SAE TECHNICAL PAPER SERIES 1999-01-3011 E

Boney A. Mathew
Mathson Industries, Inc.

Dr. Helio Wiebeck
Engenharia Quimica
University of Sao Paulo

Copyright © 1999 Society of Automotive Engineers, Inc.

ABSTRACT

There are many advantages to air intake manifolds molded from Nylon 6.6 Glass reinforced composite material versus a pressure-cast aluminum manifold. Weight is significantly lowered and production costs generally are reduced. Performance improves with the precise control of the interior surface finish and reduced air induction temperatures. The Nylon 6,6 Glass reinforced composite material can be molded into intricate shapes by injection molding or lost-core process with reduced machining operations as well as Nylon 6,6 material is easily recycled. Production costs will continue to decrease as optimization of material, process and part integration increases.

This study evaluates Nylon 6,6 Glass reinforced composite material in terms of the intake manifolds material key requirements such as thermal, heat aging, fatigue, impact, creep, stress and chemical resistance including multi fuels. This study would assist engineers in designing intake manifolds using Nylon 6,6 Glass reinforced composite material.

INTRODUCTION

For over 25 years Nylon 6,6 Glass reinforced composite material has been used in under the hood applications. Some of the under the hood applications using Glass reinforced Nylon 6,6 are brake and power steering fluid reservoirs, radiator end tanks, fuel injectors, etc. In recent years Glass reinforced Nylon 6,6 composite has been used for injection molded and loss core molded air intake manifold.

The Nylon 6,6 composite offers several economic benefits. An air intake manifold made from Nylon 6,6 composite can be molded with snap-on or clip-on features due to the strength and flexibility of the material. This significantly reduces assembly costs as much as 15 – 20%. The Nylon 6,6 composite manifold requires no paint, is non-corrosive and non-porous, unlike cast aluminum which requires costly finishing steps.

The improved volumetric efficiency of an intake manifold made from Nylon 6,6 composite is due to its inherent insulating properties. The Nylon 6,6 composite can be designed and molded with greater flexibility than cast aluminum. The manifold can be produced with a smoother, streamlined interior, resulting in increased airflow to the engine, which is a key factor in increasing horsepower of the engine.

An air intake manifold molded from Nylon 6,6 composite is an important factor when faced with the proposed stricter corporate average fuel economy (CAFÉ) regulations.

In short, Nylon 6,6 Glass reinforced composite offers several advantages. It saves money, reduces weight, ease of assembly, better insulation, improved airflow, excellent strength to weight ratio and is recyclable.

EXPERIMENTAL

In order to study the effect the automotive environment has on the long term mechanical durability of Nylon 6,6 Glass reinforced composite for air intake manifolds, the following methodology was established:

• Characterize the material by performing physical properties tests.
   
• Expose the material to various temperatures to evaluate thermal resistance of the material in order to simulate conditions under the hood.
   
• Expose the material to fuels to evaluate chemical resistance of the material.

MATERIAL

SSD 330 KNF, 33% Glass reinforced polyamide 6,6 provided by Nyltech North America.

EQUIPMENT

A 70mm ZSK 70 Werner and Pfleiderer twin screw extruder was employed for compounding the material.

PHYSICAL PROPERTIES TEST

Test specimens were molded and tested using SSD 330 KNF material to obtain physical properties of the material. The test specimens were exposed to various temperatures and fuels to understand the long term properties which would assist in qualifying this material for intake manifold applications.

RESULTS AND DISCUSSION

This study was conducted to characterize and to qualify Nylon 6,6 Glass reinforced composite for intake manifold applications.

Table I shows the physical properties data for Nylon 6,6 – 33% Glass reinforced composite material. Table II shows stress versus strain data at –40º to 150ºC for Nylon 6,6 – 33% Glass reinforced composite. As expected at -40ºC at given strain stress is maximum and at 150ºC stress is minimum. This is due to viscoelastic relaxation's corresponding to the onset of various types of internal motion with increasing temperature (1).

