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Shaking Up the Process of Installing Refractories

Nov. 16, 2004
The process can be faster and easier, more consistent, and less expensive.

To speed and improve refractory installations, the vibrator is mounted to a bracket and refractory material is installed in a continuous layer to fill the inductor, with a temporary baffle if necessary to over-fill the space.

The Allied Minerals Electric Vibration System package.

The EVS vibratory device and mounting clamp.

Refractory installation on a 10-ton coreless induction furnace, with vibration at two levels.

Installing refractories in melting equipment is a common concern, but perhaps not the obvious point where metalcasters might target for process improvement. Think again.

A recently patented device for installing dry vibratable linings reduces installation time, labor, and overall cost because it does away with manual de-airing prior to form vibration.

The Electric Vibrating System developed by Allied Mineral Products is proven effective for induction furnaces, and recent applications with channel furnace inductors are demonstrating similar results. The installations are faster and more uniform, and the system delivers advantages in labor cost and worker safety, as well.

Dry vibratable monolithics are commonly — and effectively — used by metalcasters in place of other refractory forms, such as brick, castables, or wet-ram linings. There are a series of critical steps to the installation process, according to Allied Minerals' manager of product services, David C. Williams: controlling the refractory thickness, de-airing it, compacting it, and scoring it.

Typically, an electric vibration tamper or air-driven vibrator is used to compact the refractory, as the specific furnace demands. The electric vibration tamper is time-and labor-intensive, so it may not be suited to some inductor designs and larger furnaces. The success of the effort also depends on the skill of the installation crew. Air-driven vibrators can make the installation faster and/or simpler, but a consistent and clean source of thoroughly dry compressed air is needed to power the device.

Allied Minerals developed the Electric Vibration System (EVS) to eliminate airpressure and air-quality problems common in the operation of pneumatic or airpiston vibrators. According to Allied's Bill Opatt, the greatest advantage for furnace operators is the ability to install refractory into induction furnace sidewalls (coreless or channel induction furnaces) without the manual effort of de-airing and scoring the refractory material.

The system consists of an electric vibrator and vibrator control panel. The panel's main element is a variable-frequency drive that controls the output to the electric vibrator. It can be programmed to operate at various frequencies for a selected amount of time, and offers a digital output display that indicates vibrator operating status and drive output.

The VFD is available for low (200-240 V) and high voltage (380-480 V) applications. The control panel allows automatic or manual control of the vibrator, via frequency control and vibrator motor direction. A safety lock prevents opening the control panel while the unit is operating, and overload protection protects the vibrator. The panel is of " dusttight" (NEMA 12) so it may be mounted near the furnace or installation area.

The electric vibrator operates at multiple frequencies (0-6,500 rpm) and unbalance/amplitude to optimize refractory installations. During de-airing, the vibrator operates at a lower frequency (3,000-3,600 rpm, the high weight setting), to maximize material flow. Once de-airing is complete, the rotation is reversed so the vibrator runs in the low weight setting at high frequency (4,600-6,500 rpm) to achieve final compaction.

Refractory installation using the EVS is a four-stage process for coreless induction furnaces. First, the floor refractory is installed via electric tamper or a steel plate can be used in conjunction with the EVS.

Then, a metal form is lowered into the furnace and secured at the top to the furnace structure. Once the form is secure, the refractory can be added to the furnace sidewalls in one continuous layer. Bulk sized packaging makes for a quick and easy process.

For the last step, the electric vibrator is attached to the inside of the metal form at four contact points. Vibration is conducted on one or multiple levels depending upon furnace size. Additional refractory is added during vibration as the material is de-aired. As refractory is added, the vibrator is run in forward rotation at 3,600 rpm for five minutes while the refractory settles. Then, the vibrator is run in reverse rotation at 4,600 to 6,500 rpm for ten to fifteen minutes depending upon type of refractory. The vibrator may then be moved to additional levels as the prior steps are repeated. The dry vibratable refractory is de-aired during the forward operating phase, while compaction is achieved during the reverse action. The EVS can be programmed to operate automatically for this, or manually operated. Vibration frequency can be monitored during each stage.

Refractory installation using the EVS for channel furnace inductors is also a four-stage process, according to Opatt. First, the channel form is attached and secured to the inductor case. The bushings must be secured and the gap between the bushing(s) and inductor case must be sealed. (Allied explains that ceramic-fiber rope soaked in a mixture of sodium silicate and water mixture is preferred.) Any movement during vibration will halt the installation.

Next, once the inductor channel form and bushings are secured and sealed, the refractory can be added to the inductor case. The material is added in a continuous layer until the inductor is completely full, making certain that the layers are even and that material entirely fills the space.

In their reporting, Allied Mineral's Opatt and Williams emphasize that overfilling the inductor casing is important. "This can be achieved by using a temporary metal baffle or retainer around the top of the inductor casing. This will act as a reservoir for the dry vibratable as it settles/compacts during the de-airing and vibration sequences. The excess material can then be scraped away after vibration leaving a compact, level surface," they explain. A wet capping material may compensate if the casing is not overfilled. If so, the inductor should be filled and compacted to complete volume. A layer of refractory will be removed in preparation of the wet capping material.

Next, using brackets or clamps bolted or welded to the inductor casing, the EVS vibrator is mounted to the inductor casing. Bolt-on brackets are removable and can be mounted to multiple locations, depend on inductor size, inductor geometry, channelform composition, and refractory density.

In larger installations, the EVS vibrator can be attached to a metal melt-in channel form to ensure the refractory between the channel form and bushings is compacted.

Finally, the vibrator is mounted to the bracket. Refractory material is installed in a continuous layer to fill the inductor, with a temporary baffle if necessary to over-fill the space. The vibration sequence is similar for coreless induction furnaces. The only difference is vibration time.

In-plant operation of the EVS is demonstrating several advantages: it helps foundries achieve uniformly good installations. The electrical supply is constant thanks to the variable-frequency drive, resultingin predictable output and long service life.

Moreover, the quality of the installation is reliable and the labor cost is reduced significantly. Workplace health and safety improves, because physical labor is minimized, noise levels are reduced, and less dust is generated because no compressed air is involved.

Allied reports successful applications of the EVS with coreless and channel induction furnaces of various sizes and configurations. The various operating modes make it particularly adaptable.

Finally, while the initial cost of the EVS is higher than for vibrating tampers of pneumatic vibrators, the payback time is short due to the cost savings achieved in labor, installation time, and increased operating time.

A series of case studies to be cited in an upcoming report by Opatt and Williams will lay out the specific results from several EVS installations in different melt shop settings. The EVS has proven extremely successful for coreless induction furnace installations. The system has been on the market for four years with more than 150 units sold in more than 12 countries. In the meantime, the U.S. Commerce Dept. has already certified the effectiveness of the system with a patent for the installation process.