KA518 · Automotive glass bonding
KA518 Polyurethane Windshield Adhesive
General-purpose moisture-curing adhesive for bonded windscreens, 310 ml cartridges.
- Model
- KA518
- Packs
- 310 ml · 400 / 600 ml · 200 L / 250 kg
- Tensile strength
- 3.5
- Elongation at break
- 320
What it is
One-component moisture-curing polyurethane adhesive for windshield, side and rear window bonding. Good bonding and sealing, easy to apply, sag resistant, fast cure, moderate hardness after cure, water and ageing resistant, primerless.
Specification
| Test | Standard | Typical value | Method |
|---|---|---|---|
| Appearance | — | Black homogeneous paste | — |
| Density (g/cm³) | 1.5±0.1 | 1.50 | GB/T 13477.2 |
| Sag resistance (mm) | ≤0 | 0 | GB/T 13477.6 |
| Skin time (min) | 30–40 | 30 | GB/T 13477.5 |
| Cure rate (mm/day) | ≥3.0 | 3.5 | HG/T 4363 |
| Volatile content (%) | ≤5 | 3 | GB/T 2793 |
| Shore A hardness | 60–70 | 65 | GB/T 531.1 |
| Tensile strength (MPa) | ≥3 | 3.5 | GB/T 528 |
| Elongation at break (%) | ≥300 | 320 | GB/T 528 |
| Tensile shear strength (MPa) | ≥2 | 2.5 | GB/T 7124 |
| Extrusion rate (ml/min) | ≥60 | 110 | GB/T 13477.4 |
Typical values from the printed catalogue, transcribed as printed. Where the catalogue printed a unit that does not fit the value (density in g/m³), the page shows g/cm³ — see the note below.
How the numbers were measured
3.5 MPa and 320% are brochure typicals measured to GB/T 528 on cured dumbbells; the batch certificate carries the result for your lot. They describe the cured rubber, not the strength of a particular bond — adhesion depends on the frit and the preparation.
- Density is printed as g/m³ in the brochure; at 1.50 the unit should be g/cm³ — a typesetting error in the original, read here as g/cm³.
Engineering analysis: bead volume, cure depth and load path
The catalogue gives KA518 a 3.5 MPa tensile strength, 320% elongation, 2.5 MPa tensile shear strength and a 3.5 mm/day cure rate. Those numbers are useful only when they are connected to the geometry of the bead and the load path in a bonded windscreen. This section does that explicitly, so the assumptions can be checked rather than hidden.
Basis: catalogue typical values for KA518; density 1.5 g/cm³; a 4.5 m windscreen perimeter and a triangular bead are planning assumptions, not vehicle-specific dimensions. Values marked [Calculated] follow from those inputs. [Judgment] is an engineering interpretation, not a measured result.
1. Bead volume and cartridge coverage
For a triangular bead, the cross-section area is half the base times the height. Volume per metre is therefore:
V per metre = 0.5 × bead width × bead height
At a 4.5 m perimeter, a 12 mm wide × 10 mm high bead contains about 270 mL of adhesive. At 1.5 g/cm³ that is about 405 g, or roughly 0.87 of a nominal 310 mL cartridge before applicator loss. A 12 × 12 mm bead reaches 324 mL and exceeds one cartridge before waste.
| Bead (w × h) | Volume / 4.5 m | Mass | 310 mL cartridges |
|---|---|---|---|
| 8 × 8 mm | 144 mL | 216 g | 0.46 |
| 10 × 10 mm | 225 mL | 338 g | 0.73 |
| 12 × 10 mm | 270 mL | 405 g | 0.87 |
| 12 × 12 mm | 324 mL | 486 g | 1.05 |
[Judgment] A 310 mL cartridge is a sensible one-car pack only when the bead stays near 12 × 10 mm and applicator waste is controlled. A wider bead, a longer perimeter or a high purge loss can push a single vehicle over one cartridge. Quote the pack mix from the actual bead drawing, not from a nominal “one cartridge per car” rule.
