Gap clearance is indeed a very important brazing criterion that must be carefully controlled, since it can, in fact, have a significant impact on overall joint strength, fatigue resistance, and corrosion resistance of brazed joints (due to minimal exposure of BFM at joint edges), among other benefits.
Important Question: What is your company’s attitude about this key topic of gap clearance in brazing? Does it prefer not to pay for anything closer than only “standard commercial tolerances” for parts, which could result in joint fit-ups that may not be tight enough for high quality joints? Where multiple-layered components are being brazed, regular commercial tolerances may not be good enough when the “stack up of tolerances” for all joint components are taken into account. In my own experience I’ve seen how poor joint fit-ups can lead to premature braze-failures in the field, or increased scrap during production at a number of brazing shops. I’m not saying that ALL brazing with loose fit-ups will not work adequately in service. But I have seen situations where that was the case. With well brazed, tight-joints, I have NEVER seen problems in the field, EVER!
So, what will you do in your brazing shop about this important topic of joint-clearance (gap-control)? Is it “good enough”, or does it need to be improved?
Next Month: We’ll look in more detail at surface roughness and its effect on joint fit-up and brazeability of parts when tight joint clearances are used.