Sight wheel with wear protection for hybrid sight wheel blades

Abstract

Classifier wheel with hybrid classifier wheel blades, each consisting of at least one blade body, the radially outward area of ​​which is provided at least on the side leading in intended operation with at least one armor strip made of wear-resistant material different from the material of the blade carrier, ideally a carbide material or a ceramic material, characterized in that the at least one armor strip has at least one, preferably several, positive locking elements, which engage with a corresponding positive locking element of the blade body.

Description

[0001] The invention relates to a centrifugal classifier or a classifying mill with an improved classifying wheel and a classifying wheel for such a classifier. TECHNICAL BACKGROUND

[0002] Classifier mills operate high-speed rotating wheels, one of which is a safety wheel and the other for grinding. Both wheels are arranged in the same chamber and achieve comminution and classification of the feed material. The classifier wheel is typically drum-like in shape. Its outer surface is formed by numerous closely spaced classifier wheel blades held between two classifier wheel discs. Adjacent classifier wheel blades each leave a gap called a "classifying gap" between them.

[0003] Classification is typically achieved by the carrier gas carrying smaller particles, which develop only low centrifugal forces during circular motion, into the interior of the classifier wheel. These smaller particles then form a fines fraction, which is discharged along with the carrier gas through one end of the classifier wheel.

[0004] This doesn't work with larger particles. In a pure classifier, the coarse particles are discharged through the coarse material outlet, either as a usable fraction or for re-grinding. In a classifier mill, the coarse particles collide They collide – often repeatedly – ​​with the working area of ​​the grinding wheel and are thereby shattered. The newly formed smaller particles are carried into the interior of the classifier wheel by the carrier gas stream. The larger particles that remain after the collision described above experience further collisions in rapid succession. They are further crushed and separated. They are also accelerated further in the circumferential direction.

[0005] This also results in the impact of the particles still being ground onto the classifier wheel blades

[0006] It is obvious that the classifier wheel blades used here for crushing are exposed to high impact wear, especially in their radially outward area leading in the direction of rotation.

[0007] To control wear, it is already known to manufacture classifier wheel blades from particularly wear-resistant materials, such as ceramic or carbide. However, these materials are more sensitive to impact stress. Therefore, solid classifier wheel blades made of hard materials can occasionally fracture a classifier wheel blade. This occurs particularly when a particularly large particle impacts the classifier wheel blade without immediately disintegrating. Due to the high operating speed, a blade fracture usually leads to considerable consequential damage.

[0008] For this reason, the use of hybrid classifier wheel blades has already been considered.

[0009] In such classifier wheel blades, the base body is still made of steel. To protect it from wear, it is coated with a ceramic or carbide armor strip in its most highly stressed area. This has the advantage that even if such an armor strip breaks, almost no or only tiny fragments of the armor strip are released into the classifier, thus largely preventing subsequent damage.

[0010] Nevertheless, problems continue to arise. If particularly high-strength adhesives are used to bond the armor strips, their regular replacement becomes very time-consuming. If an adhesive that creates a less strong bond is used, the risk of the armor strips becoming unexpectedly detached increases. This can then lead to damage similar to that seen in the fracture of a solid blade.

[0011] DE 10 2016 015 051 B describes a classifying wheel for a centrifugal air classifier, through which the classifying air flows from the outside to the inside, counter to its centrifugal direction. DE 190 03 948 C2 describes a centrifugal classifying wheel with a ring-shaped arrangement of classifying wheel blades. OBJECT OF THE INVENTION

[0012] In light of this, the object of the invention is to provide a classifier wheel with easily replaceable, yet highly reliable armor plating for a classifier mill or a classifier which, although predominantly only classified, is nevertheless exposed to abrasive wear. INVENTIVE SOLUTION

[0013] According to the invention, a separator wheel with hybrid separator wheel blades is proposed. Each separator wheel blade comprises a blade base body. This can be made of one or more parts. The blade base body itself is preferably made of a steel with increased abrasion resistance compared to structural steel. The radially outward region of each blade base body carries – at least on its leading side during normal operation – at least one armor strip made of a wear-resistant material different from the material of the blade carrier. Ideally, a carbide material or a ceramic material is used for the armoring. The separator wheel blade according to the invention is characterized in that the at least one armor strip has at least one, better several – preferably integrally formed – form-fitting elements formed therewith.The interlocking element(s) each engages with a corresponding interlocking element of the blade base body. In other words, the interlocking element on the armor strip side is made of the same, particularly wear-resistant material as the armor strip. This also makes the interlocking elements themselves more resistant to wear, as the complementary interlocking element in the blade base body also benefits indirectly.

