CORES AND CORE MAKING
DIPLOMA IN FOUNDRY TECHNOLOGY – CORES AND COREMAKING
SESSION 1: ONE BINDER SYSTEM
The decision to use binder systems in a foundry operation for moulds and cores is based on the evaluation of many factors. Some of the factors to consider are production rate, capital outlay, operating costs, required quality level, environmental impact, skill of labour force, existing equipment (pattern/core), and sand availability. Each foundry will develop a list of its own important factors when making this decision.
The underlying goal in the decision-making process is to produce quality castings at the lowest cost with the resources available.
1.2 Requirements for Binder Systems
1.3 Alternative Coremaking and Moulding Aggregates
1.4 Chemistry of Foundry Resin-Binder Systems
1.5 Properties Required and Materials Used
1.6 Chemistry of Resin Manufacture
1.7 Curing Mechanisms of Foundry Binders
1.8 Urethane Binder Systems
1.9 Cold-Setting Binders
SESSION 2: THE COLD BOX PROCESS
The cold-box process uses an organic-based binder capable of producing cured cores in a matter of seconds at room temperature. The cores exhibit good tensile strength, a high degree of dimensional accuracy, good abrasion resistance, high density, exceptional collapsibility, and low gas evolution.
Grey and ductile-iron, aluminum, magnesium, brass and steel all display excellent casting results when used with cold-box processed cores and moulds.
In addition to the routine production of excellent cores and moulds, the cold-box process has enabled foundries worldwide to increase productivity, reduce costs and lower energy consumption. With the cold-box process, the foundryman can highly automate core and mould production, using a wide variety of equipment, and unskilled labour, The coreroom can keep pace with any other segment of today’s foundry, especially high-speed automatic moulding lines. Higher productivity through automation can help reduce costs. Fewer personnel, reduced core and casting scrap, and higher production rates all contribute to reducing costs in the foundry. Let’s look at a few of the many benefits of using the cold-box process:
- It is not dependent upon a heat source for curing, and this can mean considerable savings in energy consumption and cost;
- The process is less labour-intensive so fewer people are needed to produce more cores;
- The process can be used for both core and mould production;
- It works well with all cast metals – iron, steel, aluminum, magnesium and copper alloys;
- The process is exceptionally precise – during core making there is no thermal related expansion, shrinkage, or warpage of cores or moulds;
- Cores are ejected from the box essentially fully cured and dimensionally accurate;
- Core scrap is reduced – because the cores at ejection are near full strength, and ready for use;
- Breakage from handling or improper curing is minimized;
- The binders provide allowable sand mix that is easily “blown”, and can be used with wood, metal, or plastic tooling;
- Excellent flowability produces dense cores, helping to reduce both core and casting scrap;
- Designed for excellent castings with good to excellent shakeout in all metals, the process produces sound castings with good surface finish, no gas defects, low metal penetration, and no evidence of mould-metal reaction;
- The cold-box binders can help save space and energy – no large core ovens are required, nor the energy to run them;
- The cold-box process binders are equally suited for high production use, as well as bench work.
2.2 Cold-Box Process
2.3 Effect of Binder Percentage On Core Properties
2.4 Methods for Filling Core Boxes
2.5 Curing of Cores
2.6 Core Box Construction Materials
2.7 Gas Evolution
2.8 Using the Ashland Process in Aluminium Casting
2.9 Coating ISOCURE Resin Cores and Moulds
2.11 Environmental Concerns for Thermal Decomposition Products
2.12 Tooling for the Cold Box Process
2.13 Construction of Materials
2.14 Component Design Considerations
2.15 Amine Usage and Cure Rates
SESSION 3: THE HOT BOX PROCESS
The hot-box process was introduced to the foundry industry in 1959 by work carried out at Renault and subsequent work done by Jasson. Although many years before this Ferranti Ltd. had produced cores bonded with urea resin by blowing a sand-resin mixture into heated core boxes.
The Renault process was originally based on glucose binders hardened by the addition of an acid salt, and later using binders incorporating “urea resins”. At about this time, resins incorporating furfuryl-alcohol were developed in the United States and this gave a great impetus to the use of the hot-box process, the method being adopted by large foundries such as the Ford Motor Co.
- The process is a coremaking operation in which a resin—bonded sand is blown into a heated corebox, where it hardens to form a rigid core ready for immediate use – hence the term “hot-box process “.
Basically, the process is similar to the shell coremaking technique, but moulds cannot be produced by the hot-box method unless they are manufactured as “slabs” on a coremaking machine. As with shell cores, rigid iron coreboxes are employed and the method of manufacture of coreboxes and the type of core blowers used are similar in both processes as illustrated in Figure 3-1. Two fundamental differences, however, with hot-box production are:
3.2 Description of the Process
3.3 Hot-Box Production Equipment
3.4 Core Manufacture
3.5 Casting Problems with Hot-Box Cores
SESSION 4: SHELL PROCESS
The original method of producing shell moulds and shell cores is attributed to Croning of Hamburg, and the first introduction of the shell process in the UK and the USA came from a British Intelligence Objective Survey made in April 1945. This briefly stated that by mixing silica sand with a plastic, and dropping the mixture onto a heated pattern plate, a hard refractory mould could be obtained. From that time trials were made in many foundries and the use of the shell process as a method of producing moulds began around 1948.
