Background of the Invention
Field of the Invention
The present invention relates to plier/cutter hand tools, in particular,
to tools such as lineman's tools which are designed for use in applications where
they may be exposed to high electrical voltage or current.
Description of the Prior Art
It is important in certain electrical applications that hand tools,
such as pliers, cutters and the like, be electrically non-conductive to protect
the user from electrical shock and to prevent short circuitry of electrical circuits.
It is well known to provide electrically insulating sheaths or coatings on the
handles of such tools, but such coatings provide limited electrical protection,
being unsuitable for use in very high-voltage or high-current environments, such
as may be encountered by an electrical utility lineman. Furthermore, such sheathing
or coating can be degraded by cutting, scratching and the like, which seriously
impairs its electrical insulating efficiency.
It is known to provide hand tools with handle portions formed entirely
of electrically non-conductive or insulating materials, such as plastics and the
like. Such tools have worked effectively in protecting the user from shock resulting
from electrical conductivity through the handle. However, it has been typically
necessary that the working portions, such as the jaws of pliers, cutters and the
like, be formed of metal in order to provide the requisite strength, hardness
and toughness for the particular tool application. Such metal working parts are
subject to sparking and/or to magnetization, which renders them unsuitable for
Another difficulty with cutter tools is that the cutting edges tend
to wear and dull with use, necessitating reconditioning. It is known to provide
hand tools such as pliers, cutters and the like, with replaceable metal jaw inserts,
but this does not avoid the sparking and magnetization problem.
Various types of cutting tools have been provided heretofore with
blades formed of material, such as ceramic, which has excellent wear-resistance
characteristics. However, most ceramic materials are less tenacious than metals
and have a tendency to chip or crack and, because of their hardness, once chipped,
they are difficult to recondition. Furthermore, previous attempts at ceramic cutter
design have proved to be difficult and expensive, since cutting edge and platen
designs cannot be molded directly and require expensive machining.
US-A-4023450 discloses pliers made from a plastic material which
is preferably reinforced with glass fibers, the pliers including crossed levers
with handles on one side of a non-metallic pivot joint and jaws on the other side
GB-A-945804 discloses cutting/gripping pliers including crossed levers
with handles on one side of the pivot and jaws on the other. The handles are enclosed
in a plastic insulating material. Each jaw has a serrated gripping portion and
a cutting portion.
Each of US-A-3947905 and US-A-4953248 discloses an electrician's
hand tool of the plier/cutter type with serrated gripping surfaces and cutting
surfaces disposed in shearing relationship with each other. In US-A-3947905, the
gripping surfaces and the cutting surfaces are both on the jaw side of the pivot,
with the cutting surfaces being closer to the pivot. In US-A-4953248 the cutter
blades are removably secured to the jaws and component parts of the tool, such
as the gripping surfaces, may be differentially hardened to withstand the stresses
to which these portions are subjected.
Summary of the Invention
It is a general object of the invention to provide an improved hand
tool which avoids the disadvantages of prior hand tools while affording additional
structural and operating advantages.
An important feature of the invention is the provision of a hand
tool which is substantially non-conductive, non-sparking, non-magnetic, non-corroding
In connection with the foregoing features, another feature of the
invention is the provision of a hand tool of the type set forth which has gripping
and/or cutting inserts on the tool jaws.
In connection with the foregoing feature, a further feature of the
invention is the provision of a hand tool of the type set forth, wherein the inserts
are formed of a wear-resistant ceramic material designed with shear action cutting
A still further feature of the invention is the provision of a hand
tool of the type set forth wherein the tool body is formed of a composite, glass-fiber-reinforced,
Another feature of the invention is the provision of a hand tool
of the type set forth which is of relatively simple and economical construction.
A still further feature of the invention is the provision of a method
of making a hand tool of the type set forth.
