Optimize the effective life of the screw and barrel
Por Cathy Lin
September 10th, 2024
vistas 9
Once the screw begins to rotate inside the barrel, wear begins. Wear may occur on either the screw thread or the barrel surface or both. The harder the material being processed, whether it is abrasive fillers in the polymer being processed, or metal particles "mixed in" that are not part of the melt flow, the faster the wear will occur and the original gap will increase. As the gap increases, the melting efficiency will decrease. When the melting efficiency at the original setting is reduced, many operators tend to compensate by increasing the screw speed, adjusting the barrel temperature, increasing the back pressure, or some combination of these adjustments.
So how can you avoid this dilemma? Let's first identify three types of wear.
1. Adhesive wear. This happens when the metal surface (the screw thread face and the inner surface of the barrel) is in contact. Extremely high stresses occur when surfaces briefly touch and join together and then break. Evidence of adhesive wear may be a burr or "tumbling" at the back edge of the thread face, or a scratched or missing hard surface material at the top of the thread. It should also be checked whether there are scratches or wear on the inside diameter of the damaged screw inside the barrel.
2. Abrasive wear. This is probably the most common type of wear in plastic machinery. In the case of processing unfilled or low-viscosity polymers, it can be minimal. When the particles are transported down the screw and compressed into the cylinder wall, the shearing action will cause a certain degree of wear on the screw thread and the cylinder wall. When processing resins containing fillers, additives or contaminants in recycled materials, and even when processing high-viscosity polymers, abrasive wear can become serious. Hard materials tend to scrape material away from softer surfaces. Therefore, the usual hard surface treatment of the gap area uses wear-resistant alloys. Glass and mineral-filled resins can also cause wear at the root of the screw, usually at the back of the channel, before the additive is moistened and mixed with the melted plastic.
3. Corrosion and wear. Corrosion is the gradual destruction of a material by chemical attack. Most of the atoms on the same metal surface are oxidized, damaging the entire surface. Damage to the metal surface actually makes the surface more susceptible to mechanical wear mechanisms. Corrosion is the most common situation when processing PVC or fluoropolymer series and can seriously erode components with high iron substrates.
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The close relationship between screw barrel and plastic
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The wide application of injection screw barrel
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