Note: Descriptions are shown in the official language in which they were submitted.
BA(~KGROU2~D OF THE INVENl'I ON
This invention relates to an instrument and
method for measuring tack and more particularly to a
portable tack tester.
There is a widespread need for a more effi-
cient and reliable measuxement o~f the physical property
of tack of elastomeric materials including rubber
materials. Tack is defined as the ability of two
uncured rubber or elastomeric surfaces to adhere to-
gether upon contact under moderate pressure. Tack has
also~been defined as the force per unit area required
to separate two like pieces of rubber or elastomeric
material after pressing them together. This is often
called autohesion. Tack is to be distinguished from
stickiness which is the force per unit width required
to separate a piece of rubber or elastomeric compound
from some other material, usually steel. Most of the
present instruments commercially available measure tack
by determining the pull required to separate one sample
surface from another by the force exerted in a direction
that is perpendicular to the surfaces of the sample.
Another instrument measures the peeling forces where
one sample of rubber material is peeled away from a
second sample in a direction parallel to the adhered
surfaces ~ith the result expressed as force per unit
width of the strip. Both of these instruments and their
corresponding methods measure the maximum force per
unit area or per unit width. In preparing samples for
testing in these above instruments, it is re~uired that
samples or specimens be cut by a die cutting machine to
assure the operator that the edges of the sample to be
tested be perpendicular to each other. The present
invention is directed to a portabie tack tester that
eliminates the need for precise cutting out of samples
wherein the tack tester can measure tack directly at a
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work station or taken to the processing line as on a
tread tuber line. This invention includes a new and
novel mechanism for securing the sample. A unlque
feature of the invention is that in its measurement of
tack, the instrument takes into account the time value
to thereby express the tack measurement in terms of
energy. In contrast to force per unit area the appli-
cant's units of measurement are in terms of energy per
unit contact area. The significance of this method is
that there is a strong correlation between the tack
measurement and the factory experience for quali~y
control of factory production in a factory environment.
SUM~`IARY OF THE INVE~TION
The present invention contemplates the
measuring of tack of elastomeric material wherein two
spaced specimens of material are moved into abutting
contact under a predetermined load for a predetermined
dwell time interval and thence separating the specimens
by breaking the contact therebetween in a second time
interval which is measured as Energy per unit contact
area. A load cell device measures the force exerted to
load and separate the specimens and provides a tack
reading that is based on the energy expended during
such time interval.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a front elevational vieW of a tack
testing machine of a preferred embodiment of the
invention.
Fig. 2 is a cross-sectional plan view of the
tack testing machine taken in line 2-~ of Fig. 1.
Fig. 3 is an enlarged view of the mechanism
for holding the specimen of the tack testing machine
shown in Fig. 1 with a portion thereof shown in cross-
section.
Fig. ~ is an enlarged side elevational view
of the mechanism for holding the specimen taken on line
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4-4 of ~ig. 3.
~ ~ig. 5 is an enlarged cross-sectional view of
the upper portion of the mechanism for holding the
specimen with the clamp means in a released condition.
~i,g. 6 is an exploded view of the upper
portion of the mechanism for holding the specimen.
Fig. 7 is an enlarged front elevational view
of a modified form of a specimen holding clamp.
Fig~ 8 is an enlarged front elevational view
partly broken away, of a modified form of specimen
holding means.
Fig. 9 is a cross-sectional view of the
- specimen holding means taken along lines 9-9 of E'ig. 8.
/ Fig. 10 is a diagrammatic representation of
1~ a portion of the system of Fig. 1.
Fig. 11 is a chart illustrating the force
measured as a function of time during the period of time
that the samples of material are being separated when
tack is being measured.
DETAILED DESCRIPTION
Referring now to the drawings, wherein like
.~
reference numerals designate like or corresponding
parts throughout the several views, there is shown in
Fig. 1 a base or base plate 10 generally triangular in
shape in plan view. As seen in Fig. 2, a stepping
motor 11 is mounted on the rear portion thereof, having
an output shaft connected to a drive pulley 12. Mounted
at the respective~sides of base 10 is a tubular housing
' 13. The respective housings 13 are alike and accordingly
only one will be described. A threaded shaft 14 has
its ends journaled for rotation in housing 13. The Shaft 14 and the
housing 13 act as a frame member to support a carriage to be described,
which carriage moves relative to such frame member in a manner to be
described. The lowermost end portion of housing 13 below the journaling
of shaft 14 is recessed as at 15 in the direction of pulley 12, such
that a pulley 16 keyed to shaft 14 will permit a timing belt 17 to
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substantially encompass such pulley and be directed rearward toward
- drive pulley 12.