These and other features of the invention are attained by providing
a non-electrically conductive and non-sparking pivoting plier/cutter hand tool
including first and second lever members respectively having cooperating jaws
at adjacent ends thereof and each formed entirely of plastic material, a pivot
mechanism having no exposed metallic portions pivotally interconnecting the lever
members in intersecting relationship for pivotal movement between open and closed
conditions of the jaws, and first and second ceramic inserts respectively fixedly
secured to the jaws in opposed relationship, each of the inserts having a serrated
gripping portion and a cutting surface, said cutting surfaces being substantially
parallel and disposed for movement in shearing relationship with each other when
the jaws are moved from the open to the closed condition thereof.
Although particular embodiments of the invention have been described
in detail for purposes of illustration, it is recognized that modification and
variations may readily stem to those skilled in the art, the scope of protection
being determined by the appended claims.
Brief Description of the Drawings
For the purpose of facilitating an understanding of the invention,
there is illustrated in the accompanying drawings a preferred embodiment thereof,
from an inspection of which, when considered in connection with the following
description, the invention, its construction and operation, and many of its advantages
should be readily understood and appreciated.
Description of the Preferred Embodiment
- FIG. 1 is a top plan view of a plier/cutter tool in accordance with the present
- FIG. 2 is an enlarged, fragmentary view in vertical section taken along the
line 2-2 in FIG. 1;
- FIG. 3 is a still further enlarged view in vertical section taken along the
line 3-3 in FIG. 1;
- FIG. 4 is a fragmentary view in horizontal section taken along the line 4-4
in FIG. 2;
- FIG. 5 is a front perspective view of the ceramic insert of the jaw of FIG.
- FIG. 6 is a view similar to FIG. 5, on a reduced scale, of an alternative form
of the ceramic insert;
- FIGS. 7 and 8 are views similar to FIG. 6 of a pair of ceramic inserts in accordance
with another embodiment of the invention;
- FIG. 9 is a top plan view of a female mold member for use in forming the lever
members of the tool of FIG. 1;
- FIG. 10 is a view vertical section taken along the line 10-10 in FIG. 9 and
illustrating the male mold member with the mold open;
- FIG. 11 is a view similar to FIG. 10, showing the mold closed;
- FIG. 12 is a side elevational view of the finished lever member formed by the
mold of FIGS. 9 and 10, and illustrating the formation of the pivot bore therethrough;
- FIG. 13 is a sectional view of a die apparatus for forming the ceramic insert
of FIG. 5; and
- FIG. 14 is a diagrammatic view of an oven facility for sintering the insert
formed by the die apparatus of FIG. 13.
Referring to FIG. 1, there is illustrated a pivotal hand tool in
the nature of a plier/cutter tool 20, constructed in accordance with and embodying
the features of the present invention. The tool 20 includes a pair of elongated
lever members 21 and 21A which are substantially identical in construction. Accordingly
like parts of the lever members 21 and 21A bear the same reference numbers with
the reference numbers of the lever member 21A bearing the suffix "A" for purposes
of distinguishing the two lever members. The following description will be principally
with respect to the lever member 21, and it will be appreciated that, although
they may not all be specifically mentioned, the lever member 21A has like parts.
Referring also to FIG. 2, the lever member 21 includes an elongated
handle portion 22 at one end thereof and a jaw 30 at the other end thereof interconnected
by a reduced-thickness neck portion 23, which has a flat, planar inner surface
24 bounded at the rearward and forward ends thereof, respectively, by shoulder
walls 25 and 26. Formed through the neck portion 23 is a cylindrical bore 27.
Referring also the FIGS. 3 and 4, the jaw 30 has substantially parallel
side surfaces 31 and 32 interconnected by an outer surface 33, which terminates
at the forward end of the jaw 30 in a nose surface portion 34. The side surfaces
31 and 32 are also interconnected by a serrated inner surface portion which is
opposite the outer surface 33 and defines a plurality of sawtooth-like ribs 35,
and which terminates at the rearward end thereof in an end surface 36 and at the
forward end thereof in a lip surface 37 disposed substantially perpendicular to
the nose surface portion 34.
