Choosing an Electric Motor for the Hot Air Fan of a Shrink Packaging Machine

A standard three-phase motor is the right choice for the hot air fan of a shrink packaging machine only if the motor frame stays outside the hot zone of the tunnel. The fan impeller turns in the hot air next to the heaters, while the motor stands outside the tunnel wall and reaches the impeller through an extended shaft or a belt. Before power and speed, one question must be answered: how hot is the air where the motor sits?

In this article we look at the circulation fan in shrink tunnels: the position of the motor, starting in a cold tunnel, choice of speed and mounting, and the information needed for a replacement.

How are the fan and motor arranged in a shrink tunnel?

In the tunnel, the film shrinks around the product with heat. Heating elements warm the air, and the circulation fan moves this air around the tunnel and directs it at the product. There are two common arrangements:

• Direct-coupled arrangement with an extended shaft: The motor stands outside on the tunnel roof or side wall; the impeller is fitted to the end of the motor shaft or to an intermediate shaft with its own bearings, and the shaft passes through the wall.
• Belt arrangement: The fan shaft runs in separate bearings, the motor is placed a little further away at a cooler point and power is transmitted by pulleys.

In both arrangements the motor does not run in the hot gas. Placing a standard-frame motor inside the tunnel, next to the heating elements, is outside the scope of this article; that task requires a special motor rated for high temperature and may fall outside the standard range in HEM Motor's 2026 catalogue.

Where does the temperature the motor sees come from?

Even when it stands outside, the motor is not completely free of heat. Three paths need attention on site:

• Conduction through the shaft: If the impeller is mounted directly on the motor shaft, the heat of the hot impeller travels along the shaft to the front bearing. Bearing grease and bearing life are affected by this path.
• Through the wall and leaks: Hot air escaping through the gap at the shaft passage and through tunnel covers is drawn in by the motor's fan cover. Since the motor is cooled by its own fan blowing the surrounding air, cooling weakens if the air drawn in is hot.
• Radiation: As the tunnel body heats up, it also heats the nearby motor frame.

So, when replacing, measure the air temperature at the point where the motor sits or obtain it from the machine manufacturer, and state it in the order. Instead of guessing the temperature and relying on IP55 and class F insulation, a solution should be discussed if it is high: an intermediate shaft moving the motor a little further away, a heat barrier in between, a clean air supply around the motor, or a switch to a belt arrangement. These layout decisions are part of the machine design.

Starting in a cold tunnel: why is the load higher in the first minutes?

The power a fan draws at a given speed changes in direct proportion to the density of the air it moves. Cold air is denser than hot air. When the tunnel is started cold in the morning, the fan moves heavier air than in a warmed-up tunnel and the motor is more heavily loaded. As the tunnel heats up, the air becomes lighter and the power drawn by the fan falls.

As a result, the motor should be assessed not for hot running of the tunnel but for the cold start and warm-up period. If the old motor ran without trouble, its nameplate power is the safest reference. If the thermal relay trips during warm-up, the cause may be a changed impeller or a different filter or duct layout as much as an undersized motor; check these first. For the thermal relay setting, see our motor protection article.

When shutting down the tunnel, cutting the heaters and keeping the fan running for a while longer is a method used on many machines; this way the accumulated heat does not travel towards the motor. If your machine's control includes this delay, it should be kept after the replacement as well.

Speed and speed adjustment

In direct-coupled fans, the motor speed is the fan speed; when replacing, the same number of poles as the old motor must be kept. Fitting a 4-pole model in place of a 2-pole motor clearly reduces the air flow, while doing the opposite overloads the impeller and the motor. With a belt arrangement, adjustment is possible through the pulley ratio, but the permitted speed of the impeller must not be exceeded.

Plants that want to change the air speed for different film thicknesses use a frequency inverter. Our three-phase ranges are suitable for speed control with a frequency inverter; for long periods of full-torque operation at low speed an external fan may be required, and if the cable between drive and motor is long a dv/dt or sine filter is considered; these conditions are stated with the order. Details are in the inverter question. Remember that at low speed the motor's own fan blows less air, which matters in a hot environment.

