Tialite which is chemically known as Aluminium Titanate [1] is the compound that is used throughout this research. It is a refractory material [2] which has several interesting properties such as differential thermal expansion coefficient, excellent thermal shock resistance and high melting point [3]. These properties are made to use, by sintering of aluminium dioxide and titanium dioxide to form Tialite within a ceramic. Sintering processes have been done earlier and the effects on properties have been studied [4]. Ceramic is a material which is light weight but also hard. For metal forming, investment casting is one of the methods that are employed in industries. There are lots of small components that are being made using this process. It has been known that if the investment, which is the ceramic mould is in contact with the components for a long time, there are chances of it to impart stress back to the components that are being made. The reason for bringing Tialite is that, on producing it in situ, it does not damage the mechanical properties, but at the same time reduce the strength of the mould on cooling [5]. In this way, it will not allow stress to be imparted on to the components [6]. The principle of this research is based on an interesting property of Tialite which is put into play thereby weakening the shell, which is the mould. Tialite has a property of thermal anisotropic [7] expansion in which the positive expansion occurs in two directions and negative expansion in the other direction [8]. This allows the Tialite particles to have an elongated shape. This happens when Tialite is allowed to be cooled from the fired temperature. The structure of Tialite is distorted oxygen octahedral [9]. These octahedral chains are weakly bonded to each other. It is this structure that leads to strong thermal anisotropy. The change in shape to being elongated on cooling from the firing temperature allows it to impart stress around the stucco. This leads to formation of cracks around the stucco [10], thereby weakening the shell. Tests are done to check the strengths of the shells which are made using wax patterns. Certain numbers of samples are made with different layers. From the tests done on strength, it has been found that there is a lot of weakening in the shell. Strength testing has also been done earlier to understand the effect of bonds in materials [11]. From the findings it has been understood that stuccoing the shell with Tialite has a significant effect in weakening the shell when compared to the standard shell which consists of various layers stuccoed with Molochite (fine or coarse). There are other tests that are also done to understand the structure and the chemical nature of the shell. SEM imaging was done to understand the structure this imaging has also been to understand the structure [12]. EDS was done to understand the chemical nature of the shell. XRD analysis was done on powders that were fired at different temperatures. XRD results have been used earlier to understand the structure [13]. The XRD patterns were compared to understand the phases that are present. Learning from the patterns gives knowledge about the temperature at which the aluminium oxide and titanium dioxide reacts to form Tialite.
Introduction:-
All materials have properties which make them different from each other, and thus making its use and applications different. Properties of materials would mostly include hardness, density, melting point, boiling point etc. These properties which are in general called the mechanical properties have been fondled with earlier [14].Materials in general would include metals, non-metals, insulators and so on. One of the properties, which are mainly noted for metals, is the strength. It is because of this property that substances retain a shape of their own. The effect of process parameters have been studied earlier and over here, one of the parameters is temperature [15].The research involves ceramics rather than metals. Ceramics are materials with certain advantages of being light weight and being harder than metals. For ceramics the high temperature mechanical properties have been studied, and the mechanical properties are manipulated by researchers [16]. Due to certain properties of ceramics, it has been used as the refractory for investment casting.
Investment casting is one of the methods that are being employed for manufacturing process that is used for metal forming [17]. In this process, first a wax model of the desired shape is made. The mould which is the investment is made from three different stages which involve creation of wax pattern, coating, stuccoing and hardening by sintering. Stuccoing is the application of coarse powder over the coated surface to build volume. Investment castings are mostly used for small castings, rather than large castings. It is the production of the investment casting ceramic shell mould which is a crucial part in the whole of the investment process [18] and its shape is determined by the wax pattern. The product manufactured by this method ideally does not require any finishing. There are different types of castings that are present, which are die casting, sand casting and many more. The advantage of investment casting is that it can make more complicated parts than the latter types. In this particular research, the property of the investment cast (shell) which forms the ceramic mould is varied in such a way that the strength of shell reduces.
