CAST IN “BOWIE COMPETITION” TECHNICAL REPORT

UNIVERSITY INSTITUTO TECNOLÓGICO DE SALTILLO

COMERCIAL STEEL FOUNDRY MAHLE PLANTA CAMISAS, RAMOS ARIZPE

FACULTY ADVISOR DR. EFRAÍN ALMANZA

TEAM MEMBERS MAGDIEL ALVAREZ EDGAR HUERTA MIGUEL HERNANDEZ

JUNE 2020 ABSTRACT

A 12-inch was fabricated using a ferrous high alloy for the best quality and properties, such as, toughness, strength, machinability, impact and corrosion resistance.

There were used two different types of molds. One made of refractory cement (60%Al2O3 - 40%SiO2), and the other made with a simple green sand mixture. After experimenting with both of them, it was determined which could be the best option when pouring the metal at very high temperatures, and also which could replicate on the best way the shape of the knife, that consist on 1/5-inch thick (4mm) and 18-inch long (including tang and blade).

The guard and the pommel were made of bronze, and along with the design and the handle, were characteristics thought, to give the knife a complete control and well balance over its total weight.

Acknowledgements

The team involved on the making of this report, and the entirely project is completely grateful for all the help and assistance provided by:

 Mahle Planta Camisas whose guidance and supported material were essential for the fabrication, machining, and properties of the knife.  All the teachers from the Instituto Tecnologico de Saltillo disposed to support, advice, provide the media, knowledge and technical analysis to succeed on the project.  All people involved in order to complete the project, carpenter for its support making the model for the casting, and people of Helical SA de CV for machining operations.

Table of Contents

1. Introduction ...... 1

2. Historical Reference and feautures ...... 1

2.1 Main features and designs ...... 2

3. Design and model ...... 7

3.1 Blade and Tang ...... 7

3.2 Crossguard ...... 8

3.3 Handle ...... 9

3.4 Pommel ...... 9

3.5 Final Design ...... 10

3.6 Model ...... 12

4. Casting process ...... 13

4.1 Molding ...... 13

4.2. Refractory cement mold and casting ...... 13

4.3. Green sand mold and casting ...... 16

4.4 Alloy ...... 22

5. machining and assembly ...... 24

5.1 Blade ...... 24

5.2 Guard and Pommel ...... 28

5.3 Handle ...... 30

5.4 Assembly ...... 31

6. Microstructure Analysis, Properties and defects ...... 33

7. Conclusions ...... 38

References ...... 40

1. INTRODUCTION From the kitchen to army, are a very common instrument or device that consist in a large sharpened and thin sheet of metal. They were used since ancient ages for hunting, survival, defense, cutting, to transform big pieces of food into more little and eatable pieces.

The principle of a knife is the same, that is something that even history cannot change. However, there are knives with different applications, or specific uses, and depending the application, knives varies on their shapes, jagged edges, sizes, manufacturing process, handles, metals alloys, etc.

Bowie knives are the type of knife that has become very popular since their very particular design, interesting history, uses and aesthetics.

On this technical report, a complete description is given for the fabrication process of a Bowie knife.

The main purpose of the manufacturing, was to use the casting process to obtain primarily the shape, that includes the blade and the tang. This is clearly challenging, because knives are commonly fabricated by forging, or just machining, due to their very small thickness, something that is hard to achieve by metal casting.

The steps for the fabrication were the following: design process, casting, machining, sharpening and polishing; meanwhile the guard and pommel were also manufactured.

2. HISTORICAL REFERENCE AND FEAUTURES First of all, it was necessary to determine how the knife was going to look like, which properties it should have, ideal materials to get those properties, and size, in order to get a completely useful and beautiful knife. It was necessary to search what makes a knife a Bowie knife, so, that way it can be proved and ensured that the knife fabricated along this report is an authentic Bowie.

History says that the Bowie knife was designed by Rezin P. Bowie and he gave it to his brother for protection after he went bullet wound. After recovering from the shot James and his knife becomes very popular at the “Sand Bar Fight”, where after being shot at one lung and repeatedly stabbed with swordcanes, James on a last effort rise and sank the knife on its aggressor heart.

Despite this, nowadays there is not an exact representation, of how does the first Bowie Knife looked like.

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The description of the original Bowie knife paraphrasing Norm Flayderman's book, “The Bowie Knife: Unsheathing an American Legend” (2004), the knife was made for hunting, and the blade was 9¼-inch large and 1½-inch width, was a single edge, was not curved, and did not had a hand guard. The knife was much more like a triangular blade or a “” like how was described at that time.

Regardless of its original shape, Bowie knifes soon assumed some of their legendary characteristics, with a crossguard, and a deep remarkable clip-point. It was described by researcher Russell T. Johnson on his article “The Bowie Knife and the Toothpick” (2006) as a knife that must be long enough to use as a , sharp enough to use as a razor, wide enough to use as a paddle, and heavy enough to use as a hatchet. On figure 1, different types of are shown; the “” type of blade, shows the respective shape of a Bowie Knife.

Figure 2.1. Different types of knife blades. The “clip point” type corresponds to the shape of a Bowie Knife. 2.1 Main features and designs Now that it has been discussed about the very popular history that surrounds Bowie Knives, it is going to be described the principal features that compound the actual designs. One example of a generic scheme/shape, of different parts of a Bowie knife, is represented on Figure 2. As it can be seen, the typical clip-point shape, a crossguard, and pommel, are present. Some other variations could be encountered, with a jagged edge, fuller, or no pommel, but basically that is how many Bowies knives look like, and the parts which compound them.

