Simple Solutions That Work! Issue 9

BACK-2-BASICS room. With more jobs than workers in the US, workers are selecting jobs with the highest pay, and best working environment. With all of these options, working in a cleaning room will not be high on the list. For this reason, many foundries are spending large amounts of capital on automated casting grinding machinery. The cleaning room is also a source for a large percentage of silica dust. Foundries typically perform silica mapping and testing procedures very near the shakeout / reclamation equipment. In today’s international market, every foundry could be competing with others around the world. Quality requirements never become lesser - it is something of an intangible, but today’s casting buyers do not want parts that have been ground more than necessary. Some buyers are requiring zero parting line grinding. Some buyers simply will not accept castings that are ground all over to make up for poor foundry practices, nor will they accept parts that require machining fixtures that require adjustable stops simply because the foundry has poor molding process control. It is critical to have the right equipment to properly compact and to follow procedures that are consistent and repeatable. While rotary vibrators are comparatively inexpensive and the accepted norm until recently, there is a much better alternative. 39 Electromagnetic Vertical Vibrators Rotary vibrators simply cannot provide true vertical vibration, even when there are multiple vibrators counter rotating. Vertical Vibrator(s) can be turned down to a low level to compact a small mold or core, and turned right back up to compact larger work. It is critical to closely match the force output to the weight of the total of the tooling and sand. High frequency vibration is important to the no-bake process. Vertical vibrators can be turned up or down without sacrificing frequency. Many times a rotary compaction table will be set up with a system to raise and lower the speed of the vibrators in an attempt to raise or lower the force. While the force does change, so does the frequency; with differencing frequencies for different weights of work coming across the compaction table, it is almost impossible to achieve any consistency with rotary vibrators. Immediate Stop – rotary vs vertical vibrators Rotary vibrators are difficult to stop immediately. However, that is exactly what’s needed to properly compact the mold. The vibrators must stop immediately in order to keep from imparting more force into the mold and over-compacting. Rotary vibrators attempt to achieve this number of ways, although none of which could be called stopping immediately and results in “loping.” This essentially turns the compaction table into a jolt table which can quickly defeat the whole compaction process, whereas vertical vibrators stop as soon as power is removed. Over-compaction It is possible to over-compact as well as under-compact your molds. A poorly compacted mold can result in burn in/on, increased demand for resin levels, poor surface finish, and increased cleaning room time as discussed above. An over-compacted mold or core can result in a part with lines of weakness or fault lines that might not show up when handled, but could result in a mold failure when metal is introduced into the mold potentially resulting in run- outs. As we all know, run-outs are inconvenient and expensive at the least and very dangerous at the most. Continued on page 40