Base 10 betw~en pu]leys 16 is recessed as at
20, ~Fig.l) such that the tack testing instrument with
~ase 10 can be placed onto a specimen to be tested. A
circular plate member 21 having a conical portion is
received by the recess 20 and is suitably secured to
the base 10. A specimen holder, to be described, is
mounted on such plate member 21. Housing 13 has a
longitudinally extending slit or recess 18 extending
from the upper-end portion thereof to below the inter-
mediate portion thereof. A carriage 24 having a pair of
laterally extending brackets 25 which extend through
the respective slits 18 are suitably secured to nuts 26
which in turn are threadedly engaged to the threaded
shaft 14. Such shaft 14 and the housing 13 act as a support or
frame member for the carriage 24. Carriage 24 moves up OT down
as controlled by the rotation of threaded shafts 14 which in turn
is controlled by the energization of stepping motor 11 with its
connection to pulleys 16 via timing belt 17. A load cell l.C is
mounted on carriage 24.
Suitably connected to carriage 24 for movement therewith
via cylindrical rods 28~ 29 and 30 is an upper specimen holder having
a first block member 42 that is trapezoidal in shape. ~ppermost rod
28 is threadably connected to the load cell LC in carriage 24 while
the lower end of rod 28 is centrally recessed as at 35 for pivotal
connection to the upper end of intermediately located rod 29 as at
36. Lower rod 30 is pivotally connected to rod 29 as at 37. The
lower end portion of rod 30 has a threaded bore 38 ~Fig. 6) to
receive a bolt 40. The block member 42 of such specimen:holder has
an upper forwardly extending portion that is recessed at both side
portions as at 44 and 45 to provide pairs of spaced abutments 46 and
47. The respective projecting abutments 46 and 47 have hori~ontally
extending aligned bores 48 receiving pins 49. In assembling such
: 35 pins 49 into such bores 48, a sleeve 50 is first inserted between the
abutments 46 and 47 in alignment with such bores 48 before the pins
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49 are slid into position. The respective lower edges
of trapezoidal block member 42 of the upper specimen
holder 61 have triangular shaped abutments 55 extending
outwardly therefrom. A bore 56 extends vertically
through the upper portion of block member 42 such that
bolt 40 extends therethrough and retains such block
member 42 to rods 28, 29 and 30. Bolt 40 is of such a
length as to provide a clearance between block member
42 and rod 30 for a purpose to be described. Cooperative
with first block member 42 is a second block member 60
which together define the upper specimen holder 61.
Block member 60 (Fig. 6) of specimen holder
61 is an arcuately shaped block having a pair of
spaced upper planar surface 62 with an abutment 63
therebetween. Abutment 63 has a bore 65 therein,
receiving a compression spring 66 which biases the
arcuate portion into contact with the laterally spaced
abutments 55. The respective outer upper ends of block
member 60 have a clevis 67-68 receiving pins 69-70 for
connection to L-shaped lever members 71-72 for pivoting
such lever members 71-72. A second pin 73 (as seen in
Fig. 3) is mounted in the respective clevises 67 and 68
below the location of pins 69-70 but parallel thereto.
~lock member 60 of upper specimen holder 61 has a pair
of spaced threaded bores 74 and 75 receiving threaded
bolts 76 and 77, which bolts 76 and 77 ride in vertically
extending slots 80 and 81 in trapezoidal shaped block
member 42. This permits the vertical movement of block
member 60 relative to block member 42.
The respective L-shaped lever members 71-72
pivotally mounted on block member 60 as on pins 69 and
70 have inwardly extending abutments 82 and 83 which
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ride on the respective sleeves 50. Rotation of the
upper ends of lever members 71-72 toward each other
about pins 69 and 70 will move the lower specimen
holder portion 60 upwardly relative to the triangular
shaped abutments 55 providing a clearance space between
such abutments 55 and the lower arcuate surface of
block member 60 so as to permit the insertion of a
sample along the arcuate surface and into such clearance
- space, as shown in Fig. 5. Release of the lever members
71 and 72 will move the block member 60 downwardly
relative to abutments 55 to clamp the specimen 85 in
position due to the biasing action of spring 66 as seen
in Fig. 1 and 3.