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Figure 2.2. Different parts that compound a Bowie Knife. This kind of knives are very particular, and may be easily differentiated from other knives. However, for a better understanding and quick recognition, a list of some of the key characteristics, that illustrate on the best way Bowie Knives, accompanied with a brief description of each, are the following:

 Clip-point blade shape:

As shown on the figure above, it can be described as a cut-out concave area, resulting on a well- balanced and high-control knife. This shape provides a sharp and thin point, perfect for tasks where precision is required, such as chopping, skinning and piercing. Despite its many advantages, this shape disables the use on heavy-duty tasks, such as chopping very hard and thick materials.

 Guard:

This device is meant to ensure that the hand of the person, that is wielding the knife does not get injured, by avoiding a slipping towards the blade. Typically a crossguard, it could be or not crossed, but primarily Bowie knives has it crossed, and many sketches, or shapes, could be done as denoted on Figure 5.

 Pommel:

Due to the weight of this type of knives, a pommel is the perfect counterbalance, when wielding the knife. The pommel has become a very common feature, and its design has been changing along years. First models had “bird-head” pommel, as shown on the next figure. Actual models may vary on their designs, or even many knives could not have any particular pommel, like the examples presented on Figure 5.

Figure 2.3. Bird-Head pommel typically from western Knives. Page | 3

 Full tang:

Another peculiar feature of Bowie knives, is their fixed blades that are due to tangs. Bowie knives require a full tang, so stresses when hitting or cutting, could be well distributed, otherwise with a half tang, or even a welded tang, may provoke a complete disaster breaking the knife on two pieces. Bowie knives can be designed with hidden tangs, where no tang is visible because of the handle, but remains part of the blade. There are also tangs designed when a partial part of the tang can be seen sticking out from the handle. Tangs may vary among full, partial, skeletonized, designs etc. as it can be seen on the next figure. a) b)

c)

Figure 2.4. a) Representation of different types of tangs, preferably a full tang is desired for Bowie knives. b) It is shown a scheme of how may be conformed a knife with a hidden tang. c) A broken welded tang can be observed.

 Blade size:

Blade lengths varying from 5-in, the smallest, to 25-in, the largest ones depend upon the use or application.

Mainly, shortest ones are used for hunting, more specific when skinning an animal, so the person would have a better accuracy on the cuts. The largest ones are preferred for camping, when cutting bushes, firewood, and cleaning undergrowth, it is more likely to a .

Medium sizes, or average sizes around 10-in to 20-in are the most common commercialized Bowie knives, mainly used for survival, and both hunting and camping.

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Talking about the wide and thickness of the blade, for the smallest and the largest ones, sizes should be varying from ½-in wide and 1/8-in thick, to 2-in wide and ¼ -in thick respectively. Thicker knives are characterized for being used for fighting, and, it is not hard to think about it, being that the first Bowie knife was intended to use as a personal protection weapon.

 Mainly steel material

Entering to the materials section, all commercialized Bowie Knives are made of steel, principally from medium to high carbon content. This ranges variate from .31 to 1.5%wt. of carbon, according to the AISI designation. A very popular steel used for this type of knives, is the 1095 grade, mainly because of its high carbon content which endows higher hardness and fracture toughness, and its machinability, welding, forging and heat treating are still easy to achieve, meaning also that sharpening is not a hard task. Also it is not an expensive steel compared with the alloyed ones.

One important feature looked on this type of knives is their longevity, which means that they are required to maintain their properties, which are clearly affected by the environment, on which knives complete their duties or service. This is one of the main problems of carbon . Despite this, many posterior surface treatments can be done, such as anodizing.

However, there are two other types of steels used as base materials for this knifes:

 Stainless Steels:

With a high chromium content, which endows a protective passive layer that avoids premature failure, caused by corrosion, stainless steels are very popular among materials used on Bowie knives; further, this steels are well known by their good mechanical properties, which can be yet highly improved by heat treatment.

 Alloyed Steels

It could be encountered knives with this type of materials, for more specialized applications, such as higher strength, corrosion resistance, magnetic properties, etc. Nickel, chromium, titanium, silicon, are different elements added in a range of 1.5-5%wt. for low alloy steels to more than 10%wt. for high alloy steels. Stainless steels could be considered as high alloy steels because of its chromium content above 10%wt. Thus, knives produced with this kind of materials are more expensive than carbon steels, but, regardless to its price, they are highly long-lived, maintaining their properties along time.

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As it can be denoted, the design, and the size of Bowie knives, are characteristics that depend upon the application, and the likes of each person. On the figure below, different Bowie knives are presented, and their main features are described:

Figure 2.5. Different Bowie Knives designs are represented, each of them presenting a large clip-point blade. Most of them present a hand crossguard excepting g), which only has a directed downwards hand guard. Pommels are not always presented, such as, in examples a) and f). A wooden handle is also almost presented in all examples excepting b), d) and i), where the material of the handle is made of a polymer. A jagged edge is also a common feature of this type of knives, and it can be seen on examples d) and i). From examples c), e), g), h) and i) it can be observed a fuller, which is principally added to reduce weight; on example i) a complete perforated fuller can be seen.

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3. DESIGN AND MODEL The basic concept of the knife was understood at this moment, and, several modifications during the entire manufacturing process had been made over the starting design. Below it is showed the design process generated by 3D digital models.

3.1 Blade and Tang It was decided first, the dimensions of the knife, which are the following:

1. 18-in length (including blade, tang and pommel) a) 12-in length (blade) b) 5.5-in length (tang/handle) c) ½-in length (pommel) 2. 2-in wide (blade) a) 1.65-in wide (tang) 3. 1/5-in (5mm) thick

After this a scheme was made as it is shown next:

Figure 3.1 An ismometric and a frontal view of the knife designed on SolidWorks.

