Heat Shrink Tunnels Explained – Part One of Three

​A heat/shrink tunnel, is an enclosed and heated area that is used to not just apply heat to an object, but create a heated local environment around said object. Heat tunnels are generally found above or enveloping a section of conveyor belt to allow for automated travel through the tunnel. The most common use for a heat tunnel is the activation of heat shrink labels, packaging, and tamper bands on a container; however, they are also used to cure paints and heat parts. This article series will cover the most common types of heat tunnels available, their advantages and disadvantages, and the technical complications of heat shrinking. 

Types of Heat Tunnels

​The type of heat tunnel is determined by the heat source used. Common heat sources include infrared, steam, and hot air. Regardless of the type, all heat tunnels work by transferring energy from a heat source to an object within an enclosed area. The goal may be to a shrink film/label, cure a coating of paint, remove excess water/moisture, or any other application requiring immersion in heat but the principals remain the same. The amount of energy transferred depends on the output capacity of the heat source, the material being heated, and the residence time of the object in the tunnel. 

Figure 1: Example of infrared bulb.

Infrared tunnels do not require a transfer medium. The interior of an infrared tunnel is lined with infrared bulbs (see Figure 1) which transfer energy to the target object’s surface via electromagnetic radiation. No physical contact with the object is necessary for the energy transfer to occur. Infrared heat tunnels are suitable for applications that require only the surface of an object to be heated, as the heat does not effectively penetrate into the body of the object.
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Steam tunnels use steam as a heat transfer medium. Steam is injected into the tunnel, enveloping any objects therein, and transferring heat to the object. Steam tunnels are suitable for shrink applications but are unfit for drying or curing applications.

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Figure 2: Close-up of interior of custom heat tunnel.

Hot air tunnels use air as a heat transfer medium. A hot air tunnel is typically double walled, with a solid exterior wall and a perforated interior wall (see Figure 2). Hot air is injected at an adequate pressure between the walls by either a hot air blower or an air heater and blower combination. The pattern of perforations in the interior wall, in combination with the volume and pressure of hot air supplied, control the flow and application of air, allowing for manipulation of multiple heating zones. Hot air tunnels are suitable for most applications as the amount of heat and air flow within the tunnel are highly customizable. 

The next article in this series will cover the advantages and disadvantages of each type of heat tunnel. ​

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Figure 1 Source: "Infrared Illustration" by Tatoute is licensed under CC-BY-SA-2.5.
Figure 2 Source: STANMECH Technologies Inc.