Dosing pump, furnace get to the bottom of aluminum oxides.

The European term "dose" means to deliver an exact quantity. Traditional dosing furnaces have been pressure pour furnaces, but five years ago, Stotek Danmark ApS, Naestved, Denmark (represented in North America by Meltech, Inc., Brookfield, Wis.), developed a different approach to aluminum melting and pouring. Frustrated with the limitations and problems associated with a pressure vessel, the firm developed the Dosotherm Furnace and Dosing Pump.

A simple, bottom filling crucible de sign had been around for decades. And although it could be used for transferring aluminum, it was very sensitive to changes in the bath depth and the quantity of metal dispensed wasn't accurate enough. Stotek overcame the limitations by developing and patenting a check valve in the fill port, making the crucible more robust and adding additional sensors. This dosing pump was incorporated in the Dosotherm Dosing Furnace, which is an unpressurized, reverberatory holding furnace. The furnace is filled via a teapot spout at the back, ensuring that most of the floating oxide and dross is contained and easily removed.

The holding chamber is fully enclosed with no gas exchange and consequently very high thermal efficiency, resulting in very low oxide formation. A large cleaning door ensures access with minimal thermal variation. Because the furnace is unpressurized, maintenance can be completed with out interrupting dosing.

The dosing pump is suspended in a fully-enclosed well at the front of the furnace. A vacuum is applied to the top of the pump and aluminum is drawn in from near the bottom of the furnace via the check valve. Electrodes in the cast iron lid sense when the pump is full and the vacuum is released. Excess metal drains back into the furnace, ensuring that the starting level is always constant.

Once receiving the signal to dose, nitrogen (regulated at low pressure) is applied to the pump, the check valve is forced closed and aluminum rises in the spout. An electrode senses when the dosing begins and a timer in the controlling PLC starts. The flow is regulated by time pressure and the volume is regulated by time. The time can be adjusted to 0.001 of a sec., ensuring accurate dosing, which is typically better than [+ or -] 1%.

A ceramic foam filter can be installed across the bottom of the pump, with both 20 PPI and 30 PPI filters available, eliminating most of the oxides and impurities in suspension. This, combined with the inert atmosphere inside the pump, ensures extremely clean metal.

The aluminum flows to the mold via an open stainless steel launder angled at 10-15 degrees. The flow is controlled to minimize turbulence, and because of the very short time that the aluminum is in the launder, oxidation, heat loss and gas pickup are minimal.

Apart from a wash-coat that is applied to the spout and launder each shift, regular maintenance consists of cleaning the metal surface and walls of the furnace once a week and lifting the top off the pump once a month. Filter life is normally 4-8 weeks (depending on volume and metal quality), and the ceramic pump body 6-18 months.

The thermal efficiency of the Dosotherm is typically about 80% better than an equivalent open-well furnace with a ladle, and maintenance, metal loss and consumable costs are considerably lower.

Applications include diecasting, permanent mold and automatic molding lines. Where required, a variable pressure regulator can be fitted so that pouring curve can be programmed The Dosotherm is mounted on a scissor jack so that the dose height can be adjusted and the furnace can be back tilted for emptying and alloy changes. A load cell is fitted and the volume of metal displayed on the PLC and in series of lights.

Two sizes of pump are available: 380 mm with a dosing range of 244 lbs. (1-20 kg) and 480 mm with a dosing range of 22-121 lbs. (10-55 kg).

Select No. 001 at www.moderncasting.com/info

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