How to Braze – Cold Joints
Cold Braze Joints on Monday Morning
I once had an issue where a customer was having braze failure on saw blades made on Monday mornings.
It started out with a report of a braze failure. I asked them to see if they could identify any common circumstances between the failed saws and the great majority of the saws which were beautifully done.
Some record-keeping show that the problems occurred with saws brazed Monday morning.
This was in the winter.
They were following a common brazing practice and brazing on a large, thick, steel brazing table. They come in sizes but think of a piece of steel that is about a yard across and about a foot thick. They would lay the saw plate on top of the piece of steel. Then they would insert shims under the saw plate to raise it enough to give them the proper side clearance. This left the plate raised above the table and only the tungsten carbide tips were resting on the table.
They turned the heat off in the shop on the weekends and turned it back on Monday morning. The turned the heat on early enough to get the shop up to a working temperature. However this was not nearly long enough to bring that huge chunk of steel up to warm.
So what they were doing was brazing with one side of the saw tips resting on this huge, cold chunk of steel. They were getting beautiful joints, as usual, on the upside. However, so much heat was being sucked out of the downside that the joints were too cold and not strong enough.
Once we had this figured out they developed the practice of using the torch to warm the top of the table and the failures disappeared.
Some brazers make it a practice to always warm the top of the table before brazing and some do not. There are brazers that get excellent results with either practice.
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