| Welding Data >> Technical Articles |
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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. |
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| 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%.
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| 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. |
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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 |
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Lemon |
1150 |
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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]
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| 1 ton per square inch (tsi) |
= 1.575 kg/mm2 |
| 1 kpsi |
= 0.703 kg/mm2 |
| 1 ft.lb. |
= 0.1383 kgm |
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