This research is conducted in order to find out the effect of stuccoing the ceramic mould with a particular chemical compound called Tialite precursors. The aim is to reduce the strength of the shell which will be used as the mould. When stuccoing the investment mould with different components, may help vary its strength. Here it's done by stuccoing the shell with a compound called Tialite, during manufacture. It has certain unique properties which might help in getting the desired result. Tialite is the name given to aluminium titanate. It is a refractory material which has several interesting properties such as low thermal expansion coefficient, excellent thermal shock resistance and high melting point [19]. The thermal shock resistance is the property of a material not to vary its strength even though there are rapid temperature changes. Most materials expand isotropically when heated, if there is no phase change [20]. This happens in the case of Molochite which is highly calcined kaolin [21]. In cases of Molochite and the shell matrix, they have similar properties and when the shell is fired and cooled down stresses are induced onto the shell. Whereas on the addition of Tialite into a shell, its differential thermal expansion would weaken the shell due to thermal stresses both during the firing process and the cool down, without hindering the high temperature properties as well as the weakening of shell. Instead the Tialite is made during the sintering process, so that both the plastic behaviour at elevated temperatures can be used as well as stresses can be developed on cooling which will help in forcing failure of the shell. The structure of Tialite forms distorted oxygen octahedra. These octahedral form chains which are weakly bonded to each other. It is this structure that leads to strong thermal anisotropy [22]. This property leads to the creation of localized internal stresses which happens during cooling from the firing temperature. Micro cracking occurs during cooling from the firing temperature. This extensive micro cracking leads to the mechanical weakening of material. The thermal expansion coefficient is positive along two of the crystal directions and negative along the third axis. The anisotropic expansion which occurs thermally is the reason for severe micro cracking (during cooling from firing temperature) which leads to poor mechanical properties of the shell.
It is generally obtained by a solid state reaction between aluminium oxide and titanium dioxide. According to the equation,
Al2O3 + TiO2 1350 C Al2TiO5 (Tialite)
It can be easily understood from the above equation that the stoichiometric ratio is 1:1. The molecular mass of aluminium oxide is 101.96grams and that of titanium dioxide is 79.9grams. There are various processes that are followed throughout the research. They would include agglomeration, firing, drying, coating, stuccoing, de-waxing, cutting etc. These processes are the ones that are included in the making of shell. Once it has been made, there are certain properties that are to be examined and tested. The weakening of the shell on the stuccoing of such a compound can be examined using different techniques which involve 3- point bench loading, Scanning Electron Microscopy, EDS etc. SEM will help us to find out the new phase that will be present and also will tell about the development of cracks around the stucco. The size of the particles will be compared to the standard system. In the standard system, the stuccoing is done by Molochite. Using the EDS technique will help us to understand the chemical product formed due to the various processes. There is certain amount of samples that were fired at various temperatures. And on these samples, X-ray diffraction should be done, thus helping us to understand all the phases that are present. The strength has to be measured using a 3 point bench loading equipment. This equipment helps in understanding on what amount of load, the bars that have been created cracks. From knowing the load, the strength can be calculated using a certain formula [23];
where is the strength, 'F' is the load that is applied for cracking the bar, 'L' is the length of the bar, 'B' is the breadth of the bar and 'H' is the height of the bar. Comparison of strengths of standard shell for casting steel is done with that of customised bars. This standard shell is fired at normally at 8000C before being fired in the casting furnace to 14000C. It comprises for the shell formulation and also the stucco that has been applied. This is also done for the customised sample where the shells are stuccoed using Tialite.
There could be possible errors in the amount of mixing that could have occurred. There were so many factors that were neglected. In order to make sure that there is a consistency in the powders that were mixed; a certain amount was made in ball mill. This is done by a stoichiometric mixing of aluminium oxide and titanium dioxide. Once the mix was made, it was made to slurry by adding a solution of 5% polyethylene glycol. The slurry formed was put into a bottle containing around 50 balls. This bottle is then rotated in the ball mill for around 6 hours to get a well mixed solution. This solution is then filtered to separate particles from the solution. Sample from the filter paper is then taken from the paper by warming it in an oven at around 400C for an hour. This is done in an Heraeus Oven. The powder from the filter is then allowed to be fired to around 14000C. Fired powder is then allowed to undergo XRD analysis. The pattern received from this sample is then compared with the powder got by pan agglomeration. The patterns will tell us about the amount of in mixing in both processes.
