As part of LBBC Technologies’ extensive R & D into the core leaching process, as presented in a paper at ICI 2013 by Howard Pickard, the company have developed a new ceramic core leaching model to extend the range of component and core geometry that can be efficiently leached. This unit now provides a solution for the commercial and medical sectors as well as low volume aerospace components.
The unit maintains the same basic processing system as has been proven on the many larger core leaching systems supplied to aerospace and IGT foundries throughout the world. As with all LBBC Technologies systems, the unit incorporates the highest levels of safety design. The new unit has demonstrated how ceramic cores, traditionally removed by other techniques in days, can be removed in hours in a safe and controlled environment.
LBBC who were founded in 1876 have invested in a new manufacturing and R & D facility at their Leeds site moving into the new facility at the end of July.
LBBC Technologies are exhibiting at ICI Equipment Show on 6th and 7th October 2014, in Covington, Kentucky, USA they will be in Booth 411 and 413 where they will be demonstrating their new core leaching unit.
LBBC’s Boilerclave® leads the industry for autoclave dewaxing applications whilst the Core Leaching Autoclave remains the benchmark in efficien[...]
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by Howard Pickard, LBBC Technologies
EDITOR’S NOTE: This article is based on a longer paper presented at the investment Casting institute’s 60th Anniversary Conference and Expo in Pittsburgh, PA.
Ceramic cores have been used in castings for many years to assist in achieving ever more complex internal geometry. In the investment casting industry, ceramic cores have played an important part in the development of improved performance of blades and vanes in gas turbines.
In order to form the passageways within the components, cores with the same intended geometry as the cooling channels are positioned in an investment casting shell. Once the component is cast and the majority of the shell removed, a process known as caustic leaching is widely used for dissolution of the encapsulated core, thus leaving behind the empty cooling channels. Although widely used for many years, the fundamentals of the process physics and chemistry are little understood.
Following some initial experimental work performed in LBBC Technologies’ facility in 2010, Rolls-Royce PLC and LBBC Technologies agreed to cosponsor a Post Graduate Doctoral Studentship through the University of Birmingham’s four year engineering doctorate program with the project aim to investigate the physics and chemistry of the present investment casting core removal process in order to enhance its industrial application.
To recap on the process operation, components are loaded within a basket and the basket is placed in the autoclave. The autoclave is filled with a caustic base solution with approximate concentrations of typically 20% sodium hydroxide (NaOH) or 40% potassium hydroxide (KOH). This breaks down the bonds in the ceramic core which is typically made up of silica (70-100%) and zircon etc (0-30%). The solution is heated to around 320°F (160°C) under a pressure of around 90 psi (6-7 bar) to suppress boiling at this temperature. Through venting, dwelling and repressurizing of the autoclave at regular intervals the solution boils and creates a ‘flow’ of solution within the autoclave. This flow enables the alkaline solution to be replenished at the interface with the core as well as physically removing the core material that has softened or ‘broken away’.
Key Components of the Process
To understand what is happening during the leaching process, consider the three main areas of the process:
1. Caustic solution– Caustics are strong alkaline chemicals that destroy soft body tissues resulting in a deep penetrating type of burn, in contrast to corrosives, that result in a more superficial type of damage via chemical means or inflammation. Caustics are usually hydroxides of light metals. The
alkali metal hydroxides are the most basic of all hydroxides; sodium hydroxide (NaOH or caustic soda) and potassium hydroxide (KOH or caustic potash) being the most widely used caustic agents in industry.
2. Ceramic Core– The most commonly used core material in turbine blade manufacture is fused silica due to its chemical removability, well documented high temperature properties, abundance, and economic cost. The material development and complexity of future superalloys formed via directional
solidification or single crystal techniques is limited by the capability of conventional silica-based core and shell materials to withstand longer casting times at high temperatures (~1700 °C). Preformed cores fashioned from alumina, Al2O3, are suitable for investment casting application as they exhibit good dimensional tolerance, high strength and high refractory properties. The leaching of alumina is however often economically not feasible for production and manufacturing operations due to longer
dissolution rates relative to silica.
3. Boiling at Diffusion Layer– When a liquid is heated in an open vessel, the liquid vaporizes from its surface. The condition of free vaporization throughout the liquid is called boiling. The temperature at which the vapor pressure of a liquid is equal to the external pressure is called the boiling point at that pressure. Boiling does not occur when a liquid is heated in a rigid, closed vessel. Instead, the vapor pressure, and hence the density of the vapor, rises as the temperature rises. Factors which control the rate of a reaction are:
- Concentration of reactants in solution.
- Surface area of any solid reactants.
