written by: Jesma•edited by: Lamar Stonecypher•updated: 11/5/2009
In this informative article about laser printers, we specifically focus in on the fuser in a laser printer and how it works, as well as how to spot a bad fuser and find a replacement.
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Laser printers are complex machines. Part of my training in school was to become intimitely familiar with every component of a laser printer and how it works. I once had a test question where I had to describe every single step a laser printer takes to create a picture on paper medium - talk about boring! And, while I have never found any use for this knowledge (mostly because I'm about as likely to stick my hands near a burning hot fuser as I am to dip them in bacon greese and hand feed a pitbull) some people are much braver than I, and may find it useful to, at the very least, know how a laser printer works and, more importantly, what a fuser is and does.
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Laser Printer Parts
I will confess, the nice thing about laser printers is pretty much every part is relatively easy to replace. They cost a lot of money when compared to, say, Inkjets, so people are very big on making them last a long time. The fuser is definitely one of the replaceable components, and one of the more likely to eventually need it simply because of it's crucial role and the toll high heat takes on all electronic components. To get an idea of the availability and cost of new fusers, do a simple google search for "buy new fuser", or just click here.
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How it Works - Static Electricity
While the term "inkjet" pretty effectively describes the technology inside the machine (little nozzles shooting ink very quickly), the term " laser printer" is a bit more elusive. How, exactly, does a focused beam of light inscribe information on a piece of paper? I'm sure you can guess that it isn't by burning an image into it, but let's go into how exactly this technology works.
The principle behind laser printing is actually static electricity. Static electricity is the same stuff that makes your clothes cling, shocks you when you touch your car door handle, and also what causes lightening bolts. In scientific terms, since oppositely charged atoms are attracted to each other, you can oppositely charge objects to make them cling.
The first step of printing on a laser printer is the photoreceptive drum (a rotating cylinder) is given a positive charge across its whole surface. From there, the laser unit will essentially draw the image onto the roller by discharging certain points. After the image has been invisibly inscribed on the drum, the printer coats the drum in a positively charged toner. Laser printer toner is a very fine black powder - not ink at all. Since the inscribed area has a negative charge, the toner will cling to it. Since the rest of the drum, the "background", so to speak, has a positive charge, it rejects the toner. After that, the drum rolls across a heavily negative charged piece of paper, pulling the toner onto it.
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The Fuser's Job
After the loose powder is set on the paper via static electricity, the paper is passed through the fuser. The fuser is basically two heated rollers. As the paper passes through, they actually melt the toner causing it to bind onto the paper permanently. Out of the whole machine, the fuser has one of the least technically confusing jobs. Basic science tells us that very hot things melt - or combust.
A lot of people reason, though, that the fuser really isn't that hot since, if it were, it would burn up the paper. Wrong. The only thing that keeps the paper from combusting is the speed at which it passes through the fuser. If it were to become stuck along the way it would most certainly catch on fire. This means that fusers can be very dangerous to body parts as well - you don't want to go near a recently used or active fuser.
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Identifying Fuser Problems
The fuser component, as mentioned above, is one of the most common to wear out simply because of the effect intense heat has on electronics. Since its operation is temperature based, it can be adversely effected by electronic deterioration, which can cause the temperature to rise or fall.
One of the easiest ways to spot a faulty fuser is smudging on the page. Laser Printers are nice because when a page come "hot off the press" (quite literally, HOT) the "ink" is completely dry. A faulty fuser, however, will often not heat the toner enough to set it, or dry it, resulting in smudging on the page.