Automobile Plastics Repair
September, 1980 RESEARCH BULLETIN No. 02 - 80INTRODUCTION More than 8,000 types of plastic are currently being produced for industrial usage. Fortunately, automobile manufacturers are presently using only 14 different types of plastics. The automobile industry forecasts greater use of plastics in a further effort to reduce weight, thereby increasing gasoline efficiency. The three major American automobile manufacturers are experimenting with the use of plastic in the production of fenders, hoods and deck lids. The Ford Motor Company advises that it is evaluating a graphite-reinforced plastic radiator support. Considering the extensive use of plastic parts on current models, coupled with an even greater anticipated usage, it is imperative that auto damage appraisers and repairers become knowledgeable of the various types of plastics and the repairs adaptable to each. Today's automobile plastic parts are divided into two general categories: thermosetting and thermoplastic. Thermosetting plastic hardens under heat and chemical reaction. Once a part is formed, its shape cannot be changed by the application of heat. Therefore, thermosetting plastics
(1) - Available from:
General Motors Service Information P.O. Box 7124 Detroit, M148202 "Plastic Repair and Refinishing" Bulletin B22
(2) - Available through:
^ Seelye Plastics Inc. 9700 Newton Ave. S. Minneapolis, MN55431
^ Laramy Products Co. Inc. Rt. 5 Lyndonville, VT 05851
^ Kamweld Products, Inc. 90 Access Road P.O. Box 91 Norwood, MA 02062
^ Karmen Inc. P.O. Box 4 Northbrook, IL 60062
cannot be welded. The largest use of this thermo setting plastic in automobiles is in the forming of parts using fiberglass reinforced plastic. This material is commonly used in the production of grille opening panels (grille header panels) and to a limited extent on automobile bodies, such as Chevrolet's Corvette. Thermoplastic differs from thermosetting plastic in that it will soften when heat is applied; therefore, it can be welded when fractured. Thermoplastic is commonly used in the production of fender aprons, fan shrouds, grilles, bumper covers and many other automobile parts.
REPAIRS The repair of cracks or fractures to parts produced using thermosetting material, such as fiberglass reinforced plastic, has been thoroughly researched at Tech-Cor. We have experimented with several well- known products during the repair of such parts as header panels, fenders and hoods. Excellent results were achieved when the instructions given by the product manufacturer were followed. A very descriptive fiberglass repair bulletin is available from General Motors. (1) Parts formed from thermoplastics lend themselves to multiple types of damage and repair. Bent or misshapen parts can be reformed after the application of heat to make them pliable. Hot water, infrared lamps and heat guns can be used to supply the necessary heat.
PLASTIC WELDING Thermoplastic parts that have cracks or fractures can be re-fused by welding with a hot air welding torch. Two types of plastic welding equipment are available: electrically heated, and gas heated (2). We have used the electric type most satisfactorily. This type is a relatively
inexpensive unit which offers good mobility. It can be used in any shop location which has compressed air and a 110 volt electrical outlet available. There are some electric types available which incorporate a minicompressor, eliminating the need for an outside source of compressed air.
The hot air welders have several different tips for the welding of thermoplastics.
Tacking tip used for tack welding long fractures to hold material in proper alignment.
Round tip used for small fractures and where many different curvatures are involved.
Speed ribbon tip uses a ribbon 1/2" wide, rather than a circular rod; excellent for welding fractures difficult to span with a round rod; also excellent for the repair of fender aprons where attaching bolt holes have been torn open.
Speed tip used for long fractures, preheats round rod, welds faster and automatically feeds rod once the rod is fused to the material.
To use the plastic welder it is necessary to prepare, by sanding, the damaged surface to be welded. This not only cleans the plastic of any die release agent but also "V" shapes the fracture, creating an additional surface for better adhesion. The torch temperature is controlled by the amount of air regulated th rough the torch. Increased air pressure reduces welding temperature. Proper temperature, material preparation, plastic identification and some practice will produce excellent results. If the area being welded is on an appearance part, sanding of the weld may be accomplished in the same manner as the sanding of conventional plastic filler. The only major problem we have incurred in the welding of thermoplastic is in identification of the type of plastic to be welded. The proper type of plastic welding rod must be used for each type of thermoplastic to be welded, or the repair will be unsuccessful. The auto manufacturers have begun placing international code letters on major plastic parts to identify the type of plastic used in forming the parts. The following is a list of codes and some of the common uses of these plastics:
ABS - Acrylonitrile Butadiene Styrene (flexible or hard) use - grilles, headlamp
doors, instrument panels.