Then, in order to make the design more interesting, and with various applications, a jagged edge, and a fuller were thought for camping, survivor uses and reduce the total weight of the knife respectively.

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Figure 3.2. The jagged edge and fuller are shown. Fuller was made on both sides of the blade.

3.2 Crossguard A basic design of a crossguard was considered, and the model was intended to serve also as an ergonomic device being that, the thumb could be settled on the superior surface of the guard, so when chopping, a better accurate and finer cut could be done. The material of the crossguard was decided to be bronze, because of its properties of toughness, wear and corrosion resistance, besides of its great bright yellowish aspect.

Measurements:

 Length: 3.6-in  Wide: ¾-in  Thickness: 0.2-in

Figure 3.3. Crossguard design.

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3.3 Handle The handle, since the beginning was determined that it was going to be made out of wood, and on its firsts draws was a regular oval shape, however the basic concept changed at the end of the process, but it was still made of wood.

Figure 3.4. Handle first draft. 3.4 Pommel The pommel had suffered many changes along its design process. First sketches began with the shield of the Instituto Tecnologico de Saltillo, but, primarily this was not the greatest idea, because of its difficulty to machine and that it was going to be too big, and it will make the knife very heavy. So a formal and simpler design was made. Also the pommel material was thought to be the same as the guard: bronze.

Figure 3.5. Pommel designs, the right designs were the chosen one.

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3.5 Final Design As it was said before, many changes were done to the original concept during the manufacturing process, for adapting the knife to best possible design; they were not changes that completely change the knife, but very subtle and important ones.

For example, to avoid the sliding of the crossguard ahead of the blade, the tang was reduced by the wide few millimeters, so that way 2 locks (upper and lower) were created, as it can be seen on the next figure.

Figure 3.6. Change made to the tang of the knife during machining process. The crossguard also change a bit, by modifying the angle of aperture, first sketch had 30°, and final piece had 45°.

Another example was the pommel; the first design was something that had been taken for granted, but evaluating the possibilities for doing it, and the physical characteristics that implied to have it on the knife, the design was rejected and finally, another shape was created.

The fuller, also changed during marching, the thickness of it, was outlined to be 0.04-in, but at the moment of making it, it was to tiny, so a thicker 0.1-in fuller was made.

The general 3D view of the knife, and the blueprints used on the models can be seen on the following figures.

Figure 3.7. Isometric view of the final 3D model of the knife.

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12.2 2.01

Figure 3.8. Blueprints were printed on real scale so when making the models, and starting with machining, both processes could be easier by seeing the real sizes.

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3.6 Model The sizes plotted on the designs were a bit bigger (few millimeters), than the hoped on the final piece, this, because it was considered the shrinkage that metal could present when solidifying, and also because of the machining, they were acting as tolerances.

Once having the final design of the knife, four wood models were fabricated, with their respective crossguard, and according to the sizes presented on the blueprints. Since this stage, the earliest modification was made over the initial design: the first block on the lower part of the tang was created, in order to avoid sliding of the crossguard to the blade. The second lock (upper) was made during machining. As it can be inferred, the knife (already solidified) would initially have this lower lock.

LOCK

Figure 3.9. Wood knife and crossguard models.

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4. CASTING PROCESS At the beginning of the process, it was thought that 4 knives will be cast in conjunction with the crossguards, that is why four models were fabricated.

The knives would be made by the alloy provided by Mahle, and the crossguards would be made of bronze. At the end it was decided that only two knives were cast, one from the refractory mold, and other from the green sand mixture mold, so, both processes could be evaluated, and more time could be inverted on the post-casting processes, with the handle, the machining of the blade, and the microstructure analysis of the obtained alloy, in other words, it would be time saver concentrating only in two knives rather than four.

The crossguard as well as the pommel were machined from an ingot of bronze, due to its good forming capacity, and because pieces could highlight.

4.1 Molding Mahle Camisas is an enterprise dedicated to the fabrication of cylinder sleeves, and their casting process consist on the centrifugation of the liquid metal in order to obtain the final shape of the cylinder. Due to this, the idea of testing two molding methods arises, since the permanent molds that Mahle uses are not made of sand, or their fabrication process does not involve methods like: pressure die casting, investment casting, or lost foam process, where the knife could be potentially cast.

The green sand mold was something that for sure was going to work, so from Instituto Tecnológico de Saltillo, it was asked for a permission for using the sand, and additives that are used for school practices.

At the same time an idea emerged about refractory cement, on which an exact shape of the model could also be portrayed, and it could support high temperatures.

4.2. Refractory cement mold and casting

A refractory mold of composition 40% Al2O3 and 60% SiO2, was used for the casting process. This composition allows the mold to resist very high temperatures due to the high grade of refractoriness of the alumina.

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Figure 4.1. Refractory cement mold, just after removing models. The blend was mixed with water, and poured into a wood container, then over the surface two models were collocated, with the idea of obtaining two knives. A day was enough to solidify, and then, models were retired.

It was decided that an open mold should be more effective, due to liquid metal could spill out through the thin walls.

Then, to avoid pasting of liquid metal on the surface of the mold, a graphite coating was applied over the top of the mold, and also the coating helped for covering the pores, and to give a smoother surface.

Figure 4.2. Refractory mold with graphite coating. Sizes: 20 – in large, 8 – in wide, 1 – in thick.

It was experimented with this mold, days before the sand mold was manufactured, and the alloy used for the refractory mold was different from that used in the sand mold. This was due to the fact, that, as part of an experimental process, for which there were no revealing records in literature, attempts were made to carry out preliminary tests, until obtaining a good knife that could be potentially used.

