A method of repairing cracks or damaged areas in glass, in particular, glass coatings provided on tile. The method includes removing the damaged area using a high speed diamond burr drilling out a cavity that extends slightly into the base material of the tile. All loose material is then cleaned from the drilled out cavity and the cavity is filled adjacent the upper surface of the coating with a filler material including chopped silica fibers mixed with a binder. The filler material is packed into the cavity and a repair coating is applied by means of a brush or sprayed thereover. The repair includes borosilicate suspended in solution. Heat is applied at approximately 2100 F. for approximately five minutes for curing the coating, causing boron silicide particles of the coating to oxidize forming a very fluid boron-oxide rich glass which reacts with the other frits to form an impervious, highly refractory layer

Helman, D. D.

Holt, J. W.

Smiser, L. W.

English

NASA Technical Reports Server

United States Patent [I91 11 11 4,330,572 
Holt et al. [45] May 18, 1982 
[54] METHOD FOR REPAIR OF THIN GLASS 
COATINGS 
[76] Inventors: 
[21] Appl. No.: 
[22] Filed: 
Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Jack W. Holt, Walnut, 
Calif.; Donald D. Helman, Buena 
Park, Calif.; Laurence W. Smiser, 
Downey, Calif. 
172,100 
Jul. 25, 1980 
[51] Int. Cl.3 .............................................. B32B 35/00 
[52] U.S. CI. ................................. 427/140; 427/372.2; 
427/397.7 
[58] Field of Search ............... 427/140, 193, 292, 203, 
427/299, 309, DIG. 3, 372.2, 379, 397.7; 
156/94, 98; 264/36 
1561 References Cited 
U.S. PATENT DOCUMENTS 
2,826,508 3/1958 Giles .................................... 427/140 
2,955,952 10/1960 Herbst ................................. 427/140 
3,865,774 2/1975 Malone .................................. 264/36 
4,244,721 1/1981 Gupta .................................. 427/309 
OTHER PUBLICATIONS 
Narken, “Ceramic Surface Preparation”, IBM Techni- 
cal Disclosure Bulletin, vol. 16, No. 2, Jul. 1973. 
Primary Examiner-Norman Morgenstern 
Assistant Examiner-S. L. Childs 
Attorney, Agent, or Firm-James 0. Harrell; John R. 
Manning 
[571 ABSTRACT 
A method of repairing cracks or damaged areas in glass, 
in particular, glass coatings provided on tile. The 
method includes removing the damaged area using a 
high speed diamond burr drilling out a cavity that ex- 
tends slightly into the base material of the tile. All loose 
material is then cleaned from the drilled out cavity and 
the cavity is filled adjacent the upper surface of the 
coating with a filler material including chopped silica 
fibers mixed with a binder. The filler material is packed 
into the cavity and a repair coating is applied by means 
of a brush or sprayed thereover. The repair indudes 
borosilicate suspended in solution. Heat is applied at 
approximately 2100” F. for approximately five (5 )  min- 
utes for curing the coating, causing boron silicide parti- 
cles of the coating to oxidize forming a very fluid bo- 
ron-oxide rich glass which reacts with the other frits to 
form an impervious, highly refractory layer. 
3 Claims, 8 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820025644 2020-03-21T17:25:10+00:00Z
akllt May 18, 1982 Sheet 1 of 2 
i3kne May 18, 1982 Sheet 2 of 2 9 
V 
4,330,572 
1 
METHOD FOR REPAIR QP THIN GLASS 
COATINGS 
ORIGIN OF THE INVENTION 
The invention described herein was made in perfor- 
mance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronau- 
tics and Space Act of 1968, Public Law 85-569 (72 Stat. 
435,402 U.S.C.P. 2457) 
BACKGROUND OF THE INVENTION 
Heretofore, space vehicles have been launched from 
space platforms into outer space and normally no at- 
tempt was made to recover the entire space vehicle for 
subsequent use after it has been returned to earth. One 
reason for this is that the space vehicle was normally 
damaged extensively by heat generated as it returned 
back through the atmosphere. In order to protect astro- 
nauts and space capsules forming part of the space vehi- 
cle from being injured or damaged by the re-entry heat, 
ablative coatings have been provided on the space cap- 
sule. Normally these ablative coatings were designed 
for a single re-entry trip. If it were desired to utilize the 
space capsule again, it would be necessary to remove 
the remains of the ablative coating from the space cap- 
sule and place another one thereon. 
In recent developments in the space industry, it has 
been proposed to utilize a space vehicle which will be 
launched from earth and after orbiting the earth for a 
period of time, brought back to earth and landed on a 
runway. In order to protect the space vehicle from the 
extensive heat generated upon re-entering the earth's 
atmosphere, heat protective tiles have been placed on 
the skin of the space vehicle. The thickness of these tiles 
varies from approximately one inch up to approxi- 
mately five inches depending on the particular surface 
that is to be protected and the exposure that that surface 
encounters during re-entry into the earth's atmosphere. 
