U.S. patent application number 12/300970 was filed with the patent office on 2010-03-11 for top hammer rock-drilling tool, a drill rod coupling sleeve.
Invention is credited to Bo Carlstrom, Johan Linden.
Application Number | 20100059285 12/300970 |
Document ID | / |
Family ID | 38694155 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100059285 |
Kind Code |
A1 |
Carlstrom; Bo ; et
al. |
March 11, 2010 |
TOP HAMMER ROCK-DRILLING TOOL, A DRILL ROD COUPLING SLEEVE
Abstract
In a first aspect, the invention relates to a rock-drilling tool
that comprises a drill rod (1) having a male thread (5) as well as
a coupling sleeve having a female thread for the co-operation with
the male thread of the drill rod. The male thread (5) of the drill
rod may consist of a martensitic stainless steel. Axially inside
the male thread (5), a waist (32) is formed in which the drill rod
(1) has the smallest diameter thereof. Furthermore, an external,
cylindrical guide surface (31) is positioned between the male
thread (5) and the waist (32) and has the purpose of co-operating
with an internal guide surface positioned between the female thread
and a free end of the coupling sleeve. Furthermore, the invention
relates to a drill rod as such as well as a coupling sleeve as
such.
Inventors: |
Carlstrom; Bo; (Sandviken,
SE) ; Linden; Johan; (Gavle, SE) |
Correspondence
Address: |
DRINKER BIDDLE & REATH (DC)
1500 K STREET, N.W., SUITE 1100
WASHINGTON
DC
20005-1209
US
|
Family ID: |
38694155 |
Appl. No.: |
12/300970 |
Filed: |
May 15, 2007 |
PCT Filed: |
May 15, 2007 |
PCT NO: |
PCT/SE2007/000467 |
371 Date: |
March 25, 2009 |
Current U.S.
Class: |
175/320 ;
285/390 |
Current CPC
Class: |
E21B 17/0426
20130101 |
Class at
Publication: |
175/320 ;
285/390 |
International
Class: |
E21B 17/042 20060101
E21B017/042; E21B 17/00 20060101 E21B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2006 |
SE |
0601117-5 |
May 17, 2006 |
SE |
0601119-1 |
Claims
1. A top hammer rock-drilling tool comprising a drill rod having a
male thread, and a coupling sleeve having a female thread for the
co-operation with the male thread of the drill rod, wherein the
male thread of the drill rod may consist of a martensitic,
stainless steel, and that a waist is formed axially inside the male
thread, in which waist the drill rod has the smallest diameter
thereof, an external, cylindrical guide surface being positioned
between the male thread and the waist and having the purpose of
co-operating with an internal guide surface positioned between the
female thread and a free end of the coupling sleeve.
2. Rock-drilling tool according to claim 1, wherein between the
guide surface and male thread of the drill rod, an envelope surface
is formed, the diameter of which is smaller than the diameter of
the guide surface, and in which the groove of the male thread runs
out.
3. Rock-drilling tool according to claim 1, wherein the waist of
the drill rod transforms into the guide surface as well as into a
cross section-wise hexagonal section or round section of the drill
rod, via concavely arched, successively expanding transition
surfaces.
4. Rock-drilling tool according to claim 1, wherein the axial
distance between the guide surface of the drill rod and the end
surface thereof is only somewhat smaller than the distance between
the free end of the coupling sleeve and an internal partition wall
against which the free end of the drill rod is pressable.
5. Rock-drilling tool according to claim 1, wherein the guide
surface of the drill rod has a diameter that is at least twice as
large as the axial extension thereof, and wherein the male thread
has a wear volume that is larger than the wear volume of the female
thread.
6. A top hammer drill rod for rock-drilling tools, comprising a
male thread that is formed adjacent to a free end and in the form
of a helix thread ridge having a crest and two flanks, which
delimit a likewise helix groove having a bottom, wherein said male
thread may consist of a martensitic, stainless steel, and that
axially inside the male thread, a waist is formed in which the
drill rod has the smallest diameter thereof, a cylindrical guide
surface being formed between the waist and the male thread, the
diameter of which guide surface is larger than the outer diameter
of the thread ridge.
7. Drill rod according to claim 6, wherein an envelope surface is
formed between the guide surface and the male thread, the diameter
of which envelope surface is smaller than the diameter of the guide
surface and in which the groove of the male thread runs out.
