The Anglo-Canadian Corner
Lotus Seven Research and Musings by William Fayers

Bronze Welding Rods suitable for repairs to your Lotus
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Nickel Bronze Brazing Rod.

Contemplating some minor chassis frame repairs to my Lotus Seven Series 3, I decided to investigate the availability of suitable nickel bronze brazing rod to complete the repairs.

In January 2014, I commenced a search of the web for suitable sites regarding Nickel Bronze Welding. I found a forum whereby contributors were asking questions and receiving good advice regarding bronze welding on Formula Ford and other sports racing cars manufactured in the U.K. The name of Calor Bronzecraft No.3 cropped up a few times. One contributor noted that it was now unavailable (2011 post), but that it was the rod of choice for Lotus, Arch Motors, and a number of other U.K. manufacturers of sports road and racing cars until its demise.

I already had a good article on braze welding written by Bill Steagall, who had kindly forwarded a copy to me. It has been published in a couple of Lotus club magazines, describing how to braze weld with nickel bronze rod using a jet fluxer. Bill had also added a postscript advising that Calor Bronzecraft No. 3 was unavailable since writing his original article.

I found the Murex Company (U.K.) web site, and at the time of writing (March 2014) Murex still had the specifications of their "Saffire" Nickel Bronze rod (10% nickel content) displayed on their site. An email reply from the Murex Technical Section advised that Murex had 'moved on' from gas welding products, and their line of braze welding rods and associated fluxes were no longer available.

A rod called SifBronze No. 2 (from Weldability Sif U.K.) was highly recommended by a few of the forum contributors. These included an ex-Arch employee now living in New Zealand who still prefers a jet fluxer for braze welding, and a U.S. auto repair shop specializing in sports racing car repairs, likewise using a jet fluxer.

I have recently been in contact with Bruce Robinson at Arch Motors and although he is a busy man, he kindly took the time to answer a few questions regarding their history with Lotus. Bruce advised that Arch has been using the gas jet flux braze welding process since the 1950s. They initially manufactured wishbones, brackets, pedals etc., for Lotus, and in January 1968 commenced construction of the Lotus Seven Series 2 chassis frame and associated parts. This was followed by the remainder of the Seven line (Series 3 and 4 cars), as well as Formula Ford chassis for Lotus and other constructors. Colin Chapman fully approved of the braze welding process for tubular chassis frame construction.

Bruce noted that since the demise of Calor Bronzecraft rod, Arch now use SifBronze No.101, which is specifically formulated for use with the jet flux process. No.101 is a manganese/silicon bronze rod with no nickel content (according to the specification sheet on their web site), and has an ultimate tensile strength of 66717 p.s.i. (converted from the Newton/mm2 on the spec. sheet). For anyone interested in seeing how this product flows, please see the 'YouTube' videos "Ariel Atom Bronze Welding"; "Bronze Welding V8 Ariel Atom"; and "Bronze Welding" all by an excellent welder - Brian Ashcroft, using jet flux equipment and SifBronze No.101 rod. Brian Ashcroft advised me of the following: "I have used the Sif No.2 and it does weld very similar to No.101, it just doesn't run quite as nicely. We found that No.2, although having a higher ultimate tensile strength, did tend to be more brittle than 101 which is why we prefer 101. I haven't come across a weld failure with 101 yet in my 18 years of using it" (Note: Michael Costin and David Phipps allude to nickel bronze or manganese bronze welding in their book "Racing and Sports Car Chassis Design" published by Robert Bentley Inc.).

I checked SifBronze No.2 and this rod has a u.t.s. of 78,320 p.s.i., and has a 9 or 10% nickel content (both values provided on the spec. sheet). 1/16" diameter rod seems to be the preferred size according to the users I have communicated with, but larger diameters are available in 1kg., 2kg., and 5kg. bundles. A check of the specifications between No.2 and Murex Saffire rod shows almost identical chemistry. A welding supply company in Poole, Dorset U.K., advised me that Murex did not manufacture their own bronze rods or fluxes, but instead obtained them from Weldability Sif. In fact, as noted by John Mihalich Jr., a contributor to the original forum, Calor, Murex and SifBronze No.2 all have the same BSS 1453 (1972) (1987) C5 designation in the U.K.

