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Produced by the NASA Center for Aerospace Information (CASI) 



1183-10113 


(HiSA-Tfl-82499) fi^FOBfilSUHMIiT OF SBB 
ALUHIMUa COHPONEliTS BX UALBUT BULL BLAST 
MBHOVAL OF PBOIBCIIVE COATIAGS (BASA) 19 p 
HC 402/SF A01 CSCL 21tt Uncias 

03/20 383B2 


NASA TECHNICAL 
MEMORANDUM 



NASA 7M-82499 


REFURBISHIVENTOF SRB ALUMINUM COMPONENTS 
BY WALNUT HULL BLAST REMOVAL OF PROTECTIVE 
COATINGS 

By Wendell R. Colberg, Gail H. Gordon, 

and Charles H. Jackson ^ 

Materials and Processes Laboratory 


July 1982 


NASA 

George C. Marshall Space Flight Center 
Marshall Space Flight Center, Alabama 



1. aeaMT NO. t. SOVOINMiNT aocisa on no. 

NASA TM-82499 

S. RCCINItNT*S CATAI.OO NO. 

4. TITCi ANQ SUtTtTCt 

Refui!^iBhment of SRB Aluminum Components by Walnut 
Hull Blast Rmnoval of Protective Coatings 

t. RtaORT DArt 

July 1982 

a. MCaFOSMINO OR6AN1IATION CCOC 

7. AUTNoais) Wendell R. Colberg. Gail H. G(»^n. and 
Charles H. Jackson 

•.RtarORMINO oaOANttATION NtRONr » 

S. NtarONMINO OnaMilCATKHt N«.Mi MM AHOaCfl 

(Jeorgo C. Marshall Space Flight Center 
Marshr.ll Space Flight Center. Alabama 35812 

10. 'NONR UNIT NO. 

n. CONTRACT OR SR ANT NO. 

1$, TVRf OR RtROR'. S RCRIOD COVKRCD 

Technical Memorandum 

12 . sroNsoaiKO aoincv namc ano Aooacss 

National Aeronautics and Space Administration 
Washington, D.C. 20546 

14. SRONtORINO ASCNCY CODE 

1 IS. SUNIH.tMCNTANY NOTtS I 


Prepared by Materi^s and Processes LaboratcMry. Science and Engineering Directorate. | 


te. MtTMACT 

A test program was conducted to develop, optimise, and scale-up an abrasive 
blasting procedure for refurtislanent oi speciflc SRB com^xmcnts ; Aft Skirt. 
Forward Skirt. Frustrum. and painted piece parts. 

Tes* specimens utilising i2l9 T87 aluminum substrate of varying tldckjtessos 
were pre^mred and blasted at progressively increasing pressures (2.76 ^ 10® • 5.52 
^ 10^ N/m*) with selected abrasives. Specimens were then analysed for material 
response. The optimum blasting parameters were determined on panel specimens 
and verified on a large cylindrical Integrated Teat Bed (ITB). This report 
presents findings and conclusions of that study. 









ACKNOWLBDQMBNT8 


The euttiore express eppreetetlon to the ialloirinf personnel Ibr thehp euHMMPt 
end essistence: 

