in terms of shrink, and therefore best used for a fast shrink on packaging material not affected by more robust heat. They use radiant heat to provide the energy required to complete the shrink process. These tunnels use various energy sources from quartz panels, tubes, and in some cases, standard Cal rod-style heating elements with reflectors. They are ideal for neck bands on containers such as wine bottles. Radiant or infrared tunnels normally are used in conjunction with other types of tunnels that can serve a finishing unit.
Why you need to know
The distinctions among machine types are vital to note since certain myths pervade the industry. One of the more prevalent ones is that heat tunnels used for standard shrink packaging or bundling are capable of processing all kinds of tamper-evident bands and sleeves. People assume this is true due to a lack of understanding about the different types of packaging methods. A standard tunnel is not as effective because the air-flow requirements differ for each application. Various films also differ in shrink characteristics. The shrink-sleeve tunnel requires amore directed and controlled air flow, while the standard tunnel uses more of a cyclonic air flow with higher velocity. Some factors are typically not considered that should be, such as the utilities required to operate a heat-shrink tunnel, as well what additional products could be processed through the tunnel in the future. In addition, environmental concerns will dictate the tunnel’s location. For example, a steam tunnel will increase the humidity in the area around the tunnel, and can release excess steam into the room. The end user must take this into consideration. A manufacturer of dry products (e.g., spices) might not use a steam tunnel for this reason.