Screw Jack

1. Standard gearboxes with standard trapezoidal threads achieve efficiencies between 25-35%.
2. Increasing the pitch makes the thread slip more easily, thus increasing efficiency.
3. The combination with a ball screw can also achieve an efficiency of up to 50%.
4. Best combination: bevel gear lifting drives with ball screws, which achieve over 80%.

Yes, the use of stainless steel materials is a common practice for environments with aggressive media.

For continuous monitoring, rotary encoders can be mounted on the motor or the worm shaft.

If only the end positions are relevant, limit switches can be used to query the desired end positions.

In hydraulic cylinders, we also often use potentiometers, which then return a certain resistance value that can be read out by the controller.

The confusion sometimes arises because in both cases, there's an additional element at the back of the spindle.

1. The spindle travel limiter is merely a ring on the thread that prevents the spindle from falling out.
2. The rotation prevention additionally prevents the spindle from twisting.

Customer side: The customer bears the load, preventing it from twisting. If the spindle is then attached to the load, it also cannot twist.

Gear side (product itself has a prevention rotation): We either use a groove running completely through the spindle with a corresponding key as a counterpart. Alternatively, a square block can be screwed onto the back of the spindle, and the protective tube is designed as a square tube.

The specification '20% duty cycle per hour' is always associated with a certain power consumption at the gear unit. Therefore, if the permissible power value is not exceeded, less heat is generated, and the gear unit requires less time to cool down. This allows achieving more than 20% duty cycle.

Yes, screw jacks can be manufactured entirely in stainless steel and equipped with food-grade grease approved according to H1 standards.

The housing is made of aluminum die-casting or gray cast iron, the spindle, protective tube, and worm shaft are made of steel, while the worm wheel or traveling nut are made of a bronze alloy. Additionally, there are many variants.

Yes, with motor adaptors, motors or geared motors can be flexibly attached. You decide whether you want to provide the motor yourself or if GROB takes care of it.

Yes. A lifting gear unit can be operated with any rotary drive, whether electric, mechanical, or manual.

When under compression, typically buckling is the limiting factor. Under tension, it's either the availability of raw material (rods commonly available up to 6m) or the critical bending speed (in the case of the traveling nut version). For larger strokes, the spindle can also be made in multiple parts.

In applications with high safety requirements, two independently acting holding mechanisms may be required. This could be dynamic self-locking + motor brake or, alternatively, an independently switchable dual brake on the three-phase motor.

Yes. Common voltage types are 24 VDC / 230 VAC / 400 VAC. Additional voltages in both direct and alternating current ranges are available upon request.

A three-phase motor rotates depending on the mains frequency. The higher the frequency, the faster the motor rotates. Rated speeds at 50 Hz are as follows: for 2-pole motors, 3000 rpm; for 4-pole, 1500 rpm; for 6-pole, 1000 rpm; for 8-pole, 750 rpm.

Lubricating grease of NLGI grade 1 or 2, suitable for heavily loaded sliding and rolling bearings. Compatibility with the existing lubricant must be ensured. It's crucial whether the grease is mineral or synthetic-based.

It depends on the operating cycle and conditions. Typically, every 500 double strokes.

The lubricant quantity depends on the size and type of the gear unit. You can find specific data in our general catalog. Here's an example for our cubic screw jacks: General Catalog 2023 (grob-antriebstechnik.de)

0 - 6000 mm in the standard range. Lengths over 6 m are also possible for special applications, but then with a multi-part spindle. Gradations can be made in the millimeter range.

Grease lubrication in the gearbox: up to 1500 rpm; >1500 rpm to 3000 rpm flow grease or oil lubrication.

You can install mechanical, magnetic, or inductive limit switch solutions. Preparation for custom sensors is also possible. Please note that it's not possible to implement end position detection on traveling nut version screw jacks.

For detailed information, refer to the beginning of each screw jack chapter in our catalog. Here's an example for cubic screw jacks: General Catalog 2023 (grob-antriebstechnik.de)

For grease-lubricated screw jacks, the mounting position can be freely chosen. For oil-lubricated screw jacks, the orientation of the ventilation must be considered.

