FOREST PRODUCTS LIBRARY
FOREST RESEARCH LABORATORY
OREGON STATE UNIVERSITY
4r)
RATE OF DEVELOPMENT OF JOINT
STRENGTI1 13Y FOUR RESIN GLUES
ON EIGI-IT SPECIES OF WOOD
Information Reviewed and Reaffirmed
March 1956
No. 1547
FOREST PRODUCTS LABORATORY
MADISON S. WISCONSIN UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
In Cooperation with the University of Wisconsin
Prc
RATE OF DEVELOPMENT OF JOINT STRENGTH BY
1
FOUR RESIN GLUES ON EIGHT SPECIES OF WOOD —
By
W. Z. OLSON, Technologist
H. D. BRUCE, Chemist
V. R. SOPER, Technical Aide
Forest Products Laboratory,— Forest Service
U. S. Department of Agriculture
In using resorcinol- and phenol-resin glues in the fabrication of wood
aircraft the question arises as to whether these glues cure at the same
rate on different species of wood. In an attempt to answer this question, joints were made with three room-temperature-setting glues and
one intermediate-temperature-setting glue on eight species, cured for
various lengths of time at two temperatures and tested in shear to follow
the rate of development of the joint strength in the various species.
It was anticipated that the results would follow one of the three idealized
patterns sketched in figure 1. If pattern (A) was found to be the case,
in which the curves are coincident below the points where they depart
from one another by virtue of differences in the strength of the woods,
it could be concluded that there was no effect of species on the rate of
curing. In the case of (B) and (C), on the other hand, a species effect
could be inferred.
The glues employed were commercial glues and mixed according to the
manufacturers' directions. The glues were designated as follows:
1
— This report is one of a series of progress reports prepared by the
Forest Products Laboratory relating to the use of wood in aircraft.
Results here reported are preliminary and may be revised as additional data become available.
2
— Maintained at Madison, Wis. , in cooperation with the University of
Wisconsin.
Rept. No. 1547
-1-
Agriculture-Madison
Designation
Type
Room-temperature-setting
resorcinol
Room-temperature-setting
resorcinol
Room-temperature-setting
resorcinol
Intermediate-temperaturesetting phenol
A
B
C
D
The eight species of wood employed were: yellow birch, Douglas-fir,
noble fir, sweetgum, Western hemlock, mahogany, sugar maple, and
Sitka spruce. Most of these woods are in common use in aircraft, and
as a group provide a wide range in density and strength as well as the
characteristic differences between softwoods and hardwoods. The maple,
birch, and sweetgum were in the form of rotary-cut veneer and the other
species as quarter-sliced veneer.
Procedure
All veneer had a nominal thickness of one-sixteenth inch, but each sheet
was calipered and only those measuring 0.061 inch to 0.063 inch, inclusive, were selected for use. The selected veneer was cut into small
slips 1 by 2-1/8 inches in size, with the grain running lengthwise.
In preparing the joints, the slips were clamped in a special frame (not
shown) so that the glue could be applied quickly by brush to each surface
area to be glued. The slips were then laid together in pairs with a 1inch overlap in a special metal jig (fig. 2). After 15 minutes of closed
assembly, a rubber caul was laid over the jig, and the specimens were
subjected to a pressure of 150 pounds per square inch. The jig accommodated 32 lap joints, which made it possible to press one joint of each
species with each of the 4 glues at the same time. Four sets were made
at each gluing condition, and the results of these were averaged.
The joints for this study were cured at 80° F. and at 120° F. For curing
at 80° F., the jig loaded with specimens and under pressure was kept for
the curing period desired in a room maintained at 80° F. For curing at
120° F., the jig with specimens was pressed for the curing period desired
between platene heated to 120° F. with hot water. At this higher temperature, approximately 3 minutes were required for the temperature in the
Rept. No. 1547
-2-
glue line to rise to within 5° F. of the platen temperature. Measurement of the time of heating was begun after this initial heating interval.
Immediately after the desired curing period, at both 80° F. and 120° F.,
pressure was released, and the individual specimens were removed
from the jig and dropped into a beaker of cold water to lower their ,
temperature and inhibit further cure of the glue. The beaker with immersed specimens was set in a vacuum desiccator and a vacuum was
drawn for 30 minutes, then released. The moisture content of the
specimens wet in this way was from 100 to 300 percent, and the wood
of all species appeared to become wet through to the glue line. After
wetting, the specimens were tested at once in a standard plywood-jointtesting machine loading at a rate of about 750 pounds per minute.
Results
The averaged results of the shear tests on the joints are given in tables
1 and 2.
