For how long and at what temperature should I heat low hydrogen manual metal arc electrodes when baking is required?

TWI Frequently asked questions

by David Abson

Care should be taken to ensure that the conditions employed for baking actually achieve the intended heat treatment. The fact that the electrode coating is a thermal insulator, as well as an electrical insulator, should be recognised, and allowance must be made for the thermal mass of an oven charge of cold electrodes. The slow rate of heating of a large charge of cold electrodes has been investigated by Boniszewski and Paveley, who monitored the oven temperature and that of a thermocouple located in the centre of the mass of electrodes for charges of 20kg and 80kg of manual metal arc electrodes, with an initial oven temperature of 250°C. (See reference below.) The approximate times for the oven to recover temperature were 45 minutes ( Fig.1) and 2.5 hours ( Fig.2), respectively. For the smaller charge of electrodes, the thermocouple monitoring the temperature of the electrodes reached 230°C after a further period of approximately 50 minutes, while the thermocouple located in the larger mass of electrodes reached a temperature of 200° after approximately 6 hours. Clearly, only shallow layers of electrodes should be allowed, and allowance should be made for the time taken for the holding oven and the electrodes to reach the required temperature range, after a charge of electrodes has been introduced.

Fig.1. Temperature rise after loading 20kg of electrodes into hot oven at 250°C original temperature

Fig.2. Temperature rise after loading 80kg of electrodes into hot oven at 250°C original temperature.

Reference