Materials and Methods:-
Materials: Chemical compounds
The list of chemicals that were used throughout the research activities.
Trisol 60 Plus
This is an environmentally safe wax pattern. This is supplied by Blayson Olefins Limited which is located in London. It is a blend of high purity hydrocarbons and biodegradable emulsifiers and surfactants.
Silica or fused Silica
The Manufacturer is Minco, Inc. from Tennessee in U.S.A. It consists mainly of amorphous fused silica and less than 1% crystalline Silica.
Molochite
This is chemical is supplied by ECC International Limited which is located in Cornwall, United Kingdom. This is actually china clay which is calcined at 14500C. It consists 55% of Mullite and 45% of a silica rich amorphous glassy phase.
A7-FR/60
This chemical is supplied by Blayson Olefins Limited located at London. It consists of natural waxes, synthetic waxes and natural/refined resins. This is used as a filler material.
Nalco 1056 Colloidal Silica
This is provided by Nalco Chemical Company which is located in Illinois. It consists of colloidal silica which is amorphous.
Aluminum Oxide
This chemical was brought in online through Sciencelab.com, Inc which is located in Texas. It is called as Pechinet PFR15 which was rutile grade. It is α- alumina.
Titanium Oxide
This chemical is supplied by Sigma- Aldrich Company Limited which is located in Gillingham. It is mainly Titanium Dioxide of rutile grade.
Methods employed: Equipment used
Methods of Manufacture
Weighing and Blending: Equipment- Weighing scale, Kenwood Blender
The process of making Tialite would mainly involve the solid state reaction between aluminium dioxide and titanium dioxide. At first the powders are taken and mixed in the stoichiometric ratio, according to the reaction. From knowing the molecular masses of each of the compounds the amount to be mixed is known and they are weighed out on a weighing scale with maximum limit of 500 grams. Once the powders are taken, they are mixed thoroughly in a Kenwood Major (Blender). The blades used must be efficient for the blending of powders.
Agglomeration: Equipment- Eirich Pan Agglomerator, Spray gun (Atomiser)
After the blending process, powders of aluminium dioxide and titanium dioxide are made to agglomerates using a pan agglomerator. For the agglomeration to take place a solution has to be sprayed onto the rotating mass and this is done using an atomiser. The solution used is 5% polyethylene glycol. The molecular mass of the PEG which is used for the making of solution is d 2000 grams. The higher the molecular mass, better the agglomeration will be. This is because they gain granular strength through the firing process which follows. An optimum molecular mass must be used for the preparation of the solution. During this agglomeration process, particles of various size ranges are made.
Separation and Firing: Equipment- Laboratory Test Sieve, Bench Mounted Chamber Furnace
The particles of mixture of Aluminium oxide and titanium dioxide are then separated to the required sizes (300µm-600µm) using laboratory test sieves. Once the separation of the required sizes is done, they are fired at 8000C at a rate of 100C/min in a bench mounted Chamber Furnace. This is done so that the particles gain strength and be tougher. For this reason, the particles are allowed to dwell at the temperature of 8000C for an hour before it is allowed to cool down.
