[Introduction]

Industrial adhesive selection and dispensing process control directly determine bond quality and production efficiency. In automotive manufacturing, electronic packaging, aerospace, and new energy sectors, adhesive selection spans mechanical performance, environmental resistance, processability, and cost. According to Chemical Engineering Research and Design and the Journal of Adhesion Science and Technology, about 35% of bond failures are not due to the adhesive itself but to incorrect selection or poor dispensing process. This guide systematically organizes the key parameter framework for adhesive selection and provides dispensing optimization to close the loop from selecting the right adhesive to using it correctly.

[Technical Features and Mechanism]

Adhesive selection should follow a three-dimensional matching model of substrate, service condition, and process: (1) Substrate - surface energy (metals >40 mN/m, plastics 25-40 mN/m, rubbers <25 mN/m) determines wetting; (2) Service condition - temperature range, load type (static/dynamic/impact), media (humidity/chemical/UV) determines durability; (3) Process - dispensing method (jet/spray/stream), cure condition (room temp/heat/UV/moisture), and takt time determine feasibility. The key control variables are bond line thickness, surface roughness, cure ramp rate, and clamping time.

[Application Case 1: Steel Structural Component Epoxy Selection]

A construction machinery manufacturer bonded Q355 steel structural members with epoxy structural adhesive. Substrate was sandblasted to Ra 6.3 um; service condition was -30 C to 80 C cyclic temperature under static shear. A bisphenol A epoxy/polyamide system was selected, bond line 0.2 mm, cured at 80 C for 60 min. Measured lap shear strength was 22.8 MPa (GB/T 7124), and strength retention after 500 h salt spray was 88% (GB/T 1771). Process optimization: dispense within 4 h after sandblasting, assemble within 20 min, clamp at 0.1-0.3 MPa.

[Application Case 2: ABS Plastic Polyurethane Selection]

A home appliance maker bonded ABS plastic housings with polyurethane structural adhesive. The challenge: ABS has low surface energy (35 mN/m) and poor wetting by ordinary epoxy. Plasma treatment raised surface energy to 52 mN/m. A one-component moisture-curing polyurethane was selected with bond line 0.5 mm. Peel strength measured 6.5 kN/m (GB/T 2791), and after 500 h at 40 C/90% RH no delamination. This follows plastic surface treatment methods from the Journal of Adhesion Science and Technology.

[Application Case 3: UV Adhesive for SMD Fixing]

An electronics maker used UV-curing adhesive to fix SMD components. Requirements: cure time <10 s, insulation resistance >=10^12 ohm, temperature range -40 C to 125 C. An acrylate UV adhesive was selected at 365 nm, light intensity 100 mW/cm2, cure time 5 s. After cure, shear strength was 8.5 MPa, insulation resistance 2.3x10^13 ohm (GB/T 1410), and after 1000 thermal cycles no cracking. Key: UV energy density >=3000 mJ/cm2, with secondary moisture cure for shadow areas.

[Key Selection Parameters and Usage Recommendations]

Table 1: Industrial adhesive selection key parameters

+--------------+--------------+--------------+----------------+

| Category     | Key Index    | Test Standard| Selection Note |

+--------------+--------------+--------------+----------------+

| Mechanical   | Lap shear    | GB/T 7124    | Static >=15MPa |

|              | Peel strength| GB/T 2791    | Dynamic >=3kN/m|

|              | Tensile      | GB/T 6328    | Per design load|

| Env Resist.  | Temp range   | ASTM D4065   | +20% margin    |

|              | Humidity     | GB/T 1740    | 500h retent>=80%|

|              | Salt spray   | GB/T 1771    | 500h no rust   |

| Process      | Viscosity    | GB/T 2794    | Match dispense |

|              | Pot life     | GB/T 7123    | >=1.5x work time|

|              | Cure time    | Mfr spec     | Match takt     |

| Durability   | Tg           | DSC/TMA      | Above service  |

|              | Volume resist| GB/T 1410    | Insul >=10^12  |

+--------------+--------------+--------------+----------------+

Dispensing optimization: (1) Surface preparation: metal sandblast Ra 3.2-6.3 um, plastic plasma/flame treatment, dispense within 4 h; (2) Bond line: structural 0.1-0.3 mm, sealant 0.3-0.8 mm; (3) Cure: ramp <=2 C/min to avoid internal stress; (4) QC: sample shear strength per batch and fracture analysis on first article.

[Conclusion]

Industrial adhesive selection needs a three-dimensional matching model of substrate, service, and process. Key parameters are shear strength, peel strength, temperature range, Tg, and pot life. Surface preparation, bond line thickness, and cure schedule are the three process factors that determine bond success. DENSON provides matching color paste solutions for various adhesives; see product pages.

[FAQ]

Q1: How to choose the right adhesive shear strength?

A: Shear strength should be at least 3 times the actual working load. Choose >=15 MPa for static structural parts; for dynamic/impact parts also require peel strength >=3 kN/m and fatigue performance, not shear alone.

Q2: Why is bond line thickness controlled at 0.1-0.3 mm?

A: Too thin (<0.1 mm) causes voids and bubbles; too thick (>0.5 mm) increases internal stress and shrinkage and lowers strength. The optimum structural bond line is 0.1-0.3 mm.

Q3: Why dispense soon after surface treatment?

A: Sandblasted metal surface activity decays over time; dispense within 4 h for best strength. After 24 h an oxide layer forms and strength drops 20-40%. Plasma-treated plastic surface energy decays within hours; dispense within 30 min.

Q4: What if UV adhesive cures incompletely?

A: Shadow areas with blocked light will under-cure. Solutions: (1) Use dual UV+moisture cure systems; (2) Add secondary heat cure (60 C/30 min); (3) Provide light-transparent windows in shadow zones.