Molten metal is a serious hazard in melting pouring applications of metal casting. Workers who execute tasks with or near the molten metal are highly prone to risks, such as coming in contact with metal splashes or be exposed to electromagnetic radiation.

Some of the circumstances that may increase the risk of hot metal splashes are -

• Charging a furnace with impure or moist scrap metal and alloys
• Using damp tools, molds or other material when touching the molten metal
• Pouring or tipping the molten metal into a holding furnace or ladle
• Slagging or skimming processes
• Pouring the molten metal from ladles into molds

Extreme caution should be taken to ensure that the metal or metal slag does not come in contact with water, as it may result in an explosive reaction or ejection of molten metal with catastrophic effects.

Molten metal also emits electromagnetic radiation in the furnace and pouring areas. Foundry workers are primarily endangered to infrared and UV radiation.

Workers and other visiting people with medical implants, plates, joints or similar objects should move into the induction furnace region with care as the magnetic fields of the melting process may cause a charge in the metallic implant. People with cardiac pace makers are especially at risk and should be restrained from entering the induction furnace or touching the equipment.

Health consequences of molten metal
Splashes of the molten metal and the radiant heat during the melting and pouring process may result in serious burns on the body. Sparks from molten metal may also affect the eyes. Vulnerability to infrared and ultraviolet rays may result in the damage of eyes including cataract.

Control measures
There are several measures and options, which can be adopted alone, or in combination, to prevent or minimize the risks associated with the handling of molten metal in foundries. 

Mechanical control measures
The risks associated with the molten metal can be reduced or minimized by implementing mechanical controls. Barriers and other protecting covering, including the mobile shields should be used or set up to protect workers against the splashes of molten metal and electromagnetic radiation.

Administrative control measures
Administrative controls include the development and inclusion of safe working practices and procedures.
Some of common examples of administrative control measures for molten metals include -

• Keep all the combustible materials and volatile liquids at a safe distant place from the melting and pouring areas. 
• Make sure that the molten metal does not come in contact with water or other contaminants. All charge materials, ladles and other equipment, which may come in contact with the molten metal should be totally dry.
• Restrain the unauthorized access by barriers and signages to the furnace and pouring areas. 
• Restrain the workers and other personnel from wearing synthetic clothing, including undergarments while entering the furnace and pouring regions.
• Ensure proper use and maintenance of personal protective equipment.

Personal protective equipment
Personal protective equipment are a must to reduce or eliminate the risks associated with the handling of molten metal in foundries. These may include -

• Heat resistant protective clothing - headgear, footwear, face shields, aprons, fire retardant spats, coats and gaiters
• Eye protection with side shields
• Special UV and infra-red glasses

Substantial concentrations of airborne contaminants can be found in various aspects of foundry operations. These contaminants can be found in several areas including pattern making, core making, mold making, fettling and sand plant regions.  

The airborne contaminants in foundries are generally released from the -

• Preparation of scrap using heat and solvent degreasers (carbon monoxide)
• Melting procedure (carbon monoxide, sulfur dioxide, nitrogen oxide, chloride and fluoride compounds)
• Scrap handling (receiving, unloading, storage and conveying)
• Treatment and inoculation of molten metal prior to poring
• Core and mold making processes  during sand reclamation, preparation and mixing of sand
• Mold and core forming processes, including core baking and mold drying from additives, binders and catalysts
• Cooling of casts causing decomposition of organic binders
• Casting knockout and shake-out
• Fettling

Along with these, airborne contaminants are also generated from various other foundry operations, including – furnace operations of melting and pouring carbon monoxide), cupola furnaces (sulfur dioxide), working of electric arc furnaces, treatment and inoculation of molten metal (dust), contaminants released during pouring (hot metal fumes), etc.

Gases & Vapors
Gases are formless fluids, which expand to occupy the space or enclosure in which they are enclosed. At normal temperature and pressure, true gases exist in the form of vapor. Many gases can be stored under pressure in liquid form until they are vaporized for use. These pressurized gases should be controlled in order to make the workplace air free from contamination.

Gaseous contaminants may also arise as a result of a chemical reaction or due to the breakdown of a complex chemical.

Some of the gases that are generally found in a foundry are -

Some of the vapors that are generally found in a foundry are -

Gases and vapors are mostly invisible, however, some may have strong and characteristic smell, which may give the hint of their presence in a foundry. Instead, in some cases, the gases may have no such smell and may induce health problems at extremely low concentrations.

