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Resins reach the engine

Resins reach the engine

Take a look at the car you drive. Chances are the bumpers and instrument panel are made of plastic. What about the lamp housings, front grille, and wheel covers? Plastic, plastic, plastic.

In the short span of 20 years, the amount of plastics designed into an automobile has skyrocketed; at the same time, automobile weight has plummeted. Resulting gains in fuel efficiency have been well documented.

For the world's resin suppliers, replacing metal with plastic in the millions of automobiles produced globally each year represents a huge market. Still, it could be bigger, given that applications within the automotive market have generally stopped at the engine compartment. Temperatures to 300F (149C), shock and vibration, oils and grease--the message from under the hood had been clear: "No place for plastics."

Today, the engine compartment is fair game for resin suppliers. Recent formulations of high-performance and engineered polymers give product design engineers unprecedented options when seeking the optimum mix of performance properties.

Electromechanical interconnects. Consider, for example, a new semi-crystalline polymer under development by Dow Plastics. Different from conventional styrenics in structure and physical properties, Syndiotactic Polystyrene (SPS) represents the basics for an entirely new family of materials based on crystalline polystructure. Properties include resistance to moisture and automotive fluids, good electrical performance characteristics, and a melting point of 520F (270C).

Presently in the market development stage, SPS is being targeted for automotive interconnect systems. A wide range of products have been formulated for specific applications, including impact-modified and glass-reinforced grades. The latter, reports Dow, has the thermal, mechanical, and electrical performance capabilities to compete in the engineering thermoplastics arena.

Similarly, GE Plastics is promoting its Valox(R) glass-filled polyester resin for underhood applications where electrical and mechanical components interface. Applications: throttle bodies, air flow meters.

"When our customers seek to integrate parts for an electrical/mechanical application," says Robert Nelson, GE Plastics industry manager for underhood applications, "engineering thermoplastic resins such as Valox 735 and 732E can provide the characteristics they need." For throttle body design, Nelson cites basic performance requirements of predictable and consistent bore diameter, chemical resistance to underhood fluids, impact resistance, and stiffness in temperatures ranging from -40F to 275F (-40C to 135C).

Valox 735 resin meets these requirements with the benefits of weight reduction and parts consolidation. Also, Valox resin offers improved processability vs. PET resins due to the faster cycle times of PBT. "Dimensional capability is better than competing materials because of its low moisture absorption," Nelson claims.

Powertrain performance. In pressure-velocity ratings to 300,000 PV dry, 1.2 million PV lubricated, and 4.0 million PV instantaneous for lubricated applications in contact with steel or cast iron, DuPont's Vespel(R) SP-262 is well-suited for automotive bearing and bushing applications. These non-melting polymers are rated at 600F (316C) for continuous service and a 740F (393C) max surface temperature for bearings. The ability to withstand brief excursions to temperatures as high as 1,200 F (649C), furthermore, allows for die casting aluminum over bearings.

"Many high-performance polymer compositions," states Tom Ruffalo, Vespel automotive product manager, "have a much higher coefficient of thermal expansion than steel, requiring very large clearances between the bearing and shaft to prevent binding." Vespel's low coefficient of thermal expansion, he says, permits minimal shaft/bearing clearance for noise reduction. Engine applications under development include bearings for EGR valves, cooling fan bearings, engine valve guides, and transmission needle bearings.

As new thermoplastic resins rise to the challenge of under-the-hood applications, design engineers should not overlook the advantages of other plastic types. Thermoset polyester composites, for instance, can withstand long-term exposure to hot motor oil or antifreeze better than, say, mineral-filled nylon or glass PET--which is why Ford Motor Company has successfully employed the material (BMC) in the development of lightweight valve covers.

Customization is another benefit. Because polyester-based, high-performance composites are cold blended instead of cooked, small batch compounding is possible. This lets design engineers develop a property performance profile to meet the specific needs of an application at the lowest cost.

The point to remember? Today, there are plenty of plastics--at both ends of the materials spectrum--tough enough for duty under the hood. Read through the following examples to learn how automotive suppliers put them to use.


