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Engineering Benefits
Randcastle Extrusion Systems was started with a specific goal: Make extruders smaller and better. Historically, two issues had stopped machine builders from making quality extruders less than 1 inch screw diameter. The weak screws were easy to break and many materials would not feed. The basic solution to these problems was the "discharge driven" concept of the Microtruder,

Strong Screw: An extruder screw must withstand the stress of feeding, melting, mixing, and pumping. To withstand this entire stress, Randcastle drives the screw through the metering section of the screw. The metering section root diameter is about 2.4 times as strong' as the weak feed section root diameter. This has allowed Randcastle to extend the useful range of extruders far below the 1 inch barrier.

Excellent Feeding: A functional extruder gets the feed stock to the screw. In a typical extruder, there is a hole in the barrel that allows the feed stock to enter the screw from the hopper. The hole is proportional to the barrel diameter. The hole becomes so small in extruders under one inch that the feed stock arches (also called "bridging" and "piping") over the hole. Once the feed becomes erratic, the extruder cannot pump uniformly. Randcastle's vertical design extends the screw into the feed stock to solve the problem. Attachments to the rotating screw can extend into the hopper to aid in feeding particularly difficult powders and cohesive (non-free flowing) feed stocks.

1. Model : RCP-0250 1/4
Inch Microtruder & Typical Control
panel(shown with stand Die and "post" Mounting system
2. Stand Die
3. Optional "Post" Mounting system

Standard panel Feature

4. Auto Tuning Temperature control :
(3) for the barrel & (1) for the Die

5. DC Motor Ammeter : A recommended option is an automatic shut-down ammerter for "overload" conditions.
6. Digital Tachometer
7. "Ten Turn" Motor speed Control and " start/stop" buttons.
8. Optional controls for downstream equipment such as pelletizer, chillroll, etc..
9. Main Power Switch

Feeding Further Enhanced: Randcastle pioneered unique smooth bore feed sections that can make for significantly better feeding and consequently more uniform pressures'. These feed sections can be changed in under one minute with just four clamping screws. So often, if you select the wrong screw design for an experiment, you can simply change the feed section to solve the problem without removing the screw and cleaning it.

Uniform Pumping: Randcastle discovered a novel method of making extruders pump better. We named this method, "Surge Suppression" and we incorporate it into every screw we make. Essentially, if you view a surge as a wave, the Surge Suppressor' stores the top part of the wave and inserts the stored material into the trough of the wave. The Surge Suppressor operates automatically giving every Randcastle screw more uniform operation.

processing: Until the Microtruder, researchers were forced to make multiple expensive batches to make a single trial. Using the Microtruder, complete trials with as little as 10 grams of polymer are possible. Production applications, such as catheters and coextrusion, also benefit from the Microtruder. Extruders that are too large for the application degrade the polymer because the screw turns too slowly. This makes the residence time excessive and causes a loss of properties in the extrudate. The Microtruders permits normal screw speeds to prevent burning.

Space Savings: The vertical design has an extremely small footprint so it is readily engineered into small spaces.

1)A technical buiietn or a published paper is available on this topic.

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