Simple Solutions That Work! Issue 9

Drop & Stop In order to select the proper force setting, it is common to run a “drop and stop” test. This is a test where the selected box is filled normally and then struck-off before compaction. The compaction cycle is started with the vibration time set at 5-10 seconds. The sand surface is monitored as it compacts: • If the sand is still going down when the vibrators stop, more force or duration of vibration is needed. • If the sand drops and stops before the vibrators stop, less force or duration is needed. If this test is performed on every job that comes in, the proper effective compaction settings can be determined quickly. It is not as simple as picking a force/ time setting based on weight, as deep work behaves differently than shallow wide work. In order to keep the compaction process simple and repeatable, it is recommended to keep the duration of vibration the same for all jobs. We normally recommend a setting of 5 seconds. It is critical that the operator is not in control of either the force setting or the duration of vibration. The operator can certainly turn the force output dial to the correct setting as determined by the technical manager, but that setting should not be under the operator’s control. Force Setting Documentation Documenting the force setting is as simple as writing the force output setting on the box. The compaction table dial is labeled as 0-100%. The tech simply performs the drop and stop test and writes the number on the side of the box. The operator runs the correct amount of sand For instance, a shallow job with a lot of surface area could generate a higher amount of gas and usually venting should take care of this. However, if the configuration of the mold is such that mechanical venting isn’t practical, it is common to cover the pattern, compact, and then fill out the rest of the box without compaction. This gives a good mold / metal interface with a permeable zone close to it thereby allowing gasses to escape through the mold itself. Obviously, start time is another variable that needs to be controlled. It is a simple matter to tie the mixer run time into the compaction sequence where the compaction sequence is initiated after a certain amount of mixer run time. The mixer run time for a given mold should also be controlled by the technical manager, not the operator. Strike-off sand isn’t sand—its money. The less strike-off sand that is generated, the lower the mold cost. The bottom line is this, there are few processes in the foundry that require only 15-20 seconds that can do as much as compaction can do for your castings – it’s just that simple. into the box, turns the dial to the correct setting and presses the “cycle start “ button. At this point, the airbags inflate lifting the box off the rollers or support structure. Once the box is lifted, the vibrators run at the selected force output for the predetermined amount of time. Once this time runs out, the airbags are deflated, lowering the box back onto the conveyor rollers and, completing the cycle. This typically is a 15-20 second process. Then the top of the mold is the struck-off, moved to the next station, and the next job is moved into place. When to Compact In order to achieve consistency and repeatability, it is important to take as many of the decisions as possible away from the operator. We have already said that the force output and the duration of vibration is already predetermined. The other two decisions are: • when to initiate the compaction process • amount of sand to put in the mold If one operator starts the compaction process when the box is half full and the next operator starts it when the box is completely full, the results will be variable. The simple thing to do is to fill the box and then compact, while this is simpler, sometimes it is desirable to do this differently. Contact: JACK PALMER [email protected] 40 SEE IT IN ACTION!