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One of the main points of the refractory cement mold, was that it had to be completely dry in the first place, since any trace of water in the mold, when making contact with the hot metal, could explode. Secondly, it was also important to preheat the mold, due to the casting temperature was at 1540°C. During melting, the mold was preheated above 300°C, over the graphite-coated surface, this, in order to avoid a strong thermal shock, causing defects in the cast metal, and, although the mold was specially manufactured to withstand high temperatures, it could fail.

The results received by this mold were not entirely pleasant; although final shapes replicated the model, large gaps (pores) formed on the graphite-coated surface.

Fourteen attempts were made in a row, and gaps continued to occur even in the same parts. This mold was broken from the first attempt, however, both parts were attached, and mold continued functioning without the need of any special glue.

Three different molds were made, the first of them, was in which the 14 attempts were made. In the second mold, it was decided to make perforations on the coated surface, this, in order that the trapped gases that generated these holes, had a way out. In this second mold, on the first attempt, the shape of the knife was obtained. One remarkable difference from the first mold to the second one, was that only one hole formed, and it was thought, that, this gap could serve as an interesting application, such as, rope cutter. No other attempt was made with this mold because like the first, this also broke.

In the third mold, a difference from the previous ones, it was decided to build a closed mold, to discard the idea of the formation of these gaps, due to the thermal shock of liquid metal surface, with the environment. However, on the first try, like the other two molds, this one broke. From this point on, time will be spent making the sand mold.

In all three molds a repetitive pattern is observed, since all of them, when pouring the hot metal, they got broke, this is mainly attributed to the fact that preheated temperature, was not high enough to prevent thermal shock that break the mold. Furthermore, each time that liquid metal was poured, moments after solidification had started, orange spots were observed along the knife blade, the same spots that coincided with the gaps. This meant, that the mold, in addition to not being well preheated, some parts of the mold were hotter than others, causing premature solidification and mayor shrinkage in these parts. Either the preheating temperature and the gases that could not escape, were both combined factors which form these gaps.

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Another observed and unavoidable pattern was the formation of a bulging surface, which was the one that had contact with the environment, however, this defect would be tried to fix in the machining process.

Below are different photographs of the melting process with this mold:

Figure 4.3. a) Preheating the mold on the coated surface. b) First mold broke. c) Orange spots are observed, meaning that metal has solidified in those areas. d) Results obtained by the first mold; primary shape was obtained, but the formation of gaps (pores) was observed. Gaps coincided with orange spots. e) Second mold fabricated, on the first attempt a regular shape was obtained. f) The gaps were reduced in size, and in number, by the holes maked on the coated surface, so trapped gases could have a way out. All refractory molds were coated, preheated, and broken. 4.3. Green sand mold and casting Green sand mixture is for long the most used and well known process to obtain any primary shape of a metal. 30 kg of recycled sand were prepared according to the following amounts:

 Silica sand (SiO2) = Balance  Bentonite (clay) = 2%  Pulverized coal = 2%  Water = 3.5 %

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By saying recycled sand, it was sand that already has been used, and thus prepared. To the blended sand, the percentage of active bentonite was determined with methylene blue, that is the reason why only two percent is added to the mix; regularly values between 6% and 12% are used.

Figure 4.4. A calibration factor was first determined, then the lixiviation process with methylene blue took place. The blueish halo indicates, that reaction has fully occur, and that calculates could be done. The mix was blend with a shovel, since Mahle does not manage any kind of mixer mill. The blending was thought to be mixed at the Instituto Tecnologico de Saltillo, but transportation could be in some way menacing, and mold could crack.

A wood box was prepared, bigger enough to cast one knife. A metallic box was considered to use, but because of the amount of sand that this box requires, and the labor that involves, the idea was discarded. That is why also, only just one model was used, to avoid workforce.

Figure 4.5. Green sand mold. Sizes: 20 – in large, 7 ¾ - in wide, 5 – in thick. (Cope and drag were same sizes). Page | 17

Talking about the casting in this mold, it is important to say that 2 molds were made. The first one did not work, because cope and drag did not fit, primary because sand was tamped on a metallic surface, provoking that the rebound caused that some sand get into the inner surface of the mold, and, accompanied with a lot of tamping force, the mold adopted an oval shape as it can be seen on Figure 4.6a. Besides, the feeding system was pretty much smaller than the ones that can be seen on figure 4.5, which corresponds to the mold 2. All this factors combined made that liquid metal spilled out from the mold, and thus, the shape of the knife could not complete (Figure 4.6b).

a)

b)

Figure 4.6. a) Mold 1 was not made on the optimal conditions, making metal spilled out from it. b) The obtained shape form mold 1.

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Then, a second mold was made, but now taking special care when tamping, and at the moment of pouring a press was collocated to tighten the walls of the mold, and pressing it from the top. Is worth to mention that pouring, either on the refractory cement mold, either on these green sand molds, was made from the side of the tip of the knife, this because, being this part the thinnest, pouring by this side, it was going to ensure that liquid metal will full this part.

The pouring basin also served as a riser, however, another riser was collocated at the other end of the mold, which corresponds to the part of the tang, by this way, when filling up this riser, it would mean that, liquid metal completely filled up the shape of the knife. These risers also served as heating points, being the last ones on solidify, and, endowing hot metal to the knife if it had lack of it. Also there were put two venting gates, so air could find a way out, and, by doing this, avoiding pores or blows formation.

On the following pictures, the obtained piece by mold 2 after the shake out, are shown:

Figure 4.7 Knife casting after shake out, obtained by mold 2 (figure 4.5).

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Figure 4.8. Knife with feeding system. Primary shape was obtained, nevertheless, a lot of work was needed to be done. Much of the machining work could be avoided if the conditions of the casting were better. After cleaning the knife, a crust of sand was observed over the whole shape, in other words, the sand had pasted over the surface of the knife.