V. L. Hopper, BTS9 

J. A. Cox, ET39 
y. L. Cox, BT39 

B. Petton, ET39 

E. R. Reiech, EH13 

C. F. WiUiemeon, EH13 
k. H. Higgins, EH34 

K. Jordan, CO-OP (EH43) 

C. Wagner, CO-OP (BH43) 

K. McCarty. CO-OP (BH43) 

G. R. Marsh, EH22 

C. Salmon, ET39 
Dr. W. E. Hill. BH43 



TABLK OF CONTENTS 


Pag® 

INTRODUCTION 1 

SURFACK 1‘RKPARATION /BACKGROUND 1 

ABRASIVES 3 

PRELIMINARY TESTING 3 

HARDWARE TESTED 4 

Sul)^^trato 4 

Eijuitxuont 4 

Instrunu'ntation 7 


TESTING 


S t ross 7 

Warpa^io 8 

Rou^'hiu'ss 9 

CoiM\>sion 9 


BLASTING OF INTEGRATED 


TEST 


BED (ITB) HARDWARE 


9 


ITH KEFUKBISIIMENT 


10 


CONCLUSIONS U 

RECOMMEND AT U)NS 12 


REFERENCES 


13 



LIST OF TABLES 


Table Title Page 

1. PhysUal Properties of Abrasives 3 

2. Average Compressive Stress (40-80 psi Pressure Range) 8 

3. Average Warpage (40 80 psi Pressure Ram^e) 8 

4. Average Roughness (40 80 psi Pressure Range) 9 

5. Optimum Blasting Parameters for Aluminum SRB Structures 10 

6. Abrasive Cost and Availability 11 


IV 



TECHNICAL MEMORANDUM 


REFURBISHMENT OF SRB ALUMINUM COMPONENTS BY WALNUT 
HULL BLAST REMOVAL OF PROTECTIVE COATINGS 

INTRODUCTION 


The Solid Rocket Boosters (SRB) were designed and developed to be used with 
Space Shuttle Main Engines to provide the ii^tial thrust to lift the Shuttle from the 
launch pad to an altitude of 44 km. At that altitude, the SRBs will separate and 
start their return to Earth. A parachute recovery subsystem provides for controlled 
descent. The SRBs are recovered from the ocean and transferred to Kennedy Space 
Center (KSC) for disassembly and refurbishment. 

Refurbishment consists of cleaning, analysis, and repair of the SRB Structures 
Subsystem Components and return to the inventory for the next flight. The Struc^ 
tures Subsystem, Thermal Protection System (TPS), will be completely removed after 
each flight with an assessment of paint degradation and repair, as required, prior to 
replacement of the TPS. After 3 to 5 flights the paint will be totally removed and new 
new paint applied. This study was initiated to develop an abrasive blasting process 
to strip paint from the aluminum components in the nost economical and expeditious 
manner with minimal damage to the aluminuii substrate. 


SURFACK PREPARATION /BACKGROUND 


Bare aluminum, exposed to the elements, particularly ocean water and spray 
will corrode rapidly, therefore the surface must be provided with a barrier to the 
destructive forces in the form of a well Ixnided protective (paint) coating. Before 
application of the p*’otective coating, the svibstrate surface must be prepared with 
consideration to prt>cessing economics, harmful effects to the substrate and the ease of 
operations. Available surface preparation methods for surfaces already coated with 
oxidized or damaged paint inchKie chemical stripping which is slow and presents 
effluent disposal problems, and mechanical metlx>ds such as wire brushing and hand 
sandiiig. wiiich are slow and labor intensive. 

Experience acquired at this Center and descriptions in the literature show the 
most efficient and practical method for paint removal from SRB structures to be 
abrasive blast cleaning. This is a process in which iwitaminants. old paint coatings, 
etc. . are removed from metal surfaces by forceful impingement of an abrasive material 
to provide a clean surface suitable for the application of protective coatings (the 
abrasive blast cleaning proc*ess is not final in itself but is the initial stage of a sub 
sequent three coat finish pn>cess . in the case of aluminum, insisting of a chrtimate 
conversion coating, primer coat, and paint topcoat). The type and availability of 
equipment to propel the abrasive particles was a consideration. There are basically 
two ways of providing the energy source to the abrasive media in the blasting process. 
One utilizes compressed air as the vehicle to propel the abrasive to the surface of the 



work article, and the other is airless blasting whereby power of a hardened blast 
wheel provides centrifugal force to propel the abrasive. The latter method was not 
considered for this work, since correctly sized equipment was not available. 

The compressed air blasting techniques use compressed air to propel a stream 
of abrasive particles at high velocity onto a substrate surface. The expended energy 
of these particles on impact has the effec' of breaking up surface contaminants and 
coatings and effecting their removal with creation of a patterned or cratered surface 
profile on the substrate surface. This surface pattern is often referred to as anchor 
pattern. 

In order to achieve optimum conditions for maximum efficiency in the operation, 
the abrasive cleaning equipment must have integrated design features. The equipment 
components, such as. hoses, nozzles, metering valve, pressure controls, couplings, 
etc. . must be properly sizes and configured with the appropriate relationship to the 
selected abrasive and the total energy of the system. The kinetic energy the abrasive 
transmits is computed according to the formula; 


E ^ 1/2 mV^ 


or energy transnitted is proportional to the mass (or weight) of abrasive and to the 
square of its ve ocity. 

Selection of abrasives for evaluation was therefore governed by the following 
characteristics of the abrasives and of the substrate/ process. 

