Lining element for pulp refiners

A lining element for pulp refiners is made by casting from a steel alloy containing from 1.0 to 5 percent by weight of titanium present as titanium carbide grains having an average size of 10 microns or less and being uniformly distributed throughout the lining element. The titanium carbide prevents polishing of the working faces of the lining element.

BACKGROUND OF THE INVENTION 
This invention relates to pulp refining apparatus, i.e. apparatus for 
producing and/or mechanically processing pulp, such as wood pulp and other 
fiber slurries. More particularly, the invention concerns a lining element 
for application to relatively rotatable backing members of a refiner, such 
as, for example, a face plate for a disc refiner. 
A pulp refiner essentially is a milling apparatus used for producing pulp 
from wood chips or other fibrous raw materials and/or for processing pulp 
to modify the fibers to the desired condition. A common type of pulp 
refiner includes two relatively rotatable, concentric discs the 
confronting faces of which are lined with removable wear resistant face 
plates having a pattern of ridges and grooves. The lined refiner discs 
define between them a narrow annular clearance. The material to be refined 
is fed into this clearance at the center of the discs and is subjected to 
the refining action (i.e. the defibration of the wood and/or the 
conditioning of the fibers) of the ridges of the face plates as it flows 
radially outwardly through the clearance. 
Face plates and other lining elements for pulp refiners are commonly cast 
from alloys of various types. Cast iron, stainless steel and other steel 
alloys containing nickel and molybdenum and various other ingredients are 
customary materials. 
Lining elements for pulp refiners have to satisfy various requirements 
which are conflicting in some respects and which are difficult or even 
impossible to meet in one and the same lining element using the customary 
materials. For example, the lining elements should maintain an excellent 
and uniform refining action to be able to produce pulp of high and uniform 
quality throughout their life. Moreover, they should have high resistance 
to wear so as to have long life, as well as high impact strength to be 
able to resist the impact loads to which they may be subjected even in 
normal operation. A further desired quality is high resistance to 
corrosion and erosion. The material from which the lining elements is 
produced also should have good castability so that the elements can be 
cast in complicated shapes, and naturally the material should not be too 
expensive in relation to the properties of the finished elements. 
A requirement related to the above-mentioned requirement for an excellent 
and lasting refining action is that the lining elements should be 
self-sharpening. This means that the lining element surfaces defining the 
narrow refining clearance, the working faces of the ridges, must not be 
polished too easily by the pulp, but must retain a certain limited, 
uniform roughness throughout the life of the element. Most known lining 
elements of alloyed steel require frequent regrinding of the working faces 
of the ridges, because these faces are rapidly polished by the pulp and 
because the edges of the ridges rapidly become blunt. 
SUMMARY OF THE INVENTION 
The present invention has for its general object of provide a refiner 
lining element meeting the above-stated requirements in an advantageous 
way. In accordance with the invention a pulp refiner lining element is 
made from an alloy containing between 1.0 and 5.0 percent by weight of 
titanium present as titanium carbide grains in a steel matrix, the 
titanium carbide grains being substantially uniformly distributed 
throughout the lining element and having a maximum average size of about 
10 microns (throughout the specification and the appended claims, wherever 
numerical values of the average grain size are given, these values 
represent the nominal grain diameter, i.e. the square root of the average 
grain sectional area). Preferably, the average size is less than about 8 
microns. For best results, the majority, preferably at least 95 percent 
and, still better, at least 99 percent, of the titanium carbide grains 
should have a size less than 10 microns. It is also preferred that the 
average size of the titanium carbide grains and the titanium content are 
matched such that the average distance between adjacent grains, as 
determined according to a technique herein termed "Nearest Neighbor 
Measuring Technique", abbreviated NNMT, is at least about 3 microns, 
preferably at least about 10 microns. The NNMT is described in detail in 
UNDERWOOD, E.E.: "Quantitive Stereology", Addison-Wesley, Reading, Mass. 
(1970), 84. An alternative technique, herein termed "Linear Measuring 
Technique", abbreviated LMT, includes determining the average distance 
between adjacent grains on a large number of randomly distributed and 
oriented straight lines on a photomicrograph. LMT figures for a given 
specimen are generally substantially higher than NNMT figures for the same 
specimen, and measurements on lining elements according to the invention 
have shown that the NNMT figures given above, i.e. 3 and 10 microns, 
roughly correspond to LMT figures of 15 and 30 microns, respectively. A 
preferred upper limit of the distance between adjacent titanium carbide 
grains is about 30 microns, NNMT (about 100 microns, LMT). Unless 
otherwise specified, the NNMT figures are used hereinafter. 