' As seen in Figs. 1 and 4, a lower specimen
holder 86 has a post 87 suitably secured to the circular
plate 21 which in turn is suitable connected to the
base 10. Vertically extending post 87 has a horizontally
disposed block 90 with a dovetail groove 91 extending
therethrough ~Fig. 3). A bore in block 90 and post 87
receives a spring 93 which biases a ball 94 located
directly above it into one of a plurality of recesses
95 ~Fig. 4) in the lower surface of a slide member 96
thus acting as a detent. Slide member 96 has a dovetail
lower portion which is slidingly received by the groove
91 to guide the slide member 96 on block 90. The
respective outer ends of slide member 96 has a bore for
receiving a pin 97. Pivotally mounted on each pin 97
on each end of slide member 96 is a plate member 100
having a bifurcated upper end portion that receives
such pin 97. Only one side of lower specimen holder 86
will be described, it being understood that like elements
are located on the other side of slide member 96, which
elements -are designed with like numerals. The respective
intermediate side portions of plate member 100 each
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have a block 101 pivotally mounted thereon as at 102.
Each b]ock 101 has a bore 103 extending vertically
therethrough. A latch member or means is slidably
mounted on each side pair of blocks 101 and includes a
pair of vertically moveable rods 106 slidably received
by bores 103. The upper portion of the pair of rod 106
which is square in cross-section includes cross rods
107. That portion of each rod 106 located below block
101 has a spring 108 encompassing it with the lower end
portion of spring 108 seated on a nut 109 -threaded
thereon. Such latch member or latch means is coopera~
tive with a flat plate 110 which has groove 111 along
the respective outer edge portions for receiving one of
' the cross rods 107. Plate member 110 has a plurality
of laterally spaced rectangular openings 112 for the
purpose of exposing a sample of material to be tested.
A sample of material 113 to be tested is placed on the
upper flat surface of slide member 96, afterwhich the
plate member 110 is placed over the sample as depicted
by Fig. 4. The respective latch means are then used to
secure the sample by swinging or pivoting the pair of
vertically moveable rods 106 about pins 97. As seen in
Fig. 4, the rods 106 on the left has the lower portion
pivoted in a counterclockwise direction so that one of
the rods 107 engages the groove or recess 111 on plate
member 110 while its corresponding plate member 100 is
swung counter clockwise so that pivot 102 is also swung
beyond the pin 97~thereby movin~ the plate ~ember 100
beyond dead center. The spring 108 exerts a downward
pressure on rod 106 and the rod 107 to clamp the plate
member 110 into abutting engagement with the sample
113. Simultaneously with this action plate member 100
and rod 106 on the right side of the apparatus as seen
in Fig. 4 is operated in a similar manner to positively
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secure the sample 113 in position for testing. It will
be observed in the right hand side of Fig. 4, that when
plate member 100 is pivoted counter cloc~wise about
pivot 97, that the sample will be released when pin 102
is moved counter clockwise a sufficient distance past
the vertical line passing through pivot or pivot pin
97.
In the operation of the apparatus as described
above, the operator places a flat sample of material on
the slide member 96 and clamps the material in place
with the latch means as described above through the
pivotal movement of the plate members 100 which has
rods 107 engaging the recesses 111 on the top plate
' 110. The slide member 96 is moved rectilinearly on
block 90 to allow ball 94 to engage one of the recesses
95 which aligns one of the openings 112 and the sample
of material exposed thereby for contact with the
specimen of material to be positioned on the upper
specimen holder 61. To load the upper specimen holder
61, a strip of material 85 to be tested is placed
around the arcuate portion of holder 61 as disclosed by
Fig. 5. It will be noted that in Fig. 5 the levers 71
and 72 are biased toward each other which action pivots
the levers 71 and 72 about pivot means 69 and 70 while
abutments or extensions 82 and 83 of levers 71 and 72
engage collars 50 to maintain the specimen holder 61
upwardly relative to trape~oidal shaped bloc~ member 42
and abutments 55.- ~hen the specimen 85 is in position,
the lever ~embers 71 and 72 are released and will move
the specimen holder 61 with the specimen 85 downwardly
due to the action of spring 66 until the sample or
specimen 85 engages the laterally spaced abutments 55.
I-t should be noted that the cylindically shaped weight
120 with a central bore 121 CFig. 6~ is assembled onto
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rod 30 prior to securing of screw 40 thereto which
provides a pre~etermined force between the specimens 85
and 113. With the specimens 85 and 113 retained in
their respec-tive holders as described above, the
operator actuates the stepping motor 11 by depressing
the appropriate start key on keyboard 125 which through
microcomputer 126 sends a signal to energize the
stepping motor 11. A load cell designated LC in Figs.