Some other gases show their presence through various irritating effects, such as coughing, respiratory irritation, asthma, acidic taste and watering of the eyes.

Dust & Fumes
Dust is particulate matter produced from solids and dispersed into the air due to the movement, loading, cleaning and handling of inorganic materials, such as metal, wood and sand. Fumes are airborne solid particles, which are formed as a result of the condensation of a material from a volatilized solid, generally molten metal in cool air.
The different types of dust and fumes that expose workers to various health risks in foundries are -

• Wood Dust
• Metal Dust
• Silica Dust

Control Measures for Airborne Contaminants
There are a number of control measures, which can be adopted alone, or in combination with other methods to prevent or minimize the exposure to risk.  

Some of the general rules that can be followed to reduce / minimize airborne contaminants are -

• Replace silica sand with chromite sand.
• Adopt wet or vacuum processes instead of compressed air to minimize the creation of dust while removing loose dust or sand in the mold making method.
• Shut in major emission points, such as conveyor belt transfer areas.
• Set canopy hoods near the doors of furnace and the tapping outlets to seize contaminants and direct them through an emission regulation system.
• Supervise the carbon monoxide levels in the area of operation.

The metal casting industry has been, and continues to be, a key component of the industrial backbone of various nations and countries. The industry gives employment to a large number of people and supplies huge amount of castings thereby impacting almost every other industrial and commercial domain. The metal casting industry is also a major recycler of metal scrap, a major energy user, and an important pollution prevention partner in different countries.

Good foundry practices address critical technology deployment needs, which will help foundries in saving costs and improving profits. These practices help in reducing the energy consumption and environmental impact of the metal casting industry and improve its competitiveness.

Given below are some of the practices that can be adopted for cost savings and increase in profits -

Energy Saving Practices
By adopting following measures and practices, foundries can make significant cost savings -

Upgrade motor drive belts
Using energy efficient cog belts instead of drive belts help in reducing energy requirements. Cogged belts can function on existing v-belt pulleys, but at lower temperatures.

Set variable frequency drives on motors
Getting rid of voltage imbalances helps in reducing losses from vibrations, mechanical stresses, torque pulsations and overheating.

Switch off equipment and lighting when not in use
Specifically place a start-up and shut-down process to control energy usage spikes.

Cut down the compressed air pressure set point by 10%
Maintaining excess air system pressure is very expensive. Set points can be cut down with proper maintenance of system and continual repair of air system leaks.

Install high efficiency lighting
Using fluorescent lighting with magnetic ballasts instead of older ballasts is always cost-effective. Install targeted lighting at inspection points rather than less efficient ceiling lights.

Adopt superior melting practices
Specific recommendations may vary depending on the type of melting system used by the foundry. Furnace manufacturers can be of great help in helping to identify good melting practices for energy savings. The use of preheated air/oxygen and optimized burner designs have found to be good for gas-fired furnaces.

Short cycle heat treatment
Most of the heat treatment practices followed by many foundries are overly conservative and waste energy. High efficiency furnaces and furnace linings are generally cost effective.

Improved compressed air practices
Compressor should be properly sizes, it should not smaller or over-sized. Use air storage systems to limit idling of compressors. Reduce leaks at valves, couplings and pipe joints.

Low Cost Technology Practices
By adopting following measures and practices in different technical domains, foundries can save costs -

Molding
Upgrade the sand testing quality assurance – Better control of sand systems ensure superior mold quality and reduction in scrap. Make consistent use of sand supplier testing capabilities. In various cases, improved molding practices can help in reducing the biggest single contribution to casting scrap.

Melting
Melt cold, pour hot, pour fast – This will reduce the consumption of melting energy to minimum, while at the same time increases the quality of melt and reduces dis-functioning. It is generally much economical in the long run to completely preheat ladles than to melt hot and admit high temperature drops during the transfer of metal.

Scrap Reduction
Improved reporting and analysis of scrap – The single effective way to reduce scrap is to identify the scrap and its root causes in a right manner. Lack of attention to detail in reporting of scrap may badly affect the bottom line; for instance, it is crucial to identify ‘sand’ or ‘slag’ as the causes of scrap instead of simply grouping them together as 'dirt'.

Data Collection
Decisions should be based on sound data collection - Make sure that the data, which you have collected has sufficient gage R&R; it is useless to collect data if you are not going to use it. Employees will be much more accurate and efficient collection of data if they know how that data is going to be used.