8. Drill rod according to claim 6, wherein the waist thereof
transforms into the guide surface as well as into a
cross-section-wise hexagonal section or round section via concavely
arched, successively expanding transition surfaces, and wherein the
cross-sectional area of the thread ridge is larger than the
imaginary cross-sectional area of the groove.
9. A coupling sleeve for top hammer rock-drilling tools, the
coupling sleeve comprising two hollow spaces, which terminate in
opposite directions and are separated by a partition wall, and in
which female threads are formed, wherein a first female thread is
spaced-apart from a free end of an internal, cylindrical guide
surface, the first female thread being a thread ridge having a
crest and two flanks that delimit a helix groove having a bottom,
the width of the thread ridge being smaller than the width of the
groove.
10. Coupling sleeve according to claim 9, that wherein the
partition wall has an axial thickness, and wherein the guide
surface has an axial length, said length being greater than said
thickness.
11. Rock-drilling tool according to claim 2, wherein the waist of
the drill rod transforms into the guide surface as well as into a
cross section-wise hexagonal section or round section of the drill
rod, via concavely arched, successively expanding transition
surfaces.
12. Drill rod according to claim 7, wherein the waist thereof
transforms into the guide surface as well as into a
cross-section-wise hexagonal section or round section via concavely
arched, successively expanding transition surfaces, and wherein the
cross-sectional area of the thread ridge is larger than the
imaginary cross-sectional area of the groove.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] In a first aspect, this invention relates to a rock-drilling
tool intended for top hammer drilling and of the type that
comprises a drill rod having a male thread and a coupling sleeve
having a female thread for the co-operation with the male thread of
the drill rod.
[0002] In other aspects, the invention also relates to a drill rod
as well as a coupling sleeve for such rock-drilling tools.
BACKGROUND OF THE INVENTION
[0003] Many types of equipments for practical rock drilling
comprise, on one hand, a stationary placed machine having a shank
adaptor, and on the other hand a drilling tool in the form of a bit
and at least one drill rod as well as a coupling sleeve for the
connection of the drill rod with the shank adaptor. Furthermore,
the drill rod connected to the shank adaptor may be connected with
one or more additional rods while forming a longer drill string for
drilling deeper holes. In top hammer drilling, the shank adaptor is
arranged to provide a combination of impact and rotary motions,
which are transferred to the bit via the drill rod or the
string.
[0004] In rock-drilling equipment in general and equipment for top
hammer drilling in particular, high requirements of technical as
well as economic character are made. In a technical respect, the
drilling tool should be capable of drilling the straightest
possible holes fast and efficiently in rocks of most varying
nature. Of economical interest to the user is not only the
technical performance of the newly manufactured drilling tool, but
to a great extent also the service life thereof. This depends on a
number of different factors, one of which is the capacity of the
drill to resist corrosion fatigue. Such fatigue, which may result
in rupture of the drill rod, arises when the same, during the work
thereof of transferring the impact and rotary motions to the bit,
is subjected to corrosive attacks, which in combination with
pulsating loads in the form of shock waves and bending motions,
initiate cracks, which gradually grow large finally resulting in
fatigue. Particularly sensitive to crack formation are the
thread-groove bottoms in the male thread of the drill rod, where
the drill rod has a small cross-area. Another service
life-determining factor is the inevitable wear of the threads that
arises when the flanks thereof wear against each other as a result
of the intermittently repetitive, axial impulsive forces, as well
as the relative rotary motion that constantly is active when the
torque is transferred between the coupling sleeve and the drill
rod. Thus, in contrast to rigidly tightened threaded joints of the
conventional type, the severely exposed threaded joint of a rock
drill is dependent on the fact that the torque transfer between the
coupling sleeve and the drill rod provides a "constant" screwing-in
of the male thread into the female thread, which leads to wear of
primarily the flanks of the threads that tighten the joint. The
thread wear becomes particularly troublesome in economical respect
if the male thread of the drill rod is worn out faster than the
female thread of the coupling sleeve, since this requires
replacement of the expensive drill rod before the requisite
replacement of the cheaper coupling sleeve. An additional factor of
importance to the service life of the drill as well as the
technical performance thereof, is the capacity of the threaded
joint to counteract deflection, i.e., the tendency of the drill rod
to deflect or turn out at an angle to the coupling sleeve. Ideally,
the drill rod and the coupling sleeve should extend along a common
centre axis (in extension of the shank adaptor) in order to
guarantee that the drilled hole becomes desirable straight. The
further the wear of the threads proceeds, the more the stiffness is
deteriorated and the play is increased in the joint between the
coupling sleeve and the drill rod, the deflection phenomena
propagating into the threaded joint and accelerating the wear.
