The information on this page is from "Ladle Relining Lift Equipment-Ergonomic and Technical Design Considerations" by Kelly S. Chadwick and Gary G. Royer.

Ladle Lift Design Considerations

The following section is provided for steel mill personnel as a layman's guide to the various powered ladle lift design specifications and options that should be considered when working with a lift supplier.

Ladle sizes suited to the use of powered lift devices

A two-stage scissor lift is a commonly used lift style for the ladle rebricking process. This type of lift features two sets of scissors one atop the other, and provides an ergonomic bricking range from approximately 5 feet above the refractory base to 13 feet or more. The low end of this range is based on an approximate collapsed lift height of 2 feet plus the roughly 3 feet required to reach the waist height of a typical worker standing on the lift. The upper range of the lift's vertical travel is determined by the diameter of the ladle at its base: the greater the diameter, the longer the scissors can be and the higher the lift can travel.

Figure 3 shows a typical two-stage lift inside a ladle in both the fully collapsed and fully raised positions

The diameter of the ladle at the base in Figure 3, from brick face to brick face, is 96". An allowance of 3" between the lift's circumference and the wall face results in a maximum lift platform diameter of 90". At this diameter, the maximum vertical travel of the lift is 96" measured from the top of the collapsed lift to the top of the fully raised platform.

It should be noted that ladles smaller at the base than the example in Figure 3 may be suitable for a powered lift device however a different number of scissor stages may be required depending on the depth of the ladle. Your lift manufacturer should have the engineering expertise to advise you on the lifting device best suited for your particular ladle.

Ladles measuring 71" or less from the top of the ladle to the top of the refractory base are not suitable for powered lifting devices for practical reasons. The height of the collapsed lift is often enough of a boost to the worker that no additional elevating is required. Therefore, the use of a stationary "pie" would be a more cost effective solution for ladles of minimal depth.

Customizing Top Platform to the Ladle

To keep the amount of stretching and reaching by the refractory masons minimized as much as possible during the ladle rebricking process, it is important to keep the lift as close to the brick face as possible. For this reason, the top platform of the lift should be customized to fit the exact shape and size of the ladles being serviced. When the collapsed lift is placed via overhead crane into the ladle, the top of the collapsed lift platform should be within 3" of the refractory face around the full circumference of the lift.

Since most refractory ladles are tapered with the narrowest diameter at the base of the ladle, the distance from the edge of the lift to the brick face increases as the workers travel upwards (see measurement "x" in Figure 3). Platform extensions of various types have been tried in the field to help narrow the gap between the lift platform and the brick face in the upper work zones of the ladle with mixed results. A frank discussion with your lift manufacturer of the extension options available - including sliders, fold-downs, clipons, etc. - is recommended.

Other safety recommendations for the design of the top platform include a toe plate around the edge of the platform and anti-slip provisions. The toe plate is recommended so that the refractory masons have a tactile warning of where the edge of the platform is and to prevent tools and debris from being brushed or kicked off the platform. An anti-slip surface such as checker or diamond plate on the platform is also strongly recommended to prevent accidental slips and falls.

Lift Actuation - Why Hydraulic Scissor Lifts are Recommended

Hydraulically actuated scissor lifts are the recommended lift solution for ladle rebricking applications for several reasons. In terms of lift style, scissors are the optimal design for this application (as opposed to a single or multi-post design) for the simple reason that a lift actuated from below the platform provides unobstructed 360° access to the bricking area. Post lifts would by nature have one or more posts sticking above the platform during most of the lift's travel that would partially obstruct access to the work area.

In terms of lift actuation, hydraulic is superior to both mechanical (usually screw) and pneumatic compressed air) actuation options for ladle rebricking. The two most important considerations for a ladle rebricking lift are lift low / collapsed height and cost. Secondary considerations include the potential for actuator contamination and ease of maintenance.

Lift low height

When comparing lifts with the same platform size, a hydraulically actuated lift offers a lower collapsed lift height than a mechanically or pneumatically actuated device. This is primarily because the power source for a hydraulic actuator need not be attached directly to the actuator: it can be placed at a distance within the lift base frame at a point that allows the lowest collapsed lift height possible. A mechanical actuator requires the power source to be directly attached thereby increasing the collapsed height of the same lift. A pneumatic lift's low height is not affected by the physical presence of a power source but by its operating pressure. Since the operating pressure (psi) of compressed air is approximately 20 times lower than that of a hydraulic actuator, a cylinder with a bore 4.5 times larger than the one required for a hydraulic lift of the same capacity must be used. This increase in cylinder size translates into an increased lift low height. Minimizing lift low height is important for maximizing the useful bricking range of the lift.

Cost

At the lifting capacity typically required for a ladle rebricking operation (roughly 8,000 to 12,000 lbs.), hydraulic actuation is the most cost effective of the three actuation options. Pneumatic actuation would be second due to increased costs associated with the larger cylinders required. Mechanical actuation would be the most expensive option due in large part to the cost of the drive-line.

