For metalcasters, advances in technology and engineering standards may be difficult to counter as staffs grow smaller and expertise gets more scarce. But, for melting and other applications, foundries need effective and reliable cranes. We found an expert to update us on standards and trends for hot-metal cranes. Steve McCormick, P.E., is the director of purchasing and quality for Morris Material Handling.
Aren’t cranes for foundries the same as any other crane? What sets them apart?
Hot-metal service cranes and hoists have a long history in the U.S., and they are critical to industrial production in this country since steel and other metals are central to the needs of domestic manufacturing. In our case, Morris Material Handling and our P&H brand of equipment we have made foundry-rated and -specified cranes since the 1940s. Throughout this time, specific hot-metal industrial standards have been developed to ensure consistency in design and manufacturing, and to increase productivity and safe operation with these cranes.
These types of cranes can vary greatly in configuration, lifting capacity, and sophistication. Common designs can be as simple as a five-ton monorail wire hoist, or as complex as a custom-designed double girder overhead ladle crane capable of lifting 400 tons of molten steel for large, integrated mills. The common details of these two extremes are the use of consistent engineering, manufacturing, and the application of “hot-metal” standards.
Some of these standards are:
- ANSI Z241.2 1999, American National Standard. Safety requirements for melting and pouring of metals in the metalcasting industry.
- HMI (Hoist Manufacturers Institute) Hoist Inspection and Hoist Maintenance Personnel Manual.
- ASME HST-4-1999 Performance Standard for Overhead Electric Wire Rope Hoists.
- ASME B30.16-1998 Safety Standard, Overhead Hoists (Underhung).
- CMAA (Crane Manufacturers Assn. of America) Specification No.70, Revised 2000, Specification for Top Running Bridge and Gantry Multiple Girder Electric Overhead Traveling Cranes.
What are the most common cranes now in use for foundries, and their applications?
Generally, we see requirements for units that carry molten metal. A subset of this category of machines are the ladle cranes, which also pour molten metal, by tipping or upending the ladle. This can be a small manually operated unit with a hand wheel used by a single operator to pour material into sand molds. On the high end, we have large steel mill cranes processing a complete “melt” of steel for ingot, bloom, or slab casting.
Scrap-handling units are commonly used, too. These are process cranes used to re-handle scrap steel. Many of these are dedicated magnet cranes. An electromagnet is the quickest and most efficient way to lift and move scrap for processing.
Charge cranes are a special type of scrap handler used specifically to load a melting furnace. These, in the strictest sense, are not hot-metal cranes but in many cases the customer specifies the same stringent requirements as “hot metal” units.
Shipping is at the other end of the metal production cycle. “Shipping” cranes again are not “hot-metal” cranes, but they tend to be very high duty units. Many are multiple-shift, constant service machines with H4 (hoist rating), or crane class E or F duty-class ratings.
One very specialized unit is what is called a hot-metal carrier. These are monorail-supported units that are used in continuous casting operations.
A good example of this type of operation is an iron engine block manufacturing line. The volume of production is high enough to require custom-designed and -built cranes. Many of these are “cab on,” with a dedicated operator on board to drive the unit from furnace and molding line (though there has been recent demand for automated carriers.) One style allows the operator to raise and lower himself along with the ladle. Others keep the operator at one level and the ladle travels separately. These are normally based around a commercially available wire-rope hoist unit. After the proper size is selected a special-purpose structure, transport, and tilting mechanism is designed around the basic monorail hoist.
How is automation used?
Typically automation is used to increase the speed of the crane, improve its productivity, and make the operation safer.
Automated hot-metal carriers moves the operator away from the hot-metal ladle. Another application of crane automation is to achieve precision placement of material. Automation allows the crane to place objects with accuracy that is more consistent than any human operator can be achieved.
What are the typical operating conditions, and how do these affect designs?
The operating conditions tend to be very arduous. Foundries are very hot, and dirty, and the demands of the process indicate a high duty cycle. For that reason, the machinery is designed to be structurally sound and very sturdy. Electrical controls are designed to be exposed to high temperatures, or it’s designed with special enclosures that are hardened and air-conditioned, to counter the high heat and dirty conditions.
Are there common maintenance and repair problems with foundry cranes?
The problems with maintenance are related to high use, dirty conditions, and high temperatures. Controls are easily damaged; wire ropes need special attention to keep them clean and lubricated. Powertrain oil needs to be replaced as necessary to eliminate airborne debris and to counter the effects of high heat; a synthetic oil is a good choice. Air conditioning for onboard operators must always be in good working condition. This is not for comfort, but rather to prevent the operator from suffering any heat-related illness.
What is a standard inspection program for foundry cranes?
Crane inspections fall into two categories: Frequent and periodic. Frequent may mean as often as daily visual inspections by the operator. A skilled maintenance person who has been specially trained normally performs periodic inspections. The specifics of inspection programs vary according to the crane but the standards listed above show specifics. The OEM supplies maintenance manuals with each machine. Also, manufacturers offer training courses that will teach the proper inspection methods. We also offer a comprehensive inspection service for this machinery.
What sort of training is required to operate these systems?
Training is very important in order to make sure the operator and others in the area are safe. The OEM supplies operators’ manuals with each machine. They should be read thoroughly and understood by the operators prior to operating the crane. The manufacturers also offer training courses. It is highly recommended that operators be re-certified over a specific time period: Yearly (re)certification is common.
How effective are crane modernization or upgrade projects?
A good portion of the work done by OEMs is related to modernizations. We have a complete group of engineers and sales professionals to handle this work. Cranes can last a very long time — over 40 years is very common. The structures may be sound, but the motors, wheels, and gearboxes will wear out. Control technology changes very rapidly. These new improvements can radically enhance the productivity of these older cranes. The payback on these projects can be much quicker than a total crane replacement.
What are your recommendations for the best available equipment and technologies for the types of cranes commonly used in foundries?
- Dual brakes (load brake and electric gearcase brake) or two electric brakes. A load brake cannot be used as long as ladle and below-the-hook devices are equal to or greater than 10% of the rated load of the hoist;
- Heat shield — hoist motor, hoist gearcase, control enclosure, or any other sensitive electrical device that cannot withstand the design ambient. The design criteria provide a 1-in. air gap between device and shield, to allow airflow;
- Heat shield — bottom block. This is an anti-spatter shield only, and it’s used to protect wire rope entryways, sheave, and hook bearings. There is no design intent for ambient protection with this shield;
- High-temperature wiring (SMRL). Standard “Sealcon” flex tubing is good to 240°F. Hard piped conduit is preferred, wherever possible;
- Power circuit limit switches as actuated by the lifting block offer better solutions over control circuit limit switches;
- 8:1 safety factor is needed for wire ropes;
- Geared limit switches are needed as a primary upper and lower limit;
- If safety warning equipment is asked for, the standards are blue strobe for transport and a warning horn for pouring;
- Redundant kingpins are required on threaded pins in tension for monorail hot-metal carriers. A good alternative is to use non threaded pins;
- Safety chains should be used on ladle guides;
- Cab air conditioning is needed in high-ambient conditions.