The 'dos and don'ts' of melt deck safety.

Respect the forces at work in your induction melting operation and prevent accidents, situations, and procedures that put your workers at-risk.

With distressing regularity, the media report accidents in foundries, and, while this coverage is often sensational, there is little doubt of the seriousness of the incidents themselves. As we have come to expect, most of the incidents involve the "hot end" of our business - where metal is melted and poured. Sometimes there are injuries and even loss of life, and we are reminded that manufacturing, especially hot, heavy manufacturing, can be a dangerous activity. Hazards are everywhere in life, but metalcasting certainly has its share.

This article discusses the nature of some of these hazards in the melt shop and suggests preventive actions. More importantly, it encourages a state of mind designed to eliminate or minimize the hazards. Even though this article covers safety in the induction melting of cast iron, these suggestions pertain to other metals and melting equipment with equal force.

There is a concept frequently employed in the casualty insurance business known as the "named perils" clause. What this concept means, in effect, is simple: if the particular calamity that just occurred wasn't a circumstance specifically named on your policy (a "named peril"), you're not covered! However, in this article, "named perils" is extended to those all too familiar and often ignored hazards that metalcasters face every day.

The common named perils in a melting operation are:

* explosion - typically the kind that occurs when molten metal contacts water,

* fire - also caused by contact between molten metal and water, as well as other sources;

* electric shock - from low-voltage control circuits to main line megavoltage;

* blunt trauma - striking or being struck by falling or otherwise moving objects.

Certainly, there are others, but these are the big four. Unfortunately, a single unhappy event may involve more than one and possibly all of them at the same time.

Powerful Forces

There is a further expression that seems to apply here, drawn this time from the early days of aviation, that puts the topic in a proper perspective: "If you're not terrified, you really don't understand the situation."

There are enormous forces and energies concentrated in even the most modest melting plant, and they present very serious potential hazards to personnel and property. As an example, consider the powerful forces at work in a "minimal" melting plant with a single 9-ton, 3000 kW coreless furnace supplied with power through a single transformer and switchgear set - a typical setup. Consider that 3000 kW is equivalent to more than 4000 HP. In other words, this equipment consumes energy at a rate sufficient to lift itself and its contents vertically at 40 mph! There are some induction furnaces that are more than three times as powerful, and some arc furnaces easily exceed 100,000 kW.

All furnace manufacturers are dedicated to ensuring that their products are as safe as they can be. When new means are found to make them even safer, they strive to incorporate them into their products. However, those that work with furnaces should respect their power. This is energy not to be trifled with and certainly most intelligent melters never do. But we - all of us are not always as thoughtful and alert as we ought to be. The "cardinal rules" of electric melting are:

* emergencies always occur at inopportune times;

* uninspected furnace pits always have water in them;

* the molten bath may be at high voltage.

Safety 'Punch List'

With these rules in mind, re-examine your melting operation, and consider this "punch list" of safety dos and don'ts for the melt shop.

1 In the design stage of a new melting plant and over and above the bare-bones of what the manufacturer and/or construction contractor provide, add features and details to minimize hazards. By no means are the following recommendations restricted to new installations only - all of the suggestions, with varying ease, can be added and adapted to existing facilities:

* The economics of foundry construction often require that induction furnaces be placed in pits with even deeper runout pits in front of them. This setup is required even where the furnaces are at grade level. Provide bright lighting in the runout pits, illuminate all the corners, paint the walls and floors white or another light color and plan to leave the lights on continuously. This can permit a quick inspection every time the furnace is tapped. You won't know you have a water or hydraulic leak if you can't see it.

* Install a protected try-well at the sump or lowest point of the run-out pit [ILLUSTRATION FOR FIGURE 1 OMITTED]. Inspected frequently, this feature can give advance warning of a hydraulic fluid or cooling water leak or ground water seepage. Consider that many, if not most, furnace pits extend below the local water table for at least part of the year. In time, concrete may crack, and leaks can develop. Don't rely on float switches to tell you when there's a problem. White plastic pipe is recommended here so that a flashlight directed down the bore will show easily whether fluids are accumulating. Alternatively, some sort of plumb bob also will work.

* Determine which furnace pits and enclosures are to contain furnaces, which switchgear vaults are to hold switchgear and which control rooms will be used to control the melting area as soon as possible. Resist auxiliary uses for these spaces.