Accumulator piston

Proving that automotive plastics can take high loads and sustained heat, this transmission component saves General Motors 30% the weight, and more than 10% the cost of an aluminum part. Molded to 0.02 mm tolerances in Fortron(R) linear polyphenylene sulfide (PPS), the accumulator piston eliminates the machining and cleaning associated with diecast aluminum components, and avoids the deflashing common to detailed plastic parts.

During operation, the pistons feed collected transmission fluid to different parts for smooth gear shifting. Not only must they withstand internal pressures of 220 psi, and transmission fluid temperatures of 300F (149C), they need to meet tight tolerances and the dimensional stability requirements necessary to maintain effective sealing. Any softening or bowing allows fluid to blow by the seals.

Fortron, a product of Ticona (formerly Hoechst Technical Polymers), meets these design challenges. For example, the aluminum piston had an o-ring groove; the plastic replacement has an o-ring formed in the mold by moving slides. The first of the accumulator pistons to be molded in Fortron linear PPS are now in production. Other Fortron applications for demanding automotive environments: water circulating pumps, heat exchanger parts.


Air-intake manifolds

When Porsche's new Boxster approaches the red line, less than 1/100th of a second is available to optimally fill its horizontally-opposed cylinder banks with the right fuel/air mixture. Vibration-welded, twin air-intake manifolds help get that job done.

Manifold development was a joint project involving Porsche, Le Profil Industries of Orbeg, France, and DuPont. Material of choice? Zytel(R) 70G35 HSL, a fiber-reinforced, heat-stabilized nylon specifically developed for air-intake manifold applications.

The material withstands continuous temperatures up to 130C and shorter excursions to 150C. Welding, moreover, saves weight and cost.

While fusible core-injection molding techniques account for the majority of all nylon air-intake manifolds on today's cars, the number of welded manifolds is increasing. Not only is vibration welding less capital intensive, recent design advancements now allow fabrication of multi-piece welded manifolds. "It wasn't too long ago," recalls Al Winterman, director of BASF Automotive Materials, "that complex air-intake manifolds such as those needed for V-type engines could only be met by using the fusible core injection molding technique."

Other examples of welded air-intake manifolds can be found on current-model Volkswagens and BMWs. These are made with glass-fiber reinforced Ultramid(R) nylon from BASF.


Clutch ring

Plastics in the powertrain contribute to this self-adjusting clutch. Manufactured by LuK Inc., Wooster, OH, the clutch permits constant pedal effort even as the clutch wears (see DN 12/2/96). Its spring-loaded thermoplastic ring features serrations which wedge forward to maintain the proper gap between pressure plate and cover fulcrums.

Normally, as friction material on the clutch disc wears, the diaphragm spring fingers move upward. Increase in finger height adversely affects clutch engagement and pedal effort. The self-adjusting clutch overcomes these drawbacks, wedging forward to maintain the gap.

Made from DSM Stanyl TW200F6, 30% glass reinforced, the clutch ring has 15 equally-spaced serrated ramps which ratchet downward as the clutch adjusts itself. Stanyl's low post-mold shrinkage meets the part's extremely narrow dimensional requirements. In addition, dimensional stability over the part's life ensures a maximum deflection of 0.3 mm under a load of 8,000 N.


Vacuum pump

Traditionally, automotive vacuum pumps are cast iron or machined metal. Robert Bosch GmbH is challenging that tradition with a glass-reinforced, phenolic molding material. All three pump components-housing, rotor, and vanes-will be molded from the new FM-4065 engineering grade thermoset.

Developed by Fiberite, Inc., FM-4065 retains over 70% of its room-temperature mechanical properties in operating environments up to 300F (149C). High flexural strength, combined with superior heat and corrosion resistance, makes the composite suitable for underhood applications.

Bosch intends to use the all-composite vacuum pump in a braking system for automotive and off-highway diesel engine vehicles. Other applications for Fiberite FM-4065: cooling system/fuel components, power transmission reactors.


