Simple Solutions That Work! Issue 18

and the movement of finished product after the process both require careful consideration. Obviously, there are two main raw materials used in the core room, sand and binder – and additives such as oxide powders along with anti-veining products. The first decision is the mixer type and the second decision is whether to have one mixer for multiple core machines or a dedicated mixer for each core machine. In general, there are two types of batch mixers that are most commonly used; the S-blade vertical shaft batch mixer and the horizontal shaft batch mixer. S-BLADE VERTICAL SHAFT MIXERS The most popular is the S-blade, vertical shaft mixer. This tried- and-true foundry mixer is known for its durability and affordability. This design has been in service in the foundry for well over 50 years. S-blade mixers are comparatively inexpensive, require minimal maintenance, and are easily cleaned. Disadvantages include long mixing cycles (with the inherent potential to create fines), higher resin requirements for equal strengths compared to other mixer types, and, many times, inaccurate pumping systems given the era of technology when they were originally designed and built. The chemicals are added after the sand is in the mixer and the mixer has started. There really isn’t a better way to add the chemicals than a simple “overflow pipe” which is a short length of properly sized pipe mounted horizontally over the sand bed. When the chemical is introduced to the chamber, the chemicals overflow and run into the active sand bed. This design lessens the potential for post flow of chemicals after the mix cycle has started and the desired amount of chemicals are added. A small amount of post flow is inevitable given the nature of the viscous liquids. This post flow is quite detrimental to the process since it is very common for this liquid to either fall on the S-blade or simply float across the top of the sand bed, building up on the side walls of the mixing chamber. This adds to the cleaning time required which is a waste of expensive chemicals and also adds variability to the final product HORIZONTAL SHAFT BATCH MIXERS This much more modern technology requires much less time to properly blend a batch of a given size as a result of the high intensity, very efficient mixing action. Most modern core machines are equipped from the manufacturer with some form of this mixer design. Fines generation is reduced compared to S-blade mixers as a result of the greatly reduced cycle times, and hourly throughput is high since cycle times can be as much as 20% of the venerable S-blade mixers. This type mixer forces the sand back and forth against itself from one side of the chamber to the other while the mixer shaft rotates Modern horizontal shaft batch mixers are higher priced than S-blade mixers but have a much higher level of technology for all functions. However, the greatest advantage of this higher level of technology is the accuracy and repeatability of the batch, primarily from the accuracy and repeatability of the liquid addition. The sand batch amount is very accurately metered into a properly sized hopper above the mixer where the inlet valve is opened for a variable amount of time. This hopper is equipped with a discharge valve directly connected to the HSM main chamber – once the sand is delivered to the chamber, and the valve closes the discharge valve on the sand supply to the feed hopper for the programmed amount of time. Since this is accomplished while the previous batch is mixing, the next batch can be started immediately once the mix cycle is completed We use the phrase “liquid addition” in place of the commonly accepted “pumping system “since the more accurate and higher technology batch mixers uses a bellows type mechanism to meter the liquid into the mixer at the correct time in the cycle at the most beneficial place in the mixer, and in a very accurate and repeatable manner. Essentially the bellows type metering device is very similar to a medical syringe. When the 40