How can you specify the right lift table?
The nature of your load
What are you lifting? Is it stable on a level surface? Will its size fit on a standard platform? You should understand:
...what the load consists of,
...the weights of the load components,
...the load's center of gravity (if it is not centered on the load, and the physical dimensions of the load). Off centered loads can reduce lift life dramatically if not properly handled. They put more demands on a structure than the simple lifting effort.
In all cases, assume the worst loading to be encountered with the lift in motion will be no more than half of the load on half of the platform. The critical information in these cases is where the center of gravity of the load will be in relation to the center of the platform (center of the supporting leg structure as described by the minimum platform size) when the unit is put in motion. Ideally, the center of gravity of a load should be placed in the center of the platform.
How do you intend to load your scissor lift?
How loads are transitioned onto and off of the lifts can be the critical factor in choosing an appropriate lift design. These movements determine the “edge loading” and/or “impact” that the structure must sustain and they may contribute to off centered load conditions during the lifting cycle.
The most common ways loads are transitioned on and off lifts are as follows:
ROLLED ON/ ROLLED OFF – with a wheeled vehicle or cart. Much is dependent on the type of rolling. If you are rolling a double axle cart or pallet jack with an even load onto the lift, the load is split 50/50 as the first axle rolls onto the table top. A single axle load, such as a large roll or a hand truck, places 100% of the load in one spot. A forklift radically splits the load, as much as 80 to 90% depending on the counterweight.
SLID ON/ SLID OFF – as in sheet feeding operations or conveyor operations.
The loading that requires the most judgment is the sliding load. When a load is sliding onto a conveyor, there is less of an impactfactor on the lift than a rolling axle would apply and the end conveyor roller (and platform edge) would never see the entire weight of the load because of deflection within the lift mechanism. In the case of supple incremental loads such as sliding sheets of paper onto a unit, the edge loading and impact are trivial and not a factor in selecting a lift. In the case of an ingot of lead being slid onto a platform, impact and edge loading requirements may be the deciding factor in lift selection. Therefore when considering the entire range of applications, judgments must be made about all of the following factors:
- Friction and impact
- Horizontal impact against stops
- Incremental layers (Each load increment must be considered as a percentage of both the total lifting capacity and the edge loadrating.)
- Footprint of the load increments relative to the overall platform size
- Footprint of the load increments relative to the minimum platform size
- Location of center of gravity of the load increments relative to the minimum platform size
PLACED ON/ PICKED OFF – as in stacking operations or crane loading. Some loading produces no edge loading requirements. Manually stacking layers of boxes would be a good example. This type of operation imposes negligible impact and no edge loading.Vertical loading with a crane or other overhead device is a good example of no edge loading, but the possibility of very highimpact to the lift. With a maximum capacity load, a lowering speed of 17 ft. per minute (fpm) will produce acceptable impact loadson opened lifts. Speeds in excess of 17 fpm may create damage to cylinder packings, hoses or structural members. Most industrialcranes are limited to speeds of 17 fpm or less, but applications with vacuum assist lifts, vertical conveyors or free fall applications,may produce destructive impacts. Obviously, the slower the rate of vertical impact the better.
Load Capacity and Side/End Loading Capacities
Load capacity is the amount of weight of an evenly balanced and centered load the lift can handle. Most loads should be lifted in this manner. Side/End capacity is the weight of the load over the edge when lift is in a fully raised position (it's often less than balanced load capacity).
What matters most with edge loading is what loads will pass over the edge of the lift in anything other than the fully loweredposition. In the fully lowered position the base frame, cylinders and leg assembly are fully supported and only the overhang of larger than minimum tops are subject to any bending forces.
A maximum capacity load may pass over the edge of a minimum size platform of a fully lowered lift without concerns about the edge loading of the lift in some situations. If the platform is larger than minimum, then proper supports must be placed under the platform to prevent any potential deflecting or bending. Typically these are rare applications, but if you are planning a lift project that includes them, contact us for assistance.
Vertical Travel
Determine the maximum raised height requirements to selectvertical travel model. Depending on your application, you'll be able to find a range in most standard lift models.