[0005] The problem of premature wear of the male thread of the
threaded joint between a drill rod and a coupling sleeve has been
observed by U.S. Pat. No. 6,196,598 (SE 521790), more precisely by
the fact that the male thread is designed with a wear volume
(proportional to the cross-sectional area) that is from 5 to 25%
larger than the wear volume of the female thread. In such a way, it
is guaranteed that the comparatively expensive drill rod does not
need to be discarded and be replaced before the cheaper female
thread of the coupling sleeve has been worn out. However, this
measure solves neither the problem of corrosion fatigue nor the
problem of successively growing play and deflection.
OBJECTS AND FEATURES OF THE INVENTION
[0006] The present invention aims at obviating the above-mentioned
shortcomings of the known rock-drilling tool and at providing an
improved tool. Therefore, a primary object of the invention is to
provide a rock-drilling tool adapted for practical top hammer
drilling, which has optimal properties in respect of technical
performance as well as economic attractiveness, above all by being
able to offer a long service life and a persistently reliable
serviceability during the entire active service life thereof. Thus,
the user should not only be able to count on the drill rod to last
at least as long as the coupling sleeve, but also to efficiently
and in the long term resist, on one hand, the tendencies to
corrosion fatigue, and on the other hand the deflection phenomena
that increase the thread play that inevitably arises during
practical drilling in rocks of varying structure. An additional
object is to provide a rock-drilling tool that is structurally
simple and therefore inexpensive to manufacture and easy to
use.
[0007] According to the invention, at least the primary object is
attained by the rock-drilling tool according to the invention by
means of the features defined in the characterizing clause of claim
1. Preferred embodiments of the rock-drilling tool are further
defined in the dependent claims 2-5.
[0008] Furthermore, the invention relates to a drill rod and a
coupling sleeve as such. The features of the drill rod according to
the invention are seen in the independent claim 6, while the
features of the coupling sleeve according to the invention are
defined in the independent claim 9.
FURTHER ELUCIDATION OF PRIOR ART
[0009] By U.S. Pat. No. 6,547,891, a drill rod intended for top
hammer-drilling equipment having a male thread made of a corrosion
resistant, martensitic steel is previously known. In this case, the
publication does not contain--except for the specified material
use--any information about how a drill rod could be optimized in
respect of the capability of the male thread to provide a threaded
joint free of play.
[0010] Threaded joints for rock-drilling tools of different types
are further disclosed in SE 9904324-2, SE 0103407-3 and SE
0201989-1.
BRIEF DESCRIPTION OF THE APPENDED DRAWINGS
[0011] The invention will be described closer below, reference
being made to the appended drawings. Because neither the adaptor to
which one of the ends of the drill rod of the tool is connected,
nor the bit connected to the opposite end of the drill rod, are of
any immediate interest, these components, as the proper drilling
machine, have not been shown in the drawings.
[0012] Therefore, in the drawings:
[0013] FIG. 1 is a side view of a drill rod according to the
invention,
[0014] FIG. 2 is an enlarged longitudinal section through a
coupling sleeve according to the invention, intended to co-operate
with the drill rod,
[0015] FIG. 3 is an enlarged view showing the end of the drill rod
that co-operates with the coupling sleeve,
[0016] FIG. 4 is a cross-section through the drill rod, and
[0017] FIG. 5 is an extremely enlarged detailed view showing the
design of a threaded joint between the drill rod and the coupling
sleeve of FIGS. 2 and 3, respectively.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0018] The drill rod, in its entirety designated 1, comprises
opposite ends 2, 3, such as the same are represented by planar,
annular end surfaces, and has a length that is many times greater
than the diameter thereof. In practice, the rod 1 may have a length
of 4-6 m and a largest diameter of about 38 mm. The end 2 is
usually called shank end, since the same should always be facing
the shank adaptor. In a main section S, which extends along the
major part of the total length, the rod has a conventional,
hexagonal cross-section shape (see FIG. 4), a central flush duct 4
extending through-going from end to end. At a distance from the two
ends 2, 3, the hexagonal cross-section shape ceases and transforms
into generally rotationally symmetrical surfaces in which external
threads are formed, i.e., male threads. More precisely, a first
male thread 5 is provided adjacent to the end 2, while a second
male thread 6 is provided adjacent to the end 3. The last-mentioned
thread 6 is intended to be screwed into a female thread in a drill
bit or into another coupling sleeve of a conventional type (not
shown), and is of minor importance.