[0014] In this way, the adhesive can only be omitted in exceptional cases, but it is significantly strengthened.

[0015] The form-locking element(s) are preferably selected such that they are capable of holding the armor strip to the blade carrier during operation, even if the bond fails. They are preferably designed to deflect some of the radially outward loads from the bond even during normal operation. This allows a lower-strength adhesive to be used, allowing the armor strip to be separated from the blade body more quickly and easily for replacement. Nevertheless, the reliability of the bond is increased, and failure is reduced to the realm of the improbable. PREFERRED DESIGN OPTIONS

[0016] Ideally, the bonding isn't purely optional—the armor strip is then additionally bonded to the blade body. This creates an effect that can be described as a composite glass effect: If the armor strip is hit hard by a larger particle, it may shatter. However, all larger fragments remain in place instead of being tossed around in the sifter and causing subsequent damage.

[0017] Ideally, the adhesive that bonds the armor strip to the blade base body has a heat resistance that is adjusted in such a way that the bond between the blade base body and the armor strip can be released by heating the hybrid classifier wheel blade to a temperature that does not yet cause any significant structural influence on the blade base body.

[0018] Preferably, heating is in the range of at least 220°C and less than 280°C.

[0019] In this way, the bond can be removed very efficiently when changing the armor strips.

[0020] Preferably, the form-locking elements interact with each other in such a way that the centrifugal forces acting on the armor strip during operation are predominantly, better substantially and ideally completely absorbed by the form-locking elements.

[0021] This significantly reduces the stress on the bond; bonds of lower quality are sufficient.

[0022] Ideally, the blade base body has a recess into which the armor strip can be inserted flush – preferably in such a way that, together with the blade base body, it forms a classifier wheel blade that is, at least essentially, smooth on all sides. This way, there's no particular point where powder can get stuck, which could then potentially generate imbalances if it accumulates significantly.

[0023] Preferably, the recess into which the armor strip is inserted flush is formed substantially on the leading large surface of the blade base body during operation. The recess preferably extends over at least the radially outermost 25% of said large surface of the blade base body. In this way, the radially leading part of that of the two large surfaces that experiences the most particle collisions is well protected.

[0024] It is particularly advantageous if at least one form-locking element of the armor strip is formed in the area of ​​its end closest to the operating rotation axis. The form-locking element can be designed to be large and insensitive in this area, and any notch effect emanating from it will not radiate, or not significantly, into the highly stressed area, where fracture could even occur due to impact from oversized particles. Furthermore, the form-locking element is located outside the area subject to the highest wear load.

[0025] For the same reason, it is advantageous if the form-locking element is a projection that protrudes - preferably radially - from the narrow surface of the armor strip that is closest to the operating rotation axis.

[0026] It is advantageous if the armor strip has a smaller thickness in the circumferential direction than the section of the blade base body to which it is glued.

[0027] Irrespective of the above, protection is also claimed for the use of an armor strip with at least one form-fitting element for armoring - ideally with a smooth surface - a classifying blade of a classifying wheel according to one of the preceding claims by hanging the armor strip in a blade base body.

[0028] Protection is also claimed for a classifier mill for impact grinding and classifying preferably soft to medium-hard materials, ideally up to 3.5 Mohs, ideally within a single housing in which the mill and classifier are integrated, with at least one classifier wheel according to one of the claims already made.

[0029] Further modes of operation, advantages and possible embodiments of the invention will become apparent from the following embodiment, which illustrates the invention. LIST OF FIGURES The Fig. 1 shows a turbo classifier in section, in which the classifier wheel according to the invention can also be used, for example for classifying particularly abrasive materials. The Fig. 2 shows a section of a classifying wheel according to the invention. The Fig. 3 shows a detailed view of a classifier wheel according to the invention. The Fig. 4 shows a classifier wheel blade with a blade base body carrying an armored strip. EXAMPLE OF IMPLEMENTATION

[0030] Similar to the classifier mills mentioned above, things can also behave in a turbo classifier primarily used for classifying – as described below as an example. These devices are comparable in terms of their basic operating principle. Therefore, unless otherwise stated, the following description also applies to the mill classifiers also claimed.

