Green Cars

Vehicle Assembly: Priming Operation

The vehicle body is the structural frame and exterior panels that form the shell, or body, of the vehicle.


Body Assembly Process Description
Various metal pieces are joined at vehicle assembly facilities to form the vehicle body. The structural supports, floor pan, door and side panels, hood, trunk, and roof represent the various parts of the vehicle body. Spot welding and adhesives are used to join them. Spot welding joins metal pieces by applying heat, and sometimes pressure, at the joints between the parts; more than 3,000 points are spot welded on a typical vehicle. Adhesives are most often used to bond dissimilar materials (e.g., aluminum to steel).

Primary Wastes: air releases

Likely TRI Chemicals: acetone, toluene

Likely AIRS Chemicals: VOCs

 


Body Assembly Pollution Prevention Options
Air emissions of volatile, often toxic, chemicals from adhesives have been the focus of pollution prevention initiatives within the body assembly process. During application and curing, adhesive solvents evaporate, contributing to the release of VOCs and toxic chemicals into the air. Alternatives to solvent-based adhesives that can reduce or eliminate the air releases from assembly processes include low-solvent and solvent-free formulations and two-part adhesives. Across the country, assembly facilities are slowly replacing solvent-based formulations with solvent-free alternatives. Volatile and toxic air releases are eliminated by this switch. When considering adhesive alternatives, the health and safety of workers must also be evaluated on a case-by-case basis. For example, solvent-based adhesives may harm the respiratory system but solvent-free or two-part adhesives may harm the skin.

The use of adhesives in vehicle assembly, while causing the release of chemicals into the environment, may also have negative implications for End-of-Life Management. When used to bond dissimilar materials, adhesives minimize or eliminate the recycling potential of many vehicle parts. Plastics recycling, in particular, is limited if adhesives are used to bond dissimilar plastics. Few plastics can be recycled into high-end products if contaminated with dissimilar polymers; adhesion between bonded parts is so strong that complete separation is difficult to achieve. The use of adhesives, therefore, should be evaluated from both a vehicle assembly perspective (i.e., air emissions) and a life-cycle perspective (i.e., recyclability).

When using two-part adhesives, care must be taken to mix only the quantity needed for the job at hand in order to minimize adhesive waste. In assembly processes, this can be achieved with an adhesive application process that feeds the two components separately through the application gun, mixing them just prior to application on the vehicle.


Pollution Control
As part of an effective environmental management scheme, pollution control technologies, if used, should be efficiently operated. Although not the first choice within the waste hierarchy, control technologies can protect human health and the environment from potentially harmful materials. Industry must be held accountable for the efficient operation of these processes, while encouraged to implement pollution prevention options that may eliminate the need for such controls.

 

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