Extending the life of dies improve capacity, stability and quality

Graintec is ready to offer high-performance dies that will improve your process stability and final feed quality. The dies utilize a ceramic surface treatment based on Chromium Carbide (CrC), which provides a five fold increase in steel hardness without impacting the flexibility of the metal core.

Based on a total of more than 30,000 observations, it is clear that the new die technology improves the quality of extruded fish feed pellets by lowering the variation of essential parameters, i.e. pellet length and diameter, as well as extruder torque and capacity.

High-performance dies for the aqua feed industry

The present trial relates to ø5.0 mm salmon feed and covers more than 30,000 t final feed production. Relevant process and product parameters were measured and compared for the two sets of dies. The only difference between the standard die set (Standard) and the new die set (CrC) is the CrC treatment. For the new die set, a layer of approx. 10.5 µm CrC was applied.

Reduced variation in pellet length indicates a more homogenous flow throughout the dies. This is the result of lower friction in the land section of the dies, which additionally reduces the risk of fouling and the impact of pulsation. The more homogenous flow reduces pressure differences at die exit, and consequently, variations in radial expansion – and hereby pellet diameter – will drop. In this trial, the relative standard deviation in radial pellet expansion, i.e. diameter, was significantly lower for the CrC dies (p < 0.01).

Reduced pellet size variations improve the product quality, as drying, coating and cooling will run more stably, which will positively impact the uniformity of final product parameters such as sinking speed, pellet strength (DORIS) and oil content (and hereby feed composition).

For the given trial, the extruder torque was defined as a set point, why the mean values for both die configurations were identical. However, the relative deviations from the set point were significantly lower for the CrC dies. This highly supports the hypothesis that the CrC dies reduce the impact of pulsation and enable more stable process conditions.

The reduced friction and more homogenous flow also flow for increased extruder capacity. For this comparison, the relative standard deviation for capacity as lower for the CrC dies, while the average meal-to-extruder mass flow was 140 kg/h higher. After coating to 38% fat, this increased mass flow corresponds to approx.
1,850 t/y at 100% OEE (overall equipment efficiency).

Percentagewise, the increased mass flow when using the CrC die technology is expected to increase even more for small pellet sizes as friction in the dies is the limiting factor for the extruder.