|
Welding
Data
REDRYING
AND HOLDING RECOMMENDATION
|
Redrying may be repeated
twice within the total time of 3 hours.
NOTES:
| A) |
Redrying of
electrodes should be carried out by taking them out of the
packaging and placing the electrodes in layers of about 3
cm thickness in temperature controlled air circulation oven.
Severity of redrying conditions (Time-Temperature) will depend
on:
| a) |
The permissible
level of diffusion hydrogen; |
| b) |
Relative
humidity in the shop or at the site, i.e. in open area
or in a tunnel. Thus, during the rainy seasons, redrying
should be more severe within the time-temperature range. |
|
| B) |
Storage areas:
Storage of electrodes in cardboard boxes required due control
on humidity and temprature.Recommended storage conditions
are:
Temperature : 30-45oC
Relative Humidity : 50% Max.
Heaters or high wattage lamps may be fixed in the enclosed
store room to maintain temperature in the range of 30-45oC,
so that the relative humidity remains below 50%. Generally,
a temperature of about 15oC above the ambient temperature
is considered safe for such store room. A dehumidifier of
adequate capacity may be installed as a part of the storing
facility. The dehumidifier may be operated as and when the
relative humidity in the atmosphere rises above 80%, as during
the rainy season, so that with or without the use of heater
or lamps, the R. H. in the store room is kept under 50%.
|
| C) |
Whenever hydrogen-controlled
electrodes EXX16 or E XX18 or E XX28 or E XX48 are recommended
and selected, it is equally important to ensure that moisture
in electrode coating is kept at a low level through redrying.
In the case of austenitic stainless steel types (E 300 series),
control over coating moisture is necessary to prevent starting
porosity. The climatic conditions in large to the redrying schedule.
Within the frow in sophisticated welded fabrication, and the
rising quality standards, due attention has to be paid to the
redrying schedule. While the recommendation in the Table is
given as a guideline, it is hardly possible to lay down a definite
redrying schedule for the entire country with its widely varying
climatic conditions and the seasonal changes. |
Judging Temperature
by Colour(Steel)
| Temperature
Colour |
oC |
Luminious
Colour |
oC |
| Pale Yellow |
200 |
Faint dark red |
590 |
| Straw Yellow |
220 |
Cherry red (dark) |
650 |
| Yellow brown |
240 |
Cherry red (medium) |
700 |
| Bluish purple |
270 |
Red |
760 |
| Violet |
285 |
Light red |
815 |
| Pale blue |
300 |
Orange |
930 |
| Blue |
325 |
Pale orange
lemon |
1000 |
| |
|
Lemon |
1150 |
| |
|
Yellow |
1260 |
Colour temperature
are useful as a rough guide and surprising accuracy can be attained
with practice.
Conversion of Faherenheit
and Centigrade Temperatures:
| t(oC) |
=5/9 [(oF)-32]
|
| 1 ton per square
inch (tsi) |
= 1.575 kg/mm2
|
| 1 kpsi |
= 0.703 kg/mm2 |
| 1 ft.lb. |
= 0.1383 kgm |
|
Welding
Data
|
