Liquid Nitrogen Shrinking Fitting Box - Essay Example

? Liquid Nitrogen Shrink Fitting Box One of the major challenges of metal systems is the tendency of various metal components to expand when heated and contract when cooled. The conventional approaches used to mitigate this problem involve heating the out components before assembly to allow it expands so that the inner component can be effectively fitted into it. However, these techniques often consume a lot of time, are costly to operate and can also lead to significant mechanical damage due to stress resulting from uneven or poor heating procedures. Contrastingly, the use of liquid nitrogen shrinking is more efficient, faster and can significantly help eliminate the potential distortions of components. This paper proposes a practical, efficient shrinking fitting system that requires low initial implementation costs as well as minimal operation or maintenance costs. Executive Summary The proposed procedure will employ the phenomenon of thermal expansion in the make strong joints. The technique particularly involves using liquid nitrogen as the preferred cryogenic fluid for compression shrink fitting. Numerous literatures reveal that the conventional heat and fitting techniques often consume a lot of time, are costly to operate and can also lead to significant mechanical damage due to stress resulting from uneven or poor heating procedures. This paper proposes an alternative shrink fitting system that: Is cost effective Does not damage the components Has a low capital cost Efficient Among all the cryogenic fluids reviewed such as helium, hydrogen fluid is the most applicable in this project. Although there are several cryogens that are currently available for use in compression shrink fitting, liquid nitrogen is one of the cheapest and most common of them and can be legally purchased in nearly every part of the world. Lastly, if it succeeds, the proposed project will ill particularly find a wide range of applications not only in the metal working industry but also in various other mechanical and constructional fields such as automotive and building industries. Table of Contents One of the major challenges of metal systems is the tendency of various metal components to expand when heated and contract when cooled. The conventional approaches used to mitigate this problem involve heating the out components before assembly to allow it expands so that the inner component can be effectively fitted into it. However, these techniques often consume a lot of time, are costly to operate and can also lead to significant mechanical damage due to stress resulting from uneven or poor heating procedures. Contrastingly, the use of liquid nitrogen shrinking is more efficient, faster and can significantly help eliminate the potential distortions of components. This paper proposes a practical, efficient shrinking fitting system that requires low initial implementation costs as well as minimal operation or maintenance costs. 1 1.Problem Statement 4 Metals normally have a tendency to contract when cooled and expand when heated. This property is a major limitation in most mechanical systems because it may result in a significant difference between the inner and outer dimensions of mechanical components. One of the most widely solutions is shrinking fitting in which components of a structure may be pre-heated or cooled, based on the phenomenon of thermal expansion, to fit them together. Traditionally, various heated metal systems are usually used to resize one of the fitting components. However, both the force fit and expanding the outer components techniques are not only costly to operate but can also lead to significant mechanical damage due to stress resulting from uneven or poor heating procedures. On the other hand, heating the outer component may sometimes take longer time and may be hindered by the metallurgical properties of the components. 4 According to Heinz, P. (2008), liquid nitrogen shrinking fitting is one of the most cost effective and safest methods that can be invariably used as an alternative to the traditional shrink fitting. Compared to the conventional heat and force fitting approaches, the use of liquid nitrogen shrinking is more efficient, faster and can significantly help eliminate the potential distortions of components. Such properties not only help reduce mechanical damage but also stress during interference fittings. Lastly, with regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. 5 The proposed compression shrinking fitting box uses liquid nitrogen cooling as alternative to the conventional shift fitting methods. The technique involves subjecting the inner components of the fittings in liquid nitrogen (temp. -196 oC) in order to make it shrink into a smaller size that can easily fit in. This is particularly attributed to the fact that liquid nitrogen has no permanent effect on both ferrous and non-ferrous metals apart from a few austenitic irons. This paper proposes an efficient cost effective and safe shrink fitting method that can be invariably used as an alternative to the conventional force and heating shrink fitting techniques. 5 2.Overall Objectives 6 The primary objective of this project is to develop a practical, efficient shrinking fitting system that requires low initial implementation costs as well as minimal operation or maintenance costs. The proposed procedure will employ the phenomenon of thermal expansion to make strong joints with liquid nitrogen as the preferred cryogenic fluid. The technique particularly involves subjecting the inner components of the fittings in liquid nitrogen (temp. -196 oC) in order to make it shrink into a smaller size that can easily fit in. As opposed to the heating based fitting techniques, liquid nitrogen fitting minimizes warping and other unwanted metallurgical effects and this is expected to improve its efficiency while at the same time lowering the potential costs of maintenance (Rudnev and Loveless, 2002). 