AKG Polyurethane. Like No Other.
All polyurethane is not created equal. It is available in a wide range of compounds and durometers, from an even wider range of suppliers. It can have a variety of formulated characteristics, with quality ranging from substandard to high-grade. With this in mind, let’s dig deeper into this material – exploring the benefits of AKG’s Military Spec polyurethane and why it is not only superior to other cheap polyurethane, but also superior to plastics such as Delrin and UHMW, for automotive performance applications.
It’s Rubber. Not Plastic.
Polyurethane is a synthetic, engineered material. It is a liquid in raw form that is cured to a solid state at the appropriate elevated temperatures after the molding process. Most people think polyurethane is a plastic, but it’s actually an elastomer – a member of the rubber family. It is one of the most versatile materials around, and possesses many properties which can be isolated and manipulated to create unique performance characteristics lacked by other materials.
Don’t Fall For Cheap Poly.
It is important to understand that hardness (durometer) alone is not a sufficient indicator of either the quality or the performance capability of a particular piece, and can not be relied upon as a specification by itself. There are many compounds with very different quality and performance characteristics that can be produced at the same durometer.
This is because there are many chemical structures from which polyurethane systems are derived, each having very different physical and engineering properties – and this doesn’t even take into account the quality of the raw materials used, or the manufacturing process! Polyurethane is a difficult material to formulate correctly and manufacture consistently; it requires teamwork between engineers, chemists and the entire production team.
If a polyurethane compound is selected, formulated or applied improperly, it very often performs poorly in its application. Cheap polyurethanes almost always contain fillers and extenders to reduce cost; this, along with highly questionable manufacturing processes, are leading causes of premature component failure.
Even though certain AKG bushings or mounts for BMW may have the same relative hardness as those available elsewhere, the chemical structure of the elastomers are completely different, and can only be identified through spectrograph and chemical analysis. Luckily, the quality of our polyurethane is so much better than anything else available, you can actually see and feel the difference for yourself!
Compounds So Good. They’re Proprietary.
Our customers are astounded at the noticeable difference in quality between AKG polyurethane and that which is used by others – and it’s because our polyurethane isn’t their polyurethane. We use premium Military Spec compounds containing no cheap fillers or extenders. We also take full advantage of several proprietary chemical modifications to our compounds – providing for improved product performance in automotive racing applications.
One of a Kind Process. One of a Kind Performance.
AKG polyurethane is produced under strict ISO 9001:2008 certified processes, with many important production steps including constant machine calibrations and a continuous, stringent analysis of raw materials. Our process also relies heavily on stoichiometry to help set the correct amount of reactive elastomer polymer to both the amount, and choice of curing agent used. This plays an all-important part in the compression set resistance, the cut and tear resistance, and the flex fatigue resistance of our polyurethane – all of which have an important role in the quality, durability and consistent reliability of our performance parts.
Durometers: Track Capable. Race Proven.
Polyurethane compounds can be formulated with hardness ranging from soft (A scale) to hard (D scale). Hardness is measured with an instrument called a durometer, and therefore the hardness of the material is usually referred to as the “durometer” of the material.
Polyurethane in and of itself can be made in a wide range of durometers, from as soft as an eraser to as hard as a bowling ball. Within this wide range are durometers we at AKG deem suitable for specific performance parts applications. The durometer of BMW OEM bushings is generally around 55A. The softest durometer we use is 70A, which although relatively soft, is still harder than the stock rubber bushings (70A is also the same hardness as the BMW factory Group N parts).
From there, durometer increases from our medium 80A-95A street performance compounds, all the way to our rock solid, race proven 75D compound. Many try to advertise 95A (or lower!) as a racing durometer, which is ill-advised. Although 95A does provide a drastic increase in performance over the stock rubber bushings, we consider it a medium durometer, as it has nowhere near the performance capability that an AKG 75D compound provides.
The comparisons below strictly apply to high-quality polyurethane manufactured through proper processes only. Low-grade polyurethane, especially those which contain cheap fillers and extenders, and those not manufactured properly, may have drastic variations in expected properties – including poor performance.
Abrasion & Impact Resistance Properties
It’s undeniable that quality polyurethanes have outstanding abrasion resistance. In fact, they often outwear metals, plastics and other rubbers by up to 8 times! This abrasion and impact resistance is part of what gives these polyurethanes a longer life expectancy than cheap plastics, such as Delrin and UHMW.
Load Bearing & Resilience Properties
Hard plastics, such as Delrin, have a major drawback in that they are inherently brittle materials, and lack memory. UHMW isn’t brittle, but it does lack memory. If a material lacks memory, that means when it is compressed or impacted, it will not return to its original dimensions and is forever deformed.
For instance, you may have found that bolts used with suspension bushings or mounts made of Delrin or UHMW begin to loosen with time; this is because both Delrin and UHMW lack the memory to return to their original shape after deformation – the bolt isn’t loosening, the parts’ dimensions are virtually changing! Quality polyurethanes, on the other hand, have memory and elasticity, and also resist cracking even in their hardest durometers – including our 75D race compound.
This toughness makes quality polyurethanes ideal for parts that must withstand high-impact or repeated impingement. Since these polyurethanes have a high-load capacity in both tension and compression, a piece that undergoes a change in shape under heavy load will return to its original shape once the load has been removed, and assuming it was designed and manufactured properly – will do so with minimal compression set in the material.
This performance also extends to high flex-fatigue applications as is the case with an automotive suspension. As we stated earlier, chemical manipulations can be made to improve the performance characteristics of polyurethane for a specific application. A good example of this is the isolation and modification of the flexural properties – which can improve the elongation and recovery properties of a component. In fact, rebound values can be formulated anywhere from 10% – 70% dependent upon the frequency of vibration a piece is being designed for.
Temperature, Stability & Substance Resistance Properties
Polyurethanes can be formulated to remain quite flexible even in very cold temperatures and are remarkably resistant to thermal shock which allows them to withstand large, sudden temperature drops. This means that quality polyurethanes are also great performers in harsh environments. Harder durometers remain stable in water and will not deteriorate or swell even when immersed for long periods of time at elevated temperatures. The absorption rate is practically zero – less than 1% by weight.
Although many plastics and rubbers provide excellent resistance to certain oils, solvents and chemicals, polyurethanes are capable of resisting a much wider range of these harsh substances without causing material degradation.
Raw Materials Cost Comparison
We’re proud to offer high-quality, US Military Spec polyurethane performance parts, made entirely in the USA under strict ISO 9001:2008 certified processes. What’s even more amazing is that our products are competitively priced compared to other much cheaper alternatives (low-grade poly, Delrin and UHMW), even though the raw-materials cost of our proprietary US Military Spec polyurethane is over 3 times the price of Delrin and over 6 times the price of UHMW!