[0019] In this case, the coupling sleeve 7 is exteriorly
cylindrical and comprises two hollow spaces 8, 9, which are
separated by a partition wall 10, and mouth in opposite ends 11, 12
of the sleeve. The partition wall 10 has an axial thickness L5.
Each individual hollow space 8, 9 is delimited by cylindrical wall
portions or skirts 13, 14. On the insides of the same, female
threads 15, 16 are formed, the first-mentioned one of which is
intended to co-operate with the male thread 5 on the rod 1, while
the last-mentioned one is intended to co-operate with a male thread
on a spigot included in the shank adaptor (not shown) that has the
purpose of driving the drilling tool. The two hollow spaces 8, 9
communicate with each other via a central hole 17, which extends
through the partition wall 10.
[0020] When the male thread 5 of the rod and the female thread 15
of the sleeve co-operate during operation, the end surface 2
bottoms against the surface 18 of the partition wall 10.
Analogously, the end (not shown) of the adaptor spigot bottoms
against the opposite, planar surface 19 of the partition wall
10.
[0021] According to the invention, at least the male thread 5 on
the drill rod 1 may be manufactured from a martensitic, stainless
steel. If so, it is most convenient that the drill rod in its
entirety is manufactured from this material, the two male threads
5, 6 being integrated parts of the rod body. The steel may
advantageously be of the type disclosed in U.S. Pat. No. 6,547,891,
i.e., have a structure comprising primarily martensite and
containing at least 10% by weight of chromium (Cr), as well as
minute quantities of carbon (C) and nitrogen (N), respectively. The
steel may also contain varying quantities of molybdenum (Mo),
tungsten carbide (WC), and copper (Cu). The content of martensite
should amount to at least 50% by weight, suitably at least 75% by
weight.
[0022] By making the drill rod of a corrosion resistant alloy, a
passive surface layer is obtained as a consequence of the addition
of chromium, which layer efficiently counteracts corrosion, above
all in the bottoms of the thread grooves. Therefore, in comparison
with conventional steels, the corrosion rate is reduced most
considerably in the sensitive thread-groove bottoms. Hence,
undertaken tests have indicated an increase of at least 50% of the
service life (from about 2000 to about 3000 drilled metres).
[0023] The positive impact of the stainless material on the service
life of the drill rod is consequently irrefutable. However, the
desirable corrosion properties have been gained on the expense of
the wear resistance of the material. Thus, the martensite steel of
the rod has a hardness of about 50 HRC, while a conventional rod
material in the form of hardened steel has a surface hardness
within the range of 57-62 HRC.
[0024] Advantageously, the material of the sleeve 7 may be a
hardened low-alloy steel, e.g., case-hardened or carburized steel,
since the problems with corrosion fatigue in the sleeve are not as
critical as the problems with such fatigue in the thread-groove
bottoms of the drill rod.
[0025] Reference is now made to FIG. 5, which on an enlarged scale
illustrates the two helix thread ridges 5A, 15A that form the male
thread and the female thread, respectively. The male thread ridge
5A has a profile shape that is defined by a crest 20 and two flanks
21, 22, which delimit a root or a groove 23 that has a bottom 24
and, like the proper ridge, extends helically along the rod. In
this case, the profile shape is symmetrical by the fact that the
flanks 21, 22 are inclined at equally large angles. In the example,
the thread ridge crest 20 has the shape of a helix surface having a
width B1 that determines the cross-sectional area of the thread
ridge 5A. The cross-sectional area of the thread ridge 5A of the
male thread 5 is calculated from a tangent T2 of the crest 20 of
the female thread 15, while the cross-sectional area of the thread
ridge 15A of the female thread 15 is calculated from a tangent T1
of the crest 25 of the male thread 5, such as the same are
represented by the shaded fields in FIG. 5. Furthermore, the groove
bottom 24 of the male thread has a smoothly rounded cross-section
shape, which substantially is defined by an arc line. The
cross-sectional area of the thread ridge 5A is larger than the
imaginary cross-sectional area of the groove 23. The imaginary
cross-sectional area of the groove 23 is determined by the area
between the tangent T1, the bottom 24 and the flanks 21 and 22.