6 Another important goal of this project is to reduce the handling time of the system and enhance its efficiency. The box will be particularly designed in such a way that allows for an inlet for liquid nitrogen as well as an outlet that can be used to vacuum used liquid nitrogen. In this regard, the use of liquid nitrogen shrinking is expected to make the fitting process more efficient, faster while at the same time eliminating the potential distortions of components. Such benefits will not only help reduce mechanical damage but also stress during interference fittings. 6 Lastly, with regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. Cryo-treatment of metal components is also intended to improve their material properties in terms of increased toughness, stress relied and wears resistance. Based on the expected potential benefits of the proposed liquid nitrogen shrinking fitting box, it will be applicable in automotive industry and mechanical engineering particularly for tasks such as inserting shafts into metal hubs or wheels, press fitting of metallic rings around shafts, inserting bushings into metal hubs and fitting of guide pins into die shoes among others. 6 3.Historical and Economic Perspective 7 In the past, compression shrink fitting was widely used as the preferred technique for fixing railroad axles as well as assembling tires and wheels. According to many experts, the preference of this technique was primarily attributed to its potential significant advantages over other shrink fitting techniques such as heating and fitting. For example, unlike heating, cooling does not change the material properties. Shrink fitting based on cryogens particularly employs the phenomenon of thermal expansion to make strong joints. The history of cryogenic thermodynamics date back to 1702 when the concept of absolute zero based on the observation gases was introduced by Guillaume Amontons (Salvador, 2003). 7 The development of thermodynamics was particularly advanced by the discovery of atomic theory which later motivated new directions in thermal expansion phenomenon among other fields of knowledge. Compression shrink fitting based on cryogens such as liquid nitrogen has been used for several decades to help fix or separate various mechanical components. However, it was not until after World War II that the use of compression shrinks techniques become widespread. This was particularly attributed to the advancements in cryogenics and the discovery that frozen metals not only shrink in size but are also more resistance to wear. Compared to the conventional interference fit approaches such as heating, the proposed technique is cost effective in terms of the energy requirements and does not have the drawback of softening the metal components due to high temperatures. 7 4.Candidate Solutions 8 A number of theoretical and practical solutions have previously been used to improve the efficiency of interference fitting. Some of the most widely used potential solutions include: 8 Oil baths and heating shrink techniques 8 Use of other cryogens such as helium 8 Oil baths and heating shrink heating techniques are effective but they require significantly high initial costs and are also costly to maintain and operate. Additionally, although there are several cryogens that are currently available for use in compression shrink fitting, liquid nitrogen is one of the cheapest and most common of them and can be legally purchased in nearly every part of the world. Liquid nitrogen has no permanent effect on both ferrous and non-ferrous metals apart from a few austenitic irons (Rapoport and Pleshivtseva, 2006). This greatly reduces the problem of the metallurgical change and bends such as the reduction in these metallic objects hardness. Finished elements in the nitrogen shrinking fitting can also be assembled by the use of LN lining without any damage thus rendering this process a cost effective one. 8 With regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. When nitrogen box is used, there is no loss of time in this process for the furnaces as the major component in this process is placed in the liquid nitrogen bath. This reduces the handling time as well as the cost of the whole process. 8 5.Proposed solution Concept 9 The proposed nitrogen liquid shrink fitting box will primarily employ the concept of thermal expansion to create firm fitting joints of different components. The simple box will have both an inlet for liquid nitrogen and an outlet that can be used to vacuum used liquid nitrogen. This is largely based on the understanding that certain materials and metals contact and reduce in size when subjected to certain levels of cooling for a given period of time. While the material is still at its new state, it would be possible to fit it in another material that is at room temperature. However, once the material is removed from the cooling agent, it will gradually begin to expand and eventually regain its original size (Lippmann, H. (2002). In this regard, the end result will be a tight strong fit that ensures a very stable joint between the two components. 