Kent Henry 
EASA Technical Support Specialist 

To repair electrical apparatus, obviously we need to use certain spe­cialized machinery. These machines have some common safety hazards as well as unique potential dangers. This article will review a few of the more common machines and their safety risks with examples of how to address them. The main objective is to get everyone to stop, take a step back, and find ways to address potential safety issues. 

If questioned, most experienced machine operators could quickly point out the dangers of a certain machine he or she uses. For some hazards, safety devices are not available. The only protection is knowing the danger points and training your staff to stay clear of dangerous areas. 

Balancer safety 
The typical balancing machine is designed to calculate unbalance at approximately 400 to 700 rpm; some can be operated at lower rpm depend­ing on their design. Customers may ask for balancing to be performed at operating speed. Don’t make the mistake of try­ing to balance a rotor in a conventional balancer at the rated nameplate rpm. The rotor may come out of the balancer resulting in injury and dam­age. 

If the balancing speed is increased above the typical operating range, install rotor safety hold-down devices (Figure 1) to positively hold the shaft against the trunnion rollers and prevent the part from “climbing out” of the machine. These safety hold-down devices should also be used when balancing overhung loads. Never rely on the drive belt pressure as a means to keep the part secure in the balancer; as the name implies, it is a “drive” belt. 

When balancing blower wheels, you may need to block the airflow to reduce the load in order for the balancer’s limited torque capability to accelerate the blower wheel to an rpm adequate for balancing. 

Any materials that are applied to the fan to reduce airflow must have enough mechanical strength to endure any air pressure developed at balanc­ing speed. If the material fails, it may sound like a grenade going off due to the sudden air pressure change. 

The audible boom is loud enough to startle a person and possibly cause injury by coming in contact with the part rotating in the balancer. In some circumstances, the sudden pressure change may lead to instability of the part, causing severe oscillation; it may be severe enough to cause the part to jump out of the balancer. If the safety hold-downs are properly installed, they will protect against the part coming out of the balancer. 

A good method to safely block airflow is to wrap the circumference of the fan with duct tape to reduce the windage load. In an application such as this, it pays to buy good duct tape. Specifications from one major manufacturer of duct tape shows that they have several different types that range in tensile strengths from 22 lbs./in. width (3.85 N/ mm) up to 50 lbs./in. width (8.76 N/ mm). The number one rule with adhesive tapes is to wash your hands before handling so that the adhesive can fully bond; otherwise it is weakened. 

A situation such as a synchronous rotor with a fraction of the number of poles rewound may be considerably unbalanced. The best practice is to level the rotor in the balancer and then check the static unbalance. If you find a heavy area, begin by correcting the static balance. This practice safeguards against driving a severely unbalanced rotor to a speed that may damage the balancer.

Or worse, it could become unstable and jump out the trunnions. Therefore, be sure to lock the trun­nions until the rotor is brought up to balancing speed. Once the rotor has been static balanced, it should be safe at minimum speed to begin dynamic balancing. 

Use of slings 
Slings work great to lift parts into the balancer. However, the woven fabric cuts easily when under load and then compressed between the edges of metal objects such as the shaft and the balancer rollers. The combined load and pressure acts like a pair of scissors to shear the sling, causing an instantaneous failure. For safety when loading and unloading a rotor or armature in the balancer, the lifting sling should not be located at or near the shaft journals. 

Depending on the design of the ar­mature or rotor, the best practice is to use wide slings which are also known as “belly bands” (Figure 2) to support at the rotor/armature core (or standard slings.) They should be used in com­bination with protectors, also known as wear pads (Figure 3). This pro­tectors help prevents abrasion and give some measure of protection against incidental contact that might lead to sudden sling failure. 

The protector slides over an eye type sling, or in the case of an endless type sling there are types that wrap around the sling and close with Velcro. With regular use, the protectors reduce general wear and tear on slings so they last longer. When compared to the cost of new slings, these protec­tors are a win-win situation, resulting in improved safety and a reduction in annual rigging material costs. 

Welding safety tips 
Welding in the balancer is another area with potential safety issues. A circuit must be completed with a ground cable. If a proper ground is not present, the welder current may flow through the technician’s body to ground, leading to shock or elec­trocution. In addition to the safety hazard, the lack of proper ground may allow a welding current to pass through the balancer’s bearings, or damage the balancer’s electronic components. 