* In place of the customary reinforced rubber hydraulic hose serving the furnace tilt cylinders, substitute aircraft-quality armored hose. This hose generally is covered with a basket-weave of stainless steel wire and can withstand contact with molten metal longer than bare rubber can - perhaps long enough to empty a leaking furnace. Note that modern hydraulic fluids do not bum in the usual sense, but they do certainly smoke - thick, acrid smoke sometimes so voluminous that it can completely prevent access to the furnace or controls at critical times - just the sort of thing that can turn a bad day into a bad month.

* Correct all tripping and slipping hazards on furnace decks and stairs gratings that don't quite fit, old weld beads, gouged or spalled concrete, etc. Remember that furnace operators wear tinted face shields and glasses and their eyes are often "light-struck" when dealing with open furnaces.

* Plan for more than "just sufficient" general lighting. What is adequate at plant start up can quickly degrade - anticipate that fixture cleaning and relamping often will be delayed.

* Ensure that all ladle monorail switches and rail runs are fitted with adequate safety cables. Ladle rail systems make excellent fatigue test rigs. Think of the impact loads imposed on welds and rail supports thousands of times a day as multi-wheel ladle trolleys clatter across the gaps and joints with a full ladle swinging below. A melt shop tapping 80 ton/shift into 400-lb ladles hung from six-wheel trolleys will generate 250,000 impact loads/joint in a 10-week shift. Minimize the consequences of a weld or fastener failure.

2 Plan for safe operations at all times. Don't forget that sometimes things do go wrong, and in the heat of the moment safety may be neglected. Very minor incidents often can mushroom into disasters when safety is set aside.

* Establish, post, and enforce operating and safety procedures. Review them frequently and regularly. Don't wait until after something has happened. Anticipate instead, and don't permit things to happen.

* Identify and prominently tag all furnace cooling water and hydraulic fluid valves. Someday, in the heat of an emergency, everything may depend on an untrained person finding and closing the right valve.

* Severely limit access to furnace controls and switchgears. These are not places for the idle and curious.

* Establish control room and switchgear vault fire procedures. Remember that plant, municipal or volunteer fire personnel may suddenly arrive on the scene and may be entirely unaware of the hazards awaiting them. Establish a firm procedure - what is to be locked out, by whom, and before anyone enters the control rooms and vaults or otherwise begins firefighting efforts.

* Train, train, train - not just for the routine stuff, but for the bad days too, and not just for new hires either - keep everyone involved. Hold fire drills, and simulate other emergencies. See what happens.

3 Always operate in a way that minimizes hazards.

* Never permit operators to slag a furnace, use temperature lances or sample spoons or otherwise allow any device, hand tool or anything to contact the furnace charge, whether solid or molten, unless the power is off [ILLUSTRATION FOR FIGURE 2 OMITTED]! The furnace bath could be at maximum furnace voltage - an unquestionably lethal situation.

* Recognizing the possibility for direct power coil shorts at maximum voltage, the furnace manufacturers uniformly design their melters to minimize the likelihood of the shorts and equip them with elaborate, redundant safety devices to automatically interrupt power and sound alarms if they do happen. Nevertheless, persistent, direct shorts from the power coil to the furnace contents have occurred in the past, so don't rely on blind faith that they will never happen again.

* Remember that should charge buckets, alloy chutes, mechanical deslaggers, etc. contact a shorted bath, they also will be at high voltage.

* Place no reliance on "non-conductive" tool handles, etc. Just as there are no perfect conductors, there are no perfect insulators either. Even the thinnest film of dirt or graphite on the tool could present a high-voltage hazard.

* If need be (or if in doubt), dry the metallic charge, and don't confuse heating with drying. Some charge materials can harbor hidden fluids. Dry them thoroughly. Remember that wet charge materials are the number one cause of severe incidents in melting. Likewise, consider all bagged or palletized charge materials to be wet unless proven otherwise.

4 Run a tight ship, and practice intelligent housekeeping.

* Keep floors and decks swept clean of spilled slag conditioner and granulated alloys. Better yet, minimize spillage of these materials - and the possibility of splashing molten iron - by using chutes or other devices to concentrate and constrain them.