9 The mechanism of operation of the proposed nitrogen fluid shrink fitting box will involve dipping the inner components of the fittings in liquid nitrogen (temp. -196 oC) contained in the box in order to make it shrink into a smaller size that can easily fit in. In this regard, the smaller part of the components to be fitted is cooled to ensure a force free insertion into the larger component. The force fitting method needs only a singular dies and a well-balanced heavy press in order to complete the whole industrial process. This method is particularly useful in helping to avoid the conventional energy consuming and often costly heating and fitting techniques. Additionally, the proposed technique of using a liquid nitrogen shrink fitting box to assemble components only temporarily affects the mechanical properties of the components. 9 According to the phenomenon of thermal expansion, atoms have a tendency to move further when temperature increases and moves closer and contracts when the temperature decreases. However, this effect applies to solids, liquids and gasses and is not limited only to metals. Additionally, the expansion is not permanent and the objects often regain their original size when the temperature returns to normal. This is particularly attributed to the fact that during the thermal change, the atoms or the mass of the material normally remains unchanged. According to Schroeder, 2010), thermal expansion normally applies to the linear dimension of the materials involved. The change in the linear dimension of a material after cooling or heating can be got by the formula: ?L = L0??T where L0 is the original length, ?T is the change in temperature while ? is the coefficient of the linear expansion. 10 6.Major Design and Implementation Challenges 10 Despite the numerous potential benefits of the proposed liquid nitrogen shrink fitting box, there are a number of design and implementation challenges that should be taken into consideration. For example, materials such as cooper, aluminum, and cooper alloys such as bronze and brass are not always affected by the low temperatures of nitrogen liquid. On the other hand, carbon-steel and other low alloy steels are usually temporarily embrittled when they are subjected to liquid nitrogen temperatures and this is often a serious limitation of this technique (Angel, 2010). 10 Although nitrogen shrinking fitting is one of the safest methods of the gases’ assembly in its inert form, workers may sometimes be exposed to risks such as frostbites, cold burns and asphyxiation when proper precautions are not taken. Lastly, the implementation of the project requires highly trained staff with the required expertise to effectively carry out liquid nitrogen shrink fitting and this may sometimes be expensive. In this regard, even though the whole nitrogen fixation process is coast effective, the labour and human resources needed is expensive. In cases of the nitrogen gas leakages into the environment, there will be environmental pollution. The gas nitrogen gas leakages will as well affect the liquid nitrogen shrinking fitting workers health-wise. 10 7.Implications of Project Success 11 The success of the proposed project will come with a number of potential benefits. Liquid nitrogen shrinking fitting box will particularly find a wide range of applications not only in the metal working industry but also in various other mechanical and constructional fields such as automotive and building industries. Based on the expected potential benefits of the proposed liquid nitrogen shrinking fitting box, it will be applicable in automotive industry and mechanical engineering particularly for tasks such as inserting shafts into metal hubs or wheels, press fitting of metallic rings around shafts, inserting bushings into metal hubs and fitting of guide pins into die shoes. On the other hand, in the industrial sectors, the straight forward technique will provide an efficient alternative for fitting various mechanical components such as gear wheels and cylinder liners among others. 11 References 12 Liquid Nitrogen Shrink Fitting Box 1. Problem Statement Metals normally have a tendency to contract when cooled and expand when heated. This property is a major limitation in most mechanical systems because it may result in a significant difference between the inner and outer dimensions of mechanical components. One of the most widely solutions is shrinking fitting in which components of a structure may be pre-heated or cooled, based on the phenomenon of thermal expansion, to fit them together. Traditionally, various heated metal systems are usually used to resize one of the fitting components. However, both the force fit and expanding the outer components techniques are not only costly to operate but can also lead to significant mechanical damage due to stress resulting from uneven or poor heating procedures. On the other hand, heating the outer component may sometimes take longer time and may be hindered by the metallurgical properties of the components. According to Heinz, P. (2008), liquid nitrogen shrinking fitting is one of the most cost effective and safest methods that can be invariably used as an alternative to the traditional shrink fitting. Compared to the conventional heat and force fitting approaches, the use of liquid nitrogen shrinking is more efficient, faster and can significantly help eliminate the potential distortions of components. Such properties not only help reduce mechanical damage but also stress during interference fittings. Lastly, with regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. The proposed compression shrinking fitting box uses liquid nitrogen cooling as alternative to the conventional shift fitting methods. The technique involves subjecting the inner components of the fittings in liquid nitrogen (temp. -196 oC) in order to make it shrink into a smaller size that can easily fit in. This is particularly attributed to the fact that liquid nitrogen has no permanent effect on both ferrous and non-ferrous metals apart from a few austenitic irons. This paper proposes an efficient cost effective and safe shrink fitting method that can be invariably used as an alternative to the conventional force and heating shrink fitting techniques. 