FIEUD OF THE INVENTION

This invention relates to the field of metalworking and manufacturing processes.

Particularly, this invention relates to the field of investment casting.

Specifically, this invention relates to a process for manufacturing of copper- titanium alloys by lost wax process (investment casting).

BACKGROUND OF THE INVENTION

‘Investment casting’ and ‘forging’ are some of the oldest metal working techniques.

‘Investment casting’ is a manufacturing process in which a wax pattern is coated with a refractory ceramic material. Once the ceramic material is hardened its internal geometry takes the shape of the casting. The wax is melted out and molten metal is poured into the cavity where the wax pattern was.

Investment casting is a manufacturing process in which a wax pattern is coated with a refractory ceramic material. Once the ceramic material is hardened its internal geometry takes the shape of the casting. The wax is melted out and molten metal is poured into the cavity where the wax pattern was.

The first step in investment casting is to manufacture the wax pattern for the process. This is done by injecting molten wax into an aluminum die on a injection hydraulic press. Since the pattern is destroyed in the process, one will be needed for each casting to be made. When producing parts in any quantity, a mold from which to manufacture patterns will be desired. Since the mold does not need to be opened, castings of very complex geometry can be manufactured. Several wax patterns may be combined for a single casting. Or as often the case, many wax patterns may be connected and poured together producing many castings in a single process. This is done by attaching the wax patterns to a wax bar, the bar serves as a central sprue. A ceramic pouring cup is attached to the end of the bar. This arrangement is called a tree, denoting the similarity of casting patterns on the central runner beam to branches on a tree. The metal casting pattern is then dipped in a refractory slurry whose composition includes extremely fine grained silica, water and binders. A ceramic layer is obtained over the surface of the pattern. The pattern is then repeatedly dipped into the slurry to increase the thickness of the ceramic coat. Once the refractory coat over the pattern is thick enough, it is allowed to dry in air in order to harden. The hardened ceramic mold is turned upside down and heated to a temperature of around 100°C. This causes the wax to flow out of the mold, leaving the cavity for the metal casting. The ceramic mold is then heated to around 1050°C for at least 90 minutes. This will further strengthen the mold, eliminate any leftover wax or contaminants and drive out water from the mold material. Then the molten metal is transferred from the furnace to a ladle and the metal casting is then poured while the mold is still hot. Pouring the casting while the mold is hot allows the liquid metal to flow easily through the mold cavity, filling detailed and thin sections. Pouring the metal casting in a hot mold also gives better dimensional accuracy, since the mold and casting will shrink together as they cool.

‘Forging’ is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it is performed; cold forging (a type of cold working), warm forging, or hot forging (a type of hot working).

Conventionally, Copper Titanium (Cu-Ti) alloys are made by a Hot Forging process which is time consuming and expensive. These alloys are not made by investment casting processes.

Non-sparking tools are made of materials that do not contain iron (non- ferrous metals) and therefore the risk of a spark being created while the tool is in use is reduced. Non-sparking tools protect against both fire and explosion in environments that may contain flammable liquids, vapors, dusts or residues. When working in confined spaces and areas where flammable gases or dusts are present, using a non-sparking tool is the best practice.

Common materials used for non-sparking tools include brass, bronze, copper-nickel alloys, copper- aluminum alloys or copper-beryllium alloys. Beryllium alloys are becoming less favorable due to the potential toxicity of beryllium dust. Non-metals such as wood, leather and plastics can also be used to create non- sparking tools.

Some common tools that are available in a non-sparking option include hammers, axes, pry bars, chisels, utility knives, mallets, pliers, screwdrivers, sockets and wrenches. Non-sparking polypropylene shovels are often used for hazardous material spill clean-up. Because non-sparking tools are non-ferrous, they are softer than standard tools which are usually made of a high strength alloy steel. This may cause non- sparking tools to wear more quickly than their steel counterparts.

Non-sparking tools were previously manufactured by hot forging process which is time consuming and expensive. Casted Copper Titanium after heat treatment showcase excellent physical and mechanical properties of uniform hardness as well as tensile strength compared to conventionally used Aluminum Bronze, Monel (Copper-Nickel alloys) and Copper Beryllium used for manufacturing Non Sparking Tools by conventional forging process.

Commercial production of non-sparking hand tools, welding and plasma nozzles and plunger tips for applications in oil and gas, automotive, heavy engineering, defense, electrical and general industry.

There is a need to make Copper Titanium products / alloys by casting process instead of forging process. Copper Titanium castings of non sparking, non-magnetic safety tools are safe for use in all potentially explosive environments, all areas where combustible or easily ignitable vapours, liquids and dusts are present and anywhere that a potential fire and explosion risk from sparks is possible.

