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Vertical Gate Filters for Aluminum Die, Permanent Mold, and Sand Casting Foundries

provide high-quality filtration for central melting and holding furnaces possess superior strength, corrosion resistance, durability, and thermal conductivity increase metal fluidity, castability, and machinability

 

MetaullicsTM Vertical Gate Filters (VGF) offer the best way to eliminate inclusions, foreign materials that are a major source of quality problems in molten aluminum alloy. Serving as walls between hearths and dip-out wells in melting or holding furnaces, these bonded-particle filters remove inclusions and help you meet ever increasing demands for quality and productivity.

 

Features That Set Metaullics^TM Filters Apart

While filtration is generally beneficial, Metaullics Vertical Gate Filters offer important features that distinguish them from others:

Strength

Bonded -particle filter construction provides a rigid, durable filter medium you can easily handle in a metal casting environment. This type of filter is significantly stronger than a ceramic foam filter at both ambient and application temperatures. Consequently, you can use wide filters to span the full furnace width, up to 35 inches (889 mm).

Trapezoidal Vertical Gate Filter

 

Low Temperature Gradient

Silicon carbide is the preferred composition. This ceramic composition is thermally conductive (ceramic foam filters are insulating oxide ceramics). Therefore, there is less temperature gradient between the hot and cold sides of the filter. This means less superheat is required in the hearth, and less sludging occurs because temperature can be maintained in the dip-out well. Actual temperature gradients depend on furnace design, well area, metal throughput, and filter cleanliness. Gradients less than 20°F (5°C) exist with steady metal flow - for example, during continuous dip-out, ladling, or pouring - and when oxide buildup, which is insulating, is removed periodically.

Rectangular VGF installed at wall separating hearth from dip-out well

 

Durability

MetaullicsTM bonded-particle filters are fully chemically stable in all common aluminum casting alloys. Practical filter life ranges from one to two months depending on usage, periodic cleaning, avoidance of mechanical damage, and inherent melt cleanliness.

 

 

Filtration Efficiency

The MetaullicsTM bonded-particle filter can remove a much greater fraction of fine particulate than is possible with a ceramic foam filter. Our filter can remove inclusions as small as ten microns, depending on pore size (grit number) of the filter in use. A typical die casting application uses 6 or 8 grit size, capable of removing virtually all inclusions (above 30m) that are considered detrimental. Finer filters also are available.

 

How Efficient Filtration Improves the Whole Process

Metaullics^TM Vertical Gate Filters offer benefits that improve molten metal handling, casting, machining, and the finished product itself.

Increased Fluidity	Removal of inclusions makes the metal more fluid, resulting in easier mold fill, better cast structure, and better thin section castability.
Reduced Mold and Die Wear	Removal of inclusions and other nonmetallic debris from the melt reduces die soldering and mold-metal interaction, which degrades the mold surface and service life.
Longer Tool Life	Oxide as well as intermetallic inclusions create “hard spots” that damage tools in machining and finishing operations. Filtration reduces tool wear and increases productivity.
Fewer Rejects	Inclusions nucleate porosity, create hot tears during solidification, cause surface defects that mar appearance, and often reduce mechanical properties. In many cases, filtration cuts rejects from such causes to virtually zero. Improvements in yield to near 100% and reduced reject rates to at or near 0% are common.

 

Types of Inclusions and Their Origins

Inclusions show up as alumina, silica, intermetallic sludge compounds, and other refractory and ceramic hard particles. The come from many sources: dirty charge materials, tools, ingot, oxides, foundry sand debris on returns metalworking lubricant pigments from trim, gates and risers, machined scrap castings refractory wear debris from furnaces, ladles, and other molten metal handling vessels oxidation of aluminum, magnesium, and other reactive alloy elements in the melt itself sludging in die cast alloys (precipitation of intermetallic compounds at lower temperatures) fluxing salts and/or other metallurgical additives Good furnace practice helps minimize the generation and entrapment of inclusions, but good practice alone often is not enough. You usually need effective filtration to ensure quality.

 

Installation

Installing a large Vertical Gate Filter

The vertical Gate Filter may be supplied with /without lifting clamps for ease of handling and installation. The clamps are studded for thread/nut eye-hooks or other lift hardware. Jib hoist, crane, or slotted spanner bar may be used to hoist the filter into place. The VGF fits into slots or a channel in the refractory furnace sidewall. To minimize thermal gradients, such slots should be located as close as possible to, but not directly in, the heated hot zone of the furnace. Large archways should exist between the hot zone and the well. Direct filter exposure to flame impingement should be avoided in any gas-fired furnace. Often a fiber gasket is utilized on the edges of the filter to further ensure a good seal although it may not always be necessary. The VGF may also be installed into a furnace well without slots. In this case, compressible ceramic fiber rope is affixed to the perimeter of the filter. This allows a snug “seal fit” between the filter and the sidewall refractory, and takes up any irregularity to the gap. The Vertical Gate Filter may be installed either into an empty furnace, or into a furnace nearly full of molten metal! The following specific installation procedures are advisable: For optimum priming and to avoid thermal shock, the filter should be preheated to at least 400 degF (202 degC) for two hours. Do not exceed 1000degF (535degC). Skim the furnace (if full) just prior to filter installation & immerse the filter continuously & as quickly as safe handling will allow. Two inches of freeboard (exposed filter above the metal line) should be maintained. If greater, cover the filter with fiber blanket to avoid excessive heat loss through the filter.

 

Maintenance

Periodic, careful scraping or scarfing (with N2 or Ar) of oxide buildup on the inlet side of the filter will extend filter life. Avoid full thermal cycling, with excessive drawdown and refill, because solidified inclusions, and oxide buildup on and within the filter body, will not remelt out as the filter returns to normal operating temperature.

Availability

MetaullicsTM Vertical Gate Filters are available in a variety of shapes (square, rectangular, trapezoidal, circular) and many standard sizes. Usual thickness is 1 inch (25 mm). Any other sizes and shapes (rectangular, square, round) are possible up to 35” (889 mm) maximum dimension. Tapered sides can be supplied if desired. A nominal, one-time engineering charge accompanies an order for a custom size.

 

©2006 Metaullics Systems, a Division of Pyrotek

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