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Microwave Reclamation of

Casting Sand M

Microwave technology could offer the industry an energy-efficient,


icrowave technol- ogy has been used in many indus- tries, most notably

textiles, drying and food processing. Until recently microwave technology has not been largely investigated in solving high temperature industrial processing, such as reclamation of foundry sand, which has become an important consideration in the operat- ing costs for the metalcasting industry in recent years. Microwave technol- ogy potentially offers the industry an energy-efficient, low-emission, small- footprint system for sand reclamation as microwaves primarily interact with the sand constituents while leaving the sand relatively cool. A rotary kiln prototype system

for metalcasting sand reclamation is being tested at Midwest Metal Prod- ucts (MMP), Winona, Minnesota, for nobake sand reclamation and by Grede-St. Cloud, St. Cloud, Min- nesota, for green sand reclamation. It is 2 ft. (0.61m) in diameter and 12 ft. (3.66m) in length with an insulated hot processing section that is 1 ft. (0.301m) in diameter and 6 ft. long, and uses 10 kW microwave energy. Preliminary data shows that achiev-

able loss on ignition (LOI) levels are less than 0.1 for nobake sand with the actual sand temperatures as low as 392F (200C). In the case of green sand, prelimi- nary data shows a Methylene Blue-

36 | MODERN CASTING April 2016 Clay value of 76 (and LOI of 3.0).

Setting The Scene MMP is a steel and iron facility that employs 45 people. All molding is done in nobake sand. Cores are all made in plant and are airset, phenolic urethane coldbox, shell, and a small amount of oil sand. Melting is accom- plished using an induction furnace system with a batch size at about 2,800 lbs. (1,270 kg.). Te product size offering is governed by this molten metal batch size with castings ranging from a couple of pounds to just under 1,900 lbs. (861.8 kg). Sand reclaiming at both MMP and in the metalcasting industry is a long- standing practice. Most operations have employed it from both practical and cost savings aspects. MMP has employed mechanical

reclamation, which consists of a rotary drum with a series of dams to retain sand as it rotates. Te sand is broken down by

contact with itself and is essentially ground down to grain size. At that size, it passes through the last dam as well as a screen for a final sort of larger pieces and any hard contaminants that do not break down in the fairly gentle grinding process. Te waste from this operation

includes both fine sand grains and any resin dust or other lightweight mate- rial and is removed via dust collection, leaving a working mix of reclaimed

grains for reuse in the molding and core process. Tis reclaimed sand has both

positive and negative properties when used to create new molds or cores for part production. Tese effects are caused by several aspects of the reclaimed material – it carries some amount of residual resin coating, a significant level of agglomerated grains, and a significant LOI from the retained resin. Due to the retained resin and the

problems it can bring, MMP pur- chases some virgin sand to: • Blend with the reclaim to improve properties with more clean grain bonds.

• Use for some molds or cores that have better results for dimensions- strength.

• Improve metal penetration. Te need for this “new sand”

along with the disposal-related costs and competition for material with other users (the fracking industry in particular) pushed along the thermal reclamation development and installa- tion at many facilities. Termal reclamation typically

involves radiant metalcasting facility heating of both the material and usu- ally the recycling vessel. Tis approach has been proven but the process is a considerable energy consumer. Since the device is heated to impart the temperature to the sand and resin, these units are best run as a 24-7 con-

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