Common Guidelines to Prepare Surfaces for Bonding
Although many of Permabond’s industrial adhesives provide excellent bonding to “as received” surfaces, proper preparation will dramatically improve adhesion strength and bond performance. A properly prepared component will present a surface that is uniformly clean, mechanically sound, and correctly textured. A prepared surface will ensure strong and durable bonds; particularly when harsh usage environments are present. This guide provides an overview of several methods. Consult a Permabond representative for a complete assessment of your assembly surfaces and determination of the best surface preparation method for your specific application.
Surface Preparation – Solvents
If possible, remove surface oil or grease with an aqueous-based cleanser. If aqueous-based cleansers are ineffective, isopropyl alcohol is recommended. If isopropyl alcohol is ineffective, solvents such as acetone or methyl ethyl ketone can be used. It is recommended that the surface material first be tested as certain thermoplastics may crack or dissolve when reacting to various solvents.
Surface Preparation – Mechanical
Mechanical abrasion is a process of slightly roughening the surface of the component to be bonded. The surface roughness should be kept to less than 0.1 microns (0.004 millimeters) to reduce the possibility of small contaminants or air bubbles becoming trapped in the roughened surface and degrading the bond performance. Scarification is typically done with either an abrasion or a blasting process.
Surface Preparation – Abrasion
Abrade using 45 to 106 micron grit or a three-dimensional, non-woven abrasive fabric. Abrading can be done as either a wet or a dry process. If doing wet abrading, use only media designated as water-resistant. When preparing aluminum surfaces always use the wet method to prevent the oxide pores from clogging with abraded contaminants. The proper surface condition has been achieved when the surface can be immersed in clean water, and when removed a water film remains unbroken for 30 seconds. Do not use iron- or steel-based grits on aluminum, copper, or stainless steel components.
Surface Preparation – Dry Blasting
Typically used on metallic components. May also be used on heavy-duty plastics. Blast using 45 to 106 micron grit until the surface is uniform in cleanliness and texture.
Surface Preparation – Wet Blasting
Typically used on small metallic components. Blast using 1000 mesh grit suspended in either water or steam. In the event a system uses water-soluble additives, consult the system manufacturer to eliminate contamination of the surface by the additives.
Surface Preparation: Non-mechanical
Non-mechanical surface preparation methods are typically for only high volume plastic or composite component production applications. Non-mechanical surface preparation modifies the chemical characteristics of the component’s surface to an optimum condition for adhesive bonding. Gas Flame Oxidizing: Economical and effective method of preparing plastic or composite surfaces. Rapidly adapts to changes in component topography.
Surface Preparation – Plasma Discharge
Also known as Corona Discharge. Economical and effective method of preparing plastic or composite surfaces. Best suited for components with simple, or flat topography.
Surface Preparation – Plasma Chamber
Utilizes a discharge chamber to process large volume component batches. Best suited for batches with complex, or multiple component shapes. Requires greater initial capital investment; provides greater volume and part type processing than other non-mechanical surface preparation processes.
Surface Preparation – Laser
Can be used for metal and plastic component surfaces. Requires extensive system design, and calibration.