OCTOBER 2005 GENERAL INFORMATION 87
SIEMENS
MAINTENANCE MANUAL
5.4 SOLVING THE
THERMAL EXPANSION
PROBLEM
5.4.1 GENERAL CON-
SIDERATIONS
A simplified description of the thermal environment in machining would state that heat
is generated through friction, and also input through ambient factors. That heat is
transferred among the system components, and is either removed from the system
through radiation, convection and evaporation, or absorbed by the components of the
system (part, fixture, VMC).
In its simplest form, any solution designed to combat thermal expansion must reduce
friction, reduce ambient influences, or increase heat removal through radiation,
convection or evaporation. A complementary approach is to simply compensate for the
changes brought on by thermal expansion. In a real life situation, a balance of
approaches is required.
5.4.2 AMBIENT
SOURCES
Sunlight
Do not allow direct sunlight on the VMC. Window shades that diffuse sunlight can be
acceptable, but any source of warmth that only heats one side of the VMC at a time will
cause uneven warming and further complicate thermal considerations.
Cooling Systems
Diffusion gratings on air conditioning vents can be used to prevent any air from directly
blowing on the machine or part. Again, an unevenly heated part or machine will cause
the heated, or cooled, portion of the part or machine to expand at rates different from
the rest of the part or machine.
Radiant Heat
If an operator can detect the radiant heat from other devices, a protective wall needs to
be erected between the machine and the device radiating the heat. This type of heat
source will cause the machine to heat up on one side and cause uneven expansion.
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