Magnetic tightening tool for preventing overtightening and undertightening

A tightening tool comprises a head having a socket for a nut to fit in, a head support supporting the head rotatably about the axis of the socket, and a handle integral with the head support. A magnet is attached to each of the head and the head support. The head and the head support are joined together by a force of attraction permitting these portions to rotate relative to each other upon the torque of tightening up the nut reaching a proper value. When the head support is rotated by turning the handle by hand, the head moves with the head support to tighten the nut. After the nut tightening torque has reached the proper value, the head support merely rotates idly with the head and the nut remaining unrotated even if the handle is turned.

BACKGROUND OF THE INVENTION 
The present invention relates to tightening tools for use in cases 
involving the problem of over-tightening or undertightening as in 
tightening up pipe joints. 
The production equipment of the chemical industry and semiconductor 
industry includes piping systems for transporting or controlling fluids 
and maintaining or controlling a vacuum. Joints are generally used for 
connecting pipes together and for connecting a pipe to a valve, flow meter 
or like instrument, or reactor. High gastightness, corrosion resistance to 
fluid substance and a superhigh degree of cleanliness with the utmost 
freedom from dust are required of the piping system especially in the 
semiconductor industry. For example, FIG. 8 shows a joint which is used as 
the most suitable one from this viewpoint. 
With reference to the drawing, a first joint member 21 and a second joint 
member 22 are butted against each other with an annular gasket 23 
interposed therebetween, and the first joint member 21 is fastened to the 
second joint member 22 with a nut 24 provided on the second member 22 and 
screwed on the first member 21. A pipe 25 is inserted in the second joint 
member 22 from the other end thereof and fixed to the second member 22 at 
a welded portion 26. Gasket holding annular ridges 27, 28 are formed on 
the butting ends of the first and second joint members 21, 22, 
respectively, The gasket 23 is held to the end of the first joint member 
21 by a retainer 29. 
With the pipe joint described, it is not desirable that the nut tightening 
torque be too small or too great. If the torgue is too small, gastightness 
is not available, while too great a torque will excessively deform or 
break the gasket 23 to result in creation of dust or lower corrosion 
resistance, consequently leading to impaired gastightness. Thus, it is 
important that the nut 24 be tightened up with an appropriate torque. This 
is also true of the case wherein a metal ring, such as an O-ring or 
ferrule, is provided between the butting ends of the first and second 
joint members 21, 22 in place of the gasket 
A spanner is usually used for tightening up such a joint. The joint is 
tightened up suitably by manually tightening up the nut 24 on the first 
joint member 21, making a mark on each of the member 21 and the nut 24 in 
this state and thereafter rotating the nut with the spanner through a 
required angle (e,g., 1/4 of a turn) with reference to the marks. 
The use of the spanner as a tightening tool thus necessitates the procedure 
of making a mark on each of the first joint member and the nut as 
tightened up thereon by hand and thereafter rotating the nut with the 
spanner through the required angle while visually recognizing the marks. 
However, this procedure needs labor, depends largely on intuition and has 
the problem of low reliability, for example, because the manual tightening 
force differs from person to person or varies according to the mood of the 
moment, 
A device therefore appears useful which is adapted to tighten up the nut 
white detecting the tightening torque and determining whether the detected 
torque is proper, but such a device will be a great one and inferior to 
the conventional tool in respect of the manufacturing cost and easiness of 
use. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a tightening tool which is 
adapted to tighten up pipe joints or the like reliably without 
necessitating much labor and which is nevertheless inexpensive and easy to 
use. 
The present invention provides a tightening tool comprising a head having a 
socket for an engagement portion of a threaded member to fit in, a head 
support supporting the head rotatably about the axis of the socket, and a 
handle integral with the head support, a magnet being attached to one of 
the head and the head support, an attracted portion being provided in the 
other and attractable to the magnet, the head and the head support being 
joined together by a force of attraction so as to be rotatable relative to 
each other upon the torque of tightening up the threaded member reaching a 
proper value. 
When the head support of the tightening tool of the invention is rotated by 
turning the handle with a nut fitted in the socket of the head, the head 
and the head support, which are joined together by the force of attraction 
of the magnet, move together to tighten the nut with an increasing torque. 