Air-intake manifolds

When Porsche's new Boxster approaches the red line, less than 1/100th of a second is available to optimally fill its horizontally-opposed cylinder banks with the right fuel/air mixture. Vibration-welded, twin air-intake manifolds help get that job done.

Manifold development was a joint project involving Porsche, Le Profil Industries of Orbeg, France, and DuPont. Material of choice? Zytel(R) 70G35 HSL, a fiber-reinforced, heat-stabalized nylon specifically developed for air-intake manifold applications.

The material withstands continuous temperatures up to 130C and shorter excursions to 150C. Welding, moreover, saves weight and cost.

While fusible core-injection molding techniques account for the majority of all nylon air-intake manifolds on today's cars, the number of welded manifolds is increasing. Not only is vibration welding less capital intensive, recent design advancements now allow fabrication of multi-piece welded manifolds. "It wasn't too long ago," recalls Al Winterman, director of BASF Automotive Materials, "that complex air-intake manifolds such as those needed for V-type engines could only be met by using the fusible core injection molding technique."

Other examples of welded air-intake manifolds can be found on current-model Volkswagens and BMWs. These are made with glass-fiber reinforced Ultramid(R) nylon from BASF.


DOW SPS, 40% glass, ignition resistant, impact modified
Specific gravity 1.47
Notched Izod Impact, J/m 91
Flexural strength, MPa 188
Flexural modulus, MPa 12,760
Tensile strength, MPa 122
Dielectric constant 3.1
Deflection temperature @ 1.82 MPa 240C
Melt temperature 270C/520F


GE VALOX 735
Specific gravity 1.62
Impact strength, ft-lb/in, Izod notched 1.4
Flexural strength, break 18,000 psi
Flexural modulus 1.2 x 106 psi
Tensile strength, break 11,000 psi
Compressive strength 14,600 psi
Dielectric constant, 100 Hz 4.3
Dielectric constant, 1 mHz 4.0
Melt temperature 490-530F



FIBERITE FM 4065
Specific gravity 1.84-1.89
Impact strength, ft-lb/in notch, side 0.8
Flexural strength @ room temperature 26,000 psi
Flexural strength @ 300F 20,500 psi
Flexural modulus @ room temperature 3.0 x 106 psi
Flexural modulus @ 300F 2.6 x 106 psi
Tensile strength @ room temperature 17,500 psi
Tensile strength @300F 12,500 psi
Compressive strength @ room temperature 42,000 psi
Compressive strength @ 300F 31,000 psi
Deflection temperature @ 264 psi 400F



TICONA FORTRON PPS, glass-fiber reinforced 1140 L4
Specific gravity 1.6
Impact strength, notched, ft-lb/in 2.0
Flexural strength 40,000 psi
Flexural modulus 2.0 x 106 psi
Tensile strength 29,000 psi
Deflection temperature @ 264 psi 266C/510F
Dielectric constant, 1kHz 4.0
Dielectric constant, 1mHz 4.1



DUPONT ZYTEL 70G35 HSL
Density, g/cm3 1.41
Notched Izod, kJ/m2 12
Deflection temperature, MPa 254C
Melt temperature 262C



BASF ULTRAMID A3 HG7
Density, g/cm3 1.4
Tensile strength @ yield, dry 30,450 psi
Tensile strength @ yield, moist 23,200 psi
Notched Izod @73F, dry, ft-lb/in 2.2
Notched Izod @ 73F, moist 5.3
Deflection temperature 482F
Melt temperature range 535-575F
Dielectric constant, 1 mHz dry 3.5
Dielectric constant, 1 mHz moist 5.7



DSM STANYL TW 200 F6
Specific gravity, g/cc 1.41
Impact strength, Izod notched, ft-lb/in, dry 2.0
Impact strength, conditioned 3.5
Flexural strength, dry 43,000 psi
Flexural strength, conditioned 27,000 psi
Flexural modulus, dry 12.0
Flexural modulus, conditioned 6.6
Tensile strength, dry 30,000 psi
Tensile strength, conditioned 17,000
Deflection temperature @ 264 psi 545F
Melt temperature 563F
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