Abrasive Characteristics Substrate/Process Characteristics 


1 . 

Abrasive 

size 

1. 

Condition of surface to be cleaned 

2. 

Abrasive 

shape 

2. 

Surface finish required 

3. 

Abrasive 

hardness 

3. 

Type of component 




4. 

Component hardness 




5. 

Economics 


Given the intent (guidelines) to completely remove the SRB paint every 3 to 5 
flights with no more than 9 mils total metal removal over the duration of 20 flights, 
the rationale was to find a fast, successful, and realistically priced method that would 
inflict minimal component substrate damage in terms of: 


1) 

Metal removed 

2) 

I nd uced 

St ress 

3) 

Warpage 


4) 

Surface 

roughness 


This document is the result of that effort. 



ABRASIVES 


Natural abrasives used for surface finishing include the diamond, emery, car- 
borundum, sand, crushed garnet and quartz, trlpoli, and pumice. ArtifidUd abrasives 
are mostly silicone carbide, aluminum oxide, boron carbide, or boron nitride marketed 
under trade names [1]. Apricot pit, pecan, black walnut, english walnut, and rice 
shells (hulls) as well as corn robs also serve as natural organic abrasive materials 
when properly crushed and graded with sdeves [3]. 

Successful processing depends on the uniformity of size of the abrasive employed. 
Coarse or oversize particles cause deep scratches which are difficult to remove, land an 
excess of finer particles will slow production. Abrasive grains are graded on a series 
of screening and grading devices and should not be allowed to become mixed or to 
come in contact with oil or oily dust [2]. Recirculation of abrasives eventually renders 
tlwm ineffective, since continued inpact causes grain cracking, rounding of edges, and 
loss as dust. 


TABLE 1. PHYSICAL PROPERTIES OF ABRASIVES 14] 


Abrasive 

Chemical Formula 

Specific Gravity 

Hardness (Moh's) 

Aluminum Oxide 

^^2^3 

3.5 - 3.9 

9 

Silicon Carbide 

SiC 

3.217 

13 

Silicon Dioxide 

Si0 2 (.quartz) 

2.653 - 2.66 

7 

Garnet (common) 

3CaO . Fe gO 2 . 3S iO 2 

3.64 - 3.9 

6.5 - 7.0 

Walnut Hulls 

— 

1.25 

- 

Carbonite 

Al 20 g (corundum) 

3.97 - 4.10 

9 


PRELIMINARY TESTING 


At the beginning of the study several test samples were prepared and blasted. 
This served as a mechanism through which operators were trained in proper use and 
maintenance requirements of test instruments. This initial analysis was also used to 
standardize the angle and distance of gun from substrate that would produce optimum 
results. It was concluded that a 90 deg angle and 0.127 m (5 in.) from the sub- 
strate gave best results. Samples for preliminary testing were prepared in the same 
way as the study test specimens 


3 












HARDWARE TESTED 


Substrate 

Since the aft skirt, forward skirt, and frustum, the major SRB components to 
be refurbished by NASA are built of Aluminum 2219-T87, it was chosen as the sub- 
strate to be used in the development of an abrasive blasting process for the removal 
of the protective coating. Tho test specimens were prepared as rectangular panels 

-2 2 2 

with an exposed area of 9.29 x 10 m (144 in. ) from three different thickn^ses: 

1.57 X 10'^ m (0.062 in.), 3.18 x lO"^ m (0.125 in.), 6.35 x lo’^ m (0.250 in.). The 
test specimens were prepared using the procedure specified in Marshall Specification 
10A00528: 


1) 

Clean 


2j 

Iridite 


3) 

Prime with 

Bostik 463-6-3 

4) 

Paint with 

Fiostik white epoxy top coat 

5) 

Cure. 



Because of the physical characteristics of this substrate and past experience with 
abrasive blasting processes, different abrasives and sizes were deliberately selected 
to inflict minimal substrate damage. 