Potential for Contamination of Actuator

Both hydraulic and pneumatic actuators are by design better sealed against contamination from dust and debris than mechanical devices. Essentially the rod is cleaned of debris each time it moves into and back out of the tightly sealed cylinder used in both hydraulic and pneumatic applications. Mechanical actuators are typically protected from debris by bellows boots. The problem with bellows is that they require air movement into and out of the actuator area each time the bellow is stretched and then compressed with the motion of the lift. Although air filters are typically incorporated in the bellows to prevent contamination, the filters may frequently become blocked with debris and require manual cleaning. In some cases, workers will remove the filters completely due to frustration with the regular cleaning required in particularly contaminated work environments. Unfortunately, this leads to contamination of the actuator which reduces its lifespan and increases the costs associated with spare parts, downtime, and maintenance over the life of the lift. With the significant amount of dry and wet mortar being dripped onto the lifts, complications from contamination should be a consideration.

Maintainability

Of the three actuation types, hydraulic has the potential for requiring the least amount of maintenance. Hydraulic lifts can be designed using sealed for life bearings or bushings resulting in a lubrication free device. The frequency of lubrication for pneumatic lifts is determined by the quality of the compressed air being used to actuate the lift. Finally, mechanical lifts have parts which require periodic lubrication making them the lift type requiring the most maintenance.

Further Recommendations

Having made the case for hydraulic actuation, it is further recommended that a discussion occur between the lift purchaser and his supplier regarding the type of hydraulic fluid to be used in the lift. Often times it is possible (and desirable from a practical standpoint) to design the hydraulic lift to utilize a fluid already cleared for use within the purchaser's steel mill.

Capacity

The capacities of both the personnel lift and the brick lift are an important consideration when specifying a powered lifting device for ladle rebricking. The capacity of the primary lift should account for:

• the combined weight of the maximum number of brick pallet(s) piled simultaneously on the lift plus
• the combined weight of the maximum number of personnel working on the lift at any one time plus
• the weight of the brick lift (if used) plus
• the weight of mortar and tools used onboard the lift.
  Depending on your lift manufacturer, they may build to suit your exact capacity requirement or they may recommend one of several standard ladle lift designs with a capacity adequate to cover your needs.

To calculate the capacity requirement for your brick lift, determine the weight of the largest brick load to be used on the lift at any time during a typical rebricking process including the pallet(s). Add to that weight any other tools or supplies typically stored on top of the brick pallet(s).

It is recommended that when making any lift capacity calculations, any potential capacity changes in the future should be taken into careful consideration in order to extend the useful life of your lift equipment.

Durability of Design

The harsh working conditions of the average steel mill require that equipment built for such an environment be durable and rugged. A powered lift must be designed to endure not only the jarring and bumping encountered while being moved into and out of ladles via overhead devices but also the impact that occurs when pallets of bricks are being loaded onto the lift. Such a lift must also be able to operate dependably in an environment where wet and dry mortar is routinely being dripped or chipped onto the equipment.

Of primary importance is how the main platform on the lift is engineered. Platforms may come as a plate or as an engineered platform. A plate is described as a flat disc of metal. An engineered platform is best described as a plate with tubular steel supports welded to the underside. This extra structural support can handle the impact and concentrated point loading of brick pallets better than a plate which may deform under the repetitive stress of such loading.

The use of metal piping for hydraulic fluids are important for avoiding punctures, breaks and the resulting hydraulic fluid leaks which can lead to lift failure, downtime and repairs.

Leveling Capability

Depending on the requirements in each steel mill, leveling devices may or may not be required. If, for example, the powered lift is to be used during slag relines, where the base of the ladle may be uneven due to previous pours, a leveling feature may be very desirable. In mills using precast bottoms in their ladles, leveling may not be an issue. However, a lack of leveling devices may limit the future usefulness of the powered lift. Consideration of long term needs is again recommended when steel mills make the decision on whether or not to include leveling devices.

If leveling capability is requested of the lift manufacturer, leveling should occur at the base of the lift using a minimum of three but preferably four leveling devices. Four devices improve overall weight distribution and load handling stability. Furthermore, it is important that the leveling devices be accessible from the lift platform since leveling will occur once the collapsed lift has been placed within the ladle. Leveling devices will no longer be accessible from the side of the lift when this occurs.

Figure 4 Example of a leveling leg being manually adjusted from the top of the lifting platform via a special access cover

The nature of the leveling device is limited only by budget considerations. Leveling devices may be automatically activated by push button or they may be manually adjusted via crank. Your lift manufacturer should be able to provide a variety of leveling options for you to choose from.

Lifting Shackles

Like the leveling devices, lifting shackles should be attached to the base of the lift to ensure maximum stability and safe load handling via overhead device. These lifting shackles should also be accessible through the top platform of the lift when the lift is in the fully collapsed position. Ideally, such access should be via removable access covers on the lift platform to avoid creating trip hazards.