This casting defect is a very common known as “burnt on-sand”, and is occasioned when a thin sand crusts firmly adheres to the casting. The defect is more common to occur on thick-walled castings and at castings with high pouring temperatures, and, both were the cases presented on the casting of the Bowie Knife, but the problem was not on the walls or in the temperature, but in the sand. The temperature had probably higher impact on the defect, considering that melting point of a 316 stainless steel is about 1400 ° C, and, the casting was melted up to 1542 ° C, almost a hundred and fifty degrees more.

Figure 4.9. Pouring temperature of knife casting, measured with a thermocouple.

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The reason of the high temperature, was because to obtain higher fluidity when pouring, and, to ensure that the melt was homogenized, being that, steel scrap was added to dissolve carbon content on the liquid metal.

Different reasons were considered to explain why the burnt on-sand defect happened, and are explained below:

 The sand was not mix on a mill, or the time of mixing the components was not enough, and that could provoke inhomogeneity between sand, water and clay (bentonite). Some zones could be rich on water, and bentonite, while other could be poor of them, changing properties of resistance and making sand to fall easily on the melt, which is the case on the zones where more sand crust can be seen.  Besides, pulverized coal was not added to the blend. It was considered that the recycled sand had the necessary amount of pulverized coal, but, clearly not. The content of pulverized coal shown before, corresponds to the content added to the first mix of the sand, so then, it can be considered that content was around 1% or less. This additive is added because when heating, it forms a layer, covering the grain of sand, improving surface finish, and avoiding this adherence of the sand over metal surface to happen.  Facing sand was not used, but it was clearly necessary, to give the casting a smother finish, it was not used, not because lack of it, but because it was just not considered.  The sand also was not high quality, it presented a lot of contamination, even before its mixing, because it is worth noting that was mixed on the floor of the factory, although the zone was cleaned, this could raise the percentage of contaminants on the sand. Contamination can be seen of figures 4.5 and 4.6. as white dots.

In summary, the most affecting factors which lead to the burnt on-sand making that the whole knife presented this defect, were the bad mixing process of the sand, and the lack of pulverized coal on the sand.

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4.4 Alloy One important issue with which was needed to deal, was the carbon content on the alloy, since the chemical composition on the cylinder sleeves is too high to be considered as a steel (more than 2.4%wt. of carbon).

In order to reduce the carbon content on the liquid metal, steel scrap was added to dissolve the quantity of carbon, and by consequence reduce it, about two hours took to decrease the carbon percentage. The lowest content that could be reached was 2%; lowering more this number could be in some extent dangerous, because raising the carbon percentage until the required by the cylinders, is more difficult than reducing it. In terms of an induction furnace higher levels of frequency (Hz) are needed to blend homogenously the liquid metal, and melt the added carbon, besides composition levels need to be continuously monitoring. In other words, more energy is required to stir out the alloy.

The other alloying elements were kept, to give the knife enough strength, toughness, and in some extent, corrosion resistance, and magnetic properties. On the following table, are explained the main effects of the alloying elements present on the knife:

Table 1. Effect of alloying elements present on the knife (obtained from).

ELEMENT INFLUENCE USES

NICKEL Toughness - Strength - Hardenability Used up to help refine grain size. Used in Stabilizes gamma phase by raising A4 and lowering A3. large amounts in stainless and Refines grains in steels and some non-ferrous alloys. heat-resisting steels. Strengthens ferrite by solid solution. Unfortunately is a Nickel based alloys can offer corrosion powerful graphitiser. resistance in more aggressive environments Can take into solid solution larger proportions of and nickel is used as the basis of complex important elements such as chromium, molybdenum super alloys for high temperature service. and tungsten than can iron.

COPPER Corrosion Resistance - Strength SILICON Hardenability - De-oxidizes melt. Helps casting fluidity. Up to 0.3% in steels for sandcasting, up to Improves oxidation resistance at higher temperatures 1% in heat resisting steels. CHROMIUM Corrosion Resistance - Strength Small amounts in constructional and tool Stabilizes alpha phase by raising A3 and depressing A4. steels. About 1.5% in ball and roller Forms hard stable carbides. Strengthens ferrite by solid bearings. Larger amounts in Stainless and solution. In amounts above 13% it imparts stainless heat-resisting steels. properties. Unfortunately increases grain growth.

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MANGANESE Strength - Hardenability - More Response To Heat High manganese (Hadfield) steel contains Treatment 12.5% Mn and is austenitic but hardens on Deoxidizes the melt. Greatly increases the hardenability abrasion. of steels. Stabilizes gamma phase. Forms stable carbides.

On the next image, the chemical composition of the knife is presented. The sample was taken moments before the pouring, and was analyzed by the following tests: optical emission spectrometry (OES) and combustion (LECO).

Figure 4.3. Chemical composition of the liquid metal when pouring. A stamp of rejected can be seen because according to the nominal compositions of the cylinders, some elements, such as carbon, were out of it.

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5. MACHINING AND ASSEMBLY All the machined parts of the knife were made on a universal milling machine, principally with different end mill cutters with a tip of tungsten carbide. Machining operations were guided and done at Helical – Generador de Engranes SA de CV, a professional machining workshop.

5.1 Blade This piece was the one that required more work, due to the thick sand shell it presented.

Before performing the machining operations, the feeding system was retired. The first of these was cut with a hacksaw in the laboratory of the Instituto Tecnológico de Saltillo, this, in order to obtain a sample for a microstructural study. After this, everything else related to machining, and the cutting of the other runner, was carried out at the enterprise.

