A useful guide to sand casting, from design to finishing
Precision sand castings are the core of Haworth Castings’ metal castings business. As one of the top casting foundries in the UK, we specialise in producing high-integrity cast and machined components and take pride in our technical ability to solve the most complex metal casting challenges. Over 70 years we have developed and refined our techniques and are now one of the leading sand casting companies internationally, supplying fully machined and finished sand castings to a wide range of industries.
Our expertise as castings suppliers means we can help customers from the earliest product design stages, providing advice on the best way to manufacture their components and suggesting other processes where appropriate. If sand casting is the optimal solution, our professional team will manage the development of every aspect of the sand mould design and manufacture and will work with our casting foundry experts to ensure that the casting is created and tested to perform effectively even in safety-critical environments.
We are often asked exactly how sand castings are made, and at which points the expertise of Haworth Castings is vital to ensure that your component meets specifications. This article aims to address these questions.
We have also published an eBook which provides further information on the key stages in the sand casting process that you can download here
Sand Casting is a method of manufacturing metal components using a mould made of sand. A pattern shaped like the finished product is imprinted into the sand, and then molten metal is poured into that cavity and solidifies in the desired shape. The product is also referred to as a metal casting.
Sand casting was first recorded in 3200BC in Mesopotamia. It launched the Bronze and Iron Ages and accelerated the Industrial Revolution. In the hands of experts, this ancient process can produce solutions to complex modern-day technical challenges. Over 70% of all metal castings are now made using the sand casting process. It is a versatile manufacturing method and can be used by experienced casting suppliers to produce everything from simple to complex parts in a wide range of sizes.
The key elements of the sand-casting process
Every step of the sand casting process requires precision and expertise, but the most critical steps in sand casting are:
Running system design
From the initial design stage through to delivery, Haworth Castings draws on its years of experience in metal casting to ensure that customers receive sand castings of high quality and integrity.
2) Casting design in sand casting
Successful sand casting is both an art and a science. It requires an understanding of how the materials will behave, from the correct grade and mix of sand used to form the mould to the optimum pouring temperature of the selected metal, and how it will behave as it cools.
Haworth Castings helps our customers right from the initial design stages to ensure the manufacture of high-quality, cost-effective castings. Our experts use their skills in metallurgy and engineering to design the right casting and the best running system for your specific metal component. They are supported by powerful casting simulation software and 3D printing facilities to optimise production accuracy and cut down development time.
High-quality sand castings demand a casting foundry which understands how to design the casting elements and process to achieve the required specification for your component. We advise on the suitable metal for your metal casting and ensure the sand casting is designed to work effectively for that metal. Alloys have different characteristics as they cool, which will affect shrinkage: some alloys solidify quickly and predictably from the mould walls inwards, whilst unpredictable alloys can solidify in random internal areas. This can be carefully managed through good geometry design.
3) Running system design in sand casting
The running system in sand castings is a series of connected channels which allow the molten metal to fill every area of the mould cavity and control the liquid flow, turbulence, cooling rate and shrinkage.
Good running system design requires a scientific understanding of metallurgy and expertise in the practical challenges of sand casting. The gating and riser system for pouring metal into the mould must be carefully designed to take into account of the order in which areas will cool so that the casting is fully fed with alloy and will continue to draw molten metal in the early stages of cooling. At Haworth Castings we combine our expertise with the latest simulation technology to optimise the running system for each casting, reducing the risk of problems such as turbulence, inclusions, porosity and air entrapment.
There are three main types of running systems. Typically, at Haworth Castings we use a ring runner system in our casting foundry, the main elements of which are:
a pouring cup – a funnel that allows metal to be poured into the mould
filters – to remove impurities and reduce the risk of casting defects
down sprue – the passageway through which molten metal enters the mould
risers – vertical cylinders that compensate for shrinkage as the metal solidifies
runners and gates – channels that connect the down sprue and risers.
The second option is Kalpur technology. Using this system, molten metal can be introduced at a single point through an all-in-one pouring cup, filter and sleeve. The thermal insulating sleeve helps to keep the metal ‘life’ and feed the casting properly. Kalpur technology offers many economic and environmental benefits but is not suitable for all sand castings.
Finally, three-part (bottom-fed) systems can be used to reduce turbulence by introducing metal from below the casting to flow up through the mould.
Our experienced casting foundry team looks at each customer project individually and will select and design the most appropriate running system based on the specific requirements for casting configuration and integrity.
At Haworth Castings, our specialist pattern makers receive original designs, 3D models or software drawings supplied by our customers. The pattern makers interrogate the design to identify issues and limitations, such as the desired metal thicknesses in the pattern and the potential for shrinkage or porosity.
The pattern will usually be manufactured from a high-quality resin, the hardness of which is determined by the expected life of the pattern. Patterns may be machined or 3D printed, and sets of patterns will be made to allow multiple castings to be made concurrently.
5) Core making in sand casting
If cavities or specific internal features are required within a sand casting, these will be created using cores made of sand and resin. At Haworth Castings we create cores for sand casting using three main techniques:
Shell core making Fine AFS-graded sand is coated with resin and blown into a pre-heated core box, ideally made from cast iron, forming the desired shape. The surface is heated to 210-250°C, depending on the required core. This allows the chemical components in the sand to bond together and form the shape within the core box.
