One of the most important factors for the success of any twin-screw extruder application is the structural materials used on the Screw Barrel , barrel, and other wearing parts. The success or failure of a twin-screw extruder, especially when processing highly abrasive or corrosive materials, depends on the good performance of the parts under difficult processing conditions

Corrosion resistance

Corrosive applications make the total wear resistance more complicated. Corrosion wear is represented by the rounding of the pit surface and sharp corners. High chromium tool steel is usually the best and most cost-effective defense against corrosion and wear. Please note that traditional stainless steel, such as 304SS, is almost never used for extrusion. Although 304SS is difficult to process, it has very low abrasion resistance and has no good value for the extruder barrel or screw.

In the presence of extreme corrosion, such as when processing fluoropolymers and their monomers, more specialized materials may be required. Iconel and Hastelloy are commonly used in these applications. These alloys provide excellent corrosion protection through high nickel and chromium content. However, these rare alloys have Rockwell C hardness values ​​of 35 or lower, so they cannot provide good wear resistance. They are also expensive; the raw materials are very expensive and difficult to process. For these reasons, high-nickel alloys are not widely used for extrusion unless the corrosion is severe enough to cost and reduce wear resistance.

Bucket and screws

Today, the barrel is almost entirely made of replaceable linings. This will be more expensive upfront due to the additional machined surface where the lining and the bracket meet, but the long-term cost of ownership is significantly reduced. The lined barrel can be refurbished by removing the worn liner and inserting a new liner. The main body and flange of the barrel-containing the cooling channel, thermocouple well, injection port, and counterbore for connecting the barrel together-can be reused indefinitely. Processing all these features requires considerable expense, which is why the higher upfront cost of lined barrels can be quickly recovered compared to installing a brand new barrel each time.
The core of the spiral spline resists torque overload better than the high-wear but more brittle HIP material on the outside of the component. When the torque exceeds the normal limit, the ordinary solid HIP screw is easy to break, such as when the extruder is over-feeding and the screw stalls.

The typical method in extrusion is to make the screw with a material that is the same as the barrel material or slightly lower than the wear resistance. The geometry of the screw is more complex than that of the barrel, with similar tolerances, but because a large amount of material needs to be removed to manufacture the barrel, it is cheaper to replace the screw than the barrel.

Years of experience helped us understand the most suitable materials for screw and barrel wear-resistant structural materials. We use this knowledge to manufacture the highest quality wear parts for our customers. However, it is important to note that each application is unique.