Silicone gives an assembly flexibility, a wide temperature range, and weather resistance. Its usual drawback is cure speed: a moisture cure can take hours and stalls in shadowed areas. Incure Pyra-Sil™ 901 is a one-part silicone rubber that cures primarily with UV light and finishes in shadow with a secondary moisture cure.
The dual-cure advantage
A UV-only silicone cannot cure where light does not reach, under an opaque part, inside a lap joint, or in the shadow of a standing component. A moisture-only silicone cures everywhere but slowly, and thick sections take a long time.
901 combines both. UV light fixes the exposed material in seconds, locking parts in position and letting the line index forward. The secondary moisture cure then completes hidden and shadowed regions over the following hours, so the final part is fully cured throughout without holding the assembly on the line.
What Pyra-Sil™ 901 is
901 is a one-part UV/moisture-cure silicone adhesive that works as a form-in-place gasket (FIPG), a conformal coating, or a sealant. The cured rubber resists ozone, weathering, and elevated temperature, which suits it to outdoor and under-hood service.
Where it is used
- Consumer and industrial electronics: bonding and sealing components in enclosures and modules.
- Automotive: securing sensors and connectors, and forming gaskets on housings and covers.
- Renewable energy: sealing inverter and combiner-box enclosures, and gasketing outdoor electrical housings against weather and UV.
- General industrial manufacturing: general-purpose bonding and sealing where a flexible, temperature-tolerant joint is needed.
Form-in-place gasketing
For FIPG use, 901 is dispensed as a bead along a sealing flange, given a UV pass to fix the bead so the housing can be closed and moved, and then left to complete its moisture cure. The result is a gasket shaped exactly to the flange with no die-cut part to inventory and no compression set from a pre-formed gasket sitting in storage.
Dispense path control and bead consistency matter more than for a bonding application, because a gap in the bead is a leak path. An automated dispense head and a fixed UV station give repeatable results.
Application and cure control
901 is applied by manual brushing for repair and low volume, or by automated dispensing or spray for production. The UV step needs a measured dose; verify it with a radiometer and account for lamp aging. Batch fixturing under Incure L-Series UV LED flood lamps covers trays at a set intensity, and inline work runs on an Incure CDM UV conveyor.
For help matching Pyra-Sil™ 901 to a gasket flange, seal geometry, or bonding application, Email Us with the part details.
Failure modes to design against
- Assuming the UV fix is a full cure: shadowed material still needs its moisture-cure time before the part sees load or pressure.
- Bead gaps in a FIPG seal: control dispense path and flow rate; inspect the bead before closing the housing.
- Curing in very dry air: the secondary moisture cure slows when humidity is low; deep or fully shadowed sections may need more time.
- Expansion mismatch at a rigid bond: silicone tolerates movement well, but see how CTE mismatch causes adhesive bond failure for the general mechanism.
Designing a flange for form-in-place gasketing
A form-in-place gasket performs only as well as the flange it sits on. The sealing surface should be flat and continuous, with no interruptions where the bead would have to bridge a gap. A shallow groove or a raised bead stop helps locate the dispensed material and controls how much it spreads when the housing is closed. Corners are the usual leak point, so the dispense path should slow through corners to keep the bead cross-section constant rather than thinning as the head changes direction.
Compression is the other variable. The closed housing should compress the cured gasket by a defined percentage, enough to seal against surface irregularities, not so much that the silicone is over-strained. Because 901 is dispensed and cured in place, each gasket matches its own flange exactly, which removes the fit and inventory problems of die-cut gaskets.
Frequently asked questions
Q: How fast does the UV step fix the material?
A: Exposed silicone fixes in seconds under adequate UV, enough to handle and index the assembly. Full through-cure of shadowed regions takes hours via the moisture mechanism.
Q: Can it be used purely as a moisture-cure silicone?
A: Yes, in areas with no light access it will cure on ambient humidity alone, just more slowly.
Q: Is it a coating or an adhesive?
A: Both. It works as a conformal coating, a sealant, and a form-in-place gasket depending on how it is applied.
Getting support
Incure can help select a silicone grade, define the cure process, and troubleshoot seal or bond issues. Contact Our Team to discuss your application and request technical data.
Visit www.incurelab.com for more information.