Lighting
Good housekeeping & lighting results in improved quality – A little extra KW of energy use, primarily in inspection areas, actually results in money savings. Good housekeeping leads to pride among workers and improved quality of products.

Training
Training helps in improving the skills and productivity of employees – Make use of all internal and external training resources to improve the skills of your employees. If production employees are better trained they are better problem solvers.

Profitability
Superior costing & pricing systems – This is essentially a challenge especially in the jobbing foundry, but is necessary to ensure the long term success of the organization.

While steels constitute less than 2% and generally less than 1% carbon; all cast irons comprise more than 2% carbon. Two percent is the maximum carbon content at which iron can become solid as a single phase alloy with all of the carbon in solution in austenite. Therefore, we can say that cast irons solidify as heterogeneous alloys and always contain more than one constituent in their micro structure.

Along with carbon, cast irons also contain silicon (Si), generally from 1–3%, and hence, we can say they are actually iron-carbon-silicon alloys. The high carbon and silicon content of cast irons make them excellent casting alloys. The melting temperature of cast irons is significantly lower than for steel. Iron when melted is  more fluid than molten steel and is less reactive with molding materials. During the solidification process, low density graphite is formed in the iron. This low density graphite reduces the change in volume of the metal from liquid to solid state and makes it possible to produce more complex castings possible. However, as a matter of fact, cast irons do not have adequate ductility to be forged or rolled. 

Cast irons come in a variety of types, however these cannot be specified by chemical composition because of the similarities between the types. The table given below shows the distinctive composition ranges for the most frequently determined elements in the 5 generic types of cast iron.   

Range of Compositions for Typical Unalloyed Cast Irons 

For the commercial purposes, the range of compositions can be categorized into a sixth type - the high-alloy irons. These have a broad range in base composition and also constitute other elements in significant quantities.

The presence of some minor elements also is critical to the successful production of different types of iron. For instance, nucleating agents, known as inoculants, are used in the production of gray iron to control the type and size of graphite. While bismuth and tellurium are used in little quantities to produce malleable iron; the presence of a few hundredths of a percent magnesium (Mg) drives the formation of the spheroidal graphite in ductile iron.

Moreover, the composition of an iron requires to be adjusted to befit specific castings. A particular composition of metal cannot be used to produce small and large size of castings of the same grade of iron. Due to this reason, most of the iron castings are purchased on the ground of mechanical properties instead of composition. An important exception is for castings, which necessitate special properties, such as - corrosion resistance or elevated temperature strength.

The different types of cast irons can be classified on the basis of their micro structure. The classification depends on the form and shape in which the major component of carbon occurs in the iron. This system facilitates five basic types - gray iron, ductile iron, malleable iron, compacted graphite iron (CGI) and white iron. All these different types of irons can be heat treated or moderately alloyed without altering its basic classification. The high-alloy irons, which normally contain over 3% of the added alloy, can be separately classified as gray or ductile iron or white, however the high-alloy irons are classified commercially as a distinguish group. 

Foundries generally have a very hot working environment because of the furnaces and molten metal. The molds and core heating, the ladles preheating and the heat treatment of metal castings make additional sources of heat. Personnel employed in furnace or ladle slagging and those executing tasks in close proximity to the molten metal, including furnace workers, welders, arc-air operators, oxy-cutters and crane operators, are most vulnerable to severe heat effects. 

The human body functions normally within 1° C to 1.5° C of the core body temperature of 37° C. The body sustains this temperature by balancing the heat generated within the body and the transfer of heat from body to the environment.

Working in hot environments causes strength to decline, and may result in fatigue sooner than it would otherwise. It may also affect alertness and mental capacity.

Effects of heat exposure on health
When the body is unable to loose heat as required through the evaporative cooling procedure to maintain a steady core body temperature, it starts experiencing physiological heat strain with several illnesses depending on the degree of heat stress.

Some of the potential health effects for persons working under high heat stress environments include -

Heat cramps, heat exhaustion and heat stroke are the most severe heat illnesses. Heat stroke is a life endangering condition, which may result in permanent damage to the heart, brain or kidneys. Effects of heat stress are most likely to increase during the months of summer.

Acclimatisation
Persons who regularly work in a hot working condition become acclimatised to a specific degree of heat. Acclimatisation reduces heat discomfort, increases the effectiveness of sweating, reduces salt loss and returns recovery rate to normal. Persons differ in their ability to acclimatise to heat.

