Stehr-News

The Technology behind Stehr-HF Compactor Attachments

Stehr - known for solving problems

Anyone who has ever used hydraulic compactor attachments is familiar with the problems caused by vibrations being transmitted into the immediate area adjacent to where you are compacting. Serious damage to structures, pipes and electrical lines are ot uncommon - the latter often causing computer systems to crash. The specialist from Stehr confronted this problem and designed a device that became a "hit" among users shortly after it was placed on the market.

Jürgen Stehr: "Our goal ist not to compete with the many name-brand manufacturers, but instead to solve the problems that others create".

Eccentric shafts mounted in the vibration gear set the base plate of the Stehr compactor attachment into single-sided, vertical vibration. Driven by a hydraulic motor and gear wheels, this system produces an equal rotation speed for each of the individual weight shafts. Arranged in pairs or fours, these shafts rotate in opposite directions at the same angular velocity. As the illustration below shows, the two weight shafts generate the centrifugal force Fc. The horizontal components fh neutralize each other while the vertical components fv add up to the total centrifugal force of Fc.

These small, individual weight shafts can generate a high number of revolutions and in turn a high level of oscillation frequency. The cumulative centrifugal force Fc is directed vertically downwards so that almost 100 % of the force is transmitted into the material to be compacted. Vibration transmitted into surrounding areas, so common when using conventional compactor attachments, is virtually eliminated. Conventional equipment often creates problems when compacting in cities and towns. Not only do residents complain about excessive vibrations, many a construction site has had to be shut down because ot it. The powerful resonant vibrations that occur have frequently been known to cause extensive damage to structures, piping and electrical systems. These problems are particulary prevalent in construction work done in built-up areas, where the vibration velocity levels clearly specified in DIN 4150-3 (Structural Vibration) are for the most part vastly exceeded. As a rule, construction sites are not installations required to be licensed in accordance with Articles 2 and 5, and Article 22, Section 1/6.1 of the German Federal Immission Control Act. (BimSchG). The work performed at such sites must, however, be carried out in a manner that prevents harmful environmental impacts, such as are avoidable according the state of the art. Unavoidable harmful effects on the environment must be kept to an minimum according to the state of the art.

In most cases, the compaction equipment available on the market has been unable to meet these standards - until now. The Stehr compactor attachment's hexagonal base plate lets you use it anywhere. And there is no troublesome rotational joint with rotary-action motor. But the real icing on the cake is how leakage oil from the motors is vacuum extracted, passed through a filter and sent over the return line to the tank without any third hydraulic circuit. A mere 65 liters of hydraulic oil at 180 bar is all you need to operate the biggest Stehr compactor attachment with its 120 KN (4 x 30) of centrifugal force. This means that it can even be operated on a 7-metric-ton mini-excavator.

The Stehr SBV 120 HF plate compactor was successfully empoyed on a 7-metric-ton Bobcat 442 at a Trautmann construction company canalization site in Aschaffenburg, Germany. The Schütz engineering consultancy from Gross-Zimmern is using sensors to monitor, measure and record vibrations according to DIN  4150 at this construction site located on extremely sensitive subsoil directly along the Main River. The Stehr plate compactor was the only compactor with this impact force to satisfy these oscillation testing requirements. The vibrations it produced were within the prescribed tolerance levels. The Weilburg-based Feickert company, which focuses on specialized pipe and conduit construction, now has numerous Stehr HF plate compactors in use. These help the company avoid the kind of downtimes it suffered when using conventional compactors. Mr. Hansen of the Wieben company headquartered in Westerröhnfeld in Schleswig-Holstein reports that, "so far we have been using eight Stehr HF compactor attachments with the Oil-Quick coupler. In the future we will be employing them exclusively in built-up areas in order to avoid trouble with the residents right from the start."

Stehr offers high-frequency compaction attachments for excavators of 2.5 metric tons and larger: the SBV 60 with 60 KN of centrifugal force, a weight of 395 kg and an oil consumption of 40 liters; and the SBV 120 HF with 120 KN of centrifugal force, a weight of 764 kg and an oil consumption of 65 liters. These can be attached to all types of quick couplers - whether hydraulic or mechanical.

Like so many times in the past, Stehr has found a simple solution, shown the big manufacturers what the market wants and delivered yet another Stehr product that boldly redefines the state ot the art.