Quality Control and the Adhesive Bonding Process

The adhesive bonding is a complex, multiple part process, complete with interacting and unexpected parameters that may contribute to bond failure. Thus, it is important that the quality control process consider the entire operation from receipt of materials to final product testing. This SpecialChem editorial reviews some of the basics of quality control in the end-user's shop.

In designing a quality control process with suitable specifications and test methods. It must be realized that the adhesive itself is only part of the joint, and somewhat surprisingly does not always play a significantly important role in determining the strength of a joint. The latest SpecialChem article "Important Characterisitcs of Several Common Adhesive Tests" discusses how several minor and unexpected variables may surprisingly contribute or detract from the joint strength as measured by common quality control tests.

A typical flow chart for the adhesive bonding for sealing process is shown below (Figure 1). It must be realized that the decisions made in one process segment may affect the other process segments. Therefore, all of the individual processes in the adhesive bonding operation must be carefully controlled. Although there are sophisticated testing and analysis equipment available, many of these processes do not require advanced equipment or skilled knowledge. Simple equipment, visual examination, and common sense are the main tools in most quality control departments. They are supported by strong specifications and proper training.

Figure 1: Basic steps in the adhesive bonding process.

Quality control then encompasses all of the processes and activities that ensure adequate quality in the final product from receipt of materials through joint manufacture to final product test. Quality control is very important when using adhesives because once fully bonded, joints are difficult to take apart or correct. By the time it takes to notice that one step in the bonding process is out of control, significant costs could occur.

For adhesives, quality control must be defined in the broadest sense. This consists of defining the means to prevent problems as well as detect problems. These may include training, controlling manufacturing procedures, incoming inspection of materials, and visual or physical examination of the finished product.

A flow chart for a quality control system is illustrated in Figure 2 below. This system is designed to ensure reproducible bonds, and if the substandard bond is detected, to make suitable corrections. However, good quality control will begin even before the receipt of materials. This usually begins with proper training of personnel and conditioning of the manufacturing area..

Figure 2: Flow chart of a quality control system for adhesive bonding.

Specifications are, perhaps, the cornerstone, of any good quality control system. Specifications are intended to define what is needed for all parties involved. These parties include outside suppliers as well as internal departments within the factory. The following is a short list of do's and don'ts for specification writing. ² The language of the specification should be clear, definite, exact, brief, technical, and to the point.

References:

1. Smith, D.F., and Cagle, C.V., "A Quality Control System for Adhesive Bonding Utilizing Ultrasonic Testing", in Structural Adhesive Bonding, M.J. Bodnar, ed., Interscience, New York, 1966.
2. DeFrayne, G.O., "Adhesive Specification and Quality Control", in Adhesives in Manufacturing, G.L. Schneberger, ed., Marcel Dekker, New York, 1983.