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B

D

Airflow varies from 0 to 15 times per hour, which has a major effect on the evaporation rate of the volatile component. In diagram (A) we have a winding completely saturated with varnish, which has been drained until dripping of surplus varnish has ceased. As the job warns up, volatile solvent begins to evaporate (blue arrows) into the surrounding atmosphere. At the same time the varnish becomes thinner, and the equilibrium is destroyed and secondary drainage takes place, consequently much of the varnish ends up on the oven floor (diagram B). The oven atmosphere becomes laden with solvent vapor literally “stewing the winding in its own juice”. The longer this goes on the longer varnish will continue to drain. (diagram C). After a while, the varnish will tend to dry on the surface indicated by the yellow skin. This skin restricts evaporation of the volatile matter from the deeper parts of the winding so a variable factor is introduced between different machines in the same load. All we can be sure of is:

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Y

The Ayrodev Oven is essentially a direct-fired re-circulating oven, in which air is taken from the top of the oven, passed through a flame and fan unit and fed through delivery ducts at the open bottom of the oven. The emerging hot air forms a heat seal in a horizontal plane, coupled with a general vertical flow to the top of the oven, so that the air is recycled. The air temperature is 200 Deg C and the velocity produces an air change of 15 to 20 times per minute, compared with 0-15 times per hour in the conventional oven and temperature at any part of the 1,000 cu. ft. oven space is within 2 deg C of the operating temperature. Air at this temperature is extremely dry and therefore has a high absorptive capacity for volatile matter as compared with the lilac atmosphere in the conventional oven. See Ayrodev Oven diagram (X) showing:

Diagram (Y)

The winding is then moved vertically through the heat seal. The high velocity hot air removes the specially selected solvent from the Ayrodev varnish (blue arrows show rising) in seconds. The volatile matter is carried away on the air stream, passed through the flame and burnt so fresh air (solvent-free) is delivered back to the work point (red).

The rapid solvent removal thickens the varnish in spite of the temperature rise and no drainage takes place. The high ambient air temperature on the end windings allows heat to be rapidly conducted down into the slots. This heat transfer volatizes the solvent in the slots, which then comes to the surface, is picked up on the air stream and burnt in the flame (red arrows up and over). As the winding below the heat seal is still cold, there is no drainage from this area. By the time the winding has passed completely through the heat seal (diagram Z) it will be evident that:

All volatiles have been removed cleanly and effectively

Full varnish retention has been maintained without drainage

It is now necessary to achieve the appropriate curing temperature in the slots and the effect of the high ambient temperature on the lower turns, rapidly produces this condition, resulting in a winding, which is adequately impregnated and fully cured.

Plotting changes in capacitance, tan delta, I.R and copper temperature monitors the whole of this procedure..

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