For more than 100 years, balancing technology has been closely related to the name Carl Schenck

100 years of balancing technology

For more than 100 years, balancing technology has been closely related to the name Carl Schenck:

In 1908, the Darmstadt-based company built its first balancing machine. Even though balancing was not the main focus for the industry for that time, it was a primary requirement for rotors of the earliest steam engines having to run smoothly that made balancing a point of interest - even in those early days.

Here, you will see some of the important milestones for the history of balancing.

Balancing the early stages

150 years later and now in the age of extreme industrialization, we find it hard to believe the balancing of a steam turbine rotor took three to four weeks of hard manual labor – the technology available then was still comparatively simple and the results of the balancing process very inaccurate. Boilers exploding and flywheels disintegrating at high speeds contributed to hazardous work environments and inadequate balance quality also caused bearings to wear down quicker. Experienced engineers recognized these dangers and began looking for solutions.

Canadian engineer H. MARTINSON was one of the first to look into the subject of balancing from a theoretical point of view. In 1870, he was granted what was probably the first patent for a balancing machine. The rotor was mounted isotropically on soft coil springs, driven by a universal-joint shaft. By gradually moving a piece of chalk towards the rotating rotor, you were able to determine the position of the unbalance with some degree of accuracy. No records were ever found as to whether this machine actually worked, or if it was ever built in major quantities.

... from roll-balancing facilities to balancing machines – Schenck appears on the scene

As technical development advanced rapidly, the problems caused by rotor vibrations became more and more obvious. Workers required more skill, training, experience and time to statically balance rotors on knife-edges, using the "roll-off “ method. A workable solution was described in 1907 by Dr. Ing. FRANZ LAWACZECK, in his paper: "Zur Theorie und Konstruktion der Balanziermaschine" (Theory and design of a balancing machine).

In 1908 CARL SCHENCK, who had also started looking into "roll-off" balancing at that time concluded a license agreement with Lawaczeck. The "Lawaczeck principle" remained valid right up to the forties: It consisted of a pendulum-mounted fixed bearing on the one side of the rotor and a radially flexible bearing on the other side. After initial correction in one plane, the rotor was re-installed. In 1915, Schenck took over the sole worldwide license for this machine.

During this period, a number of new optical and mechanical measuring methods were developed, whose measuring accuracy was quite remarkable. The "Lawaczeck model" was capable of achieving a balance quality equivalent to a center of gravity displacement of 0.001 mm (.00003937 inches) - a balance quality which would even today be perfectly adequate for many applications.

From mechanical to "electrical machines"

In 1935 a machine patented in the USA, featuring electrodynamic vibration sensors and stroboscopic determination of the unbalance angle pioneered a change over to a new design.

In 1942 Schenck was granted a patent for a "Method and facility for dynamic balancing by determination of the angular position of unbalance by means of a periodic curve displayed on the screen of an oscillocope".

This was the first balancing system suitable for large-volume production. Due to its high accuracy, the system was used right through World War II for balancing gyroscopic stabilizers for naval vessels.

The wattmeter method, the next step in the development, suppressed undesirable parasitic vibrations. With the basic components known at this time - i.e. wattmeter, vibration sensor and angle reference generator, it was possible to determine the position and magnitude of the unbalance in one measuring run. Unbalance values were displayed on two pointer instruments.

In 1953, the illuminated-spot vectormeter brought a newer advancement. The combination of both values in a single display unit and the "storage" of the measured values in the form of a light spot on a screen significantly simplified the balancing process.  The unbalance was now visible.

Even today, the vectormeter is an indispensable part of modern measuring instruments - a practice-proven method of showing the position and magnitude of the unbalance on modern measuring instruments with display screen.

Now referred to as Universal Balancing Machines (formally known as Workshop Machines) - automation of the balancing process has forged forward in great strides. "Balancing lines" for crankshafts determined the unbalance of crankshafts and the required drilling depth for its correction. A simple transport system transferred the crankshafts from the measuring station to the drilling unit and back. Altogether, unbalance measurement, correction and check run for a crankshaft took about 2 minutes.

The dawning of a new age in balancing

The rapid economic and technical development in the post war period also left its marks on balancing technology. Until the present time, the automotive industry, aeronautical and aerospace technology, energy generating and electrical industries, and mechanical engineering with their constant increase in standards and requirements were the driving forces in the technology’s continuous development.

In the early fifties, a completely new method was developed for large-volume production of crankshafts: mass centering of crankshaft forgings or castings. This was a new process which enabled the actual axis of inertia of a crankshaft forging or casting to be determined and marked with centering holes.

Also in the early fifties, rapidly increasing demand for electrical power resulted in larger power stations being built with ever increasing power generation capability. The development of Series RI and DI balancing and over-speed test rigs for turbines and generators made it possible for the first time to systematically correct the unbalance of rotors with a total weight of up to around 80t.

For the first time, mass correction was performed by a drill unit integrated into the balancing machine. These systems were suitable for many tasks in large-volume production and took into account the economical aspect of balancing. As a result, the cost of balancing decreased significantly, as the time-consuming task of removing the rotor from the balancing machine and re-installing it on the drilling machine was no longer necessary.

The aeronautical and aerospace industries presented their own challenges for balancing technology. A number of innovations for demanding tasks were developed, often venturing on to new terrain. The emergence of jet engines brought a new advance in balancing technology.A series of horizontal and vertical machines was built, tailored exactly to the requirements of the jet engine manufacturers.

During this period, the aerospace industry emerged as a new partner. The first balancing machines for satellites and rockets were developed, along with moment weighing scales.

On the other hand, the problems of motorists were much more down-to-earth. In the early sixties, as cars got faster and faster and new types of tires emerged, unbalance became a real challenge. Motor car manufacturers started balancing tires during the production process. In addition, special workshop machines were required for retrofitting.

Towards the end of the sixties, the product range was extended with a series of MAN spin test rigs manufactured under a license. Apart from turbine and compressor discs, their main areas of application were in fatigue testing of fast-moving tools such as polishing and grinding discs.

After 1968, hard-bearing machines were much more common in the industry. Although early models were not able to achieve the same accuracies, they had a practical advantage in everyday operation in that they were significantly faster.

There was no need for a rotor-specific calibration - all the machine operator had to do was enter some basic geometrical dimensions and start the balancing run. It only took one run for the machine to display the magnitude and angular position of unbalance. Revolutionary for the time, this was a significant advantage. Today, most balancing machines (with the exception of machines intended for specific purposes) operate according to this principle.

From electronic to microprocessor-based measuring units - the start of the digital age

In the 70s, the mechanical foundations for balancing machines basically established themselves - electronics made their appearance in balancing and diagnostic technology. In 1971, the electronic wattmeter measuring principle was introduced, the first computer-controlled balancing systems followed in 1974. The next major change came with the emergence of digital technology  In the early 80s, microprocessors started appearing in measuring systems.

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