[0031] The Fig. 1 shows a vertical sifter with a sifter wheel according to the invention.

[0032] The mixture of coarse and fine material is fed from below via the feed pipe 3 with the aid of a carrier air stream. The feed pipe 3 ends centrally in the separator drum 6. It maintains a distance from the inner circumferential surface of the separator drum 6, along which the coarse material fraction is discharged.

[0033] From there it enters the classifying chamber 4, which is formed between the outer circumference of the classifying wheel 5 and the classifying drum 6 which houses it.

[0034] The separator wheel 5 with its spaced-apart separator wheel blades 9 is in Fig. 1 can already be seen quite clearly.

[0035] The fines carried by the carrier air stream can pass through the separating gaps between adjacent separator wheel blades 9. They thus enter the interior of the separator wheel 5 and are then discharged by the carrier stream through a perforated end face of the separator wheel 5 into pipe 7, which forms the discharge for the fines fraction. The coarse material cannot pass the separator wheel blades 9 and enter the interior of the separator wheel 5. Instead, it is accelerated in the circumferential direction by the separator wheel 5. They then fall—usually in a descending spiral line—along the inner circumferential surface of the separator drum into pipe 8, which forms the outlet for the coarse material fraction.

[0036] Especially when classifying harder or abrasive material, the classifier wheel blades are also at risk of wear in the area of ​​their radially outward leading edge, which runs in the direction of movement - even if the wear intensity may be less pronounced than in the case of a classifier mill.

[0037] The Fig. 2 shows a section of what is actually already in Fig. 1 clearly visible separator wheel 5. As can be seen, the separator wheel 5 has a drum-shaped form. Its outer surface is formed by numerous closely spaced separator wheel blades 9. As can be seen in Fig. 2, adjacent separator wheel blades 9 each leave a screening gap 10 between them. The closely spaced separator wheel blades 9 are held between two separator wheel discs 11 arranged on the front side of the separator wheel, usually in a form-fitting manner.

[0038] As can be seen, the classifier wheel blades 9 have large surfaces 12. These define the aforementioned separation gap through which the carrier air stream containing the fines fraction can flow into the classifier wheel. At the very outer periphery, the classifier wheel blades have a radially outward narrow surface 13.

[0039] How best to use the Fig. 3, in many cases the classifier wheel discs 11 are also provided with an armor plating, typically with a carbide coating or with a ceramic coating.

[0040] The Fig. 4 shows an embodiment of one of the classifier wheel blades 9 according to the invention.

[0041] It is clearly visible that the separator wheel blade 9 comprises a blade base body 14. This blade base body 14 is typically made of steel. It has proven ideal if this steel is hardened or otherwise provided with increased wear resistance.

[0042] It is clearly visible that the blade base body 14 – essentially on its leading large surface during operation – has a step-like recess 15. This provides space for the preferably smooth insertion of a bulging strip 16. The bulging strip is preferably constructed in one piece. The blade base body generally supports the bulging strip over its entire surface on its rear side, opposite its free large surface. Furthermore, it is preferred that the blade base body additionally supports the bulging strip on one, or even better, three, of its narrow front and side surfaces.

[0043] The said smooth-surface insertion optionally means that the armor strip is inserted in such a way that it does not form an edge or projection protruding beyond the blade base body 14 at any point on which visible material could accumulate.

[0044] The radially outward end face of the classifier wheel blade is also clearly visible here.

[0045] As can be seen, according to the invention, the armor strip has at least one, and here preferably several, positive-locking elements 17. The positive-locking elements 17 protrude in the region of the end of the armor strip closest to the operating rotation axis. They have a shape similar to that known from the positive-locking element of a puzzle piece. This means that the respective positive-locking element is a flat structure. This flat structure is connected to the actual armor strip via a "neck" that is narrower than the rest of the flat structure. It is the narrow edge surfaces of the flat structure that create the positive connection to the blade base body, which is crucial within the meaning of the invention.