For Lotus owners in the U.S. wishing to source bronze rod from their own country, there are a few choices. In the U.S., nickel bronze rod (usually 9-11% nickel content) is described as RBCuZn-D, with the 'RB' standing for 'Rod Braze Welding'. It is also known as 'Nickel Silver' rod, and can be bare or flux coated. Inweld Corporation (U.S.) advise that the name 'Nickel Silver' refers to the weld deposit colour and does not imply the existence of silver in the chemistry. The weld deposit is described on another site as having the appearance of 'white brass'. This may be a different colour from the original Calor Bronzecraft rod as reported by another forum contributor.

Other nickel bronze rods found on the web are: Eutectic ( Eutec #16, claiming a u.t.s. of 100,000 p.s.i.; Allstate No. 11; and Harris 'D' rod No.17 (only shown on their web site as '17 FC' i.e. flux coated). I noted three companies on-line (there are a few more), who advertise nickel bronze rod to RBCuZn-D specifications, and all three company web sites show identical chemistry, however the u.t.s values of their rods vary. These are: The Gas Flux Company of Ohio (rod GF-72); Welding Material Sales Inc. of Illinois; and Unibraze of Texas. I contacted Unibraze, and a very helpful sales technician provided the address of a distributor for their product close to where I live. He further advised that their rod, and possibly the nickel bronze rod from other sources in the U.S., now comes from China. Considering that China has really improved on the quality of the metals they export (e.g. SCCA Formula Ford crankshafts available from Jay Ivey and Pegasus etc.), it may hopefully follow that their nickel bronze rod is of a high quality. However, be advised that I have no evidence to back this up!

If you wish to purchase your own gas jet fluxer, Plasmatech U.K. sells a complete system as well as liquid flux. They do not sell bronze welding rods. Mr. Bill Ross of Plasmatech advised that as a former Sales Director at Calor Weldcraft, it was a sad day when that company went out of business with the loss of its popular products. Mr. Ross purchased the manufacturing rights of the Model 'W' gas fluxer, and highly recommends Weldability Sif products. He noted that with the higher cost of nickel, SifBronze No.101 may be preferred by manufacturing and repair companies as a cheaper alternative to No.2, as it is still a strong rod and easy to use especially with a jet fluxer.

The Gas Flux Company of Ohio, U.S.A, sells a jet flux system and can supply liquid flux and consumables.

The late Carroll Smith in his series of excellent books on race car construction and preparation – particularly 'Prepare To Win', noted that before attempting to nickel bronze weld, the metals to be joined must be totally free of oil, grease, rust, or any other contaminants in order to obtain an excellent bronze weld. He suggested using Methyl Ethyl Ketone to clean the tubes prior to welding. It may also be appropriate to give the bronze rod a wipe of MEK prior to use. Blasting medium, such as soda or walnut shells, may also be used to clean mild steel tubing of paint prior to braze welding or even fusion welding.

If anyone is contemplating a partial or full rebuild of their Lotus, I have documented cross-references to the alloy specifications originally used by Lotus. These can be found here on the 'SimpleSevens' website by clicking this link: Lotus Seven Parts and Repair and scrolling down the page to "Repairs to Aluminium Panels".

In conclusion, I would like to thank the following Lotus owners:

Bill Steagall for providing excellent details on how to braze weld using a jet fluxer.

John Mihalich Jr., Lotus 61FF owner/racer; Registrar Lotus Formula Ford Register; Registrar Historic Lotus Register. John compiled and supplied me with a spread-sheet comparing five of the leading nickel bronze rods that he has tried.

John Donohoe. Compiler/owner of the 'SimpleSevens' web site, for allowing me to contribute to the site with information I have collected from very helpful owners, racers and factory mechanics involved with Lotus sports cars.

- William Fayers