Any effect of species on the rate of curing of the glue could be expected
to be revealed more clearly in the initial stages of the curing in which
the joints break without wood failure and the shear values are less dependent on the strength of the wood. To analyze the data for the effect
of species, therefore, the joint strengths given in tables 1 and 2 for
those curing periods at which the wood failure percentages were usually
low have been plotted in figures 3 to 6. To avoid confusion of lines,
points have been connected for selected species only. In the figures it
may be seen that the glues did not develop joint strength at the same rate
on all species but that the curves for the several species fan out early,
more like (B) and (C) of figure 1 than like figure 1 (A). From these
observations it may be concluded that, aside from any effect of density
and strength of the wood on the shear strengths of the joints there is an
effect of the species of the wood on the rate at which these resin glues
harden.
The effect of species on the development of joint strength is revealed in
the data for both the phenol and the resorcinol glues. In general, the
curves for the several species are in about the same order for each of
the three resorcinol glues but not in the same order for the phenol glue.
The resorcinol glues built up strength more slowly on Douglas-fir than
on maple, whereas the reverse was true for the phenol glue. The
Rept. No. 1547
-3-
influence of species was seen at both the 80° F. and 120° F. curing
temperatures. The order of the curves was roughly the same at both
temperatures.
The difference between the 'slowest' and the 'fastest' species may be
enough to be of considerable practical importance. For example (fig.
5), glue C took about 3 hours longer at 80° F. to develop 200 pounds
per square inch joint strength in Douglas-fir than it did on sugar maple.
Glue A (fig. 3) required about 10 minutes more heating at 120° F. to
develop 300 pounds per square inch strength on Douglas-fir than it did
on sugar maple. These are, however, extreme examples and most of
the species tested did not vary as widely in their effect on the curing of
the glue.
The data of tables 1 and 2 were plotted in the form of graphs (not shown),
and smooth curves drawn to fit as closely as possible the points for each
species. From these smooth curves the estimated time for the joints
to reach particular shear-strength levels has been tabulated in tables 3
and 4. The differences in the lengths of time shown in column 3 for a
glue to reach 200 pounds per square inch are presumably due to the effects of the species on the rate of curing. The differences in the lengths
of time to reach high joint strengths are due not only to the influence of
the wood on the curing but also to differences in the strength of the wood
of the different species.
No attempt was made herein to explain why a resin glue may not cure as
rapidly on one species of wood as on another; instead it is the purpose of
this report merely to point out that such differences do exist and that they
may be great enough to be of practical importance in commercial gluing
operations.
Rept. No. 1547
-.4-
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Table 3.--Estimated curing periods at 80 • E. to develop shear strength of several levels in lap-,joints of
1/16-inch veneer of eight species glued with four resin glues
species
:Approximates
t ultimate s
: shear
:
: strength :
: P.s.i.
Curing period required to develop shear stren gth of:
200 p.s.i. :
s)
119.1a
r
400 p.s.i. i
300 p.s.i. s
500 p.s.i. s
sMinutess Hours :Minutes: Hours sliinutqa: lime
600 p.s.i.
:Anti': ibsza sank'
Glue As Room-temperature-setting resorcinol formaldehyde
Noble fir
Western hemlock
Sitka spruce
Douglas-fir
Mahogany
Sweetgom
Yellow birch
Hard maple
s
:
s
s
:
s
1
:
:
380
1
4:;
:
380:
.
F.;
a
720
:
725
:
2 :
3 1
3
3
2
2
2
2
45 a
1
10
;
i
10 1
40 A
s
i 50 ;
;
s
:
4g :
1
35 s
:
4 1
5 s
3 c
3 s
3 :
3 s
55 1 30 s 25 1 4
s
1
:
A :
4
s
5 :
15 s
?: s:
4 I
3:
5 s
30 4
35
8
s
1. 4. t
I. s :
1
4
1
s
25
5 :
s
4 :
15 A
25 a
••
t
4
8 4
3
4
-
7 1
7 s
20
Glue B: Boom-temperature-setting resorcinol formaldehyde
Noble fir
s
Western hemlock :
Sitka spruce
8
s
Douglas-fir
Mahogany
Sweetgum
:
Yellow birch
:
Hard maple
:
380
38 5
25
380
s
4 s
4 ;
4 g
6 a
4
3 :.
i
i
4 1
s
s
s
1
.
535
720
725
e
20 s
45 s
35 s
30 s
15 1
4 5 ,
25 s
20 :
5
1
40 A
6:
45
g
9 30 ; s
10 i
6 2
5 s
5A
5 1
s
4
4
10 25 1
15 a
15
s
1
1
;
1
8 i
6 1
6 s
30
1
s
1
1
1
:
...s 4
4
17 i
20 s 7 :
20 ;
8
s
.
