NATIONAL BUREAU OF STANDARDS REPORT

9838

EXAMINATION OF FAILURE OF

PRINTING PLATE, NO. 29724

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C.

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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. provides the central basis within the United

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includes Radio Standards Physics and Radio Standards Engineering—Office of Standard Refer- ence Data. THE INSTITUTE FOR MATERIALS RESEARCH . . . conducts materials research and provides

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

3120641 9838

EXAMINATION OF FAILURE OF

PRINTING PLATE, NO. 29724

By

I , J . Fei nberg

Engineering Metallurgy Section

Metal 1 urgy Division

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C„

IMPORTANT NOTICE NATIONAL BUREAU OF ST t for use within the Government. I and review. For this reason, the whole or in part, is not authori Bureau of Standards, Washingto

the Report has been specifically 1

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015

s accounting documents intended

subjected to additional evaluation

listing of this Report, either in Office of the Director, National

the Government agency for which

ipies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL DUREAU OF STANDARDS

These dimensions show appreciable deviations from intended slot

separation and from intended slot base length in both plates. As a result

of these deviations and because the Roosevelt plate is thinner, the net

material section area between slot corners is approximately 8 per cent less

in the Roosevelt plate. The Roosevelt plate is also approximately 10 per

cent thinner in the slot areas. Interestingly, the Lincoln plate did not

crack at the slot corners as did the Roosevelt plate. Because the overall

thickness of the Roosevelt plate is less than the Lincoln plate, and the

steel under the gripper slots is substantially thinner, the cooling rate

during a quench from 1550°F would be greater in the Roosevelt plate. This

would produce a slightly higher hardness than previously observed in other

plates, and in particular, the hardness in the vicinity of the gripper

slots would be higher. Less available material to resist cyclic bending

and higher hardness at the notch corners could produce an unfavorable

combination that would accelerate the formation of fatigue cracks.

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

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

The arrow in Figure 4 points to the apparent crack origin which is located

at a point where there is a change in section thickness that could cause severe stress concentration. 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 hardness of the reverse face of a section

adjacent to the crack examined averaged 84 Rockwell lj>N (47 Rc). A surface

hardness of 80-82 Rockwell 15N for this plate was reported by the Bureau of

Engraving and Printing.

The results of a hardness traverse across the thickness of the section

on which hardness impressions were made at intervals of from 0.0008 inch

to 0.010 inch are tabulated below:
\ Jl

"Vi

-

-

<1
- 3

-

Hardness

Reading Distance from KHN Equi va lent Approximate

No. obverse surface 500 g load r

b R c

1 nch

1 0.0024 564 51

2 .0032 532 49

3 .0048 420 41

4 .0072 310 30

5 .0096 286 26

6 .0120 253 20

7 .0144 241 98

8 .0168 241 98

9 .0268 227 95

10 .0368 226 95

1

. .0468 216 93

12 .0568 223 94

13 .0668 220 94

14 .0768 217 93

15 .0868 222 94

16 .0968 221 94

17 .1068 223 94

18 .1168 221 94

19 .1268 224 95

20 . 1 368 223 94

21 .1468 226 95

22 .1568 231 96

23 .1628 253 20

24 .1652 284 26

25 .1676 328 32

26 .1700 509 48

27 .1716 497 47

28 .1724 454 44

Reverse surface . 17^0

The hardness traverse indicated the presence of a case approximately 0.001

inch deep on both faces. It also indicated that the interior was un i formly

hardened throughout inasmuch as there was no appreci.able variation in hardness

in the interior.

- 4 -

Meta 1 loqraphi c Examination : Uniformly distributed thin inclusions, probably

manganese sulfide, were found in the plate sample. These are shown in

Figure 5- The inclusion rating using ASTM Designation E-45 as a reference

is A=1 to A-2 which indicates a clean steel.

No evidence of ferrite banding was observed in a longitudinal section

of a core area. Figure 6. The fine-grained structure exhibited has a grain size rating of 8 using ASTM Designation E 1 12 as a reference. Figure 7

shows the microstructure of a longitudinal section adjacent to the crack

mouth. There are no indications of decarburization adjacent to the surface.

The case shown is predominantly martensitic and is approximately 0.0015 inch

deep. The core is composed of partially spheroidized carbides (dark) in a ferrite matrix (white).

Discussion and Conclusions : Examination of the sample removed from the

cracked printing plate revealed a number of conditions that could have

contributed to premature failure of the plate:

1. The chafing of the plate adjacent to the cracks (Figures 1 and 2 ) indicates cyclic stressing that 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 deep tool marks in the gripper slots and the sharp corners of the

gripper slots (Figures 1 and 2) are objectionable features. They are heterogeneities creating stress concentration and could be sites for crack

initiation and/or propagation.