[0026] In the same way as the male thread ridge 5A, the female
thread ridge 15A is delimited by a crest 25 and two flanks 26, 27,
between which a helix groove 28 having a bottom 29 is delimited. In
the example, said groove bottom 29 is defined by a straight
generatrix. The crest 25 of the female thread ridge has a width B2
that may be smaller than the width B1 of the crest surface 20. This
means that the cross-sectional area of the female thread ridge 15A
may be smaller than that of the male thread ridge, from which it
follows that the wear volume of the male thread ridge may be larger
than the wear volume of the female thread ridge. In the example,
the wear volume of the female thread ridge 15A amounts to about
81.8% of the wear volume of the male thread ridge. In other words,
the wear volume of the male thread ridge is about 22% larger than
the wear volume of the female thread ridge. However, this
proportion between the respective wear volumes may vary most
considerably, above all depending on the choice of material of the
rod and the coupling sleeve, respectively. More precisely, the
greater the difference in wear resistance/surface hardness there is
between the stainless steel of the male thread and the hardened
steel of the coupling sleeve, proportionally the larger wear volume
the male thread ridge 5A may have. Therefore, in practice, the male
thread ridge may be given a wear volume that is more than 20 or
25%, e.g., 50-75%, larger than the wear volume of the female thread
ridge.
[0027] In FIG. 3, A, B, C, D and E designate a number of axially
spaced-apart cross-planes, which extend perpendicularly to the
centre axis CL of the rod and between which the rod 1 has
longitudinal sections of different character. Between the planes A
and B, the male thread 5 extends with full thread (with the
exception of a tapering entering surface 37 adjacent to the end
surface 2). The outer diameter of the thread ridge (counted along
the thread crest 20) is designated D1, while D2 designates the
inner diameter of the groove bottom 24. Between the planes B and C,
a generally cylindrical envelope surface 30 extends, in which the
thread groove 23 runs out. The envelope surface 30 may
advantageously have the same diameter as the outer diameter D1 of
the thread 5. Furthermore, between the planes C and D, a
rotationally symmetrical, more precisely cylindrical guide surface
31 is delimited, which has a diameter D3 that is larger than the
diameter of the envelope surface 30 and thereby also larger than
the outer diameter D1 of the thread. Said guide surface 31 is
formed between the male thread and a tapered waist or reduction 32,
which extends between the cross-planes D and E. Approximately
halfway between the cross-planes D and E, the waist 32 has a
smallest diameter D4, which advantageously is at most as large as
the inner diameter D2 of the male thread 5. Suitably, the smallest
diameter D4 of the waist 32 is even somewhat smaller than the
diameter D2 of the thread-groove bottom. The waist 32 transforms
into the guide surface 31 and the hexagonal main section 3,
respectively, via concavely arched, successively expanding
transition surfaces 33, 34. Alternatively, the hexagonal main
section may be a round section.
[0028] The hexagon shown in FIG. 4, which forms the main section S
of the drill rod, has a cross-sectional area determined by the
width dimension H between two diametrically opposed, planar
surfaces. The inner diameter of the flush duct 4, which is
designated D5, is considerably smaller than the dimension H.
[0029] The axial lengths of the different bar sections are
designated L1, L2, L3 and L4. In FIG. 3, it is seen that the length
L1 of the thread 5 is greater than the length L2 of the envelope
surface 30, which in turn is greater than the length L3 of the
guide surface 31. Just the guide surface 31 has a limited length
L3. More precisely, the guide surface 31 may be considerably
shorter or thinner than the envelope surface 30 in which the thread
groove runs out. The guide surface 31 of the drill rod 1 has a
diameter D3 that is at least twice as large as the axial length L3
thereof. The length L4 of the waist 32 may advantageously be only
somewhat smaller than the length L1 of the full-profile thread.
