Nitrided versus Bimetallic Injection or Extrusion Barrels. A Comparison

"Nitrided" Injection or Extruder Barrels

"Standard" Barrels on most OEM Extruders and Injection Presses

How do they "stack up" against bimetallic barrels?

What you should know before making your selection:

Primary Applications:

For Extrusion and Injection Molding Non-filled, Non-corrosive Polymers

The “technical stuff”:

"Nitrided" plasticating barrels are manufactured typically from AISI 4140 HT steel.
The barrel bore is nitrided using either a gas-nitriding or ion-nitriding process. Gas-nitriding is the more common method since it is considerably less expensive than ion-nitriding.

A typical gas-nitrided barrel bore has a "hardened" surface to a depth of about .002 - .004 inch, while the typical ion-nitrided bore is hardened to a depth of about .015 inch. [Compare that to the typical depth of .050-.062 inch for a bimetallic barrel].

Nitrided plasticating barrels certainly have their role in processing non-abrasive, non-corrosive polymers, but when used for any other types of polymers, expect frequent machine tear-down for barrel replacement. So, why do some machine builders offer their injection presses or extruders equipped with nitrided barrels as their "standard"? Well, read on....

The "economic stuff": (It's your company's money....)

Since machine builders and dealers do not know beforehand what type of resin a machine buyer may wish to process, they often sell their "off-the-shelf" plastic processing machines with nitrided plasticating cylinders as "standard" equipment to keep the cost of the machine down in a very competitive market.

In our view, this is perfectly appropriate as long as the customer is made aware of the limitations in performance of the nitrided cylinder, especially if the customer intends to process corrosive resins or those exhibiting highly abrasive characteristics. Many (but certainly not all) machine builders will offer bimetallic cylinders as an "upgrade" when they encounter highly abrasive or corrosive resin processing applications or on request by the buyer.

While WEXCO has produced nitrided cylinders on customers' specific requests or when the cylinder wall is too thin for our spin-casting process, we do not consider nitrided cylinders a part of our regular production program. As a manufacturer of "high-performance" plasticating cylinders, we prefer not to offer cylinders whose bores are protected only by a relatively thin case-hardened surface layer.

We believe that our WEXCO 666 cylinders offer a much better value for non-corrosive resin processing, typically yielding at least 3 - 4 times the wear life of a nitrided cylinder at marginally higher initial cost, and if any of the polymers you process are corrosive, your nitrided barrel surely will not last very long! Select a WEXCO 555 bimetallic barrel instead! It will last up to 10 times longer than nitrided barrels when processing corrosive polymers.

When ordering a new processing machine or a replacement plasticating cylinder, consider specifying a WEXCO high-performance bimetallic cylinder. Your machine or equipment dealer will be happy to honor your request! If not, call WEXCO, and we will refer you to machine builders or distributors that offer WEXCO high-performance bimetallic cylinders.

The "bottom line" of Nitrided vs. Bimetallic Plasticating Barrels:
In our view, based on serving the plastics processing industry world-wide for more than 30 years, nitrided extruder or injection barrels are no match to properly selected high-performance bimetallic barrels in terms of service life, output yield, and resistance to the detrimental effects of corrosive and/or abrasive polymers on your processing equipment.

The "bottom line" is that bimetallic plasticating barrels initially cost a little more than nitrided barrels, but that small difference is made up many times over by much longer service life and fewer machine tear-downs for barrel replacement. The old adage "You get what you pay for" certainly applies to your decision on whether to choose a nitrided barrel or a high-performance bimetallic barrels made by WEXCO.

One last comment: You will no longer be able to compete successfully in a highly competitive global market with anything but high-performance equipment and processes. Let us help you succeed by allowing us to offer you our vast experience, knowledge, and our high-performance WEXCO plasticating components. Consult with us before you finalize your machine order with your favorite OEM, or call us to replace a worn barrel and screw on your existing injection press or extruder. We will be happy to advise you and to serve you.