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Consultant’s Corner – Getting the Most From Your Feedscrews and Barrels

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Consultant’s Corner – Getting the Most From Your Feedscrews and Barrels

 

By Wendell Whipple, Vice President, Aftermarket Global Sales

 

We all know feedscrew and barrel wear leads to lower outputs, poorer quality components and an eventual loss in profits. As a matter of fact, losses in output can often be more costly than a new feedscrew or barrel. The good news is, by understanding the causes of wear and learning to identify potential issues, we can minimize the damage. Following is information that will help you get the most from your feedscrews and barrels.

 

There are three main types of wear:  Adhesive, Abrasive, and Corrosive

 

Common Causes of Adhesive Wear (metal-to-metal contact)

 

  1. Straightness of barrel and screw

  2. Alignment of drive, barrel, feedsection, and feedscrew

  3. Screw design

  4. Lack of uniformity of barrel heating

  5. Screw surface treatment and barrel liner finish being wrongly matched

  6. Improper support of the extruder barrel (common with extended L/D ratios)

  7. Unsupported dies at the end of the barrel

  8. Unsupported dies at the end of the barrel

 

Common Causes of Abrasive Wear

  1. Processing polymers with fillers such as talc, calcium chloride, glass fibers, barium ferrite and titanium oxide
  2. Processing silicones

 

Common Causes of Corrosive Wear (material attacking the surface metals)

  1. Processing of corrosive polymers such as some PVC’s, corrosive flame-retardants  and fluorocarbons

 

Tips for Delaying Wear

  1. Check for component straightness and machine misalignment.  Davis-Standard service technicians can provide alignment visits, screw and barrel checks accompanied with advice about the right screw geometry for your application. Make sure that screw and barrel finishes are matched and that one is not trying to induce premature wear in the other.
  2. Only use extrusion barrels and screws with the right surface treatment for the abrasive and/or corrosive nature of your application.  Your Davis-Standard representative can advise you on the correct treatment.

 

Barrel Treatments

Davis-Standard fits bimetallic barrel liners to all extruders as a standard service to offer protection of the inner processing surface of the barrel. There are three main bimetallic grades, DS1000, DS6000 and DS8000.

 

DS1000 is an iron-based lining for general purpose wear environments. It is the most common liner and fitted on nearly all Davis-Standard machines. This lining provides adequate protection for most applications, but not those that are corrosive.

 

DS6000 is a nickel-based product for corrosive wear environments. It is best for processing compounds such as those with flame retardants, fluoropolymers and high-temperature resins.

 

DS8000 is a nickel-based alloy engineered with a high percentage of tungsten carbide particles suspended within its matrix. Designed for corrosion and wear resistance, it is recommended for applications requiring highly filled/reinforced compounds and/or extreme corrosion as well as fluoropolymers and high-temperature resins.

 

Feedscrew Finishes

Feedscrew finishes can range from high-quality steel for standard applications to Inconel, Hastelloy & Duranickel for highly corrosive applications. Heat treatments such as flame hardening and nitride are also available. To improve wear characteristics on the flight tips, Davis-Standard can in-lay a variety of substrates such as stellites and Colmony 83 for improved abrasion resistance. Root surface treatments such as chrome and spray coatings for extreme wear conditions are als available.

 

By speaking with your Davis-Standard representative about wear prevention, processing techniques, feedscrew designs and measurements, materials compatibility, and barrel and screw alignment, you can extend the life of your equipment and avoid costly downtime.

 

For more information, contact:

Rick Siciliano: rsiciliano@davis-standard.com (North & South America and Asia)

Mark Woodgate: mwoodgate@davis-standard.com (Europe, Middle East and Africa)

 

 

 

 

 

 

 

 

 

 

 

 
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