Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1997-12-05
1998-12-01
Thornton, Krisanne
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562733, 1562735, 1562751, 1562757, B32B 3100
Patent
active
058432655
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for joining materials. More particularly, it relates to the bonding of materials by passing polychromatic, non-coherent, electromagnetic radiation through a material and into a second material that absorbs the radiation with the generation of heat and formation of a bond or weld.
2. Background
Although one piece items are preferred because of their strength and exclusion of assembly operations, mechanical limitations and other considerations often make it necessary to join plastic materials to each other or to other parts. As a consequence, a number of methods for joining plastic materials have been developed. Probably, the simplest of these methods is the use of mechanical fasteners such as screws or bolts, nuts and washers. In addition to the fact that the use of such fasteners is labor intensive, fastening techniques tend to be unsatisfactory as the integrity of the plastic is corrupted by the hole necessary for use with the fasteners, such mechanical joints often leak, and the fasteners can cause weakness of the joint. Press and snap fits are also used as a mechanical method of joining plastic. For many applications this also tends to be unsatisfactory since the method involves high stress components which may be unacceptable when the materials are subject to thermal cycling or to harsh environments.
Ultrasonic welding makes use of ultrasonic vibrations that generate frictional heat that melts the plastics and allows them to join. However the method is limited to small parts with simple geometries and vibration of composite materials may cause the composite fibers to abrade and dislocate. In heat welding, a heated platen, typically coated with polytetrafluoroethylene, is placed between the two parts to be joined. The parts are brought in contact with the heated platen until the joint is melted after which the platen is retracted and the pieces brought together and held in place with slight pressure until the bond is formed. A tendency for some plastics to stick to the platen causes the polymer to string out like taffy and may result in part rejection if such strings mar the plastic surface. Electromagnetic welding uses microsize ferromagnetic particles that are dispersed within the thermoplastic matrix. Exposure to a high frequency alternating current source causes the ferromagnetic particles to respond and melt the surrounding plastic material. In vibration welding, one of the parts is held stationary and the other is vibrated through a small displacement to produce frictional heat. When a molten state is reached at the joint interface, the vibration is stopped, the parts aligned and pressure applied. Alignment is critical and bonds may not be as strong as expected. For circular plastics, spin or friction welding may be employed. One part is held stationary while the other is rotated under sufficient pressure to keep the parts in contact with each other. The heat generated by the friction melts the surface at which point the rotation is stopped and pressure applied to complete the bonding process.
Solvents and adhesives have also been used to join thermoplastic materials. For plastic materials that are soluble in the same solvent, the bond area is treated with solvent to soften the surfaces after which the parts are clamped together until bonding occurs. Because solvents can adversely effect some plastics, it may not be an attractive form of bonding. Also, solvents present potential hazards to assembly personnel. Plastics can also be bonded with a variety of adhesives but these can also be troublesome in view of the fact that some adhesives are solvent based and present the solvent problems noted above. Both solvent and adhesive methods are complicated by waste and chemical disposal problems in addition to surface preparation requirements. In addition, adhesives can complicate polymer recycling.
Grimm et al., U.S. Pat. No. 5,313,034, sets forth a number of welding techniques involving resistance and magnetic susc
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Edison Welding Institute
Thornton Krisanne
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