Some might argue that the best practice is to remove the part from the balancer for welding. However, many service centers weld in the balancer without damaging it by using the proper safeguards. When welding in the balancer, insulate the shaft from the balancer trunnions. The precision bearings in the machine are expen­sive; a careless approach will not only damage these bearings but also the support and pivot needle bearings. 

An easy method is to use strips of slot cell paper between the trun­nion rollers and the shaft journals to insulate the balancer components while welding. The slot paper can be rolled between the shaft and roller or inserted by lifting each end to slide the insulation in place. Some service centers use NEMA GPO-1, a low-cost board type insulation at the balancing stand for this purpose. The thicker insulation provides greater reliability. 

The ground clamp should be clamped directly to the part or at­tached to a section of woven ground strap wrapped around the shaft. Be certain to remove the ground cable and or ground strap after welding. 

The ground cable and clamp can quickly become wound into the part leading to injury or damage. Some find it helpful to manually rotate the shaft a revolution or two to be sure the ground has been removed before energizing the balancer to bring the part up to balancing rpm. 

A special exception to welding in the balancer is TIG (tungsten inert gas) or GTAW (gas tungsten arc weld­ing) welding. High frequency is often used to ease starting the welding arc and the best practice is to remove the part from the balancer. 

The balancer area should be partitioned off using welding curtains to protect others against inadvertent arc flash exposure while welding. Portable weld curtains work well for these areas since they can be easily positioned to provide optimum pro­tection and yet allow a rapid exit if a fire occurs. A fire extinguisher should be readily accessible to the technician within the partitioned area. 

Using trial weights 
Trial weights pose a safety hazard if they become unsecured and get thrown off due to centrifugal force. When possible, try to apply the trial weights so centrifugal force holds them in place on the inner surfaces of the rotor or armature. An example would be using clamp style weights (Figure 4). Instead of sliding the weight over a rotor fin from the outside, simply slide them over the back side of the fin before tightening the screw. When mounted on the inside surfaces, they are less likely to be thrown from the fins while rotating. 

The exposed surfaces of a part rotating in the balancer increases the potential for contact injuries. Rotor fins and cooling fan blades may catch the technician off guard when manu­ally rotating the part to add or remove weights. This could result in injuries to fingers and hands. Injuries also occur when a technician becomes impatient and fails to allow the part to come to a complete stop before moving toward it.

Potential pinch points 
When working in a balancer, pay close attention to any potential pinch points (Figure 5) that are exposed, particularly in areas where shaft journals contact the trunnion rollers; fingers can easily be pinched, cut, crushed, or even severed between these rolling surfaces. Use caution when rotating the part to perform corrections. When the machine is decelerating the part, the best prac­tice is to stay back until it comes to a complete stop. 

Lathe safety 
Before loading a part in the lathe, check the spindle speed control settings. The last operator may have set the spindle speed at a high rpm to polish a small diameter shaft. If a part with a substantially larger diameter and mass is loaded in the lathe, there is a serious risk of injury if the operator forgets to adjust the speed before operating it. Take the time to set the spindle speed to a low speed that is safe for the weight and diameter of your part. 

Safety type self-ejecting chuck wrenches (Figure 6) are a great way to ensure the wrench is not left in the chuck after an adjustment. The wrench has a spring action that ejects it from the chuck. 

A safety type chuck wrench also reduces the likelihood of a machinist inserting the wrench in a chuck key slot to use it as a lever arm to rotate the lathe chuck and part being machined. While this gives the machinist some lever­age to manually rotate the chuck, it creates a safety risk. Once that mass begins to turn, we may not be able to remove the wrench or brake the momentum to a stop. If that happens, our hand can get trapped between the wrench and the lathe bed, leading to crushed bones, lacerations, or severed body parts. 

Block axial movement 
Many lathe accidents result from the failure to control or block axial movement of the part away from the tailstock and supporting center. If a shaft is chucked and works loose, it will likely creep deeper into the headstock leading to the loss of centering support at the tailstock. If the part is rotating when this occurs, it will likely come out of the lathe. No matter how fast your reflexes are, it is difficult, if not impossible, to escape before that rotating mass of metal catches you in a no-win situation. 

The majority of work is performed with 4-jaw chucks. A simple solu­tion is to fabricate a parallel surface shaft block using 3 pieces of bar stock welded into an “X” (Figure 7). 

The “X” shaft block must be machined so both sides are flat and parallel to each other. The key ele­ment is that front and back faces are jaws and install fasteners parallel to each other. The shaft block acts as a parallel block between chuck face and the end of the shaft while it prevents axial movement. This “X” shaped shaft block is placed into the chuck so the “X” fits 
in the areas between the jaws. If you have an application where you need to use a 3-jaw chuck, then a “Y” shaped shaft block can be built using 3 pieces of bar stock. 