Coating and Drying: Equipment- Rotating Diffuser
Once sufficient amount of powders of aluminium oxide and titanium dioxide have been made, then wax samples are prepared and cleaned using a chemical Remasol (which is a cleaning agent). Initially standard bars are made, before bars stuccoed with mixture of aluminium oxide and titanium dioxide are made. When standard bars are made, the initial coating is done by sprinkling of fine Molochite (up to 4 layers) and the remaining layers are coated with coarse Molochite. In case of primary coating, the wax pattern is allowed to dry overnight, whereas the secondary coatings have to be dried for an hour and a half each time. After each coating, the sample is dipped in steel slurry and coated with the required stucco. The slurry composition is given in table 1. And the final coating is made by dipping the wax pattern in the slurry which is then left to dry overnight. Drying is done in a drying room which consists of a rotating diffuser. After the primary coating a total of 8 layers are made, in total of 9 layers. Similarly the test samples are made, except for the part that instead of coarse Molochite the samples are stuccoed with Tialite. A sample with all layers stuccoed with Tialite is also made, just to give us a better understanding of the stuccoing. The dipping of bars have been shown in Table2, Table 3 and Table 4.
De-waxing and Firing: Equipment- De-waxing machine, Bench Mounted Chamber Furnace
Once the samples have been made, de-waxing is done. The wax pattern around which the shell is made is melted and removed thereby giving a hollow shell. The process of de-waxing has been studied in detail by researchers [24]. The de- waxed sample is cut into bars of the required size using a cutting machine. These bars are then fired to 14000C at 200C/min and allowed to dwell for an hour. They are cooled at 200C/min to room temperature, which may take overnight. Cooling is an important part, because it is during this cooling that Tialite is formed and the interesting property of the stucco comes into play.Methods of Measurement
Strength
3 Point Bench Loading
All these bars once fired, are to undergo mechanical strength testing. This is done using 3 point bench loading equipment. Using this machine, we can get the strength of each of the bars, which are made of different combination of layers. Before the bars are placed into the equipment for the measurement of strength, the dimensions are measured using vernier callipers.
Structure
Scanning Electron Microscopy
On these bars, the SEM test is undertaken. A 20 KeV is used for the measurement. The spot size chosen is 69. The magnification chosen in this particular case, since the images of different shells are compared is 60. The sample part which is examined is the fractured part. The sample is carbon coated before the test is done, because the sample is non conductive. The sample is placed on a stud with a carbon sticker, which is then allowed to be coated with carbon in a coating machine. This helps us understand the development of new phases and also for development of cracks around the stucco.
Energy Dispersive X-ray Spectra-photometry
EDS helps us understand, the chemical composition of the product. They will help tell about the compositions within the bars. This is understood because different elements give out different electron emissions within the JEOL 6060 SEM equipment. The working distance for observing the image imported from SEM is 10 mm. And the spot size is changed from 69 to 75. If the spot size is increased more than 75, the clarity of the image received is lowered.
X-ray Diffraction
The radiation used for XRD is CuKα [25]. The 2Ѳ scanning is done between 00 and 1700 [26]. The sample used is directly the powder that was sieved using laboratory test sieves. The size of the particles used are in the range of 300 µm- 600 µm. It is due to this reason that the pattern observed was found to be noisy. If the powder were powdered to 10 µm, the XRD patterns observed will be very specific. The peaks will be very clear, rather than being spread out. This gives us an understanding about the phases present.
Sample Replicates:
Wax Samples: Different Compositions (For mechanical strength testing)
3 Wax samples were made up of 4 layers of fine Molochite and 4 layers of coarse Molochite.
2 Wax samples were made up of 4 layers of fine Molochite and 4 layers of Tialite.
1 wax sample was made up of 8 layers of Tialite.
Powders: Fired at various temperature (For XRD analysis)
20 grams were fired at 10000C
20 grams were fired at 12000C
20 grams were fired at 13000C
20 grams were fired at 14000C
20 grams were fired at 15000C
Powder: Fired at particular temperature (For XRD analysis)
Sufficient amount of powder containing a mixture of aluminium oxide and titanium dioxide is also made using ball mill. And this mixture was also allowed to undergo XRD. The equipment was made of PASCAL Engineering.
Powder fired at 14000C
Results and Discussions:-
Following includes the results and findings attained from strength tests, XRD analysis, SEM tests and EDS tests.
XRD Analysis:
The mixture of powders of aluminium oxide and titanium dioxide which were blended using a blender is sieved using laboratory sieves. These samples were fired at different temperatures to understand the different phases that were being developed. These analysis were done in Philip's Panalytical X'Pert device.