In the event that the lift must be lowered without the use of power, it is recommended that a manual lowering valve which is also accessible from the lift platform be incorporated in the lift.

Secondary table for positioning pallets of refractory bricks

When considering the type of table best suited to the ergonomic positioning of pallets of refractory bricks, there are several options to consider: a stationary table, a spring-actuated table, or a powered scissor lift table.

Stationary Table

A stationary table is the least expensive option of the three and is best suited for pallets of bricks that are of a height that does not require the mason to reach very far above or below wrist height. The study of bricklayer productivity and ergonomics by Rasha Stino found that "masons prefer brick supply stacked three to five rows high and material height at wrist/hand height."

Spring-actuated Table

A spring-actuated pallet table is one that automatically rises as the load on the lift lightens. However, if any of the pallets used during the ladle relining process contain more than one size and weight of brick, this type of table is not recommended. The unloading of a pallet containing a variety of brick sizes may cause the table to react in unpredictable ways. These types of tables are best suited for unloading and positioning pallets containing uniform products.

Powered Scissor Lift Table

A powered scissor lift table can be repositioned by the user as the need to raise or lower the load arises. The size of the lift platform should closely match the length and width of the brick pallet because a lift platform larger than the pallet will decrease the amount of space available between the lift and the brick face for the masons to work and move. Tipping of the load during movement and during loading/unloading of the lift can be prevented by ensuring that the lift platform is the same size as the pallet and by attaching the brick lift to the primary lift platform.

Control Options

Lift functions should be controlled from the lifting platform for ease of use and to avoid unexpected motion. This can take the form of a hand-held pendant with push buttons or a guarded foot switch to control up and down motion. In either case, controls should be dead-man style - where buttons require constant pressure to operate the equipment. The use of one control of each type is recommended when a secondary brick lift is used onboard the primary lift (i.e. a foot switch on one lift and a pendant on the other) to prevent controls confusion and the unintentional movement of either lift. Upper travel of the lift should be controlled via adjustable limit switch. Adjustability is recommended so that upper travel limits can be reset for use in ladles of various depths. It is further recommended that the limit switch be located beneath the lifting platform rather than at the baseframe as this offers the maximum protection for the switch.

Meeting ANSI MH29.1 -2003 Safety Requirements for Industrial Scissor Lifts

All lift manufacturers in the United States should voluntarily adhere to the ANSI MH29.1 - 2003 safety standard.9 Published by the Lift Manufacturers Product Section (LMPS) of the Material Handling Institute of America (MHIA), this document sets out in detail suggested safety practices regarding the design, manufacture, marking, installation and maintenance of industrial scissor lifts. It is recommended that purchasers require their industrial scissor lifts to be supplied in accordance with this safety standard. Purchasers should also be sure to install and maintain their industrial scissor lifts in accordance with the standard. To obtain a copy, please contact either the American National Standards Institute (www.ansi.org) or the Material Handling Industry of America (www.mhia.org).

Ladle Lift Maintenance Considerations

As with any piece of equipment, some consideration of future maintenance requirements should be undertaken prior to purchase. Powered ladle relining lifts are no exception.

CSA / UL Approved Lift Components

The use of CSA / UL approved components in your ladle relining lift simplifies the process of obtaining and stocking spare parts.

Armored HPU

It is recommended that the hydraulic power unit (HPU) at the base of the lift be covered by a sturdy metal enclosure to prevent damage from regular usage and the accumulation of mortar (please see Figure 6). The better protected the HPU is, the longer it will run without requiring repair.

Figure 6 An example of an HPU whose cover was accidentally damaged during usage allowing mortar to accumulate inside. Had the HPU not been covered, the power unit may have required replacement instead of just a thorough cleaning.

Wash-down

Figure 6 also clearly demonstrates the need for periodic wash-down of the ladle relining lift to remove mortar accumulation. You may choose to perform this type of maintenance in-house or have your manufacturer to provide you with a scheduled maintenance program where the lift can be cleaned, inspected and repaired on a regular basis.

Type of Hydraulic Fluid Used

As stated previously, it is desirable for the manufacturer to configure the hydraulic lift to operate using the same hydraulic fluid that is approved for use in your melt shop. This avoids compatibility issues and reduces purchasing / stocking requirements.

Lubrication

Where practical, sealed for life bearings or bushings should be incorporated into lift design to minimize or eliminate the need for lubrication.

Safety Lock-up Bars

Per the ANSI MH29.1 - 2003 safety standard, safety lock-up devices should be incorporated into the design of your lift.9 These devices are specifically for use when performing lift maintenance to prevent the accidental collapse of the lift.

Lift Documentation

Per the ANSI MH29.1 - 2003 safety standard, the owner's manual provided with your powered ladle relining lift should include detailed instructions on installation / start-up, operation, maintenance, trouble-shooting , and replacement parts information. Please be sure that you receive this manual with your lift and are familiar with the contents of the manual prior to installing and using your ladle relining lift.