2. Overall Objectives The primary objective of this project is to develop a practical, efficient shrinking fitting system that requires low initial implementation costs as well as minimal operation or maintenance costs. The proposed procedure will employ the phenomenon of thermal expansion to make strong joints with liquid nitrogen as the preferred cryogenic fluid. The technique particularly involves subjecting the inner components of the fittings in liquid nitrogen (temp. -196 oC) in order to make it shrink into a smaller size that can easily fit in. As opposed to the heating based fitting techniques, liquid nitrogen fitting minimizes warping and other unwanted metallurgical effects and this is expected to improve its efficiency while at the same time lowering the potential costs of maintenance (Rudnev and Loveless, 2002). Another important goal of this project is to reduce the handling time of the system and enhance its efficiency. The box will be particularly designed in such a way that allows for an inlet for liquid nitrogen as well as an outlet that can be used to vacuum used liquid nitrogen. In this regard, the use of liquid nitrogen shrinking is expected to make the fitting process more efficient, faster while at the same time eliminating the potential distortions of components. Such benefits will not only help reduce mechanical damage but also stress during interference fittings. Lastly, with regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. Cryo-treatment of metal components is also intended to improve their material properties in terms of increased toughness, stress relied and wears resistance. Based on the expected potential benefits of the proposed liquid nitrogen shrinking fitting box, it will be applicable in automotive industry and mechanical engineering particularly for tasks such as inserting shafts into metal hubs or wheels, press fitting of metallic rings around shafts, inserting bushings into metal hubs and fitting of guide pins into die shoes among others. 3. Historical and Economic Perspective In the past, compression shrink fitting was widely used as the preferred technique for fixing railroad axles as well as assembling tires and wheels. According to many experts, the preference of this technique was primarily attributed to its potential significant advantages over other shrink fitting techniques such as heating and fitting. For example, unlike heating, cooling does not change the material properties. Shrink fitting based on cryogens particularly employs the phenomenon of thermal expansion to make strong joints. The history of cryogenic thermodynamics date back to 1702 when the concept of absolute zero based on the observation gases was introduced by Guillaume Amontons (Salvador, 2003). The development of thermodynamics was particularly advanced by the discovery of atomic theory which later motivated new directions in thermal expansion phenomenon among other fields of knowledge. Compression shrink fitting based on cryogens such as liquid nitrogen has been used for several decades to help fix or separate various mechanical components. However, it was not until after World War II that the use of compression shrinks techniques become widespread. This was particularly attributed to the advancements in cryogenics and the discovery that frozen metals not only shrink in size but are also more resistance to wear. Compared to the conventional interference fit approaches such as heating, the proposed technique is cost effective in terms of the energy requirements and does not have the drawback of softening the metal components due to high temperatures. 4. Candidate Solutions A number of theoretical and practical solutions have previously been used to improve the efficiency of interference fitting. Some of the most widely used potential solutions include: Oil baths and heating shrink techniques Use of other cryogens such as helium Oil baths and heating shrink heating techniques are effective but they require significantly high initial costs and are also costly to maintain and operate. Additionally, although there are several cryogens that are currently available for use in compression shrink fitting, liquid nitrogen is one of the cheapest and most common of them and can be legally purchased in nearly every part of the world. Liquid nitrogen has no permanent effect on both ferrous and non-ferrous metals apart from a few austenitic irons (Rapoport and Pleshivtseva, 2006). This greatly reduces the problem of the metallurgical change and bends such as the reduction in these metallic objects hardness. Finished elements in the nitrogen shrinking fitting can also be assembled by the use of LN lining without any damage thus rendering this process a cost effective one. With regard to its reliability, liquid nitrogen is relatively inert and this makes the box to be safe to use particularly in well ventilated areas. When nitrogen box is used, there is no loss of time in this process for the furnaces as the major component in this process is placed in the liquid nitrogen bath. This reduces the handling time as well as the cost of the whole process. 