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Extruder Wear Parts: Tungsten Carbide Option?

When extruder performance begins to suffer because of worn barrels, barrel liners, screws or dies, what are the options?

First, there was the first choice. In the past, the plant manager or production supervisor naturally would order matching replacement parts from the original equipment manufacturer (OEM). For many aquafeed and petfood manufacturers such periodic wear parts replacements may have been part of the original extruder purchase agreement or a long-term service contract. Alternatively, some feed makers would opt to have the barrel liners replaced and the screw reconditioned or rebuilt by an outside machine shop. However, larger extrusion operations mostly would avoid this practice due to the technical challenges of matching modern extruder metallurgy and engineering, the inconvenient logistics involved and potential warranty risks. They would rely upon the OEM for wear parts.

Now, extruder operators have another option–new replacement barrels, barrel liners, screws and dies from metallurgical design-engineering firms that specialize in custom tools for extreme wear conditions. One of the leading suppliers in this field, Conforma Clad, Inc., based in New Albany, IN, specialized in rock drilling tools for oil and gas industries in the late 1960s. Today, the company’s proprietary wear-resistant process involves “cladding” high wear components with tungsten carbide.

Conforma Clad extrusion sales engineer Lorrie Muzzone told FEED MANAGEMENT that the company got its start with feed extruders by applying the tungsten carbide cladding to OEM screws and barrel liners supplied by petfood manufacturers. But, given its own in-house engineering and fabrication capability, the company soon started manufacturing wear parts “from scratch” for the most popular types of petfood and aquafeed extruders. What made retrofitting with tungsten carbide-clad parts attractive to feed makers, she said, was their much longer wear life: “Our pricing can be about twice that of the OEM, but with tungsten carbide cladding we expect anywhere from four to eight times the life of the OEM parts.”

The higher the cost of tungsten carbide-clad parts stems from the manufacturing process. Basically, the company first manufactures the “substrate” for example, a cast and machine extruder element with metallurgical properties to optimize cladding and subsequent operation of the extruder under specific conditions. The technicians apply a flexible, organic cloth impregnated with evenly-distributed, size-controlled particles of tungsten carbide. The cloth can conform to complex geometries, such as surfaces of screw flights. Then they heat the screw element in a vacuum furnace, which burns off the organics and “infiltrates” a molten braze alloy throughout the tungsten carbide layer.

“The resulting coating,” the company says, “has no interconnected porosity, is uniform in depth and loading, and is metallurgically bonded to the substrate with a bond strength in excess of 60,000 psi (415 mpa).”

The performance of the tungsten carbide surface, the company states, extends beyond much greater resistance to abrasion from ingredient particles (see figure, Dry sand abrasion).

There also is improved resistance to corrosion from chemical reactions (see figure, Corrosion) and erosion caused by liquid cavitation (see figure, Erosion). According to Conforma Clad, tungsten carbide provides overall wear performance that is also superior to other steel wear protection methods (see table, Performance).

Wide range of maintenance approaches

Many factors play into just how the aquafeed or petfood manufacturer approaches extruder maintenance–especially replacement of relatively high cost wear parts. There are factors of scale: A single extruder in a single plant or several in multiple plants? There are factors of product type and quality: Catfish feed from a large single screw extruder, or salmon starter feed on a twin screw? There are factors of plant personnel maintenance skill and experience–a major consideration in diagnosing existing wear problems or anticipating potential problems. Also, there may be technical service and other contractual or less formal relationships with the extruder supplier.

In any case, Muzzone says, the feed manufacturer probably has the benefit of knowledge of working with the OEM. If a particular extruder was purchased new, both should know the history of the machine based on service and maintenance records. Therefore, she says, the feed manufacturer should have the ability to make a “competitive value analysis” on OEM parts versus others.

Muzzone acknowledges that the OEM is totally familiar with the design of the screw, for example, and has installed and, at least initially, configured the extruder for a particular range of jobs. She points out that the feed manufacturer and the extruder supplier may still enjoy a close working relationship. Nonetheless, she notes, tungsten carbide-clad components currently are installed in extruders operated by the majority of large petfood manufactures and many aquafeed manufactures.

The rebuild option

The quality of the rebuild of rebuilt component — mostly barrels and screws — greatly depends upon the specialized skill of the rebuilder and which technology is used.

“You can put anything on the ‘OD’ (outside diameter),” Muzzone says, “from a mild steel to a version of carbide hard-facing. So the life expectancy on the components could vary along with the cost. Typically, rebuilding is cheaper because the rebuilder is just taking the existing part and ‘welding it up’, then grinding it down to spec.

“But there are some serious issues with the rebuilding process. The profile of the screw changes under wear during normal operation. In the process of rebuilding it, the grinding and polishing further changes the profile. Even the metallurgical structure of the steel substrate can alter because welding by hand results in variable heat application.”

“In operation, the screw flights typically wear on the ‘pusher’ side, in the corner of the top radius. So, as the rebuilder brings the OD back to spec, he might add some welded reinforcement, but usually no hard-facing or other protection for the pusher side of the flight. With each rebuilding, then, the working face of the flights get thinner and thinner.”

In any case, she emphasizes, the rebuild is not brought back to original specs nor is the hardfacing comparable to a new tungsten carbide-clad component. In “cladding”, the tungsten carbide is applied as a coating, then goes through a furnace cycle with brazed infiltration. “This forms a cladding with uniform thickness and a strong metallurgical bond, without the check cracking typically present with hardfacing.”

Piecemeal or matched component replacement

Typically, Muzzone says, original equipment screws wear out before the matching barrel liners. In such cases, a tungsten carbide screw could replace the OEM screw. She points out that no matter whether the replacement screw or the OEM screw came into contact with the liner, there would be accelerated wear. Still, Muzzone adds, it is preferable to replace screws and liners simultaneously, while it is less important to install new tungsten carbide shearlocks, dies or wearplates at the same time.

What about the OEM’s warranty on the extruder if the manufacturer uses non-OEM parts, especially tungsten carbide-clad parts, which are going to be tougher than almost anything else in the machine?

Muzzone points out that there has been an “after market” for extruder parts for many years. “I am not aware of any warranty issue where any of the OEMs void the warranty of an extruder if, after initial installation, the customer switches to high quality, non-OEM wear components.”

Other tungsten carbide feed applications?

Where in feed processing does tungsten carbide cladding technology go from extruder wear parts? Muzzone says aquafeed and petfood manufacturers have many ideas.

“We ask ‘where it hurts’ as far as component wear in the whole plant,” she says. “Once the manufacturer understands the cladding technology, we’ll go through the graveyard of worn parts and suggest what would be a good application and what wouldn’t.”

As a practical matter, however, the costly proprietary cladding process makes application most economical on relatively expensive components. At the same time, Muzzone says, there are significant “soft cost” savings associated with longer wearing parts. First, maintenance downtime is reduced. Also, there is less logistics work and shipping expense. “Because barrels, screws and other components are expensive, there is a tendency for the operator to let the old parts wear longer than they should for optimum performance.” FM