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Material Specification for Pumpable Adhesives

Posted on 12/20/2012 9:54:17 AM By Sandy Niks
  

Materials specifications have been mentioned in all of the blogs written to date – and will probably continue to figure prominently. They are a type of standard (see 2012Oct17 blog) that consists of a set of requirements that defines and describes the material.  This article will review this information in more detail.

The specification will cover several aspects of the material, including requirements for the material as received by the user, basic material properties, processing requirements, and performance requirements.

A Material Safety Data Sheet (MSDS) is required for any material. Also, general requirements regarding restricted materials, recycled content, reusability, and sustainability have also found their way into most, if not all, material specifications.

The in-coming adhesive material is characterized by properties including color, odor (ASTM D4339), density (ASTM D1875) or specific gravity, solids content, volatile organic content (VOC), slump resistance (SAE J243), viscosity (ISO 2555), and flash point. Some additional tests may be run to check for potential problems in shipping – homogeneity/settling, temperature resistance –hot and cold, and storage stability or shelf life (ASTM D1337). Viscosity tests may be used as a quality control check.

Processing requirements are to ensure the adhesive is compatible with existing conditions in an assembly plant. If a two-part adhesive is used, the mix ratio is stated, with an equal mix ratio of 1:1 being preferred. The two components are different colors so striations in a mixed bead of the adhesive, indicating improper mixing, can be easily seen by inspection and corrected. Additional processing related requirements are open time, cure time, handling strength, weld-through compatibility, and wash-off resistance.

Additional material characterization testing is done on cured “bulk” samples of the adhesive, generating data for properties of hardness, tensile strength, tensile modulus, flexural strength, flexural modulus, Poisson’s ratio, cured density, and shrinkage. Some of these are used by designers to model and optimize the joint design.

Performance requirements are the functional requirements specific to an application. They are ideally captured in a separate specification (to facilitate better management of the documentation) and included in the material specification by reference. If a material is approved for more than one application, then multiple performance specifications would be listed. The performance requirements include strength properties, environmental conditioning, and durability. These requirements test the adhesive bond in various configurations to represent the loads applied, including shear tests (ASTM D1002, SAE J1523, SAE J1525, SAE J1529), cleavage and peel tests (ASTM D5041, SAE J1863), and tensile tests (SAE J1553). Multiple specimens are made, then exposed to various environments and/or tested under various conditions to simulate the environment for the application. The environments include hot, cold, humidity, salt spray, water immersion and combinations thereof.

That’s enough for today’s blog. This topic could easily expand, diving deeply into many of the tests and requirements listed, but that’s best saved for another time.

Best wishes to the readers of this site for a wonderful 2013!



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