These tiles are designed for absorbing the heat encoun- 
tered in a large number of missions. It is anticipated that 
the space shuttle protected with these reusable tiles can 
be launched and recovered approximately one hundred 
times. 
The shuttle reusable surface insulation (RSI) is com- 
posed of machined lightweight fused silica tiles, coated 
with a thin ceramic coating. This coating is very fragile 
and highly susceptible to damage, punctures, dings, 
chips and cracks. These damaged tiles must be removed 
and replaced if they cannot be repaired. To remove a 
tile from the skin of the space vehicle and to replace it 
with another undamaged tile is a time consuming and 
expensive procedure. Thus, it is desirable to provide a 
method of in situ repair of the tiles and it is estimated 
that l/lOth of the manpower is required to repair a tile 
in accordance with the present invention as compared 
to removing a tile and replacing it. 
Repair of punctured or cracked thin glass has been 
relatively unsuccessful due to thermal stresses and has 
not been considered feasible. Attempts have been made 
to drill a hole at the base of the crack to prevent further 
crack propagation, but instances of puncture repair or 
crack healing are relatively non-existent. The process 
developed according to the invention is used to repair 
The RSI tiles that are to be repaired include a ce- 
ramic coating which is a borosilicate, reaction cured 
glass from 0.010 to 0.020" thick. 
SUMMARY OF THE INVENTION 
A method in accordance with the present invention 
for repairing thin glass coatings similar to those used on 
high temperature insulation tile of the United States 
space shuttle. 
In one particular mode of the invention, the damaged 
area of the ceramic tile is drilled out, forming a cavity 
that terminates close to the surface of the lightweight 
fused silica main body portion of the tile. All loose 
particles are then removed from the drilled out cavity. 
15 The drilled out cavity is then filled flush adjacent the 
upper surface of the coating with a filler material con- 
sisting of pulverized silica fibers, which is packed firmly 
into the cavity. A repair coating is then either sprayed 
or brushed over the repaired area and allowed to air dry 
20 for approximately five ( 5 )  hours. The applied coating is 
then heated with quartz lamps to a temperature of ap- 
proximately 2100" F. for about five (5) minutes causing 
an impervious, highly refractory layer to be produced. 
When repairing only the ceramic coating or glass, 
25 then it is only necessary to apply the coating material 
over the damaged area and curing it in the same manner 
as discussed above which will be discussed in more 
detail below. 
Accordingly, it is an important object of the present 
30 invention to provide a method for repairing glass coat- 
ings. 
Another important object of the present invention is 
to provide a method and apparatus for in situ repairing 
glass coatings utilizing relatively inexperienced person- 
35 nel to produce a repaired surface that is integral with 
the coating being repaired. 
These and other objects and advantages of the inven- 
tion will become apparent upon reference to the follow- 
ing specification, attendant claims and drawings. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
FIG. 1 is a side elevational view of a typical hyper- 
sonic space shiphe-entry vehicle showing, diagrammat- 
ically, reusable surface insulation in the form of tiles 
FIG. 2 is an enlarged perspective view of a tile with 
a coating damaged by a ding. 
FIG. 3 is a side elevational view showing an operator 
pulling out the damaged portion of the tile; 
FIG. 4 is a side elevational view showing an operator 
filling the cavity with a filler material; 
FIG. 5 is a side perspective view illustrating an opera- 
tor packing the filler material into the cavity using a 
thin piece of paper placed over the repair cavity and 
FIG. 6 is a perspective view illustrating a repair coat- 
FIG. 7 illustrates a modified means of applying the 
FIG. 8 shows the repaired surface being heated to 
5 
10 
40 
45 positioned thereon. 
50 
55 pressing with his thumb; 
ing being brushed onto the repaired area; 
prepared coating to the repaired area, and 
form integral coating. 
60 
DESCRIPTION O F  A PREFERRED 
EMBODIMENT 
65 While a process according to the subject invention 
can be utilized for repairing holes in cracks and glass, 
the following descrirhon will be made in reference to 
punctures, dings and chips in thin glass. repairing a t i e  bloci that is presently being utilized on 
4,330.572 
3 
a space re-entry vehicle. Normally, the tile blocks are 
from 1" to 5" in thickness and include a main body 
portion formed of fused silica (Li-900) supplied by 
Lockheed Missile and Space Company of Sunnyvale, 
Calif., which has a ceramic coating positioned thereon 
that may vary from 0.010-0.020 inch thickness. It is to 
be understood, of course, that the process could be used 
for repairing glass of other thickness. The ceramic coat- 
ing is very brittle and as a result, dings, cracks, and 
punctures often occur that have to be rapaired prior to 
