Dan Kay's blog series on eliminating "holds" in brazing cycles continues.

Slow Down the Ramp Rates

Since my experience has shown that parts can actually distort while being heated up to brazing temperature, I strongly recommend that the heating rates used be slowed down significantly so that all portions of the load being brazed can come up to brazing temperature together without the need for any temperature holds during the heating cycle.

This will involve some experimentation to find the fastest heating rate that can be used that will allow the entire load to reach brazing temperature with no holds. Today’s furnace-programming instrumentation (Fig. 2) can easily allow furnaces to be programmed at whatever heating rates are desirable.

Wrong Objection

People will sometimes tell me that they cannot use a slower ramp rate for heating in their vacuum furnace since that will obviously extend the brazing cycle to the point that it could significantly hurt their shop’s productivity. This is not true! I have actually found that the total brazing cycles are often shorter when using the slower ramp rate, since the holds are being eliminated and all the “hold time” has been removed from the furnace cycle!