OBJECTS OF THE PRESENT INVENTION

An object of the invention is to provide a process for manufacturing of copper- titanium alloys by lost wax process (investment casting).

Another object of the invention is to manufacture Copper Titanium Alloy non-sparking tools and other parts by Investment Casting process.

Yet another object of the invention is to achieve commercial production of products like non- sparking hand tools, welding and plasma nozzles and plunger tips for applications in oil and gas, automotive, heavy engineering, defense, electrical, and general industry.

SUMMARY OF THE INVENTION:

According to this invention, there is provided a process for manufacturing of copper-titanium alloys by lost wax process (investment casting), said process comprising: a) fixing a silicon carbide crucible in an induction melting furnace packed with a basic or neutral ramming mass surrounding said silicon carbide crucible; b) preheating said crucible at a temperature ranging from 700 to 800°C, followed by charging said crucible with copper scrap in an amount of 90% to 99% by weight, based on the total weight of charge to be melted to attain a temperature of about 1100 to about 1200°C ; c) adding at least 99% pure titanium scrap having 0.5 mm to 10 mm thickness in an amount of 1% to 10% by weight, based on the total weight of charge to be melted into said crucible to obtain a mixture; d) continuously stirring said mixture using a stainless steel rod for about 5 to about 10 minutes to attain a homogenous melt in the crucible placed inside said induction furnace and maintaining the temperature of said furnace to about 1000 to about 1500°C; e) pouring said homogenous melt into an investment casting shell of a desired/pre-determined product followed by cooling and baking to a temperature of about 900 to 1200°Cfor at least about 90 minutes followed by cooling to obtain copper titanium cooled castings; f) knocking off cooled copper titanium castings and subjecting said castings to fettling operation, and shot blasting /s and blasting operation to remove surface impurities; and g) solution annealing said copper titanium castings at a temperature of about 700 to about 800° C in an electrical heat treating furnace for about 2 to about 4 hours and quenching into rapidly cooled water followed by precipitation hardening process where copper titanium castings are aged in the electrical heat treating furnace at about 350 to about 550°C for about 3 to about 5 hours.

In at least an embodiment, said induction melting furnace is a medium frequency induction furnace.

In at least an embodiment, said induction melting furnace is a medium frequency induction furnace, characterised in that, said medium frequency induction furnace being lined with ramming mass selected from a group of ramming masses consisting of basic ramming mass, acidic ramming mass, and neutral ramming mass fixed with a silicon carbide crucible to avoid slag generation and oxidation of titanium alloy reacting with the furnace ramming masse.

In at least an embodiment, said copper scrap comprises copper in an amount of 95% by weight, based on the total weight of charge to be melted and said titanium scrap comprises titanium in an amount of 5% by weight, based on the total weight of charge.

In at least an embodiment, said step of charging said crucible comprises a step of skimming generated slag, if any, from top of said crucible using a stainless steel rod with a spouted-cup end.

In at least an embodiment, said step of charging said crucible comprises a step of powering said furnace, incrementally, till molten bath reaches a temperature of about 1250°C (±250°C) by a dip type pyrometer.

In at least an embodiment, said step of addition of titanium scrap comprises a step of maintaining furnace temperature without increasing it in order to avoid degassing, pinholes and superheating related defects in said casting.

In at least an embodiment, said stirring is limited to less than 10 minutes in order to avoid oxidation of titanium with atmospheric gases.

In at least an embodiment, said step of pouring is directly from said crucible into a pouring basin of said casting shell using a fork end in order to avoid slag generation and oxidation of titanium alloy. In at least an embodiment, said process comprises an additional step of breaking said ceramic mold from said copper titanium investment casting and cutting parts from its tree.

According to this invention, there is also provided a copper titanium alloy melt composition comprising copper in an amount of 90 to 99 % by weight, based on the total weight of the composition and titanium in an amount of 1% to 10% by weight, based on the total weight of the composition, wherein the weight ratio of copper to titanium is 19:1 to 13:1.

According to this invention, there is also provided a copper titanium alloy casting comprising copper in an amount of 90 to 99 % by weight, based on the total weight of the alloy and titanium in an amount of 1 % to 10% by weight, based on the total weight of the alloy, wherein said alloy casting is characterized by hardness of about 200 to 350 HV, yield strength of about 500-700 MPa, and tensile strength of about 700-1100 MPa.

The heat treatment process is to attain desired mechanical and physical properties.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

The invention will now be described in relation to the accompanying drawings, in which: FIGURE 1 illustrates an induction furnace and silicon carbide crucible assembly.

