Cores are used by foundries to cast holes and interior features into castings. These separately made sand forms are then placed into the green sand mould to replicate these special features in the casting. Lethbridge Iron Works uses two processes to make high production smaller cores.

Shell cores are made using a resin coated silica sand that is invested (blown) into an iron corebox. The corebox is preheated to about 550 degrees fahrenheit and the core(s) cure and become rigid due to the reaction between the resin and heat. The cores are yellow in color and are hollow, having a wall thickness of 1/8 to 3/4 inch depending on casting size and configuration. The hollow shell that forms the core gives it its name. Shell cores are made on vertically parted semi-automated machines yielding 20 to 60 cycles per hour. Shell cores provide the best cosmetics and dimensional tolerance of all the core processes.

Cold set cores are made using silica sand that is premixed with a resin. After investing (blowing) the premixed sand into the core cavities of the corebox, amine gas is passed through the core reacting with the resin to form a rigid and solid core in a very short time. Lethbridge Iron Works uses a Laempe LL10 fully automated core machine to make cold set cores. This state of the art German equipment is noted for its high production rates of up to 120 cycles/hour and excellent quality. Cores can be made from vertically parted coreboxes, horizontally parted coreboxes, or a combination of both, unlike shell cores which are normally made only in vertically parted coreboxes. This and other attributes of the Laempe machine can provide some significant design and cost advantages when compared to other core processes.

The advantages of cold set cores vs. shell cores are detailed in the pictures below. The first casting shown was made before the installation of the Laempe machine and was made using shell cores. Two separate shell cores were assembled into a single unit before being placed in the mold. The second casting is a newer version of the first, but uses a single cold set core.

The above 3 pictures show the first casting.
Notice the passageway for seed to flow from the top tube connection
down to the two discharge ports on the bottom of the casting.

The above picture shows the 2 cores required to make the casting.

The above picture shows the 2 cores after assembly.

The above 3 pictures show the newer casting.
Notice the similarity to the first casting
Also notice the cast holes in the first picture.

The above picture shows Laempe cold set core.
It is made as a single unit using a multi-part corebox.
It incorporates the feature required to make the bolt holes as-cast.

The advantages of the Laempe cold set core compared to the shell core assembly are:

• core labor cost lower by in excess of 50%
• 2 piece assembled shell core now made as one piece cold set core saving additional time in setting core in the mould and grinding/cleaning of casting
• holes formed by core instead of drilled, saving machining costs
• raw material cost of cold set core sand is less than shell sand
• due to the completely automated cycle of the Laempe machine (individual job information stored in PLC), each core is an exact likeness reducing variability and the potential for operator error
• corebox tooling can be made in plastic, aluminum, or wood depending on production levels, usually generating significant tooling savings when compared to iron shell coreboxes

Cost savings to our customer were in excess of 10% when comparing the old style shell cored Seed Boot to the new style cold set cored Seed Boot. Also, our customer saved the costs of drilling the holes and is much happier with all the attributes of the new Seed Boot compared to the old Seed Boot ... a win-win situation!