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Proposed merge from Freeze plug
Page needs work
The page needs a bit of work, as a core plug can be several things, such as the earth removed from a lawn when a lawn aerator is used, or a deep hole drilling sample taken when a hollow bit is used to drill into the earth, and other items. Technically the editor who created this article did not use an incorrect name, as what he is trying to describe is a combination of the process of making a core to support the water jacket of the internal combustion engine, how and why the hole is formed in the casting, and how and why the cored hole thus formed is closed over to maintain water-tightness in the engine block. The sketch below somewhat explains the steps by showing what would happen without the use of the cored hole in the casting process and the resultant hole produced by the core. In order to form the internal water jacket of the engine a core is used. The core is placed in the mold and the forces acting upon it are gravity and the bouyancy of the core itself. Gravity can be understood, although a countermeasure to this would be to use chaplets. Chaplets are often not permitted as a watertight connection cannot be maintained for various reasons. Therefore the cored hold first acts as a way to support the core in the proper position. When the molten metal fills the mold cavity the property of bouyancy must be considered according to Archimedes principle. Sand has a density of approximately 100 pounds per cubic foot, about 0.06 pounds per cubic inch. Iron has a density of about 0.25 pounds per cubic inch. Therefore when casting iron with sand, the sand core will be bouyant in the iron and will float. When the metal freezes the core could rise in the mold cavity and contact the upper surface. Sometimes in light metal the differential is not so great and the core will sink in the molten metal. This is especially true if the core is made hollow. In any case there can be holes formed in the sidewall, either by the use of small pin cores or a change in the shape of the core to add core prints. This supports the core into the proper position preventing gravity from lowering the core or bouyancy in the molten metal from 'floating' the core. After the metal freezes the casting is left with the cored holes. These holes are often machined to a precise diameter and then a thin sheet metal insert can be installed to maintain the water tightness.
In order to put a positive spin on this process using the required opening (the cored hole), the engine manufacturers called the sheet metal insert a freeze out plug to indicate there was a definite purpose for the hole in application as opposed to the use of the hole in the casting process. Often these sheet metal inserts will corrode preferentially to the block and leak.
Sorry about the sketch it is not too good for an article but here for example.
- The page is a mix up of vaguely related processes and terms. The core plugs and welch plugs need to be split off into their own desperate pages. The previous editor is correct about the term " core plug" being a generic description of many different types of processes. It includes drilling cores (in ice, earth, etc) , casting cores (when casting various molten metal alloys).
- Welch plugs are not a sub section of core plugs in any way.. Welch plugs are used to block off openings made by [core plugs] or openings drilled or machined into cast or manufactured components.
Convex out vs.in
The correct orientation of a Welch plug is with the convex dome facing outwards, as is shown in the photo. In the correct orientation, a hammer blow will expand the plug so that it locks firmly in place and seals the hole. Installed backwards, the plug will not seat properly, and must rely solely on glue/sealant to hold it tenuously in place against internal pressure. Some mechanics may have been taught the wrong way based on received authority, and have never thought carefully about the physics of metal deformation involved in seating the plug securely. I have added a reference to the company that originally developed the Welch plug. The reference also shows a "cupped plug" design, which has a different design and is installed differently from a Welch plug. Reify-tech (talk) 05:19, 11 March 2015 (UTC)