5. Proposed solution Concept The proposed nitrogen liquid shrink fitting box will primarily employ the concept of thermal expansion to create firm fitting joints of different components. The simple box will have both an inlet for liquid nitrogen and an outlet that can be used to vacuum used liquid nitrogen. This is largely based on the understanding that certain materials and metals contact and reduce in size when subjected to certain levels of cooling for a given period of time. While the material is still at its new state, it would be possible to fit it in another material that is at room temperature. However, once the material is removed from the cooling agent, it will gradually begin to expand and eventually regain its original size (Lippmann, H. (2002). In this regard, the end result will be a tight strong fit that ensures a very stable joint between the two components. The mechanism of operation of the proposed nitrogen fluid shrink fitting box will involve dipping the inner components of the fittings in liquid nitrogen (temp. -196 oC) contained in the box in order to make it shrink into a smaller size that can easily fit in. In this regard, the smaller part of the components to be fitted is cooled to ensure a force free insertion into the larger component. The force fitting method needs only a singular dies and a well-balanced heavy press in order to complete the whole industrial process. This method is particularly useful in helping to avoid the conventional energy consuming and often costly heating and fitting techniques. Additionally, the proposed technique of using a liquid nitrogen shrink fitting box to assemble components only temporarily affects the mechanical properties of the components. According to the phenomenon of thermal expansion, atoms have a tendency to move further when temperature increases and moves closer and contracts when the temperature decreases. However, this effect applies to solids, liquids and gasses and is not limited only to metals. Additionally, the expansion is not permanent and the objects often regain their original size when the temperature returns to normal. This is particularly attributed to the fact that during the thermal change, the atoms or the mass of the material normally remains unchanged. According to Schroeder, 2010), thermal expansion normally applies to the linear dimension of the materials involved. The change in the linear dimension of a material after cooling or heating can be got by the formula: ?L = L0??T where L0 is the original length, ?T is the change in temperature while ? is the coefficient of the linear expansion. 6. Major Design and Implementation Challenges Despite the numerous potential benefits of the proposed liquid nitrogen shrink fitting box, there are a number of design and implementation challenges that should be taken into consideration. For example, materials such as cooper, aluminum, and cooper alloys such as bronze and brass are not always affected by the low temperatures of nitrogen liquid. On the other hand, carbon-steel and other low alloy steels are usually temporarily embrittled when they are subjected to liquid nitrogen temperatures and this is often a serious limitation of this technique (Angel, 2010). Although nitrogen shrinking fitting is one of the safest methods of the gases’ assembly in its inert form, workers may sometimes be exposed to risks such as frostbites, cold burns and asphyxiation when proper precautions are not taken. Lastly, the implementation of the project requires highly trained staff with the required expertise to effectively carry out liquid nitrogen shrink fitting and this may sometimes be expensive. In this regard, even though the whole nitrogen fixation process is coast effective, the labour and human resources needed is expensive. In cases of the nitrogen gas leakages into the environment, there will be environmental pollution. The gas nitrogen gas leakages will as well affect the liquid nitrogen shrinking fitting workers health-wise. 7. Implications of Project Success The success of the proposed project will come with a number of potential benefits. Liquid nitrogen shrinking fitting box will particularly find a wide range of applications not only in the metal working industry but also in various other mechanical and constructional fields such as automotive and building industries. Based on the expected potential benefits of the proposed liquid nitrogen shrinking fitting box, it will be applicable in automotive industry and mechanical engineering particularly for tasks such as inserting shafts into metal hubs or wheels, press fitting of metallic rings around shafts, inserting bushings into metal hubs and fitting of guide pins into die shoes. On the other hand, in the industrial sectors, the straight forward technique will provide an efficient alternative for fitting various mechanical components such as gear wheels and cylinder liners among others. References Angel, R. (2010), Equations of state, High-Temperature and High-Pressure Crystal Chemistry, Rev. Mineral. Geochem, 41, 1, 35-59. Heinz, P. (2008). Improving machinery reliability (3rd ed.). New York: Gulf Professional Publishing. Lippmann, H. (2002). The effect of a temperature cycle on the stress distribution in a shrink fit. Int. J. Plasticity 8, 567–582. Rapoport, E. Pleshivtseva, Y. (2006). Optimal Control of Induction Heating Processes. CRC Press. Rudnev, V., Loveless, D. (2002). Shrink Fitting: Handbook of Induction Heating. New York, NY: CRC Press. Salvador, R. (2003). Zero thermal expansion due to an Electronic Valence Transition. Nature 425, 5, 702-714. Schroeder, V. (2010). An Introduction to Thermal Physics. New York: Addison Wesley Longman. Glossary of Terms Cryogens: Are substances that can be used to produce extremely low temperatures Interference fit: This is the fastening that is normally achieved between two components through frictions by compressing one component against the other. Shrink fitting: This is a technique in which relative changes in the size of objects after they are assembled is used to achieve inference. Read More