Equipment 

The equipment selected was a Pauli & Griffin Type I Dry Honer model DH48 
(Fig. 1). This is a self-contained abrasive blast unit. The abrasives are suspended 
and propelled by a high velocity air strean. After striking the work surface, abra- 
sives fall to the cabinet hopper and are conveyed to the cyclone separator. The dust 
and light weight abrasives that do not settle down are directed to a dust collector for 
disposal. The heavier abrasives that pass through the screen are returned to the 
storage hoppar and then back to the blasting system: Model DH48 has a 4.54 kg 
(10 lb) cleaning powder capacity and the blasting gun is a suction type with a 4.7<^ 

- 3 - 3 

X 10 m (3/16 in.) air jet and 9.53 x lO m (3/8 in.) nozzle. Figure 2 shows a 
front view of the gun, nozzle, and hose. The nozzle is considered the most important 
component of the system. The amount of energy dissipated and cleaning speed are 
functions of the nozzle distance to the work surface. The nozzle diameter is selected 
in accordance to the air power supply available and system design. Another factor 
in the selection of the nozzle is its length. A long nozzle will provide a high velocity 
with increased concentration of abrasive on impact, while a relatively short nozzle 
provides a wider area of impact with the abrasive being spread and decreased 
velocity [4]. 


4 




m . • 

V ^ VI 

V' ' ^ 




mi V- 






T-iffure 2. Gun, nozzle, and hose. 






Instrumentation 


Non-destructive techniques were utilized to measure residual atrMS and surface 
roughness. The X-ray method was used to measure the induced stress in the alumi- 
num specimen; it was possible to use this method oecauae of the elasticity of the 
aluminum [5]. A Brush Instruments Surf Indicator was used to measure tlM average 
surface roughness. Test specimen's warpage and thickness were measured with a 
Vernier Caliper and a straight edge. All readings used are an average of data 
collected . 

A Dermitron thickness measuring instrument was used to determine the paint 
thickness. Test specimens were weighed before and after blasting and the metal loss 
was found to be negligible. 


TESTING 


Stress 

In abrasive blasting, particles are propelled toward the material being blasted 
with velocity which causes surface indentations. These indentations resttlt in local 
plastic yielding. As the expansion of an affected area occurs, adjacent material, not 
plastically affected, restrains this imposed expansion. The plastically deformed layer, 
being dimensionally deformed and yet restrained from compensating expansion into 
adjacent space, is compressively stressed during the operation and retains a certain 
amount of residual stress. Residual stresses may be defined as stresses that would 
remain in an elastic solid body if all external loads were removed. One important 
consideration was to find an abrasive that would induce minimum compressive stress 
in the surface being cleaned. 

Eight different abrasives were selected based on past experience and desired 
results on the substrate: 

1) Silica sand 40/70 

2) Silica sand 80/90 

3) Garnet 25 

4) Garnet 80 

5) Silicon carbide 30/60 

6) Aluminum oxide 36 

7) Aluminum oxide 80 

8) Walnut hulls 12/20. 

Test specimens were analyzed with a Faststress Analyzer (automated X-ray diffraction) 
This is a non -destructive technique used to determine induced surface stress on the 
substrate: strains are measured only at the surface where the stress is relieved in 


7 



the normal direction. Table 2 shows the average stress v:^iues recorded from the 
analyzer. No surface stress was detected in penels blasted with walnut hulls when 
analyzed with Fastress Analyzer. 

TABLE 2. AVERAGE COMPRESSIVE STRESS (40-80 psi PRESSURE RANGE) 


Abrasi^'e 

Average Compressive Stress (ksi) 

Garnet 25 

— 

Silicon Carbide 30/60 

23.6 

Aluminum Oxide 36 

25.81 

Silica Sand 40/70 

30.51 

Garnet 80 

28.43 

Aluminum OxiJe 80 

33.85 

Silica Sand 80/90 

S'!. 10 

Walnut Hulls 12720 

no stress detected by analyzer 


Warpage 

When a specimen is blasted, re.«'idual compressive stress induces convex curva- 
ture (warpage) on the peened side. Warpage is dependent upon the amount of abra- 
sive striking the surface (the amount is proportional to blasting time) and to abrasive 
particle size, speed, direction, hardness, and rheological properties. 

Table 3 represents average warpage induced by each abrasive for pressures in 
5 5 2 

the range 2.76 x 10 to 5.52 x lo N/m (40 to 80 psi). As shown, blasting with 
walnut hulls gives the least amount of convex curvature. The abrasive producing 
the next smallest warpage was Aluminum Oxide 80. 

