How to Choose an L-Bar Sealer and Shrink Tunnel

By US Packing Equipment Team · · Updated

An L-bar sealer and a shrink tunnel work as a pair: the sealer closes the film around the product, and the tunnel shrinks it tight. Size the sealer from your largest pack and your packs per minute, then choose a tunnel whose belt, opening and heating length match the sealer. This guide shows how.

How an L-bar and tunnel line works

Shrink packaging with an L-bar sealer starts with centerfold film: a roll of film folded in half along its length. The product is placed between the two layers. The L-shaped sealing bar comes down and seals the open side and the end of the pouch in one stroke, cutting the sealed pack free from the roll. The pack now sits in a loose film bag.

The heat step follows. In a shrink tunnel, the pack rides on a conveyor through hot air, and the film shrinks tightly around the product on all sides. Small perforations let the trapped air escape. The result is a clear, tight wrap that keeps dust out and shows if the pack has been opened.

Step 1: choose the sealer type

Manual L-bar systems

Manual systems such as the AIE L-Bar Shrink Wrap System are the simplest start. The operator lowers the bar by hand; an impulse bar needs no warm-up. The film is shrunk with a heat gun. AIE offers seal areas from 13″ × 13″ to 24″ × 32″.

Hood sealers

Hood sealers seal and shrink in the same chamber, so they need no tunnel. The Maripak Compack 5800i wraps about 5–10 packs per minute per Maripak, runs without compressed air and has a 23″ × 17″ seal area.

Semi-automatic L-bar sealers

On semi-automatic machines such as the Maripak LMC 5844-M, a motor closes the bar, either at a set interval or at the push of a button. Per Maripak, the LMC series wraps about 10–15 packs per minute. These machines feed a separate tunnel.

Sealer and tunnel in one

The Maripak TMC Pro 5844-M combines a semi-automatic L-bar and a tunnel in one machine, at about 10–12 packs per minute per Maripak. It saves floor space and the work of aligning two machines.

Automatic L-sealers

Automatic machines such as the Maripak RLS e-Pro detect product length with a sensor and wrap products continuously from an infeed conveyor. They are the step for continuous production.

Step 2: size the seal area

Measure the length, width and height of your largest pack. The seal area must be larger than the length and width, with room for the film to wrap around the height. As a rule of thumb, taller products need more margin, because the film has to cover the height on both sides. Also check the bar opening: standard Maripak semi-automatic models open 10″, and taller chambers are available as an option on several models.

Step 3: match the tunnel

Belt width and opening height

The pack must fit the conveyor belt and the tunnel opening, with some room on each side. The Maripak Diamond T-45 has an 18″ belt and a 10″ opening (16″ optional); larger Diamond tunnels go up to 59″ belts. The AIE infrared tunnel comes with openings from 14″ × 6″ to 16″ × 12″.

Heating length and speed

The film needs a certain time in the heat. A tunnel that is too short for the line speed leaves loose film; you can slow the belt, but then the tunnel limits the line. For faster lines and thicker film, an extended-length or double-chamber tunnel gives more time in the heat at the same speed.

Airflow

Diamond tunnels have the heater and fan in the bottom and adjustable flaps and channels to direct the air. AIE infrared tunnels heat from four sides with separate upper and lower controls. Good airflow control is what turns a loose wrap into a tight one without burn-through.

Setup Sealer Heat step Output per maker Compressed air
Starter AIE L-Bar Shrink Wrap System Heat gun (sold separately) 1–4 s per seal (AIE) No
Hood sealer Maripak Compack 5800i In the same chamber About 5–10 packs/min No
Semi-automatic Maripak LMC 5844-M Separate tunnel, e.g. Diamond T-45 About 10–15 packs/min No
Combination Maripak TMC Pro 5844-M Built-in tunnel About 10–12 packs/min No
Automatic Maripak RLS e-Pro 5844 Separate tunnel Conveyor up to about 98 ft/min Not for standard products

Step 4: choose the film

Polyolefin is the most common shrink film for retail packs: it is clear, strong and shrinks evenly. PVC is still used for some applications. Each sealer lists the films and thicknesses it handles; the LMC series, for example, lists POF of 30–120 gauge and PVC of 60–100 gauge. Read Shrink Film Types for details and estimate film use with the Shrink Film Calculator.

Step 5: check power and space

Hood sealers and the LMC series run on 200–240 V single-phase power without compressed air. Shrink tunnels need more power: the Diamond T-45 needs 220 V three-phase, 51 A, and larger tunnels need more. The TMC Pro needs 220 V single-phase, 50 A. Check your supply with an electrician before ordering, and plan floor space for the sealer, the tunnel and a table at the tunnel exit where packs cool and are collected.

How fast do you need to be?

Count your packs per hour in the busiest hour, not the average. Up to a few packs per minute, a manual system or hood sealer works. From about 10 packs per minute, a semi-automatic L-bar with a tunnel or a combination machine makes sense. Continuous production calls for an automatic L-sealer or a side sealer with a tunnel and conveyors.

L-bar or side sealer?

L-bar sealers suit lines where packs are similar in size. If your products are long or their lengths change often, a side sealer may fit better, because it seals along the product and the length is not limited by a bar. See Side Sealers.

Common mistakes

Choosing the tunnel last is the most common mistake: a tunnel that is too narrow or too short limits the whole line. Others are underestimating power needs, forgetting space at the tunnel exit, and using a film that does not match the sealer's film list. Plan sealer, tunnel, film and utilities together.

Starter and hood systems: the AIE L-Bar Shrink Wrap System and the Maripak Compack 5800i.

Semi-automatic: the Maripak LMC 5844-M with a Diamond T-45 tunnel, or the TMC Pro 5844-M.

Browse all L-bar sealers and shrink tunnels, or use the L-Bar Sealer & Shrink Tunnel Selector.

Machines in this guide

Frequently asked questions

Do I need a shrink tunnel with an L-bar sealer?

Not always. Manual L-bar systems can work with a heat gun, and hood sealers shrink in their own chamber. From about 10 packs per minute, or when every pack must look the same, a shrink tunnel gives a faster and more even result. Combination machines such as the TMC Pro include the tunnel.

How do I match the tunnel to the sealer?

The tunnel belt must be wider and the opening taller than your largest pack, with some room around it. The heating length must keep up with the sealer's speed. For faster lines and thicker film, choose an extended-length or double-chamber tunnel.

What is centerfold film?

Centerfold film is shrink film folded in half along its length and wound on a roll. The product is placed between the two layers, and the L-bar seals the open side and the end. Choose a film width that matches the sealer and your pack size.

Why does my shrink wrap have loose corners or holes?

Loose corners, often called dog ears, usually mean too little heat or air, the wrong film or too much film around the pack. Holes usually mean too much heat or too slow a belt. Adjust the tunnel temperature, speed and airflow, and check that the film matches the sealer's film list.

Which warranty applies to these machines?

Each machine is covered by its manufacturer's warranty; the terms are listed on each product page. If you have a question about a specific model before ordering, call +1 469-809-4363 or send a quote request, and we will answer it in writing.