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3M™ Aerospace Sealant AC-251 Black Class B are two-part, quick curing, polysulfide based canopy and windshield sealants. These products are formulated for sealing acrylic, glass, and polycarbonate aircraft canopies and windshields. 3M™ AC-251 Black Class B Sealants contain no solvents and do not craze. The sealants quickly cure and exhibit excellent adhesion and resistance to UV and weather exposure.

3M™ AC-251 Black Class B Sealants have a thixotropic, non-sag consistency. They can be readily applied with a spatula or extrusion gun on vertical surfaces.
Unit of Measure

Typical Physical and Application Properties

Base Color

 N/A Black

Accelerator Color

 N/A Black

Mixed Color

 N/A Black

Mix Ratio (By Weight)

 N/A 100 Base/10 Accelerator

Non-Volatile Content

 N/A 98 %
Base Viscosity1 N/A 9,000 to 16,000 Poise

Note for Typical Physical and Application Properties

 N/A The technical information and data should be considered representative or typical only and should not be used for specification purposes.

Application Life and Cure Time at 77 Degree Fahrenheit (ºF) and 50 Percent (%) Relative Humidity

Class

 N/A B-1 B-1/2 B-2

Minimum Application Life for Class B-1/2

 N/A 1/2 hour

Minimum Application Life for Class B-1

 N/A 1 hour

Minimum Application Life for Class B-2

 N/A 2 hour

Note for Minimum Application Life

 N/A Application life refers to the length of time the mixed compound remains at a consistency suitable for application with spatula or caulking gun. Application life is always measured as a standard temperature of 77 ºF with a relative humidity level of 50 %. In general, for every 20 ºF rise in temperature, the application life is halved; and for every 20 ºF drop, it is doubled. High humidity levels during the mixing process will shorten application life.

Typical Tack-Free Time for Class B-1/2

 N/A 4 hour

Typical Tack-Free Time for Class B-1

 N/A 5 hour

Typical Tack-Free Time for Class B-2

 N/A 8 hour

Note for Typical Tack-Free Time

 N/A Tack-free time is the length of time after which a mixed sealant will no longer tightly adhere to L-LP-690 standard low density polyethylene film.

Typical Cure Time for Class B-1/2

 N/A 4 hour

Typical Cure Time for Class B-1

 N/A 7 hour

Typical Cure Time for Class B-2

 N/A 9 hour

Note for Typical Cure Time

 N/A Cure time is defined as the length of time it takes 3M™ Aerospace Sealant AC-251 Black Class B to reach 30 A hardness. It depends on three factors: remaining application life, temperature and relative humidity. The temperature/humidity factors for application life also apply to curing. To accelerate the curing process, apply heat up to (but not more than) 160 ºF . If the humidity is low, increasing the humidity will cure the sealant more quickly.

Typical Physical and Performance Properties of Cured Compound after 14 Days at 77 Degree Fahrenheit (ºF) and 50 Percent (%) Relative Humidity when Tested Per AMS-S-8802

Specific Gravity

 N/A 1.59

Hardness

 N/A 55 Shore "A"

Low Temperature Flexibility

 N/A No cracking, checking or adhesion loss when tested at -65 ºF (-54 ºC)

Service Temperature

 N/A -65 to +250 ºF-54 to +121 ºC

Intermittent Exposure Temperature

 N/A 360 ºF182 ºC

Thermal Rupture Resistance

 N/A Does not blister or sponge

Corrosion

 N/A None

Repairability

 N/A 35 piw to itself and other AMS-S-8802 qualified sealants

Weight Loss and Flexibility

 N/A No cracking when bent 180º over 1/8 inch mandrel. No more than 6% loss of the sealant compound after fluid immersion.

Fungus Resistance

 N/A Meets MIL-STD-810 Requirement

Crazing

 N/A No effect on acrylic or polycarbonate

Specifications

Industry Focus

 N/A Aerospace

Applications

 N/A Canopy and Windshield Sealant Exterior Mold Line Applications

Color

 N/A Black

Storage

Storage

 N/A The shelf life of 3M™ Aerospace Sealant AC-251 Black Class B is 9 months from date of packaging, when stored at temperatures below 80 ºF in its original container. Pre-mixed and frozen sealant has a shelf life dependent upon the storage temperature.

Mixed 3M™ AC-251 Black Class B Sealants may be stored under refrigeration as follows:
  • 15 days at -10 ºF
  • 30 days at -40 ºF
It is important to remember that freezing, storing and thawing procedures reduce application life. In addition, frozen storage will reduce application life by varying amounts depending on the storage temperature and length of storage time. All aspects of storage, freezing and thawing should be planned carefully and it is not recommended to mix and freeze with less than 1/2-hour application time.

Mixing Instructions

Mixing Instructions

 N/A Two-Part Sealant Cartridges
  1. Holding the cartridge, grasp the dasher rod and pull back approximately one inch.
  2. Insert the ramrod into the hollow of the dasher rod, break the piston loose, and inject about 1/3 of the contents into the cartridge.
    3. Note: Do not inject all of catalyst in one location. Distribute evenly throughout base material.
  3. Repeat steps 1 and 2 until all the contents of the rod are emptied into the cartridge. Remove the ramrod.
  4. Mix for the required number of strokes (hand mixing) or for the required amount of time (machine mixing) indicated in the kit instructions.
  5. When mixing is complete, remove bottom cap.
  6. Pull the dasher rod back to the neck of the cartridge, grasp the cartridge firmly at the neck, unscrew the dasher rod and remove.
  7. Screw the nozzle into the cartridge, insert into the extrusion gun and use as required. For hand extrusion, press the used dasher rod against the plunger to force the material from the cartridge.

Health and Safety Precaution

Health and Safety Precaution

 N/A 3M™ Aerospace Sealant AC-251 Black Class B are safe to use and apply when recommended precautions are followed. Before using this product, read and understand the Material Safety Data Sheet (MSDS), which provides information on health, physical and environmental hazards, handling precautions and first aid recommendations. An MSDS is available on request.

Technical Information

Technical Information

 N/A The technical information, recommendations and other statements contained in this document are based upon tests or experience that 3M™ believes are reliable, but the accuracy or completeness of such information is not guaranteed.

Product Use

Product Use

 N/A Many factors beyond 3M™'s control and uniquely within user's knowledge and control can affect the use and performance of a 3M™ product in a particular application. Given the variety of factors that can affect the use and performance of a 3M™ product, user is solely responsible for evaluating the 3M™ product and determining whether it is fit for a particular purpose and suitable for user's method of application.

Warranty, Limited Remedy, and Disclaimer

Warranty, Limited Remedy, and Disclaimer

 N/A Many factors beyond 3M™'s control and uniquely within user's knowledge and control can affect the use and performance of a 3M™ product in a particular application. Given the variety of factors that can affect the use and performance of a 3M™ product, user is solely responsible for evaluating the 3M™ product and determining whether it is fit for a particular purpose and suitable for user's method of application.

Limitation of Liability

Limitation of Liability

 N/A Except where prohibited by law, 3M™ will not be liable for any loss or damage arising from the 3M™ product, whether direct, indirect, special, incidental or consequential, regardless of the legal theory asserted, including warranty, contract, negligence or strict liability.

Note

Note

 N/A These products were manufactured under a 3M™ Quality Management System registered to the AS9100 standard.
  • 1 Brookfield #7 spindle @ 2 rpm