DETAILED DESCRIPTION OF THE ACCOMPANYING

DRAWINGS:

According to this invention, there is provided a process for manufacturing of copper-titanium alloys by lost wax process (investment casting).

Specifically, this invention discloses a manufacturing process for Copper Titanium alloy castings by an investment casting process, the alloy having chemical composition of 90% to 99% Copper and 1% to 10% of Titanium. This investment casted alloy is used for manufacturing of non sparking tools, plunger tips, die inserts, welding tips, and plasma nozzles.

FIGURE 1 illustrates an induction furnace and silicon carbide crucible assembly.

In at least an embodiment of this invention, the process comprises a first step of fixing a Silicon Carbide crucible (12) in an induction melting furnace (10) rammed and packed with basic or neutral ramming mass (14) surrounding the Silicon Carbide crucible (12). Reference numeral 16 refers to induction coils of the induction melting furnace. Preferably, for this step, a medium frequency induction furnace, which is generally lined with basic/ acidic or neutral ramming masses, is fixed with a Silicon Carbide Crucible as shown in the Figure 1. This arrangement is done to avoid contact of Titanium with the lining surface which leads to oxidation and to avoid the erosion of lining increasing slag content in the melt charge.

In at least an embodiment of this invention, the process comprises a second step of preheating the crucible (12) to a red hot condition, then, charging the crucible with commercially available copper scrap to attain 1225°C ( ±100°C) temperature.

Preferably, for this step, the induction furnace (10)is powered so that the inserted Silicon Carbide crucible (12) can be preheated to a red hot condition. If the crucible is charged with metal scrap at room temperature, it might lead to cracking of the crucible. Once, the inserted Silicon Carbide crucible is visibly heated to the red hot condition, the charging (putting metal ingot in the furnace for melting) of Copper scrap into the furnace is done. The total weight of Copper should be of 90% to 99% of the total melt calculation. The Copper scrap must be free of dust, oil, or any kind of impurity which might cause slag generation. The generated slag (if any) must be skimmed from the top of the crucible using a Stainless Steel rod with a spouted-cup end. The furnace should be powered, incrementally, till the molten bath reaches 1225°C (±100°C) temperature by a dip type pyrometer. In at least an embodiment of this invention, the process comprises a third step of addition of 99% purity or above Titanium scrap (0.5mm to 10mm in thickness) by weightl% to 10% of the total charge to be melted.

Preferably, for this step, once the temperature of the molten bath reaches the desired temperature, the melt is cleaned by deslagging (removal of slag by Stainless Steel rod), and the Titanium Scrap is charged into the furnace. The titanium scrap must be of 99% purity or above and must be 0.5mm to lOmmin thickness. The thickness of the Titanium scrap is essential as Titanium’s melting point is higher at 1670°C, however, it has to homogenously mix with Copper at approximately 1225°C. The temperature of the furnace cannot be increased to avoid degassing, pinholes and superheating related defects in the casting. Preferable scrap source could be thin pure Titanium sheets used in Heat Exchangers. The total weight of Titanium scrap should be 1% to 10% of the total melt calculation. E.g. for a 50 kg batch to be melted in the Induction Furnace 3.50 kg of Titanium and 46.50 kg of Copper is to be melted for 7% Titanium addition ratio.

In at least an embodiment of this invention, the process comprises a fourth step of continuously stirring by stainless steel rod in the silicon carbide crucible for 5-10 minutes to attain homogenous melt in the induction furnace and checking the temperature to approximately 1350°C(±250°C) by the pyrometer. Preferably, for this step, it is essential to ensure that the melt is homogenously mixed and there are no Titanium chunks in the batch. The same can be ensured by continuously stirring by stainless steel rod. Removal of slag at this stage should not be done to avoid loss of Titanium. Also, avoid stirring time of more than 5-10 minutes to avoid oxidation of Titanium with atmospheric gases.

In at least an embodiment of this invention, the process comprises a fifth step of pouring the melt into a conventionally made investment casting shell of the desired product which is baked to a temperature of 1050 °C (±150°C) for at least 60 minutes and is in red-hot condition during pouring. Pouring should be directly from the furnace into the pouring basin of the shell by using a fork end. No ladle transfer should be done from the furnace to avoid slag generation and oxidation of titanium alloy.

