Core plugs, also called freeze plugs or Welch plugs, are used to fill the

sand casting Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced i ...

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

holes found on water-cooled

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...

Purpose

Sand cores are used to form the internal cavities when the

engine block In an internal combustion engine, the engine block is the structure which contains the cylinders and other components. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attac ...

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ...

(s) is cast. These cavities are usually the coolant passages. Holes are designed into the casting to support internal sand forms and to facilitate the removal of the sand after the casting has cooled. These holes have no purpose after the sand has been removed. A core plug is a cap at the end of these passages used to prevent water or coolant leaking from the engine.

Design

Core plugs are usually thin metal cups

press fit An interference fit, also known as a pressed fit or friction fit is a form of fastening between two ''tight'' fitting mating parts that produces a joint which is held together by friction after the parts are pushed together. Depending on the am ...

ted into the casting holes, but may be made of rubber or other materials. In some high-performance engines the core plugs are large diameter cast metal threaded

pipe plug A fitting or adapter is used in pipe systems to connect straight sections of pipe or tube, adapt to different sizes or shapes, and for other purposes such as regulating (or measuring) fluid flow. These fittings are used in plumbing to manipula ...

s. Core plugs can often be a source of leaks due to corrosion caused by cooling system water. Although modern

antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...

chemicals do not evaporate and may be considered "permanent", anti-corrosion additives gradually deplete and must be replenished. The slang term "freeze plug" was derived many years ago in situations where the water in an engine block could freeze (due to plain water being used in winter rather than anti-freeze coolant). The expansion of the water as it froze would cause the core plug to pop out of the engine, leading to the term "freeze plug".

Welch plug

The Welch plug is a type of core plug that is made from a thin disc of metal. The Welch plug is dome-shaped and inserted into the casting hole with the convex side facing outwards. When installed by striking the Welch plug with a hammer, the dome collapses slightly, expanding it laterally to seal the hole. This differs from other dish-shaped core plug designs, which form a seal when their tapered sides are pressed into the casting hole. The Welch plug was originally designed in the 1900s at the

Welch Motor Car Company The Welch Motor Company was an American automobile company headquartered in Chelsea, Michigan. It started in 1901 and continued production of luxury vehicles until 1911 when it merged with General Motors. History A.R. Welch started working a ...

in the United States. Prior to the invention of the Welch plug, the core holes were sealed using pipe plugs. During the testing of a car, one of the pipe plugs backed out. In order to get back on the road, one of the Welch brothers installed a press-fit

quarter A quarter is one-fourth, , 25% or 0.25. Quarter or quarters may refer to: Places * Quarter (urban subdivision), a section or area, usually of a town Placenames * Quarter, South Lanarkshire, a settlement in Scotland * Le Quartier, a settlement ...

or half dollar coin into the hole using a hammer. The design of the Welch plug was refined based on this principle of a press-fit metallic disc.

References

{{Automotive engine , state=expanded Engine components