Figure 1 graphically shows tensile creep of the Nylon 6,6 – 33% Glass reinforced composite. A percentage creep at 70ºC is higher than at 20ºC. At higher temperatures, the atoms and groups in the polymer molecules acquire an increasing amount of thermal energy, causing them to vibrate and move about. The higher the temperature, the greater the thermal motion. The larger the sequences of atoms in the polymer chain which become mobile, and in turn increase creep at higher temperature (2).

Figure 2, 3 and 4 shows the effects of heat aging at 150ºC on tensile strength, ultimate elongation, and Young's modulus for Nylon 6,6 – 33% Glass reinforced composite. After 2000 hours at 150ºC Nylon 6,6 – 33% Glass reinforced composite showed good thermal durability based on retention of the properties. The properties after 500 to 1000 hours remained fairly constant or increased slightly. This indicated that while chain scission is occurring on the surface due to oxidation, chain linking (solid-state polymerization) occurs internally, resulting in a constant or higher stiffness. Additionally, it is attributed to stress relieving and further crystallization at 150ºC.

The reduction in properties at 2000 hours at 150ºC is primarily caused by free radical chain scission and cross-linking of the polymer molecules close to the surface. Three primary mechanisms that change the mechanical properties of a polymer exposed to higher temperatures are chain scission, cross-linking and oxidation. In most cases, all three mechanisms occur simultaneously. Their effects may balance each other for a while, but eventually one of the reactions prevails, leading to embrittlement of the polymer (4).

Figure 5 shows the effects of M-20 fuel soak at 121ºC for 500 hours on tensile strength for Nylon 6,6 – 33% Glass reinforced composite. The tensile strength dropped significantly after 500 hours at 121ºC when soaked in M-20 fuel. Nylon 6,6 is known to be adversely affected by exposure to methanol. Methanol is absorbed by nylon and thus causes reversible mechanical property changes due to plasticization. Methanol will also hydrolyze nylon at higher temperatures. Dried out samples after exposure to M-20 fuel regained most of the original tensile strength due to evaporation of absorbed fuel.

Figure 6, 7 and 8 shows Peugeot, Fiat and Alfa Romeo air intake manifolds using Nylon 6,6 Glass reinforced composite material.

CONCLUSIONS

Within the limit of this study, it is shown that Nylon 6,6 – 33% Glass reinforced composite material is suitable for intake manifold applications. This material has high strength and toughness, and excellent retention of properties after heat aging.

REFERENCE

(1) Kohen M.I., Nylon Plastics, John Wiley & Sons Inc., N.Y. 1973, P. 313

(2) Deanin R.D., Polymer Structure, Properties and Applications, Cahner Publishing Co.,
N.Y., 1972, P. 88

(3) Murty E.M., The Effect of the Automotive Fuel System Environment on the Long
Term Durability of Reinforced Nylon, Thesis to GMI Engineering and Management
Institute, April 15, 1989, P. 28

(4) Ibid, P. 29

AUTHOR'S BIOGRAPHY

Mr. Boney Mathew, President & CEO, Mathson Industries, Inc., Troy, Michigan USA.

Mr. Mathew's background includes 16 years in the automotive and plastics industry.

Prior to starting Mathson Industries, Inc., he was a Marketing and Technical Executive for Nyltech North America – Joint Venture of Rhone-Poulenc – France and Fiat – Italy.

He also served as Plastics Manager for Teleflex, Inc.'s Automotive, Aerospace and Medical Company. Mr. Mathew is the inventor and co-inventor of several patents including "Method of Making Fluorocarbon Coated Composite Braided Hose Assemblies", "Hose End Fitting Assembly" and "Expanded Fluoropolymer Tubular Structure, Hose Assembly and Method for Making Same".

He is a member of Society of Plastics Engineers, Society of Automotive Engineers and ASEI. He has published and presented six technical publications on various plastics and composites at various international technical conferences and is the co-author of "Passage to India, A Comprehensive Study on the Indian Automotive Industry."

Mr. Mathew earned a M.S. degree in Plastics Engineering from the University of Massachusetts, Lowell, USA.

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ISSN 0148-7191
© Copyright 1999 Society of Automotive Engineers, Inc.

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