A brazing ring or preform is filler metal formed into the exact shape and quantity one joint needs, so every joint on a production line gets the same amount of alloy in the same place. Metline supplies rings, washers, shims, strips and drawing-specific preforms in aluminium-silicon (4047, 4045) and zinc-aluminium alloys to AWS A5.8 and ISO 17672, to customers worldwide; silver and copper-based fillers are covered here for comparison.
Hand-fed rod depends on the operator: one joint gets too little alloy and leaks, the next gets too much and leaves icicles inside the tube. A preform removes that variable. The filler is weighed out once, at the design stage, and then placed on the part before heating.
The commonest preform is a wire ring slipped over a tube before it enters a socket or fitting. When the assembly reaches brazing temperature, the ring melts and capillary action draws the liquid alloy into the clearance between tube and socket. Because the ring sits in a fixed position and holds a fixed volume, joint quality becomes a matter of temperature and time, which are easy to control on an induction coil, a tunnel furnace or a rotary flame machine.
Preforms also make automation practical. Rings can be loaded by vibratory feeders, washers can be stacked in fixtures, and strip can be fed from a coil, so a line can braze hundreds of identical joints per hour without an operator feeding rod. For manual work the benefit is different but just as real: less wasted alloy, fewer reworked joints, and a clear count of filler consumed per assembly for costing.
The base metals decide the alloy family; the heating method and service conditions then narrow the grade. Metline supplies the aluminium-based families, aluminium-silicon and zinc-aluminium; silver, phos-copper and copper fillers appear in the table only for comparison, because many assemblies that carry aluminium rings also have copper joints brazed with those alloys. Melting ranges below are the solidus and liquidus published for each AWS A5.8 classification; brazing is carried out at or above the liquidus.
| Family (AWS) | Typical grades | Melting range | Joins | Flux |
|---|---|---|---|---|
| Silver, cadmium-free (BAg) | BAg-7 (56 % Ag), BAg-28 (40 % Ag), BAg-24 (50 % Ag, Ni), BAg-36 (45 % Ag) | 618 – 652 °C (BAg-7) to 660 – 707 °C (BAg-24) | Copper, brass, carbon and stainless steel, nickel alloys, carbide | Required in air |
| Phosphorus-copper (BCuP) | BCuP-2 (silver-free), BCuP-3 (5 % Ag), BCuP-5 (15 % Ag) | 710 – 793 °C (BCuP-2); 643 – 802 °C (BCuP-5) | Copper to copper; copper to brass with flux | None on copper-to-copper joints |
| Pure copper (BCu) | BCu-1 (99.9 % Cu) | 1083 °C | Carbon and low-alloy steel, stainless steel, in a protective furnace atmosphere | Reducing atmosphere instead of flux |
| Aluminium-silicon (BAlSi) | BAlSi-4 (4047, 12 % Si), BAlSi-5 (4045, 10 % Si) | 577 – 582 °C (4047); 577 – 591 °C (4045) | Aluminium to aluminium (1xxx, 3xxx, low-Mg 6xxx) | Fluoride flux (NOCOLOK-type) or vacuum |
| Zinc-aluminium (Zn-Al) | Zn-22Al (78/22), Zn-15Al | 427 – 482 °C (Zn-22Al) | Aluminium to aluminium and aluminium to copper at low temperature | Caesium-fluoroaluminate flux, usually cored |
Melting ranges for the AWS families are from the AWS A5.8 classification tables; the Zn-Al range is the published value for the 78/22 alloy. Actual brazing temperatures depend on part mass, heating rate and flux; confirm them in a trial before production.
Lowest working temperature of the high-strength fillers and the widest range of base metals. BAg-7 flows almost like a eutectic and is the usual choice for stainless steel and food or medical equipment; BAg-24 adds nickel for wetting on steel and carbide. Cadmium-free grades are now the norm for new designs.
The standard for copper refrigeration and air-conditioning circuits. Phosphorus deoxidises copper, so copper-to-copper joints need no flux. Never use them on steel, stainless or nickel alloys: the phosphorus forms brittle phosphides at the interface.
Used almost only in controlled-atmosphere furnaces, where pure copper flows into very tight, even press-fit clearances on steel parts. The result is a strong, clean joint with no flux residue, common for hydraulic fittings and automotive steel assemblies.
4047 and 4045 melt about 50 – 60 °C below most aluminium alloys, which is the working window for flame, induction or controlled-atmosphere brazing of aluminium tube, fittings and heat-exchanger headers.
