Electrodes- storage and handling of electrodes, Mechanical Engineering

STORAGE AND HANDLING OF ELECTRODES

It is recommended that the electrodes should be stored in a warm and dry place. Generally, conditions of storage in the shop are not very conducive to desirable performance of the electrode. At this juncture a knowledge on the factors leading to deterioration of the electrode can be helpful. The coating of the welding electrode is produced from powdered materials bound together with binders, usually including sodium or potassium silicate. Such a coating is not impervious to water vapour, which is absorbed from the atmosphere and held by the binders, in the capillary spaces between the powder grains.  This action takes place until equilibrium is reached between the coating and the atmosphere surrounding it and may proceed in either direction.

The relative humidity is the percentage of moisture in the air compared with the quantity to saturate it at the same as its temperature rises, so that if there is no change in the total moisture content of the air, the relative humidity fal ls as the temperature rises and increases as the temperature fal ls. When the temperature falls below the point where the relative humidity becomes 100 %, moisture is deposited. The temperature at which this happens is known as the dew point temperature. When the relative humidity is high, heating the electrode is resorted to reduce the moisture content in the electrode. If the coating is impervious the steam cannot  escape and this will result in the bursting of the coating. Some electrodes have a moisture content as low as ½ % and loss while some with as high as 6 % moisture content perform well. The diversity in their performance can be attributed to the degree of porosity of the electrode coatings.

Electrode coatings containing as high proportion of cellulose or cellulose like material must contain a proportion of water if they are to give the best results. Excess of moisture leads to porosity of the weld, but unsatisfactory results are also obtained if the electrodes are dried excessively.

Electrodes with coatings of predominantly mineral composition appear to be more tolerant. They do not pick up such a high proportion of moisture from the atmosphere and may be redried at temperatures not exceeding 100 ° C and held at this temperature for some hours without serious harm.

"LOW HYDROGEN" o "HYDROGEN CONTROLLED" electrodes are intolerant even to trace of moisture and drying immediately before use at temperatures of the order of 400 °C is recommended for them. These values are meant for guidance only and for exact details electrode manufactures should be consulted.

A second form of deterioration is the formation of white fur on the electrodes. This is produced as a result of the irreversible chemical reaction between the carbon monoxide of the atmosphere and the sodium silicate binder. When formed in excessive quantities this fur disrupts the coating leading to the rusting of the core wire. The appearance of this may be taken to indicate the unsatisfactory storage conditions.

Posted Date: 9/14/2012 6:09:31 AM | Location : United States







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