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Core 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 ...
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 A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...
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 co ...
s.


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 ...
or
cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinder (engine), cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas ...
(s) are 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 generally have no factory designed purpose after the sand has been removed although some aftermarket temperature sensors may be installed into the location of a core plug on some engine designs. Another use is to install an aftermarket system designed to act as a block heater which is installed to keep an engine warm due to sub-freezing temperatures as found in far northern climates such as in the state of Alaska. Basically, a core plug is a cap at the end of these passages used to prevent water or a coolant mixture from leaking out of 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. The most common metal plugs used in automotive engines are made from plated mild steels, stainless steels, brass or bronze. 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 manipulate ...
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, al ...
chemicals do not evaporate and may be considered "permanent", anti-corrosion additives gradually deplete and must be replenished via a flush and refill. Automotive manufacturers specify time and mileage numbers for cooling system maintenance in their published factory maintenance manuals. The slang term "freeze plug" was coined many decades ago out of ignorance of the true purpose of the core plugs - they were never designed to be displaced by water freezing inside the block due to a lack of an anti-freeze/water mixture and their displacement is merely coincidental if freezing does occur. The sole purpose of a core plug is to literally act as a plug in the holes designed to be in a casting which allows the casting sand to be removed during the manufacture process.


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 at ...
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 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