Breakers: weight does not equal performance

How can you be sure that a given breaker is right for your application. Atlas Copco uses the established AEM method to calculate single blow impact energy. This article reviews both the method and the state of the market when it comes to published impact energy figure.

Are only heavy hydraulic breakers powerful breakers? Even after over 40 years of hydraulic breaker development and several hundreds of thousands of tools in use across the world, users are often unsure when it comes to choosing a suitable hydraulic breaker.

There are, in fact, only two approaches in the selection of a hydraulic breaker. Approach One: The customer requires a recommendation for a hydraulic breaker to match the size of an existing carrier. Approach Two: The job scope includes a time limitation and the customer requires a specific demolition performance from a breaker to finish the job within the time frame. In this case the hydraulic breaker is determined based on the demolition performance specifications with a suitable carrier being recommended accordingly.

Regardless of the chosen method, it must in both cases be possible to determine the output power of the hydraulic breaker. But how can the output power of hydraulic breakers be compared with each other on paper?

There are more than one hundred hydraulic breaker suppliers on the market, yet the knowledge about relevant selection criteria for hydraulic breakers is only made more difficult due to different ways of reporting the output power ratings.

There are only a handful of hydraulic breaker manufacturers in the market who have the crucial knowledge and who continuously invest in design and development. Many manufacturers work according to the copy and paste principle and do not even possess the original knowledge of dimensions and specifications that were initially ascertained and selected. This has given rise to a wide variety of mounting recommendations and ways to publish output power ratings that only confuse the customer even more, sometimes with unequal comparisons that can lead to incorrect purchase decisions.

But how can a user find a suitable hydraulic breaker for the job requirements? What must the user pay attention to and how can output power ratings be compared?

At first glance, this question is difficult to answer. Today, hydraulic breakers are assessed in different ways in different areas of the world. In Europe, this is primarily based on the operating weight of the hydraulic breaker according to the lift capacity (weight in kg) of the carriers. In Japan it is very similar as the attention is focused more to the relation of the bucket volume (m³). When applying both methods, the lift capacity is used to estimate the maximum allowable weight of the attachment units to ensure the stability of the carrier.

“In China and South East Asia, hydraulic breaker users look mainly to the working steel diameter for the selection. And finally, in North and South America, hydraulic breakers are assessed according to an energy classification which can be chosen individually by each manufacturer”, explained Torsten Ahr. “Therefore, at first glance, it is difficult to define general and comparable selection criteria. But the customer’s sole concern is how he can operate most efficiently." Operational efficiency depends directly on the demolition performance of a hydraulic breaker. The demolition performance is influenced primarily through single blow energy and secondly through frequency.

The output power of a hydraulic breaker is calculated: Energy (Nm) x frequency (1/min). Now, from a physical point of view, output power equates to output power, but this is not equivalent to the same demolition performance.

An example:

Two hydraulic breakers of different designs each have an output power of 42 kW.

The output power of breaker one is determined from 5,000 Nm energy and 504 1/min frequency, vis:

5000 Nm x 504 1/min = 42 kW
60.000

The output power of the second hydraulic breaker is determined from 2,500 Nm and 1008 1/min.

2500 Nm x 1008 1/min = 42 kW.
60.000

In both examples the output power is the same. But which breaker has the better demolition performance? “Based on output power alone, this cannot be answered. Therefore the material to be broken up has to be incorporated into the considerations", explained Stefan Lohmann, development engineer at Atlas Copco. “As previously mentioned, energy is the prime influence of the demolition performance of the hydraulic breaker. Frequency is a secondary factor. The single blow energy is the energy that is discharged per percussion piston stroke against the working steel and is roughly comparable with the force that affects the material to be broken. If this energy is too low to break up the material quickly, the hydraulic breaker can strike 10,000 times per minute and the demolition performance would still be running around zero. In contrast, the hydraulic breaker with the higher energy would produce a higher demolition performance despite the lower frequency.”

Or inversely: If the lower single blow energy from the second hydraulic breaker is sufficient to break up the material, this breaker would produce a higher demolition performance due to its higher frequency.

