Shrink Tunnel Differences

The first question you may ask is, what is a shrink tunnel? Shrink tunnels use various warming methods to heat materials designed to shrink and conform to the item(s) being wrapped. Many shrink materials are sold with multiple tunnels to accommodate each type of material. We will discuss various shrink tunnels, the materials they are used with, and the differences between each.

How Does a Shrink Tunnel Work

Before diving into tunnel differences, let’s discuss how a shrink tunnel works. Though heat tunnels can have significant differences, some aspects are common in many models. The first is heat; all shrink tunnels will use a form of heat to shrink the packaging material. The second is a chamber holding heat within the enclosed area to accomplish a total shrink rate. The last item most tunnels have in common is a continuous conveyor moving through the tunnel. Adjustable conveyor speeds help attain the best results with a shrink tunnel. See the section below for minor adjustments to reach the best shrink results.

Shrink Tunnel Types and Differences

There are three shrink tunnel types we would like to cover and discuss the differences. They are made to package different items with efficiency and speed. Each tunnel has various chamber widths, lengths, and heights available. The wrapped products' size determines the correct chamber size for each tunnel. Before diving into sizing, we urge customers to be sure the right tunnel is purchased for the shrink material used. This guide should assist with that; we also recommend testing your products and shrink materials in a tunnel you are interested in purchasing. Testing will provide a conclusive answer in finding a suitable machine.

Recirculating Shrink Tunnel

Commonly Used Shrink Materials – Bags and Centerfold PVC & Polyolefin Shrink Wrap

Arguably the most used shrink tunnel made. Any recirculating shrink tunnel will have at least one blower. The blower moves air throughout the tunnel chamber. As the heater coils produce heat, the blowers use fans to circulate the heat throughout the tunnel.

Smaller tunnel chambers require less electrical supply and fewer blowers and heaters. Of course, this limits the capabilities in the size of the product wrapped, production speeds, and compatible materials. Smaller shrink tunnels are great for lighter PVC and Polyolefin shrink products.

As the shrink tunnel size increases, the number of heaters and blowers increases. Some more extensive tunnels can have two to three heaters and multiple blowers for air recirculation. They are capable of wrapping larger and smaller products. In addition to larger product sizes, extended shrink tunnels can heat thicker materials more quickly than smaller options.

Recirculating Bundling Shrink Tunnel

Commonly Used Shrink Materials – Single-wound Polyethylene Bundling Film and Polypropylene

A prime example of increased tunnel size and power is a bundling shrink tunnel that packages cases of drinks with single-wound polyethylene shrink film. Larger heaters and beefed-up blower motors enable these tunnels to maintain higher temperatures with less wear on the machine. Blower motors and heating zones are often fully adjustable to achieve a professional finished look. A noticeable feature of many bundling tunnels is the exterior cool-down fans. As a polyethylene shrink film cools, it continues to shrink. The exterior fans assist with the cooling and continue shrinking after the package leaves the tunnel.

Infrared Shrink Tunnels

Commonly Used Shrink Materials - PVC Neck Banding and Sleeves, Shrink Labels

The difference between infrared and recirculating tunnels is a blower motor is found in the recirculating tunnel but absent in the infrared tunnel. Precise heat can be applied to a specific product area without a blower motor. For products with a safety seal around the cap, infrared tunnels will heat only the cap without warming the rest of the product. This can be important for products vulnerable to heat exposure. Neck banding tunnels also have a smaller heat chamber for less wear and energy usage. Depending on the size of the heating area, the inside will have infrared heat lamps along the inside walls. As products pass by the lights on a conveyor, the heat exposure shrinks the material conforming to the product, which is often a bottle or rigid container.

Steam Tunnels

Commonly Used Shrink Materials – PETG Printed Shrink Sleeves

Many printed shrink sleeves over bottles use a steam tunnel for wrinkle-free branding on bottles and containers. Steam tunnels are different than the other two devices mentioned. Unlike infrared and recirculating tunnels, steam tunnels use water and create steam for heat to obtain a total shrink rate. Due to the moisture, steam tunnels are made from stainless steel. The stainless tunnels enclose the steam and heat as products pass through the conveyor.

Though the stainless steel tunnel itself is expensive and has a large footprint, the steam generator is as much or more important. A waterline is connected to the generator, which has a high-pressure chamber filled with water and heated to create steam. The steam then moves from the generator into the stainless steel tunnel cavity, where the material is shrunk down. Any quality generator will have pressure relief valves and exterior drain lines for safety.

In addition to the steam tunnel and generator, conveyor belts will be required to transport products through the tunnel. They will need to be specialized conveyors made from stainless steel parts and frames. Many conveyors will have plastic top belting for washdown and moisture exposure. With all three components, expect to spend at least twenty thousand for smaller tunnels and up to fifty thousand or more for larger units.

How To Get the Best Results with a Shrink Tunnel

Due to the vast differences in controls, sizes, and heating sources, it can be challenging to troubleshoot or offer specific instructions for your machine. Three primary adjustments can be made separately to help get the best results with a shrink tunnel. Those adjustments are conveyor speed, tunnel temperature, and possible hot/cold spots. It is important to only change one option at a time when looking for the best results.

Conveyor Speed

Increasing how fast or slow products move through the heated area can be a difference maker. If not enough shrink has been made, reduce the speed of the conveyor for a longer dwell time. If burn holes appear, increase the speed of the tunnel for less heat exposure. A temperature change will be needed if the conveyor moves at the slowest or fastest pace possible and does not achieve the best results.

Temperature Adjustment

If you notice a partial shrink and have already slowed the conveyor down, increase the temperature of the shrink tunnel. It is essential to do this in small increments without adjusting the conveyor speed. If experiencing too much shrinkage in the form of burn holes, lower the temperature inside the tunnel in small five-degree increments. The goal is to run the tunnel at the lowest temperature possible to obtain a total shrink. Less heat means less wear on the motor and internal parts. Our prior study shows how many products a shrink tunnel can package with the proper adjustments.

Hot/Cold Spots

Tunnels can have areas within the chamber that experience more or less airflow than other areas. Adjusting the product placement on the conveyor can solve problems. Products traveling through the tunnel can be moved to hit or miss these areas as needed. Another option is changing the orientation in which the products are sent through. For example, try laying products down if they are not shrinking properly when standing up.

Conclusion

There is an endless selection of heat tunnels to choose from. They vary in size, shape, and capabilities. Pay attention to the heating source. Does it come with infrared, recirculating heat, or steam? This detail will help better determine the right shrink tunnel for the application.  If you have any questions about heat shrink tunnels, call us at 1-800-441-5090.