Acclimatization provides only a partial protection from extreme heat and workers may still suffer from adverse health effects. Once the exposure to heat has discontinued, the protection from acclimatization is progressively lost. If a worker who has been absent from a hot work environment for a long period, such as a week; he should be first re-acclimatised to the hot environment for protection against heat related effects.

 Factors regulating heat stress

Some of the important factors that contribute to the heat problems are -

Factors associated with job

• Work of an arduous nature
• Work, which is prolonged for extended periods
• Uncomfortable or awkward body position 
• Insufficient cooling off or rest periods

Factors associated with the environment and season

• Extreme air temperatures
• Radiation heat from hot objects such as machinery
• Radiation heat from the sun if working in outdoors
• Higher levels of relative humidity 
• Low air movement

Factors associated with workers

• Inappropriate clothing
• Level of acclimatisation
• Degree of adequate hydration
• Approachability to water and cool recovery regions 
• Health condition e.g. heart, circulatory or skin disorders
• Medication, which impairs temperature regulation or perspiration (consult with doctor)
• Age and weight
• Level of physical fitness
• Insufficient salt in the diet

Control measures

Elimination controls
The best control measure is to eliminate situations, which may result in heat related illnesses. This can be done by -

• Eliminating radiant heat sources that are not essential; 
• Eliminating the sources of water vapor in the workplace (e.g. leaks from steam valves, evaporation of water from wet floors, etc.).

 Modifying the work environment
Several control measures, which have found to be effective in preventing or minimizing the vulnerability to risk by reducing heat in the workplace include - 

• Reducing the emissions of radiant from hot objects and surfaces (insulation and shielding);
• Altering the air temperature, air movement and relative humidity using local or general ventilation, spot coolers, fans, blowers and air conditioning;
• Reducing the metabolic heat production of body using automation and mechanization of tasks;
• Using ventilation e.g. setting flues extending from a foundry to the open air to ventilate cooling racks and fixed sources of heat; and
• Humidity reducing techniques (e.g. set a dehumidifier — seek engineering advice).

 Administrative controls
Administrative controls generally include the development of safe working procedures and practices. Some of these controls are -

• Scheduling the hot tasks to cooler times of the day and maintenance to cooler seasons;
• Supporting the workers to take short breaks;
• Providing opportunity to the new workers or workers returning from holidays to acclimatize to the heat;
• Rotating workers to reduce the heat exposure duration;
• Programming routine work / rest breaks in cool, shady areas with protective clothing removed;
• Keep apart the hot work practices to times / locations distant from other workers;
• Use extra workers or ensure job sharing / rotation of workers;
• Workers with heart and blood pressure problems or previous heat illness should not be allowed to work in extremely hot areas.;
• Providing training to workers in the hazards related with working in hot environments, recognizing heat related illnesses, adopting safe work practices, control measures and the use and maintenance of personal protective equipment;
• Restricted consumption of diuretics (caffeinated drinks and alcohol);
• Access to sufficient supply of clean and cool drinking water; and
• Formulate a contingency plan for the treatment of affected workers.

Personal protective equipment (PPE)
Where heat exposure cannot be reduced or prevented by any other form of control, all exposed persons should be provided with personal protective equipment. Personal protective equipment used to prevent heat associated problems include -

• Eye wear, such as UV glasses
• Non-flammable and heat reflective equipment and clothing
• Water cooled bodysuits / vests and other equipment
• Protective footwear and gloves

The capability to apply SSM casting or die-casting with metal in a semi-solid state is an outcome of the successful evolution of a high temperature nickel-base alloy die system. This high temperature nickel based alloy die system prolongs the die life in die casting metals and alloys with high melting temperatures. As the process typically uses easily available cold chamber horizontal die casting machines as the casting unit; it has the potential for far-flung applications and uses by existing casting professionals equipped with such machines and technology.

Semi-solid metal casting is made with metal at a temperature between the temperatures of liquid and solid state, with the fraction solid being in the range of 30-65 % approximately. The semi-solid billet holds its form and shape and is suitable for loading into the shot sleeve of a traditional die casting machine. For the semi-solid metal to have adequately low viscosity, the structure at the working temperature should comprise of a globular primary solid state surrounded by the liquid state. The technical and economical feasibility of the Semi-solid metal casting process are ascertained, to a great degree, by the approach used to develop the starting stock with the necessary precursor structure.