Upon the tightening torque reaching a proper value, the head support 
merely rotates idly with the head remaining unrotated even if the handle 
is further turned, whereby the nut can be tightened up with the proper 
torque. When pipe joints or the like are to be tightened up, it is 
conventionally necessary to make a mark on each of the first Joint member 
and the nut as tightened up thereon by hand and thereafter rotate the nut 
with a spanner through the required angle while visually recognizing the 
marks, whereas the present invention eliminates tile need for this 
procedure, making it possible to tighten up the pipe joint or the like 
reliably without much labor. The invention further obviates the need for 
the procedure of determining whether the tightening torque is proper while 
detecting the torque. The present tool is therefore easy to use and 
inexpensive to manufacture. 
Preferably, the position of the magnet is made adjustable. The force of 
attraction is then adjustable by moving the magnet and thereby varying the 
distance between the magnet and the attracted portion. This makes it 
possible to tighten up different threaded members each with a torque 
proper thereto. 
According to an embodiment, the head support is a nonmagnetic member, and a 
ferromagnetic member is movably disposed in the magnetic circuit 
comprising the magnet and the magnetically attractable member. The 
ferromagnetic member inserted in the magnetic circuit increases the force 
of attraction of the magnet, and this force is adjustable by moving the 
ferromagnetic member within the magnetic circuit, so that the threaded 
member can be tightened up with a greater torque. It is also possible to 
tighten up different threaded members each with a torque proper thereto. 
According to another embodiment, the head support is a ferromagnetic 
member, and a nonmagnetic member is movably disposed in the magnetic 
circuit comprising the magnet and the attracted portion. The head support, 
which is ferromagnetic, then adds to the force of attraction of the 
magnet, and the force of attraction is adjustable by moving the 
nonmagnetic member within the magnetic circuit. This makes it possible to 
tighten up the threaded member with an increased torque and further to 
tighten up different threaded members each with a torque proper thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the invention will be described below with reference to the 
drawings. In the following description, the terms "upper" and "lower" are 
used based on FIG. 2; the upper and lower sides of FIG. 2 will be referred 
to by "upper" and "lower," respectively. These terms are relative, and the 
tool may be used with its upper side positioned down, laterally or 
obliquely. 
FIGS. 1 to 3 show a first embodiment of tightening tool. The tightening 
tool comprises a platelike head 1 having a socket 9 which is open at one 
side for an engagement portion of a threaded member (such as the head of a 
bolt or nut or a flange of a pipe joint) to fit in, a head support 2 
supporting the head 1 rotatably about the axis of the socket 9, a handle 3 
integral with the head support 2, and a cover 4 provided over the head 1. 
For the convenience of description, FIGS. 1 and 3 show the tool with the 
cover 4 removed. 
The head 1, head support 2 and handle 3 are each made of stainless 
The width of opening of the socket 9 is in conformity with the size of the 
engagement portion of the threaded member to be tightened up, for example, 
with the external size of the nut, size of the bolt head or size of the 
flange of the joint member. 
The head support 2 is slightly larger than the head in section. The head 
support 2 is formed with a recess 10 for the head 1 to fit in. 
The bottom surface of the head 1 is formed with two circular-arc grooves 12 
centered about the axis of the socket 9. Circular-arc guide ridges 11 
fittable in the respective grooves 12 are provided on the bottom surface 
of the recessed portion 10. 
A rectangular cavity 14 is formed in the head support 2 from above. A 
permanent magnet 5 is fitted in the cavity 14 and bonded to the support 2 
with an epoxy adhesive. A rectangular cavity 13 positioned as opposed to 
the cavity 14 of the head support 2 is formed in the head 1 from below. An 
magnetically attractable member 6 is fitted in the cavity 13 and bonded to 
the head 1 with the epoxy adhesive. 
The permanent magnet 5 is in the form of bar and fitted in horizontally. 
The magnetically attractable member 6 is a bar magnet like the magnet 5 
and fitted in in opposite relation with the magnet 5 in polarity. 
Consequently, the head 1 is joined to the head support 2 by a force of 
attraction between the magnet 5 and the magnetically attractable member 6, 
Openings 15, 16 coaxial with the socket 9 are formed in the held support 2 
and the cover 4, respectively, and are so sized as to avoid interference 
with the threaded member to be fitted into the socket 9. 