TABLE 3. AVERAGE WARPAGE (40- 80 psi PRESSURE RANGE) 


Abrasive 

Warpage (m) 

Garnet 25 

1.14 > 10'^ m (0.4506 in.) 

Silicon Carbide 30/60 

1. 18 ' 10'^ m (0.4636 in. ) 

Aluminum Oxide 36 

9.41 X 10'^ m (0.3706 in. ) 

Silica Sand 40/70 

1. 3 X 10'^ m (0.5120 in.) 

Garnet 80 

8.08 > 10'^ m (0.3183 in. ) 

Aluminum Oxide 80 

6.15 X ic'^ m (0.2421 in. ) 

Silica Sand 80/90 

7.98 X 10'^ m (0.3142 in. ) 

Walnut Hulls 12/20 

4.90 X lO"* m (0.0193 in.) 


i j 


of POOR QOALlTf. 


8 





Roughness 


Surface finish of the test specimens blasted was modified by the pee ting action 
of the abrasive gi'ains. Different factors such as abrasive si ?e, hardness, speed, 
shape, and impact angle provide a wide range of irregularities. This surface irregu- 
larity is generally called anchor pattern or surface roughness. A Surf Indicator was 
used to measure surface finish of blasted panels. This instrument measures height 
irregularities created by abrasive impacts. An arithmetic average of the irregularities 
yields an average roughness value for a particular area being measured. Table 4 
shows average roughness results for each abrasive. These values clearly indicate 
that panels blasted with walnut hulls exhibited the least amount of surface roughness. 

TABLE 4. AVERAGE ROUGHNESS (40-80 psi PRESSURE RANGE) 


Abrasive 

Average Roughness (ym) 

Garnet 25 

5.05 (199 yin.) 

Silicon Carbide 307 60 

4. 19 (165 yin.) 

Aluminum Oxide 36 

4. 17 (164.33 yin.) 

Silica Sand 40/70 

3. 55 (140 yin.) 

Garnet 80 

3.11 (122.30 yin.) 

Aluminum Oxide 80 

2.06 (81.33 yin.) 

Silica Sand 807 90 

2.03 (79,99 yin.) 

Walnut Mulls 12/20 

1.06 (41.70 yin.) 


Corrosion 

Several test panels were randomly selected to simulate hardware I’efurbishment 
after being exposed to a salt water environment for seven days (it has been estimated 
that it would take no more than one week to recover SRB hardware in the worst 
possible conditions). The aluminum panels (2219 and 6061 alloys) wei*e blasted with 
walnut hulls to remove the Bostik topcoat and primer, acetone wiped, and repainted 
with the Bostik system. The test specimens were then prepareil for and placed in a 
5 percent salt spray chamber for 4032 hr. Tape adhesion tests were then performed 
on each panel. 

Test results indicated that the refurbished Bostik coating system performance 
was. indeed, very similar to the Bostik touting system as originally applied to the 
substrate. Based on the test results, it is recommendeti that the chromate conversion 
coating be thoroughly examined after walnut hull blasting, and if bare aluminum is 
exposed, a re application of the chromate conversion coating is required prior to 
re upplication of the Bostik coating system. 


BLASTING OF INTEGRATED TEST BED (1TB) HARDWARE 

A relatively large cylindrical ITB segrnem was blasted with the selected abrasive, 
walnut hulls 12/20. 'I ' results of this blasting were used as the basis for scale-up 
estimations and recommendatiotjs. 


9 







Equipment used for blasting the ITB segment included: 

1) Comprei jr: Schramm model JD18A. serial No. UDP26662 512 

2) Helper: Clemco model SCFW 24 52. serial No. 1*^067 

3) Nozzle: 1.27 ^ lO’^ m (0.5 in.) I.D, 

4) Hose: 5.08 x lo'^ m (2.0 in.) O.D. 

2 2 

The selected blasting seqi^nce cleaned an area of 6.233 m (67.09 ft ) and took 

-3 2 2 . 

2040 sec (34 min) thus producing a removal rate of 3.055 ^10 m /sec (1.97 ft /min) 
Complete paint removal was accomplished without harm to the underlying chromate 
conversion coating and without detectable substrate damage. Presuming the removal 
rate is constant, we can estimate the cleaning time for flight hardware: 


1 ) 


Aft Skirt: 

2 

Area = 34.36 m 
Time = 34.36 m^ 


(369.85 ft^) 


( sec \ / 1 hr \ 

o ARC ,A 3 2 / 1 3600 sec / 

3.055 > 10 m / \ / 


2) Forward Skirt : 

Time = 3.48 hr 

3) Frustrum: 

Time = 2.5 hr 


3. 13 hr 


The optimum blasting parameters determined for aluminum SRB structures are listed 
in Table 5. 