The lever member 21 is of unitary, one-piece construction, being
formed of a composite plastic material, preferably by a compression molding process
which will be described more fully below. Specifically, the lever member 21 is
molded from glass-fiber-reinforced thermoset polymer matrix sheet molding compound,
with the glass-fiber reinforcement being utilized in chopped or discontinuous
random form. Alternatively, continuous, unidirectional glass-fiber reinforcement
could be used. Preferably, the thermoset polymer matrix molding material is vinyl
ester, which affords significant processing advantages, including fast cure rate
and high workability. However, the lever member 21 could be formed of glass-fiber-reinforced
epoxy materials or other plastics.
Referring also to FIG. 5, there are respectively fixedly secured
to ribbed surfaces of the jaws 30 and 30A, as by a suitable adhesive 38, two inserts
40 and 40A which are substantially identical in construction. Thus, the parts
of the insert 40A bear the same reference numerals as the like parts of the insert
40, but with a suffix "A", but the description will be principally in terms of
the insert 40, in the same manner as was described above in connection with the
lever members 21 and 21A.
The insert 40 is of unitary, one-piece construction, and is preferably
formed from powdered ceramic material dry compressed in a die and then sintered,
as will be explained more fully below. The insert 40 has a pair of parallel side
surfaces 41 interconnected at the opposite ends thereof by front and rear end
surfaces 42. The side surfaces 41 are also interconnected at the forward end of
the insert 40 by a flat, planar outer surface 43 which has a plurality of transversely
extending, sawtooth-shaped serrations or teeth 44 formed therein to provide a gripping
surface. The opposite side of the insert 40 is provided with an inner surface
with lateral serrations defining a plurality of transversely extending ribs 45.
The insert 40 is provided on the outer side of its rear end with a retaining surface
47 and a recessed surface 48 joined by a shear surface 49 which extends substantially
perpendicular to the recessed surface 48. The recessed surface 48 is disposed
substantially parallel to the outer surface 45. The retaining surface 47 intersects
the shear surface 49 at a cutting edge 46 and slopes laterally outwardly and downwardly
away from the edge 46.
It will be appreciated that the width of the insert 40 is substantially
identical to the width of the jaw 30, while the inner surface of the insert 40
which defines the ribs 45 is shaped and dimensioned for mating engagement with
the inner surface of the jaw 30 which defines the ribs 35 in a mounted condition,
with the adhesive 38 being disposed between the two mating surfaces. In this mounted
condition, it will be appreciated that the side surfaces 41 of the insert 40 are
respectively substantially coplanar with the side surfaces 31 and 32 of the jaw
30, with the rear end surface 42 of the insert 40 abutting the end surface 36 of
the jaw 30, and with the front end surface 42 of the insert 40 being substantially
continuous with the nose surface portion 34 of the jaw 30. Preferably, the adhesive
38 is a two-part epoxy adhesive which effectively permanently bonds the insert
40 to the jaw 30.
In assembly of the lever members 21 and 21A, they are arranged in
intersecting relationship, with the neck portions 23 and 23A overlapping, with
the inner surfaces 24 and 24A in facing relationship and with the bores 27 and
27A coaxially aligned. The lever members 21 and 21A are then pivotally interconnected
by a pivot assembly 50 (FIG. 2), which includes a cylindrical pin 51 which is press-fitted
in the aligned bores 27 and 27A, the pin 51 being provided at one end thereof
with an enlarged head 52 which may be slotted. Preferably, when the pin 51 is inserted,
it is fitted through an annular retaining ring 53 which receives the head 52,
the pin 51 being inserted until the retaining ring 53 is held firmly against the
outer surface of the associated one of the lever members 21 and 21A (21, as illustrated)
by the head 52. The other end of the pin 51 has an internally threaded axial bore
54 therein, in which is threadedly received a screw 55 having a slotted head 56.
Preferably, the shank of the screw 55 is received through an annular retaining
ring 57, which is substantially identical to the ring 53, the screw 55 being threaded
into the pin 51 until the retaining ring 57 is held firmly against the outer surface
of the associated lever member 21A by the head 56. Thus, the pin 51 and the screw
55 cooperate to define a pivot shaft interconnecting the lever members 21 and 21A
for pivotal movement between the closed condition illustrated in FIG. 1 and an
open condition (not shown). The screw 55 is tightened until the parts are firmly
secured together while allowing substantially free pivotal movement. Caps 58 are
respectively snap-fitted over the retaining rings 53 and 57 for concealing them
and the heads 52 and 56. The caps 58 are formed of an electrically non-conducting
material, such as a suitable plastic or rubber, and they cooperate with the neck
portions 23 and 23A to completely enclose the pivot assembly 50, so that no metallic
portion thereof is exposed.