1
1
50 :
14 : 03 s
16 I Glue 01 Room-temperature-setting resorcinol formaldehyde
Noble fir
Western hemlock
Sitka spruce
Si
Douglas-fir
Mahogany
Sweotgmn
Yellow birch
Hard maple
s
:
1
:
s
4
s
:
3801
385
1
i
425
380
1
A
55455
720
725
s
1
1
2 t
2 1
4:
5
1
40 l
40 s
5 ;
45
:
25 t
4 1
2 1
25 :
2 A
2
2 ; 4:
3
50 8 3 :
3
3 3
50 i s
5 s
7 s
12 1
15 1 7: 15 8 13 6 8
30 :
3 :
s
1
3 a
3 .
15 s
3 :
•
4
3
4
S
t
:
:
45 2 55 :
20
3
3
4
S
•
s
2
:
s
s
5 i 1 5 .
s
9 e
s
s
11 :
20 i Glue D: Intermediate-temperature-setting phenol formaldehyde
Noble fir
Western hemlock
Sitka spruce
Douglas-fir
Mahogany
Sweetgum
Yellow birch
Hard maple
380
A
385
;
10 :
:
425
380
i
11 i s
8
t
s
:
1
14 679Ba F
8 s
i
1
;4;
720
725
;10 ;
4
9 s
t
9 t
11 t
:
i
.2
10 8
.
25 1 42 s3 1
40 I 16 s
25 : 1
17 2
10 1 16 :
25 .
8
:
55 s
15 s
50 : 15 s 10 s
30 -1
50 t
19 t 8
16 s
20 8
2
1
:
a
4
s
4
3
s
8
0 1
21 I 33 I 22 1 8
4
:
8
1
e
s
s
s
s
:
8
:
:
:
:
:
s
3
s
1
s
:
:
3
8
1 _
•
_I_
3
___1_
30
Table 4.--Bstimated curing periods at 120* 7. to develop shear n tranohs of several levels in
lap-joints of 1/16-inch veneer of eight species glued with four resin glues
Spe c i e s
:Approximates
s ultimate s
Curing period required to develop shear strength level of;
s shear
:s strength : 200 p.s.i. s 300 p.s.i. a 400 p.s.i. s 500 p.s.i. s 600 p.s.i.
P.s.i. s
GlueA4
Glue
A4
Noble fir
:
Western hemlocks
Sitka spruce
s
Douglas-fir
i
Mahogany
s
Sweetgum
s
Yellow birch
s
Hard maple
:
Sweetgus
Yellow birch
Hard :maple
:
:
s
ss
Minutes 1
Minutes s
Minutes i
44"i
25
25
ii
;;
380
380
33
535
aa
11
720
720
725
725
11
oo
19
19
oo
19
19
i20
20
26
26
11
11
16
16
11
16
16
::
14
14
ss
13
13
ss
ss
ss
$
tt
ss
ss
$$
47
47
s
22
22
25
25
19
19
17
17
i
6
i
a
16
16
s
s
211
22
s
s
a
17
1
25
720
725
i
Minutes
Boom-temperature-setting resorcinol
Boom-temperature-setting
resorcinol resin
resin
11
11
12
12
11
11
15
15
12
12
11
11
11
11
11
11
380
380
Minutes $
s
s
4
s
i
1
I
22
s
:
$
s
s
37
35
1
60
s
3
P.
I
5
3
5I
_,
s
34
I
114
I
56
1
s
32
38
26
s
32
31
s
Glue Cs Boom-temperature-setting resorcinol resin
s
Noble fir
Western hemlock $
Sitka spruce
&
Douglas-fir
s
380
385
25
380
Mahogany
s
Sweetgiss
Yellow birch
Hard maple
s
s
Pt;
t
725
s
s
4
li
27
$
38
i
720
s
i
:
21
11
13
11
s
s
t
s
1
a
I
8
28
30
52
o
s
s
130
:.....
1
1
1
$
s
75
s
s
8
38
8
I
$
20
$
20
s
19
s
Z
27
27
I
s
s
80
35
37
8
s
s
4►
46
Glue Ds Intermediate-temperature-setting phenol resin
Noble fir
3
360s
Western hemlocks
385
1
Sitka spruce
8
i
:360
Douglas-fir
s
Mahogany
1
s
545
4
Sweetgms
s
Yellow birch
:
a
720
Hard maple
1
a
725
a
A7984 s.
a
31
35
39
36
a
1
g
s
46
49
67
60
46
a
t
1
;
s.
I
110
4
s
73
s
s
1!