2. Cure depth is not drive-away time
The catalogue cure rate is 3.5 mm/day. If the rate is treated as a one-sided cure-front velocity, the time to reach a given depth is:
t = depth ÷ 3.5 mm/day
| Bead depth | Cure-front estimate | Meaning |
|---|---|---|
| 8 mm | 2.3 days | Full-depth estimate, one-sided exposure |
| 10 mm | 2.9 days | Full-depth estimate, one-sided exposure |
| 12 mm | 3.4 days | Full-depth estimate, one-sided exposure |
[Judgment] This is a cure-front estimate, not a safe-drive-away specification. A bonded windscreen has two exposed bead edges, so moisture can enter from more than one side; that shortens the diffusion path but does not make the bead fully cured. The vehicle manufacturer's drive-away time, the glass weight, the bead geometry and the workshop temperature remain the controlling requirements.
The 3.5 mm/day figure is a 23 °C / 50% RH catalogue value. Cold glass, dry air and a thick bead slow the front. Do not turn the table above into a winter promise; measure glass temperature and follow the vehicle-specific procedure.
3. Shear load path and the tensile-number trap
A windscreen bead is primarily loaded in shear, not in direct tension. For a 4.5 m × 12 mm bond line:
A = 4.5 m × 0.012 m = 0.054 m²
F = τ × A = 2.5 MPa × 0.054 m² = 135 kN
That is a theoretical shear capacity using the catalogue's 2.5 MPa tensile shear value. A 15 kg windscreen imposes about 147 N of static shear, which is only about 0.1% of that theoretical capacity. The calculation is deliberately absurd as a design check: it shows why a static weight calculation does not prove crash retention.
[Judgment] The 3.5 MPa tensile number is not the number to use for a shear joint. Use the 2.5 MPa shear value, apply a design factor, and then check peel, impact, airbag deployment and the vehicle manufacturer's validation. A high static safety factor can coexist with a poor crash result if the bead geometry or substrate preparation is wrong.
4. Thermal movement is small; constraint stress is not
For a 4.5 m glass span and a 60 K temperature change, linear expansion is approximately:
ΔL = α × L × ΔT ≈ 9 × 10⁻⁶/K × 4.5 m × 60 K ≈ 2.4 mm
The movement is small compared with KA518's 320% elongation at break, but elongation at break is not a working strain allowance. The adhesive is constrained by the glass, the frame and the bead geometry; the relevant question is the stress at the service strain, not the ultimate elongation. A soft bead can reduce stress transfer, but it can also allow more glass displacement before the bead takes load.
[Judgment] KA518's 320% elongation is useful for accommodating thermal and body movement in passenger-car glazing. It is not evidence that the same bead is suitable for a bus or coach opening, where the span, frame flexibility and glazing mass are different.
5. What this means for specification
- Use the bead drawing to size the cartridge. The 12 × 10 mm, 4.5 m case uses most of a 310 mL cartridge before waste.
- Do not equate cure rate with drive-away time. The catalogue rate is a material property at 23 °C; the vehicle procedure is the acceptance criterion.
- Design for shear, not tensile. The 2.5 MPa shear value, joint area and a design factor belong in the calculation; the 3.5 MPa tensile value does not.
- Keep KA518 in its application envelope. Passenger-car glazing and general replacement are its intended use; bus and coach glazing should be checked against KA520 or KA530F.
These calculations are planning estimates from catalogue typical values and stated geometry. They are not a batch certificate, a crash-validation report or a substitute for the vehicle-specific repair procedure.
Packaging
| Format | Size | Carton / unit |
|---|---|---|
| cartridge | 310 ml | 12 / 20 / 24 pcs |
| sausage | 400 / 600 ml | 20 pcs |
| barrel | 200 L / 250 kg | — |
Where it is used
- Bonding of windscreens, side windows and rear glass
The rest of the family
Further reading
Windscreen adhesive: the specification guide — the guide this model belongs to
- KA518 vs KA520 vs KA530F: choosing a windscreen adhesive
- How to read a sealant data sheet
- Importing PU sealant from China: DG, heat and documents
- Windscreen adhesive cure time: why a bead stays soft
- How much windscreen adhesive a car actually takes
- Batch certificate vs catalogue value
- Primerless windscreen adhesive: what it covers
- Installing windscreen adhesive below 10 °C
- Bus and coach glazing needs a different windscreen adhesive
- Ten questions for a sealant factory visit
- Diagnosing a failed windscreen bond
- Windscreen adhesive shelf life and storage
- Sealant shelf life after opening: what still works