The XRD patterns shown are taken in the range where 2Ѳ is between the angle 00 and 1700. But to give a better understanding the pattern is magnified to view the pattern between of 2Ѳ equal 200 and 700. Different elements are identified as symbols in the plot. Each peak is circled and labelled to identify the element giving out the peak. In all of the following patterns 'A' represents Aluminium Oxide, 'X' represents Tialite and 'T' represents Titanium dioxide.
XRD pattern taken at
10000C: Figure 1
Figure
12000C: Figure 2
Figure
13000C: Figure 3
Figure
15000C: Figure 4
Figure
XRD pattern attained from the well mixed powder of aluminium oxide and titanium dioxide which are fired at different set temperatures. From the patterns taken, it helps in understanding what all phases are present. It gives an understanding of the materials that are involved in the powder. At different 2Ѳ there are certain peaks for different materials. From the peaks present, it can be understood of the presence of aluminium oxide and titanium dioxide and also Tialite.
14000C: Figure 5
Figure
XRD pattern taken at 14000C- XRD pattern attained from the well mixed powder of aluminium oxide and titanium dioxide which are fired at 14000C. From these patterns, similar as above, it helps in understanding what all phases are present. From the understanding of the materials that are involved in the powder. At different 2Ѳ there are certain peaks for different materials these can be understood from the standard pattern set for each compound. From the peaks it can be understood of the presence of aluminium oxide and titanium dioxide and also Tialite. There is an unusual peak at 2Ѳ equal to 480(approx). This could be some particles picked from pan agglomerater.
To make sure of the mixing of the powder, a sample of mixture of aluminium oxide and titanium dioxide were made using the ball mill. The XRD pattern is shown in Figure 6.From the XRD pattern given by the powders fired at 14000C, which was made in a pan agglomerater there was an unusual peak which is marked as '?'. This was made clear when the powder made in the ball mill, after being fired at 14000C showed out a similar pattern, but there was a difference in one of the peaks that occurred at 2Ѳ equal to 480(approx). From discussions it was understood that it could probably be from the metallic particles that could have peeled from the rotating pan agglomerate, when scraping the powder.
XRD pattern of the powders made from ball mill, which is fired at 14000C. (Figure 6)
Figure
Tialite does seem to have a peak in the range of 2Ѳ equal to around 500 for the sampled that is fired to 14000C. But the contradictory part is that a peak is observed at 10000C also. Even if there is Tialite in that range, there must be more than one peak showing the presence of Tialite. Therefore it can be concluded that it could be from some metallic powder that could have come up during scraping of powder.
Strength Analysis:
Mechanical Strength of the bars that were made is tested. They are done on a 3 point bench loading machine. From the machine, the load that is required for breaking the bars is noted.
Bar
No. Of Fine Molochite Layers
No. Of Coarse Molochite Layers
No. Of Tialite Layers
Force(N)
1
4
4
0
264.926
2
4
4
0
371.476
3
4
4
0
278.818
4
4
4
0
213.946
5
4
4
0
295.731
6
4
0
4
77.581
7
4
0
4
78.572
8
4
0
4
77.484
9
4
0
4
65.211
10
4
0
4
77.839
11
4
0
4
82.365
12
4
0
4
88.478
13
4
0
4
54.676
14
0
0
8
32.4
15
0
0
8
24.62
16
0
0
8
25.852
17
0
0
8
24.04
From these loads, the strength of each of the bars that were made is calculated using a strength equation,
where is the strength, F is the load that is applied for cracking the bar, L is the length of the bar, B is the breadth of the bar and H is the height of the bar.
