Classifying – separating – and assorting solids – Sorting special items – and certain methods and apparatus for... – Separating means
Reexamination Certificate
1999-08-23
2001-07-03
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Sorting special items, and certain methods and apparatus for...
Separating means
C209S673000
Reexamination Certificate
active
06253927
ABSTRACT:
The present invention relates to a roller screen comprising several successive, rotating rollers that are spaced apart and set transversally with respect to the proceeding direction of the material. In particular, the invention relates to a roller screen designed for screening pellets to be sintered, wherein the pellets that are too small and too large in cross-section are screened off the sintering furnace feed.
Many material treating processes require that from the finely divided material to be processed, there is removed for instance the coarsest and the finest particles, so that the material obtained to be processed is formed of particles with a size essentially between two determined limit values. Thus the obtained material essentially conforms to a desired size. Consequently, several different screens are developed for screening material in order to obtain a lump size that is advantageous for the next processing step. Normally the screens are arranged in an inclined position, so that the material to be screened passes over the screen by gravitation, or the screens are provided with vibrator devices, so that the material is made to move on the screen.
In addition to this, many smelting processes require that the material to be smelted is not too finely divided, and therefore a finely divided material, such as concentrate, must first be pelletized and thereafter sintered in order to improve the strength of the pellets. However, the capacity of the sintering furnace is dependent, among others, on the size of the pellets fed therein. Therefore there is normally arranged a roller screen in between the pelletizing device and the sintering furnace, which roller screen separates the smallest pellets from the sintering furnace feed and returns them to pelletizing in order to increase their particle size and hence the capacity of the sintering furnace. This type of roller screen is described for example in the Fl patent 56,131, which includes several rotating transversal rollers in succession. By means of said rotating rollers, the material is made to pass over the screen. Moreover, the roller screen according to the Fl patent 56,131 can be adjusted so that in the proceeding direction of the material, the distance between the rollers grows in order to adjust the screen overflow, so that essentially all pellets constituting the overflow are larger than the pellets that were separated and returned to pelletizing. Thus, in the roller screen according to the Fl patent 56,131, oversized pellets are not screened off the sintering furnace feed, wherefore the size of the feed pellets varies within a wide range. In addition, according to the Fl patent 56,131, the rollers are rotated by means of a chain, and the speed of rotation is regulated roller group by roller group. Furthermore, the rollers are installed above the screen frame, so that concentrate is gathered in the frame structure, and the roller spaces are easily choked.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved roller screen which is more reliable in operation, by which the obtained pelletized material to be screened is in its average size advantageous for the next process step. The essential novel features of the invention are apparent from the appended claims.
According to the invention, the roller screen is composed of three separate screening parts. In the first screening part, the roller spaces are adjusted so that all pellets that are smaller than the desired size are removed from the material to be screened. In the second screening part the roller spaces are adjusted so that the size of the screen underflow to be removed from the material to be screened can be altered essentially rapidly when necessary, and thus the average size of the pellets to be fed further in the sintering furnace can be adjusted. In the third screening part, the rollers are advantageously installed in a stationary fashion, so that the pellets to be fed into the sintering furnace are advantageously applied onto a conveyor located underneath the screen, to form an essentially even layer. In this third screening part, the screen underflow is a pellet on its way to the next process step, i.e. to sintering, whereas the pellets that surpass the desired size and are obtained as the screen overflow are sent back to pelletizing after crushing. The rollers of the screening parts in the roller screen according to the invention are advantageously installed underneath the frame of the roller screen, so that for instance a single damaged roller can be easily replaced by a new, undamaged one when necessary.
In the roller screen according to the invention, the speed of rotation of the rollers is advantageously adjusted, so that the speed of rotation advantageously grows in the proceeding direction of the material, towards the final end of the roller screen. Thus the material layer to be screened becomes thinner, and the screening accuracy becomes remarkably better. At the same time, the rollers of the roller screen advantageously improve the quality of the pellet surfaces prior to sintering. In order to adjust the speed of rotation of the rollers, each roller is provided with a separate rotation motor. Advantageously the rotation motor is pressure compensated and hydraulically operated. Owing to these separate rotation motors, the speed of each roller can be adjusted. Thus the mutual speed of the rollers can be adjusted to be for instance such that the roller speed increases in the proceeding direction of the material, towards the final end of the roller screen. Consequently, the speed of rotation of the rollers is highest in the third screening part, and in the second screening part it is higher than in the first screening part.
The placing of the roller screen rollers underneath the roller screen frame according to the invention also results in that the roller spaces are easily adjusted in order to divide the material to be screened into desired particle sizes. In the first screening part, where the finest element of the material to be screened is removed, the adjusting of the roller spaces is advantageously carried out manually. The adjusting can also be carried out automatically, if so desired. When the roller spaces are adjusted to be of the desired size, the rollers can be permanently installed in a desired position with respect to each other. In the second screening part, the roller space is advantageously adjusted by means of an adjusting member that can be controlled either manually or automatically. The adjusting member as such can be operated pneumatically, hydraulically or electrically. By means of this adjusting member, the operation of the screen can advantageously be regulated essentially rapidly by increasing or reducing the average size of the pellets that are proceeding to the next process step. In the third screening part, the roller space is advantageously adjusted manually, so that the pellets of the desired size are made to set on the conveyor located underneath the roller screen as an essentially even layer in order to obtain an advantageous weighing result. If desired, the adjusting of the roller space in the first and third screening part can also be performed automatically by means of a similar adjusting member as in the second screening part.
REFERENCES:
patent: 3438491 (1969-04-01), Haley et al.
patent: 4627541 (1986-12-01), Johnson
patent: 5890600 (1999-04-01), Laatikainen
patent: 1729615 (1992-04-01), None
Jankkila Martti
Mustikka Lauri
Rantala Pekka
Väänänen Eero
Morgan & Finnegan , LLP
Nguyen Tuan N.
Outokumpu Technology Oy
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