The metals casting, or foundry operation is an amazing and intriguing process where abrasives play a very important role throughout the entire foundry process. Although the focus may have shifted from casting bells and cannon barrels to products that influence our daily lives like the engine block in your vehicle to the impeller in the pump at the water purification plant supplying water to your city or town right to the gears and components driving the wind turbines powering our homes.
With processes becoming more mechanised and controlled, throughput and quality remains the most critical elements in the foundry process, although the fundamentals of creating a masterpiece in metal has for the most part, remained unchanged. The foundry process is started with a design concept and created from an engineering need for a metal casting, be it sand moulded, die cast, investment or spun (centrifugal) cast.
Based on the design and type of casting method selected, tooling in the form of a pattern may need to be manufactured. These patterns are mostly made from wood, “housing” the sand, and resembling the positive impression of the casting as well as any cores that may be required. Abrasive solutions used in this process include coated abrasives in sheets, rolls and discs, for primary and secondary finishing of wooden and metal parts. Grinding Techniques offer a complete abrasive basket that caters for all the foundry applications and more.
Once the pattern and its various components have been completed, the moulding process will follow. In a foundry, where the pattern is filled with sand, cores are placed for funnels and channels in order to direct the flow of molten metal into the mould. Following the sand process, is possibly one of the most dangerous, but also most exciting part of the process – the melt.
Metal is added to a furnace and melted down to liquid form making it pourable. Included in this melt can be scrap metal, raw virgin metals, and or a combination of both, creating the desired alloying materials that may be required. The melting process also provides an opportunity to remove any contaminants in the mix. When using scrap metal in the melting process it is vitally important to use high-quality, fit-for-purpose abrasive cutting discs for chopping metal scraps to eliminate some of the contaminants, before melting. It is equally important to select metal specific abrasive products to eliminate any potential contamination (such as processing aluminium scraps with products that contain ferrous contaminants).
Once the metal has reached the desired melt stage and has been tested for chemical make-up and impurities, the molten metal can be poured. This is when the moulds are filled with the glowing hot metal and allowed to cool.
Depending on the type of metal and the size of the casting, the cooling period can range from a few minutes to several days. Once sufficiently cooled and solidified, the fresh castings will be removed or ejected from their moulds and potentially shaken to remove all the remaining sand or other moulding materials.
One such technique for initial cleaning is shot blasting. At this time, the sprues, gates, and risers can either be broken off or cut off with abrasive cutting discs. Depending on the size, either angle grinders or larger, engine driven machines can be used with cut-off discs to remove the excess. Rough grinding of any burnt-on sand can also be done by using a specialist angle grinding discs. The Superflex and Andor range of products boasts an extensive range suitable to any cutting or grinding application.
Following the initial cleaning process the casting now needs to be fettled for further processing. Where large amounts of material need to be removed, resin bonded snagging wheels are the industry standard. Depending on the metal cast, these are manufactured with a number of abrasive grains. Newer technology ceramic grains are proving to be the premium go to product as their stock removal rate is substantially higher, while keeping the casting much cooler. Smaller areas of metal removal can be conducted by utilising a handheld abrasive angle grinding discs, also available in various grit and grain derivatives depending on the metal and application. For very small or hard to reach areas, we offer various shapes and sizes of abrasive mounted points and tungsten carbide burrs.
The next phase, checking and inspection allows for visual and or x-ray inspections, die-penetration tests (especially on heat sensitive metals) and other non-destructive tests. Castings are also measured for accuracy and selective destructive testing to check may be conducted for internal porosity, inclusions and or shrinkage dependent on the requirement.
Not all castings are finalised at the rough stage though, some castings require further machining to achieve the desired result. Milling and turning can be done to extreme tight tolerances on CNC machines. Some components that require an abrasive finishing, such as automotive crank shafts must be ground and polished, first with a vitrified bonded abrasive grinding wheel and then with coated abrasive belts.
Cylindrical components can be internally and or externally ground with various sizes, grades, and grits of abrasive grinding wheels. Large surfaces that need to be absolutely flat can be surface ground with abrasive wheels, cups or segments. These abrasive products are made from a range of conventional (aluminium oxide, zirconium alumina, ceramic) and super (diamond, CBN) abrasives based on the application and end product requirement. Non-woven and mounted abrasives are available for applications requiring finer, more precise finishes, and where smoothness to the final finish is imperative, polishing points are also available for super-finishing of dies.
Grinding Techniques’ abrasive basket offers complete solutions to all foundry markets. Their products are locally manufactured with only the best raw materials, for maximum output, and they offer the perfect balance between cost and performance, the company says.