CA2200368A1

CA2200368A1 - Mixer rotor

Info

Publication number: CA2200368A1
Application number: CA 2200368
Authority: CA
Inventors: Norbert Guerard
Original assignee: Magotteaux International SA
Current assignee: Magotteaux International SA
Priority date: 1996-04-05
Filing date: 1997-03-19
Publication date: 1997-10-05
Also published as: BE1010118A3

Abstract

The rotor includes a certain number of blades (12) which extend in a spiral from a rotary central hub and which include, viewed in the direction of rotation, a leading edge (16) substantially perpendicular to the direction of rotation. Each blade (12) is a bimetallic cast element most of the leading edge (16) of which consists of an insert (18) made of an alloy having good resistance to wear which is supported by a more ductile base alloy, the connection between the two alloys being a mechanical connection achieved by clinching the two alloys together.
Application to paper pulp mixers.

Description

3 6 ~

MTYRU ROTOR

The present invention relates to a mixer rotor comprising a certain number of blades extending in a spiral from a central hub which is supported in such a way that it can rotate in the direction in which the blades are wound, each blade having, viewed in the direction of rotation, a leading edge substantially perpendicular to the direction of rotation.
The invention relates more particularly to mixers used in the paper industry, especially for preparing paper pulp from virgin fibres or for treating fibres recycled from paper or board waste.
These rotors rotate past a perforated plate through which the pulp is forced. This pulp contains in particular, in the case of recovered cellulose, a large amount of waste which has to be separated from the fibre by means of the rotor of the mixer scraping against the perforated plate. Depending on the nature of this waste, which may be metal, plastic, glass, stone, etc., the mixer blades, especially their leading edge, may be subjected to intense wear by abrasion.
These mixers are generally cast components made of austenitic stainless steel of type 316 or 304. For low-wear applications, a hardness of 100 to 300 HB may suffice, which means that these mixers can be used as they are. By contrast, in the event of heavier duty, especially in the treatment of recycled fibres, it is necessary to take precautions to reduce the wear on the leading edge of the blades. A solution co~o~ly employed consists in protecting the leading edge of the blades by hard facing with weld material. The filler metal is often an alloy based on cobalt or on tungsten carbide. This method of protecting the blades is, however, very expensive owing to the nature of the filler metal.
Although increasing the hardness of the entire rotor of the mixer would indeed increase the abrasion-- resistance of the le~;ng edge it would, on the other hand, make the rotor more brittle and therefore less able 3 6 ~

to withstand mechanical stresses and impacts and would make its hub more complicated to machine.
The object of the present invention is to provide a novel mixer rotor which has both good resistance to wear and good ability to withstand mechanical stresses.
In order to achieve this objective, the present invention proposes a mixer rotor of the sort described in the preamble, which is characterized in that each blade is a bimetallic cast element most of the leading edge of which consists of an insert made of a material having good resistance to wear and which is supported by a more ductile base alloy, the connection between the insert and the alloy being a mechanical connection achieved by clinching the insert into the base metal.
Each insert preferably includes a curved elongate body the concave side of which is extended along its entire length by a narrower rib penetrating the base alloy, the said rib along its entire length having a series of perforations through which the said second alloy extends.
The insert may be made of martensitic steel with a hardness of between 50 and 55 Rc, while the base alloy may be a stainless steel with a hardness of between 25 and 30 Rc.
Other specific features and advantages of the invention will emerge from the detailed description of one preferred embodiment which is given hereinbelow by way of illustration with reference to the attached figures in which:
- Figure 1 represents an overall view of a mixer rotor according to the present invention;
- Figure 2 represents a lateral view of a mixer blade insert, Figures 2a, 2b and 2c being cross-sections at various points of Figure 2;
- Figure 3 represents a longit-l~;nAl section through a blade, and - Figure 4 represents an enlarged section through a blade on the sectioning plane IV-IV of Figure 3.
The mixer rotor 10 represented in Figure ~n3~

consists of a series of blades 12 which are wound in a spiral around a hub 14 which i8 carried by a rotation spindle, not shown, to rotate in the direction represented by the arrow in Figure 1. Each blade 12 includes a leading edge 16 which scrapes against a perforated plate through which the paper pulp is forced.
It is therefore this leading edge 16 which i8 subjected to the most amount of wear by abrasion in contact with the solid waste and contamination to be found in the 1 0 pulp .
In order to improve resistance to wear while maintaining enough ductility to guarantee good ability to withstand mechanical stresses, the invention proposes bimetallic or composite blades, the leading edge 16 of which is formed by an insert with high hardness and good resistance to wear. Such an insert is represented as 18 in Figure 2. This insert includes a curved elongate body 20, the convex dorsal fac-e 26 of which is intended to form the leading edge 16 of the blade 12. There is a thinner rib 22 on the concave ventral face of the body 20, and this extends in the middle region of the body 20.
This rib 22 along its entire length has perforations 24 which pass right through the thickness of the rib 22.
The insert 18 is cast in an appropriate mould. It is made of martensitic steel and its hardness after quench and temper is of the order of 50 to 55 Rc. Its high chromium content gives it good resistance to corrosion and abrasion.
The inserts 18 intended for the various blades 12 of the rotor are arranged in a mould with shapes which complement those of the rotor 12 and are fixed temporarily therein, for example by bonding. The ba~e alloy 28 i~ then cast to form the rotor 12. This alloy may be made of stainless steel, for example of the type UNSJ 91540, for which the hardness after guench and temper is relatively low, of the order of 25 to 30 Rc.
As this base alloy 28 is poured, it partially coats the inserts 18, the body 22 of which will form a large part of the leading edge 16 of each blade, as ~nn3~
_ - 4 -represented in Figure 3. As this base alloy 28 is being poured, it more particularly coats the entire rib 22 of each insert and forms bridges through the ~arious perforations 24 as represented in Figure 4 in order to establish a rigid mechanical connection with each insert.
This connection is further strengthened, as the base alloy cools and shrinks and thus forms a good clinched connection between the insert and the rest of the blade.
Instead of casting the entire rotor, it is also possible to cast the various blades 12 separately and then attach them to the central hub 14 by welding. This has the advantage, should the blades wear, that the hub, which is relatively expensive to manufacture owing to the mach; n~ ng required to be able to mount it on a drive shaft can then be recovered.

Claims

1. Mixer rotor comprising a certain number of blades (12) extending in a spiral from a central hub (14) which is supported in such a way that it can rotate in the direction in which the blades (12) are wound, each blade (12) having, viewed in the direction of rotation, a leading edge (16) substantially perpendicular to the direction of rotation, characterized in that each blade (12) is a bimetallic cast element most of the leading edge (16) of which consists of an insert (18) made of an alloy or of a material having good resistance to wear which is supported by a more ductile base alloy, the connection between the two parts being a mechanical connection achieved by clenching the insert into the base metal.

2. Rotor according to Claim 1, characterized in that each insert (18) includes a curved elongate body (20) the concave side of which is extended along its entire length by a narrower rib (22) penetrating the base alloy, the said rib (22) along its entire length having a series of perforations (24) through which the said second alloy (28) extends.

3. Rotor according to either one of Claims 1 and 2, characterized in that the said insert (18) is made of martensitic steel with a hardness of between 50 and 55 Rc.

4. Rotor according to either one of Claims 1 and 2, characterized in that the base alloy is a stainless steel with a hardness of between 25 and 30 Rc.