The manufacturer's rated load capacity should not be exceeded. However, screw jacks typically have safety factors ranging from 1.5 to 2.5 times the rated load.

Temporarily possible, however, this results in a significantly reduced lifespan.

Yes, for screw jacks with ball or roller screw mechanisms, a lifespan can be calculated. However, for trapezoidal screw mechanisms, lifespan calculation is not possible. More information on the calculations can be found here.

The required power depends on the load and lifting speed. A 30% reserve to the required power is recommended for the drive. The screw jack should be operated within the maximum specified parameters, which depend on the version and size. You can find exemplary power limits for cubic screw jacks here: General Catalog 2023 (grob-antriebstechnik.de)

The safety margin can be increased or reduced. If reduced, it's important to ensure that block drive is always prevented during operation of the system.

A block drive describes the execution of the lift against a fixed stop. In this process, the lifting element is 'blocked' by the fixed counterpart.

The driving element, usually a three-phase motor, doesn't stop automatically but needs a signal for shutdown. This signal can be generated through limit switches, encoders, potentiometers, or other displacement-monitoring components.

Mechanical drives are very sensitive to movement against fixed stops. Depending on the force of the motor, a block drive typically results in damage to the spindle-nut system.

Ball screw spindles make sense when:

1. The power consumption is too high in combination with trapezoidal screw spindles
2. A higher lifting speed is desired
3. A higher precision is desired

The axial play of a trapezoidal screw spindle typically ranges from 0.1 to 0.3 mm. When the axial play reaches 1/4 of the trapezoidal profile, replacement of the trapezoidal screw nut is recommended.

Although lateral forces significantly reduce the lifespan of screw jacks, there are certain limits within which lateral forces can be absorbed. You can find relevant information here: General Catalog 2023 (grob-antriebstechnik.de)

The standing spindle creates relative motion through the rotating worm wheel, while the rotating spindle generates relative motion for the traveling nut. The advantages and disadvantages depend on the space constraints of your lifting system.

Yes, each size (regardless of the screw jack type) offers 2x reduction stages (-> Normal and Slow). The exception is bevel gear screw jacks. Here, gear ratios of 1:1, 2:1, and 3:1 are possible.

Spindle extension defines a dimension that provides a certain extra length compared to the standard when in the retracted state. For example: You only need an effective stroke of 100mm, but there's a distance of 400mm to cover between the start of the stroke and the gearbox. Then we extend the spindle by 400mm, so when fully extended, you reach a total of 500mm.

For the spindle end, the standard range offers options including threaded end, articulated head, ball joint head, flange plate, bearing flange plate, and pin. You can find corresponding dimensions in the General Catalog 2023 (grob-antriebstechnik.de)

Yes, appropriate protection can be achieved through painting or the use of stainless materials.

Yes, the functions of 'lifting' and 'moving' can be performed by any mechanical lifting element.

This version uses an additional tube to protect the spindle, which sits on the traveling nut. The piston tube version thus describes a lifting cylinder that has been modified based on a screw jack.

In standard operation, the SFM runs load-free with the main nut. If the main nut fails, the SFM takes over the load. A stroke can then be performed to shut down the system. Additionally, the SFM is also used as a reference nut for wear measurement.

The spindle can be protected by folding bellows or spiral protective sleeves.

It prevents rotation of the spindle. If a translational spindle were to rotate, linear motion would no longer be possible.

1. Electronic bridge: If each lifting element of the system is driven by a motor, electronic synchronization can be achieved through encoders.
2. Mechanical linkage: More cost-effective and fail-safe are cardan shafts and bevel gearboxes, which can connect all lifting elements of a system together.

A travel limiter (AS) prevents the spindle from accidentally falling out in the basic version. It is not intended as a mechanical end stop.

Yes, screw jacks and MINI cylinders can be used within certain limits for ATEX zones as well.

In the case of the traveling nut version, only the nut connection dimensions change. In the basic version with the ball screw spindle, it may occur that the bearing cover is raised to accommodate the ball screw nut in the gearbox.

Yes, threaded spindles can also be equipped in stainless steel.