As refrigerators replaced ice-boxes, it became convenient to tell the brazing shop personnel that the brazing paste “should be refrigerated prior to use”. But shops actually got “cooler” over the years as more efficient furnaces became available, and much more so when cold-wall vacuum furnaces came online. Additionally, much of the braze-prep is done today in environmentally controlled rooms, rather than out on the hot shop floor, and boxes of brazing-paste cartridges are often stored in cabinets within those rooms at comfortable, ambient temps. BUT — some BFM-paste manufacturers still place the warning on their BFM-paste containers: “Must be refrigerated prior to use” in order to warn end-users about leaving the paste in excessive heat where it can break down. Printing such a statement on labels is unwise, in my opinion, unless detailed clarification is also provided.
A number of years ago I was visiting a brazing company for a few days in order to help them with their brazing. They did a lot of brazing, but were having some issues with their brazing paste, and asked me to investigate. Their brazing prep was being done in a nice, clean, environmentally controlled room, and as I audited their prep processes, I noticed that the shop leader, at the end of the workday, went over to the nice wooden cabinets lining the back wall of the room and removed a box of BFM-paste cartridges from one of those cabinets. Each BFM cartridge held approximately 8-oz (225-gms) of BFM paste. He opened the box and took out all the paste cartridges and placed them in a small refrigerator that was sitting on a low bench near the door to the brazing shop. The next morning he took all the paste-cartridges from the refrigerator and took them out to the shop where he placed them at each of the brazing stations out there on the shop floor. I observed some of the shop workers then trying to extrude this cold paste, and watched as they had to keep increasing the air pressure shown on the dispenser (like the one shown in Fig. 2) until the paste finally began to move slowly out of the cartridge tip. Instead of only about 20-psig, they had to keep raising the pressure until it was almost 90-psig (620 kilopascals)! This is dangerous! At that point, I asked the leader to call all his workers together during their first break to discuss this concept of using paste properly, without having to refrigerate it!
Please note that there is absolutely nothing about refrigeration that has any benefit to the BFM-paste’s inherent ability to perform when being used. Again, it was merely an old-time suggestion made to keep the pastes from breaking down when stored in high heat environments. Brazing paste should be held at a comfortable room temp and used in such a way that the pressure setting on the paste dispenser is never higher than about 20-psig (135 kilopascals). To achieve this (as discussed in another article) you may need to switch to using the tapered plastic cartridge tips (preferred) rather than the thin stainless-steel needles commonly seen today. Please note that thin stainless needles were actually designed to be used with thin oils and adhesives, and were never designed to be used to extrude thick pastes! That’s why cartridges of caulk you buy in the store always have tapered plastic tips.
All that is actually needed for BFM paste storage today is that it be protected from any dirty/oily shop atmosphere and from excessive heat. Thus, by keeping the BFM paste cartridges in a storage cabinet, at ambient temperature, in the room where the BFM is applied to the parts, or in an insulated cabinet (such as the yellow safety cabinets in use today) out on the shop floor (if the BFM paste is applied to the parts out in the shop), you will achieve all the desired level of protection to the paste that is needed.
Bear in mind, too, that a refrigerator can actually de-humidify objects placed therein (you know this from what happens over time to vegetables that are stored unprotected in refrigerators). The water content of the gel-binders in brazing pastes can actually be slowly removed by steady refrigeration, even though the paste is in plastic cartridges since the cartridges aren’t actually as well sealed and “water-tight” as you might think.
Therefore, it is NOT necessary to ever refrigerate the BFM-paste! Specs and labels requiring refrigeration should be changed!
NOTE: If you want to use a refrigerator to store BFM paste, that’s fine. Just unplug it! Then it makes a fine storage cabinet!