Reducing the size an extruder or GEARTRUDER^®, to make smaller tubing or thinner layers, quickly runs into some very unfortunate arithmetic. Standard sizes of plastic pellets are 1/8" and 5/32". Accommodating both these sizes requires channels in the screw typically .200" or more deep in the feed and beginning transition sections.

The smallest screw diameter which can handle both these sizes comfortably is 1". Subtracting channel depth on both sides of the screw still leaves typically 0.600" of metal in the center; this diameter can handle the torque of a 5 HP heavy duty 1" machine.

If the pellet size is limited to 1/8" -- the smaller of the two standard sizes --a 3/4" screw can have 0.160 grooves and will still have enough root diameter to handle the torque of a 2 HP drive motor.

But the output of a standard 3/4" extruder or GEARTRUDER^® is still about 7 lbs/hr at 100 RPM screw speed -- more then is desired for microbore tubing or thin layers. Worse yet, the residence time in the screw at very low RPM's can lead to degradation in heat sensitive materials such as PVC.

One possible solution is to use a 1/2" extruder with a conical screw. The output of such an extruder is satisfyingly low. The residence time, however, is still uncomfortably large, because both the feed and transition sections have to be of larger diameter to accommodate the standard size pellets, and this leads to larger inventory of plastic in the screw.

To solve this dilemma, Harrel has developed the special LO-OUTPUT series of extruders and GEARTRUDERS^®. Instead of designing the screws for maximum output per revolution, as is commonly done, the LO-OUTPUT machines are designed for the absolute minimum output per revolution and inventory of plastic consistent with good melting and mixing. Instead of being mostly grooves with narrow lands, like a normal screw, it is mostly land with a small groove. It's rather odd looking, but it works!

Using a 3/4" LO-OUTPUT screw, the inventory in the grooves and the residence time are both reduced by a factor of about 5 -- to levels well below those of standard 1/2" extruders with conical screws. The resulting LO-OUTPUT extruder or GEARTRUDER^® is thus far better for microbore tubing or thin coextrusion layers than a 1/2" conical-screw machine.

THE GEARTRUDER^®:

If there ever were applications which require a constant and closely controlled throughput they are microbore tubing or thin layers. A precision melt pump is thus strongly indicated. To meet this need, Harrel has developed a special precision melt pump with only 0.14 cc/rev output. This is used in place of the usual 0.5 cc/rev or 1 cc/rev melt pump of the normal 3/4" GEARTRUDER^®.

There is one other major advantage of this new machine over the conical 1/2" unit. The 1.4 lb/hr LO-OUTPUT extruder or GEARTRUDER^® can be converted to a normal 7 lb/hr machine by merely substituting a normal screw and a larger (mechanically interchangeable) 1/2 cc/rev or 1 cc/rev melt pump. It can then be used anywhere in the lab by simply wheeling it into place and connecting it up.

SUMMARY:

The result of all this is a high precision device with maximum outputs at 100 RPM screw speed ranging from about 1.4 lbs/hr all the way up to about 7 lbs/hr. In the LO-OUTPUT configuration, the inventory of heated plastic, and the residence time are both very low, restraining degradataion of the plastic. In the normal configuration, the system is a very convenient, general purpose auxiliary extruder, or GEARTRUDER^® which may be used anywhere in the plant. Best of all, the throughput stability will be held to 0.1% tolerance for both the LO-OUTPUT form and the normal one!

Another Harrel breakthrough for precision tubing!

SPECIFICATIONS

• RUGGED 3/4" EXTRUDER, PRECISION GEAR PUMP, AND MICROPROCESSOR CONTROLLER -- all in one integrated assembly!
• O.1% THROUGHPUT STABILITY -- for accuracy in microbore tubing, striping, or coextrusion.
• DIGISYNCH MELT PUMP DRIVE (optional) gives exact synchronization to external RPM -- 0.000% steady state synchronization error.
  • ALLOWS AUTOMATIC, HIGH PRECISION CLOSED LOOP CONTROL OF BOTH OD AND ID of microbore tubing, using the Harrel TUBETROL system.
  • OR ALLOWS AUTOMATIC, PRECISE CONTROL OF LAYER THICKNESS IN COEXTRUSION. by exact synchronization to RPM of melt pump on main extruder and melt pumps feeding other layers.
• FAR SUPERIOR TO CONICAL SCREW 1/2" EXTRUDERS for high precision microbore tubing or for thin coextrusion layers:
  • LOWER OUTPUT. About 1.4 lb/hr output at screw RPM of 100, versus 3. 5 lbs/hr for typical 1/2" machine.
  • MUCH LOWER INVENTORY OF PLASTIC IN HEATED FLIGHTS. 1/2" machines must have large inventory in large feed and transition screw sections.
  • MUCH LOWER RESIDENCE TIME.
  • FAR HIGHER PRECISION -- melt pump gives 0.1% throughput stability.
  • LONG WEARING FEATURES OF LARGE EXTRUDERS -- bimetallic barrel with Xaloy 102 liner. Colmonoy 56 screw flights and water-cooled throat.
  • HARREL DIGIPANEL^® EXTRUSION CONTROLLER -- up to 22 PID temperature zones, 3 are heating and cooling, with separate trim adjustments on heat and cool sides for maximuim accuracy. Monitors screw and melt pump RPM and current and pressure before and after the screens and just before the die.
  • TWO-STAGE PRESSURE MONITOR AND ALARM FOR SAFETY. First level alerts operator; second level shuts system down.
  • CLOSED-LOOP CONTROL OF MELT TEMPERATURE AND MELT PRESSURE OPTIONAL.
• EASILY CONVERTED TO STANDARD OUTPUT 3/4" GEARTRUDER -- by swapping screw and (mechanically interchangeable) melt pump. Typically 7 lbs/hr.
• COMPLETELY SELF-CONTAINED. Sturdy tripod mount easily moved anywhere in plant; tilts 0-45 degrees (90 degrees optional). The front of the barrel is not cantilevered, as some unit are, but is rigidly supported.

For full details fill out inquiry form or call Harrel at (203) 866-2573.

MODELS AVAILABLE:

OPTIONS AND ACCESSORIES:

ORDER EXTRUDERS ON LINE

To order an extruder, fill in the form below and click on "submit". Harrel will enter your order and send you an Email or FAX acknowledgement stating engineering data and credit information required, if any.