Product managers from Johns Manville, a company that uses both flame attenuation and rotary methods for insulation production, recently delved into why they usually use flame attenuation for HVAC products over rotary. Their Linacoustic RC duct liner, for example, is flame attenuated; the finer fibers make for easier processing on duct fabrication equipment.

“If you imagine you're cutting through something with a knife and all of a sudden you have a dense spot, your knife slows and then you get stuck there. It’s a lot easier if you can just be smooth and consistent through the cut,” said Cassie Todtenhagen, product manager of insulation systems at Johns Manville.

Todtenhagen broke down the difference between these two insulation recipes by first defining flame attenuation as a process that usually relies on a pot that melts marbles, dripping strands down using gravity for its first stage of attenuation, as a gas burner elongates the fibers for the second phase.“

‘Pot and marble’" and ‘flame attenuation’ are generally considered synonymous, although the latter is a bit more general,” Todtenhagen said. 

From the insulation manufacturer’s perspective, sourcing marbles can be a constraint to production, as the marbles need to be produced before they can be used. The multiple phases of production limit scalability. 

That’s why JM pioneered the development of rotary fiberizers in the 1960s, with the rotary method of fiberizing glass yielding a higher throughput at much lower energy usage. Today, JM deploys over 100 rotary fiberizers across its manufacturing plants, using high speed air jets to attenuate the strands of glass instead of gas burners, although there are a number of hybrid fiberizers.

But when it comes to the manufacturers of HVAC equipment, who require thin insulation, JM relies on the flexibility of their pot and marble infrastructure to produce more consistent fibers for those narrower depths. Likewise, they have the flexibility to produce smaller rolls than rotary lines.

And while marbles do add an extra step to production, they also add a step of quality control.

“We make the marbles, we quality control the marbles, and then you’re remelting those marbles instead of melting them for the first time. That allows the fibers to be more consistent than the batch rotary process,” Todtenhagen concluded. “The rotary process is continuous and makes much more, less refined fiberglass than the pot and marble process.”