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11-29-2005, 01:47 PM #1
Is there such a thing as food grade solder or brazing filler rod that's rated for direct contact with food products? The material being soldered, brazed, or welded would be stainless steel, probably 303.
The food material is similar to pancake batter, which would flow over the solder joint.
I'm trying to improve some equipment for a customer and need to understand all my possible design constraints.
11-29-2005, 02:10 PM #2
Do not know anything about welding, but No lead, No zinc comes to mind.
You may wish to check the NSF (formerly the National Sanitary Foundation), which are certifiers of food service equipment. They are the authorized organization for establishing ANSI (American National Standards Institute) standards for food service items.
Their "Food Equipment Program begins with voluntary standards that represent a consensus between manufacturers, users, and regulatory authorities."
The certification process is:
"Material review: Provides verification that the materials used to fabricate the equipment are nontoxic. Materials must be corrosion and heat resistant; coatings are tested for durability against impact and abrasion."
You may have to purchase manufacturing standards from their bookstore. Their web site is:
I hope this helps.
11-29-2005, 02:14 PM #3
The first item comes to mind for this is silver solder - tin/silver. THis was a commonly used material for attaching things to stainless containers used in brewing - pipe bungs and the like.
DId a fair bit of that and never had a problem with cracking over heat/cool cycles.
11-29-2005, 02:15 PM #4
Stainless TIG filler wire is used commercially in food-contact & food processing applications. Is TIG welding an option?
11-29-2005, 02:40 PM #5
I believe you are looking for a cadmium-free silver solder.
11-29-2005, 02:41 PM #6
Does anyone remember the small solder dot, located in the center of one end, of each can of condensed milk? Carnation or Pet brands?
Participated back in '68, to modernize a density measuring instrument which controlled milk solids in a condensed milk canning plant. What an interesting place.
The plant had a Rube Goldberg setup which would exactly place the solder dot, sealing the fill hole in each can prior to sterilizing the can/contents. It ran at 100 cans filled/sealed per minute.
The really simple method they devised for testing each can, to check for an excess droplet of solder being inside and loose, was the real trick.
This plant was probably built in the early 20's. The unloading dock, where horse drawn wagon loads of 10 gallon milk cans used to be unloaded, now contained two modern, packaged boilers.
11-29-2005, 02:56 PM #7
Harris has what you need, Safety-Silv 56. This page says it's NSF accepted, and used onfood service stainless steel:
I can't tell you how well it works, though.
11-29-2005, 02:57 PM #8
Thanks for your suggestions.
TIG was the first thing to come to mind, but I'd want the entire seam sealed so food and bacteria can't find a place to hide. I'm considering a flat lap joint that's ~10 inches long by 1/4" wide and thought it might be easier and cheaper to flow solder under the entire seam than to TIG all the way around it.
11-29-2005, 05:20 PM #9
Staybrite makes a line of food safe solders. I think ENCO and probably others tooling supply houses sell this. Melting point is about 400-425. Whatever the components are it is pretty hard stuff after cooling.
11-29-2005, 05:33 PM #10
11-29-2005, 07:55 PM #11
Pure tin will work for food contact, it has a low melting point, easy to work with and will match stainless fairly well.
Not a lot of strength though, I would think it would work for a lap joint. If you need the strength then you are stuck using silver braze. However you might have a problem with warpage from the high heat.
I repaired some holes in thin SS with a copper iron and flux and it worked great.
Tin is used for a coating in mixer bowls and also in copper pans used for cooking.
Pure tin is available from McMaster Carr (isn't everything) in bars and wire. The flux is available also. Clean well after soldering.
11-29-2005, 08:44 PM #12
I will have to find out exacty what I used to use where I worked at Horix, they made liquid food bottling machines and each valve had a lot of solder on it. I know one thing though, for the stainless parts that food came in contact with, it was 316 stainless only that we could use. Everybody says stainless is tough, but that was about all I worked with for those years, machining, cutting, grinding, welding, soldering, and I liked it! I do know that the solder/braze that we used was gold colored, I will see if I can find that out for you. I will try to call tomorrow.
11-30-2005, 02:01 PM #13
The Eutectic Corp. makes an excellent food pure low temp solder marketed as Eutectic 157B.
Flow point is 450/F and the tensile is somewhere around 15,000 psi.
11-30-2005, 02:30 PM #14
"The really simple method they devised for testing each can, to check for an excess droplet of solder being inside and loose, was the real trick."
