Dont know if you got this repaired but FYI there is a special locktite (green wicking) that is supposed to be applied to the screws AFTER the adjustment is made. That will keep your screws from moving. It is heat resistant also.

i,ve seen it on electromag brakes that after they have been toasted first time they don,t last as long and break up within a few weeks causing bigger air gap and failure

Is it normal for this brake system to tighten itself up every every 2 to 3 months? After adjusting the air gap to what u suggested, its been working fine. This morning i was notified the brakes were locking up again.

the air gap in the electric brake is.010mm

also check the connector plug at the brake unit and make sure it is good, any resistance and it will not get enough voltage to energise the magnet properly.

Only a couple of possibilities (IMO)

If the gap between the magnet and the armature is too large, the magnet can't pull it in when it get's hot.
-adjustment depends on the type of brake, but a quick setup method is to tighten the assembly together then back the 3 adjusting screws off~1/2 a turn each.

The second possibility is that you need a new brake. In a nutshell, the heat causes the insulation on the magnet windings to break down, and as they short together the magnet gets weaker and weaker.
-be prepared for the price shock :-)

The newest nacco electric brakes are completeley non-serviceable and non-adjustable. They are in spec or they're replaced... so much for progress.