As is well known, titanium carbide has properties which are very useful 
where hardness and wear resistance are desired. In the past, it has been 
customary to employ powder metallurgy techniques for making objects from 
alloys containing titanium carbide. One reason for this is that it is 
difficult to avoid excessive growth of the titanium carbide grains or the 
formation of large dendritic aggregates of titanium carbide grains. Since 
its is hardly feasible to employ any other method than casting for the 
production of lining elements of the kind referred to, the problems 
connected with titanium carbide and molten metallurgy techniques have to 
be considered. 
In making the lining elements according to the invention, the 
just-mentioned problems are avoided by first providing a melt which is 
essentially free of titanium but has a carbon content corresponding to the 
desired total carbon content of the finished lining elements and then, 
immediately prior to the casting, combining this melt with titanium and 
any other alloy components that are still missing. Preferably, the 
titanium is added as ferrotitanium to the melt (which contains all the 
other essential alloy components) in the ladle or other container from 
which the molten alloy is poured into the casting mold. The titanium very 
quickly combines with a portion of the carbon to form titanium carbide, 
and because of the addition of titanium at a late stage, the time 
remaining until the casting in the mold has solidified is insufficient to 
permit the titanium carbide grains to grow to a harmful size or form 
unwanted aggregates; since lining elements of the kind referred to are 
relatively thin structures, the molten metal in the mold solidifies 
rapidly. 
In use, it has been found that disc refiner face plates according to the 
invention are capable of producing pulp of high and uniform quality during 
extended periods of operation without regrinding of the ridges. For 
example, face plates made in accordance with the invention (approximate 
composition: C 1.6 %, Si 0.65 %, Mn 0.45 %, P 0.030 %, S 0.025 %, Cr 17.0 
% Ni 1.60 %, Mo 0.70 %, Ti 2.3 %, Fe balance) have been used for pulp 
production for periods ranging from 1600 to 1900 hours without regrinding. 
Conventional face plates having approximately the same composition except 
for the titanium (no titanium) used under identical or similar conditions 
have required regrinding at intervals averaging approximately 600 hours. 
Assuming that both types of plates can be reground the same number of 
times before they have to be discarded, face plates according to the 
invention thus have a useful life approximately three times that of the 
titanium-free face plates. 
In addition to the advantages of a substantially longer life and a uniform 
pulp quality, disc refiner face plates according to the invention have 
been found to reduce the specific energy consumption of the refiner 
considerably. In refiners having conventional face plates, the working 
faces of the ridges gradually become polished by the pulp, resulting in a 
gradually increasing specific energy consumption until the ridges are 
reground. In face plates according to the invention, on the other hand, 
the titanium carbide grains result in a constant self-sharpening of the 
working faces, and as a consequence of this self-sharpening, the specific 
energy consumption remains substantially constant and at a low level 
throughout the useful life of the face plates. 
Examples of suitable alloy compositions for face plates and other lining 
elements according to the invention are given in Table 1 below. for some 
alloy components two percentage ranges are given, the narrower range being 
the preferred range. All percentage figures are by weight. 
TABLE 1 
__________________________________________________________________________ 
Alloy 
compo- 
nent 
Alloy A Alloy B Alloy C Alloy D Alloy E 
__________________________________________________________________________ 
C 0.9 
- 1.8 
0.4 
- 1.3 
0.4 
- 1.2 
1.3 
- 2.2 
0.5 
- 1.8 
1.2 
- 1.4 
0.5 
- 0.7 
0.6 
- 0.9 
1.5 
- 1.7 
0.6 
- 1.6 
Si 0.3 
- 0.5 
0.3 
- 0.5 
max. 0.4 
0.5 
- 0.7 
max. 2.0 
0.3 
- 1.0 
Mn 0.6 
- 1.0 
0.6 
- 1.0 
max. 0.4 
0.9 
- 1.3 
max. 2.0 
0.2 
- 1.0 
P max. 0.03 
max. 0.03 
max. 0.03 
max. 0.03 
max. 0.03 
S max. 0.03 
max. 0.03 
max. 0.03 
max. 0.03 
max. 0.03 
Cr 0.8 
- 5.0 
10.0 
- 15.0 
-- 10.0 
- 15.0 
14.0 
- 20.0 
0.8 
- 1.2 
12.0 
- 14.0 11.5 
- 13.5 
16.8 
- 18.0 
Ni 2.5 
- 8.0 
4.0 
- 12.0 
12.0 
- 20.0 
-- max. 3.0 
3.5 
- 4.5 
7.0 
- 9.0 
17.5 
- 19.5 1.0 
- 2.0 
Mo 1.5 
- 5.0 
1.0 
- 3.5 
3.0 
- 6.0 
-- max. 2.0 
2.5 
- 3.5 
1.5 
- 2.5 
4.5 
- 5.3 0.5 
- 1.0 
Ti 1.5 
- 5.0 
1.5 
- 5.0 
1.5 
- 5.0 
1.5 
- 5.0 
1.5 
- 5.0 
2.5 
- 3.5 
2.5 
- 3.5 
3.2 
- 3.9 
2.5 
- 3.5 