It is a significant aspect of the invention that when the parts are
thus assembled, the inserts 40 and 40A are disposed in opposed facing relationship
so that, when the jaws 30 and 30A are closed, the outer surfaces 43 and 43A of
the inserts 40 will be disposed in an abutting, substantially coplanar relationship.
It will be appreciated that the teeth 44 and 44A define cooperating gripping surfaces
for gripping associated workpieces in a known manner. The shear surfaces 49 and
49A are disposed in facing, parallel, closely-spaced shearing relationship with
each other, as can best be seen in FIG. 3. More particularly, it is important
that the parts be carefully aligned so that the clearance distance between the
shear surfaces 49 and 49A is less than 0.076 mm (0.003 inch) to ensure proper
shearing action. The sloping nature of the retaining surfaces 47 and 47A serves
to decrease the included angle at the cutting edges 46 and 46A, providing a narrower
cutting edge, and also serves to provide clearance, which has been found to reduce
the tendency for separation of the jaws 30 and 30A axially of the pivot assembly
50 during use.
Referring to FIG. 6, there is illustrated an alternative form of
insert, generally designated by the numeral 60, which could be substituted for
the inserts 40 and which is substantially similar thereto with like parts bearing
the same reference numbers. The fundamental difference is that the insert 60 has
a retaining surface 67 which, instead of sloping, is substantially parallel with
the recessed surface 48. The insert 60 operates in substantially the same manner
as the insert 40, but it exhibits a greater tendency to axial spreading of the
jaws 30 and 30A.
In FIGS. 7 and 8, there is illustrated another alternative form of
insert. In this case, the inserts on the jaws 30 and 30A are not identical, but
are rather complementary and are respectively designated by the numerals 70 and
75. Again, each is substantially similar to the insert 40, with like parts bearing
the same reference numbers. The insert 70 has at its rear end a flat planar retaining
surface 71 from which there projects, centrally thereof, a tongue 72 which is substantially
rectangular in transverse cross section and defines a pair of parallel shear surfaces
73 and 74. The insert 75, on the other hand, has a flat, planar retaining surface
76 in which is formed centrally thereof an elongated groove 77, which is substantially
rectangular in transverse cross section and defines a pair of parallel shear surfaces
78 and 79. In operation, the tongue 72 is adapted to fit in the groove 77 with
the shear surfaces 73 and 74 respectively cooperating with the shear surfaces 78
and 79 to provide a double shearing action. This arrangement effectively eliminates
the tendency for axial jaw spreading, but requires a greater cutting force than
do the inserts 40 and 60.
It is a significant aspect of the invention that, except for the
pivot assembly 50, the plier/cutter tool 20 has no metallic parts, being formed
substantially entirely of electrically insulating, non-sparking, non-corroding
materials, lightweight and non-magnetic. Furthermore, the ceramic inserts 40,
60 and 70 afford excellent cutting performance, their shear edges having high wear
resistance and superior hardness and strength, while maintaining the non-conductive,
non-sparking, non-corroding and non-magnetic characteristics of the tool 20.
