Oven Soldering

[hobnob]

Noel,

I have not done oven soldering by any means, nor have I seen or
heard of the toaster oven technique, but I think I can answer your
question about the toaster oven.

The 450 degree temperature indicated in the oven is essentially the
air temperature in the oven but not necessarily the temperature of
individual objects within the oven - the heating element itself
being the best example of that as it glows red hot. 450 air
temperature is plenty hot for most cooking operations. The
thermocouple (heat sensor) which measures the temp is not in contact
with nor exposed to direct infra-red radiation from the heating
element. It responds to the ambient air temperature. The air is
constantly moving in the oven, convecting, and is losing heat
through the walls and door etc so it tends to stabilize at some
level consistent with a balance between input of calories from the
heating element and loss of calories to the surroundings. I should
think that a metallic object under the toaster or broiler element
could very easily be raised to soldering temperatures far in excess
of the air temp in the oven. The air in the oven itself is a
relatively poor conductor of heat ( trapped air pockets are the
essential element in most insulating materials) and so the
temperature of the soldered object in the oven can be driven up
quite high and not carried off quickly by the surrounding air in the
oven.

Baking operations in a toaster oven may, depending on design, be
governed by a thermocouple which turns off the heat when a pre-set
temp is reached and turns it back on when the temp falls below that
level. However, toasting operations, when done as intended by the
mfr, that is, to a slice of bread rather than metalwork, are
typically governed by a timer rather than by a temperature sensor.
The element turns off after a pre-determined time passes rather than
at a pre-set temperature, thus determining how dark your toast will
get. If the timer is de-activated or over-ridden, perhaps simply by
manually turning it back on instantly when the little bell goes
ding, I imagine you could get the temp quite high.

I know this is fairly primitive but if you are not doing high volume
production I bet a toaster oven would be a good way to do some
one-off oven soldering without the huge expense of one of those
automated conveyor belt devices - and you could heat up your lunch
too!

Marty in Victoria - where I hope to get the heat installed in my
basement shop pretty damned soon!

[bethkatz]

Hi Brian,

Using a toaster oven to solder a piece of jewelry is highly unlikely
as has been pointed out by several others.

I think it is important to understand that when you do solder in an
oven (read kiln), you are reaching the temperatures on both the metal
and the solder that is required for the solder to flow onto the
heated metal and make a bond (solder point). The metal and the solder
are both at the same temperatures at the same time by doing it in a
kiln. BUT… the most important factor, that is not noted by most, is
that there is an oxygen deprived atmosphere in the kiln that allows
the solder to react in a proper method and join the items to be
soldered together by allowing the solder to flow at the proper
temperature. The temperatures are critical, as is the atmosphere in
the kiln. The flux is self contained in the paste, allowing the
solder flow once the proper temperatures are reached.

You cannot do this process in a regular kiln; it is not manufactured
for this application for all of those thinking what a great idea it
would be to solder in a kiln. Most commercial kilns used for
soldering are of the “belt” type, where the pieces are put onto a
conveyer belt type of operation, the atmosphere in this situation is
conditioned so that the proper conditions are met, and as the pieces
are placed on the belt, the temperatures are adjusted to meet the
goal of having the metal reach proper temperature and the solder
flow, then temperatures are brought down to “cool” the pieces. The
critical part of this operation is that the METAL and the SOLDER
reach temperatures at the same time, allowing the process to be
successful, all while maintaining the proper atmosphere. Most belt
type operations require that the pieces be set into a type of
soldering plaster that hold the parts in the exact placement for the
join. The smallest amount of the paste solder that will accomplish
the job is utilized. The pieces move along as the belt is moved
along, transferring the items in order of temperatures needed and
processing stages, thus “belt” kiln, this is a manufacturing process.

In using paste solder with a torch, which is a totally wonderful
technique since solder and flux are all self contained, the same
process of bringing the metal and the solder to temperatures at the
same time applies. If the metal and the solder are not at the proper
temperatures at the point of attachment, you can end up with a cold
join, even if the solder flows. This makes the attached part
(finding) not as strong and may even break off… read ear post
detaches. I think the novice has a lot of trouble with the concept
that the two parts joined must be of like temperatures. Practice
makes perfect. My technique for making strong ear posts: Place post
in a cross lock tweezers. Put main piece to which the ear post will
be joined on a soldering surface. Apply paste solder to main piece.
Heat main piece on the soldering surface while holding the ear post
just a bit away from flame, preheating the post, always remember to
keep the flame moving at all times so you do not get a hot spot and
melt something. When solder flows, stick post into the flow point
hold it steady and draw the solder up the post by applying the torch
heat to the post, assuring the proper temperatures are reached by
both the post and the main part. Solder flows towards the heat,
making a good and solid join since both pieces will be at the same
temperature. It is not necessary to add any paste solder to the ear
post as there will be plenty of solder in the liquid stage to bring
it up with heat onto the post. Make sure your post is in the proper
position before taking off torch flame. Hold for a few seconds after
taking off flame while solder looses flash, starts to solidify and
will hold the post steady, then release the cross locks, leaving the
properly soldered earpost in the correct position.

A great exercise to practice this technique is to make a flat
surface on a piece of scrap, cut round wire about the size of an ear
post, you can start with thicker gauge and gradually change to small
gauges if you have a fear of melting until you get the correct
technique. Make sure wire is flat on the end where it is to be joined
to the main scrap. Apply paste solder to the scrap piece. Heat scrap
bringing the flame in from the outside to bring the metal to
temperature. Have the wire (ear post) in the crosslocks, close but
not directly in the flame. Then do the technique. Good practice. I
have my students start with silver. This exercise can be done to gain
even greater control by using one or two different melt formulas for
the paste solder and soldering on the same scrap, from hard on down
to extra easy. Let cool down between operations. Makes you appreciate
temperature control.

Beth Katz
www.myuniquesolutions.com
Paste Solder and Powder Solder for Jewelers and Metalsmiths