| Excerpt Germany is
winning the battle of England. Only a few years ago it seemed
that the best trade fair for cable, satellite and multimedia
would be held in London, England, but about two years ago
one couldn't help noticing the Mediacast losing its position
in the international ranking. One after another, the exhibitors
of the London show had been dropping out, which made this
year's Mediacast appear in its slimmed down version. Anga,
which has only a five-year history, is becoming the largest
European meeting for the cable, satellite and multimedia sector.
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Terra presented some new elements for the main station: receivers
equipped with modulators with NICAM stereo audio. Thanks to
its 19" housing, built-in power supply, and programmability,
the device can work independently. The new 17-input multiswitches
enjoyed a great deal of attention.
.............
ADB, Polish tycoon of the "intelligent tuners"
branch, is broadening its product assortment with equipment
based on the MHP platform. ADB-3100TW is an integrated machine
combining a SAT receiver and a Video over IP. The features
like 128 MB RAM, 64MB flash EEPROM, FireFox browser speak
for themselves. The device comes with the IF and RJ-45 sockets.
It is capable of playing films coded in MPEG-2 and 4 at the
of 1.5 and 4 Mbit/s.
............
The work formulates equations describing the electromagnetic
field in the inductive soldering process and the temperature
field both in the inductive and the torch soldering. It allows
the two methods to be treated in a more complex way. The mathematical
and numerical models prepared can be used as a tool to determine
parameters such as the electromagnetic field and thermal field
for the soldering process. The proposed mathematical model
provides optimal solutions for a given problem. In the modern
technology, soldering (as a metal bonding technology) is one
of the most popular. Its whole idea is based on joining metallic
surfaces with solder, without the melting of the base materials.
Solders are made of fusible alloys whose melting temperature
is much lower than that of the base materials. In the soldering
process there is no melting of parts being joined. The melted
alloy bonds with the material thanks to the intermolecular
attraction of elements, which is called cohesion. The work
presents a numerical model for soldering of cylindrical elements
in the inductive and torch soldering. The model allows to
determine the temperature field in an object being soldered,
which is dependent on the type of torch, its distance from
the object, and heating time. In case of the inductive soldering
one can determine the temperature of the objects being soldered
by analyzing parameters of the inductor in use. Thanks to
its numerous advantages, the inductive technology is widely
applied. The only problem is to set the right parameters for
the soldering process. The parameters are usually set through
experimentation, which sometimes tends to prove rather expensive.
The models presented can be utilized for setting parameters
in a numerical way. The spread of heat in a material during
the heating process depends on the type of material, its thermal
properties, geometry, location, type of environment it is
in, and the power delivered. The temperature range and the
spread of heat are affected by not only the power itself but
also by the heating time. A detailed description of all phenomena
of physics taking place in the heat exchange (between the
material and its surroundings) is rather complicated and difficult
to be generalized. The problems of the heat exchange have
been discussed in the monograph, in which the author conducts
a thorough analysis of them based on a reference model. In
reality, the physics of the heat exchange is even more complex.
For convenience, the model has been simplified to heat exchange
through radiation and convection, under the assumption that
the thermal exchange coefficient a depends on temperature.
The heat produced by cohesion can be calculated by certain
relationships. The value of the a coefficient depends on the
following factors: the size of object, its location (horizontal,
vertical), surface material properties, environment properties
(density, thermal conductivity, specific heat), and temperature
differences. Energy radiated per unit surface area (the energy
flux density) in unit time can be determined by Stefan-Boltzmann
law.* In calculating temperature of elements being soldered,
it is convenient to express the radiated energy flux by *
where a is a thermal exchange coefficient. Since the flux
q in not proportional to the difference of temperatures, the
a coefficient will not be a constant, but it will change according
to temperature. The entire thermal flux can be determined
as a total of thermal flux produced by convection and radiation.
The a coefficient describes the ability of the heated object
to release energy through its surface into its surroundings.
The temperature-dependent value change of this coefficient
has been approximated with the use of empirical data.
With the application of Bubnow method in the equation * that
has a base function f withing the A area, and after integrating
the equation, the result is the classic numerical formula.
Because the temperature in the intersections of the grid depends
on time, a proper approximation should be thus used. The cooling
after the heating is modeled on the Newton boundary condition. |
