Structural Adhesive Film

AF 555

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XIX. Cure Conditions & Characteristics

3M™ Scotch-Weld™ Structural Adhesive Film AF 555 is designed to provide

short cure times in the 300 to 355°F temperature range. While performance outside

this cure temperature range has not been fully investigated, limited results suggest

that cure temperatures as high as 375°F may be used as well as longer cure times at

200°F (6 hrs.) to obtain useful performance.

A. Standard Cure Cycle for Positive Pressure (Autoclave) Cure

– 4.5ºF/min. rise rate to 355 ± 5ºF.

– Vacuum bag target: 28 inches Hg.

– Release (vent) vacuum bag pressure when positive pressure reaches a level of 15 psi.

– Positive pressure target: 15-20 psi. Pressures as high as 45 psi can be used. If 45 psi

pressure is being used to cure overlap shear specimens, shimming must be used to optimize

bond line thickness.

– Soak time: 120 minutes ± 5 min. @ 355ºF bond line temperature.

– Cool down @ 10ºF/min. to 75ºF.

– Release positive pressure when bond line temperature reaches 100ºF.

B. Weight Loss During Cure (3M Test Method C-274):

Less than 1% (60 min at 250°F)

C. Cure Time and Temperature

For temperatures from 325 to 355°F, a cure time of 120 minutes at temperature

is suggested. Following cure, it is suggested that pressure be maintained until

the assembly has been cooled to 100°F or below.

D. Heat up rate

Bond line temperature rise rates between 1°F/min. and 20°F/min. have been used

successfully with Scotch-Weld AF 555 films. It must be noted that hot entry cures

at 300°F and above can be expected to produce reduced performance due to

formation of bond line porosity.

E. Cure Pressure

1. Positive Pressure Cures

During cure, pressure is required to keep parts in alignment and to overcome

distortions and thermal expansion of the adherends. When bonding honeycomb

assemblies with non-perforated core, pressure is required to overcome the

thermal expansion of air in the honeycomb cells. Positive pressure between 20

and 80 psi have been used successfully with 3M™ Scotch-Weld™ Structural

Adhesive Film AF 555. For very small area bonds, however, pressures at the

higher end of this range may produces excessive squeeze out and adhesive bond

line starvation. For large solid panel constructions which are autoclave cured,

application of vacuum for 15 to 20 minutes prior to application of heat and

pressure is suggested to assist in removing any residual air trapped in the assembly.

Normally, the vacuum is released following application of positive pressure @

15-20 psi. For problem assemblies, maintain the vacuum during the heatup cycle

to about 130°F to further assist in providing void free bonds.

2. Vacuum Curing

Scotch-Weld AF 555 films can be successfully cured using vacuum cure

techniques. For performance comparable to positive pressure cures, Scotch-Weld

AF 555 films should be cured using a vacuum level in the range of 8-22 inches

of mercury. Higher vacuum levels yield excessive porosity and corresponding

strength reductions. Scotch-Weld AF 555M versions have shown a high level of

performance retention across the 10-25 inches of mercury vacuum level range.