Brother HL-4000CN Service Manual page 92

1.3.10 Fixing
In the fixing process, toner is fixed on the paper by heat and pressure.
Finished toner image transferred from the belt is easily broken only by touching it
with fingers. The toner image is fixed on the paper with the fuser ASSY (fixing unit).
The toner melts by heat of the heat roll with the heater lamp as the heat source and
is deposited on the paper under pressure given by the belt opposed against the heat
roll.
Paper
Spring Nip
Fixed toner
Nip Head
Belt
Heat Roll
Felt
Heater Lamp
Frame Belt
Sheet
Not fixed toner
Pad
Fig.3-21
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