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Within a few seconds only, a paper passes through the printer/copier/MFP (printing device) and comes out with high quality texts and graphics imprinted on it. The printing device is made of different parts and assemblies. The Fusing-Unit is one of these parts that play a very important role in printing. This is where toner is melted and compressed to leave impressions on paper with the use of heat.


Fusing-Unit of HP LaserJet 8150N Laserprinter


Fusing-Unit of Konica Minolta Bizhub C252 MFP

The Fusing-Unit usually comes as a removable unit with parts that needs to be replaced from time to time. The printer Fusing-Unit is seen as two heated rollers (some even with very thin flexible metal coating) – a reason why papers come out warm and crisp on trays. However, there is more than meets the eye. The fusing is an intricate and exact process of pressing the toner on paper with heat; along with other mechanical and electrical parts.

Main components

Heat roller. There are two pairs of rollers in the fuser assembly. One is made of a hollow tube loaded with heating properties and the other fitted with rubber backing that is responsible for compression and having a better grip on paper. Both rollers are also coated with Teflon (a similar coating found in non-stick frying pans) which keeps toner and paper from sticking as it passes through.

Discharge lamp. Also known as the quartz lamp, the discharge lamp is an ultraviolet light source (strong bluish light) made of mercury vapor in an arc tube. This is located internally in rollers which makes the heating process easier and faster.

Function in the Printing Process

Fusing concludes the printing process. It covers the final steps of creating the desired impression on the paper. Although much of image development occurs on the drum-unit, the two rollers of the fuser unit are responsible for the final output.

As paper passes through the fuser assembly, the upper roller melts and fuses the toner on paper via the internal quartz lamps – depending on the device – at around 200 °C (392 °F). From there, the plastic in toner is melted and thereafter bonded with paper. It is necessary for both rollers to be heated at the same temperature in order to leave high quality impressions and in a faster pace. The slower the fuser heats up, the more decelerated the printing speed will be. This can be observed in inexpensive printers or those units set on eco-mode.

The warm-up time in printers is set to give rollers enough time to heat up. During the fusing process, the paper faces the heated roller while the other roller compresses the toner to create the desired impression before making its way out to the output tray. The same process applies to color laser printers; only it is repeated 4 times or as many times depending on the number of toner color used.


The Fusing-Unit uses heat and pressure during the printing process. Frequent printing therefore makes it prone to wearing out. Keeping this printer component in good shape requires periodic cleaning and replacement of the parts of its assembly.
More often than not, a bad or broken fuser causes numerous print defects leading to wasted supplies and energy.


Toner Powder Build Up. During the printing process, toner powder latches not only on the paper’s surface but also on other printer parts. This predisposes the machine to toner build-up along with other dust particles. When left uncleaned, it causes scratches on the fuser’s surface which is responsible for the linear defects on printouts. Once these lines appear over printouts, it is time to replace the fuser assembly. In most printers, a warning sign is prompted on screen to alert the user on the need for installing new parts.

Overheat. In some cases, fusers may overheat or not warm up at all– both of which causes the printer to halt printing. Overheat transpires when the printer prints more pages than its stipulated monthly duty cycle. A small workgroup printer for example that frequently handles large volume print jobs would eventually succumb to overheating the fuser unit. With this, the printer will flash an error message and desist with print jobs until the fuser unit cools down.

Power Issue. When printer does not have enough power to heat up the rollers, this leads to malfunction or defective printouts. What is therefore recommended is to provide the printer and computer with direct power supply from the wall sockets instead of the surge protector.

The rollers are the easiest to wear out. Therefore, constant replacement is needed. There are two types of kits most printer owners use: the fuser kit and the maintenance kit. Both kits are supplied with almost the same replacement parts. The difference lies in the brand of the kit and printer.

As its name suggests, the comes supplied with the printer fuser assembly or heating roller unit. Some parts of the fuser assembly are sold separately. Thus, users can opt to buy only the heating roller (upper roller) or pressure roller (lower roller). Some fuser kits may include the fuser film in the package. The mentioned parts are also supplied in some maintenance kits. Fuser kits are available from both OEMs and remanufacturer. So far we have decided not to supply Fuse

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