launching or relaunching the space vehicle. 
Prior to starting the repair of the tile, a filler material 
and a coating material is prepared. The filler material 
includes pulverized fused silica (Li-900). This is 
chopped silica fibers mixed with a binder into a slurry, 
centrifuged, dried and sintered. Final weight = 9 
Ibs./cu. ft. This is pulverized and screened through 
-325 mesh. The filler material is supplied by Lockheed 
Missile and Space Company of Sunnyvale, Calif. 
The material for preparing the filler material may be 
derived from broken tiles of scrap parts not found to be 
repairable. Such powdered particles are then heated in 
a dry atmosphere to dry off the moisture contained in or 
on them. The resulting material then becomes quite 
formable and of a powdery consistency. 
The coating material includes a slurry of the follow- 
ing formulation: 
4 
must be maintained to prevent additional coating dam- 
age, and no more tile (Li-900) as identified by the refer- 
ence character 14 should be removed than is necessary. 
When the punctured or damaged area is less than i", no 
5 grinding of the coating should be done unless there is 
some obvious crack initiators as determined by an alco- 
hol wipe. 
When the puncture or damaged area is from i'' to %'' 
in diameter, a circle guide 17 large enough to include 
lo the entire damaged area is positioned over the damaged 
area. A high speed turbine motor 18 with a fine 
diamond burr 20 is used to trepan a hole in the coating 
such as illustrated in FIG. 3. It is noted that the burr 
extends only slightly below the ceramic coating layer 
When trepaning the hole in the tile coating 16, care 
should be taken to prevent the diamond burr 20 from 
going any deeper into the tile material 14 than is neces- 
2o sary to cut through the coating. No more tile should be 
removed than is absolutely necessary. 
After the trepan hole has been ground through the 
coating 16, the coating debris is gently removed from 
the damaged area with a spatula or other small instru- 
25 ment and vacuumed. The edge of the coating around 
the periphery of the damaged area should then be in- 
spected for obvious cracked initiators. If such cracks 
exist, the high speed turbine motor 18 and fine diamond 
l5 16 into the tile base 14. 
Coating Solids burr 20 should be used to polish the coating edge in the 
Glass Frit (7 50% Fusing Works The next step of the process includes utilizing a spat- 
nominal B2O3 Content) Temperature Corning, New ula or similar instrument 22 for pressing the filler mate- 
- 325 Mesh 2100") York rial as described above into the cavity that has been 
5% Borosilicate Corning Glass previously drilled out. A weighing paper 24 is then 
Glass Frit #7740 Works 35 positioned over the repaired area such as illustrated in 
-325 Mesh Corning, New York FIG. 5 and using a thumb to rub over the outer surface 
of the paper, the filler is packed firmly into the cavity. 0 28% Potassium Alfa Products silico fluoride 152 Andover St 
99% K2SiF6 #89-23 Danver, MA The filler material is then again added with the spatula 
2 66 Boron Silicide SiB4 Cerac, Inc and the packing procedure is repeated until the tiller 
Milwaukee, Wis. 40 surface is smooth and the edge of the coating around the 
(High in Bl4) periphery of the damaged area can be barely felt. 
The weighing paper 24 is removed and clean cheese- 
14 0% Methocel stock cloth is used to wipe the surrounding tile coating for 
removing any filler material from the surface of the tile. 
45 Care must be taken during this procedure not to disturb 
the filler surface. 
There are two methods of applying the repaired coat- 
ing. The first method is illustrated in FIG. 6 wherein an 
artist's brush 26 is used for applying the coating over 
and 50% liquid 5o the filled cavity. In FIG. 7, there is illustrated the use of 
a spray bottle 28 for spraying the repair coating Over the 
Supplier 
30 area to remove these crack initiators. 
92 06% Borosilicate (Composition Corning Glass 
#LAC-42-4561-0100 
Grade AA Special 
Coating Liquids 
86 0% Ethyl Alcohol 
The methocel stock solution is 2% methocel and 98% 
The above solids are measured into a borundum mill 
distilled water. 
according to the above listed percentages and the liq- 
mixture. The solids and alcohoVmethoce1 mixture is 
are added to make a 50% 
for three (3) hours' After three (3) hours, the 
mixture is removed and poured Out Of the borundum 
filled cavity. When brushing the repair coating such as 
described above over the damaged area, it should be 
to pro- 55  done in steps until there is a coating buildup ofapproxi- is then added to the vide a repair coating of 36% solids. mately 20 mils. with an overlap over the surrounding In FIG. 1, there is illustrated a space re-entry vehicle 
that is adapted to re-enter the atmosphere after orbiting coating edge of approximately 3/16". The coating 
surface thereof for protecting against extreme heat en- sufficient to keep from dripping Or running. 
countered as the vehicle re-enters the earth's atmo- 60 After the desired buildup has been obtained, the re- 