ABS/ -ABS/vinyl PVC use - crash pads
EPDM - Ethylene - Propylene Diene - Monomer use - bumper impact strips
PA - Nylon
use - exterior finish trim panels
PC - Lexan
use - grilles, instrument panel parts
PPO - Noryl use - chrome grilles, headlamp doors, bezels, ornaments
PE - Polyethylene
use - valance panels
PP - Polypropylene
use - interior kick panels, hard plastic trim, fender aprons, splash shields, fan shrouds and some heater-evaporator cases
PUR - Thermoset Polyurethane use - bumper covers
TPUR - Thermoplastic Polyurethane use - soft filler panels, bumper face bars, gravel deflectors, soft bezels
PVC - Polyvinyl Chloride (Vinyl) use - upholstery and in-
terior trim
SAN - Styrene Acrylonitrile use - instrument panel gauge lenses
Up - Polyester use - fiberglass panels, grille opening, auto body fillers
TPR - Thermoplastic Rubber use - valance panels, filler panels
The repairs to thermosetting or thermoplastic parts depend to a large extent on the severity of damage and are limited only by the cost of repair. This should not exceed the cost of replacing the part.
SERVICEABILITY OF PARTS At present, the Ford Motor Company services a partial grille opening panel on many models for use when only a section of these panels are damaged beyond repair. Ford plans to increase the serviceability of this type of part on future models. A detailed explanation of procedures to follow when installing partial fiberglass panels has been prepared by Ford Motor Company (3). Gen- (3) - Available through:
Helm Inc. P.O. Box 5286 Detroit, MI 48211 "Body Repair Tips" Volume 1/number 2/1978
eral Motors Corporation is presently researching the feasibility of servicing partial grille opening panels. We will keep you informed as to the progress of their research.
STRUCTURAL ADHESIVES On bumper face bar covers where additional filling and featheredging are necessary, the use of a structural adhesive is recommended. We have found this repair method highly satisfactory. In repairing fractures in polyurethane face bars, the use of a quick fix type adhesive for structural strength will bond the two sides of the fracture together very effectively. To restore surface shape, the area is filled with a structural adhesive and then sanded to the exact contour.
REFINISHING Plastics require special products or additives when refinishing. Several paint manufacturers offer products for the refinishing of thermosetting and thermoplastic parts. Additional information is available from
the major paint manufacturers and local paint suppliers.
AREAS REMAINING TO BE RESEARCHED Problems still exist in the area of plastic repair, specifically in the repair of instrument panels. Instrument panels generally are made from ABS plastic and commonly sustain collision damage when occupants' knees contact the instrument panel causing plastic fractures. We have been able to repair these fractures with plastic cements and hot air welding. However, the technique to restore the grain pattern to the exposed surface has yet to be developed. Tech-Cor, and other companies are working on this problem. We will keep you informed as to future developments in the repair of these costly parts.
STRUCTURAL ADHESIVE REPAIR OF A URETHANE BUMPER*
^ Carefully read and follow all directions and warnings on labels.
^ Clean the front of the bumper with wax and grease solvent to remove all contamination. On the back-side, clean only the area to be repaired.
^ When working with tears, use an adhesive to hold both sides in alignment.
^ Grind the repair area with a 36-grit disc, then featheredge the surrounding surface with 180-grit paper on an orbital sander.
^ Singe the repair area with a torch to further improve adhesion. Caution should be used so that the surface is not burned. If a hole or puncture is being repaired, apply tape to the underside of the repair area. Using a rubber squeegee, apply a light coat of structural adhesive to the repair area and allow to cure for 30 minutes.
^ Apply a second coat of adhesive to restore the contour to the surface, working from the edges of repair toward the center.
^ Upon curing (heat lamps, four to five feet away, may be used to accelerate drying) the adhesive is sanded with 240-grit paper on an orbital sander.
^ Wet sand the repair area with 400-grit paper backed by a rubber squeegee or a sanding block for support.
^ Clean the bumper of all sanding residue.
^ Proceed with appropriate refinishing method.
*For additional information contact:
3-M Company Automotive Trades Division 3-M Center
St. Paul, Minnesota 55101