Zinc-aluminium rings fill the gap between these families. Because Zn-22Al is fully liquid at about 482 °C, well below the solidus of 3003 or 6063, it lets an aluminium tube be joined to a copper stub or service valve without the risk of melting the aluminium wall. That makes it the usual aluminium-based choice for mixed aluminium-copper refrigeration circuits, and the alloy Metline recommends when a drawing pairs aluminium tube with a copper fitting.
| Preform | Typical dimensions quoted | Best for |
|---|---|---|
| Wire rings (closed or butt-joined) | Ring ID to suit tube OD from about 2 mm upward; wire 0.3 – 3 mm | Tube-to-socket and pin-to-hole joints; HVAC, refrigeration, automotive lines |
| Internal rings | Sized to sit in a groove inside a fitting | Blind joints, where filler must start inside and flow outward to a visible fillet |
| Washers and discs | Stamped from strip 0.05 – 2 mm thick | Flat face joints, studs, carbide tips, contacts and terminals |
| Shims and foils | Thin strip cut to the joint footprint | Large lap joints and carbide-to-steel joints where filler must cover an area |
| Strip and wire on spools | Coils or cut lengths | Long seams, automatic feeding, in-house forming of preforms |
| Custom stampings | Made to drawing: slots, tabs, irregular outlines | Complex assemblies where filler has to sit in more than one place |
Dimensions in the table are the ranges we are normally asked to quote for aluminium-silicon and zinc-aluminium preforms; very small or very large rings, unusual cross-sections (flat or D-section wire) and special alloys can be checked against a drawing. Tolerances are agreed per part; ring inside diameter and wire diameter are the two dimensions that matter most for fit and filler volume.
A ring should hold enough alloy to fill the joint clearance completely and leave a small fillet at the mouth, plus an allowance for alloy that wets the surrounding surfaces. Too little filler leaves voids; too much runs into the bore or leaves a heavy bead that wastes filler.
| Filler family | Recommended joint clearance (radial) |
|---|---|
| Silver (BAg) with flux | 0.025 – 0.125 mm |
| Phos-copper (BCuP) | 0.025 – 0.125 mm |
| Copper (BCu), furnace atmosphere | 0 – 0.05 mm (light press fit works) |
| Aluminium-silicon (BAlSi) | 0.15 – 0.25 mm for short laps; wider for long laps |
Clearances follow the ranges published in the AWS Brazing Handbook; they are measured at brazing temperature, so allow for different expansion of dissimilar metals.
No flux on the ring. Use them with brushed or dispensed paste flux, in controlled-atmosphere or vacuum furnaces, or as phos-copper rings on copper-to-copper joints that are self-fluxing.
A thin, bonded flux layer on the outside of the wire. The flux becomes active early in the heating cycle and protects the joint area as it heats, which suits flame and induction brazing of silver alloys.
Flux sealed inside a seamed or seamless wire. It survives handling and feeding without chipping, releases at the moment the alloy melts and leaves less residue, so it suits automated lines and aluminium brazing.
Flux chemistry follows the alloy. Silver and copper-based fillers use fluoride-borate fluxes active up to roughly 800 – 900 °C (AWS type FB3 family). Aluminium fillers need non-corrosive potassium fluoroaluminate flux, often with caesium additions when the base alloy contains more magnesium. For aluminium and aluminium-to-copper joints, tell us your base metals and heating method and we will match flux and Al-Si or Zn-Al alloy as one system.
| Factor | Rings and preforms | Rod and wire |
|---|---|---|
| Filler quantity | Fixed per joint, set at design | Depends on the operator |
| Consistency | High; suits sampling plans and leak testing | Variable between operators and shifts |
| Speed | Fast; heating is the only manual step, or none | Slower; heating and feeding together |
| Tooling cost | Ring forming or stamping set-up for custom sizes | None |
| Best volume | Repeat production, hundreds to millions of joints | Repairs, prototypes, site installation |
| Alloy waste | Minimal | Off-cuts and over-feeding |
Many buyers use both: preforms on the production line and the same alloy in rod form for repairs and field service. We can supply matching rod, wire and rings in the same aluminium-silicon or zinc-aluminium alloy from one specification so that qualification records stay valid across both.
No. Phos-copper rings are self-fluxing on copper-to-copper joints, and copper or silver rings used in a hydrogen, nitrogen-hydrogen or vacuum furnace need no flux. Silver rings brazed in air and aluminium-silicon rings both need flux, either applied separately or built into a coated or cored ring.
A ring is one type of preform. "Preform" covers every pre-shaped piece of filler: rings, washers, shims, foil cut-outs, strip and custom stampings. Rings suit round tube and pin joints; the other shapes suit flat, area or irregular joints.
Yes, but brass contains zinc, whose oxide the phosphorus cannot remove, so a flux is needed. For copper-to-steel or copper-to-stainless joints, use a silver alloy instead, because phosphorus embrittles iron and nickel.
Calculate the volume of the joint clearance, add 25 – 50 % for the fillet and wetting, then choose a wire diameter whose ring volume matches. The worked example above shows a 15.88 mm tube needing a ring of about 1.3 mm wire.
Coated rings release flux early and suit flame brazing, where the joint area needs protection while it heats. Cored rings protect the flux during handling and feeding and leave less residue, which suits automated induction lines and aluminium brazing.
Yes, for Al-Si and Zn-Al alloys. Send the drawing or ring dimensions, alloy and expected annual use, and we will quote samples for qualification together with production pricing.
Send your joint drawing, base metals, heating method and annual quantity. We will propose the Al-Si or Zn-Al alloy, ring size and flux option and quote samples and volume supply.
