Bonding a molded plastic connector to a metal fitting is one of the hardest joints in disposable device assembly: two materials with nothing in common chemically, a small bond area, and a requirement for a leak-tight, pull-resistant joint made in a few seconds on a fast line.
The plastic-to-metal challenge
Plastics and metals differ in surface energy, in stiffness, and in how much they expand when warmed. An adhesive that bonds well to one often bonds poorly to the other, and the joint carries stress every time the assembly is pressurized, pulled, or temperature-cycled. Solvent cements do not work on metal. Two-part epoxies bond both but cure slowly, holding up a high-volume line.
Incure’s Cyro-Weld™ 5005 is a high-strength, multi-substrate adhesive that cures rapidly under UV or visible light. It is formulated to bond engineering plastics such as polycarbonate and polyester to metals including stainless steel, and it develops high bond strength quickly so the joint can be handled immediately. A fluorescing companion grade, 5005F, adds a tracer for inspection. Both are formulated to meet ISO 10993-5 and are validated for EtO and Gamma sterilization.
Where Cyro-Weld™ 5005 is used
- Bonding molded luer and threaded connectors to metal fittings
- Attaching metal reinforcement and strain-relief hardware to plastic housings
- Assembling fluid-transfer sets where a rigid fitting meets a molded body
- Bonding metal inserts and bushings into plastic components
- Fixing sensor and transducer bodies into disposable cartridge housings
These are external, disposable fluid-handling and instrument components. The adhesive is not used for implanted parts.
Why visible-light cure helps
A pure-UV adhesive needs UV to reach the bond line. When one of the parts is an opaque plastic or a metal fitting that blocks the light, the joint sits in shadow. Cyro-Weld™ 5005 responds to visible light as well as UV, which lets the cure energy get to the bond line through translucent plastics and around edges that would shade a UV-only adhesive. Grades in the family also carry a secondary cure mechanism for resin that no light reaches.
Delivering the dose is still a lamp problem. Incure’s guidance on matching a spot lamp light guide to reach and working distance and on what a light guide does in a spot-lamp system covers cure of the small, often curved joints these connectors present.
Surface preparation
Metal fittings should be clean and free of drawing oils and oxide; a solvent wipe or a light abrasion improves anchorage. Low-surface-energy plastics benefit from plasma or corona treatment right before bonding. Incure’s discussion of matching a glass-and-metal bonding grade to viscosity and tensile requirement is a useful reference for the metal side of these joints.
The role of CTE mismatch
Because plastic expands several times more than stainless steel, a rigid bond line between them builds internal stress on every heat-up. Over many cycles, or through a sterilization exposure, that stress can start a crack at the edge of the joint. Incure’s explanation of how CTE mismatch causes bond failure covers the mechanism, and it is why bond area, bond-line thickness, and cured modulus all matter in a plastic-to-metal joint.
Joint geometry for a leak-tight connector bond
A connector-to-fitting bond is usually a slip fit: the fitting enters a molded socket and the adhesive fills the annular gap. That gap should be sized so the adhesive is 50 to 250 micrometers thick on the radius. Too tight and the adhesive is wiped out during assembly, leaving dry spots that leak; too loose and the joint relies on the adhesive’s bulk strength rather than a thin, strong bond line. A lead-in chamfer on the socket helps the adhesive form a fillet at the mouth of the joint, which is where a burst failure usually starts.
Assemble to a positive stop so the engagement depth is repeatable. Engagement depth sets the bond area, and bond area, not adhesive choice, is usually what determines whether the joint meets its pull-off spec.
Handling opaque fittings
When the metal fitting blocks all light to part of the bond line, three tactics apply: use the visible-light response to reach the bond through a translucent plastic socket, rely on the grade’s secondary cure mechanism for the fully shadowed region, or design the socket with a thin translucent window so a spot lamp can reach the critical fillet directly. The first two are usually enough for a connector-sized joint.
Qualification
A plastic-to-metal joint qualification typically measures pull-off and burst strength, strength after thermal cycling, strength after the full sterilization dose, and leak rate at the rated pressure. Locking cure dose, surface preparation, and joint geometry at the end of that study makes production repeatable.
Get a recommendation
Send Incure the plastic and metal grades, the joint geometry, the pressure and pull requirements, and the sterilization method. Email Us for a recommendation.
For sample material or qualification support, Contact Our Team.
Visit www.incurelab.com for more information.