When Was Solder with a Flux Core Invented?

[redg]

Wikipedia suggests that the use of solder wire with a core of flux dates to the mid-20th century. However, I came across a Popular Science article that suggests that such wire was available to hobbyists before World War II.

The article, dated January 1930, is titled New Kit Sets for the Radio Builder.

The screen capture is from page two of the article. Note the sentence "A soldering iron, preferably of the electric type, should available; also some rosin-core solder". I assume that "rosin-core" meant the same thing then that it means today.

Does anyone know the history? I guess there are two questions. When was solder wire with a flux core invented? When did it come into widespread use?

Cheers

[Ian.M]

J.F. Kester of the Chicago Solder Company had a patent for an improvement to plain flux cored solder, granted in 1899: https://patents.google.com/patent/US628541A/en
Flux cored solder must therefore predate that and its use must have been sufficiently common that Kester was aware of it.

This page may be of interest: https://stevenjohnson.com/soldering/solder.htm

[redg]

Further to Ian's post, here is a direct link to Jesse Kester's patent #628541: https://pdfpiw.uspto.gov/.piw?PageNum=0&docid=00628541&IDKey=3BB9E94D2AB8%0D%0A&HomeUrl=http%3A%2F%2Fpatft.uspto.gov%2Fnetahtml%2FPTO%2Fpatimg.htm

In paragraphs two and three of the screen capture below, Kester says how his invention differs from how flux cores were previously made.

[redg]

In addition to Ian's link to photos, here are more, together with some Kester company history: http://progress-is-fine.blogspot.com/2013/05/we-used-to-make-things-in-this-country.html

A site called Find a Grave says that Jesse Kester was born in 1851 and died in 1901, just two years after his patent was granted: https://www.findagrave.com/memorial/23091878/jesse-f-kester

[redg]

References in the above links suggest that solder wire with embedded flux was successful as a product because it made soldering faster, increasing the efficiency of assembly lines. If so, that raises a question. In the hands of someone who isn't rushed for time, what is the difference, if any, between soldering with wire that's embedded with flux and bringing flux and wire together separately?

To offer an example... In the case of tinning stranded wire, I would think that coating the wire with flux and dipping it in liquid pure solder would tin at least as well, if not better and possibly faster, than tinning with wire with embedded flux. Indeed, tinning stranded wire is one of the contemporary uses for a solder pot.

[exe]

I'd like to try a solder wire without any flux because I think I have better fluxes than rosin. Also, rosin leaves residue on the tip that, if not removed, makes joints dirt and messy.

[redg]

I'd like to try a solder wire without any flux because I think I have better fluxes than rosin. Also, rosin leaves residue on the tip that, if not removed, makes joints dirt and messy.

I’d also like to try using wire and flux as separate components. The price of solid wire appears to be something of a deterrent. I’ve only checked Kester, but its solid wire is more expensive than its flux core wire.

The prices in the table below are from the website of a U.S. vendor that is on Kester’s authorised dealers list. The table shows prices for two Kester metallurgical formulations, one with lead (63/37) and one without (SAC305), for bars, solid wire and wire with flux. Both wires are 0.8mm (0.031”) in diameter. The wires with flux are Kester 44 and Kester 48, for which Kester recommends 3.3% flux.

The solid wire is significantly more expensive than the flux core wires, regardless of whether 3.3% flux refers to weight, as I assume, or volume. By weight, 3.3% of 16oz is 0.528oz.

[jannie]

There are three main types of fluxes in use today: rosin flux, organic acid flux, and inorganic acid flux.

Rosin flux is the oldest and still one of the most common fluxes used for electrical components. It is only active when heated, and generally safe for unheated electrical circuits. Rosin flux can be cleaned using an isopropyl alcohol solution.

Organic acid flux is also commonly used for soldering electrical circuits. This flux cleans oxidation on electrical leads much more quickly. It is very important to clean this flux off electrical circuits because it leaves residue which will conduct electricity, causing shorts in your circuit. Organic acid flux is water soluble and can be cleaned with water.

Inorganic flux is used on stronger metals such as copper and stainless steel. It is not commonly used in electrical circuits, instead being used mainly for plumbing applications.

There is solder is available with flux inside the wire, called flux core solder 240. Flux core solder has flux in the center of the solder wire. Additional flux is unnecessary for most applications, but using additional flux still may make the solder easier to work with for some tasks. When selecting flux core solder, it is important to use rosin core solder for electrical applications. Acid core solder should only be used for plumbing applications.

Overall, I recommend rosin flux because it is most commonly used for soldering electrical circuits and is intended specifically for that purpose.