Figure 5.1. Different cuts were made to the feeding system in order to analyze them microstructurally, chemically and physically. The lower parts of the figure correspond to the cuts made on the Instituto Tecnológico de Saltillo, and the upper part was cut on the enterprise. Once the feeding system was retired, the work consisted first of milling the entire piece, until leaving a “smooth” surface.

In the first instance, three presses were placed along the knife to fix it to the table, and by this way start to milling the surface of both sides of the knife. After finishing milling, the places where the presses did not interfere to mill, the knife was moved in such a way that now the parts from where it was pressed could be milled.

This operation was the first one, because being the knife too long, and milling it by the edges, without first having cleaned the surfaces, as these surfaces were too rough (because of the sand crust), milling by the edges would cause too much vibration, and it would run the risk for cracking. So, milling the surfaces, before any other operation, was safest one.

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In each milling action, 10 thousandths were milled, and between the two faces of the knife, 7 actions were carried out, until the initial thickness was reduced from 5.8 mm to 4 mm. This means that initially the knife must have measured 5mm, or even slightly less due to shrinkage, however, around 1mm was added due to the sand shell formed. Figure 5.2 shows how the knife was held, and how it was being milled. (One action corresponds to moving the cutter from one side to another milling 5 thousandths, and return it back, but, with 5 thousandths more, that is why one action correspond to 10 thousandths).

a) c)

b)

Figure 5.2. Milling the Surface of the knife. a) The surface of the knife fixed by b) 3 presses, and milled by c) the end mill cutter. Then presses were collocated in other areas, so it could be milled on the surfaces where they were positioned at the beginning.

After having both surfaces milled, the next operation was to mil the edges of the knife, pressed know with more accuracy, and with minor risk of cracking by vibration. By doing this operation, the upper lock for the crossguard was made. The only edges that were not mill were the ones near to the tip of the blade, since they were too much curved, to use the end mill cutter. Once again milling actions were made from 5 to 5 thousandths until the desired wide was reached (2 in). The blade was around 2.5 hundredths bigger from wide, (around because the whole surface was irregular), so 5 actions were made involving the two edges of the blade.

Talking about the wide of the tang, in average, around 2 hundredths were milled just from the upper edge, this, in order to make the upper lock, as it can be seen on figure 3.6. From the lower part of the tang, around 5 thousandths were milled. So the final wide of the tang was 1.625-in, 0.025-in less than the original designs.

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More milled surface was on the part of the blade, because it had the thicker crust. On image 5.3 the milling-edge operation can be seen.

Figure 5.3. The milling-edge operation on the lower part of the tang. Same milling operation was done on the upper part of the tang, and on the edges of the blade. The curved zones at the tip, were the only ones that were not milled. The next operation consisted on the machining of the fuller. Another end mill cutter of a different size was used to give the desired wide of the fuller. The designs pointed out, that the thickness of each fuller was going to be 4 hundredths, but when machining, it seemed not to give the desired aspect, so another modification was made to the original design, and it was continued milling, until 8 hundredths were reach. A red mark was drawn, in order to have a visual reference of where to start milling. On Figure 5.4, it could be seen how this process was done.

Figure 5.4. Milling the part of the fuller.

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After milling operations, the curved zones at the tip of the knife, were “polished” with an emery machine. Then, the knife looked as shown on the figure below:

Figure 5.5. The appearance of the knife after milling was done. The machining process of the blade continue with the machining of the jagged edge. This process consisted on perforating the edge of the knife setting the milling machine on an angle of 45°, alternating spaces from one tooth by one tooth, and the empty spaces were perforated when turning the knife by the non-perforated face, and repeating the same operation with the milling machine.

Figure 5.6. Knife with jagged edge and without sharpening.

Finally, the edge was sharpened also at “Helical – Generador de Engranes SA de CV”.

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5.2 Guard and Pommel The guard and the pommel, were both obtained from a bronze ingot. Using first the edge mill cutters to clean the surface of the ingot, it was cut from the half, so, one part would be machined for the guard, and other for the pommel.

Figure 5.7. Bronze ingot. Guard

For the guard, it was first cut for the dimensions that this piece required. Then, a primary-cubic shape was obtained from the borders, for which a cutting with angle was needed. Finally, this angle was given by positioning the milling machine on 45°. The rounded borders were obtained by the use of an emery machine.

Figure 5.8. Primary obtained shape for the guard.

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Figure 5.9. Final obtained primary shape after milling machine operation. Finally, the guard was perforated through the middle along a longitudinal cut, in order to give the required space to enter through the tang.

In order to give a smother surface, and a mirror-like finish, the crossguard was roughed until 2000 sandpaper, the final aspect was reached by a metal polisher named “Brasso”.

In order to give a smother surface, and a mirror-like finish, the crossguard was roughed until 2000 sandpaper, the final aspect was reached by a metal polisher named “Brasso”.

Figure 5.10. Final look of the crossguard.

Figure 5.11. Knife without sharpening and with the crossguard superimposed.

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Pommel

As well as the crossguard, the pommel was first cut on the indicated sizes, then a primary and rectangular form from the back face was obtained. The first obtained shape of the pommel consisted on hard and very geometric surfaces, shape that was achievable by the milling machine positioning it on different angles. Then, the pommel was final shaped on an emery machine, and final, softer, rounded and mirror-like aspect was done by roughing it up to 2000 sandpaper, and by using the metal rinse “Brasso”.

a) b)

Figure 5.12. a) First primary shape obtained from the milling machine. b) After using the emery machine in order to give smoother surfaces a final mirror like aspect was obtained by roughing and polishing. 5.3 Handle The handle was made of alternating blocks of different kinds of wood. There were used blocks of caoba, and blocks of banak. They were cut in such a way that they could enter easily through the tang of the knife. Then, they were pasted with an epoxy resin, and after resin dry, the oval-like shape, was given with a rotary sandpaper, and the fingers shape was given by roughing with a cylindrical sandpaper tool.

