Quality control procedures need to be meticulously followed to assure bonded assemblies meet end user requirements. Not to be overlooked is the necessity for the substrates being mated to have lot to lot consistency. In many instances the same substrates employed in manufacturing operations may not be identical even though they satisfy the suppliers specifications. Testing should be performed to detect any deficiencies in the adherends. Lot to lot differences could have an impact on the strength and durability of an adhesive joint. Determination of the proper test procedure as part of the quality control process is essential in preventing product failure and securing highly desirable reproducible results.
It is important to note that metal surfaces can be contaminated by corrosion due to oxidation. Often this oxidation can occur in a shop environment. Other metal contaminants range from dust, dirt, oil, grease. The degree of surface cleaning, method employed, abrasive blasting and priming will enhance the wetting characteristics. Bonding strength and longevity of adhesion will be greatly augmented by these techniques. A prerequisite to obtain identical results is that the procedure used in pretreating the surface be duplicated including the amount of surface roughening so there will be no alteration in results. Uniformity in tolerances between surfaces inhibit the possibility of adhesive-starved areas or unwanted bond line thickness. It is recommended that parts should be proven simulating actual production processing and service environments.
Organic substrates are frequently subjected to subtle formulation adjustments which could have a significant effect on bonding performance. Elastomeric formulations contain a wide range of fillers that are designed for specific tailor made applications. These compositions when modified contain also different levels of extender oils/plasticizers, accelerators, anti-agents. Tests need to be carefully conducted to determine if the fundamental properties of systems being used are within end user spec and the previous adhesive system can be utilized to achieve the exact same bonding ability.