Agitating – Rubber or heavy plastic working – Stationary mixing chamber
Reexamination Certificate
1998-12-08
2001-04-17
Cooley, Charles E. (Department: 1723)
Agitating
Rubber or heavy plastic working
Stationary mixing chamber
C366S305000, C366S331000
Reexamination Certificate
active
06217206
ABSTRACT:
FIELD OF INVENTION
The invention relates to an extrusion method wherein material to be extruded is fed into an extruder comprising at least one stator and at least one rotor, whereupon the stator has a conical surface at least on the side of the rotor, and which rotor has a conical surface at least on the side of the stator, the ratio of the length of the rotor to its greatest diameter being at most five-fold, and which rotor is rotated, the rotor resting on bearings provided in its widest point as it rotates.
The invention further relates to an extruder comprising at least one stator and at least one rotor, the stator having a conical surface at least on the side of the rotor, and the rotor having a conical surface at least on the side of the stator, the ratio of the length of the rotor to its greatest diameter being at most five-fold, and which rotor is mounted in bearings from its widest point to the extruder.
The invention also relates to a product prepared with the method.
BACKGROUND OF INVENTION
The length of the screw an the extruder is typically rather great with respect to the diameter of the screw. It is very difficult to mount in bearings a long screw. No matter how firmly the screw is mounted in bearings from one end, in difficult situations the screw can still bend to such an extent that it touches a cylinder positioned outside, which immediately leads to fast wearing. Arrangements have been disclosed where a long screw is also mounted in bearings from the end near the nozzle in such a way that melt plastic flows through the bearing. Such a bearing arrangement does prevent the screw from bending, but it leads to disadvantageous weld lines in the plastic mass, thus producing a weak spot in the product to be extruded.
When products having a very slippery surface are to be prepared, a large amount of slip agent must be mixed with the plastic mass to be extruded. However, a large amount of slip agent, such as silicone oil, that does not dissolve in plastic mass also results in the friction between the screw and the plastic mass being small, whereupon only a little heat is generated by the friction. The small friction results in the mass sliding in some places in the groove of the screw against the cylinder with perfect glide. However, since the plastic mass sticks in other places, a very strong bending moment easily occurs in the screw. Therefore the use of the very slippery plastic mass described above surprisingly leads into a situation where the screw wears greatly and the screw must be firmly mounted in bearings.
DE 1 961 078 discloses an extruder comprising a conical stator and a rotatable conical rotor placed outside the stator. The material to be extruded is fed between the stator and the rotor. The outer edge of the rotatable rotor is mounted to the frame with roller bearings in such a way that the bearings receive axial forces that are directed downwards in the figure. The rotor is also mounted with rolling bearings, which receive radial forces. This extruder cannot be used in a situation where the rotor is subjected axially to a force directed upwards in the figure. Further, it is not possible to monitor the forces acting on the rotor, nor to control and regulate them.
EP 89 906 779 discloses an extruder comprising at least three conical stators and at least two conical rotors placed between the stators. The material to be extruded is fed between the rotor and the stator via supply conduits. The lower surface of the rotors is mounted in bearings against a lower stator. This bearing arrangement receives the forces directed downwards, i.e. when the pressure outside the rotor is greater than the pressure inside. This bearing arrangement cannot receive radial forces or forces that are directed upwards. It is not possible either to monitor and regulate in any way the forces acting on the rotor.
The purpose of the present invention is to provide an extrusion method and an extruder comprising none of the aforementioned drawbacks.
SUMMARY OF INVENTION
The method according to the invention is characterized in that, as the rotor rotates, it rests on at least two bearings, whereupon the first bearing receives the force acting in one axial direction of the rotor and the second bearing receives the forces acting in the opposite axial direction of the rotor, and that the bearings are positioned diagonally with respect to the axial and radial direction of the extruder, the bearings receiving together the forces acting in the radial direction.
Further, the extruder according to the invention is characterized in that the rotor is mounted at least with two bearings, whereupon the first bearing receives the forces directed in one axial direction of the rotor and the second bearing receives the forces directed in the opposite axial direction of the rotor, and that the bearings are positioned diagonally with respect to the axial and radial direction of the extruder, the bearings receiving together the forces acting in the radial direction.
Further, the product prepared with the method according to the invention is characterized in that at least 0.5% of slip agent has been blended with the material of the product, and that the product is substantially without weld lines, and that the tolerance of the wall thickness of the product is less than 2%.
The efforts to solve the problem have surprisingly indicated that the sufficient length of the screw passage that is needed for melting and homogenizing the mass can be fitted into the form of a shorter screw, if the screw itself has a strongly conical shape. In such a case, the length of the screw in proportion to its diameter can be made very short, which enables a very firm bearing arrangement.
The essential idea of the invention is that the extruder comprises at least one conical stator and at least one rotatable conical rotor, and that the rotor is mounted at least with two bearings in such a way that the lower bearing receives forces directed axially downwards and the upper bearing receives forces directed upwards. Further, the idea of a preferred embodiment is that the bearings are positioned diagonally with respect to the axial and radial directions of the extruder so that the bearings receive together a radial force. The idea of yet another preferred embodiment is that the bearing arrangement comprises means for measuring the elastic displacement of the rotor, whereupon this measurement reveals the forces acting on the rotor and the stator.
The invention has the advantage that the bearing arrangement can be made very strong, whereupon products containing a large amount of slip agent can also be produced. Further, measuring the elastic displacement of the rotor makes it possible to control the forces acting on the extruder. With the arrangement according to the invention, the tolerances of the product walls can also be kept very small
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Jarvenkyla Jyri
Kirjavainen Kari
Cooley Charles E.
Ladas and Parry
Nextrom Holding S.A.
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