In at least an embodiment of this invention, the process comprises a sixth step of knocking off the cooled castings and solution-annealing, after the fettling operation, and the castings are shot blasted / sand blasted to remove any surface impurities. The Copper Titanium castings must be solution annealed at approximately 780°C in an electrical heat treating furnace for 3 hours and then quenched into rapidly cooled water. Followed by Quenching and Tempering process. The heat treatment process is to attain desired mechanical and physical properties. In at least an embodiment of this invention, the process comprises a seventh step of breaking the ceramic mold from the investment casting and cutting the parts from the tree. After that the Cast Copper Titanium parts are ground to match the excess material to final surface size. The Castings are then Shot Blasted/ Sand Blasted. The Copper Titanium castings must be solution annealed at approximately 780°C in an electrical heat treating furnace for 3 hours and then quenched into rapidly cooled water. Followed by Quenching and Tempering process. The heat treatment process is to attain desired mechanical and physical properties. The hardness after this process is between 200 to 350 HV, Yield Strength after this process is of 500-700MPa and the Tensile Strength after this process is of 700-1 lOOMPa.

In accordance with one preferred embodiment, the process for manufacturing of copper-titanium alloy by a lost wax process , includes the following steps:

- fixing a silicon carbide crucible (12) in an induction melting furnace (10) packed with a basic or neutral ramming mass (14) surrounding said silicon carbide crucible (12);

- preheating said crucible (12) at a temperature ranging from 700 to 800°C, followed by charging said crucible with copper scrap in an amount of 90% to 99% by weight, based on the total weight of charge to be melted to attain a temperature of about 1100 to about 1200°C ;

- adding at least 99% pure titanium scrap having 0.5 mm to 10 mm thickness in an amount of 1% to 10% by weight, based on the total weight of charge to be melted into said crucible to obtain a mixture;

- continuously stirring said mixture using a stainless steel rod for about 5 to about 10 minutes to attain a homogenous melt in the crucible placed inside said induction furnace and maintaining the temperature of said furnace to about 1000 to about 1500°C;

- pouring said homogenous melt into an investment casting shell of a desired/pre-determined product followed by cooling and baking to a temperature of about 900 to 1200°Cfor at least about 90 minutes followed by cooling to obtain copper titanium cooled castings;

- knocking off cooled copper titanium castings and subjecting said castings to fettling operation, and shot blasting /s and blasting operation to remove surface impurities; and

- solution annealing said copper titanium castings at a temperature of about 700 to about 800°C in an electrical heat treating furnace for about 2 to about 4 hours and quenching into rapidly cooled water followed by precipitation hardening process where copper titanium castings are aged in the electrical heat treating furnace at about 350 to about 550°C for about 3to about 5 hours.

Typically, said induction melting furnace is a medium frequency induction furnace.

Typically, induction melting furnace being a medium frequency induction furnace, characterised in that, said medium frequency induction furnace being lined with ramming mass selected from a group of ramming masses consisting of basic ramming mass, acidic ramming mass, and neutral ramming mass fixed with a silicon carbide crucible to avoid slag generation and oxidation of titanium alloy reacting with the furnace ramming masse.

In one preferred embodiment, said copper scrap comprising copper in an amount of 95% by weight, based on the total weight of charge to be melted and said titanium scrap comprises titanium in an amount of 5% by weight, based on the total weight of charge.

Typically, said step of charging said crucible comprising a step of skimming generated slag, if any, from top of said crucible using a stainless steel rod with a spouted-cup end.

Typically, said step of charging said crucible comprising a step of powering said furnace, incrementally, till molten bath reaches a temperature of about 1250°C (±250°C) by a dip type pyrometer. Typically, said step of addition of titanium scrap comprising a step of maintaining furnace temperature without increasing it in order to avoid degassing, pinholes and superheating related defects in said casting.

Typically, said stirring being limited to less than 10 minutes in order to avoid oxidation of titanium with atmospheric gases.

Typically, said step of pouring being directly from said crucible into a pouring basin of said casting shell using a fork end in order to avoid slag generation and oxidation of titanium alloy.

Typically, said process comprising an additional step of breaking said ceramic mold from said copper titanium investment casting and cutting parts from its tree.

In accordance with another aspect of the present invention there is also provided a copper titanium alloy melt composition comprising copper in an amount of 90 to 99 % by weight, based on the total weight of the composition and titanium in an amount of 1% to 10% by weight, based on the total weight of the composition, wherein the weight ratio of copper to titanium is 19:1 to 13:1.

In accordance with another aspect of the present invention there is also provided copper titanium alloy casting comprising copper in an amount of 90 to 99 % by weight, based on the total weight of the alloy and titanium in an amount of 1% to 10% by weight, based on the total weight of the alloy, wherein said alloy casting is characterized by hardness of about 200 to 350 HV, yield strength of about 500-700 MPa, and tensile strength of about700-l 100 MPa.