Bar
Force(N)
Breadth(m)
Height(m)
Length(m)
Strength '' (Pa)
1
264.926
0.02229
0.00967
0.05
9532852
2
371.476
0.02371
0.01102
0.05
9676032
3
278.818
0.024
0.01023
0.05
8325677
4
213.946
0.0224
0.00963
0.05
7724402
5
295.731
0.02296
0.01105
0.05
7911552
6
77.581
0.02479
0.00658
0.05
5421111
7
78.572
0.02296
0.00654
0.05
6000697
8
77.484
0.02138
0.00654
0.05
6354920
9
65.211
0.02482
0.0064
0.05
4810834
10
77.839
0.02084
0.00738
0.05
5143374
11
82.365
0.02477
0.00691
0.05
5223022
12
88.478
0.02148
0.00672
0.05
6841065
13
54.676
0.02275
0.00677
0.05
3932776
14
32.4
0.02259
0.00445
0.05
5432128
15
24.62
0.02151
0.00423
0.05
4797646
16
25.852
0.02112
0.00432
0.05
4919195
17
24.04
0.02066
0.00422
0.05
4900501
From the above tabular column it gives us an idea of the variation in strength of different bars. All of the bars are made of different composition.
Bars 1, 2, 3, 4, 5 are made of 4 Layers of fine Molochite and 4 layers of coarse Molochite.
The bars which were made of 4 layers of fine Molochite and remaining 4 layers of coarse Molochite gives an average of= 8634103 N/m2= 8.6 MN/m2= 8.6MPa
Bars 6, 7, 8, 9, 10, 11, 12, 13 are made of 4 Layers of fine Molochite and 4 layers of Tialite.
Bars which were made of 4 layers of fine Molochite and remaining 4 layers of Tialite gives an average of= 5465974.875 N/m2= 5.4 MN/m2=5.4MPa
Bars 14, 15, 16, 17 are made of 8 layers of Tialite.
Bars which were made of all 8 layers of Tialite gives an average of= 5012367.5 N/m2= 5.01 MN/m2=5.01MPa
From the above findings, we can understand that there is a drastic effect on the strength of the shell due to the in situ formation of Tialite within the shell. By taking into account the unique properties of Tialite, it can be understood that anisotropic thermal expansion has played a major part in getting these results. Normally materials have isotropic thermal expansion, but this weakening in the bars is due to unique expansion of Tialite. There happens to be positive expansions in two of the crystal directions and a negative expansion in the third direction. The final appearance of the particles will be an elongated shape. This happens when it is allowed to cool from the fired temperature of 14000C. As this elongation of the particles takes place, they impart stress to the surrounding layers. This stress leads to the formation of cracks around the stucco. Evaluating the mathematical values, it can be understand that there is almost 37.2% reduction in the strength of the shell when stuccoed with Tialite in comparison with the standard shell which is stuccoed with Molochite.
SEM Images:
This is done in Scanning Electron Microscope of model JEOL 6060. The SEM is done on the fractured surface. The bars on which SEM is done includes
A bar which is coated with 4 layers of fine Molochite and 4 layers of coarse Molochite.(Figure 7)
Figure
Bar which is coated with 4 layers of fine Molochite and 4 layers of Tialite. ( Figure 8)
Figure
A bar which is coated with 8 layers of Tialite (Figure 9).
Figure
From the Figure 7, Figure 8 and Figure 9, it can be observed that there are cracks around the globules that are seen on the image. There could be two possible reasons
This could be due to the phase transition and sintering that occurred during the process. The globules might have tried to shrink away from the matrix.
This could also be due to the thermal anisotopic expansion that could have occurred by Tialite.
This equipment helps us understand about the internal structure of the shell that has been designed. The bars are different in composition, because of the different layers that have been created.
EDS Patterns:
This is done in Scanning Electron Microscope of model JEOL 6060. Here the spot size used is 75 to make the patterns received from the sample more clear and understandable. The bars on which EDS is done includes
A bar which is coated with 4 layers of fine Molochite and 4 layers of coarse Molochite.
There are three points that are done, to make sure of the consistency of the chemical composition
Spectrum 1 is just a point. (Figure 10)
Figure
Spectrum 2 is just a point. (Figure 11)
Figure
Spectrum 3 is an area. (Figure 12)
Figure
A bar which is coated with 4 layers of fine Molochite and 4 layers of Tialite.
