In the late 1970’s General Kinematics (GK) applied the air classifier concept for the hog fuel industry where stones in the wood chips hurt BTU values and caused slag to form on boiler tubes. These early units solved the problem.

As processors in the recycling market sought ways to more effectively classify and clean material GK applied their technology to the scrap industry where it took hold for handling ASR (auto shredder residue) to concentrate valuable metallics. Today, the technology is deployed in a range of MSW, glass recovery, and C&D operations.

With hundreds of units operating throughout the world GK has decades of experience applying air and vibratory technology to classify recyclable commodities.

As GK refined the functionality of the units, recyclers today have better control of the fluidized air, air knives and landing plates. Operators benefit from a very flexible system.

The GK units combine vibratory action with high velocity/low pressure air streams to fluidize and stratify material according to differences in their terminal velocity. This allows effective removal of heavy items such as glass, metallics, stones, dirt and more from the product stream.


GK calls its unit a DE-STONER® Air Classifier. They are available in single, dual, and triple-knife models.

A typical processing line removes large items with a primary screen and then goes to further processing. Subsequently a DE-STONER® Air Classifier is used to classify stones, non-ferrous or other heavy materials, for example. Humans cannot pick minus materials from the screens over the course of a day as effectively as the GK DE-STONER® does routinely and accurately.

A typical system uses a dual-knife design. There are two independent air knives to clean material. The first does a coarse cut of bulky material. Material that hits the second knife gets a clean cut from the heavy stream and separates according to the system’s requirements.

A triple knife unit separates material using the two air knifes on the interior of the machine and a third one located at the outlet, creating a cleaner product for mixed, high volume materials. Units can also include pre-classification for additional material separation, providing a cleaner, higher-value end product.

The DE-STONER® Air Classifier actually provides three distinct separations: heavies, mid-range and ultra-lights. Ultra-light materials are discharged to 20 feet from the end of the unit. Heavies fall out. The mid-range material is conveyed along the bottom to its end for further processing.

In addition to the ability to process heavies, lights, and ultra-lights, optional pre-screening sections can be added to remove fines or oversized material. Optional drop-out boxes complete with air recirculating systems are also available.


While many of these units are installed at C&D recycling operations, the GK DE-STONER® Air Classifier is ideal for MSW applications and multi-stream operations.

It delivers exceptional performance, for example, in glass clean up separating the lights fraction on a glass line. It also allows MSW lines to drop out heavy, wet organic materials from the stream.

In systems applications they help increase recovery, maintain throughput and optimize downstream equipment. They are heavily constructed to withstand the shocks associated with disparate material, such as heavy iron items in an MSW stream and rocks in a C&D stream.

Yet, they efficiently deliver properly sized materials for sophisticated downstream separation. “It is all about better material presentation for manual picking and for the other machines on the line,” says Bill Guptail, GK engineer emeritus.

Not only is the GK DE-STONER® Air Classifier a flexible system component, it is easy to use and maintain. It is virtually jam-proof since its design has no moving separator parts. And, with this inherently simple, fully isolated design, the requirement for foundation depth is minimized.

There are energy savings, too. The GK DE-STONER® Air Classifier is driven by an energy efficient low-horsepower motor that is designed for continuous, high volume production in a wide range of separation applications. We are not talking five-day, eight-hour shifts. These units have rugged, heavy duty construction that withstands 24-hour operation. Many systems have DE-STONER® units operational for thirty years.