Storage
Basic low hydrogen electrodes should be stored in dry conditions,
off the floor on pallets or racks in their unopened containers. The rate of
moisture re-absorption which takes place is determined by the resistance of the
electrode to the atmospheric conditions of relative humidity and temperature prevailing
during storage.
Storage is not really the most important issue in
determining subsequent weld metal hydrogen content of low hydrogen electrodes,
but rather, the rate at which moisture is lost during re-baking of electrodes
prior to use.
Storage under the correct conditions will provide indefinite
product shelf-life.
Re-baking
It is essential that hydrogen-controlled electrodes be re-baked
prior to use. The re-baking temperature recommendations depend on the maximum
permissible hydrogen content tolerable in the deposited weld metal and the hardenability
of the parent material.
Standard Re-baking Temperatures
|
Product
|
5-10 ml H2/ 100 g
|
<5 ml H2/100 g
|
|
7018-1
|
350 - 370°C
|
-
|
|
78MR
|
250 - 270°C
|
370 - 400°C
|
|
Ferron 1
|
350 - 370°C
|
-
|
Baking time one-two hours
Diffusible hydrogen content determined using Yanaco gas
chromatograph
Optimum conditions for
re-baking are achieved when electrodes are placed on the oven shelves not more
than five deep. This is normally only required when diffusible hydrogen
contents of less than 5 ml H2/100 g of weld metal
are specified and hardenable materials in thick sections have to be welded.
For general shop
conditions, the electrode pile in the oven can be increased provided
consumables in the centre of the pile achieve the minimum re-baking temperature
for a minimum period of one hour.
Note: When electrodes are placed in a baking
oven, the temperature in the electrode pile rises far more slowly than it takes
for the oven’s own temperature to rise to the set temperature. It is therefore
incorrect to take the oven temperature as an accurate indication of the actual
baking temperature reached by the electrodes and hence a guide to the time at
temperature.
Unless the temperature
during baking is timed on the basis of the electrode temperature, the
electrodes cannot be considered properly re-baked prior to use.
If possible, it is
recommended that fabricators carry out checks on their re-drying ovens to
establish the correct conditions for actual electrode re-baking temperatures
and times as compared to oven temperatures and times.
It is important to note
that if the electrodes are maintained at the re-bake temperature for long
periods of time, the coating may become brittle. Coating brittleness may also
result if the electrode is re-baked above the maximum recommended temperature.