The invention is now explained with the help of following non-limiting examples:

Example 1: (Working)

The total charge for this working example was of 20 kg. The charge consisted 19 kg Copper Scrap and 1 kg Titanium Scrap of at least 99% purity. The Copper Scrap was first charged into a preheated (upto 750°C) induction furnace, with a prefixed silicon carbide crucible. The copper scrap was melted till the furnace attains 1150°C. Upon checking the desired temperature by pyrometer or any other temperature checking device, the copper scrap was cleaned with commercially available fluxes like Borex. Thereafter, 1.5 mm thickness Titanium scrap weighing to 1 kg was added to the liquid copper scrap. The charge was continuously stirred using a stainless steel rod for about 5 to about 10 minutes to attain a homogenous melt in the crucible placed inside said induction furnace and maintaining the temperature of said furnace to about 1250°C. The said homogenous Cu-Ti melt was poured into an investment casting shell (of a desired/ pre-determined product baked to a temperature of 1050°C). After that the investment casting were cooled to room temperature, they were cleaned by knocking and shotblasting. Excess material was cut off and grinded to dimensionally attain the desired finished part and remove surface impurities. The casting was then solution annealed at 780°C in an electrical heat treating furnace for 3 hours and quenched into rapidly cooled water followed by precipitation hardening process where Copper Titanium Castings were aged in electrical heat treating furnace at 450°C for 5 hours.

Physical and Mechanical Properties of the 95% Copper and 5% Titanium are provided in the Table 1.

Table 1:

In this batch only 0.5% of Titanium was added to the melt. The total charge for this Comparative Example 1 was of 20 kg. The charge consisted 19.90 kg Copper Scrap and 0.10 kg Titanium Scrap of at least 99% purity. The process of example 1 was repeated.

Physical and Mechanical Properties of the 95% Copper and 5% Titanium are provided in the Table 2. Table 2:

Example 3; (Comparative)

In this batch 12% of Titanium was added to the melt. The total charge for this Comparative Example 3 was 20 kg. The charge consisted 17.60 kg Copper Scrap and 2.40 kg Titanium Scrap of at least 99% purity. The process of example 1 was repeated.

Findings: The molten alloy in the crucible became deoxidized and the entire charge got spoilt. Because of the high Titanium percentage (higher than the recommended 10%) the material interacted with the furnace lining (silicon carbide crucible as per Figure 1) and reacted with atmospheric oxygen to deoxidize and spoil the entire melt. The casting poured from this batch found to have severe defects like pin-holes and blow-holes.

Example 4: (Comparative)

In this batch no Titanium was added to the melt. The total charge for this Comparative Example 4 was 20 kg. The charge consisted 20 kg Copper Scrap. The process of example 1 was repeated except addition of titanium.

Physical and Mechanical Properties of the 95% Copper and 5% Titanium are provided in the Table 3.

Finding: The product is found to break under extreme pressure, torque or load.

Conclusion:

• The results as shown in table 1 to 3 shows that the copper- titanium alloy of example 1 (present invention) exhibits significantly improved properties such as hardness, tensile strength and yield strength compared to the alloy(s) of the comparative examples.

• The results establish significance of specific proportion of copper and titanium in the alloy in order to achieve the desired properties. • Further, this alloy is found to be non-hazardous unlike the Beryllium alloys which are used in Non Sparking Tools & other products manufacturing.

TESTS: i) Test certification IS 4595-1969 of from Central Institute of Mining and Fuel Research (CSIR-CIMFR) Dhanbad.

A test for certification of Cu-Ti alloy for non-sparking characteristics was carried out at Central Institute of Mining and Fuel Research (CSIR-CIMFR) Dhanbad in an explosion chamber fabricated for the purpose. The Cu-Ti alloy samples on subjection to abrasive action as per specification laid vide Indian Standard specification IS: 4595- 1969, with the environment inside the chamber consisting of 50% each gasoline and oxygen mixture maintained at 28 °C, did not result in an explosion. CMRI therefore, issued the certification of "non-sparking" conforming to Indian Standard specification, IS 4595-1969 to the Cu-Ti alloy samples prepared by the process of this invention.

The TECHNICAL ADVANCEMENT of this invention lies in providing a process for manufacturing of Copper Titanium alloy based non-sparking tools and other parts by Investment Casting process. This invention focuses on commercial production of products like non sparking hand tools, welding and plasma nozzles and plunger tips for applications in oil and gas, automotive, heavy engineering, defense, electrical, and general industry. While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.