[0046] As can be seen here, the respective form-locking element 17 is completely rounded, meaning it is essentially free of angular edges. This minimizes the stress stress that weakens the form-locking element, which is particularly important for a kerf strip made of ceramic material. Therefore, the form-locking elements used here are superior to other form-locking elements – for example, compared to pins, which are inserted through a hole in the kerf strip into the blade base body to ensure positive anchoring.

[0047] As already mentioned, the form-locking element 17 is assigned a complementary recess 18 on the blade base body 14.

[0048] The form-locking element 17 and the recess 18 interact in such a way that it is impossible for the armor strip to be flung radially outwards even if the adhesive that additionally holds it fails.

[0049] Ideally, there is a division of labor with regard to applying the holding forces required for the armor strip: The centrifugal forces acting in a radially outward direction are absorbed to a more than insignificant extent, usually even to a large extent, by the form-locking elements. The adhesive is at least primarily, and usually almost exclusively, responsible for preventing the armor strip from detaching from its form-locking radial anchorage.

[0050] It is also noteworthy that it is particularly advantageous if the recess 15 does not extend all the way to the short end face of the blade base body 14, as in Fig. 2 shown on the left. This is because the bucket base body 14 then offers the possibility of changing the armor strip even when the bucket base body is still held by the classifier wheel discs at its short front edge. LIST OF REFERENCE SYMBOLS 1 vertical sifter 2 not occupied 3 Feeding tube 4 Classification room 5 Classifier wheel 6 Classifying drum 7 Pipe that serves as discharge for the fines fraction 8 Pipe that forms the discharge for the coarse material fraction 9 Classifier wheel blade 10 viewing gap 11 classifier wheel discs 12 Large surface of a classifier wheel blade 13 radially outward narrow surface of a classifier wheel blade 14 Blade body 15 Recess 16 armored stripes 17 Form-locking element 18 complementary recess

Claims

[1] Classifier wheel (5) with hybrid classifier wheel blades (9), each consisting of at least one blade base body (14), the radially outward region of which is provided, at least on the side leading during normal operation, with at least one armored strip (16) made of wear protection material different from the material of the blade carrier, ideally a carbide material or a ceramic material, characterized by that the at least one armored strip (16) has at least one, better several form-locking elements (17), which are or are each in engagement with a corresponding form-locking element of the blade base body (14). [2] Classifier wheel (5) according to claim 1, characterized by that the armored strip (16) is additionally glued to the blade base body (14). [3] Classifier wheel (5) according to claim 2, characterized bythat the adhesive which connects the armored strip (16) to the blade base body (14) has a heat resistance which is set in such a way that the connection between the blade base body (14) and the armored strip (16) can be released by heating the hybrid classifier wheel blade (9) to a temperature which does not yet entail any significant influence on the structure of the blade base body (14). [4] Classifier wheel (5) according to one of the preceding claims, characterized by that the form-locking elements (17) interact with each other in such a way that the centrifugal forces acting on the armoured strip (16) during operation are absorbed by the form-locking elements (17). [5] Classifier wheel (5) according to one of the preceding claims, characterized by that the blade base body (14) has a recess into which the armored strip (16) can be inserted flush. [6] Classifier wheel (5) according to the immediately preceding claim, characterized by that the recess (15) is formed substantially on the large surface of the blade base body (14) which is leading during operation and preferably extends over at least the radially outermost 25% of said large surface of the blade base body (14). [7] Classifier wheel (5) according to one of the two immediately preceding claims, characterized by that the at least one form-locking element (17) of the armored strip (16) is formed in the region of its end closest to the operating rotation axis. [8] Classifier wheel (5) according to the immediately preceding claim, characterized by that the form-locking element (17) is a projection which projects - preferably radially - from the narrow surface of the armored strip (16) which is closest to the operating rotation axis. [9] Classifier wheel (5) according to one of the preceding claims, characterized bythat the armored strip (16) has a smaller thickness in the circumferential direction than the section of the blade base body (14) to which it is glued. [10] Use of an armor strip (16) with at least one form-fitting element (17) for the - ideally smooth-surface - armoring of a classifier wheel blade (9) of a classifier wheel (5) according to one of the preceding claims by hanging the armor strip (16) in a blade base body (14). [11] Classifier mill for impact grinding and classification of preferably soft to medium-hard, ideally up to 3.5 Mohs, materials with at least one classifier wheel (5) according to one of claims 1 to 9.

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