How to always spray epoxy PFP coatings on-ratio
Correct ratio assurance is critical to providing high quality when spraying intumescent fireproofing materials.
When two chemicals are mixed, the ratio at which they are combined is key to maintaining consistency and uniformity. Traditionally, plural-component equipment has relied on fixed-ratio proportioning to regulate the flow of component materials. With this approach, positive displacement pumps are used to displace a fixed amount of material on each stroke. Pressure gauges are used to monitor pressure to ensure that each pump is working properly.
However, this mechanically linked approach can lead to reliability issues with highly viscous materials, particularly with epoxy intumescent materials that often contain fibers and are heated, mixed and pressurized prior to entering the metering pump. Ratio errors can occur if one of the component materials is not fully compressed or if the pump is not fully loaded. For most coatings, compressibility is negligible, but with epoxy PFP coatings, A and B components can expand to over twice their volume.
With more recent technology, variable-ratio proportioning is used to regulate the two-component mixing. Linear position sensors and pressure sensors on each metering pump are used to measure pump rod displacement and the fluid pressure coming out of each pump. Two pumps run independent of each other and are monitored electronically to adjust flow as needed. Also referred to as dosing proportioning, this approach to plural-component spraying can provide more accurate ratio control, because the pumps are not mechanically linked, and the system can monitor the material volume after the fluid has been pressurized to near spray pressure. It can cancel out the portion of the pump stroke that compresses but doesn’t pump the material.
Are you interested in spraying your fireproofing intumescent coatings more consistently? Drop us a line and we will be happy to discuss the Graco XM PFP technology for your specific requirements.
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