Review suitable HEM Motor models and current prices on the buy electric motors page.

Mounting arrangement and frame

For impellers that come down from the roof, the motor often runs vertically with the shaft down; for impellers entering through the side wall, horizontal flange or foot mounting is seen. B3, B5, B14, B34, B35 and vertical V1/V3/V5/V6/V15 options are offered according to the frame; the flange size is confirmed with the order. In a vertical shaft-down arrangement, the impeller weight and the hot shaft load the bearing together; our vertical mounting article gives guidance on this. Do not guess shaft and flange dimensions; compare them with the 2026 catalogue and the technical drawings.

In packaging machines, motors are usually on an enclosed, relatively clean line; a light aluminium frame therefore makes installation easier for motors hung from the roof. For other packaging applications, see the packaging machinery motors page.

Example models for shrink fans

The following models are examples of the power range found in small and medium tunnel fans; the correct power is determined from the existing motor's nameplate and the fan information.

• 80M2-4 aluminium frame: 0.75 kW, 4-pole, 1,420 rpm, IEC 80M, 230/400 V.
• 90S-4 aluminium frame: 1.1 kW, 4-pole, 1,445 rpm, IEC 90S, 230/400 V.
• 100L1-4 aluminium frame: 2.2 kW, 4-pole, 1,450 rpm, IEC 100L, 230/400 V.
• 90S-2 aluminium frame: 1.5 kW, 2-pole, 2,895 rpm, IEC 90S, 230/400 V; if the existing fan runs with a 2-pole motor.

Hypothetical example: renewing a tunnel fan motor

The following situation is a hypothetical example. Suppose that in a shrink tunnel, the bearing of a 1.1 kW, 4-pole motor mounted vertically on the roof fails repeatedly. The investigation could be set up as follows:

• The nameplate reads 1.1 kW and around 1,445 rpm; the 90S-4 model with the same power and number of poles is selected.
• It is found that the impeller is mounted directly on the motor shaft and that the seal at the shaft passage is worn; escaping hot air is heading towards the motor's fan cover.
• The seal is renewed, fitting a heat barrier between the motor and the tunnel roof is discussed with the machine manufacturer, and the temperature around the motor is stated in the order.
• The flange size is compared with the technical drawing and the vertical mounting arrangement is specified in the order.

In this example, a larger motor would not have solved the problem; the cause of the failure was the path by which heat reached the bearing.

Conclusion and information to send before ordering

Choosing the motor for a shrink tunnel fan starts with correctly defining where the motor sits and the temperature around it; power and speed come from the existing motor's nameplate. Send us: a photo of the existing motor's nameplate, whether the fan is direct-coupled or belt-driven, the mounting arrangement and flange details, the supply voltage, whether speed control is used, and the temperature at the point where the motor sits. You can see suitable models and current prices on the buy electric motors page. Send a photo of your current motor's nameplate, its speed and mounting details via the send motor nameplate page and request a quote for the right model. The fan and extractor motors page also helps for fan applications; for questions, use our contact page.

Frequently Asked Questions

Can a standard motor be placed inside a shrink tunnel?

No; a standard-frame motor is not presented as running inside hot air. The motor must stay outside the tunnel and reach the impeller through an extended shaft or a belt; operation inside the tunnel requires a special motor.

Why does the motor draw more current at the first start in the morning?

Cold air is denser and the fan needs more power at the same speed. As the tunnel heats up the load falls; the motor should be assessed for this cold-start period.

Can I use an inverter to adjust the air speed?

Our three-phase ranges are suitable for speed control with a frequency inverter. For long periods at low speed an external fan may be required, and this condition should be stated with the order.

If bearing failure keeps recurring, should I buy a bigger motor?

Usually the problem is not the power but heat reaching the bearing through the shaft and leaks. First check the shaft passage, the seal and the temperature around the motor.