For example, in the case where a nut A on a joint (not shown) is to be 
tightened, the head support 2 is turned by holding the handle 3 with the 
nut A fitted in the socket 9 of the head 1 as seen in FIG. 3(a). Since the 
head 1 and the head support 2 are joined together by the force of 
attraction of the magnets 5, 6, the torque applied to the handle 3 is 
transmitted as it is to the head 1, moving the head support 2 and the head 
1 together to tighten the nut A (see FIG. 3(b)). Although the magnet of 
magnetically attractable member 6 is illustrated as superposed on the 
magnet 5, these magnets are opposite in porality. Stated more 
specifically, the N and S poles of the magnet of magnetically attractable 
member 6 are positioned as illustrated, but the N and S poles of the 
underlying magnet 5 are positioned in opposite relation with the N and S 
poles of the magnet of magnetically attractable member 6 (although not 
shown). With the rotation of the nut A, the tightening torque increases 
and becomes equal to the torgue due to the force of attraction between the 
magnet 5 and the magnetically attractable member 6. The head support 2 
thereafter merely rotates idly with the head 1 and the nut A remaining 
unrotated even if the handle 3 is turned (see FIG. 3(c)), Because the 
force of attraction between the magnet 5 and the magnetically attractable 
member 6 still remains although small, the head 1 will not separate from 
the head support 2, while a change in the reaction delivered to the hand 
of the worker indicates completion of tightening. 
Accordingly, the characteristics values of the magnet 5 and the 
magnetically attractable member 6 are so determined as to give a force of 
attraction which permits the head support 2 to rotate relative to the head 
1 upon the tightening torque reaching a proper value, whereby the threaded 
member can be tightened up completely without further tightening when the 
proper torque is reached. Incidentally, the optimum torque value for 
tightening up joints is, for example, about 100 kgf.multidot.cm for pipes 
having an inside diameter of 3/8 inch although variable with the type of 
pipes. 
FIGS. 4 and 5 show a second embodiment of tightening tool according to the 
invention. 
The tightening tool comprises a platelike head 31 having a socket 39 which 
is open at one side for an engagement portion of a threaded mender to fit 
in, a head support 32 supporting the head 31 rotatably about the axis of 
the socket 39, a handle 33 integral with the head support 32, and a cover 
34 provided over the head 31. For the convenience of description, FIG. 4 
shows the tool with the cover 34 removed. 
The head 31, head support 32 and handle 33 are all made of stainless steel. 
The head support 32 is slightly larger than the head 31 in section. The 
head support 32 is formed with a recess 40 for the head 31 to fit in. A 
ball bearing 48 is provided between the head 31 and the recessed portion 
40. 
Three cavities 44 close to one another are formed in the head support 32 
from above along the inner periphery of the recess 40. A permanent magnet 
35 is fitted in each of the cavities 44 and bonded to the support 32 with 
an epoxy adhesive. Three cavities 43 positioned as opposed to the 
respective cavities 44 are formed in the head 31 from above. An 
magnetically attracted member 36 is fitted in each of the cavities 43 and 
bonded to the head 3i with the epoxy adhesive. 
The permanent magnet 35 is in the form of a bar and fitted in vertically. 
The attraction member 36 is the same bar magnet as the magnet 35 and 
fitted in in opposite relation with the magnet 35 in polarity. 
Consequently, the head 31 is joined to the head support 32 by a force of 
attraction between the magnets 35 and the magnetically attractable members 
36. 
The head 31 is further provided with a restoring permanent magnet 47. This 
permanent magnet 47 is positioned in the same relation with the permanent 
magnets 36 of the head support 32 in polarity. When the head support 32 is 
rotated idly with the tightening torque exceeding the proper value, the 
magnet 47 gives the head support 32 a force acting in a direction to 
return the support 32 toward the position where the head 31 is joined to 
the support 32 with the force of attraction between the magnets 35 and the 
magnetically attractable members 36. 
Openings 45, 46 coaxial with the socket 39 are formed in the head support 
32 and the cover 34, respectively, and are so sized as to avoid 
interference with the threaded member to be fitted into the socket 39. 
The function and movement of the components of the tool of the second 
embodiment for tightening up a joint are nearly the same as those 
described for the first embodiment with reference to FIGS, 3(a) to (c). 
However, when the head support 32 of the second embodiment has rotated 
idly after the completion of tightening, the presence of the restoring 
permanent magnet 47 makes it easy for the head support to return to the 
position before the idle rotation. 