There are three points that are done, to make sure of the consistency of the chemical composition
Spectrum 1 is just a point. (Figure 13)
Figure
Spectrum 2 is just a point. (Figure 14)
Figure
Spectrum 3 is an area. (Figure 15)
Figure
A bar which is coated with 8 layers of Tialite.
There are three points that are done, to make sure of the consistency of the chemical composition
Spectrum 1 is just a point. (Figure 16)
Figure
Spectrum 2 is just a point. (Figure 17)
Figure
Spectrum 3 is an area. (Figure 18)
Figure
The EDS patterns have peaks, which tell us about the chemical composition present within the shell. The peaks are marked within the graphs.
Conclusion:-
A mixture of powder of aluminium oxide and titanium dioxide were made which were agglomerated to form particles of certain sizes and were sprinkled as different layers in the creation of the shell. The shells when fired to 14000C formed Tialite in situ. This shell when allowed to cool from the fired temperature is made to exhibit the thermal anisotropic expansion. The hypothesis for which this research was set out is that on addition of Tialite precursors there would be a significant effect on the strength of the shell. This proved to be true. The effect on the shell was the weakening. The research hoped to attain the weakening of shell using the property of the Tialite, which thermal anisotropic expansion.. Desired result was obtained when the strength test proved to show a drastic difference in the strength of the material. And further backing up was made clear from the images got by doing scanning electron microscopy on the shell samples. The SEM was done on the fractured side to understand the structure of the shell. From the images, it is clear that around the globule there are cracks around the globules which is the stucco. This cracks is either because of the phase transition and the sintering that happen within the shell, which made the stucco shrink away from the matrix or it could be due to the thermal anisotropic expansion which leads the Tialite to attain an elongated shape within the shell, thereby imparting stress onto the shell, which leads to weakening.
Appendices:-
Table 1 [27]
Table 2
Coating
Stucco
Dip time (secs)
Drain Time (secs)
Air Speed (ms-1)
Dry time (hours)
Primary
Fine Molochite
30
60
0.4
24
Secondary 1
Fine Molochite
30
60
3
1.5
Secondary 2
Fine Molochite
30
60
3
1.5
Secondary 3
Fine Molochite
30
60
3
1.5
Secondary 4
Fine Molochite
30
60
3
1.5
Secondary 5
Coarse Molochite
30
60
3
1.5
Secondary 6
Coarse Molochite
30
60
3
1.5
Secondary 7
Coarse Molochite
30
60
3
1.5
Secondary 8
Coarse Molochite
30
60
3
1.5
Seal
30
60
3
1.5
Table 3
Coating
Stucco
Dip time (secs)
Drain Time (secs)
Air Speed (ms-1)
Dry time (hours)
Primary
Fine Molochite
30
60
0.4
24
Secondary 1
Fine Molochite
30
60
3
1.5
Secondary 2
Fine Molochite
30
60
3
1.5
Secondary 3
Fine Molochite
30
60
3
1.5
Secondary 4
Fine Molochite
30
60
3
1.5
Secondary 5
Tialite
30
60
3
1.5
Secondary 6
Tialite
30
60
3
1.5
Secondary 7
Tialite
30
60
3
1.5
Secondary 8
Tialite
30
60
3
1.5
Seal
30
60
3
1.5
Table 4
Coating
Stucco
Dip time (secs)
Drain Time (secs)
Air Speed (ms-1)
Dry time (hours)
Primary
Tialite
30
60
0.4
24
Secondary 1
Tialite
30
60
3
1.5
Secondary 2
Tialite
30
60
3
1.5
Secondary 3
Tialite
30
60
3
1.5
Secondary 4
Tialite
30
60
3
1.5
Secondary 5
Tialite
30
60
3
1.5
Secondary 6
Tialite
30
60
3
1.5
Secondary 7
Tialite
30
60
3
1.5
Secondary 8
Tialite
30
60
3
1.5
Seal
30
60
3
1.5
