
B-63943EN/02 3.INSTALLATION
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3.4 THERMAL DESIGN OF THE MACHINE TOOL MAGNETIC
CABINET
The internal air temperature of the cabinet increases when the units
and parts installed in the cabinet generate heat. Since the generated
heat is radiated from the surface of the cabinet, the temperature of the
air in the cabinet and the outside air balance at certain heat levels.
If the amount of heat generated is constant, the larger the surface
area of the cabinet, the less the internal temperature rises. The
thermal design of the cabinet refers to calculating the heat generated in
the cabinet, evaluating the surface area of the cabinet, and enlarging
that surface area by installing heat exchangers in the cabinet, if
necessary. Such a design method is described in the following
subsections.
3.4.1 Temperature Rise within the Machine Tool Magnetic Cabinet
The cooling capacity of a cabinet made of sheet metal is generally 6
W/°C per 1m
2
surface area, that is, when the 6W heat source is
contained in a cabinet having a surface area of 1 m
2
, the temperature
of the air in the cabinet rises by 1°C. In this case the surface area of
the cabinet refers to the area useful in cooling , that is, the area
obtained by subtracting the area of the cabinet touching the floor from
the total surface area of the cabinet. There are two preconditions :
The air in the cabinet must be circuited by the fun, and the
temperature of the air in the cabinet must be almost constant. For
example, the operator’s panel cabinet may contain an LCD-mounted
type control unit or the display of a stand-alone type control unit. To
keep the temperature in the cabinet at 58°C or below when the
ambient temperature is 45°C, the equation below must be satisfied.
Internal heat loss P [W] ≤
6[W/m
2
⋅°C] × surface area S[m
2
] × 13[°C] of rise in temperature
(A cooling capacity of 6 W/°C assumes the cabinet is so large that
agitation with the fan motor does not make the temperature
distribution uniform. For a small cabinet like the operator's panel, a
cooling capacity of 8 W/°C, indicated in Subsection 3.4.4, may be
used.)
For example, a cabinet having a surface area of 4m
2
has a cooling
capacity of 24W/°C. To limit the internal temperature increase to
13°C under these conditions, the internal heat must not exceed
312W. If the actual internal heat is 360W, however, the temperature
in the cabinet rises by 15°C or more. When this happens, the cooling
capacity of the cabinet must be improved using the heat exchanger.
For the power magnetic cabinet containing a stand-alone type control
unit, the internal temperature rise must be suppressed to 55°C or less,
instead of 58°C.