TABLE 5. OPTIMUM BLASTING PARAMETERS FOR 
ALUMINUM SRB STRUCTURES 


Pressure 

C o 

5.52 ^ 10 N/r.r (80 psi) 

Distance to substrate 

0.3048 to 0.6096 m (12 to 24 in.) 

Angle to substrate 

45 to 90 deg 


1TB REFURBISHMENT 


In house refurbishment of the ITB segment proved no major reconversion coating 
of the aluminum substrate was required. The ITB segment was sectionally divided 
and blasted with walnut hulls. Two blasted sections were reprimed and repainted. 
Two unblasted sections were hand sanded and repainted, and one section was only 
repainted. 


10 




All five sections were tested using Adhesion (wet) Tape Test as per aSTM 6301.1 
[8]. No paint was removed in either section. 


CONCLUSIONS 


It was determined from data collected and test results that Walnut Hulls 12720 is 
the best abrasive among those tested to clean aluminum SRB components while inducing 
minimum damage to the substrate. 

Walnut Hulls were assessed as the appropriate ahi*f^.sive for SRB refurbishment 
since : 

1) No major reconversion coating of aluminum is required with Walnut Hiills 
(complete reconversion coating is reauired with other abrasives tested in this study). 

2) Walnut Hulls produced the least amount of surface roughness. 

3) No compressive stress is induced by Walnut Hulls. 

4) Negligible warpage is created by Walnut Hulls. 

5) Walnut Hulls are 100 percent biodegradable; therefore, no pollution is asso- 
ciated with their use. 


6) When purchased in large quantities Walnut Hulls are the least expensive 
abrasive tested (Table 6), 

TABLE 6. ABRASIVE COST AND AVAILABILITY 


Abrasive 

Cost, $/kg (453.59 kg) 

Availability 

Silicon Carbide 30/60 

0.63 

Yes 

Aluminum Oxide 30 

0.50 

Yes 

Silica Sand 30/90 

0. 48 

Yes® 

Aluminum Oxide 36 

0.43 

Yes 

Silica Sand 40/70 

0.23 

Yes 

Garnet 80 

0. 21 

Yes 

Garnet 25 

0.19 

Yes 

Walnut Hulls 12720 

0.14 

Yes 


a. Special Order 

b. Prices subject to change. 


11 




RECOMMENDATIONS 


Based on findings and conclusions of this study, the following are recommenda- 
tions for scale-up of an abrasive blasting syston: 

Abrasive: Walnut Hulls 12720 

5 2 

Pressure: 5.52 x lo N/m (80 psi) 

Angle to substrate: 45 to 90 deg 

Distance to substrate: 0.3048 to 0.6096 m (12 to 24 in.) 

Equipment: Abrasive blast unit equivalent to that employed in ITB blasting 

with added recirculation capability: 

Compressor: Schramm model JD18A, serid No. UDP 2S662 512 

Hqpper: Clemco model SCFW 2452, serial No. 10067 

Nozzle: 1.27 x lO ^ m (0.5 in.) I.D. 

Hose: 5.08 x lO ^ m (2.0 in.) O.D. 


12 


REFERENCES 


1. Brady and Clauser: Materials Handbook. 11th edition. 

2. Abrasive Grain and Powders: Specifications and Recommendations; The Carborun- 

dum Company, 1954. 

3. Military Specification M1L-G-5634C; Grain, Abru^ive, Soft, for Carbon Removal. 

5 June 1970. 

4. Metal Finishing: Guidebook and Directory. 1973. 

5. Almen and Black: Residual Stresses and Fatigue in Metals. McGraw Hill Book 

Company, Inc., New York, 1963. 

6. Heat Treating, Cleaning and Finishing Metals Handbook; 8th edition, Vol. 2. 

7. Baumeister; Mark's Mechanical Engineering Handbook. McGraw Hill Company, 

6th edition, 1958. 

8. ASTM Method 3301. 1: Adhesion (Wet) Tape Test. September 1, 1965. 


13