From these examples it can clearly be seen that single blow energy is the prime influence of demolition performance. And when this is sufficient, it influences the frequency of the demolition performance! Ideally the blow energy and the blow frequency for different usage types can be varied at the hydraulic breaker.

How can a customer find these two specifications that affect the demolition performance? It is comparatively easy to ascertain the frequency of a hydraulic breaker as that type of data can be found in the manufacturer’s datasheets or on their websites, and can be even proven easily in the field.

However, regarding the specifications of the single blow energy, the situation is much more difficult. “Yes some breaker manufacturers state the single blow energy or energy classes in their brochures. Unfortunately what is referred to here is energy data that is calculated or even estimated, not measured. In the case of some manufacturers, the published energy ratings are higher than is technically possible. In order to achieve the published performance, the operating efficiency of the breakers would need to exceed 100%. Claims of efficiencies in excess of 100% just do not stand up and operating efficiencies just under 100% are unrealistic", explained Torsten Ahr. And Stefan Lohmann added: “In addition, most suppliers are not able to accurately measure the single blow energy. This is not due to a lack of knowledge, but due to the fact that the measuring equipment and the corresponding personnel requires a high additional investment from which many manufacturers shy away. A calculator is cheaper and can also produce more attractive values”, he added.

How then is the energy measured and how can a comparison of the results be ensured? “We believe we have found a way to do this”, explained Torsten Ahr. “Since the early 1990s there has been a standard measuring method for this purpose and the adherence to which is monitored by an independent construction equipment association. This method stated by the AEM (Association of Equipment Manufacturers) measures single blow energy according to a specified standard.

Unfortunately, some suppliers publishing energy ratings over and above a level that is technically possible and in the same publication they state to be an AEM member, but that doesn’t mean they have measured according to AEM!”

The AEM has only committed to certify the measurement booth with the associated measuring equipment but not to inspect the accuracy of the measurement results.

In order to publish the AEM energy ratings, the measured data must also be submitted to the AEM. It is important here that not only the measured energy for the respective hydraulic breaker is recorded, but also the measured frequency with the associated measured oil flow in L/min, the measured operating pressure in bar and the return pressure, also in bar. Only when all these parameters are stated and submitted to the AEM can the accuracy of the measurement can be assured.

“Despite this situation, as one of the market leader we will adhere to the AEM measurements because we are then able to compare our own breakers with each other and also with those of our competitors, or at least with those who participate fairly and seriously," added Torsten Ahr. “We must ensure that AEM is fit for purpose for the future and also hope that our most important competitors and AEM self will support it.”

The Association of Equipment Manufacturers (AEM) founded the Mounted Breaker Manufacturer Bureau (MBMB), whose members are comprised of the relevant global players amongst the hydraulic breaker manufacturers.

The AEM-Guideline for energy measurement was developed jointly over a period of four years and defines requirements for the measurement equipment, the measuring conditions and the evaluation of the measurement results. All manufacturers agreed to ascertain the single blow energy by measuring its effectiveness. The basic premise of the test procedure is that the working steel will compress slightly when struck by the breaker’s piston.

This amount of compression is measured through a resistance strain gauge applied on the chisel, which is connected to a measurement system.

To execute the measurement, a test-bed with defined dimensions and measurement devices of determined quality are required. As the corresponding stimulus of much less than 1 ms is very short, for example a correspondingly high sample rate of at least one million samples per second >= 1.0 MHz) must be selected.

Once the measurement is completed in which additional data values such as volume flow, pressure and frequency rate are measured and determined, a standardised report is compiled by all members and forwarded to the AEM for registration.

The process is very complex. In order to continuously ensure the quality and comparability of the results, a regular certification through an independent test-bed recognised by the AEM is required where the equipment and the measurement and evaluation process are inspected.

Since the introduction of the measurement process, 14 manufacturers have had their measurement processes certified and submitted their results to the AEM.

