The Supercar Registry - Tonawanda Foundry

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Chevrolet Tonawanda Metal casting Plant

1. Core Department
By far the most labor intensive area of the Tonawanda metal casting Plant was the core department. We employed in excess of 1,000 hourly workers in the department when I served as superintendent. Except for bearing caps and brake drums, every casting required at least one core. There were about 60 core producing machines in the department, each requiring one operator per production shift. Many support employees were required to prepare the cores for use in the casting process.
Cores are used in the sand foundry process to form internal passages and re-entrant pockets in the castings. These cores are quite literally castings themselves; made of sand that is mixed with a binding agent and blown under high pressure into a metal form referred to as a “core box”. The two core binding agents used at Tonawanda were a derivative of linseed oil (“oil sand cores”) which had to be cured, or cooked, in large tower ovens, and furan resin (later replaced by phenolic resin) which was catalyzed by heat right in the core cavity during the machine cycle “hot box cores”). It is interesting to note that each core cavity required many small vents (often small screens) to help the high volume of air escape the cavity during filling while keeping the sand/binder material entrapped in the core cavity. These screens eventually manifest themselves as small, round “bumps” on the cored areas of the casting surface. The simplest casting utilizing a core at Tonawanda was the v-8 exhaust manifold. The 4 internal exhaust passages that merge into a common collector passage were formed in the casting process by a single, one piece sand core. This care was set in place in the bottom half of the foundry mold (drag mold) prior to “closing” the mold cavity (lowering the top half of the foundry mold onto the bottom half). Gray iron at 2,600 degrees ferinheit was then poured into the mold through a hole called a sprue – it flowed through a runner system in the mold and entered the casting cavity through small rectangular openings called gates. If you examine the “parting line” (joint where the upper and lower halves of the molds meet) of a casting, you will notice these small rectangular “gate” impression. When the liquid iron enters the mold, it flows around core and actually initiates surface solidification or “skins” over at the core surface. If the system is properly engineered, this solidification begins before the hot metal destroys the binder which holds the core together. By the time the casting is removed from the mold (termed “shakeout”), the once solid core (with its’ binder now thermally destroyed) literally pours out of the casting like sand flowing between your fingers at the beach.
More complicated castings like cylinder heads and blocks require commensurately more intricate core assemblies. Small block cylinder heads require 3 separate cores each – a water jacket core to form the cooling passages, an intake core, and an exhaust core. In practice, the small block exhaust core was a “Siamese” design that formed the exhaust ports of two adjacent heads that were cast in pairs - 4 heads to a mold. Cores that were very thin and fragile, as well as cores that formed surfaces that had to be free from sand adherence, were “washed” (coated) with refractory material that would prevent premature core surface breakdown in the casting process. The composition of this refractory wash could be as simple as a mixture of finely graded silica sand mixed into a watery paint like consistency, or, depending on the critical purpose of the core, could be made of fine zircon sand with graphite powder added (to chill the iron and provide a layer gas protection). The water jackets of small block cylinder heads have thin passages that completely encircle the spark holes – the core that creates these thin passages had to be protected with a high quality core wash. Both big block and small block case castings utilized 2 separate cores to form the fuel pump area as well as the oil filter bowl. Owners of 1969 Norwood built Camaros will note with aggravation that the filter bowl core had several small, round, raised areas about the diameter of a pencil eraser located right at the otherwise flat surface where the VIN was stamped. These raised “bumps” are actually made by the small screens in the core box (previously mentioned). It is also interesting to note that, had the foundry known that the filter bowl area was going to be used for VIN stamping, the screens could easily have been placed in an alternate location (probably one day’s work for a pattern maker)! The most difficult, and highest scrap castings produced at Tonawanda were the big block MIV heads. A major contributor to this quality problem was that these casting were extremely heavily cored. Also, the water jacket was a 2 piece design that had to be glued together and sent to the molding department as an integral assembly with a large, single perimeter core that formed both the intake and the exhaust ports. If you examine a big block head, you can see evidence of this perimeter core on the cast surface of either end of the head. During pouring and solidification, combustion of core binders in the mold yields “off gas” that has be vented from the mold cavity. The excessive “off gas” from big block head cores created tremendous casting defects referred to as “blows” (large air bubbles literally entrapped during solidification). Big block heads seldom ran below 10% scrap in the foundry.
At the Tonawanda Metal casting Plant, cores destined for the front 4 molding lines were delivered via shelved or fixtured racks which hung from continuously moving monorail delivery conveyor – one monorail system for each of the front mold lines. These monorails would “dip down” to floor level for loading in the core department, and then make their way to the foundry at a mezzanine level of about 25’ above the floor. The trip to the foundry varied slightly on each line, but averaged about 30 minutes.
One final comment about the core department might be of interest to the collector car community. The core tooling required to produce a big block case was as follows:

International oil sand core machine
Core boxes for front barrel cores (2 cavities per box)
Core boxes for center 2 barrel cores (common – 2 cavities per box)
Core boxes for rear barrel cores (2 cavities per box)
Core box for front end housing core
Core box for rear end housing core.
“Dryers” specially made for each type of core
Core box for fuel pump core (6 cavities per box)
Core equipment for filter bowl core (6 cavities per box)
Osborne hot box machine (massive hydraulically operated machine)
Core equipment for left hand water jacket cores (6 cavities per box)
Core equipment for right hand water jacket (6 cavities per box)
Ejector system to remove cured cores from boxes.
Special water cooled sand magazine to fill bore box
Gas fired heating manifold with temperature controllers

All of this equipment (without machines – which only automotive foundries had) weighed conservatively 10,000 pounds. Because of the massive logistics and set-up required to run this equipment, cores for use by outside vendors (i.e. Winters or Lockport Castings) were produced on the Tonawanda machines and shipped along with the molding patterns & fixtures to the vendors. I do specifically recall shipping out cores and molding patterns on our company truck, but never recall lending out core making equipment.