[0030] In one practical embodiment, the male thread 5 has a length
L1 of 75 mm and an outer diameter D1 of 38.7 mm, while the inner
diameter D2 of the thread-groove bottom amounts to 34 mm. This
means that the male thread ridge has a height of about 2.3 mm. The
envelope surface 30 may have a length L2 of 17 mm and a diameter of
38.7 mm, i.e., the same diameter as the outer diameter D1 of the
thread. However, the guide surface 31 has a diameter D3 that is
larger than the diameter D1 and, in the practical example, amounts
to 39.1 mm. In other words, the diameter difference between the
guide surface 31 and the envelope surface 30 amounts to 0.4 mm. The
axial extension L3 of the guide surface 31 may then be limited to 7
mm. In the example, the smallest diameter D4 of the waist 32
amounts to 32.9 mm. In other words, in this case the diameter D4 is
about 1.1 mm smaller than the diameter D2 of the thread-groove
bottom. The axial length L4 of the waist amounts to about 57
mm.
[0031] The coupling sleeve 7 (see FIG. 2) is formed with an
internal guide surface 35 positioned between the female thread 15
and the free end 11 of the sleeve, for the co-operation with the
external guide surface 31 of the drill rod. Said guide surface 35
is also rotationally symmetrical, preferably cylindrical, the same
having a diameter D6 that is only somewhat larger than the diameter
D3 of the guide surface 31. The guide surface 35 has an axial
length L6, which is greater than the thickness L5 of the partition
wall 10. In the practical embodiment example, D6 amounts to 39.2
mm, which means that the gap between the surfaces 31, 35 amounts to
only 0.05 mm. In other words, the fit between the guide surfaces
31, 35 is fine.
[0032] Between the guide surface 35 and the end surface 11 of the
sleeve, a chamfer 36 is formed in order to facilitate the insertion
of the drill rod into the sleeve.
[0033] When the male thread 5 of the drill rod is screwed ,into the
female thread 15 of the sleeve into full engagement with the end
surface 2 pressed against the wall surface 18, the guide surface 31
is located in the immediate vicinity of the chamfer 36. In other
words, in this state the guide surface 31 is maximally axially
spaced apart from the partition wall 10 of the coupling sleeve.
This means that possible tendencies of the drill rod to deflect or
turn inside the sleeve are efficiently counteracted by the
co-operating guide surfaces 31, 35.
[0034] By the fact that the waist 32, which is arranged axially
inside the male thread 5, has a reduced diameter, a flexibility or
elastic compliance is obtained in comparison with the hexagonal
main profile S as well as the different sections closer to the end
of the rod, which are thicker than the waist. This means that the
deflection tendencies of the drill rod, which inevitably arise
during practical drilling, are absorbed by the elastic waist rather
than propagating to the threaded joint between the drill rod and
the sleeve.
[0035] A fundamental advantage of the drilling tool according to
the invention, composed of the drill rod, the coupling sleeve and a
bit (not shown), is that the same has optimised properties in
respect of service life as well as technical performance. Thus, the
combination of the flexible waist and the two co-operating guide
surfaces between this and the threaded joint provides the effect
that the deflection motions of the drill rod are absorbed in the
waist, without propagating into the proper threaded joint. This
means that the wear of the threaded joint is limited to the wear,
inevitable per se, that arises as a consequence of the transfer by
the shank adaptor of impact and rotary motion, but which does not
grow worse or get accelerated by the deflection phenomena.
According to another aspect of the invention, the use of the
martensitic, stainless steel in the male thread of the drill rod
counteracts corrosion fatigue therein to a far-reaching extent.
Simultaneously, it is guaranteed that the expensive drill rod
obtains at least as long service life as the cheaper coupling
sleeve.
[0036] Even if the invention above has been described in connection
with a rock-drilling tool that is intended for drifter drilling and
comprises only one drill rod and one coupling sleeve, the same is
also applicable to rock-drilling tools having two or more rods and
coupling sleeves, respectively.
[0037] The disclosures in Swedish patent application Nos. 0601117-5
and 0601119-1, from which this application claims priority are
incorporated herein by reference.
[0038] The invention is in no way limited to the above-described
embodiments but can be freely varied within the limits of the
appended claims.
* * * * *