What does the fuser on a printer do?

[isasir]

The ink on the left side of the pages that are coming out of my company's HP4050 printer is smearing a bit. I recently replaced all the rollers, but did not replace the fuser, which from what little I've read is likely the cause. I couldn't find a good link online though to explain how to know for sure if a fuser is going bad.

 

[networkman]

The fuser is the part of the printer that melts the toner onto the paper, so if it were malfunctioning, smears from melted toner would likely result.

 

[Rage187]

The fuser is used to melt the toner onto the paper to create a permanent image. The fuser system is composed of the hot-roll and the back-up roller. Once the toner is transferred to the paper, heat and pressure are applied by the fuser to create the permanent image. The fuser is what makes the paper warm when it comes from a laser printer.

 

[Ken90630]

Fuser rollers not only melt the toner into the paper, they also press it in. There are 2 fuser rollers in a typical copier, laser fax machine, or laser printer: an upper one and a lower one. The upper one is typically teflon coated, hollow, and contains a halogen heat lamp (typically somewhere between 150 and 200 degreees F). The upper roller's temperature is monitored by a small sensor pad called a thermistor, which cycles the lamp on & off and keeps it hot enough (or allows it to cool down when in a "power save mode").

The lower fuser roller -- the pressure roller -- is typically made of soft rubber. Lower FRs are solid, with no lamp inside. When you print/copy a page, the toner is transferred from the drum surface onto the paper (as the paper passes under the drum). It is then transported to the fuser unit, where the combination of heat from the upper roller and pressure from the lower roller melt, or "fuse," the toner into the paper's fibers.

There can be several reasons for toner smearing. If the upper teflon roller's surface is worn away in some spots, toner can smear and not be fused into the paper in that spot. Lower fuser rollers can sometimes wear unevenly, thus providing uneven pressure to the paper in some spots. Again, smearing can result. Lastly, worn fuser bearings (upper or lower) can cause the rollers to either bind up (sometimes intermittently, sometimes entirely) or allow the rollers to 'flop around' just a little, causing a wide enough gap between the upper & lower rollers to prevent enough pressure from being applied to the paper.

There is actually a very simple way to determine if smearing is being caused by the fuser rollers (rather than some other part of the machine). You can print a page and then stop the machine -- either turn the power switch off, or open a door or something on it -- before the page has hit the fuser unit. Stop it midway, in other words (and the machine will jam -- that's okay). Open the machine carefully and look at the image on the paper. If it is smeared before it has hit the fuser, the smearing is coming from somewhere else (maybe a worn drum wiper blade). If it looks great at that stage, then smears later, then you know it's coming from the fuser. This is easy for me to do, as I was a copier/fax tech for many years, but not so easy for a novice. Any tech worth his/her salt, however, can do this quickly and easily for you. And if you can look at the upper FR, you can usually see worn spots if they're there.

Having said all this, don't just assume smearing is coming from the fuser. There can be other causes in a laser printer, copier or fax machine. Fuser rollers are typically not cheap, so be sure (nor is the labor to replace them, unless they're in some sort of module that is user-replaceable, and I haven't seen any of those on a laser printer).

Hope this helps. Good luck. 🙂