Many foundries, however, soon found that the cost of materials used in the process was too high to compete with the relatively cheap greensand practice, and for a short time, there was a lag in the use of the shell process in the ironfounding industry, although its use in other casting fields increased. Core production by the shell process, has found a wide application and over recent years shell moulding has increased in use because the rising labour costs involved in conventional greensand moulding make the shell process more competitive. And also because of the intrinsic benefits obtained with shell moulds.
The original method was referred to as the Croning or ‘CC” process, but, as its use increased, the terms “shell moulding” and “shell process”, based on the fact that a thin skin or shell of sand forms the mould, have become the universally accepted names.
4.2 Description of the Process
4.3 Materials: Sand
4.4 Materials: Resin
4.5 Sand Preparation
4.6 Production Equipment
4.7 Production of Moulds
4.8 Production of Cores
4.9 Problems with the Manufacture of Shell Moulds
4.10 Problems with Manufacture of Shell Mould Castings
SESSION 5: THE FRC PROCESS
FRC stands for “Free Radical Cure” – the unique chemical curing mechanism that makes this process so fast. Besides speed, the chemistry involved provides significant benefits for finished casting productivity and quality.
The FRC Process uses a new family of binders designed to produce cured cores and moulds at room temperature within seconds. The process requires only simple modifications of conventional cold-box core-making and mould-making equipment.
Equally important, this unique process delivers outstanding casting performance:
- Cores and moulds exhibit excellent shakeout from both ferrous and non-ferrous castings;
- Exceptional dimensional accuracy and stability at ambient and casting temperatures;
- High density;
- Good tensile strength;
- Low gas evolution;
- Castings require substantially reduced cleaning time;
- These binders offer significant improvements in bench life;
- Their extended bench life helps reduce costs associated with downtime, machine cleanup and wasted sand.
- Foundries can easily automate FRC Process core and mould production to keep pace with all other foundry operations, including high-speed, automatic moulding lines. And the higher productivity, reduced labour costs, and minimized core and casting scrap all contribute to higher profitability in the foundry.
- The following is a summary of the many benefits that can be realized by using the FRC Process:
- Binders contain no phenol, formaldehyde, sulphur or phosphorous. This can mean a more pleasant core and mould making environment and fewer incidents of casting defects;
- Nitrogen content is low;
- Binders give excellent mixed sand flowability and dense cores and moulds;
- Mixed sand bench life is exceptional – literally measured in days;
- The process easily and inexpensively adapts to existing or new cold-box equipment;
- No heat is required for curing. This can substantially reduce core room energy costs;
- Very little activator gas is required to effect cure. Gassing odours and scrubbing costs are minimal;
- Cycle times are short due to the extraordinarily fast cure speed;
- The process produces excellent cores and moulds with a wide variety of sand types and temperatures;
- Cores and moulds display excellent dimensional accuracy and stability;
- Cores exhibit improved dimensions since there is essentially no hot deformation;
- Cores and moulds are resistant to atmospheric humidity, reducing storage problems;
- Rapid thermal decomposition results in excellent shakeout from ferrous and non-ferrous castings. Appropriate binders are available for each;
- Cores and moulds deliver excellent casting surface finish;
- Veining in iron castings is significantly reduced.
5.2 Preparing the Sand Mix
5.3 Sand Selection
5.4 Binder Levels and Ratios
5.5 Factors Affecting Bench Life
5.6 Method for Filling Core Boxes
5.7 Core Box Construction Materials
5.8 Additional Performance Benefits
5.9 Safety and Environmental Considerations
5.10 Binder System Storage Considerations
5.11 The Free Radical Process
5.12 Sulphur-Dioxide Cured Epoxy Resins
5.13 The Sulphur-Dioxide Cured Furane Process
SESSION 6: OTHER PROCESSES
6.1 Carbon-Dioxide Cured Alkaline Phenolic Resin Process
6.2 Carbon-Dioxide Gassing
6.3 Ester Vapour Alkaline Phenolic Cold-Box Process
6.4 Sodium Silicate/Carbon-Dioxide Process
6.5 C02-SiIicate Process
6.6 Ester/Silicate Process
6.7 Powder-Hardened Silicate Processes
SESSION 7: COATING
7.1 Selection of Coatings
7.2 Coating Ingredients
7.3 Coatings Manufacture
7.4 Coatings – Application Methods
7.5 Selecting a Coating