PATTERNS, CORES, FLASKS, AND MOLDS 443 



prevents a weak corner which might occur because of the 

 shrinkage of the metal. In many cases this weakness does 

 not show on the outside, thus deceiving the founder and 

 rendering the machine, of which the casting is to be a part, 

 liable to break under strain. 



512. Other Terms and Processes. An opening from the 

 casting through the cope to the outside air is called a riser. 

 It is designed to carry the slag (which would otherwise form 

 part of the casting) into the iron forming in the riser. The 

 riser also serves as an escape for gas. 



A feeder-head is an opening, somewhat larger than a riser, 

 used on large castings to feed fresh iron into the mold dur- 

 ing shrinkage. All sprues, gates, risers, and feeder-heads, 

 which do not form parts of the casting proper but are merely 

 aids in getting a sound and smooth casting, are broken away 

 and remelted. 



Venting a mold is the process of providing an escape 

 for the gas formed by the mixture of the molten metal with 

 the air in the mold. A vent wire about }/% m - thick is usu- 

 ally driven through the sand of the cope to within J^ in. of 

 the pattern. It should never be driven entirely up to the- 

 opening, as it will then prevent the escape of gas. 



A chaplet is a metal device used to support a core where 

 a print is not possible. Chaplets are of two kinds stud 

 and steeple. The stud chaplet is formed with two heads, 

 the steeple has much the form of a wire nail. As the chap- 

 let becomes a part of the casting, great care must be exercised 

 to prevent rust from forming before the metal is poured. 

 Rust causes the metal to be agitated during the time 

 it is hardening or becoming set, and spongy or weak 

 places in the casting result. Rusting may be prevented 