sphere. As previously mentioned, these tiles have a very paired area is then allowed to air dry for approximately 
brittle ceramic coating 16 thereon; and if cracks, dam- five (5 )  hours. 
ages, or punctures occur in the tile, they must be re- Quartz lamps 30 are then used for curing the repaired 
paired prior to re-use of the vehicle. In order to repair area by applying heat of approximately 2100" F. for 
a damaged area 12 such as illustrated in FIG. 2, first the 65 approximately five (5 )  minutes. During this firing pro- 
damage is visually checked and if the damaged area is cess, the boron silicide particles oxidize, forming a 
i'' in diameter or less, the loose coating debris is gently boron oxidized rich glass. This glass is very fluid and 
removed using a small spatula or small instrument. Care readily wets and reacts with the other frits. In a short 
the earth. The vehicle has tiles 10 positioned on the be to dry between Only 
4,330,572 
5 6 
time, the reactive liquid consumes enough of the avail- 
able frit to form an impervious, highly refractory layer. 
Tile coatings repaired by the above process have 
successfully withstood fifteen simulated space shuttle 
re-entry cycles in vacuum at 2300" F. maximum temper- 5 
ature and twenty-five therm01 cycles at atmospheric 
pressure and the same maximum temperature. 
Where there is merely a crack in the ceramic tile 
surface, alcohol is first applied to the crack. While the 
crack is still wet with alcohol, the previously described 
coating material is applied to the crack using a brush. 
The evaporation of the alcohol helps to draw the coat- 
ing into the crack, assisting in the capillary action. The 
brushing on of the coating material is repeated until 15 
there is a buildup of approximately 10 mils. The coating 
material should be allowed to dry between applications 
only sufficiently to keep from running or dripping. 
The excess coating is removed with a clean piece of 
cheesecloth. The repair coating, when being brushed 20 
on, should overlap the crack on each side approxi- 
mately i". 
The repaired coating is allowed to air dry for approx- 
imately five (5 )  hours and then cured with heat as de- 
scribed in repairing larger cracks or dings above. 
While a preferred embodiment of the invention has 
been described using specific terms, such description is 
for illustrative purposes only, and it is to be understood 
that changes and variations may be made without de- 
parting from the spirit or scope of the following claims. 
What is claimed is: 
1. The method for repairing damaged areas such as 
punctures or cracks in a ceramic coating provided on 
lightweight fused silica tiles comprising the following 15 
(i) mixing chopped silica fibers with a binder into a 
(ii) said sintered filler material then being pulver- 
slurry, centrifuging, drying and sintering; 
ized and screened through -325 mesh; 
(d) packing said filler material into said cavity; 
(e) applying a coating Over said filled cavity, said 
coating consisting essentially of: 
97 percent borosilicate glass frit 
B203-325 Mesh; 
2.66 percent Boron silicide SiB4; and 
0.28 percent Potassium silicofluoride (K2SiF6); 
(f) applying heat to said repaired area for curing said 
coating and filler material; 
said heat being sufficient to said Boron silicide 
to oxidize in a fluid state which enough 
of said frit to form an impervious, highly refractory 
layer. 
2. The method as set forth in claim 1 further compris- 
(i) said heat being applied for curing said repaired 
area being applied by lamps at a temperature of 
about 2100" F. for about five ( 5 )  minutes. 
3. The method of repairing damaged areas such as 
cracks in a glass coating comprising the following steps: 
(a) preparing a slurry including about 92 parts of high 
fusing temperature borosilicate frit and about 5 
parts of lower fusing temperature borosilicate frit, 
about 2.6 parts of boron silicide, and 0.3 parts po- 
tassium silicofluoride in alcohol to yield about a 
fifty percent (50%) solids mixture by weight; 
10 
ing: 
25 
30 
(b) applying alcohol to said damaged area; 
(c) while damaged area is still wet from said alcohol, 
applying said slurry to said damaged area allowing 
said alcohol to draw said slurry into said damaged 
area. ._ 
steps: 
(a) drilling out said damaged area in said ceramic 
coating terminating close to the surface of said 
lightweight fused silica, producing a cavity; 
(b) cleaning all loose particles from said drilled out 40 
cavity; 
(c) filling said drilled out cavity flush with the upper 
surface of said coating with a filler material pre- 
pared by: 
45 
I_ _ _  
(d) air drying said slurry on said damaged area for 
about five (5) hours, and 
(e) curing said slurry applied to said repaired area by 
applying heat at a temperature of 2100" F. for 
about five minutes causing said boron silicide parti- 
cles of said slurry to oxidize forming a very fluid 
boron-oxide rich glass which reacts with the other 
frits to form an impervious, highly refractory layer. * * * * *  
50 
55 
60 
65 


Method for repair of thin glass coatings

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server