Finally, the handle was coated with a polyurethane varnish, in order to achieve a smother surface, and a bright-mirror aspect, besides it protect the wood from moisture.

On the next figures, the completely process is shown.

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Figure 5.13. Wood forming process for the handle. a) Blocks of wood (caoba-darkest, banak-lightest) were drilled, so they could enter through the tang. b) They were pasted with an epoxy resin. c)Using a rotary sand paper a primary shape was obtained. d) The spaces for the fingers were med with a cylindrical sandpaper. e) Final shape of the handle. f) A polyurethane coating was made with a pressure pistol.

5.4 Assembly The assembly was carried out in different parts. For instance, once the knife was sharpened, it was roughed until a mirror finish was obtained on the surface, after that, the guard and the handle were joined by combining two epoxy resins that function as a long-lasting glue. After this process the knife was sharpened again, because on the roughing process it lost some of its sharp. Then, the pommel was similarly assembled and glued with the epoxy resin (it is the same resin used to glue the wooden blocks of the handle).

Epoxy resin

Figure 5.14. Assembly of the knife, guard and handle.

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It should be noted that, like the handle, the polyurethane varnish was applied to the bronze parts, in order to provide a coating that protects the metal from water or moisture, and therefore slows down, or prevents the formation of the oxidized layer turning it an opaque and dark color.

However, because the varnish was applied to the guard already assembled, there were parts in which unfortunately the varnish did not completely cover the surface, mainly in the area adjacent to the knife blade (part that was covered by adhesive tape to prevent the blade from staining from the varnish). Because of this, the polyurethane coating on the guard was removed by sanding the surfaces. The coating made to the pommel, being assemble and coated separately, it worked perfectly, giving the finish that was sought.

Finally, as an extra detail, the initials of the Technological Institute of Saltillo (I.T.S.) were engraved, in order to show a better look-like, and to cover a notable pore on the surface of the knife, this process was professionally made by laser by … and the provided design was made by the team.

Pore a)

b)

c) Figure 5.15. a) Sharpened knife showing the place of the pore where the initials of I.T.S. are located. b) and c) Show the final aspect of the Bowie Knife.

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6. MICROSTRUCTURE ANALYSIS, PROPERTIES AND DEFECTS Microstructure reveal very interesting information about the alloy, it was only possible the observation by optical microscope, further analysis could not be done.

f)

Figure 6.1. a) As-cast microstructure without etching, dendrites could be observed. b) As-cast microstructure etched with nital 4%, a cementite network could be observed. c) and d) A cluster of irregular carbon (graphite) form could be observed. e) Some pearlite colonies could be observed. f) Cluster irregular carbon shapes could be seen at major magnifications.

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Microstructure

Due to the presence of the high carbon content in the alloy, it is possible to observe in the microstructure a cementite network, characteristic of white cast irons.

The alloy, according to the different iron-carbon diagrams, is right at the limit of the carbon percentage composition (2%), thus making the line between being considered as a cast iron, or as steel, very thin. There are authors who even handle the carbon composition range for steels, up to 2.14%wt., however, common highest carbon steels, contain a maximum of between 1.5 -1.7%wt. of carbon.

Having this clear it was concluded that, the alloy either had a very low carbon content to be considered as cast iron or a very high carbon content to be considered as steel.

This is a very interesting alloy, and thus microstructure, and even though it was looked on the literature, no microstructure resembled 100%.

The microstructure finally revealed ledeburite, an own microconstituent, or characteristic of cast irons and not of steels. There are areas in which pearlitic colonies can be observed, however, they do not present an important percentage.

In order to carry out the in-depth analysis, it was looked for the metallurgical effect of the main alloys, which correspond to nickel and copper, and these act as stabilizers of austenite, nickel even causing such a decrease in the austenite phase, that even at room temperature continues to promote its formation.

It was initially thought that the microstructure, due to the high contents of nickel and copper, would present a complete austenitic matrix, or a matrix with retained austenite from the solidification process. However, an important fact to highlight about austenite is that it does not possess magnetic properties, and the analyzed sample does present such characteristic. The magnetic properties, although for certain metallurgical aspects are not very applicable, can really help a lot, being a simple and revealing test.

When performing the magnetic test along the knife blade, it turned out that the areas where only the magnet joined, were at the borders, i.e. the tip, and the edges, contrary to what happened at the center of the knife, since it did not present any degree of attraction to the magnet.

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With these results, the idea of the formation of martensite on the matrix, in the areas where magnet does join, was thought, and it coincided with the fact that in these areas, the rate of solidification is considerably greater compared to the central areas of the piece. Despite this revealing fact, when the magnetic test was performed on the knife's tang, it turned out that this part was completely magnetic, both the edges and the center of the tang.

With these characteristics, it was thought that this was due to a solidification defect, known as segregation, since being such a thin thickness and with such high solidification rates, only the formation of certain phases depending on the chemical composition would affect the observed results.

In spite of this, the answer remains uncertain, since liquid metal was poured by the tip of the knife and the last part where the liquid metal was poured, was the part of the tang, so it is thought that the last part to solidify belongs to the tang.

Unfortunately, no microscopic studies were carried out on the other parts of the knife. The sample observed belongs to the riser/feeder of the tang, so that is why the sample also has magnetic characteristics.

