Method for saving ductile from material having a concrete lining

A saw blade possesses a base element onto which boron nitride particles are applied in the cutting region. The boron nitride particles are bonded by means of a metallic bonding layer, which preferably consists of nickel or a nickel alloy with a Vickers hardness of at least 600 HV. The bonding layer is preferably deposited galvanically. The boron nitride particles advantageously possess a particle size of approximately 0.5 to 0.8 mm, preferably approximately 0.6 to 0.7 mm. The saw blade possesses particular advantages for use as a reciprocating saw blade for sawing GGG cast iron pipes with a cement lining and fiber-reinforced cement jacket, resulting in considerably improved cutting performance and service life.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention concerns a saw blade for sawing ductile iron materials having 
a concrete lining, having a base element onto which a coating made of 
particles of hard material is applied. The invention also concerns a 
method for sawing pipes made of cast iron having a concrete lining. 
2. Background 
Pipes that supply water and carry off waste water are at present produced 
mostly from cast iron, and are additionally provided with a cement lining. 
To improve corrosion resistance, these pipes are often additionally coated 
on the outside with a layer of fiber-reinforced cement or concrete. The 
cast iron is generally cast iron with spheroidal graphite (GGG), in which 
carbon in the form of spheroidal graphite is enclosed in a basic structure 
that is usually predominantly ferrite or perlite. 
Sawing such pipes, which usually possess a diameter on the order of from 
approximately 15 to approximately 40 cm and more, is highly problematical. 
Reciprocating saws are often used because of the confined conditions, 
especially when pipes are being laid or repaired in situ. 
However, conventional saw blades coated with tungsten carbide have 
insufficient service life, and often become so deformed while cutting 
through a single pipe that it is no longer possible to continue working 
with the same blade. 
Diamond-coated saw blades are also unsuitable, since they have a tendency 
to smear because of the graphite particles contained in the gray cast 
iron, so that cutting performance is insufficient and the saw blades 
quickly deform because of the high applied pressure required. 
The sawing process is further complicated by the fact that in the repair of 
water pipes, small quantities of water continue to flow through the pipe 
despite complete shutoff of the water; this means that working conditions 
are wet, which causes caking of the cement at the cut. 
SUMMARY OF THE INVENTION 
Objects 
The underlying object of the invention is therefore to create a saw blade 
for sawing ductile iron materials, especially for sawing pipes made of 
gray cast iron with a cement lining and an outer jacket made of 
fiber-reinforced cement or concrete, which possesses high cutting 
performance and the longest possible lifetime. 
Summary 
This object is achieved, according to the invention, by the fact that in a 
saw blade of the aforesaid kind, the particles of hard material are 
configured as boron nitride particles, and are bonded onto the base 
element by means of a metallic bonding layer. 
Use of such saw blades results in considerably improved cutting performance 
and greatly increased service life. 
Since conventional diamond-coated saw blades are unsuitable, this result is 
extremely surprising given the structural similarity of boron nitride and 
diamond. 
Cubic boron nitride, which is also referred to as Borazon, is commonly used 
in the abrasives industry to produce sanding wheels, grinding disks, and 
the like, if diamond-coated grinding tools are unsuitable. 
Boron nitride has not, however, hitherto been commonly used for saw blades, 
since diamond-coated saw blades normally possess a longer service life and 
higher cutting performance. 
According to the invention, the particles of hard material used to coat a 
saw blade are boron nitride particles, which are bonded onto the base 
element by means of a metallic bonding layer. 
It has been found, in accordance with the invention, that when the 
conventional plastic bonding layer is replaced by a metallic bonding 
layer, considerably improved resistance to abrasion, and therefore a 
longer service life, are achieved. Saw blades according to the invention 
yield greatly improved cutting results even when sawing GGG cast iron 
pipes with a cement lining and fiber-reinforced cement outer jacket, even 
in the especially problematical diameter range of approximately 20 cm; on 
the one hand, cutting performance is greatly enhanced, and on the other 
hand, service life is considerably improved. Surprisingly, saw blades 
according to the invention have no tendency to smear, even with nodular 
graphite iron having spheroidal graphite inclusions. Moreover, even when 
wet cast-iron pipes are sawn, caking of cement residues (from the cement 
lining or the outer envelope) in the saw blade is eliminated. 
An advantageous development of the invention provides for the bonding layer 
to be made of nickel or a nickel alloy. 
The advantage of this feature is that a bonding layer of this kind 
possesses particularly high toughness and hardness. 
Advantageously, the bonding layer can be produced by cathodic/anodic 
galvanic means, or by wet chemical means. 
Galvanic production of the bonding layer has the advantage of particularly 
good adhesion and reproducibility; production is also relatively 
economical. 
