Automotive sheet metal PU sealant (polyurethane sealant) is a core material used in automotive manufacturing and maintenance for sealing welds/seams, waterproofing, rust prevention, and shock absorption reinforcement. It is mainly composed of single component wet curing, with good elasticity, sprayability, and strong weather resistance after curing.
1、 Core Features (Why Choose PU)
Material: One component moisture cured polyurethane (PU), with good thixotropy and non flowing surface.
key performance
Waterproof/dustproof/rust proof: Seal the gaps between sheet metal to prevent rainwater and moisture from entering and causing rust.
Elasticity and displacement compensation: fracture elongation ≥ 300%, suitable for vehicle vibration and thermal expansion and contraction.
Can be sprayed/polished: After curing, the surface can be directly painted without affecting the adhesion of the paint surface.
Weather/temperature resistance: -40 ℃~120 ℃, stable, anti-aging and tear resistant.
Strong adhesion: Excellent adhesion to steel, aluminum, galvanized sheet, and painted surfaces.
Curing: Surface drying for 30-60 minutes, complete curing for 24-72 hours (faster with higher humidity).
2、 Main purpose (full coverage of sheet metal scenes)
Body welding seam sealing (door frame, hood, trunk, floor, side panel).
Door/hood/trunk edge sealing, shock absorption reinforcement.
Waterproof of body cavities, water channels, wheel arches, and chassis joints.
Seal and rust proof the sheet metal joints after accident repair.
Sealing of seams in the compartments of box trucks/refrigerated trucks.
3、 Mainstream products (common models)
3M 8362: Single component PU, can be spray painted in 30-45 minutes, suitable for internal and external seams.
Saint Gobain Titanium Bond PU40/PU8630: High flexibility, sprayable, suitable for metal and paint surfaces.
PU813/PU818: Universal type, non vertical flow on the facade, suitable for large-scale joint filling.
Boyou 253: For automotive use, fast curing and good weather resistance.
4、 Standard construction process (key steps)
Surface treatment (determining success or failure)
Oil removal: Use oil remover/acetone to wipe off oil stains, wax, and old glue.
Rust removal/polishing: Remove floating rust and use 800 grit sandpaper for unidirectional polishing to increase adhesion.
Clean and dry: no dust, no water, no impurities, temperature ≥ 5 ℃.
Covering: Apply masking paper around to prevent contamination of the paint surface.
Glue application operation
Glue filling: Glue cylinder with glue gun, cutting nozzle (oblique mouth, diameter matching seam width).
Glue application: The glue gun moves vertically on the surface at a constant speed, with a glue strip width of 10-15mm and a thickness of 3-5mm, continuously without bubbles.
Compaction and shaping: Use a scraper/finger (wearing gloves) to compact and smooth out excess glue, ensuring that the gaps are filled.
Uncover: Remove the masking paper before the surface dries, with neat edges.
Curing and maintenance
Surface drying: 30-60 minutes (touchable and non stick to hands).
Complete curing: 24 hours (light touch), 72 hours (reaching strength).
Taboo: Waterproof, dustproof, and anti-collision before curing; Avoid high temperature/steam.
5、 Key points for selection and use
Selection: Priority is given to selecting automotive specific PU adhesive that is moisture cured, sprayable, and has good thixotropy.
Environment: Optimal temperature of 15-35 ℃ and humidity of 50-70%; Low temperature/low humidity will prolong curing.
Thickness: 3-5mm is optimal; Thin and easy to crack, thick and prone to sagging and slow curing.
Maintenance: The waterproof ring needs to be remade due to aging; Check the sealing status every 2-3 years.
Taboo: Do not mix with silicone adhesive; Avoid contact with alcoholic solvents.
6、 Common Problems and Solutions
Bubbles: surface uncleaned, glue applied too quickly, low humidity; Reprocess the surface and apply glue at a constant speed.
Flow hanging: glue too thick, temperature too high; Control thickness and reduce ambient temperature.
Non curing: too low temperature, insufficient humidity, expired adhesive; Improve the environment and replace with new adhesive.
Poor adhesion of paint surface: Spray paint before the adhesive is fully cured; Wait for 72 hours before spraying.