Platform Size
Standard platform sizes conform to standard base sizes. Platform sizes may be widened and/or lengthened up to an additional 24”. Side/End capacity is reduced by 2% per inch on oversized platforms. This is because the oversize platform overhang acts as a lever, increasing the forces incurred by the supporting leg assemblies for any given weight. Edge loading capacities are reduced or "derated" by the rule of thumb of 2% per inch for every inch that a platform is wider than minimum widthand for every inch that it is longer than minimum length.
EXAMPLE: an Advance Lifts P-2536 has a minimum platform size of 24" X 48". If it were equipped with a 48" x 54" platform, the unit would have the side edge load capacity reduced by (48" – 24") X 2% = 48%. The end of platform capacity rating would be reduced by (54"- 48") X 2% = 12%. There are many variables that go into the actual edge load capacities, but the 2% rule of thumb is a good general rule to use. Contact us for assistance if you are at all unsure.
Side Loading: Most scissor lift designs have much greater strength over the ends of the lifts than they have over the sides of the lifts. For this reason, loads should travel over the ends of lifts, parallel to the lift legs, rather than over the sides when the lifts are anything but fully closed.
Power Supply
When considering the duty requirements of the lift, it is necessary to think in terms of two systems, the lift mechanism and the power unit. It is necessary to know whether the lift application requires full stroke movement “up” or “down”, or will there be a series of incremental “jogs” in one of the directions. Specifically, we need the time intervals between operations and the direction and size of movement in each operational increment. Finally, the total number of cycles per hour, day and year should be calculated.
Applications with many short jogs in quick intervals may require the need of a special power unit. If the jogs are in a downwarddirection, the standard lowering solenoids are of a continuous duty type and nothing needs to be done. However, if the increments are in the “up” direction, the standard motor would not take the frequent motor starts without overheating. Therefore, the options to consider are going to an air operated unit, air over water unit, or a continuous running power unit. (See the power unit options for the specific table model that you are considering.)
Many lifts are hand or foot powered; you pump them to height. In Single phase 1 HP motor or three phase 1 1/2 HP motor isstandard as shown. Upon request motors can be interchanged.External/Remote power units are also available. See individual models for information. The motor you need will typically be matched with the capacity and force needs of the lift.
Controls
Hand held, push button up/down control are typical for most lifts. Optional foot operated controls, wall-mounted controls, and limit switches are alternate types of controls.
Frequency and Speed of Operation
Standard motor is intermittent duty rated. If usage is more than one full lift every four minutes or jogging action every 10 seconds, motor will overheat. Optional external power units available, as well as for increased lifting speed.
Lowered Height
For a lower than standard height, pit mounted units (ground level) are available. There are alternatives that can give you lifts with lowered heights as small as 2.9 inches (standard) and lower (custom). Pit mounted units must have beveled platform edges or electromechanical toe guards to conform to OSHA recommendations. Toe guards extend length and width of standard platform by 8”.
Mechanical factors
- Oversized Platforms: platforms can be widened and lengthened up to an additional 24”.
- Platforms with Beveled Edges: increases standard platform size 4” on each side.
- Pit Mounted Units: require electromechanical toe guards or a beveled edge platform.
- Lifting eyes are also required forinstallation.
- Portable (for moving empty lifts): 2 steel wheels – side or end mounted with wheeled dolly. For oversized platforms, please consult us.
- Turntables: custom sizes are available for rotating lifts.
- Conveyor Tops, Ball Transfer Platforms and special fixtures are also available to increase your lift's versatility.
- Optional Top Material: stainless steel skin and diamond plate.
- Transportable package available with two fixed and two swivel casters for moving loaded units.
Other Options to increase lift versatility
- Accordion (bellows) skirts: a safety option that safeguards the lifting arms, preventing human access during operation.
- Non-flammable and low temp. hydraulic fluid: in some settings, a good option to reduce chances of fire.
- Wash down units: good for food and other clean area applications.
- Adjustable flow control valve
- Fork pockets: makes it easy to move your lift with a fork truck.
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