Joint design bond line thickness

The type and amount of fillers are chosen so that a practical bond line thickness will result after application of the necessary pressure (usually only contact pressure, approximately 5 psi) during cure. Ordinarily, the objective is a bond line thickness of 2 to 10 mils. Consideration, of course, must be given to the curing temperature. Viscosity of the formulation could drastically be reduced at elevated temperatures, and unless there is a furrow designed into the joint to contain the adhesive, much of the adhesive could flow out of the joint area before the adhesive is completely cured. 

These 10 1 mix ratio acrylics show excellent adhesion to polyethylene and polypropylene with handling strengths in less than 10 minutes. The products contain glass beads or fillers to control the bond-line thickness to 0.2 mm or 0.25 mm and so the joint should be designed to accommodate these fillers. 

It is highly desirable to have a uniformly thin (2- to 10-mil) adhesive bond line. Starved adhesive joints, however, will yield exceptionally poor properties. Three basic methods are used to control adhesive thickness. The first method is to use mechanical shims or stops, which can be removed after the curing operation. Sometimes it is possible to design stops into the joint. 

Adhesive bonds will always be susceptible to environmental attack, and it is essential that any such attack should not reduce the strength of the bond to an unacceptable level. The most important factor here is the correct choice of adhesive, but design of the joint can make a significant difference. Thus, a thick bond line offers a ready path for access... 

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