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Small angle grinders used in power plant maintenance make a tough job easier and safer


Small angle grinders – with wheel diameters ranging from 4 1/2 in. to 6 in. – have become the go-to portable electric power tool in a range of maintenance and repair operations, including power plant maintenance. They are compact, lightweight, versatile, fast, effective and, when used correctly, safe.

The perceived safety threat of working at a power plant in any capacity is real. But it’s important to remember that safety measures must be taken in any setting and with any power tool – even with small handheld tools like a small angle grinder where the perceived safety threat is almost nonexistent. Fortunately, Metabo and many other power tool manufacturers recognize these safety issues and have been challenged to build safer, stronger and more productive angle grinders.

A Metabo 4 1/2-in to 5-in. angle grinder with non-locking paddle switch, brake and auto-balance makes work safe and easy.

These advancements have resulted in safety clutches, improved guards, ergonomic handles, vibration control and various electronic features. As safety on the job becomes an increasing concern for everyone, more recent developments such as mechanical or electronic braking, tethering points for drop security and cordless tools have become a focus.

Safety features

Mechanical and electronic safety clutches help reduce kickback should the operator bind or pinch a wheel. There are, however, significant differences between mechanical and electronic clutches.

While electronic clutches de-energize the tool, their reaction can be too late to prevent kickback and do not decouple the inertia from the motor components. The inertia from a motor spinning at roughly 30,000 rpm is so tremendous that the sudden stop can lead to a wheel shattering.

To greatly limit the reaction of the wheel binding, Metabo developed its mechanical S-Automatic safety slip clutch that separates the spindle from the armature, helping the operator to maintain control of the tool and avoid kickback. The clutch decouples the motor components from the spinning wheel, significantly reducing the likelihood of the wheel shattering.

Over the years, power tool manufacturers have worked to produce safer more productive products, such as the 4 1/2-in. cordless, brushless paddle switch angle grinder with brake shown here.

For additional safety, tool-free guards allow the user to easily adjust a guard to its optimal position (between the wheel and operator) without the use of tools. This provides the operator an additional level of protection should a wheel fail.

Side handles with improved ergonomics and better positioning on the tool offer a reason to keep the handle on the tool. Metabo’s multi-position handle accessory allows for positioning of the handle in a 180-degree arc across the top of the grinder, either at 90 degrees to the tool or at 45 degrees to the tool to allow for access into tight work areas. Also, vibration reduction composition reduces fatigue and helps to prevent long-term work-related disorders of the hand and arm.

Electronics offer improved power management and increased productivity as well as enhanced safety for an angle grinder. Features can include:

  • A power loss interlock prevents the sudden restart of the tool should there be an instance of power loss and reinstatement (i.e., power surge) with the switch left in the “on” position.
  • Overload protection helps prevent motor burnout if the operator overloads the tool for a prolonged period of time.
  • Soft start helps the operator maintain control of the tool at start up by reducing reactionary torque (tool jerking at startup).
  • Constant speed control keeps the wheel spinning at the optimum speed – from no-load to full-rated load. This feature greatly enhances productivity and aids in helping to reduce kickback in an extreme load by adding power to help keep the wheel at the recommended RPM.
  • Non-locking deadman switches have become common in addition to lock-on switches. The non-locking switch immediately de-energizes the motor when the switch is released, helping to reduce the likelihood of injury from the wheel spinning down.

Other anti-vibration features include Metabo’s auto-balance vibration reduction system, which reduces the vibration transmitted to the operator from the tool. Extensive and prolonged exposure to vibration can lead to repetitive motion injuries.

Getting into tight spaces is easy with Metabo’s 5-in. flathead angle grinder.

Putting on the brakes

Mechanical and electronic brakes bring a tool to a stop in a fraction of the time that it takes an angle grinder without a brake to stop. When an operator loses control of a tool that doesn’t have a mechanical or electronic brake, extended “spin-down time” of the wheel can compound and exacerbate what would have otherwise been a minor injury or near miss.