One more significant factor for the operating efficiency of hydraulic breakers is the machine efficiency. This brings us back to the output power. The output power of a machine always requires an input power. The hydraulic breaker obtains input power from the carrier, e.g. a hydraulic excavator. This input power is also stated in kW and is comprised from the oil flow rate (Q in l/min) required for the respective hydraulic breakers and the maximum operating pressure of the hydraulic breaker (p in bar). A hydraulic breaker that requires an oil flow rate of 230 l/min and develops an operating pressure of 180 bar, has an input performance of P_in = 230 x 180 = 69 kW.

Example:

Let us recall the example with the two hydraulic breakers whose output power in both cases was 42 kW. If we have an input power of 69 kW and an output power of 42 kW, this results in a machine efficiency of about 61%.

Logical conclusion: The higher the machine efficiency, the more operationally efficient the hydraulic breaker.

The carrier generates the hydraulic input power and this is reflected in the diesel consumption that represents costs to the customer. The output performance affects productivity and as a result the customers’ profit.

If two hydraulic breakers have the same output power but one of the two has a lower machine efficiency, then this hydraulic breaker requires a higher input power and as a result a higher diesel consumption.

“Now, we have spoken a lot about energy, frequencies, input and output power, demolition performance, efficiency and diesel consumption and not uttered one word about weight as an assessment criterion,” stated Torsten Ahr. “People always think that larger machines are more powerful, and this is indeed true when considered superficially. And in a rough scaling, this also applies to hydraulic breakers, since a high output power requires a proportionate operating weight and a correspondingly high input power. However, looked at more closely there are differences that overturn the "heavier = more powerful“ thesis. In the hydraulic breaker market, there are hydraulic breakers with up to 25% less operating weight that are superior to heavier hydraulic breakers as far as demolition performance is concerned.”

What accounts for the weight of a hydraulic breaker? The percussion mechanism and guide system make up about 80 percent of the weight. The remaining 20 percent is comprised of the adapter plate and working steel (chisel).

There is a range of different working steel types for the widest variety of uses for every hydraulic breaker. Usage type and useful length of the tool influence the weight. The size and weight of the adapter plate depend on the carrier used.

Weight differences between the percussion mechanism and the guide system of the hydraulic breaker are determined by their construction type. The percussion mechanism that transforms the hydraulic input power into mechanical output power can be compared to the engine of a car. The guide system that guides and protects the percussion mechanism can be compared to the body of a car. An unnecessarily heavy guide system increases the diesel consumption of the carrier and thereby the costs without offering a commensurate increase in demolition performance. The demolition performance of a hydraulic breaker is solely generated from the percussion mechanism. If therefore one wanted to work with the rule of thumb of "heavier = more power", then it is rather necessary to compare the weight of the percussion mechanisms with each other. Even better would be the weight comparison of the internal percussion pistons (the heart of the breaker) with each other.

Let’s now move on to costs. For many customers this is the most important decision criterion. “A high-quality product that meets all the aforementioned criteria and increases the productivity of the customer cannot be manufactured at a cheap price. And this will continue to be the case given the backdrop of increasing cost of raw materials. A conspicuously cheap offering is never to the detriment of the supplier, but always to the detriment of product quality. This means that the customer does not receive the best hydraulic breaker for his usage and loses money continuously,” summarised Torsten Ahr.

Conclusion

How can a customer compare hydraulic breakers with each other and select the right device?

• A hydraulic breaker must be selected according to the necessary demolition performance (usage type, stone type/concrete classification, time targets);
• The single blow energy is the prime deciding factor for demolition performance. To be able to compare the single blow energy, the energy rating must be a measured one according to the AEM guideline and not calculated and represented as an “energy class”;
• Only when the single blow energy is sufficient can it positively affect the frequency of the demolition performance;
• Heavy hydraulic breakers should be able to vary the ratio between the energy and the frequency to maximize the demolition performance;
• Overall operating efficiency (fuel consumption) is determined by the demolition performance of the breaker as well the machine efficiency, which is the ratio of output power to input power;

The total weight of a hydraulic breaker does not correlate with the demolition performance of the breaker. A comparison of the percussion mechanisms is more suitable.

If a user is really looking for the best performing suitable breaker, ask the supplier for a site demonstration - that is in all cases the best way!