Olof skrev: ↑tor 28 aug 2025, 20:13
Jag har använt Carr 138 som är blyfritt och som jag är mycket nöjd med.
Dock har det varit svårt att få tag på på senare år.
Har spanat på mässor i England men inte hittat.
Diverse kina-import firmor säljer liknande då tuberna egentligen är tänkta att använda för maskinlödning men jag har inte provat.
/Olof
Jeg har ikke hatt noen særlig suksess med Carr 138, og tror ChatGPT er inne på noe av forklaringen:
For etched brass model railway kit building, low-temperature Sn42Bi58 solder cream (138 °C) behaves very differently from the classic tin/lead/cadmium or tin/lead solders used in the finescale kit-building world (e.g. Carr’s 145). A comparison:
1. Melting behaviour
Sn42Bi58: Melts and freezes sharply at 138 °C. Reflow is “all at once,” with no plastic range.
Carr’s 145 (SnPbCd ~145 °C): Also eutectic-like and low-temperature, but spreads more readily on brass. The cadmium addition improves flow and wetting.
Implication: Both are low-melt, but Sn42Bi58 requires more careful heat control because it is less forgiving on flow and doesn’t “chase” along a joint as well.
2. Flow and wetting
Sn42Bi58: Wetting on brass is relatively poor without an aggressive flux. The fillet tends to bead and sit locally rather than wick along etched seams.
Carr’s 145: Excellent capillary flow with a suitable liquid flux (phosphoric acid-based). This makes it ideal for long seams in etched brass kits.
Implication: For fine etched brass work, Carr’s 145 is far superior in how it “runs.” Sn42Bi58 is workable but needs much more flux and tends to form blobby joints.
3. Mechanical properties
Sn42Bi58: Brittle, with limited ductility. Joints can fracture under bending or handling stress.
Carr’s 145: More ductile; joints can withstand minor stress and flexing without cracking.
Implication: Sn42Bi58 is risky for thin brass tab/slot joints that will be filed or adjusted after soldering.
4. Heat input / compatibility
Sn42Bi58: Reflows at such low temperature that you can work very close to previously soldered joints without disturbing them.
Carr’s 145: Similar advantage, but with better strength and flow. Higher-temperature solders (e.g. Carr’s 179, 188, 296) are then used sequentially.
Implication: Both allow sequential soldering, but Carr’s system (145 → 179 → 188 etc.) gives more reliable results.
5. Practicality in model railway kit building
Sn42Bi58 pastes are designed for reflow ovens, not hand-soldering. Applying with an iron is messy; the flux system in the cream is optimised for PCB work, not brass.
Carr’s solders (145, 179, etc.) with liquid flux are purpose-designed for etched kit assembly and give cleaner joints, easier flow, and better mechanical strength.
Verdict:
Sn42Bi58 solder cream works, but is inferior to Carr’s 145 or other SnPbCd/SnPb solders for etched brass kits. It lacks the easy flow, ductility, and predictable behaviour that make Carr’s 145 the “gold standard.” Its only advantage is availability in lead-free contexts and very low reflow temperature. For anyone serious about brass kit construction, Carr’s 145 (or its higher-temp companions) remains the better choice.
Men om folk har suksess med dette bly og ikke minst Cadmium frie loddetinnet er ingenting bedre enn det!
Verdict: