NATIONAL BUREAU OF STANDARDS REPORT

9923

FATIGUE FAILURE OF ELECTROFORMED PRINTING PLATES

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C.

<NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NSBS PROJECT

3120641

NBS REPORT

9923

FATIGUE FAILURE OF ELECTROFORMED PRINTING PLATES

By

L J. F einberg

Engineering Metallurgy Section

Metallurgy Division

To

Electrolytic Section

Bureau of Engraving and Printing

Washington, D. C,

NATIONAL BUREAU OF ST

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

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

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

jy the Government agency for which

opies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Fatigue Failure of Eiectroformed Printing Plates

Materia f Submitted ; Nine strips removed from e 1 ectrof ormed-n i c ke 1 currency

printing plates that had cracked in service were submitted for examination.

An investigation was requested because plate failures were being experienced at exceptionally low mileages.

AH of the strips contained cracks that were adjacent to and parallel

to the bend line in plate Vee bends - bends necessary for adaptation of

the plates to the press cylinder. The cracks observed varied in length

from approximately one inch in one plate to three-fourths of the plate

width in others. A typical view of the genera! location of the cracks

with respect to the plate bend line is shown in Figure 1. Strip identifications and pertinent plating and service life data are given in Table 1. The Bureau of Engraving and Printing (BE&P) requested NBS to determine

whether cracking could be attributed to detrimental material conditions or

to mechanical factors. BE&P also requested that the mechanical properties

of the materials be established for their records and possible future

reference

.

Visual Examination : All of the strips had grooves made by teeth on plate

fastening clamps. The grooves varied in depth and continuity from plate

to plate. It was observed that the grooves on the strips from the lowest

mileage plates, 40400 and 4042 i , were shallower than those on the strips

from the highest mileage plates, 4-0364 and 4038 1 .

A cursory examination of the O .563 inch nominal diameter punched

holes in the plate strips indicated a generally greater "out-of-roundness"

of the holes in the low mileage plates compared with that in the high

mileage plates. In punching the holes, burrs were raised on the reverse

face of the plates. These burrs were not removed after punching.

Macroscopic Examination ; Figure 2a is a view of the reverse face of a plate section containing a fracture. It shows fretting in the bend line, arrow a, and a continuous line resulting from a polishing action, arrow b.

The fracture path is between these lines. Figure 2b i s a view of the

fracture surface of the section shown in Figure 2a. !t has the characteristic features of a fracture surface resulting from fatigue. Its

appearance is typical of that observed in all of the fractured plates.

Microscopic Examination : Figures 3 a and 3b show the microstructure and

fracture profiles of Tow mileage plate, 40400, and high mileage plate,

40364, respectively. The fine-grained microstructure, Figure 3 a >

' s characteristic of that obtained in a Watts bath and the coarse grained

structure. Figure 3b, is character i s t i c of that obtained in a sulfamate

bath. The fracture path shown in Figure 3 a is predominantly flat and

intergranular while in Figure 3b, it is predominantly transgranular

.

- 2 -

Both fractures were initiated by f at i gue cracks or i g i nat i ng at the obverse

(printing) face of the plates. The flat profile of the fracture in

Figure 3® is characteristic of material that failed rapidly and in a brittle manner. The fracture of plate 40364, Figure 3b, was accompanied

by plastic deformation. The uneven fracture profile is characteristic

of a fracture that propagated through shear. Shear fractures are peculiar to material having good ductility.

The photomicrographs of secondary cracks in Figure 4 provide a clue

as to the mechanism of crack propagation in the subject plates. Figure

4a shows cracks originating at and propagating from the chromium platenickel base interface, some of the cracks having propagated to the

plating surface and to a lesser degree into the base metal. When the

cracks had penetrated the plating completely, notches were created that

acted as stress raisers promoting deep penetration of fatigue cracks into

the base metal as shown in Figure 4b.

Chemical Analysis : A conventional chemical analysis was conducted on a sample from strip No. 4o4)8 L. A copy of the report is included as addendum 1. The sample contained 99.9 percent nickel. Carbon, copper,

iron, sulfur, silicon and cobalt contents were acceptably low. The

chemical composition complied with that specified for Type II anode

nickel, Federal Specification QQ-A-677* March 22, 1957.

