NATIONAL BUREAU OF STANDARDS REPORT

9858

EXAMINATION OF FAILURE OF

PRINTING PLATE, NO. 29812

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

3120641

NBS REPORT

9858

EXAMINATION OF FAILURE OF

PRINTING PLATE, NO. 29812

By

I. J. Fein berg

Engineering Metallurgy Section

Metallurgy Division

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C.

NATIONAL BUREAU OF S

T

for use within the Government, and review. For this reason, th whole or in part, is not autho Bureau of Standards, Washingt

the Report has been specifically

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

;ss accounting documents intended

; subjected to additional evaluation

s listing of this Report, either in

ie Office of the Director, National by the Government agency for which

;opies for its own use.

<tJbs>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Examination of Failure of Printing Plate, No. 29812

I nt roduct i on : A 0.179“ * 3“ x 11" section removed from Roosevelt six-cent

plate no. 29812 that failed in service was submitted for an examination to

determine the cause of failure of the plate. As was the case in a previous

failure (plate no. 29724, NBS Report 9838 ), failure occurred because of

cracking adjacent to the gripper slots machined into the plate. The failure

of plate no. 29724 was attributed to faults stemming from fabrications, fit

of the plate on the drum and heat treatment. Because of the apparent

similarity in the failure mode, plate no. 29812 was subjected to the same

type of examination as was plate no. 29724.

Visual Examination : Figure 1 shows the reverse face of the plate section.

Tight cracks propagating from the corners of all eight of the gripper slots

on the reverse face were observed. Figure 2 is an enlarged view showing

cracks propagating from the corners of two of the slots. The plate section

was chafed adjacent to the slots, a, Figure 2. The slot edges shown in this

view are quite sharp; sharper than those found in the examination of plate

no. 29724. However, the tool marks in the slots of the subject plate were

not as deep.

Measurements made of the spacing between gripper slots, the base

length of the slots and the thickness in slotted sections of both the subject

plate, sample and of a Lincoln plate sample are presented below for comparison.

The Lincoln plate which was also used for comparisons in NBS Report 9838 did

not crack at the slot corners.

Roosevelt Plate

No. 29812

Lincoln

Plate

Intended separation

of slots (between indices), i nch 0.519 0.517

Intended base length

of slots (between indices), i nch 0.809 0.810

Actual separation of slots, i nch 0.532 0.543

Actual base length of slots. i nch 0.794 • 0.782

Overall thickness of plate, i nch 0.179 0.182

Minimum thickness in slotted

section, inch 0.070 0.088

- 2 -

These dimensions show appreciable deviations from intended slot

separation and from intended slot base length in both the Roosevelt and

Lincoln plates. As a result of these deviations and because the Roosevelt

plate no. 29812 is thinner, the net material section area between slot corners is approximately A per cent less in the Roosevelt plate than it is

in the Lincoln plate. The Roosevelt plate is also approximately 20 per

cent thinner in the slot areas.

Figure 3 is a view of a typical fracture surface. This surface was revealed when a cracked section was opened. The bright fracture surface

area resulted from completion of the fracture in the laboratory. The

arrows in Figure 3 point to two apparent crack origins which are located

at points where there is a change in section thickness that could cause severe stress concentration. The cracks propagated laterally from their

individual origins and nearly merged. The dark area has a smooth portion

adjacent to the origin and appears to be a fatigue fracture surface. This

surface was darkened by corrosion products.

Hardness Measurements : The results of a hardness traverse across the

thickness of a section adjacent to the crack are tabulated below:

Hardness

Readi nq

No.

Distance from

obverse surface

KHN

500 g load

Equivalent approximate

r b R c

1 nch

1 0.0020 402 40

2 .0044 312 30

3 .0068 271 24

4 .0092 247 99

5 .01 16 226 95

6 .0140 224 95

7 .0164 223 94

8 .0188 220 94

9 .0212 i 208 91

10 .0236 206 91

1

.0336 199 90

12 .0436 196 89

13 .0536 189 87

14 .0636 194 89

15 .0736. 196 89

16 .0836 194 89

17 .0936 194 89

18 .1036 198 89

19 .1136 195 89

20 . 1236 203 90

3

-

Readi nq

No.

D i stance from

obverse surface

Hardness

KHN

500 g load

Equivalent approximate

r

b r

c Inch

21 0.1336 201 90

22 .1436 205 91

23 .1536 218 93

24 .1636 213 92

25 . 1660 231 96

26 .1684 234 97

27 .1708 265 23

28 .1732 300 28

29 .1756 359 36

Reverse surface .1780

The hardness traverse indicated the presence of a case approximately

0.007 inch deep on both faces. It also indicated that the interior was uniformly hardened throughout inasmuch as there was no appreciable

variation in hardness in the interior.