1 and 10 is continually sensing the load on the rods
28, 29, 30 and the upper specimen holder 61. Assuming
a 20 psi pressure from weight 120, the load cell via
analogue to digital unit 127 continually sends this
loading weight as a signal along with the weight of the
~ rod and the specimen holder 61 to the microcomputer.
The load cell LC senses the 20 psi pressu.e from wein]lt 120 which
together with the weight of the specimen 85, weight of specimen
holder 61, weight of rods 28, 29, 30 and bolt 40 represents the
total weight thereon and is referred to as the dead weight. Such
dead weight is the total weight registered on the load cell LC
and is the predetermined weight from which the loading on the sample
will be calculated. This dead weight or predetermined weight will be
reduced by 20% for the loading weight in the example described.
When stepping motor 11 is energized, its output via
belt 17 rotate gear pulleys 16 which in turn rotates
threaded shafts 14 thereby moving carriage 24 downwardly,
relative to the frame member (shaft 14 and housing 13)
moving rods 28, 29, 30 therewith along with specimen 85
and specimen holder 61. When the specimen 85 makes
contact with specimen 113, the load cell accordingly
registers this change with the microcomputer which
instantly senses the change in the dead weight, which
in our example is a 20% reduction in initial dead
weigh~. Due to the fact that the load cell LC no longcr senses
the weight of the rods 28, 29J 30 and the bolt 40 but only the
weight of the specimen 85, the weight 120, and the weight of the
specimen holder 61. Physically when contact is made between the
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specimens, the rods 28, 29 and 30 have sufficient
clearance as seen in Fig. 3 to permit co~tinued travel
relative to the weight 120 and specimen holder 61.
That is, bolt 40, rods 28, 29 and 30 continue to travel
downwardly with the carriage 24. At the instant of
sensing the 20~ reduction in dead weight, the micro-
computer as a control means allows the stepping motor 11 to
run a pre-set time interval beyond the contact point and
then allows the stepping motor to sit idle for a pre-set
-time interval, which is referred to as the dwell time. The
stepping motor is then energized by the control means and
reversed in its rotation upon lapse of such dwell time
thereby separating the specimen 85 from the specimen
113. The dwell time or the first time intervals can be
pre-set by the microcomputer and is programmable. Such
dwell time includes the interval of tlme that the
microcomputer first senses a reduction in weight and
the idle interval to where the stepping motor is reversed.
The second interval of time as illustrated by Fig. 11
begins when motor 11 is reversed to where the micro-
computer or the control means no longer senses the
reduction in weight. As an example of the time element
involved expressed as a one second dwell time, such
time period includes [1] three tenths (.3) of a second
covering the period of time that the microcomputer
senses a change or a reduction in initial dead weight,
during which time there is a downward movement of rods
28, 29 and 30 with the weight stationary, [2] four
tenths (.4~ of a second of waiting or inaction time,
and L3] three tenths t. 3) of a second covering the
period of time that there is still a clearance space
where the microcomputer signals the stepping motor to
reverse its direction and there is actual rotation of
the threaded shafts 14-14 ~efore the load cell senses a
~,5 pick-up of the dead weight due to the elimination of
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the clearance spacP between the upper specimen holder
61 ~nd the head of the bolt 40. During the test time
the microcomputer or control means records the tack as
energy (inch-pounds) per unit area (square inches~. In
this process of measuring tack in terms of the ener~y
per unit contact area the test conditions utilize 1
second of dwell time. The microcomputer or the control
means energizes the stepping motor 11 to provide as an
example a contact pressure of, 20 psi,at a 10 inch per
minute separation rate which is substantially an
instantaneous separation as this is equivalent to 1
inch per 6 seconds or .16 inch per second. As a further
example of the units used to calculate the tack, the
energy is the integral of Force times differential of
dist'ance wherein E (energy) equals IFdx = fF ddt.dt
which is dt ~Fdt. The fraction of dx/dt is velocity
of separation where dx is distance and where dt is
time. The data obtained by this measurement correlate
with hand tack tests and can be used for the quality
control of factory production. Since the ~icrocomputer
has the speed of separation stored in its memory,
and it takes force measurements at small equal time
intervals (Fig. 1'13, the energy integral is easily
` calculated by a summation method. The cross-sectional
area is also a parameter stored in the microcomputer
memory, so that it can carry out the division necessary
to calculate energy/unit area. As an example consider
the following data in Table I.