3. The hardness of the reverse surface of the plate (R c 47) and of the case adjacent to the crack (R c 44-48) are slightly high. This is based on

a review of the hardness of previously examined plates that had a lower

hardness and were satisfactory.

In comparison with a previously examined plate that did not fail in

service, gripper slot separation in the subject plate was found to be closer

and slot walls thinner. These conditions weakened the plate. The first

condition increased the unit stress in the area between slots under the

loading imposed. The second condition created an area that became

excessively hard in heat treatment.

Cracking of the subject plate resulted from fatigue fractures apparently

initiated at the slot corners which had a "built-in" notch. It appears that

the hard case combined with the sharp corners of the slots was an immediate

factor in crack initiation. It is well known that a hard case has low

plastic properties and is particularly notch sensitive. Fatigue cracks were initiated in the case as the result of cyclic bending stresses that

put the reverse face of the plate in tension. These bending stresses

resulted from repeated loading and unloading occurring in rotation of the

plate during printing. It appears that the tool marks in the slots

contributed to crack propagation. Darkening of the fatigue fracture

surface is evidence that corrosive oxidation also occurred.

Remedial Suggestions :

It is considered that faults stemming from fabrication, fit of plate

on the drum, and heat treatment are responsible for the plate failure.

Adherence to the following practices should result in an improvement in

the service life of the plates:

1. Gripper slot separation, size, and depth in future plates should be

the same as that in plates that proved to be satisfactory.

2. Introduce fillets at the corners of the base of the gripper slots

(encircled areas. Figure 2). These fillets may be made by first

drilling 3/16 inch diameter holes to a depth of approximately 0.075

inch in the reverse face of the plates where the slot corners are

to be located, or by other suitable techniques. All sharp edges

resulting from drilling and subsequent machining of slots should be

removed.

3.

4.

5.

6 .

Feather edges of the gripper slots all-around and avoid leaving deep

tool marks in the slots and on the over-all reverse face of the

plates

Ensure close fitting of the plate on the printing drum to reduce

bending or cyclic stressing during rotation of the plate.

Equalize loads on the grippers.

Temper plate to obtain a hardness of 79*5 to 8 1 . 5 R|^ in the case,

as measured on an area of full plate thickness.

USCOMM-NBS-DC
III
igure

1.

Reverse

of

plate

section

cut

from

plate

no.

29724.

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

shows cracks propagating from slot corners. Arrows point to probable crack origin. Area

a , is a highly reflective surface resulting from

chafing of the plate on the drum. Note the deep

tool marks in the gripper slots and the sharp

edges of the slots adjacent to the cracks.

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

at these points is recommended. X k

03 X

03 c

03 •—

i_03 !_

03

4-> 4-J O 03

. 03

in l_cn

i_

03 03 CL i_ CL 03

s_ X

03 4-J CL C 03 — -o

lL -a

(J c

03 03 1_u 03N

4-< >

o in

• c

0) 4-J 4-» T3 o

03 •

w— -o m

CL

4-J 4-J

4-> 03 03 c X X

0) 4-1 4-> u

03 O

4-J c

03 0)

4-J •—

.

CL m

CD in > 4-J 03

<13 c <

in 03 O U in O —

OC J- c

4-> c o

o »— •

a) o 4-J

• —

i

o 03 —

-Q c l_ 3

03 X

in CL

03 E E in O o 03 i_ 4-J 4-> 4- 4- O 03

4-J 4-1 in cl 3 3

O O 4-J 4-> 03 —

c c X 03 o o 4-J >

•

•

03

4-1 4-J 03 in o <_3 4-1 O

<13 03 O O

CO CO Z cC

03

•V cn cn

03 03

l_ 1_ 3 3

cn 03

u_ U.

Figure 4. Fracture surface of failed printing plate.

Arrow points to apparent origin of crack

and direction of propagation. The surface

is typical of that resulting from fatigue.

The depth to which the crack propagated is

bracketed. X h

Figure 5* Thin inclusions, probably manganese sulfide,

found in longitudinal section of sample.

Unetched. X 100

Figure 6. Microstructure of sample. Shows no evidence of ferrite banding in longitudinal section. Etched with 2°/o picral. X 200

Depth

of

martensitic

case

approx.

0.0015

inch

Figure 7« Structure of longidutinal section of plate sample

adjacent to fracture origin. Show no decarburization

at plate surface. Martensitic case is approximately

0.0015 inch deep. Core is composed of partially

spheroidized carbides (dark) in a ferrite matrix

(white). Etched with 2$ picral. X 500


cccr—rrc