Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/08—Casting in, on, or around objects which form part of the product for building-up linings or coverings, e.g. of anti-frictional metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/02—Casting in, on, or around objects which form part of the product for making reinforced articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
  • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
  • B02C15/00—Disintegrating by milling members in the form of rollers or balls co-operating with rings or discs
  • B02C15/004—Shape or construction of rollers or balls
  • B02C15/005—Rollers or balls of composite construction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D19/00—Casting in, on, or around objects which form part of the product
  • B22D19/06—Casting in, on, or around objects which form part of the product for manufacturing or repairing tools

Definitions

• the present invention relates to a bimetallic foundry piece serving as a wearing part in mills, in particular so-called vertical mills. It also applies to a process for producing such a part and to its use in grinders of this type.
• the vertical crushers consist of rollers rotating around a vertical axis on a grinding track.
• the grinding rollers are mounted on a central hub and are provided at their periphery with wearing parts which may be in the form of segments or which may also be formed in a single piece.
• wear parts are made of cast iron having a high resistance to abrasion, in particular castings with high chromium content and, consequently, are very little ductile (their value of elongation at break is practically equal to zero). Wear parts are generally secured using clamps to the hub. precisely from their lack of ductility, it is possible to observe, under the stresses due to the various mechanical stresses, the appearance in particular of cracks which propagate in said parts.
• Various other drawbacks are manifested, including, under the effect of the constraints, in particular a deformation of the hub. This deformation of the hub causes considerable difficulty when replacing wearing parts and it is common to have to replace both the wearing part and the hub.
• the wearing part is particularly difficult to machine after casting because of its specific properties, namely its high hardness, while tolerances less than H9 are required for these machining operations.
• the combined metallurgical-mechanical connection is described as making it possible to compensate for the tensions resulting from the differences in coefficient of expansion between the base alloy (graphite cast iron) and the reinforcement material incorporated in the wear part, thus ensuring a good connection. between this wear part and the weldable part and avoiding the propagation of micro-cracks.
• the invention essentially aims to propose a new design of wear parts of mills of the type mentioned which ensures a series of specific advantages, in particular better resistance to cracking, an absence of deformation of the hub under the applied stresses and of in general, greater flexibility in the system for attaching wear parts to the hub.
• the invention relates to a bimetallic foundry part intended for vertical mills comprising a core made of ductile cast iron provided with mechanical connection elements advantageously in the form of studs, which are fixed to an envelope made of non-wearing material. ductile with high chromium content.
• This type of part can be in the form of segments or in the form of a one-piece element, with a view to their mounting on the hub of the vertical grinder rollers.
• the connecting part which is the most highly stressed consists of studs coming from casting in the core of ductile iron, which contributes to the mechanical strength of the assembly.
• the forces generated by the grinding work - instead of being transmitted directly from the wear part to the hub - are here taken up first by the studs and then by the ductile iron core.
• cracks or cracks which may appear on the external periphery of the wearing part do not propagate in the total mass of the wearing part.
• the deformations observed in the technique of hard mono-metallic wearing parts on a soft hub are thus avoided.
• the laying surface of the wear part which must be machined to adapt perfectly to the hub is constituted in this case by ductile iron which greatly facilitates machining.
• the ductile iron used is preferably a type GS iron (GGG 40 according to DIN 1693).
• the specific shape of the studs is preferably chosen so as to provide simplified threads of rounded shape.
• the parts according to the invention also make it possible to facilitate the weighting of the part in chromium cast iron and to obtain better mechanical properties thanks to the cooling effect of the part in ductile cast iron. It should be noted that the bimetallic parts thus produced thus avoid the use of a metallurgical bonding solution. This avoids the well-known drawback of a horizontal separation surface between the two cast metals.
• the studs can have the shape of a dovetail.
