High Frequency Sawing
Success Factors of High Frequency Sawing
By Ian Osborne
High-power electric, often referred to as high frequency (HF) or hi-cycle, concrete sawing machines are becoming the new normal for most of the professional concrete cutting industry due to their significant productivity and versatility. In Europe, hydraulic sawing equipment is almost a thing of the past but this shift has lagged somewhat in North America. This article looks at the success factors of HF sawing equipment: job productivity, portability and versatility.
There was significant skepticism concerning the capability of HF machines as they crept into market during the 1970s and 1980s. Up until then, hydraulics ruled the industry and for good reason. Hydraulic machines were durable, simple to maintain and had adequate power. However, companies like Concrete Coring Company introduced 400-hertz HF to the U.S. market and the success of these machines led to an increasing number of manufacturers releasing HF machines during the1990s.
The introduction of these new HF concrete sawing machines was good enough to prove that they had potential, but unfortunately they were fraught with problems and were not perceived as durable enough for the industry. However, like many good concepts, they took a long while to mature and become durable enough to be called productive. Please refer to the June 2014 Tech Talk article High Frequency Saws and Drills: Maintenance is Key to Higher Production by ICS/Pentruder’s Terry Martin for more information. As any good cutting contractor knows, a machine can cut very fast but if it frequently breaks down it really isn’t productive.
Another area of skepticism regarding HF machines has been the misconception that only hydraulic systems can drive large diameter blades. As these machines have matured, this skepticism has been turned on its head. A common depth for wall sawing is 24 inches and the new normal for HF machines is 36 inches. There is the capability for these machines to handle deeper cutting depths if necessary.
Operators have become accustomed to hydraulic systems having some “give,” meaning when the saw encounters an unexpected object like a large piece of steel, the system “bogs down” for a moment, allowing the operator to back off on the feed. The power and the auto-feed systems on HF saws operate very differently than the older hydraulic systems. Once the blade and traverse speed are set, the auto-feed system and saw adjusts to anything its path, including unexpected heavy steel.
As the industry moves beyond these early skepticisms, there are a number of advantages to HF systems over hydraulic systems that have been well demonstrated over time—specifically over the last few years.
The cornerstone of job productivity is cutting efficiency. The cutting efficiency of a HF system has been demonstrated to be as much as double that of a hydraulic system. On the surface, this has significance, but it is more significant than many realize.
The fact that a HF system with superior cutting efficiency can finish a job in half the time means large savings in man-hour costs. It also means that the generator is working at heavy loads for only half the time, therefore a valuable reduction in fuel costs.
Fuel consumption is further reduced by the size of the engine driving the generator. In a hydraulic system, it is common to run a 75-horsepower engine to power a hydraulic wall saw power pack. In comparison, a 45-horsepower engine is used to drive a 30-kilovolt-ampere generator for a HF wall saw. The smaller engine size will inherently be more fuel efficient and the reduced weight of the engine will also result in a decrease of transportation fuel.
The smaller engine size is due to the fact that HF systems are much more efficient at converting the input energy into shaft power. A very good hydraulic system has a system efficiency of around 50%, compare that to the HF system efficiency of 90+%.
The reason for the high system efficiency of a HF machine has to do with the design of the machine itself, but also due to a high level of cutting efficiency. The machine design and the auto-feed function are relatively intertwined and interact with each other. The machine efficiency is positively impacted by the fact that the electric motor and the control system, by its very nature, is very efficient. The electric motor commonly used has a very flat power curve which is beneficial in running the range of blade diameters commonly used in wall sawing. Hydraulic systems must use a variety of inefficient mechanisms, for example throttling up the engine, in an attempt to keep the shaft power constant.
Auto-feed is the most significant impact on system efficiency and cutting efficiency. The auto-feed of a HF system is constantly self-adjusting the feed load or traverse speed in order to maintain a constant blade RPM and a constant and maximum load on the blade motor. Regardless of what the system’s blade is cutting, or how deep a pass is taken, the auto-feed will make the proper adjustments.
In addition to the above, experienced operators have noticed diamond consumables are often significantly less with a HF system. This is also due to the auto-feed and cutting efficiency. Of course, this is heavily dependent on matching the proper blade with the machine and job.
Another aspect that impacts job productivity is the setup and teardown time on a job. Compare the amount of effort, and as a result time, required to lay out large diameter hydraulic hoses versus a high power electric cable. Hydraulic systems often use 0.75-inch pressure lines and 1-inch return lines. With hydraulic fluid, they can weigh twice as much as a large high power electric cable. In addition to the effort and time to lay the hydraulic lines out, the weight can have a significant drag on the wall saw when cutting vertical. Operators will often place heavy hydraulic lines on their shoulders in an attempt to minimize the drag on the saw.
The weight of the saw also impacts setup and teardown time. Modern HF saws are often much lighter than hydraulic saws. For a comparable power saw, an HF saw can be half the weight of a hydraulic saw. Also, many HF saws can be separated into a motor and a saw head to further reduce the weight. It should be noted that, in addition to the weight having an impact on setup and teardown time, there is also impact on operator safety due to fatigue and increased risk of injury or accident.
Increased job productivity is only one factor in the success of HF machines. Successful cutting contractors know there are a variety of jobsite conditions that require thinking beyond pure performance. Jobs can be difficult, cutting specs can vary or the circumstances can change from what the original details provided by the general contractor. It is common to see walls that are thicker than specified, walls that vary in thickness, high steel content, access constraints and areas partially under water—the list goes on. This is part of the industry and part of the problem-solving that a successful contractor is expected to handle.
In cases where jobs do get more complicated, there are a couple of important factors that make HF systems an attractive choice over hydraulic: portability and versatility.
Portability is significant because it can allow for cutting jobs to be performed with less setup effort, especially those with limited access. Two aspects that improve the portability of HF systems are the ability to have long cable runs and a system comprised of components.
Finding access to power supplies is a common problem during setup and sometimes there are hundreds of feet between a saw and power source. It is common to limit the length of heavy hydraulic hoses to minimize pressure losses, whereas a high power electric cable can go much farther without a large increase in cable weight or loss of power. For this reason, a HF machine is more portable as a system can be placed at greater distances from the generator.
The HF system of components, which often comprise of a wall saw head, a motor and a power pack, are all light enough to be carried by a single person. This makes the system highly portable. This is in contrast to even the most portable hydraulic power packs, which are not light enough to be carried by one person.
The versatility of HF systems is also better than hydraulic due to the fact that a HF system comprises of a group of components. HF system components can be recombined into a wire saw as well as a wall saw. In different cases, different components are reused, but generally the power pack and motor can be re-configured from a wall saw into a wire saw. This versatility allows an operator to complete a job with a varying set of cutting tasks through reinforced concrete and other materials.
HF systems have come a long way in the past few years and have overcome much skepticism. Over time, the improvements to HF systems have led to improved job productivity, portability and versatility for many contractors. These factors have been significant in the success of HF cutting systems. To summarize, here are some numbers to consider when comparing hydraulic to high frequency electric saw equipment:
• Reduction of weight as much as 40 to 60%
• Reduction of setup and teardown time as much as 10 to 25%
• Reduction of cutting time as much as 25 to 50%
• Reduction of diamond blade wear as much as 25 to 50%
• Reduction of fuel consumption as much as 25 to 50%
• Increase in cutting productivity as much as 30 to 60%