Taking into account all these aspects, the factor that causes certain parts to be magnetic or not, first of all the solidification rate factor is taken into account, in which the first parts to solidify have most probably developed a martensitic microstructure, (cementite network with retained austenite (ledeburite) + martensitic dendrites), on the contrary, those parts in the center of the knife blade most probably present an austenitic microstructure, (cementite network with retained austenite (ledeburite) + austenitic dendrites). In the case of the tang (which observed micrographs are the most likely to belong), the cementite network is clearly visible, however, the matrix in which the cementite is embedded, since it does not present any virtually and visible characteristics of martensite, could even be ferrite, since it is also a magnetic phase.

Another very peculiar fact is the visualization of graphite (or at least that is what it is thought to be), and its appearance is very similar to the type of graphite observed in malleable cast iron, the "exploded"- type graphite. This fact is not peculiar to white irons, nor to steels, since in the case of white irons the carbon content is distributed mainly in the cementite network, and for steels, the carbon content is not high enough to cause graphite precipitation in its microstructure; however, somehow graphite precipitated in such a way, in certain points of the matrix.

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The way it precipitated is probably due to the high nickel content, since one of its main characteristics is a tendency to graphitize, and therefore by the addition of chromium, this effect is avoided, a higher chromium content on the alloy could avoid or minimize this graphitization effect.

Because of this graphitization factor an "easy and relative machining" was done, since contrary to what happens with white irons, and its long process of heat treatment to obtain precisely malleable iron, and to obtain better mechanical properties, it was not so difficult to carry out this process, and the knife did not seem to be affected by it.

The presence of graphite, like malleable cast iron in the microstructure, is another factor to which a lower solidification rate can be attributed in the tang of the knife. In addition, it is common to find a ferritic matrix in a malleable iron which has undergone slow cooling.

It is not possible to assure all the above mentioned, because it has been really difficult to find references in the literature, however, many texts, articles, and books, had been useful in order to ideate on the best way, which are the elements that best describe the obtained microstructure.

Analyzing the observed results, it was initially thought to subject the knife to heat treatment. In the first instance, a homogenization treatment would be carried out, this with the purpose of breaking down the segregated structure of the solidification process and to alleviate internal tensions. Later, the treatment would consist of leaving the knife inside the furnace, annealing it, to finally obtain a completely homogenous structure as close as possible to that of steel. Finally, to give the knife greater hardness, strength, and toughness, would be again subjected to heat treatment but this time quenching it in oil.

For the temperatures and times of heat treatment, in principle, for the homogenization treatment, 900- 950 °C for 12 hours, and cooling inside the furnace. Finally, for tempering, a temperature of 750 - 800 °C for 30 minutes, would probably be used, and cooling in oil.

Properties

Talking a little about properties, the knife, although it was subjected to a hardness test, the durometer used was not the most suitable, obtaining unreliable results, so it is estimated that the unmodified metal would reach a hardness of between 230 - 300 HB, and once hardened up to 500 HB.

It could be say that despite the alloy was not subjected to heat treatment, it does have good mechanical properties, and probably enhanced by the presence of graphite in the mentioned form.

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Corrosion resistance is also another factor that it is thought to be enhanced by the subjection to heat treatment, due to the fact that it is observable a few more different types of carbides, which besides they could weaken the knife, they might also could provoke an accelerated corrosion rate when leaving the knife in a moisty environment. Stress corrosion cracking may be also improved by retarding this effect in presence of corrosion.

It was planned further investigation supported with the use of Scanning Electron Microscope (SEM), in order to look for specific chemical composition on determined zones using EDS, so by this way it would be easier to determine the present phases on the microstructure. Besides, further mechanical analysis with the correct use of the durometer, also would be taking into account to support and define better the properties that characterize the alloy.

Defects

Despite the look of the knife at simple sight, it has, and could be characterized by its defects. Porosity is the principal defect; it contains large pores located principally on the face of the I.T.S. initials, one on the adjacent blade near the guard, at the center (the biggest), and at the edge near the sharpened and curved zone of the blade. Other type of porosity is present on the back face (taking as reference the I.T.S. initials) and are present along the upper edge of the knife.

Corrosion, against what it was initially thought, could be also observed when wetting the knife; in fact, there are some observable spots that could not been removed easy. When the roughing process was being made, it was let a long time in contact with water and a moisty environment, after this, green spots started to appear. This could be regarded to the nickel content because the color of the nickel oxide is green, but this is only a supposition.

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Figure 6.2. Red arrows indicate where the pores are located. The lower figures show the general corrosion type that the knife presented after being in contact with water for up to 30 minutes. Black rectangles indicate the same face of the blade.

7. CONCLUSIONS In conclusion, the following points could be summarized:

 The green sand mix mold is undoubtedly better for obtaining the desired shape. The refectory mold, although it could be considered as an alternative option, has to be sufficiently preheated (up to 800-900 °C) to avoid its breakage and fulfill its purpose.  The proper use of green sand components and their mixing are important factors that intervene to prevent defects such as porosity or burnt on sand.  The casting temperature greatly affects the appearance of the as-cast piece, although it improves fluidity, and in the case of a small thickness it is convenient.

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 The alloy, together with solidification aspects, caused to obtain a white cast and modified iron, principally due to the presence of graphite, similar to the shapes observed on malleable cast irons.  Properties are not well explained, the alloy presented zones in which is magnetic (edges and tang) and other in which not (center of the piece). This could be caused mainly because of solidification rates and segregation phenomena.  Further analysis by SEM and EDS detector would demonstrate specific and detailed information about the alloy.  The alloy presents a certain grade of porosity, and high corrosion rate when placed into a moisty environment.  The solution for the alloy, in order to obtain a microstructure, the most similar to one of a steel, is the application of first a homogenization heat treatment, and then an oil tempering, for enhancing properties.  Despite the defects and the alloy properties, the knife can achieve its purpose, being a completely functional knife.

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Jones, C. (1940). Heating Process for white cast iron. United States Patent Office.

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