• the process for manufacturing such a part is particularly advantageous due to the choice of materials used which makes it possible to first cast the core with the studs in a first mold and then, after having applied a refractory coating intended to prevent a metallurgical bond, to sink the envelope. Finally, a quenching heat treatment is carried out taking into account the nature of the constituent elements of the part and possibly the intended use, in particular the grinder and the materials to be ground, according to the criteria well known to specialists in these materials.
• the invention will be described in more detail with reference to a preferred embodiment thereof, with reference to the accompanying drawings. Other details and characteristic elements of the invention will appear on reading the description which follows.
• Figure 1 schematically shows the arrangement of a grinding roller in a vertical axis mill.
• FIG. 2 shows, by way of illustration of a particular form of the invention, a roller segment according to the invention
• Figure 3 is a section AB in the embodiment of Figure 2;
• Figures 4 and 5 show an example of a part produced according to the invention, Figure 4 being a section along CD of Figure 5.
• a roller 3 is driven relative to the axis 1 by turning through a hub 2 shown schematically on an axis 5 which can be slightly inclined (as shown) or horizontal, in order to grind the material supplied between the roller and the grinding track 6.
• the mark 7 represents the material to be ground fed centrally in the mill. After grinding, the fine particles are extracted from the grinder and the larger ones are returned to the grinding track 6 by a stream of air shown diagrammatically by the arrow 9.
• roller 3 is rounded on its peripheral part and the track has a corresponding shape.
• the wear part properly speaking bearing the general reference 11 is formed by a core 13 comprising studs 15 obtained from foundry on which an envelope 17 is cast.
• the essential characteristic of the invention is the fact that the core 13 and connecting elements in the form of studs 15 from casting are formed from a ductile material, namely GS cast iron, while the casing 17 is made from non-ductile alloys, in particular chromium cast irons of hardness ⁇ 64 Rc usually used as wear parts .
• the offset of the casing 17 relative to the core 13 can be adapted to the different requirements of the manufacturers in a simple manner, all the more so as the peripheral junction line 21 between the casing 17 and the core 13 is located advantageously in the internal angle of recess, which avoids exposure of this line to the direct action of the material to be ground.
• the method used for producing the wearing part according to the invention consists in first casting the core 13 with the studs 15; after having applied a refractory coating on the core, the part is placed in a second mold and the casing 17 is poured. The assembly is then subjected to a thermal quenching treatment.
• a thermal quenching treatment In order to illustrate the invention, an example of the execution of a part according to the invention and the results of laboratory tests obtained will be described below.
• the casting of Figures 4 and 5 is a bimetallic block of 230x275x150mm formed by a part corresponding to the core 13 and the studs 15 in GS cast iron (GGG40) and by an envelope part there in chromium cast iron with a hardness greater than or equal to 64 Rc.
• GGG40 GS cast iron
• chromium cast iron with a hardness greater than or equal to 64 Rc.
• a refractory coating (not shown) is applied to this part to avoid reflow of the studs and the risk of a metallurgical bond with chromium cast iron.
• chrome cast iron was poured on it.
• the bimetal block was then trimmed and quenched. Fatigue tests were performed.
• the tests are carried out in a SCHENK machine with a maximum capacity of 2500 kN.
• the applied signal is sinusoidal.
• the assembly underwent an oscillating compression load 100kN-2000kN generating maximum contact pressures 3 times higher than those undergone by a roller in service.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Food Science & Technology (AREA)
• Crushing And Grinding (AREA)
• Crushing And Pulverization Processes (AREA)
• Adornments (AREA)
• Polishing Bodies And Polishing Tools (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=3888299

Family Applications (1)

Country Status (8)

Families Citing this family (5)

Family Cites Families (5)

• 1994
  • 1994-08-17 BE BE9400744A patent/BE1008577A6/fr not_active IP Right Cessation
• 1995
  • 1995-08-16 DK DK95928904T patent/DK0777542T3/da active
  • 1995-08-16 KR KR1019970700766A patent/KR970704536A/ko not_active Application Discontinuation
  • 1995-08-16 AT AT95928904T patent/ATE170783T1/de not_active IP Right Cessation
  • 1995-08-16 DE DE69504691T patent/DE69504691T2/de not_active Expired - Fee Related
  • 1995-08-16 EP EP95928904A patent/EP0777542B1/de not_active Expired - Lifetime
  • 1995-08-16 ES ES95928904T patent/ES2122670T3/es not_active Expired - Lifetime
  • 1995-08-16 WO PCT/BE1995/000074 patent/WO1996005005A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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