Initial experimental work was focused on determining the most effective chemical reagent and its optimum concentration to facilitate the dissolution of cristobalite and zircon. Observations have been;
- The higher leaching capability of NaOH compared to KOH.means or inflammation. Caustics are usually hydroxides of light metals. The alkali metal hydroxides are the most basic of all hydroxides; sodium hydroxide (NaOH or caustic soda) and potassium
- The plateau/dip in reactivity after concentrations 20 % w/v of NaOH. hydroxide (KOH or caustic potash) being the most widely used caustic agents in industry
Initial trials to investigate the optimum cycle parameters have been performed using an LBBC test unit. Studies were conducted using the core test piece shown below with 33 % potassium hydroxide (KOH) solution. The extent of core dissolution was determined by measuring the change in core depth on a number of different components with six identical cores, each with a diameter of two mm to give an average over 18 samples.
Experimental work has been undertaken to study the effect that different high and low pressure dwell times have on core removal. Observations have been;
- Varying the low and high pressure dwell time has little impact on leach effect.
- Varying the vent time has the greatest impact on leach effect .
- Lower temperatures reduce core leach but not as significantly as expected.
- Reducing suppression pressures only begins to effect leaching below 55psi when using this concentration of KOH.
The caustic leaching of ceramic cores involves a wide range of physics and chemistry concepts. Key aspects to the process have been illustrated here. Identifying and analyzing specific areas of caustic bases, core materials such as silica and zircon, boiling action, etc., is expected to result in a better understanding the process of caustic core leaching. Initial experimental work has begun to show the aspects of the process that need to be further investigated.
For more information, contact the author at [email protected]
From Incast Magazine, June 2014
The caustic leaching of ceramic cores involves a wide range of physics and chemistry concepts. Key aspects to the process have been illustrated here. Identifying and analyzing specific areas of caustic bases, core materials such as silica and zircon, boiling action, etc., is expected to result in a better understanding the process of c[...]
Howard Pickard, the fifth generation Managing Director of LBBC Group said “The new facilities will become home to LBBC Technologies and allow our sister division LBBC Beechwood to grow as they expand in the space that will then be available within the existing facilities.”
“LBBC has been on this site since 1876 and in recent times LBBC Technologies division have grown to become experts in supplying niche equipment particularly to the investment casting industry, with 70% being exported. This facility will enable the whole group to further pursue our vision and support our continuous investment in R&D as we look to achieve future growth and continue to be global leaders in investment casting.”
“This is an exciting time for LBBC Technologies as we have also recently installed our equipment in one of the most advanced investment casting foundries in the world, Rolls-Royce’s new Advanced Blades Casting Facility (ABCF) in Rotherham.”
Roger Marsh, Chair of the Leeds City Region Enterprise Partnership comments: “The LEP is really pleased to support this investment in new research and development facilities, to enable LBBC to continue as an expert in its field.
“This grant also aims to create new jobs at the site and lead to further growth for the business both regionally, nationally and with overseas markets.”
The principal contractors Triton Construction Ltd, based in Liversedge, have started on site with the construction due for completion in August. Michael Parkinson, Managing Director said “LBBC have a long and impressive 138 year history and that they are still expanding their operations is a great success story. We are proud to be a part of the team helping LBBC to continue in their growth. We wish them every success with the new facility.”
David Smithies, Relationship Director Commercial Banking, Leeds for NatWest said “This project represents the next step in the company’s continued growth and aspirations and we are delighted to be able to provide financial support for this exciting new development. The Company have been a long standing customer of NatWest and we have been able to partner the directors as they have continued to increase their international customer base. The UK manufacturing sector as a whole is incredibly diverse and NatWest is working hard to ensure its proposition supports all manufacturing businesses, regardless of sub sector, size or location.”
Horsforth, Leeds, based architectural practice, Kilmartin Plowman Partners, Managing Director Tony Plowman said “It is great to have been involved in the project from the outset, supporting the continued growth of a long established local engineering business.”
“We have been involved, from inception through to completion in the design and development of the new facilities to accommodate the development of new technologies and products reinforcing the commitment of LBBC to its traditional home.”
“The design aims to reflect the combination of traditional values with modern methods and materials being a key part of LBBC’s ethos.” added Tony.
In a testament to the historical importance of LBBC and their continued investment and support to the area The Local Authority and the Local Community were supportive throughout the Planning Process.”
Peter Smith, Managing Partner of Otley based surveyors, Banks Smith Partnership said “We are pleased to have been involved with this project since its inception in 2012, it is exciting times with the steel already on site.”
“We have received fantastic support from all the partners in bringing this new facility from being a concept vision through to reality.” added Howard Pickard.
LBBC Group of engineering companies are building a new facility adjoining their existing premises in Stanningley, Leeds.
The Group has received a grant from the Leeds City Region Enterprise Partnership’s Business Growth Programme, which is funded by the Government’s Regional Growth Fund. This funding is going towards new premises which will house modern[...]