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Volume filters

Strainer cores

Strainer cores are flat ceramic bodies with straight circular holes with diameters from 4 to 10 mm, and thickness values from 6 to 20 mm. The strainer cores are usually placed on the bottom of the pouring basin at the foot of the sprue, exceptionally in another place of the gating system. In addition to capturing coarse impurities, they have further advantages, for example, they speed up the filling of the pouring basin, prevent the appearance of vortexes above the sprue and reduce metal turbulence. The inclusions are captured only by the straining mechanism. Strainer cores mainly capture coarse slag particles but they do not capture tiny inclusions.

 

Pressed filters

Pressed filters are similar to strainer cores. They are produced by pressing a semi-dry ceramic mixture in metal moulds, with straight flow-through holes being pressed at the same time. After pressing, the filters are annealed. The filters are characterized by their dimensions, thickness, the diameter of holes and their density in the filter flow area. The holes diameters are usually from 1 to 3 mm, and thickness ranges from 10 to 22 mm. The flow area is 45 - 58 % of the total filter area. The material is selected according to the type of metal to be casted.Advantages of these filter types: low price, high accuracy and mechanical strength. Disadvantages are as follows: lower filtering efficiency, high heat capacity, high bulk density and low variability of manufacture restricted by press tool existence.

Extruded filters

Extruded filters  are also filters with straight runners. They are produced by extruding plastic ceramic material through a die with rectangular/square holes. Compared to the previous type, the grating walls are markedly thinner, and hence they have a larger flow cross section (about 65 %) and lower heat capacity. The square cross section of filter channels is more suitable than that of circular shape, and the filters are of better depth filtration effectiveness. Compared with the pressed filters, they have also lower heat capacity, higher casting capacity, but lose their accuracy and mechanical strength. Shape range of the filters is limited by existence of the extrusion tool and therefore variability of manufacture is at a low level. Flow area to the total area ratio is an important feature for both the strainers and the filters. That part of the area, created by the ceramic material, limits the flow cross section. Should throttling of metal flow by the filter be avoided, filter cross section has to be increased adequately compared with the runner cross section; the total flow cross section of the holes must at least equal to the control cross section of the gating system.

 

Ceramic foam filters

Foam filters are based on a system of mutually linked cells. The mode of metal flow in a foam filter in which local turbulences and frequent changes in flow direction occur, due to which inclusions come into contact with filter walls, is suitable for depth filtration.

 

Inclusions whose dimensions are significantly lower than the pores are captured on walls, and additionally they get stuck to one another and form "bridges" anchored on filter walls. With increasing amount of inclusions captured, the filter is gradually clogged, and it becomes closed for other inclusions. Flow capacity of the filter thus depends on quantity of inclusions, on the pore size and on adhesive forces between individual inclusions and the filter (i.e. depends on filter material).

 

A high efficiency of depth filtration is the most important advantage of foam filters compared to all other types. The thickness of foam filters provides better depth filtration. In general, the thickness of foam filters is in the range from 12 to 50 mm.High variability of manufacture belongs among further filter advantages. Based on the chosen filter design, we can use the filters with high mechanical strength, with low bulk density, low heat capacity, high refractoriness, with high filtering efficiency, high casting capacity and low price, depending on the scope of application, different dimensions and shapes.

 
created by Omega Design