Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – To form particulate product
Patent
1998-01-30
2000-10-03
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
To form particulate product
264142, 264143, 2641761, 2642111, 425206, 425313, 425382R, B02C 3100
Patent
active
06126878&
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus and a method for producing an extrudate.
The production of water-dispersable extrudates, for example in the form of extruded granules, from finely divided water insoluble powders is known. One application for such extrudates is as a delivery system for chemical substances used in agriculture. An object of such extrudates is to provide a delivery system for finely-divided water-insoluble powder which avoids the need for users to handle the materials concerned in powder form. The extrudates are more convenient to handle than the powder and reduce potential health hazards resulting from the handling of such finely divided powders. The production of extrudates by utilizing pressure or shear to force moist powder through apertures is well known.
A basket-type extruder for the extrusion of plastic or pulverant materials for obtaining an extrudate in the form of rod-shaped bodies is described in European patent application EP-A-0 163 619. Embodiments are described with a hopper having, at its lower end, an annularly extending opening with a perforated screen. The source material is inserted into the hopper and is then pressed through the perforated screen in order to produce the extruded rod-shaped bodies. A rotating extruder tool for forcing the powder through the screen and a feeding mechanism for feeding the powder to the extruder tool are provided. The extruder tool consists of a disc with extruder blades disposed around its periphery. The extruder tool is driven by means of a drive shaft from a motor located below the hopper, the drive shaft being mounted in bearings in a lower portion of the housing of the hopper. The feeder mechanism is driven via a second drive shaft from a second motor located above the hopper.
Such equipment can be used to produce extrudates of insoluble, finely-divided powders which can disperse relatively readily and rapidly in water. However, the initial performance of such equipment with materials of this type cannot be maintained. Long-term operation of such equipment with such finely-divided water-insoluble powders leads to reductions in performance. Experience shows that with such equipment and the products of the type described, a gradual increase in temperature is experienced. This increase in temperature is accompanied by a decrease in the efficiency and production rate of the machine and a degradation in the properties of the extrudate when dried. Long-tern operation of the apparatus on a continuous basis has proved impossible due to the temperature increase, which leads to a gradual reduction in the production rate and frequent stoppages due to equipment malfunctions.
By inspection it has been found that the pastes which form as the moist finely-divided water-insoluble powders are forced though the perforated screen of conventional low-pressure extruders, typified by the patent application referenced above to effect the extrusion are very invasive. When subjected to the pressures required to force these pastes through an aperture the pastes find their way into and wear seals fitted to protect the bearings for supporting the extruder tool and eventually damage the bearings themselves.
It has been proposed to modify the seal designs to eliminate bearing damage. However, no seal design has yet proved successful in preventing the ingress of the paste into the bearing housings. The provision of pressure release slots around the screen for the reduction of pressure on the seals has also been employed. However, these measures have little effect on preventing the damage caused by the pastes formed from the finely-divided water-insoluble powders. As a result of this, it does not appear possible by means of simple modifications or improvements to the prior art design of extruder typified by European patent application EP-A-0 163 619, to provide a machine capable of producing in a reliable and economic manner extrudates from finely-divided water-insoluble powders.
Patent Specification DE-C-807 187 discloses extrusion apparatus with a hopper with an
REFERENCES:
patent: 3332111 (1967-07-01), Hafliger
patent: 4599015 (1986-07-01), Krambrock
patent: 4767217 (1988-08-01), Van Den Brink et al.
patent: 5443764 (1995-08-01), Lloyd et al.
Collag Limited
Silbaugh Jan H.
Staicovici Stephan
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