There are many methods to keep the shaft block secured and centered in the chuck. The easiest is to use ex­isting slots or holes in the chuck face that are centered between each pair of jaws and install fasteners to clamp the shaft block in place.If there are no circumstances. slots or holes in the chuck Simple procedures such face, then simply drill and tap the chuck face. The fasteners hold the shaft block in place against the chuck so there is no reason to use more than one fastener per parallel leg (4 bolts for the “X” type and 3 bolts for the “Y” type). Transfer the
bolt pattern to the shaft parallel blocks and drill through boltholes from the front to back of the parallel surfaces. Countersink the holes for Allen head cap screws to keep the heads below the parallel face. This allows the shaft block to be secured to the chuck and yet easily removable.

Don’t get entangled 

A danger that often gets ignored with rotating equipment is that of being pulled into the machine due to loose, baggy clothing or long hair. Themate­rial or hair may become entangled in the machine or the rotating part,and before you know, it you are pulled off balance into the machine. Don’t get fooled. Even the smallest lathe develops a substantial amount of torque through the gear reduction and you won’t have a chance to escape. Machine as polishing or sanding with emery cloth can pose a danger as the cloth can suddenly snag and begin wrapping around the shaft, pulling your hands into the part. Best practice is to hold the ends of the cloth so that you form a 60- to 90-degree angle around the shaft (Figure 8). 

Never bring the ends of the emery cloth to a tight angle (Figure 9); this is a recipe for injury. 

Never reach over a chuck to per­form a task. For example, when using a file in a lathe the handle should go in your left hand, which is side of the body closest to the chuck. The right grasps the end of the file and applies pressure against the shaft. This meth­od forms a triangle with the file with your left arm parallel to the chuck face while the right arm reaches over the part from the tailstock end of the lathe. A person’s head, body, and arms are safest away from the rotating chuck or rotor. If the shaft between the rotor and chuck needs to be filed, sanded, or polished, the best practice is to turn the rotor end for end in the lathe. This enables us to work on these surfaces by reaching over and around the tailstock using the meth­ods described. 

The same technique described for filing works for safely sanding and polishing. The left hand holds the end of the emery cloth level with the bottom of the shaft while the side of the cloth and the arm is parallel to the chuck. The cloth runs from the left hand under the shaft and is held in the right hand directly above the shaft to form a 90° angle. 

Chips 
When metal is machined, we produce metal chips. The chips will be various lengths; the longer ones pose special dangers. They are wiry and tend to pile up around the tool post or cutting inserts. It is hard to resist the lure of using your fingers to pull them out of the way to clear the work area. The edges of the chips are very sharp, jagged, and can easily cut or tear flesh. 

Hopefully, these examples will bring to mind other dangers in your service center and point out how being proactive with some low tech, economical prevention techniques can make the workday safer for everyone. 

As the chips are moved, they may become entangled in the rotating part, pulling your hand into the lathe. The best practice is to use tooling inserts with chip breakers (Figure 10). They are designed to curl the chips tighter in diameter, breaking them into smaller pieces and thus reducing the hazard. 

The inserts with chip breakers should comply with the American National Standards Institute standard ANSI B212.20-1980 (R-2002). If you need to remove a buildup of chips, stop the machine first. 

Watch for sharp chips 
When cleaning balancers, lathes, or mills, resist the temptation to use compressed air to get the metal chips out of the nooks and crannies. These sharp-edged chips can quickly pierce or lacerate skin. Compressed air can propel the chips at high velocity and over substantial distances, creating a safety hazard to workers, not to men­tion the potential for contaminating machines being serviced. Secondary to these issues, the air pressure will easily defeat the protective wipers or guards of the machines, allowing chips to collect inside on the precision surfaces leading to abrasion and damage. The best practice is to use a brush, a mag­net and a shop vacuum in combination to remove the chips for recycling. 

We spend a great deal of time working with machinery to perform repairs. The tasks require close contact with debris, sharp edges, rotating surfaces, pinch points, and other potential dangers that are often overlooked until someone is injured. Hopefully these examples will bring to mind other dangers in your service center and point out how being proac­tive with some low tech, economical prevention techniques can make the workday safer for everyone. 

Categories: Safety, Service center equipment

Tags: Safety Service center equipment

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