7
front door plate
Fig.2-9
current-resistant
constructure
oven door
noise filter
Heating chamber is the place where the microwave and the food affect mutually. There are lots kinds of chamber.
Accord-ing to the working characters, it can be classified to carton type, cavity type, radiation type, slow type
(surface wave type), etc. The present adopt chamber for food cooking microwave oven is the typical carton type
heating. (FIG.2-8). The heating chamber is mainly composed of oven door and oven cavity. From the microwave
theory, it is a microwave resonant cavity that can contain many kinds of oscillating models simultaneously.
Microwave enters into the oven cavity through the wave guide and the coupling appliance, and most of its energy
is absorbed by the food after it is reflected in the cavity repeatedly, those which haven’t been absorbed will be
reflect to the magnetron. A good designed oven cavity should have a good impedance matching with the
magnetron, the energy should be less reflect, and distribute evenly in the oven cavity, improve the heating
efficiency. Generally, at the same input power, the larger the cavity, the less the energy density a unit volume
would have in the oven, and the more energy on the inside wall of the cavity would lose, thence, it would certainly
slow down the heating speed, low the heating efficiency. Moreover, too big of the cavity would either waste the
material or appears very heavy. The material for cavity usually use non - magnetic stainless steel or zinc - plating
steel, and have no high requirements for the conducting rate. The inside coating of the cavity requires beautiful in
look, durable when use (should be resistant against damp, heat, acid and alkali), it should also comply with the
food health requirements.
To improve the heating evenness there often fixed a turntable glass tray at the bottom of the cavity (FIG. 2-8). It is
through changing the relative place of the microwave and the heating matter to improve the heating evenness.
The turntable tray is usually made of heat – resistant glass, the glass contains some dielectric loss, it can,
somewhat, protect the magnetron when the cavity loading less.
There often fixed a dust – proof, low – loss and heat – resistant dielectric cover (such as mica sheet). Sometimes,
an impedance matching metal stick was fixed near the coupling or in the wave guide.
The door is designed for inspecting, taking and placing the heating food, it is also one side of the cavity (FIG .2 -
8). It is the most liable place where microwave leakage occurs. Especially, after a long time using, the microwave
leakage would enlarge at the hinge and the hook. Anyway, mechanic damage would also cause large amount of
microwave leakage. Therefore, the main methods designed for preventing microwave leakage of the door are as
follows:
1) Assemble a layer of steel filament or a thin metal plate with many holes at the middle of the window to made it
is possible to observe the heating as well as shielding the microwave.
2) The widely used seal measurement at present
is to assemble a current – resistant construct
between the door and the doorframe. FIG.2-9 is
the typical construction fig of the door. It was
designed according to the theory of
“THETRANSFERING LINE ONE–FOURTHWAVE
LENGTH IMPEDANCE CHANGER”. Although
there is no connecting point from a mechanical
point. It is sealed at the seam from the point of
electricity, so it is called “CURRENT-RESISTANT”.
1. Safety interlock switch
2.
Door
window
3. Air vent
4. Roller Shaft
5.
Turntable
supporter
6. Glass tray
7. Light touch control panel
Fig. 2-8
