Contents
What types of Screw Jacks are there?
Basics
Are you looking for precise and high-performance solutions for lift and positioning movements? Then Screw Jacks are the ideal choice for you. However, there are different types of Screw Jacks, each addressing specific needs. Discover below a comprehensive overview of all Screw Jacks.
1. What are Screw Jacks?
Screw Jacks are true all-rounders in drive technology. We've been manufacturing Screw Jacks since 1945. The basic principle is simple and brilliant at the same time: a rotary motion is easily converted into an axial motion – and that in the smallest of spaces.
Here's how it works: an electric motor drives a worm shaft, which sets a worm wheel in rotary motion. The worm wheel is equipped with a Threaded Spindle (standard: trapezoidal thread; special version: ball screw) – and the Screw Jack is complete.
2. You have the choice: 4 types of gearboxes are available
Which type of Screw Jack is right for your application depends on various factors: the required load capacity, the load case, and the available space. Each Screw Jack is generally available in two versions:
Basic Version
The lifting spindle performs the linear movement.
Traveling Nut Version
The traveling nut carries out the linear movement.
We cover this wide load range with our proven Screw Jacks: 0.5 kN to 2,000 kN.
3. An overview of Screw Jack types
Cubic Screw Jack - from 2.5 kN to 500 kN
The housing shape is already in the name: it's cubic, like a cube. All surfaces of this design offer many mounting options for various constructions. We can achieve load capacities from 2.5 kN to 500 kN and offer many customization options.
The Cubic Screw Jacks are designated MJ or BJ. In total, 11 standard sizes are available.
Classic Screw Jacks - from 0.5 kN to 2,000 kN
The housing shape of these Screw Jacks is already in the name: classic. Unlike the cubic design, the Screw Jacks in this series can handle higher loads up to 2,000 kN. Due to their design, you can't attach construction elements to the housing.
The Classic Screw Jacks are designated MC. There are 14 sizes available, with each size also offered in traveling nut and basic versions.
High-Performance Screw Jacks HMC - from 5 kN to 1,000 kN
The name already indicates what’s inside the gear. These High-Performance Screw Jacks are tailored for special dynamic and demanding applications, for which standard Screw Jacks are unsuitable due to their simple structural design.
The result: we can achieve higher speeds and loads. The High-Performance Screw Jacks are designated HMC. They can lift loads from 5 kN to 1,000 kN.
High-Speed Screw Jacks KH - from 15 kN to 90 kN
The GROB High-Speed Screw Jacks complement our Screw Jack program by extending the range of applications. Unlike standard Screw Jacks, bevel gear transmissions are used.
The range includes three sizes with gear ratios of 1:1, 2:1, and 3:1. Thanks to the favorable efficiency of the bevel gear sets, the overall efficiency of the GROB High-Speed Screw Jacks is approximately 75% with Ball Screw Spindles and around 40% with Trapezoidal Screw Spindles.
This is what a Screw Jack looks like inside
GROB Antriebstechnik GmbH
4. Pros and Cons
Cons
✘ Speed Limitation: In many cases, Screw Jacks are slower than other motion systems, which can be problematic in high-speed applications.
✘ Complexity: The design and installation of Screw Jacks can be complex and often require specialized knowledge.
✘ Maintenance Requirements: Screw Jacks require regular maintenance to ensure optimal performance and longevity.
✘ Costs: High-quality Screw Jacks can be expensive, especially if they're customized.
Pros
✔ Precise Motion Control: Screw Jacks allow for precise control of linear movement, which is crucial in applications where accuracy is important.
✔ High Load Capacity: Screw Jacks can lift or move heavy loads, making them ideal for high-load applications.
✔ Energy Efficiency: They can manage energy transfer efficiently, resulting in energy savings and lower operating costs.
✔ Versatility: Various types of Screw Jacks, such as Spindle Screw Jacks, Worm Gear Jacks, and High-Speed Screw Jacks, are suitable for different applications.
✔ Long Service Life: Well-maintained Screw Jacks can have a long service life, making them cost-effective.
FAQs about Screw Jacks
A Screw Jack is a combination of a spindle (screw) and a nut (worm gear or traveling nut) that converts rotational motion into linear motion through a worm gear drive.
How screw jacks work and where they are used - GROB GmbH chevron_rightBasic Version: The spindle itself performs the axial movement.
Traveling Nut Version: The spindle remains stationary in space but rotates. The nut then moves up and down on the spindle.
- Cubic & Classic: primarily external differences. A matter of personal preference regarding which one is preferred. Performance data is nearly identical.
- High-Performance Screw Jack: Standard up to 3000rpm input speed, with oil filling and cooling fins - explicitly higher dynamic load capacity.
- High-Speed Screw Jack: explicitly high dynamic capability, but load capacity decreases to a maximum of 90kN.
- Standard gearboxes with standard trapezoidal threads achieve efficiencies between 25-35%.
- Increasing the pitch makes the thread slip more easily, thus increasing efficiency.
- The combination with a ball screw can also achieve an efficiency of up to 50%.
- 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.
- The spindle travel limiter is merely a ring on the thread that prevents the spindle from falling out.
- The anti-rotation feature 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 Screw Jack 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 24V DC / 230V AC / 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 50Hz are as follows: for 2-pole motors, 3000rpm; for 4-pole, 1500rpm; for 6-pole, 1000rpm; for 8-pole, 750rpm.
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 - 6000mm in the standard range. Lengths over 6m 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 1500rpm; >1500rpm to 3000rpm 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 shouldn't 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 stroke 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:
- The power consumption is too high in combination with trapezoidal screw spindles
- A higher stroke speed is desired
- A higher precision is desired
The axial play of a trapezoidal screw spindle typically ranges from 0.1 to 0.3mm. 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)
Screw Drives: Trapezoidal Screw vs. Ball Screw - GROB GmbH chevron_rightThe 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 the High-Speed Screw Jack. 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.
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.
The following points necessitate an oil version:
- Use in explosive atmospheres with gas. A mandatory ATEX questionnaire is required.
- Input speed at the worm shaft ranging from 1500rpm to 3000rpm.
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 the rotation of the spindle. If a translational spindle were to rotate, linear motion would no longer be possible.
- Electronic bridge: If each lifting element of the system is driven by a motor, electronic synchronization can be achieved through encoders.
- 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's not intended as a mechanical end stop.
Yes, Screw Jacks and MINI Cylinders can be used within certain limits for ATEX zones as well.
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)
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.
Want to know more?
10 steps to the right Screw Jack
Choosing the right Screw Jack doesn’t have to be a guessing game. With our step-by-step guide, you can quickly and confidently select the ideal model for your application – simple and actionable.
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