An Introduction to Sand Cast Iron Engine Blocks - Impro Precision


An Introduction to Sand Cast Iron Engine Blocks

June 20th, 2023

Impro uses sand casting to produce engine blocks for high horsepower and other applications. Sand casting has advantages over other casting processes, but also poses some challenges. Here’s an introduction to how iron engine blocks are made.

Design Expectations and Alloy Selection

Engine blocks intended for vehicular applications, (i.e. not stationary generators,) present design teams with conflicting requirements. Mass must be minimized, which means reducing wall thicknesses, but the block must remain strong enough to withstand combustion pressures and temperatures. Ideally, it should also absorb and dampen vibration to lower noise levels.

Achieving these goals forces designers to look at the material options. These are cast iron and aluminum.

Cast iron has many advantages for engine blocks. It’s strong, machinable, offers high thermal conductivity and provides good damping. However, with density nearly three times that of aluminum, it results in heavy engines. Consequently, light vehicle engines subject to fuel efficiency regulations use an aluminum block. Diesels and trucks however, stick with iron.

Cast iron is produced in three main forms: gray, ductile and compacted graphite (CGI). Gray iron, with its superior damping, is usually preferred for engine blocks, while tougher ductile and CGI are used in cylinder heads.

Why Sand Cast Engine Blocks?

Sand casting is an expendable mold process where the cavity is formed in sand. This has two advantages over permanent mold casting processes: flexibility and process economics.

Flexibility is important because engine blocks go through frequent design modifications and changing permanent mold tools would be slow and very expensive. In addition, and unlike permanent mold casting, sand casting is cost-effective from very small to very large production quantities.

Two Processes for Sand Casting

Generally speaking, sand casting parts are produced by the sand mold process. This is where sand is packed around a pattern which is then removed. Two mold halves are made this way, and put together to create a cavity which will be filled with metal.

To form internal chambers or voids within the cast part something has to take up the space in the mold. This is achieved with cores. Cores are made in sand and replicate the desired internal cavity or void. They are mounted in the mold before the two halves are clamped together, and broken apart for removal once the metal has solidified.

The challenge with casting engine blocks this way is that they need a lot of cores for all their internal galleries and passageways. Plus, for 90° V engines there’s no way to produce the cavity between the cylinder banks.

The solution is to cast engine blocks using the core package method. This is where the entire mold cavity is created by assembling core pieces together. This reduces moisture because core pieces are given a coating, and permits better gas venting, which reduces nonfill and porosity problems. It also enables formation of complex external geometry, such as load-bearing ribs and bosses for mounting ancillary components.

Your Source for Cast Iron Engine Blocks

Impro has deep expertise in sand casting and in the production of cast iron engine blocks. Our foundries are capable of producing high quality sand castings weighing 600 kgs or more and in small to large quantities. We can also perform machining and inspection. If you’re looking for a source for cast iron engines, we invite you to contact us to schedule a discussion.


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