Heat Shrink Tunnels Explained – Part Two 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. Be sure to read part one of this series before proceeding. 

Advantages and Disadvantages

​Most technologies have ideal areas of application which relate directly to their strengths and weaknesses. The following is a summary of the strengths and weaknesses of the three types of heat tunnels discussed.

Infrared Tunnels

Advantages

• Only the surface of the object itself is heated
  • Energy is not wasted heating the surrounding environment
• Rapid response time
  • Heat output reaches its set point almost instantly
• Infrared heaters are very quiet
• Relatively low capital cost

Disadvantages

• Infrared is a “line of sight” heating method, meaning that any part of an object that is shadowed/obstructed from the source will not experience heating
  • This can cause shrink problems for intricately shaped parts or large parts that are spaced closely together
• Infrared heat can be produced across a wide range of wavelengths, however any given heater will only output a narrow wavelength band
  • The heater must be tuned to specifically to the heating application, which reduces the flexibility of the heat tunnel
  • Material type, thickness, colour, opacity, distance from the heater, etc. will all change the effectiveness of different wavelength bands

Steam Tunnels

Advantages

• Provides consistent heat distribution at relatively low temperatures
• Provides a very uniform application of heat to the part

Disadvantages

• Objects are wet from condensation upon exiting the tunnel
  • Drying is required before packaging, printing or secondary labelling (either through evaporation or with a blow-off system)
  • Moisture can cause corrosion problems with metal components and caps/lids
  • Not well suited for applications involving dry goods such as herbs and grains due to moisture concerns
• A source of steam generation is required
• Steam systems generally have a larger physical footprint than infrared or hot air tunnels
• Not suitable for some shrink materials
• Longer tunnel may be needed to achieve full shrink compared to infrared or hot air tunnels

Hot Air Tunnels

Advantages

• Compact
• Wide temperature range capability

• Miniature nozzles and custom hole/distribution patterns can be used to manipulate the flow of air
  • Allows for targeting of critical areas
  • Helps treat potential problem areas
• Relatively low capital cost
• Can be used for pre- or post-processing to solve performance issues with existing steam or IR tunnels

Disadvantages

• Many applications require a custom engineered solution to ensure good results
• Due to the continuous flow of hot air, the local environment can heat up
  • Ventilation and/or proper shielding may be required

The next article in this series will cover the technical complications of heat shrinking. ​