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Tube Fabrication Process
How is the Hydro-form tube made?

   Reynolds >FAQ        Printer Version

FAQs: Updated: 19 March 2007

Because it is a new metal for use in the bike industry, we are working to ensure 953 allows for frame-builder processes but will expect there will be detailed questions that may require an periodic update, or where we have had feedback that can be shared.

Possible options for frame-building with 953 have been added on this update, along with comments on staining due to salt, bottle boss diamonds reinforcements, and planned additions to the 953 range.

To cover questions that have been raised so far

  • Material - maraging stainless steel, specially manufactured for Reynolds by Carpenter Specialty Alloys, USA. This material undergoes a double vacuum remelt process to get achieve the necessary properties and purity. It has a very low carbon content, which has an advantage that machinability compared to e.g. AerMet 100 which is improved due to low carbide content.
  • Made from cold-rolled strip steel into a tube with a highly homogenous weld, done in an inert atmosphere (specialist aerospace weld mill). The Metal used is double vacuum melted by Carpenter to achieve very high purity levels that are typical of aerospace applications. Although a departure from Reynolds' preference of using seamless materials for high-end tubing, tests and cross sections of the weld area show the seam is "essentially invisible" when examined microscopically.
  • 953 passes 3 tests after ageing at 950 F a) 50% flatten from e.g. 28.6mm OD to 14mm width without any cracking along the weld seam b) drilling into the weld seam area does not cause any seam cracking c) no visible seam line on the finished tube after polishing. These tests indicate that the Carpenter process route has overcome the issues normally seen on seamed, welded tubing.
  • Ultimate tensile strength - 1700 to 2050 MPa depending on process and heat-treatment selected (853 airhardening steel UTS 1200-1400 Mpa). Density is 7.79 gm/cc. Poissons ratio is 0.30.
  • Yield strength 1500-1900 MPa depending on the combination of cold-working, butting, and ageing temperature. (1500 MPa is approx. twice the yield strength of Cold-worked, Stress relieved 3-2.5 titanium). At 950 F ageing temperature, yield strength should be in the 1650-1730 MPa range based on internal tests. Changing the ageing temperature can increase elongation.
  • Stiffness Modulus (E) is 200 GPa, similar to other steel alloys. Although Reynolds do not have frame design expertise, we assume that if higher stiffness is required when lighter tubes are used, advantage can be taken of the higher strength by using slightly oversize but thin wall tubes with a lower overall weight.

  • Can be TIG welded with AWS ER630 wire or silver brazed using recommended filler wires. NB Silver brazing trials indicate this is workable, but allow for corrosion protection on the braze area. Silver brazing into lugs will also work.
  • Brass brazing materials with melting points around 800-900 C have worked although if held at temperature for over five minutes, will effectively anneals the 953 tubing down to strengths typical of heat-treated Cr-mo. Allow for corrosion protection in the brazing zone. Builders have indicated to us that the brass flows better when a special stainless steel flux is used. (Typical examples suggested are SIF "tool tipping & brazing stainless flux" and Castolin "Castolin 181", EN1045 FH10 OR DIN8511 F-SH 1 standard).
  • Corrosion resistance is similar to type 410 stainless steels. Note that under some conditions e.g. sulphuric acid, prolonged submersion in sea water 953 will show signs of pitting and corrosion. We assume these are not normal conditions for a bike frame!
  • In normal use, brown staining of the surface does occur due to sweat, salty road etc if not protected/painted. The staining can be removed with "scotch-brite" or an equivalent, and trials have shown that this is a superficial stain that does not weaken the tubes. We have successfully tried domestic cleaners used on stainless steel sinks, which also clean off these stains - a tip for your customers when using the frames.
  • The inside of the tube and fittings may have a brown tint due to the heat-treatment process; we now use a nitrogen purge to reduce this discolouration.
  • Do not use steel wool or shot blast using steel pellets, as this will leave a residue that looks like rust after using whilst riding. Passivation of the raw frame may also help to clean off all residues on the frame if left unprotected.
  • With thin wall seat tubes and down tubes, we recommend using bottle boss reinforcing diamonds (e.g. silver brazed into place) as bosses with a small lip may cause cracking around the edge of the boss. With heavy bottles, or battery packs used inside a bottle cage, these place a very high load on the thinnest part of the tube.
  • The recommended method of building is the use of pre-aged tubing, so frame builders can fabricate the frames, but assume mitre and cutting could be slow due to tube hardness. Reynolds can supply tubes without ageing but there may be issues on Ti pickup in the weld area when the complete frame is aged - please contact Reynolds to discuss this option. Ageing will leave a superficial tint, which can be removed by light polishing, shot blasting or pickling.
  • Purging whilst welding the frame is highly recommended as this improves the weld strength. This would reduce possible contamination on the inner surface of the weld joints, improving corrosion resistance.
  • Frame alignment should be carried out before ageing but we do not expect jigs to be needed when ageing as this is a relatively low temperature for steel heat-treatment.

  • Cold worked butted walls from 0.65mm down to 0.3mm (e.g. .65/0.4/0.65, 0.5/0.30/0.50mm) depending on diameter
  • Tube diameters 28.6, 31.75, 34.9 & 36.4 mm.
  • Seatstays in 316L alloy at 19mm and 16mm diameter, chainstays in 953 at 24.0mm.
  • Seatstays 19 x 0.5 in 953 under development
  • Full range of stainless steel fittings / BB shell / head tube available in compatible alloys including 953 BB shell and rear drop-outs as well as 901 (Custom 630/17-4PH grade alloy). An alternative head tube is the 36.4mm OD/34.0mm ID at 160 and 190 mm long, made from solid bar in 901, if the lightweight head tube 38.1mm*0.7mm in 953 is too thin for your design.
  • Oval/round chainstays in 0.5mm wall underdevelopment.
  • For ATB use, cranked .7/.5 oval/round chainstays with 5 degree bend also and indent.
  • Variety of butt profiles to suit frame sizing and lugged construction if needed, please ask.
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