The hardness of the case on the reverse face of the plate in an area

of full plate thickness averaged 75 Rockwell 1 SN . The hardness of the reverse face adjacent to the crack examined averaged 78 RlSN* The hardness

of the adjacent thin slotted section averaged 8 l R 15 N. Since the steel

under the gripper slots is substantially thinner, tne cooling rate during

a quench from 1550 ° R would be greater in this section and produce a slightly higher hardness. The thickness of the slotted section is

markedly less than that in the Lincoln plate which has served as a basis

of comparison. Like plate no. 29724, less available material to resist

cyclic bending and higher hardness at the notch corners of plate no. 29812 could produce an unfavorable combination that would accelerate

the formation of fatigue cracks.

Meta 1 1 ograph i c Examination : The plate sample contained mixed stringer and

globular inclusions. These are shown in Figure 4a . The inclusion rating

using ASTM Designation E-45 as a reference is A-2 - A-3 • The steel is not

as clean as desired for this application. The inclusions acted as paths

for crack propagation and probably accelerated the rate of crack growth.

Figure 4b. Cleaner material (inclusion rating A- 1 - A-2) would be more

des i rab 1 e .

No evidence of ferrite banding was observed in a longitudinal section

of a core area, Figure 5* The fine-grained structure exhibited has a grain size rating of 8 using ASTM designation E-112 as a reference.

Figure 6 shows the microstructure of a longitudinal section adjacent to

_ 4 -

the crack mouth. There are no indications of decarbur i zat i on adjacent to

the surface. The case shown is predominantly martensitic and is approximately 0.003 inch deep. The core is composed of partially spheroidized

carbides (dark) in a ferrite matrix (white).

Discussion and Conclusions : Detrimental conditions that were considered

to have contributed to the failure of plate no. 29724 were also found in

the present plate investigation. These conditions included the following:

1. The plate was chafed adjacent to the cracks (Figures 1 and 2)

indicating that cyclic stressing could have been caused by improper

seating of the plate on the drum in this area. The stressing

involved repeated bending along a line parallel to the base of

the gripper slots.

2. The sharp corners of the gripper slots are heterogeneities creating

stress concentration and could be sites for crack initiation and/or

propagat i on

3. In comparison with a previously examined plate that did not fail in serv i ce, gr i pper slot separation in the subject plate was found to

be closer and slot walls thinner. This condition weakened the

plate by increasing the unit stress in the area between slots under

the loading imposed.

As in the case of plate no. 29724, cracki ng of plate no. 29812 resulted

from fatigue fractures initiated at the slot corners which are in effect

stress concentration notches. It is believed that the sharp slot corners

locally harder than adjoining areas created a particularly notch sensitive

condition that was an immediate factor in crack initiation. Cyclic

bending occurring from repeated loading and unloading of the plate during

printing put the reverse face of the plate in tension and provided tensile

stresses of sufficient magnitude to initiate the cracks. It appears that

inclusions in the material contributed to crack propagation. Darkening

of the fatigue fracture surface indicated that corrosive oxidation also

occurred

Remedial Suggestions :

It is believed that faults stemming from fabrication and from fit of

the plate on the drum are mainly responsible for this plate failure. The

Bureau of Engraving and Printing has reported that an improvement in the

service life of plates has resulted from introducing fillets at the base

of gripper slots and feathering edges of the gripper slots all-around.

It is suggested that adherence to these and the other remedial suggestions

for printing plates listed in NBS Report 9838 be continued.

USCOMM-NBS-DC
l:LLLL--—

rn

n
Figure 2. Enlarged view of a section of the plate sample

shows cracks propagating from slot corners. Area a , is a highly reflective surface resulting

from chafing of the plate on the drum. Note the

sharp edges of the slots adjacent to the cracks.

Feathering of the slot edges all-around and

grinding generous fillets in the encircled slot corners to reduce possibility of crack initiation

at these points is recommended. X 4.

Figure 3- Fracture surface of failed printing

plate. Arrows point to apparent

crack origins. The surface is

typical of that resulting from

fatigue. The depth to which the

crack propagated is bracketed. X 8

/

a

b

Figure 4a . Mixed stringer and globular inclusions

found in longitudinal section of sample.

Unetched. X 100.

Figure 4b. Part of fatigue crack showing the crack

propagating through stringer of inclusions

at arrow. Etched with \°]o nital. X 200.

J

J

J

Figure 5» Microstructure of sample. Shows no evidence of ferrite banding in

longitudinal section. Etched with

4'jo p i era 1 . X 200

.

Depth

of

martensitic

case

approx

. 0

.003

i

nch

Figure 6. Structure of longitudinal section of plate sample adjacent

to fracture origin. Martensitic case is approximately

0.003 inch deep. Core is composed of partially spheroidized

carbides (dark) in a ferrite matrix (white). Etched with

b°]o p i era 1 . X 250.