inlet. To prove this theory, all forward pitch of the paddles at the preconditioner inlet was removed.

Noticeable improvements

In removing the forward pitch, ETI was able to capitalize in a couple different areas. The most important improvement was retention time and residence time distribution (RTD), both of which are vital to proper operation. Retention time directly correlates to cook (thermal transfer) and liquid absorption. RTD directly correlates to the quality and homogeneity of the preconditioned material, the latter being extremely critical to acquire smooth extrusion operation.

With the new advanced configuration, retention times of more than two minutes are achieved. Another major advantage of the advanced configuration is improved clean-out efficiency. By reversing the directions

Figure 14 The new, advanced configuration achieves dramatic improvement in RTD when compared to the typical configuration.

of the shafts and increasing their speed, a complete clean-out time can be reduced from two minutes (with 20 to 30 lbs. remaining) to 20 to 30 seconds (with 2 lbs. remaining).

In Figure 14, you can easily see the improvement made with RTD when compared to the typical configuration.

RTD matters

RTD plays a huge role in preconditioning when you consider the importance of “first in first out” and the proper application/mixing of your preconditioner injections (water, fat, meat). A good RTD curve (as shown in red in Figure 14) will ensure that each specific quantity of feed receives the same amount of thermal energy, mechanical energy and absorption of any injections. Problems that arise from poor RTD (as seen in blue in Figure 14) can easily be seen in operation of the extruder (surging) and the appearance/quality of your product.

Other operational points to consider are thermal efficiency and electrical efficiency, both of which are increased substantially with a properly designed paddle configuration. Be sure to contact a service technician to assist you in analyzing your current configuration prior to committing any modifications. This will ensure the development of a proper configuration that matches your process.

The core proper preconditioning philosophy, as well as traditional tried and true components, still hold true today. ETI has merely developed a new set of rules that apply to the application of these foundation technologies. These new advanced configuration concepts will assist in smoothing out your extrusion process, help reduce utility costs and help decrease wear costs of your extrusion components. ■

September 2007 Extru-Technician 10