March 22, 2013

Large Underwater Gear Highlights Nylon's Moisture Resistance

Wear and moisture resistance are two recurring themes in the engineering problems solved by Intech Power-Core™. Oftentimes, these problems involve small components, such as gears, cam followers or rollers. Yet Power-Core’s wear and moisture resistance properties can just as easily apply to large parts. Consider, for example, the large geared ring produced in our material for underwater use in a nuclear reactor pool. Measuring 2,200 mm across and 80 mm thick, this geared ring weighs in at 100 kg. It withstands a load of 150 kN at 6 rpm.

Intech Underwater GearLarge Part Size, No Problem. The sheer size of the part stands stands out, but our gravity casting process actually allows us to scale up the size of our components easily. Gravity casting results in low internal stresses, even when the parts have metal structural inserts. So going “big” is not really an issue for Power-Core.

Physical Property Advantage. What was even more important in this underwater application were the physical properties of the polymer. The geared obviously needed to be produced from a material that resists continuous exposure to liquids and corrosion. Various metals fell short due to their poor corrosion performance compared to polymers such as Power-Core.

Many other polymers, however, do not tolerate long-term exposure to moisture. Power-Core does. Its ultra-low moisture uptake allows it to remain dimensionally stable even when submerged in water for long periods of time. In this nuclear application, Power-Core’s radiation resistance also weighed in its favor over other polymers. And its wear properties allow it to avoid the fretting that can occur when component surfaces rub together in the presence of water.

In this application like in most applications engineers had a selection of materials to choose from. The common conception of most engineers when it comes to wet environments is that a polyester material such as ERTALYTE or an Acetal (POM) would be the best choices. In many cases these engineers would be on the right track - both materials are excellent in many applications - however for underwater gears specifically these materials wouldn’t be able to accomplish the task. For one the size of the gear leaves only very few material options, second when using Ertalyte or Acetals you have to be very careful what type of environment you expose them to – chlorine – like that found in drinking water could destroy the polyester compound over time and Acetals don’t react well to acids such as those used in wash downs, and booth are susceptible to weakening caused by extended UV exposure. 

Most Nylons, on the other hand, perform poorly when submerged in water, so naturally engineers tend to steer away from the entire nylon family when designing underwater motion systems. Powercore has a unique place in the family of Polyamides in that its moisture absorption, even when fully submerged, is negligible.  Our site contains numerous studies and documentation showing the effects of moisture absorption on nylon and nylon 6 and nylon 12’s dimensional change when submerged. When designing your next motion system of marine or underwater use please remember to consider the environment and look of a suitable polymer for your application.  

Learn more about Power-Core’s moisture resistance

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