Macrohardness : Macrohardness measurements obtained in chromium-free areas

on strip specimens are as follows:

Strip Hardness, Rockwel 1 15T

No. Printinq Face Back Face

40364 L 89 88.5

40364 T 88 87.5

40377 L 91.5 9K5

40381 L 92 92

40395 4 91 9K5

40400 L 91 91.5

40418 L 93 92.5

4o4l8 T 92 92

40421 L 91.5 92

The hardness range of 88 to 93 Rockwell 1 5T obtained on strip

printing faces and 87.5 to 92.5 Rockwell I 5T on back faces results in a considerable spread in related tensile strength. These hardness values

converted to tensile strength indicate approximate equivalent tensile

strengths ranging from 77*000 to 116,000 ps i . There is no correlation

between hardness and related tensile strength and mileage. A high mileage,

365 , 161 , was obtained with the softest plate. No. 40364. However, a high mileage, 271 , 792 * was obtained also with one of the harder plates,

No. 40381. The mileages obtained from the remaining plates in the

tabulation were a small fraction of these values.

- 3

-

Tensile Properties : Tensile test specimens were obtained from areas

parallel to and adjacent to the cracks in strips 40364 L, 40381 L,

40400 L. and 4-04 38 L. The specimens were prepared with a 0.2^0 inch width

and 2.00 inch gage length in the reduced section. As-received thickness

of the strips was maintained in the machined tensile test specimens.

Tensile properties obtained are given in Table 2.

The tensile strengths given in Table 2 are absolute values and

therefore more „ re 1 i ab I e for purposes of comparison than those obtained

from a hardness relationship. Plate 40364, which yielded a superior

mileage, had the lowest yield strength and ultimate tensile strength, and

a percent elongation (ductility) roughly twice as great in comparison

with the other plates. However, plate 40381 which also provided a comparatively high mileage had tensile properties more closely related

to that of the low mileage plates listed in Table 2.

Discussion and Conclusions ; Failure of the subject plates is attributed

to fatigue. it appears that cracks could have been initiated in the

chromium plating adjacent to plate bend lines when the bends were formed.

These cracks created notches that acted as stress raisers. The presence

of polishing and fretting on the printing plates indicates that there

was relative motion between plates and press cylinder during press

operation. This motion was attended by cyclic bending stresses of such

magnitude as to favor the propagation of fatigue cracks starting from

the root of the cracks in the chromium plating and progressing through

the nickel base.

With respect to material properties, analysis of samples revealed

an acceptable chemical composition and mi crostructure. From the material

examined it is felt that differences in material properties can be ruled

out in seeking the reasons for the comparatively short life of some of

the plates. The same ruling applies to differences in the electrolyte

used, sulfamate or Watt's bath. Plate 40364, which had a long service

life, was made in a sulfamate bath. It had a comparatively low hardness,

low yield strength, low tensile strength and good ductility. Plate

40381 which also had a long service life, was made in a Watt's bath.

It had comparatively high hardness, high yield and tensile strengths and

only fair ductility. It is considered that efforts to improve printing

plate service life should be concentrated on plate fabrication

procedures, on plate alignment and on press cylinder adjustments and

1 ubr i cation.

- 4 -

Recommendat i ons : In Ji ne with MBS observations and discussions with

Bureau of Engraving and Printing personnel the following recommendations

are made:

1. If possible, look for elimination in cracking of the chromium plating

by forming plate bends before chromium plating of the printing plates

rather than after.

2 . Check printing plate bends for conformance with mating cylinder lips

and make what adjustments are possible to minimize relative motion

between the printing plate and the press cylinder.

3 . Keep plate clamp teeth sufficiently sharp and tighten clamps so that

all plates are adequately and uniformly gripped on the printing

cy i i nder

.

4. Consider whether plate fastening hole "out-of “roundness11 and burrs

raised by hole punching have a detrimental effect on plate seating.

5 . Continue Bureau of Engraving and Printing lubrication experimentation.

6 . Roll shallow grooves approximately 0.015 inch deep into the obverse

face of the currency plates. The grooves should be approximately

0.25 inch wide and blend gently into the plates. They should be so located that the groove median should coincide with the observed

path made by fatigue cracks in the leading and trailing ends of the

plates, respectively.

- 5

-

Table 1. Identification of E 1 ect reformed Plate Test Strips

Strip 8E&P Bath Plate Hi 1 eage

Number 1 Plating T ank T ype (impressions Obtained)

40364 L W Su 1 f amate-N i eke 1 365,161

40364 T W

1 6 g g 365 J 61

40377 L 3 yattS"Ni eke! 66,964

40381 L 3

1 1 1 g 271,792

40395 L 3

1 8 e 1 26,626

40400 L 3

D 1 8 8 24,805

4o4 1 8 L 3

? 8 1 1 36,543

4o4l8 T 3

g

«

1 f 36,543

40421 L 3

1 g 1 1 25,249

1 Suffixes L and T for the numbers indicate that the strips were cut

from the leading end or the trailing end, respectively, of a given

numbered plate.
ni
Table 2. Tensile Properties of E lectroformed Plate Material

BE&P

Strip Mo.

