Whether you are a high-production automated foundry or making individual castings on the molding floor, the same five processes apply to the construction of a sound chemically bonded sand mold. We refer to these as the 5 C’s. Each process builds on the previous one and each one needs to be considered carefully.

Spray and Flow Coating

Assume mold halves are drawn and ready for assembly. The first decision to be made is whether or not to use an alcohol- or water-based coating.  Alcohol-based coatings are generally faster because they can be lit off after coating, but they are falling out of favor due to environmental and safety considerations.  If you are designing a new mold assembly area and alcohol is allowed, space should be left for the eventual installation of a water-based coating process.

The most popular methods of coating are spraying and flow coating – both require that the coating be kept in the correct condition. Baume is the most common form of testing coating, but density per gallon should be used also.  Spraying is by far the most economical, because all that is needed is a supply with agitator, spray gun and hosing, and catch basin with a return pump.

It is also more labor-intensive and skill-dependent compared to flow coating. Proper adjustment of the spray gun is important in order to apply the coating correctly, with the best finish with the least possible overspray.  Flow coating requires more capital investment because a mold handling device is required to rotate the mold 90 degrees for flow coating, tip over to approximately 110 degrees to drip out, and return to horizontal for drying. The primary advantages of flow coating are speed, repeatability, and lower skill requirements to achieve acceptable results.

‘Cooking’

Cooking, or drying is the most important of the five processes in terms of safety, especially when using water-based coatings, for obvious reasons. It can also be the most expensive because it usually takes a long time to dry heavy coatings properly. Heat and large volumes of air work best for most molds of varying depths. Radiant and infrared heat work well for flat shallow work, but are not acceptable for jobs with deep pockets or vertical walls. It is critical to start the drying process slowly, because starting with the temperature too high may harden the surface of the coating, trapping moisture beneath. Proper drying requires correctly designed equipment and enough floor space to accomplish this task safely. Preheating the mold is very helpful, but not required if the mold is made from sand at the correct temperature and there has been enough time between stripping and coating.

Coring

Cores may be as simple as a one piece placed in the drag or as complex as taking “packages” that take days or hours to assemble within the drag. It is important to have enough space to keep the most complex job from setting the speed of the molding system.

In a normal jobbing shop, there will be some jobs that may not require any coring at all, along with jobs that require much more time to assemble. The molding system should have built-in provisions to allow jobs requiring longer to assemble to be moved to another conveyor line or part of the floor.  Cores should be placed in the molding area in the most logical position for coring as quickly as possible. Cranes used to set cores should have at least two speeds, slow and fast, to allow for the core to be moved into place quickly and lowered slowly. Hoists with infinite speed control are preferred. Some cores are made with integral lifting points but some will require straps or custom handling devices.