Electronic brake systems do make angle grinders safer, but at a cost to the longevity of the grinder. An electronic brake reverses polarity to the motor components and can lead to premature wear of the grinder’s components. Also, depending on the model, the electronic brake may not engage if there is a power loss or electronic failure. The Metabo mechanical brake system, however, produces less wear and tear on the tool while also stopping wheels in less than 2 sec. It is tested to more than 50,000 cycles.

A recent safety addition available on select angle grinders is a tethering attachment for drop security. This attachment allows a lanyard or “tether” to be attached to the grinder, which is in turn attached to a location near the worker. If the tool is dropped by accident, it is less likely to injure a passerby or worker below, which is quite helpful when working at heights.

Any of these features is an improvement over what was available just a few years ago. When these features are combined, they make for much safer tools overall. While these advancements are major contributing factors to a safer workplace, there is still a need for operator training of proper tool and wheel selection, usage and safety procedures.

Going cordless

A challenge of any electric power tool is distance from the power source and using the wrong extension cord. An issue that occurs regularly is voltage drop. Without getting too deep into engineering and math, any time there is a drop in voltage, there is an increase in amperage. Increased amperage results in increased heat, which is detrimental to an electric motor.

Voltage drop occurs when too long of an extension cord is in use, an improper gauge extension cord is used or a combination of both. Another disadvantage of a drop in voltage is lack of torque and RPM, which reduces the performance of the tool.

The lack of torque and RPM then causes the wheel to not spin at the required RPM. This can trigger “grabbing” of the wheel on the metal, which could lead to kickback.
An operator may think that the metal removal rate is not as expected and then put extra pressure on the angle grinder and wheel to compensate. This additional pressure can cause the wheel to fracture or the grinder integrity to be compromised (burned up) due to overloading. To avoid the domino effect of a drop in voltage, it is imperative to select the proper gauge and size extension cord when working at a distance from the power source.

Another option, cordless tools are the fastest growing sector of the portable electric power tool industry. Improved conductors, electronics, motor efficiency and battery technology have all contributed to cordless tools that perform as well if not better than their corded counterparts. Lithium-ion battery technology has allowed for tools that were only imagined in cordless form to recently become mainstream.

No matter the job at hand, it’s key to ensure that safety features have been included in the tool manufacturer’s design, such as with this Metabo die grinder.

For instance, Metabo introduced a new generation of Li-ion cells, the 21.700, which allow significantly higher power output while offering longer run times. This new power source allowed Metabo to manufacture a cordless angle grinder as strong as an 11-amp electric tool.

Cordless tools also offer additional safety advantages in the workplace over corded tools. OSHA’s website states that 39.2 percent of all industrial fatality accidents in 2017 were caused by slips, trips and falls. Eliminating cords eliminates one source of potential hazard. OSHA also states that 7.3 percent of industrial fatality accidents in 2017 were caused by electrocution. The lower voltage helps to reduce potential electrocution hazards.

Generally, the old adage “you get what you pay for” applies in most cases with power tool brand selection. Premium brand tools offer engineering and design for specific trades and applications like Metabo’s specialty flathead grinder that is designed for extended reach in tight confines, such as the type a boilermaker is confronted with when repairing or replacing a curtain wall boiler tube.

Accidents are expensive on many fronts and painful, if not life altering, for the victim. Even a minor accident from tool kickback can carry a hard cost in the range of $4,000 to $80,000, depending on the actual injury itself. And that doesn’t include any OSHA fines, increased insurance premiums or the effect that a recordable accident has on an insurance mod rating, which could affect future job contract awards as safety track records are becoming a significant factor in contract awards.

A premium tool, while costing more upfront, can provide a greater overall savings to the end user. It not only saves valuable time, but is more durable, has a longer service life and, if properly equipped with additional safety features and a strong safety program, can cut costs by reducing the chances of a potential accident.

Metabo Corp.

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