Spec i men Number

Yield Strength

0,20$ Offset

Ultimate

Tens i le Strenqth

Elongation

i n 2 i nches

ps i psi

40364 L 1 45,500 70,800 20.0

40364 L 2 45,700 71,300 21.5

Avg. 45,600 71,050 20.5

40381 L 1 64,400 94,200 12.5

40381 L 2 65,100 97,300 12.5

Avg. 64,750 95,750 12.5

40400 L 1 63,900 94,400 13.0

40400 L 2 70,700 103,900 10.0 <> cn 67,300 99,150 11.5

40418 L 1 74,500 107,700 10.

1

404

1

8 L 2 67,800 100,000 10.8

Avg. 71,190 103,850 10.5

Figure

1.

Strip

from

printing

plate

No.

40395.

The

location

of

the

cracks

with

respect

to

the

platebend

line

is

typical

of

that

observed

in

all

of

the

strips

examined.

a.

Obverse

face.

X

1/4

b.

Reverse

face.

X

1/4

a

b

Figure 2a. Reverse face of a section of strip No.

UOU 1 8 L. Arrow, a, points to fretting

in the bend line. Arrow, b, points to

a continuous line that resulted from a polishing action. Note that the fracture

path is between these lines. X 2/3

Figure 2b. Fracture surface of the fracture shown in

Figure 2a. The surface is characteristic

of that resulting from fatigue. X b
‘t ’

•

1 ’ ’

-
PRINTING

FACE

PRINTING

FACE

<L)

(D2

SZ

in 4-> <u O

-O

u

4-> c 0 —

tO1_

Ll. a)c

i_ • O

in 0

0) 4->

X

fO c 

<0 Cl SZ O 4-1 0 2 4-

+j 0) '

4-

X

O s_

Q)

0) CL • > Q. 4-1 =J c

4-1 <U

<0 0) cn

4-J JC to

<Z 4-J <U O L.

in 4-4 0) O in

s_ \ " —

Q. to O <u —

s_ 0 

fO 0

V) 4- a. 0 to — /—V i_ — cn to 4— c 0 O —

l_ 4-J JZ

Q. c 4-J

0) 1_ *2 L CL 3 v X 4-1 0) O <u SZ

fO in 0

!_ !_ 4-J 4- 0) UJ > X -O C 0 • ro

(1) in

in J= SZ 0 4-J CL u <0 D 4-1 !_

4-J to cn 0 O 0 X L.

L. <D

O

4-4 4-J • 

in ro E O — O

s_ 4-J 4-J u O

•— c X x — a.

PO

<1) !_

Z3cn

Li.

Plate

40400

produced

in

Watts

bath.

Plate

40364

produced

in

sulfamate

bath.

b

Figure 4 . Typical secondary cracks adjacent to a fracture

.

a. Cracks in the chromium plate (white)

appear to have been initiated at the

interface of the plate and nickel

base. Etched with Carapella's

reagent. X 1000

b. Cracks in the chromium plate have

propagated to the plating surface and

into the nickel base. Etched with

Carapella's reagent. X 500

Addendum 1 VALUE ENGINEERING COMPANY

Materials Evaluation Laboratory2316 Jefferson Davis Highway

Alexandria, Virginia 22301

CERTIFICATE OF TEST RESULTS

Material .... . .(?{-£ ‘.P. .^p.* . j-j No. of Samples . A

Submitted By . . .Nationd Bureau of Standards.

. . . . Date Submitted. 8/16/68.

Tests Performed . Chemical anafysis

CHEMICAL ANALYSIS

A1 Mg Pb Zn

c . . . 9:QQ72 Mn s . . .Q.004 Co . .o„oo6

Cr Mo Si X . Q*. QQ2. . Cu. .9:004. Ni ...99.9. ........ pp . . 0 . 008 p

Sn

Ti

Analysis Performed By In accordance with

T Sample No. Yield Strength,

psi

r- TENSILE TEST —

Tensile Strength,

psi

Per Cent

Elongation

in. . . Inches

Per Cent

Reduction

In Area

' ' " "

Test Conducted Bv In accordance with

«

Sample or Position No.

-

Hardne s s Sample or Position No. Hardness

1

i Test Conducted By In accordance with

Comments

By. . .'&! ft.

rl. P. Weinberg (/)

ML- 1

Approved

Laboratory Director

Date . . August. 22/. 1?68.


LCA