2.5 
- 3.5 
Al 0.06 
- 0.2 
0.5 
- 2.5 
0.03 
- 0.3 
-- -- 
0.7 
- 1.3 
0.06 
- 0.2 
Co -- -- 7.0 
- 10.0 
-- -- 
8.1 
- 9.5 
V -- -- -- 0 - 1.5 
-- 
0.6 
- 1.0 
Fe and 
impu- 
balance balance balance balance balance 
rities 
__________________________________________________________________________ 
As apparent from Table 1, the preferred titanium contents are always 
between 2.5 and about 4 percent by weight. The most suitable titanium 
content is normally in the range of 2.5 to 3.5 percent by weight. If the 
titanium content is too high, it may be difficult to avoid titanium 
carbide accumulations and consequent undesired fracture indications. In 
addition, the self-sharpening action of the lining elements is reduced at 
high titanium contents, above 5 percent by weight, because the average 
distance between the titanium carbode grains then becomes too small in 
relation to the diameter of the pulp fibers. The diameter of the fibers of 
those types of fibrous materials for which lining elements of the kind 
referred to are normally used is about 30 microns (this figure is a rough 
average value) and in view of this, the average distance between the 
titanium carbide grains should be at least 3 microns and most desirably 
should be at least 10 microns. 
However, the self-sharpening action is also reduced if the average distance 
between the titanium carbide grains is too large, more than about 30 
microns and for that reason a titanium carbide content below about 1.0 
percent by weight may not be expected to produce sufficient 
self-sharpening. 
Disc refiner face plates produced according to the above-described method 
from alloys of the compositions set forth in Table 1 have been found to 
have, in addition to other desired characteristics, a degree of 
incapability of becoming polished which, in terms of a surface finish 
factor herein termed average surface deviation (definition given 
hereinafter) is from twice to more than four times that of a customary 
material for face plates (alloyed cast iron).

DETAILED DESCRIPTION OF THE DRAWING 
In the drawing, FIG. 1 shows the front or working face of a refiner lining 
element in the form of a face plate 10 for a disc refiner for wood pulp. 
The face plate 10 is of known type and is provided with openings or other 
means (not shown) for mounting it on a circular supporting disc on which a 
plurality of similar face plates jointly form an annular refiner ring. The 
disc refiner includes two such coaxial refiner rings having their front 
faces disposed closely adjacent to each other to define a narrow refining 
clearance. In operation of the refiner, the fiber slurry or other fibrous 
material is processed by the relatively rotating refiner rings as it flows 
radially outwardly through this clearance. 
As shown in FIGS. 1 and 2, the face plate 10 has a flat body 11 which 
carries on one face thereof, the front face, a plurality of substantially 
radial blades or ridges 12 and transverse short webs 13 between the 
ridges. The ridges and the webs are integral with the body. In operation 
of he refiner, the ridges cooperate with the ridges of the face plates of 
the opposing refiner ring to refine the fibrous material. 
It should be noted that the cross-section of the face plate 10 is 
relatively thin throughout the face plate. Thus, on casting the face 
plate, the molten metal solidifies relatively rapidly throughout the 
cross-section. 
In the past years, it has been customary to make the ridges of disc refiner 
face plates relatively narrow, such as 2 to 3 millimeters, to compensate 
for the disadvantages resulting from polishing of the ridges by the 
fibrous material being refined. Because of the self-sharpening action of 
face plates according to the present invention, the ridges need not be 
made that narrow, but can have a width of, for example, from 3 to 5 
millimeters. This is an advantage, since the casting is simplified with 
wider ridges. 
FIG. 3 illustrates a surface finish factor, herein termed "average surface 
deviation", which is significant to the quality of the refined fibrous 
material. This figure shows an idealized cross-sectional profile contour 
14 of the front or working face of one of the ridges 12. The mean line O 
of the profile contour 14 is a straight line located such that the surface 
area between the line and the profile contour segments above the line is 
equal to the surface area between the line and the profile contour 
segments below the line. The segments of the profile contour below the 
mean line O are mirrored about the mean line as shown in dash lines at 14' 
and for the purpose of defining the average surface deviation R.sub.a only 
the segments above the mean line and the mirrored segments, thus the 
"rectified" profile contour, are used. 