Of course production by other means, for example flame spraying, would also 
be theoretically conceivable, but such a method is generally much more 
expensive. 
When nickel or a nickel alloy is used as the bonding layer, the hardness 
can advantageously be set at a Vickers hardness of at least 400 HV. 
A hardness of at least 500 VH is especially preferred; optimum results are 
obtained with a galvanically deposited bonding layer made of nickel, with 
a Vickers hardness of approximately 550 to 650 HV. 
An advantageous development of the invention provides for the boron nitride 
particles to possess a particle size of approximately 0.3 to 1 mm; a 
particle size of 0.5 to 0.8 m, in particular 0.6 to 0.7 m, is especially 
preferred. 
The use of such coarse boron nitride particles results, particularly in 
conjunction with the bonding layer made of nickel or a nickel alloy and 
especially in the aforementioned hardness range, in optimum cutting 
results when used as reciprocating saw blades to saw pipes made of cast 
iron with cement lining and fiber-reinforced cement jacket. 
The base element can be made of a tool steel or different material. 
Both straight and toothed saw blades lead to equally good results, in 
particular when used as reciprocating saw blades. 
In addition, saw blades according to the invention can also be used 
advantageously as circular saw blades. 
In a method for sawing cast-iron pipes, in particular for sawing GGG 
cast-iron pipes which may possess a cement lining and an outer sheath made 
of fiber-reinforced cement or concrete, according to the invention the saw 
blades described above are used in particular as reciprocating saw blades. 
It is understood that the features mentioned above and those yet to be 
explained below can be used not only in the respective combination 
indicated, but also in other combinations or in isolation, without leaving 
the context of the present invention.

SPECIFIC DESCRIPTION 
A saw blade according to the invention is designated in its entirety with 
the number 10 in FIGS. 1 and 2. 
The saw blade 10 possesses an elongated base element 12 made of a tool 
steel, which is coated with boron nitride particles 14 in its cutting 
region 18, which in the example depicted is somewhat tapered compared to 
the remaining region of the base element 12. 
The cutting region 18 possesses a thickness of approximately 2 to 2.5 mm, 
which has the advantage that the saw blade is sufficient broad that when 
large pipes are being sawn it is possible to work with wedges, thus 
preventing jamming of the saw blade. 
The boron nitride particles 14, which are made of cubic boron nitride, 
possess a particle size of approximately 0.6 to 0.7 mm, which leads to 
particularly good cutting results when sawing GGG cast-iron pipes with a 
cement lining and fiber-reinforced cement jacket. 
The boron nitride particles 14 are held on the cutting region 18 of the 
base element 12 by means of a bonding layer that is indicated 
schematically in FIG. 2 with the number 16. 
This bonding layer 16 consists of a nickel layer that is deposited 
galvanically (anodically/cathodically), with a hardness of approximately 
600 to 700 HV. 
Corresponding to the thickness of the bonding layer 16, the boron nitride 
particles 14 have approximately 30 to 50% of their diameter projecting out 
of the bonding layer. The depiction in FIG. 2 serves only for explanation 
and is not to scale, since for purposes of better clarity the boron 
nitride particles 14 are shown enlarged. In FIG. 3, an alternative 
embodiment of a saw blade according to the invention is designated in its 
entirety with the number 20. Here again, a base element 22 made of a tool 
steel is coated in its cutting region with boron nitride particles, which 
are bonded by means of a galvanically deposited bonding layer made of 
nickel with a Vickers hardness of approximately 600 to 700 HV. 
In contrast to the embodiment described previously, however, the cutting 
region 18 is not straight, but rather possesses teeth indicated with the 
number 30. 
FIG. 4 shows a pipe denoted overall by reference numeral 33 in position for 
sawing using a blade saw according to the invention. The pipe 33 comprises 
a cast iron pipe 34 covered with an outer lining 36 made from 
fibre-reinforced synthetic material. In addition, the pipe 33 has an inner 
fibre-reinforced concrete lining 35. 
The pipe 33 is clamped by a clamping means shown schematically by reference 
number 31. Preferably, the pipe is sawed by using a blade saw 32 having a 
blade 20 according to the invention (as depicted in FIG. 3) using a drive 
39 back and forth as indicated by arrow 37. Simultaneously, the blade is 
advanced towards the pipe 33 as indicated by arrow 38. In addition, 
lubrication liquid may be applied as indicated by arrow 41. However, 
normally no additional lubrication liquid is necessary because of water 
leakage in such pipes. 
FIG. 5 shows an alternative configuration of the blade according to the 
invention. In FIG. 5 the blade denoted overall by reference numeral 40 is 
configured as a circular saw blade having teeth 44 having a coating with 
boron nitride particles 42 as described before.