The benefits of shell cores include high strength, good dimensional accuracy and excellent surface texture. The surplus sand is also easier to remove, through heat treatment and other knockout processes, so that it can be recycled.
The Cold Box process 50 AFS grade sand is mixed with resin binders before being blown into the core box. This box is sealed and the triethylamine gas setting resin (TEA) is purged with air. The air passes through the sand and it is expelled from the core box through strategically placed vents. The core box is purged for a set time to allow the core to harden, depending on the shape and size of the core.
The main advantage of this technique is that no heating is required and the sand is evenly distributed into the core box, allowing it to fill hard-to-reach corners and cavities.
Hand-rammed core making 75 AFS sand is used to ram the cores manually on our foundry bench.
This process allows multiple core boxes to be made quickly, but it is not suitable for highly complex core shapes
6) Mould assembly in sand casting
Once the casting and running system have been designed and the pattern and any core have been prepared, the mould for the sand casting is ready to be assembled.
The 3D pattern is secured in a wooden moulding box with a top (the cope) and bottom (the drag). The cope and drag are assembled to form a closed casting cavity and a mixture of high-grade silica sand, binder and catalyst is packed around it and allowed to harden into a mould.
As a sustainable sand casting company, Haworth Castings uses re-useable wooden moulding boxes which:
are strong enough to retain their shape, hold weight and resist erosion,
allow gases formed within the mould to escape, and
are easily removed from the hardened mould.
Once hardened, the sand mould is released from the moulding box and can be prepared to create the final casting cavity for the manufacture of the metal component. If a core is prepared it will be added, along with any structures such as dypurs and sleeves which will be inserted to create the specific running system for this metal casting.
The sand casting mould is now ready in the casting foundry to receive the pour of liquid metal to create the final product.
7) The pour of metal in sand casting
The pouring of metal into the sand mould is often considered the most critical element of the casting process, requiring careful control and technique.During the casting process, the metal is brought to the required melting temperature in our casting foundry furnace before being poured by ladle or crane into the mould. This temperature is dependent on the choice of metal and on the required density of the casting, since heat dissipates faster in thinner castings.
Keeping the temperature at a constant level during the pour is vital to ensure the integrity of the finished product. If the molten metal is too hot, this will alter the chemical and physical properties and the casting will not meet the required specifications. If the temperature is too low, the molten metal will not flow properly. The temperature must be monitored carefully by an experienced casting foundry operator.
Only if every aspect of the pour is correct will the molten metal flow properly, retain its chemical and physical properties and avoid turbulence leading to defects.
8) Finishing in sand casting
The last critical stage in the aluminium sand casting process is finishing, the process used to prepare cast components for industrial use. Finishing can:
give the component the desired surface texture
remove excess material or surface contaminants
enhance aesthetic qualities
act as a pre-treatment for other finishing processes (such as paintingmoly spraying, anodising and alocroming).
Cutting or fettling Excess material is removed using a band saw or manual cutting device.
Linishing Grinding or sanding to improve the surface flatness, using manual or automated tools.
Shot blasting This process cleans and prepares the casting for further treatment. The component is placed in a cabinet and rotated while a stainless steel shot is fired at it from a pressurised nozzle.
Rumbling A gentler blasting process using polished stones to produce a smoother, more tactile surface.
9) Haworth Castings: high-quality sand castings
As an experienced sand casting company we have over 70 years experience in providing solutions to complex casting challenges from our foundry and machining centre in Romsey and Basingstoke, Hampshire.
Haworth Castings is a casting supplier specialising in the casting of complex parts to demanding standardsand offers a complete solution encompassing casting, machining and post-processing. The quality and integrity of our sand castings are key to our success.
We use CMM to measure tolerances for critical parts and offer UKAS-approved independent testing and inspection services to meet the most demanding specifications in terms of the mechanical properties, dimensional accuracy and tensile strength of the finished metal casting.
10) Haworth Castings: sustainability in sand castings
Sustainability is embedded in the way we work.
Recycling sand We recycle 100% of our sand in our sand casting foundry, giving significant environmental benefits whilst assuring high-quality metal castings for our customers.
Recycling raw materials Many of our other raw materials, such as metals, are reused in the casting process – only a minimal amount is sent to scrap.
Managing our emissions As a leading casting supplier, we also manage our emissions responsibly. Our facilities are inspected every two years to check on our emission levels.
11) Sand castings for performance-critical industries
Haworth Castings is trusted to provide solutions to complex casting challenges across a wide range of industry sectors.
We supply high-quality cast components to performance-critical industries including Defence, Energy, Electric Vehicle, Performance Automotive, Marine and Medical.
From small single parts to large, complex multi-parts, Haworth Castings is the best choice for sand casting expertise.
If you are looking for high quality manufacturing, particularly for performance-critical applications, find out if we can help by contacting Haworth Castings on 01794 512685 or email email@example.com.
If you have a project, talk to our experienced sales team
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