* Keep combustible materials to a minimum. As examples, store drums of hydraulic fluid away from controls/switchgears, even if inconvenient. Keep compressed gas cylinders remote from hot metal. If using a pure magnesium-treatment process, allow only the minimum amount of stored gas near sources of ignition. Promptly dispose of empty combustible containers such as pallets and sacks.

* Keep deck and stair railings in good repair. Think about having to use them in pitch-dark or smoky conditions. In anticipation of these conditions, many operators paint railings and stair treads white.

* Blow down trusses and beams at regular intervals. Foundry dust is generally combustible and is often implicated in intense chain-reaction explosions that follow the one that shook down the dust.

* Keep unnecessary items off the deck. In the dark, anything can be a tripping hazard.

5 Finally, critically inspect equipment at regular intervals - daily, if need be. When working from written inspection procedures, cover all aspects of safety with particular attention to the following:

* Confirm that furnace and run-out pits are indeed dry. Perhaps the major contributing factor to explosions and fires in foundries is the presence of water or oil in furnace pits.

* Inspect and test interlocks. Make sure they function as intended.

* Inspect all hoists, trolleys, hoist brakes, cables and hooks.

Above all, maintain a wary and suspicious attitude. Don't assume that because something has never happened, it never will. That attitude can be the final ingredient in a recipe for disaster. Everyone hopes for good luck, but the intelligent and vigilant ensure it.

RELATED ARTICLE: What to Do When Your Furnace 'Bridges'

When cold charge material in the top portion of the furnace does not come in contact with the molten metal at the bottom of the furnace, an extremely dangerous condition, known as "bridging," may exist [ILLUSTRATION FOR FIGURE 1 OMITTED]. When bridging occurs, the molten metal, which is exposed to the full melting power of the furnace, may superheat. This will occur very rapidly in an induction furnace and, combined with excessive stirring in the bottom of the furnace, may cause rapid lining erosion or complete refractory failure.

Without immediate attention to a bridging condition, a runout may occur. If the molten metal exits through the bottom of the furnace, it can cause a fire in the pit area with a loss of hydraulics, control power and water cooling. If the molten metal melts through the furnace coil and water contacts the metal, it will produce a powerful explosion.

Bridging may occur in any induction furnace, and all furnace operators must be able to recognize bridging and its dangers. The clearest warning sign that bridging has occurred is that the melt is taking longer than calculated. If this happens, power must be turned off immediately until the bath temperature is known. If the bridge has completely sealed off the top of the furnace, pressure may build up between the molten metal and the bridge. In this situation, it's safest to allow the molten metal to freeze.

If the bridge has not sealed the top of the furnace, the furnace may be tilted in an attempt to melt out the bridge [ILLUSTRATION FOR FIGURE 2 OMITTED]. Put a ladle in front of the furnace to catch any metal that may spill out, then tilt (approximately 45 [degrees]) the furnace carefully until the molten metal touches the bridged material. The molten metal should melt a hole in the bridge.

At this point, power must be turned off and all unnecessary personnel should be kept away from the furnace. Do not stand in front of the furnace, and under no circumstances should an oxygen lance or burning bar be used to cut through the bridge.

After melting a hole through the bridge, return the furnace to the upright position, and check the temperature to make sure the molten metal is not superheated. Begin adding charge through the hole to raise the bath level, bringing the molten metal into contact with the bridge and melting it into the bath. Adding charge will cool the molten bath, and you may have to turn power back on to maintain the proper pouring temperature.

Do not turn power on if:

* there has been a ground leak detector trip, indicating metal penetration to the coil;

* the variable frequency power supply has been running at a higher-than-normal frequency or the fixed frequency power supply required more capacitors than normal to be switched in, indicating an eroded lining;

* there is excessive surface slag, indicating serious lining damage;

* the water temperature in the coil is higher than normal.

Each of these conditions indicates that molten metal may be near the coil and requires an immediate evacuation of the area until all of the metal in the furnace has solidified.

If none of these conditions exist, melting the bridge can continue. Once the bridge has been melted away, the furnace should be poured empty as soon as possible so that the lining can be examined for any signs of damage. If there is any doubt about the integrity of the lining, replace it. - John McKelvie, Inductotherm, Rancocas, New Jersey