64
s
s
s
1
g
I
s
3
$
s
a
112
s
122
80
88
a
s
1
a
i
118
1116
108
130
3
s
$
a
I
150
200
SPEC/ES A
SPEC/ES
A
SPEC/ES A
SPEC/ES B
SPECIES A
SPECIES B
TIME OF CURING
Figure 1.--Idealized rate of development of Joint strength
by a resin glue in two species of wood: (A) without, 4nd
(13) and (C) with species effect on the rate of curing of
the glue.
M 68842 F
a)
a)
(r)
a)
a)
rl
O
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a)
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ri
a)
3 5
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110
ri
700
i
I
GLUE
A – CURED
Ar
BO' F
600
2
pm
11111._____
IMO
INOMILw
500
2
L,4 400
(f)
z.300
MFA
7Alltna
.211
ta, 200
/
7 PY
1..
2
tU
2 /00
14.1
o
r
2
3
5
5
4
CURING TIME ( HOURS )
600
1
1
1
GLUE A – CURED AT 120 • F.
et 500
O
▪
W 400
</)
O
cx.
300
W 200
L
ct
▪
It
/00
tri
ti
0 0
5
/5
/0
20
25
CURING TIME ( MINUTES )
LEGEND,
o
•
q
n
NOBLE F/R
WESTERN HEMLOCK
S1TKA SPRUCE
DOUGLAS-FIR
G MAHOGANY
o SWEETGUM
YELLOW BIRCH
A
A SUGAR MAPLE
Figure 3.--Shear strength of two-ply lap-joints of eight species
of wood glued with room-temperature-setting resorcinol-resin
Glue A at 80° F. and 120° F.
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t) 500
I
I
I
GLUE B — CURED AT BO°
-4111
•
Q' 400
W
Q.
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a
ad. 111100
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O
:
Z
• 200
2
Ct
•
tu
/00
cf)
0
3
4
5
6
CURING TIMEE ( HOURS )
▪ 500
k
I
GLUE
B — CURED AT
/20°
E
:
ozi 400
c4
• 300
n
200
n
Lu
ct
734
ct
/00
k
(I)
L
41
0
0
a
.111111111111111
/0
15
20
25
30
35
40
45
CURING TIME ( MINUTES )
LEGEND:
o
NOB LE FIR
•
WESTERN HEMLOCK
q
SITKA SPRUCE
DOUGLAS — FIR
n
• MAHOGANY
• SWEETGUM
A YELLOW BIRCH
• SUGAR MAPLE
Figure 4.--Shear strength of two-ply lap-joints of eight species
of wood glued with room-temperature-setting resorcinol-resin
Glue B at 80° F. and 120° F.
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50
,600
i
2
1
GLUE
I
C - CURED AT 80 • F
O
W 400
2
O
2
4. 300
EN
•
in
room
wailli
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mammawri
•.1
re
3
600
0
0G
A•
0‘ 0.
ilm
DOUGLAS-FIR
4
5
CURING TIME ( HOURS )
I
2
.0
0"6
6
I
GLUE C - CURED AT MO • F
MAP LE
I
it 500
O
W 400
ct.
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O
2
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1
2
t% 200
2
ti
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•
DOUGLAS
SPRUCE-F./R
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-
tr)
• /00
44
2
...
44,
0
5
/5
10
20
25
30
35
40
45
CURING TIME (MINUTES )
LEGEND,
O
•
O
n
NOBLE FM?
ft-5m• HEMLOCK
SHWA SPRUCE
DOUGLAS-FIR
•
•
MAHOGANY
SWEETGUM
a
YELLOW BIRCH
•
SUGAR MAPLE
Figure 5.--Shear strength of two-ply lap-joints of eight species
of wood glued with room-temperature-setting resorcinol-resin
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50
k 300
GLUE 0 - CURED AT eo• F
250
o t
.„,s._diai
mill
O
1$
Q. 200
ti
O
2
Q. /50
2
O
2 /00
tr)
14.1
50
t.
•
o Gr
2
3
300
4
5
I
1
6
7
8
CURING TIME ( HOURS)
9
10
12
1
n
GLUE 0 -CURED AT /20•F
,
250
14,
e.
200
O
2
:.i.
n
•
/50
n
2
IQ /00
%
•
%
50
ti
O
5
/0
/5
20
25
30
35
40
45
50
GUR/NG TIME ( MINUTES)
LEGEND,
O
NOBLE FIR
•
WESTERN HEMLOCK
q
S/TKA SPRUCE n
DOUGLAS- FIR
Q MAHOGANY
0 SWEET6UM
YELLOW BIRCH
• SUGAR MAPLE
Figure 6.--Shear strength of two-ply la p -joints of eight species
of wood glued with intermediate-temperature-setting phenolresin Glue D at 80° F. and 120° F.
Z M 68846 F