A formed-in-place gasket line that ran flawlessly for months can start producing intermittent leaks with no obvious change to the material, the program, or the operator — and in almost every case, the actual cause is a dispensing-process drift rather than a sudden material failure.
Why FIPG Defects Often Look Like Material Problems
Because a formed-in-place gasket bead is applied and cured in one continuous process, most of its failure modes trace back to dispensing variables — valve condition, rheology, bead placement — rather than the sealant chemistry itself. Treating an intermittent leak as a material defect first, rather than checking the dispensing process, wastes time chasing the wrong cause.
Defect One: Voids and Short Shots
A gap or thin spot in the dispensed bead, invisible until the joint leaks under pressure, is almost always caused by an air pocket in the material feed line, a partially clogged valve tip, or a dispense speed that’s outrun the material’s actual flow rate through the valve. Vision-based inspection mounted directly on the dispensing robot catches this before assembly, since a short shot is often invisible to the naked eye once the mating part is placed on top of it. Checking material feed pressure and valve tip condition on a scheduled basis prevents this defect from becoming intermittent and hard to trace.
Defect Two: Bead Sag or Slump Before Cure
A bead that looked correctly placed at dispense but has slumped or sagged by the time the mating part is joined points to a rheology mismatch — the material isn’t sufficiently thixotropic to hold its dispensed shape under its own weight before cure begins. This shows up more often on vertical or overhead joint surfaces than on horizontal ones, since gravity has more work to do pulling the bead out of position. Confirming the specified material’s thixotropic index against the actual joint orientation, rather than assuming a horizontal-tested material behaves the same way vertically, is the fix.
Defect Three: Tailing and Inconsistent Bead Width
A bead that starts and ends with inconsistent width, or leaves a trailing thread of material at the end of a dispense path, usually indicates a valve type mismatched to the material’s viscosity — a needle valve struggling with a high-viscosity paste, for instance, or a diaphragm valve poorly suited to a very low-viscosity material. This defect is often intermittent because it’s sensitive to small viscosity shifts from ambient temperature changes or batch-to-batch variation, which is why a valve that worked acceptably in initial trials can start producing tailing defects seasonally.
Defect Four: Under-Cure at the Compressed Bond Line
A gasket that cures fully at its exposed edges but remains soft or under-converted where the mating part compresses it most tightly is a common defect in wet-compression FIPG applications, particularly with UV-cure or moisture-cure chemistries that depend on some degree of exposure or ambient humidity to complete conversion. Compression can reduce a moisture-cure material’s access to ambient humidity at the sealing interface, and a UV-cure material has no light exposure at all once compressed. Email Us to discuss a dual-cure or heat-assisted cure mechanism if your process depends on wet compression against an opaque mating surface.
Defect Five: Leak Paths at Bead Start/Stop Overlap
Every continuous dispensed bead has a start and stop point, and if the path doesn’t overlap sufficiently at that junction, it leaves a structurally weaker seam exactly where two bead passes meet. This defect is easy to miss visually since the overlap region looks continuous, but it’s mechanically the most vulnerable point in the entire gasket bead. Programming a deliberate overlap distance into the dispense path, rather than a simple closed loop that just meets itself, closes this gap.
Defect Six: Residue-Driven Adhesion Failure
Oil, mold-release residue, or moisture on the substrate at the point of dispense prevents the FIPG bead from wetting out and bonding properly to the flange surface, producing a seal that looks intact visually but separates under pressure or vibration. This is functionally identical to a surface-preparation failure in any other adhesive-bonding process, and confirming substrate cleanliness immediately before dispense — rather than assuming an upstream cleaning step held through handling — resolves it.
A Diagnostic Sequence for FIPG Line Issues
Working through these causes in order — void/short-shot inspection, rheology-versus-orientation check, valve-type match to viscosity, cure completeness at the compressed interface, start/stop overlap review, and substrate cleanliness verification — resolves most intermittent FIPG leak complaints without requiring a material change. Incure supplies UV-curable, heat-curable, and moisture-curable FIPG formulations engineered around these specific process variables, and pairing the right chemistry with UV cure chambers built for consistent dose delivery addresses several of the cure-related causes above at the equipment level. For the broader material-selection background behind this diagnostic guide, see Incure’s FIPG explainer.
If an FIPG line is producing intermittent seal failures and needs root-cause diagnosis, Contact Our Team with your material, valve type, and joint geometry.
Visit www.incurelab.com for more information.