.:
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~:
. o ~ ~ ~
O ~ r o o o
X P ~ ~ ~
~D ~ O' ~ s~ '
15 ~ c: u~ ~ ~
0 ~ ~
o ~
2 0 ~, I X ",
~ ~ 0
H
2 5 E ~ ~ / Ç
~ X
~ ~ m o
:~ o
A. JL ILJ ~f ~ AIL
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As indicated by the data from this table
there is a direct correlation between the hand-tack
j testing of samples and those measured utilizing the
energy concept as detailed above whereas tack as
; 5 measured in force per unit of area have poor correla-
tion with the tack as measured and ranked 1 through 5.
In lieu of using a weight 120, the micro-
computer can be used to detect as previously described
a change in the loading on the load cell LC when
contact is made. The microcomputer can be set to stop
the stepping motor 11 whenever the load cell registers
an input to the microcomputer of 20 psi. In this instance
the loading is done ~y the stepping motor. The dwell
/ time for the stepping motor in the example chosen again
is 1 second. After the lapse of time, the microcomputer
prov~des an input signal to the stepping motor to
reverse its direction to raise the carriage 24 and
separate the materials being tested. In this instance
the interval of time is a second interval and which the
energy of separation is measured.
A modification of the above described appar-
atus includes the elimination of the lower specimen
holder 86 such that the circular plate 21 is also
removed, leaving a bore 20 on the base 10. In this
condition, the tack testing apparatus can be carried to
the site at which the measurements are to take place
and the apparatus is positioned on the material to be
tested, so as to expose a portion of the material
' through the bore 2~. The upper specimen holder 61 is
lowered until the specimen 85 comes in contact with the
~aterial to be tested that is exposed by the bore 20.
The procedure for testin~ is identical to that described
in the first embodiment except that the apparatus rests
on the specimen to be tested.
A ~urther modification is shown in ~ig. 7 and
the lower portion of ~ig. 8. Herein the post or
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support 87' is at-tached to the base 10 in the same
manner as the first embodiment. The upper end of post
or support 87' has a cylindrical shaped support 130
with a pair of vertically extending projections or
abutments 131 extending upwardly therefrom. An annular
member 132 is mounted on top of the laterally spaced
projection~ or abutments 131 and interconnected to the
support 130 by bolts 133 extending through the project-
ions 131. The outer cylindrical surface of annular
member 132 is threaded and has centrally disposed
stepped bore with a small bore portion 134, an inter-
mediate si~e bore portion 135, and a large bore portion
- 136. An annular support with a frusto-conical shaped
'specimen support 137 and a depending stem 138 is
received by such stepped bore. The stem 138 has an
annular recess 139 on its lower end portion receiving a
clip 140 to retain such stem 138 and the frusto-conical
support 137 within the stepped bore. Prior to the
assembling of the annular support into externally
threaded annular member 132, thrust washers 1~1, 142
and thrust bearings 143 are assembled on stem 138 as
the stem is inserted into bore 135, after which clip
140 is secured to the stem to lock such conical support
137 and stem 138 to the annular ring 132. A sample or
specimen of rubber material is placed on the frusto-
conical support 137 and thence an inverted annular
shaped retaining member 145 which is internally threaded
as at 146 is threaded onto annular ring 132 to captively
' secure the specimen within the lo~er specimen holder
144. A central opening 147 in retaining member 145
exposes the specimen of material for contact by the
specimen of the upper specimen holder as seen in Fi~.
7.
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A further modification of the inventiOn is
shown in Fig. 8 wherein the rod 30 with the annular
weight 120 is connected via bolt 40 to a U-shaped
support 150. Suitably connected to support 150 is a
threaded cylindrical plug 151 with a frusto-conical
shaped specimen support 152. An annular internally
threaded retainer 153 is threaded onto cylindrical plug
151 to captively secure a sample or specimen of material
as in the last described embodiment. Retainer 153 has
a central opening 154 to expose the sample and is in
alignment with the lower specimen holder 144. A cylindri-
cal plug 151 is constructed in the same manner as the
corresponding parts in lower specimen holder 144. The
~ support 150, plug 151 and retainer 153 form a upper
specimen holder 155. The operation of the upper
specimen holder 155 in cooperation with lower specimen
holder 144 can be identical as that described in the
first embodiment7 A variation on the operation is to
eliminate the weight 120 and providing a loading via
the stepping motor 11 as measured by the load cell and
the mieroprocessor described above. Such action
eliminates the need for any clearanee spaee between the
bolt 40 and the support 150 as deseribea above.
It will be apparent that, although a specifie
embodiment and eertain modifieation of the invention
have been described in detail, the invention is not
limited to the specifieally illustrated and deseribed
eonstruetions si~ee variations ma~v be made without
, departing from the prineiples of the invention.
