Vectronics VEC-1500K - Manual (Page 21)

16
Heat Source
Tip
Solderable Metals
Element
Tip
Solderable Metals
Hot
Heat Sink
in Connection
Cool
Exchange
Heat Source Heat
in Connection
Mass, Temperature, and Thermal Energy: The amount of heat energy stored
by your iron depends on several factors, but the two most important ones are the
tip's mass and the tip's temperature.
Mass: As the iron's element pumps heat energy into the barrel and tip, the
molecules move faster--causing the tip to get hotter. When the iron makes
contact with a cold connection, heat energy is liberated and the molecules start to
slow down. The greater the metallic mass, or the more molecules you have in
your tip, the more thermal energy it will store for every degree of temperature
rise.
An iron with a big tip stores more thermal energy for every degree of
temperature rise than a small one. That's because more molecules are available.
Temperature: The higher the tip's temperature rises, the more thermal energy
you can store (per ounce, gram, or whatever). That's because it takes more
energy to make a fixed number of molecules move faster. Conversely, the
further the temperature drops, the more energy you can liberate. Faster-moving
molecules have more energy to give off.
To put this in perspective, say you need to heat a connection to 400 degrees F so
it will melt solder. It makes sense that a 800-degree F tip will contribute more
thermal energy to the heating process than an identical tip heated to only 600-
degrees F. However, a more massive tip heated to 600-degrees F could
contribute the same amount of energy as the less massive 800-degree F tip--
because more storage mass is available in the bigger tip.
600-F
800-F
Thermal energy storage depends on
both MASS and TEMPERATURE.
Without getting into BTUs (British Thermal Units) and the finer points of
hermodynamics, we can generalize the concept and say: