Short answer: food and feed extrusion uses lower shear, higher moisture and far stricter hygiene than plastics compounding. Elements are usually made in stainless steel, clearances are tighter, and the kneading geometry is chosen to cook and texturise rather than to disperse pigments.
In plastics compounding the screw is fighting agglomerates. In food and feed extrusion it is managing a recipe: starch gelatinisation, protein denaturation, moisture content often between 15 and 30 percent, and a product that must be cooked to a target degree rather than dispersed to a target fineness.
Three practical consequences follow. Shear must be controlled rather than maximised, because over-working the melt destroys texture and can burn the product. Moisture is high, so corrosion resistance matters more than in dry compounding. And the machine must be cleanable, which rules out designs that trap product.
| Duty | Element | Note |
|---|---|---|
| Feeding and conveying | Wide-pitch conveying, deep channel | Handles low bulk density meal and flour |
| Cooking and gelatinisation | 45° kneading blocks, moderate stack | Generates the heat and work that cook the recipe |
| Texturising | Narrow-disc 60° or 90° blocks, short | High work for a short time; over-use burns product |
| Homogenising | SME or slotted mixing element | Evens out moisture and temperature |
| Venting | Conveying with a reverse-flight seal | Steam removal, especially in high-moisture recipes |
| Discharge | Narrow-pitch conveying | Stable pressure to the die |
Food-contact parts are normally supplied in stainless steel, most often a 300-series grade, with a surface finish that can be cleaned rather than one that is merely smooth. Carbon steel elements, common in plastics, are not acceptable where product contact occurs.
Two details are frequently overlooked. First, dead zones between elements trap product and are a genuine hygiene risk, so element-to-element fit and shaft cleanliness matter more than in compounding. Second, any coating must be food-contact compliant; a wear coating that is not approved for food contact is worse than no coating.
Food and feed extrusion is dominated by a different set of OEMs than plastics compounding — Andritz, Clextral, Buhler and Coperion are the names we see most often, alongside a large installed base of Chinese and Taiwanese machines. Part numbering differs completely between them, so dimensions are again the reliable language.
For a food or feed line, send us the machine make and model, screw diameter, the element position on the shaft, and photographs of the worn part with a rule in frame. If the line is used for a specific recipe, mention it: moisture content and product type change the element recommendation more than the model number does.
Wear is usually slower than in mineral-filled compounding, because the product is softer. The exceptions are recipes with high mineral content — bone meal, mineral premixes, some aquafeed formulations — where abrasive wear returns. Corrosion, not abrasion, is the more common failure mode, and it shows up as pitting along the flight rather than a polished groove.
For most food and feed duty, a nitrided or through-hardened stainless grade is adequate. Where the recipe is abrasive, the same 58–62 HRC logic as compounding applies, in a corrosion-resistant base material.
The barrel side of the same duty is covered in barrel liner replacement.
The parts in product contact normally are, typically a 300-series grade. Carbon steel elements are acceptable in some non-contact positions but not where the product touches the part.
Not directly. Geometry may look similar, but material grade, surface finish and cleanability requirements differ. A part that works in a compounding line may be unacceptable for food contact.
Andritz, Clextral, Buhler and Coperion are the most common, plus a large installed base of Chinese and Taiwanese machines. Send the model and dimensions and we will confirm compatibility.
Usually too much kneading work for the moisture content, or a residence time that is too long. Shortening the kneading stack or reducing the stagger angle lowers the work input without changing the recipe.
Standard Chinese machines are normally ex stock; imported-machine spares take 30-45 days with material available and drawings confirmed. Stainless grades with specific surface finish requirements can take longer if the material is not held in stock.