The double CFF filter boxes can be operated as a single filter box, where a relatively coarse filter is used for standard products. For key products, when a finer filter is required, the filter box should be used as a double filter box to provide sufficient filtration area to avoid blockage or excessive metal height difference between the front and rear of the filter box.
For the production of standard products, coarse ceramic foam filters (30-50 PPI) are usually sufficient to produce the required metal quality. For critical products, finer filters (60-80 PPI) may be required to be able to produce metal with sufficient cleanliness. It is well known that a coarser filter can allow a relatively high flow rate through the filter, and if the filter area becomes too small for a certain flow rate, the fine filter may become clogged.
The metal will rest on the bottom of the filter in the outlet cavity of the filter box because the metal has resistance to entering the filter with small holes. As the negative pressure increases, the metal will continue to rise in the inlet chamber of the filter box. When the height difference between the bottom of the filter and the metal in the inlet chamber reaches a certain level, the pressure on the bottom of the filter will be high enough to infuse the filter, that is, the metal will begin to penetrate into the filter. If one filter is filled before the other filter, the metal water level in the filled chamber will rise to the same water level as the metal level in the intake chamber. After further reducing the negative pressure, the second filter will also be activated.
When the casting is close to completion, the level of the metal interior gradually lowers the box by reducing the negative pressure, and finally, the metal is released into the casting launder.
An example can be used to illustrate the cost advantage of this flexibility. Suppose a casting factory produces 2000 castings per year, and only 10% are high-quality products that require very fine ceramic foam filters. In this case, 1800 actors can operate dual CFF filter boxes in a single mode. This means that the cost of 1800 CFF can be saved. In addition, the processing cost (used filters are processed by the scum processing plant so that the metal remaining in the filter can be reused after the casting is completed) will save 1,800 used filters as well as work and processing costs. Operating the filter box in dual mode requires additional energy. The total annual cost savings may total about 100.000 Euros.
The work of changing from dual-mode to single-mode should not take much time and may be less than 30 minutes. However, in order to avoid too many changes back and forth, high-quality products should be produced during the campaign.