Advantages of SSM Casting
As an advanced casting technique, SSM casting offers huge potential in saving costs, energy, and material, and in reducing the environmental impact of casting. The advantages are -

• Virtually net shape processing.
• Potential for enhanced tolerance control because of the inherently tight process temperature control related with SSM casting and reduced thermal cycling of dies.
• Reduced thermal fatigue heat, reduced mold or die wear, and reduced solidification shrinkage as a result of the reduced feedstock temperature.
• Lower shear strengths of semi-solid slurries, which are related with lower forming forces than fitting operations for solid metal.
• Control of viscosity, which may result in less turbulent mold and die filling that minimizes the gas entrainment, shrinkage, porosity, hot tearing, and other solidification shortcomings.
• Finer, more consistent, micro structures resulting in higher mechanical performance.
• Superior material utilization in making small components because of the productivity and accurate introduction of metal into the forming dies.
• Increased casting speed compared to liquid processing due to lower thermal demands on the dies.
• As alternative for sand casting, SSM cast parts manufacturing gets rid of the environmental costs and troubles of reclaiming and disposing of lead-contaminated sands.
• Permits for the lead content of red brasses to be highly reduced and, combined with a semi-solid charge, should enable alloys usually prone to hot tearing to be die cast.

Investment casting has the potential to create monolithic cast systems, which replace multi-piece fabrications from solid hog-outs. This has provided a new perspective for manufacturing engineers to conceive, while designing new structures. The superior design attributes of investment casting has made it useful in a variety of industrial applications, including – aerospace, defense, electronics, optical, mechanical engineering, civil, and more.

Some of the design attributes of investment casting include -

• Castings with isotropic properties have similar material attributes in all directions, as contradicted to the big differences between the longitudinal and transverse characteristics of wrought alloys generally used. This simplifies the analysis requirements for stress engineers and they can use a single level of  material characteristics or finite element modeling of their 3D CAD designs.
• In conventional fabrications – the flexibility of fasteners (bolts, rivets), stress risers in fastener holes, and the variations in installation of fasteners, induce the design knockout factors for strength that are not applied to single piece castings. Structures also generally fail at joints, hence with decrease in number of joints, the structure becomes more reliable and predictable in performance.
• The inherent stiffening capability of investment castings with complex “T” stiffeners, undulating walls, return flanges and co-incidental fluid coring passageways ensure enhanced designs in both the static as well as dynamic loading cases. This is because of the more efficient transfer of stresses from one point load to the overall structure. This enables the designer to decrease overall thickness and save weight.
• Classic assemblies are constructed by assembling large number of machined or bent sheet metal parts. Since each part has its own dimensional variation, piling large number of parts together manifolds the overall er ror. Tolerance stack-up, metal shims to align these interface areas, or use of liquid shims, and requirement for in-the-field customized joints, are expensive drivers in traditional structures. Castings are unitary systems with a centralized datum structure and guaranteed interface points for superior fit.
• Junction of walls for a structure generally takes place at attach points or mounting lugs. Traditional machined “hog-out” shapes often fly with undue weight, as it generally is not feasible to machine away low stress material in tight unaccessible areas.  The design of castings allow the designers to thin and thicken areas based on the requirements of load instead of productivity constraints.
• Stress redistribution of monolithic casting design, eradicates fears of conventional beam and frame assemblies buckling and failing at certain loads on the built-up assembly. Enhanced designs in single piece castings allow more efficient distribution of loads throughout the structure. Likewise, the defects such as  holes or saw cuts brought into the structure do not spread freely because of the ability of stresses to redistribute move across the structure.
• The characteristics of crack arrest differ in concept between the castings and fabrications. Conventional fabrications may utilize multi-piece members fastened together to produce either a redundant structure, or one where the crack grows to the extremity of a single sub-assembly. The designs of castings should be creative in order to attain crack arrest or load redundancy, however, and may utilize step sections, parallel ribs and inherent stiffening to both arrest damage in service, as well as to facilitate redundant load paths for conditions of over stress.
• Inspection ability of complex assemblies sometimes require total tear down of the structure,  with removal of fasteners and finishes so as to check for cracks. The smooth monolithic characteristic of cast structures makes the detection of crack easy.
• By replacing various assembled components with a single piece casting, stiffness of large structures and their performance can be improved significantly. Investment casting has emerged as a perfect choice for moderate size complex structures as a one-piece stiffened structure is always mechanically better in comparison to one that has stiffening elements bolted together.