|Industrial robots are some of the most advanced tools for skimming slag. |
Spurred by the widespread use of batch melting, charging systems for induction furnaces represent a rapidly expanding use of automated material handling equipment in modern foundries. As induction furnaces become more powerful and melting times become even shorter, only automated charging systems are able to supply the metal required for melting. Manual charging, magnets or charge buckets simply cannot keep pace with a large induction furnace able to melt a full charge in less than 30 minutes.
Automated charging systems are designed to deliver charge materials to the furnace quickly, maximizing use of the melting system. They also permit manpower to be used more efficiently, reducing labor costs. The enhancement of worker safety is another important reason for the growth in automated charging systems associated with induction furnaces. Many serious accidents have occurred during manual furnace charging, when foundry workers were close to the molten bath.
When linked to a melt shop computer control system and a weigh system for accurate weight data, automated charging operations can be designed to incorporate the remotely controlled assembly of charge materials to match a specific metallurgical recipe.
Using drying and preheating systems and remotely operated charging systems can reduce furnace-charging accidents significantly. Water and molten metal are an explosive combination. Any moisture introduced into a molten bath will cause molten metal to instantaneously erupt from the furnace with explosive force and speed. The most common way water gets into the molten metal is through wet or damp charge materials. The best preventive measure is a charge drying or preheating system.
Because today’s high-power density batch melting systems melt the charge so rapidly, they have driven the development of computerized melting operation control systems designed both to provide precise control of the melting process for enhanced quality and to reduce the risk of accidental superheating.
Some of these systems operate on special computers; some, like Inductotherm’s Melt-Manager® Plus™, are built into the melting equipment itself; and some are PC based, including Inductotherm’s Meltminder® 200™ system running under Windows®. This Windows-based system offers the full advantages of the Windows operating system for customizing reports and interfacing to other applications.
Batch melting is ideal for computerized control. A typical control system uses the weight of the furnace charge, either from a furnace weighing system or as entered by the operator; the heat content of the metal; and the desired pouring temperature to automatically calculate the kilowatt hours needed to complete the melt.
It then turns off the system or drops to holding power when the melt is complete. Bath temperature readings are transmitted from an immersion dip thermocouple to the computer to further enhance accuracy.
This precise melting control optimizes power usage by minimizing temperature overshooting, saves time by reducing frequent temperature checks and enhances safety by reducing the chance of accidental superheating of the bath, something which can happen very quickly in a high power-density system and which can cause lining failure.
The most advanced foundry melting automation systems also provide fully programmable control of sintering and the ability to schedule and control furnace cold-start procedures. In addition to operational control, computerized melting systems can offer real-time information about system diagnostics and operation.
System diagnostic checks are an important part of this information. Some technologically advanced systems are able to identify specific problems before any power is applied, protecting equipment from damage. Information from the computer can help the furnace operator keep track of lining condition, an important safety consideration.
Because digital information can be communicated and shared easily by a variety of systems, foundry digital control systems can link and control many pieces of equipment. These include charging systems, weighing systems, demand controllers, temperature measurement devices and spectrometers — to name just a few being linked today. Typically, this can be done with just a cable containing a pair of control wires, plus power and shielding. This contrasts to complex cabling required for non-digital control systems.
You also can link your induction-power supply to several remote control stations. You can store important operational information on your melt shop computer, as well as on your company’s mainframe computer, and coordinate charge makeup with melting operations and even with production much further down the line.
Unlike cupolas and arc furnaces, induction furnaces themselves produce no smoke or fumes. However, the charge materials being melted can generate undesirable emissions. These can be as simple as smoke or dust from oily or dirty scrap. Or, the emissions can be the inevitable by-products of melting certain metals. To capture smoke and other fumes associated with melting, induction furnaces can be equipped with highly effective fume collection hoods with integral furnace lids.
Fume collection systems can help foundries meet federal MACT (Maximum Achievable Control Technology) emission standards. These covers can be designed to operate effectively both when closed and when open for charging or back-slagging. They also can be designed to be compatible with a wide variety of automated charging systems to capture fumes effectively while charging.
As induction furnaces grow larger and faster, efficient slag removal becomes more difficult. To be effective, the furnace must allow enough reverse tilt so that sufficient bath-surface area is exposed and at the proper height in relation to the rear slag spout. Because of varying metal levels in any operation, a back-slagging furnace equipped with separate cylinders and an additional furnace frame allows up to a 33° reverse tilt for slagging.
This allows the furnace operator or industrial robot to remove all the slag from the furnace directly into the slag cart in a quick and efficient manner. The additional furnace frame allows a slag cart to be positioned under the rear slag spout of a high furnace hearth. This dedicated back-slagging system is more effective than furnace back tilting, which uses only the forward tilting cylinders in a single furnace frame and has a lower furnace hearth in relationship to the melt deck. Such arrangements will restrict the back-tilt to 10 or 12°.
This may mean that it is more difficult to reach the metal bath or utilize a slag cart under the rear spout, resulting in dragging the slag on the melt deck before lifting into a slag hopper. For most applications, furnaces of 6 tons and larger should include back-slagging.
Mechanized and automated slag removal systems also are available to efficiently remove slag from large furnaces. These can be as simple as mechanical clamshell slag skimmers or as complex as industrial robots. These systems are particularly useful where large amounts of slag accumulate due to the charge materials used, process factors or the slagging interval. Using a mechanized slag skimming device or industrial robot can greatly speed slag removal from the bath, reducing production downtime and labor costs.
Push-out lining systems will benefit large coreless induction furnaces. These systems generally consist of a moveable block in the bottom of the furnace and a hydraulic cylinder. When a lining is to be replaced, the furnace is tilted to 90° and the cylinder is attached to the furnace to push the block to the front of the furnace, with the old lining ahead of it.
When the old lining drops away into a waste bin, the pusher-block is returned to the bottom of the furnace that is then restored to an upright position for relining. The advantages offered by these systems include the speed of lining removal, fewer man-hours and reduced silica dust exposure for personnel.
Refractory wear monitoring systems help determine when a furnace lining requires replacement. This improves your knowledge of refractory wear in an induction furnace.
Automatic pouring systems are available to complement these tools, and allow pouring to keep pace with the fastest molding machines, reduce labor requirements, and enhance casting quality with accurate and repeatable pours.
In summary, remotely operated charging systems are assembling on-specification metal batches, speeding furnace charging, and increasing worker safety. Melt shop computer controls assist the furnace operator in running the melt deck systems with more precise control, saving time and energy and maintaining key operational data. Automated slag removal devices reduce labor requirements and increase the effectiveness of removing slag from large furnaces. Lining push-out systems reduce the downtime required for lining replacement.
The automated foundry melt shop of tomorrow? With the help of various tools, it’s here today, already running and producing the cost savings, quality improvements, safer work environment and productivity gains that will mark this century’s first decade.
|High-power density batch melting has driven the development of computerized melting controls, which enhance melting performance and reduce the risk of superheating. |
Emad Tabatabaei is the Director of Technology for Inductotherm Corp.