The average surface deviation R.sub.a is herein defined as the distance 
between the mean line O and a second straight line R which is parallel to 
the mean line O and located such that the surface area between this second 
line R and the sections of the "rectified" profile contour located above 
it is equal to the surface area between the line R and the sections of the 
rectified profile contour located below it (these two surface areas are 
marked by horizontal and vertical shade lines in FIG. 3). Thus, the second 
line R may be regarded as the mean line of the rectified profile contour. 
FIG. 4 diagrammatically illustrates the main steps of a method for making 
the face plate 10 or other lining elements according to the invention. A 
ladle 20 contains molten metal 21 tapped from a cupola furnace 22. Apart 
from the titanium and a small amount of iron, the composition of the melt 
21 corresponds to the composition of the finished lining element, i.e. it 
corresponds to the composition of the matrix or continuous phase in which 
the titanium carbide grains are embedded in the finished lining element. 
Titanium in the form of granulated ferrotitanium (70 percent of titanium 
and 30 percent of iron) supplied from a container 23 is added to the melt 
21 in a quantity corresponding to the desired titanium content of the 
finished element. At least a portion of the ferrotitanium may be added in 
the furnace immediately prior to the tapping. 
Immediately after the ferrotitanium has been added to the melt 21 and 
throughly mixed therewith, the metal is poured into a shell mold 24 
through the bottom of the ladle 20. The maximum time that can be permitted 
to elapse between the bringing together of the titanium and the 
carbon-containing melt 21 and the solidification of the metal in the mold 
24 may vary according to the particulars of each specific case. However, 
it should be as short as possible and in any case not longer than 30 
minutes. In fact, in many cases it will be necessary to make this time 
considerably shorter, and a general maximum time is about 15 minutes. 
After the cast lining element has been removed from the mold, it is 
subjected to a customary heat treatment. 
The following Table 2 gives four examples of alloys for disc refiner face 
plates according to the invention and shows the hardness and average 
surface deviation R.sub.a of face plates made from these alloys. For 
comparision, the table also gives the corresponding data of face plates 
made from a reference alloy of a type customarily used for disc refiner 
face plates. Composition percentage figures are by weight. In addition to 
the alloy components for which composition figures are given in the table, 
the alloys contain iron as the base metal and one or more of the other 
alloy components set forth in Table 1 and in the ranges given in that 
table. 
TABLE 2 
__________________________________________________________________________ 
Alloy Alloy Alloy Alloy Alloy Reference 
component 
I II III IV alloy 
__________________________________________________________________________ 
C 0.9 0.8 1.6 1.6 2.9 
Cr 1 -- 12 17.0 2.0 
Ni 4 18 -- 1.6 5 
Mo 3 5 -- 0.7 -- 
Ti 3 3.5 3 2.3 -- 
Co -- 9 -- -- -- 
V -- -- 0.8 -- -- 
Heat Ageing Ageing Austeni- 
Austeni- 
No heat 
treatment 
560.degree. C/3h 
480.degree. C/4h 
tizing tizing treatment 
1020.degree. C/30 
1020.degree. C/30 
min. min. 
Annealing 
Annealing 
250.degree. C/2h 
250.degree. C/2h 
twice twice 
Hardness 
after heat 
57 52-56 57 54 54 
treatment 
HR.sub.C 
Average 
surface 
0.57 0.51 0.27 0.60 0.13 
deviation 
R.sub.a microns 
__________________________________________________________________________ 
The face plates were made in accordance with the above-described procedure 
with the modification that a portion of the total quantity of the 
ferrotitanium was added to the molten matrix metal in the melting furnace 
while the rest of the ferrotitanium was added during the tapping of the 
molten metal into the ladle. 
The first and last face plate of each series were tested in respect of the 
size and distribution of the titanium carbide grains and of the average 
surface deviation. The testing of the size and distribution showed that 
the maximum average size was about 5 microns in most cases, a very large 
majority of the grains being larger than about 1.5 microns. 
The distribution was substantially uniform throughout the cross-section of 
the plates, although in some cases the grains in the ridges were somewhat 
smaller than the grains in the body. Relatively few grains, about 0.5 
percent of the total number, had a size in excess of about 10 microns. The 
average distance between neighboring titanium carbide grains varied from 
about 10 microns to about 16 microns. 
Face plates made from alloy E have been used in pulp production for 
extended periods, yielding the advantageous results accounted for 
hereinabove.