Safety in the area of high voltage using cold-rolled ballscrews

Figuratively speaking, electricity is the lifeblood of our modern society and economy. Without it, nothing is possible. Circuit breakers are essential for the safe operation of power supplies with functions such as turning the entire output of a power plant on and off (in the gigawatt range) or directing voltages of up to 1,500 kV. The cold-rolled Carry ballscrew from Eichenberger Burg (CH) has an extremely important and responsible key role in this.

High voltage, less loss

Electrical energy is transported from the power generator, for example a power plant, to the consumer. In order to minimise loss and therefore costs during this transportation process, the lowest possible electrical current is produced, but high voltages with maximum values up to 1,150 kV are used so that high outputs can still be transferred. The entire Euopean power grid totals about 1.8 million kilometres.

Challenges for a circuit breaker

Independent of its position in the grid, a circuit breaker has two jobs: daily activation of power lines during normal operation and interruption of the power supply in the event of an overload or short circuit. A circuit breaker is a mechanical switchgear. It must be able to “control” outputs of several GVA within split seconds. If the flow of current in a switch is interrupted, even for a short time, a voltage flashover between the two contacts creates a self-sustaining gas discharge called a electric arc. These arcs contain a huge amount of energy. At temperatures of over 50,000 °C and a volume of less than a litre, pressure of up to 100 MPa can be generated. The ionised gas (plasma) not only continues to conduct electricity, but also reduces the service life of the component or even destroy the switch in the case of strong currents. Circuit breakers are designed to quickly clear the electric arc generated on opening the switching contacts without damaging the switch, thus interrupting the flow of electricity.

One step ahead with the right technology partner

A leading global technology company was looking for a totally reliable drive solution to instantly separate the heavy metal contacts in circuit breakers. The search ended when the company found Eichenberger Gewinde AG. The Swiss thread specialist has been providing screw solutions which stand out not only in terms of performance, quality and reliability, but also support the essential innovative lead for decades. When it comes to the construction of specifically integrated drive components, customers all over the world benefit from the extensive knowledge and remarkable development and manufacturing potential – offered by Eichenberger.

The thread rolling company always focuses on a requirement-orientated, constructive exchange with its partners. On one hand, the trick is to develop extraordinary customer solutions and, on the other hand, to ensure powerful and sophisticated production procedures. Future-orientated, creative thinking is firmly embedded in the Eichenberger's corporate culture. The perfect “in-house” company structure means that development, production, quality assurance and flexible prototype creation, including thread rolling tools and end machining, can all be offered together resulting in exceptional flexibility and adaptability. The employees’ deep-seated awareness of quality coupled with a corresponding modern plant are factors, which make a lot happen, especially when located in Switzerland. Eichenberger has a passion for the constant development of practical customer solutions and challenge of assignments for thread shapes outside the norm.

Advantages of thread rolling

Having realised the potential of this drive, the energy technology manufacturer backed the robust cold-rolled ballscrews from Burg (CH), which are produced in large numbers using a cost-effective thread rolling process. In contrast to grinding, milling or turning, thread rolling, diverts rather than cuts longitudinal fibres of the material. The result is a compressed and extremely resilient surface which has been rolled smooth, with is essential for the long service life of a screw. The roughness values around Rz 1.0 on the edges of the thread and in the base radius as well as significantly reduced notch-sensitivity, are also significant advantages. In steel ball bearings, the rolling friction co-efficient is 0.003 to 0.001 compared with sliding friction of steel on steel (lubricated) of 0.1 to 0.05. The excellent sliding properties of cold-rolled ballscrews ensure minimal friction and provide little scope for contamination. The quiet rolling of the balls is therefore very easy.

Total reliability

«Rarely needed – but then in an instant»

A high voltage short circuit reaches its maximum value after as little as 5 milliseconds. Luckily, interrupting the power supply in the event of a short circuit is not needed very often. However, if this occurs unexpectedly, the total reliability of the mechanical drive elements is crucial. The Carry ballscrew guarantees maximum functional safety with enormous power (efficiency > 0.9) and robustness. Carry prepares the mechanical power-on and power-off operation in the circuit breaker using helical springs. Two solid thrust rods are firmly connected on both sides with the custom-made nut, the so-called carrier. These two levers move the huge strikers which are subjected to spring pressure and which separate the metal contact extremely quickly. Despite adverse weather conditions and extreme temperature differences, the cold-rolled, resilient Carry does its job totally reliably, and is maintenance-free.

The customer-specific requirements for the ballscrew with integrated customer interface in the nut are “substantial and varying”. When it comes to axial force and geometry, the demands are high. Tribological aspects such as friction, wear and lubrication are important prerequisites that must be fulfilled. The tricky task of adapting the outside of the body of the nut to the particular interface requirements and the kinematic conditions is particularly challenging. All sorts of different dimensions of the Carry ballscrew have been developed for global use, consisting of a cold-rolled screw and specific carrier nut as a result of all specifications received.

 

eichenberger_hochspannung_0000Carry ballscrew, diameter ø 14 mm, pitch p 4 mm, with customer interface in the body of the nut

When reliability and customer benefits are no coincidance

The flexibility of mechanical-dynamic functional elements is a major contribution to the success of projects in drive technology. Unterstanding that quality and reliability have to be “integrated into the development” of a product, is crucial. Eichenberger Gewinde AG high-tech testing systems are therefore indispensable during the many stages of product creation. Only when screws, nuts, balls and lubrication are in perfect balance, can the highest demands be met. Based on the tight tolerances in torque, axial play and concentricity, a 100 % test is carried out on a special test bench. The most stringent requirements, for example concerning complete traceability, are not only a must in the automation, vehicle or medical industry. On request, Eichenberger will simply etch data references on ballscrews or leadscrews using permanent laser labelling as a data matrix. These days, everything is about technological advantages and increased performance density, at generally reduced investment costs. When the inventor of the product is also its most competent manufacturer, the advantages are obvious.

 

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Service provider for development

The need for practical solutions is perpetual. Eichenberger Gewinde AG has taken this opportunity and is now successfully established in the area of drive technology with a niche for tailor-made rolled thread drives. The Swiss thread specialist has clear objectives: rolling (cold forming) threads and manufacturing thread drives (screw and nut) and to support customer innovations by using state-of-the-art production methods and developing new dimensions.

The challenge for designers working in Switzerland, a country where costs are high, is to create outstanding added technological value in a competitive product in line with the market. Not only is technical knowledge, research and development required, but the additional skills to master efficient production processes that provide the competitive edge. If the inventor of the product can also manufacture it the most economically, it can really make a difference, especially when located in Switzerland.

 

  • «Carry»: Wear-free ballscrew for applications where heavy loads must be moved without consuming much energy. Depending on the version, particularly high operating speeds are possible.
  • «Speedy»: The high-helix leadscrew converts linear motion into rotational motion with high moving speeds.
    New: Some versions available in aluminium.
  • «Rondo»: The round thread leadscrew with very quiet running properties.   
    New: Some versions available in aluminium.
  • «Easy»: The hard-anodised light leadscrew made of aluminium with an efficiency of more than 0.8, for higher loads than for normal leadscrews. The special profile prevents jamming in the nut.

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