[metalwerks]

I sometimes see a notice on our brazing filler metal paste containers that the paste should be refrigerated prior to use. Why is this necessary? Also, does braze alloy have a shelf life?

[dankay7]

It should never be necessary to refrigerate brazing pastes prior to their use. The need for any refrigeration of pastes is a carry-over from the "old-days" when brazing was being done in hot heat-treat shops where the ambient temperatures were hot enough to cause breakdown of the brazing-paste binders, and the binders could no longer suspend the brazing powder. So, in such shops the brazing paste was stored in "cool places" such as refrigerators.

Please understand that there is absolutely nothing inherent in the chemistry of the binders used in making brazing pastes (by any manufacturer) that is enhanced or made-better by refrigeration.

Refrigeration is only needed to prevent the breakdown of binder-systems from excessive heat in the brazing shop.

In most brazing shops that I visit today, the rooms where the brazing filler metal (BFM) pastes are stored are actually quite comfortable, and often air-conditioned. Thus, storing the brazing paste containers in the cabinets in the room is perfectly satisfactory, and any "refrigeration" warnings can be very safely ignored.

If the brazing paste is stored in very warm room conditions, it is possible that the excessive heat could cause the binder-systems in the brazing pastes to loose their suspending-capabilities, and the paste will be said to "break-down", i.e., the brazing powder will sink to the bottom of the cartridge or container, and the liquid binder will rise to the top. This does not mean that the brazing paste is "bad"! It merely means that the binder-system can no longer suspend the brazing powder. So, stir the brazing paste thoroughly prior to use, and then use it immediately, before it begins to settle out once again. Continue doing this until all the paste is finally consumed.

Shelf-life varies from one manufacturer to another, depending on their attitude toward paste returns to their company. If they offer a short shelf-life, then, when that shelf-life date is reached, most auditors will insist that the product be returned and replaced. So, some manufacturers offer a longer shelf-life to prevent paste from being returned "too soon", trusting that the user will consume all of the product before the shelf-life date is reached. In other words, it is possible that they may offer extended shelf-life on their paste primarily to prevent it's early return to the factory, rather than because their paste is any better than any other manufacturer's paste.

[heattreater]

Thanks for the explanation Dan!