According to the two embodiments described, examples of suitable magnets 5, 
35 are powerful ones including rare earth element magnets such as 
anisotropic sintered magnets consisting essentially of neodymium, iron and 
boron. Examples of useful epoxy adhesives for fixing these magnets 5, 35 
and magnetically attractable members 6, 36 are Araldite 138 and Araldite 
150. Instead of using the adhesive, the magnets 5, 35 and magnetically 
attractable members 6, 36 may be fixed by soldering or silver brazing. 
Preferably, the magnets are smaller in size. To incease the force of 
attraction of the magnet, the magnetic flux emanating from the magnet is 
prevented from spreading out to the greatest possible extent. The magment 
exhibits a reduced force when so shaped that the N pole and S pole thereof 
are too close to each other. A greater force of attraction is available by 
uaing bar magnets as the magnetically attractable members 6, 36 and 
arranging two bar magnets with the different poles opposed to each other. 
However, the magnetically attractable members 6, 36 may be ferromagnetic 
members instead of magnets. An electromagnet may be used in place of the 
magnet to obtain a magnetic force. Although the heads 1, 31 and the head 
supports 2, 32 are made of stainless steel, other material, e.g., 
ferromagnetic iron, may used. When the heads 1, 31 and head supports 2, 32 
are prepared from stainless steel, a ferromagnetic material such as iron, 
nickel, cobalt or an alloy thereof may be bonded to a magnet to make a 
yoke to prevent the magnetic flux from spreading out and form a magnetic 
circuit. 
According to the present invention, the proper value of torque to be 
applied to the nut of the joint, i.e., the maximum torque value of the 
tightening tool, is adjustable by altering the relative position of 
magnets attracting each other, or by strengthening the magnetic circuit 
comprising these magnets. 
FIG. 6 shows an example wherein the force of attraction of a magnet is 
variable by altering the position of the magnet, i.e., a modification of 
the head support 2 shown in FIG. 2. The modified head support 51 has a 
rectangular cavity 52 for the magnet 5 to fit in. To render the magnet 5 
movable in the cavity 52 radially of the support 51, the cavity 52 is made 
larger than the magnet 5 and provided with a spring retaining recess 53 
extending radially inward. A coiled compression spring 54 is fitted in the 
recess 53, and a screw 55 for holding the magnet 5 against the force of 
the spring is radially driven into the rectangular cavity 52 from outside. 
When advanced or retracted, the screw 55 varies the distance of the magnet 
5 from the attraction member 6 to vary the force of attraction. 
FIG. 7 shows an example wherein a magnetic circuit comprising a magnet is 
strengthened or weakened to give a variable force of attraction, i.e., a 
modification of the embodiment shown in FIG. 4. A head support 61 made of 
stainless steel is formed with a slit 62 extending radially thereof and 
has an iron plate 63 movably inserted in the slit 62 and a setscrew 64 for 
locking the plate 63 in position. When the iron plate 63 is radially moved 
to the inner-most position, the inner end of the plate is positioned 
immediately below the magnet 35 and attraction member 36, while when the 
plate 63 is radially moved to the outermost position, the plate end is 
brought out of the position immediately below the magnet 35 and the 
magnetically attractable member 36. The greatest force of attraction is 
available when the inner end of the iron plate 63 is brought to the 
position immediately below the magnet 35 and the attraction member 36, and 
the force decreases as the plate inner end moves away from the position. 
Thus, the force of attraction is adjustable by moving the nonmagnetic 
plate. The plate 63 may of course be made of a ferromagnetic material 
other than iron. 
The same arrangement as shown in FIG. 7 may be provided by using iron or 
like ferromagnetic material for the head support 61 and aluminum, 
stainless steel or like nonmagnetic material for the plate 63. The head 
support 61, which is ferromagnetic in this case, increases the force of 
attraction between the magnet 35 and the magnetically attractable member 
36, while the plate of nonmagnetic material acts to reduce the force of 
attraction. The force of attraction can be adjusted by moving the 
nonmagnetic plate. 
Although the tightening tools embodying the present invention described are 
suitable for tightening up pipe joints reliably without necessitating much 
labor, the members to be tightened up by these tools are not limited to 
pipe joints but include bolts and nuts which are widely used at present in 
motor vehicles, rolling stock, aircraft and like transport machines, 
buildings, bridges and like structures, or electric apparatus, precision 
devices, machine tools, etc. Needless to say, tightening up bolts or nuts 
with a proper torque is of extreme importance in these fields in ensuring 
reliability and safety.