Surface Preparation for Adhesive Bonding
- Tommy Tran
Porous materials are simple provided they are dry.
Surface should be sanded till clean and free from dust
Non-porous surfaces, e.g. metal and plastic materials
Surfaces should be degreased, dried, and roughened by sanding, sandblasting or chemical etching.
Avoiding Contamination of Prepared Surfaces:
Handlers should wear clean cotton gloves to prevent body oils from contaminating the clean surfaces
Contamination can be caused by a fingerprint, not perfectly clean clothing, or through the use of substandard degreasing or chemical solutions
For best results, surfaces can be prepared by three pretreatment procedures, which are listed by increasing effectiveness:
Degrease only
Degrease, abrade, and degrease again
Degrease and chemically pretreat
It is important to research the procedures and chemicals used. Some procedures are not feasible to us as a student team. Some chemicals are more hazardous than others. This will definitely be a large factor in creating pretreatment procedures.
What is degreasing? Why is it important? What factors should be considered when choosing a degreasing solvent?
Degreasing removes grease, oil, and other contaminants from surfaces. It is often used to clean parts in preparation for further finishing processes such as painting, welding, or adhesive bonding. Small amounts of contaminants can interfere with how the adhesive chemically bonds with the parts and as a result reduces the bonding strength of the adhesive.
When deciding on a degreasing solvent, it is important to keep in mind its application. There exists a variety of cleaning methods such as vapour degreasing, cold cleaning, and non-solvent cleaning. Some cleaning methods are more feasible than others, especially if you are a student design team with limited access to industrial equipment. Additionally, the degreasing solvent should be compatible with the material(s) that you are trying to bond together.
Lastly, it is vital to research the specific chemicals or products that will be used. Some chemicals can damage the human body’s biological system when exposed to any route of exposure, i.e. by inhalation, ingestion, and skin exposure. Some chemicals are certainly recommended for certain applications, but those chemicals are often used in industrial settings in which they are supplied into automated machinery (away from human personnel). Regardless, many companies are reducing their usage of these substances as more research has been done on their potential health effects, e.g. trichloroethylene (TCE). Useful sources of information such as the U.S. Environmental Protection Agency (EPA) regulate and perform documentation on these chemicals which will definitely influence your decision-making process.
What is abrasion? Why is it important to adhesive bonding?
Abrasion increases the surface area by exposing the prepared surface to abrasive material such as sandpaper. As the surface is rough, the adhesive can thoroughly spread to fill the micro-sized cracks and crevasses allowing for a stronger bond.
What is chemical pretreatment? Why is it important to adhesive bonding?
Chemicals can be used as an alternative to mechanical treatment. Specific chemicals can change the physical and chemical properties of the material’s surface to improve adhesion. This method requires a high level of chemical knowledge and laboratory skills to properly perform. Training and protection equipment according to safety regulations must be followed when handling chemicals.
Note:
It is more than sufficient to follow the provided instructions for an adhesive, i.e. read its technical data sheet. The source link provides very specific procedures for different materials. The procedures seem to be very specific and require technical expertise to perform. We would not resort to procedures researched online unless the technical data sheet of adhesives do not explicitly provide surface preparation instructions.
Source links:
https://www.smooth-on.com/page/preparation-surfaces-epoxy-adhesive-bonding/
https://www.smooth-on.com/page/preparation-surfaces-epoxy-adhesive-bonding/