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ZS6HK > TECH 13.11.04 07:03l 49 Lines 2252 Bytes #999 (0) @ WW
BID : 670523ZS6HK
Read: GUEST
Subj: Re: Radio Frequency Heating.
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Sent: 041112/1929Z @:ZS0DLD.PTA.GAU.ZAF.AF #:51306 [Pretoria] $:670523ZS6HK
From: ZS6HK@ZS0DLD.PTA.GAU.ZAF.AF
To : TECH@WW
Hi all, I only just found the message from Pete about eradicating little
worms with RF, and the reply from Dick, VE3ABK.
There are three main ways in which timber gets heated with RF for glueing
or drying. One is to position electrodes either side of the wood to be
joined, in parallel with the glue lines. The load is matched to the
oscillator with a series inductor, and the coupling to the oscillator is a
single turn link to the tank coil.. If the capaciatance of the load is too
high to obtain a match then low loss capacitors are put in series with the
output, the power output being adjusted by varying the tuning of the
inductor. this technique is commonly used for formiong shapes laminates
for seat chairs and backs. The second method is called "glue line heating,
where the RF fienld is applied, again by electrodes through and down the
glue lines. In both cases the glue line exhibits a far lossier path for
the RF and most of the energy is in the glue line.
The third method is known as "strayfield heating" and is probably the most
useful one for zapping the worms. This technique is used for fixing
veneers, "stitching" wood joints and glueing plywood skins to large
doors. This method uses two or more electrodes positioned side by side
with a coil across them to affect resonance, this meaning that there is no
need to get either side of the wood to be heated and the electrodes,
usually held in position with insulators and applied as a hand tool is
placed on the wood and the stray field penetrated the wood to some
considerable depth. The tool is normally link coupled to the generator
(only about 1kw) through a 50 ohm cable and the output power is varied
with a variable capacitor built into the hand tool and operated by a
trigger.
If anyone wants to know more just email me and I can send pics. As for
the comments about RF energy causing loss of little tadpoles or whatever,
after 40 years in the RF Heating industry my 4 grown up kids don't seem to
think so!!!
73
John in Benoni
73 - John, ZS6HK @ ZS0DLD
Proud member of the SARL
email j.ingram@eject.co.za
Tel 011-425-1125
Cel 083-763-4182
Message timed: 18:39 on 2004-Nov-12
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