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Ultrasonic sealing is the use of mechanical vibrations to join materials with a molecular bond. Electricity is converted into a high frequency acoustical signal that is combined with pressure on the pieces to be joined to produce a seal as strong as or stronger than the materials themselves. It can be used on plastics alone or a combination of plastic and metal. A computer controls the sealing time and other adjustments to permit the accurate handling of multiple materials and types of seals. The process is cost effective and potentially safer than other methods because it generally does not require heat or hazardous materials such as solvents or adhesives.
A converter expands and contracts at the same frequency as an electrical source to change electrical energy into mechanical energy in the form of specific ultrasonic frequency vibrations. Ultrasonic refers to frequencies outside the range of human hearing, i.e., above 20,000 hertz. The vibrations are amplified and directed into the materials to be sealed. The pieces are pressed together, and the vibrations force the parts together until they are bonded at a molecular level.
Common applications of ultrasonic sealing include joining thermoplastic resins such as polyethylene or polystyrene. Metal and plastic can also be joined with this method. Seals can be as simple as overlapping layers or can bond an insert into a base or stake a post perpendicular to the base. Ultrasonic seals are found on blister and clamshell packaging. Filled tubes can be closed with this technology. The strength of the seal can make this process suitable for tamper resistant packaging as well.
Microprocessor-controlled ultrasonic sealing machinery can produce consistent and reliable seals with minimal labor requirements. Fully automated machinery requires only limited training without affecting speed or quality. Adjustment of the microprocessor settings permits quick changes to sealing specifications such as frequency, size, and source material.
The ability to seal without applied heat makes ultrasonic sealing particularly suitable for food products that are temperature sensitive. It is also used in pharmaceutical facilities. The closure can be effective even if there is contamination of the seal area by food product.
In most applications, no heat is required for the process, eliminating the cost of generating heat. Most processes do not require any adhesive, thread, or solvents to assure a good closure. Elimination of extra components in the assembly line simplifies the production process and reduces the cost of production and inventory.