8 replies to this topic

[prima10]

Is it possible to use hi tech plastics for transmission internal components, ie: gears, connecting rods, ect

[BRG]

There was an experimental "plastic" engine that was run in (I think) IMSA races a few years back - I can't remember the name or the details. Did that have plastic moving components, I wonder?

[Halfwitt]

Prima,

I don't think even Titaium gears are successful yet, never mind plastics. You could make them work, but they would make the car larger than a bus. Titanium gears are used for very low speed applications, but for things like microwave turtable drives.

Polymers (even filled types) simply aren't rigid or strong enough for engine use. The obvious polymer composites are good candidates, but the rules stats metallic materials for things like pistons and cranks etc. I don't think gears would be feasible even in CFRP.

It might happen one day.

[Engineguy]

Originally posted by BRG
There was an experimental "plastic" engine that was run in (I think) IMSA races a few years back - I can't remember the name or the details. Did that have plastic moving components, I wonder?

Funny you should ask... I happen to have in front of me a six-page brochure that Amoco Chemicals sent to me in October of 1985 (I never throw this sort of thing away).

Title: TORLON Plastic Engine Parts by Amoco Chemicals

First page tells about the 1985 IMSA season in which the Polimotor Lola GTP Lights car had several top five finishes.

Second page shows the engine... appears (and from my memory) head is metal (Cosworth BDx? Ford was involved with Polimotor at some point I think). Seperate cylinder block, upper crankcase, lower crankcase (sump), are cabon fiber fabrications (resin injection molded using phenolic resin, not epoxy as I recall).

2 litre, 318HP @ 9500RPM, weighs 168 lbs, 100 lbs of which are the 59 plastic parts.

Designer of the engine and owner of Polimotor is Matty Holtzberg.

"Torlon parts are perfectly suited to the engine, because they are strong and tough at temperatures up to 500 degrees F. While some other plastics may take this temperature, Torlon poly(amide-imide) offered Holtzberg a material which can be fabricated to precise detail via injection molding. This economical process lowers unit cost, a critical factor for commercialization of the technology, given the relatively high price of the plastic when compared to traditional materials."

Third page: Torlon Plastic Engine Parts Race-proven in IMSA Competition

"These photos represent the Torlon parts actually used in the Polimotor Plastic engine" (photo shows hybrid piston, piston ring, fat con rod shaped like drag racing aluminum con rod, and wrist pin)

"The head on this piston is metal, and the skirt is made of Torlon polymer. The part is 35% lighter than an all-metal piston. Decreasing the weight of powertrain components reduces secondary shaking forces, which are of major concern in today's four cylinder engines."

"The number-one piston ring in the Polymotor Lola is metal, because it must transfer heat away from the piston. The number-two ring is made of Torlon polymer."

"The con-rods in the Polimotor Lola are made of Torlon-C, a developmental advanced thermoplastic composite from Amoco Chemicals. It represents a 49% weight reduction versus metal."

"Torlon parts are not only tough, they can absorb impact energy better than metal, which is one reason why the material is suited for wrist pins."

(another picture shows hybrid intake valve, valve spring retainer, and bucket-type tappet)

"More than 75% of the weight of an intake valve is cut by substituting Torlon stems for steel. Torlon valve spring retainers weigh only 9 grams each, while a comparable steel retainer weighs about 22 grams."

"Inverted bucket-type tappets made of Torlon polymer contribute to the lower weight of valve train components, which reduces inertia and decreses the spring load needed to prevent valve float."

Fourth page: Shows Torlon timing gears... used "as-molded"... no hobbing.

"Torlon poly(amide-imide) is an injection moldable thermoplastic which maintains high strength at temperatures up to 500 degrees F. Torlon polymers are characterized by outstanding modulus, impact strength, shear strength, fatigue strength, and creep resistance."

"Five years of dynomometer testing preceded the Polimotor Lola's debut at Watkins Glen in July 1984.... in endurance races lasting up to five hours, the Polimotor engine runs at 8,000 to 9,000 RPM. And the Torlon parts don't melt..This isn't science fiction, laughs the affable Holtzberg."

Terry Lappin, Manager of the Engineering Resins Department at Amoco... adds, "plastic engine parts can stand the stress of racing and before long may appear in passenger cars too. We are capable of producing commercial quantities of Torlon engine parts now. It's up to the car companies."

Fifth page: coupon for copy of Torlon Engineering Polymers Design manual.

Properties of Torlon 7130
"There are several grades of Torlon polymer, each designed to maximize specific properties. Graphite-fiber reinforced Torlon 7130 was used to mold parts for the Plastic Engine. Properties of Torlon 7130 are shown below."

This was 15 years ago! I'm going to do some checking to find out current development in this area.

[Engineguy]

from Automotive Industries historical review 1975-1985:

PLASTIC ENGINE

Our December 1980 cover lines said it all: "What...A Plastic Engine?" Matty Holtzberg, founder of Polimotor Research Inc., showed us his 168 lb, 2.3 L ohc motor, which he based on Ford's production 2.3 L 4-cylinder.

The engine used graphite-reinforced composites. Ceramic coatings covered the pistons and intake valves, and the only non-composite pieces were the cylinder liners, crankshaft, camshaft, valve springs, exhaust valve and combustion chamber. Though the engine worked, at $28,000/example it was much too expensive.

Holtzberg moved to a dohc design with the block, head, oil pan, cam cover, oil and water pumps, and intake manifolds made from a phenolic resin-based moldable composite. This 2.3 L design weighed 175 lb, made 178 hp, and needed 50% less machining than a steel design. Holtzberg's engine never reached production, though a 320 hp version had minor racing success.

I stand corrected... apparently the head (except for the combustion chamber surface) was also made from the phenolic resin composite

[dgsg]

Torlon is a strange material. We broach parts made of Torlon which go on the Apache helicopter. It is a plastic material which causes dulling of broaches quicker than cast iron. The parts then go through a SIX DAY heat treat cycle. Magic stuff.

[desmo]

These thermoplastics must have some fatal flaw for engine parts. Torlon has been around since the early 70s, the Polimotor and Amoco Torlon experiments showed a lot of early promise, but then dropped off the face of the earth. Do a web search on them, there is almost NOTHING in the last 10 years. There are fiber reinforced liquid crystal polymer thermoplastics that appear to have excellent properties for engine applications compression properties perhaps excepted. After the frantic attempts to find applications for PMCs in the 80s, it appears no one is even trying to find applications inside engines anymore. I assume there are good reasons why. What they are, I am not sure.

[Halfwitt]

This is a link to some Torlon properties, which are very impressive
Torlon 7130 properties

but, the tensile modulus is only 12% of steel, whilst its density is 20% of that of steel. Therefore for the same stiffness, the plastic part, even in this remarkable material would be greater, and the part would be huge.

For tensile strength equivalent to the best steels (2000MPa UTS) you would need 8 times the cross sectional area.

Before I am berated for using example too simple, these are just to point out two of the fundamental reasons why plastics are not used for structural parts.

The thermal conductivity of an injection-moulded grade is 0.53 W/mK, where that of aluminium is hundreds of times this value. It would be hard to replace casting requiring good thermal conductivity with plastic.

I love the idea of a plastic engine, but I can't see it happening for a while, at least until more suitable materials are developed.

[desmo]

Agreed. Polymers will surely only be feasible as a matrix for composites, and it appears metal and ceramic matrix materials have more promise for internal engine parts.