It is another significant aspect of the invention that it is of relatively
simple and economical construction. More specifically, the lever members 21 and
21A may be formed by molding techniques, and the inserts 40, 60 and 70 may be
formed by conventional ceramic manufacturing methods. Referring to FIGS. 9-11,
the method of forming the lever member 21 will be described. The lever member 21
is formed by a compression molding process utilizing cooperating female and male
mold members 80 and 85, respectively. The female mold member 80 has a mold cavity
81 defined therein with a raised portion 81a to form the reduced thickness neck
portion 23. A mold charge 82 is disposed in the cavity 81 and comprises a stack
of a plurality of plies 83 of sheet molding compound, which is commercially available
and may be of the type disclosed in the applicant's copending European patent
application No. 93106970.2 (578937) and entitled "Composite Hand Tool," the disclosure
of which is incorporated herein by reference representing a state of the art within
the meaning of Art. 54(3)EPC. As can be seen in FIGS. 9 and 10, the mold charge
82 has an area which is less than that of the cavity 81, but which has a thickness
greater than that of the finished product so that, during the molding operation,
the charge 82 may be permitted to flow to fill the entire cavity 81 to the desired
finished product thickness. As is explained in the aforementioned copending application,
Serial No. 913,221, the specific molding temperature, pressure and cycle and cure
times may vary according to the part size and mold charge placement.
In operation, the mold members 80 and 85 are brought together (FIG.
11), typically under hydraulic pressure, compressing the mold charge 82 in a known
manner to mold a finished lever member blank 86 (see FIG. 12). Preferably, the
mold member 85 has a core pin 84 projecting therefrom which forms a cylindrical
recess 87 in one surface of the blank 86. After molding, the recess 87 serves as
a pilot for a boring or reaming tool 88 which forms the through bore 27 in the
lever member 21, as is indicated in FIG. 12. It will be appreciated that, while
the lever member 21 is formed from a plurality of layers of the sheet molding
compound, the finished molded product is essentially a single layer composite of
unitary, one-piece construction. Because the plastic materials used to make the
lever member 21 include no metallic components, the finished product is non-conductive,
non-magnetic and non-sparking, and is also corrosion resistant and lightweight
and has reduced tendency to mar workpieces.
While compression molding is the preferred technique for forming
the lever member 21, it could also be formed by transfer molding, wherein a slug
of plastic material is placed in a heated transfer chamber and injected into the
Referring also to FIGS. 13 and 14, the method of forming the insert
40 will be described. The insert 40 is formed in a die member 90 which defines
a cavity 91 which is filled with a powdered ceramic material with a suitable binder.
Preferably, the ceramic material is a transformation toughened zirconia ("TTZ")
partially stabilized with magnesia, and may be of a type commercially available
from Coors Ceramics. The powdered ceramic material 92 is dry compressed in the
die 90 with a ram 94 to net shape. In this regard, it will be appreciated that
the die member 90 may have a sawtooth-shaped bottom surface 93 to form the ribs
45 in the finished insert, while the ram 94 has suitable formations thereon to
form the teeth 44 and the surfaces 47-49 of the insert 40. As a result of this
dry compression process, there is formed a "green" part 95 which is then fed through
a sintering oven 96 (FIG. 14) to develop part strength. In the oven 96, the part
95 is heated at an elevated temperature below the melting point of the ceramic,
but sufficiently high to allow diffusion to take place between the ceramic powder
particles. It will be appreciated that the inserts 60, 70 and 75 are formed in
the same manner.
It is a significant aspect of the present invention that the inserts
40 (and 60, 70 and 75) have superior toughness and resistance to cracking or chipping.
This results from a phase transformation toughening. More specifically, zirconia,
and certain other materials, tend to have two or more stable crystallographic phases.
The magnesia partially stabilizes a crystallographic phase that is normally stable
at higher temperatures. As a result, upon the occurrence of a local stress perturbation,
as happens with the advance of a crack front, there is triggered a transformation
to another crystallographic phase. In the case of zirconia ceramics, four-fold
increases in toughness have been demonstrated by partial stabilization of a phase
change from the high-temperature stable cubic phase to the low-temperature tetragonal
phase. In zirconia the transformation from cubic to tetragonal phase is accompanied
by a volume increase. Within the confines of a ceramic body, this expansion acts
as a compressive force to close an advancing crack. The result is that it is difficult
for the crack to propagate.
From the foregoing, it can be seen that there has been provided an
improved pivoting hand tool which is of simple and economical construction, and
which is essentially non-electrically conductive, lightweight, non-sparking, non-magnetic
and corrosion resistant, while providing gripping and cutting surfaces which have
superior strength, hardness, toughness and wear resistance.