So HOW DID THEY TEST for loose solder inside the cans????????? You can't just drop a bomb like that and not the answer.
11-30-2005, 04:15 PM #15
We do food service grade valves in one of our other facilities. They fill porosity in bronze and SS valve with nickal/copper (bronze) brazing rod.
Remember, no prorosity, gaps, holes, etc. There can't be any places for bateria to stick. Everything that comes in contact with the product is supposed to have a smooth finish.
11-30-2005, 05:29 PM #16
Try Harris Stay-Brite #8 solder with the Stay-Brite paste solder. Temp 450-550, 7% silver/93% tin. FDA appoved for foodservice and it fill voids wells, and has greatr strength. Cost for 1 lb roll + solder paste around $35 at any refrigeration supply house. After soldering wash off residual flux with cloth soaked with hot water.
11-30-2005, 06:22 PM #17
In second childhood or mere oblivion, am I missing something?
The tinplate industry was exactly that. steel plate was either dipped or had tin deposited by electrolysis. The word was tin! It could be double differential, it could have negative torroidal seams but it was all tin.
Again the side seam was tinned using a solder horse which could take perhaps three tins or cans in one- and these were spun into separate pieces for lid-ing and then sealing.
Again, I recall that peas had tins which once tinned and were also laquered.Lids were either plain or say pickle laquered.
Have I missed something?
11-30-2005, 06:46 PM #18
Sometimes I get all caught up watching my fingers dance the keys. No bomb intended---
From the time the cans were formed/rolled, had their ends soldered on and filled/soldered shut, they were on conveyors or in chutes as they moved from one room to the next. After the fill hole soldering was performed, each filled can was individually mechanically removed from the conveyor and shaken one time in front of a microphone. Each can would then fall back onto the conveyor- IF- it did not produce the sound frequency of a free droplet of solder rattling around inside.
They had one or two cans painted red, each containing milk and a minute solder droplet. To test the microphone/electronics(an old fashioned vacuum tube device), a red can would be inserted on the conveyor between the solder machine and the microphone/shaker. Sho'nuff, when the red can was shaken, the solder was detected and the can was immediately kicked out of the process line.
We sold instrumentation designed for measuring the densities of cementing slurry streams. We had more fun outside the grouting industries, finding new applications. How about canned tomato puree, telephone pole creosote, tungsten mining processes, RA muds being pumped from deep under Yucca Flats, monitoring the balast being installed in the Queen Mary, etc. Of course, if the application was interesting we had to go spend a day or two, walking-the-walk.
11-30-2005, 09:00 PM #19
Last year I had to do some soldering on a rear pan of a maple syrup evaporator, IIRC it was 304 SS. A large cast bronze flange had separated from the pan at the solder joint. I was concerned with using the correct food grade solders, as this joint is in contact with the partially boiled sap, even though it was a tiny area of solder only the thickness of the solder in the joint. I contacted the Leader Evaporator Co. of Rutland, VT. They were extremely helpful, even telling me the best methods of heating the joint and prep. The solder I was told to use was, IIRC, the Harris Stay-Brite solder. I don't remember for sure the flux I used, but I think it may have been Stay-Clean, a Harris product, as per the recommendation of Leader and a local plumbing/HVAC supply house. As per Leader's instruction, I used a propane torch on the casting for general heat, and a well tinned soldering copper for the tinning and on the SS side of the joint for the actual soldering. Leader still uses soldering coppers in their factory, from what I am told, however some of the new pans are TIG welded. I applied a relatively thick layer of solder to both surface for tinning, and then heated the surface from the back, and then wiped the excess solder off with a clean, wet rag, then immediately applied more flux to the surfaces, then fixtured them together, and heat, while applying solder around the joint. When cool, I neutralized and CLEANED EVERYTHING first with a wet rag a baking soda, followed by a thorough polishing of the joint and adjoining areas steel wool and those "S.O.S." pads. Worked great. I am not positive about the exact name of the solder I used, other than it was a lead-free, cadmium free, potable water, silver-bearing, also recommended by a local plumbing/HVAC supply house and Leader. The biggest problem was another nearby seam, so I had to clamp some large bars, "heat sinks", on either side of the SS pan side, and use wome wet rags to keep heat at that joint to a minimum. Hope this helps, sorry for the lengthy post.
12-01-2005, 02:32 AM #20
Thanks much for all the suggestions. I'll go with the solder, I like the low temp and crack filling properties.