Safety Google : Chainsaw

This article is about risk control methods specific to chainsaws and chainsaw operations. Chainsaws incorporate numerous safety features common to many engine-driven power tools. Manufacturers have invented numerous design features to improve safety. Some features have become de facto standards, and others are legal requirements in particular jurisdictions. Best practice dictates that an operator should inspect the saw before starting work and only operate the saw if all the safety features are properly functional.

Additional safety features are a significant commercial advantage to chainsaw producers. Companies continue to develop new features over time. Most chainsaw safety features are focused on the kickback problem, and seek to either avoid it (chain and bar design), or to reduce the risk of injury should it occur (chain brakes). In addition to the safety features built into the chainsaw, operators should also wear specific chainsaw safety clothing. Most older saws have few or none of these features, and extra care should be taken in their use.

Chain

The chain has to be properly matched to the guide bar and the saw. Chainsaw manufacturers specify a selection of suitable chains for each model of saw.

Best safety requires that the chain is properly sharpened. One key sharpening parameter is the depth gauge setting. The depth gauge is the small steel protuberance in front of each cutting tooth. The difference in height between the leading cutting edge and the depth gauge determines the thickness of the wood chip taken by the cutter. If the depth gauge is too low, the cutter takes too deep a bite from the wood, the saw becomes difficult to control and the chances of kickback increase.

Some chains also have guard links in front of each cutter link. The guard link reduces the tendency of the leading edge of the depth gauge to snag on small-diameter objects such as small branches, or to engage with ordinary timber if forced into contact with it.

Chainsaw bars

Kickback reduction

Chainsaw Kickback is primarily caused by cutting with the chain in the "kickback zone" on the bar, the upper quarter of the nose.[1] Some saws, usually electric saws intended for domestic garden use, shield this whole area from contact with a "tip protector". All cutting produces a reaction force on the saw: normally this should be the lower edge of the bar, where the chain is travelling towards the saw and the reaction tends to pull the saw safely towards the log, against the spur dogs. Where the chain is moving downwards, as at the tip of the bar, the same reaction force now acts upwards and will cause a kickback upwards.

Tip protectors are metal or plastic devices that fit over the bar tip and are usually fitted to small, domestic-class saws. While these are effective, they hamper the saw in terms of the type and capacity of cuts it can execute, and are not widely used. They find a useful application in pole pruners and one-handed battery-powered saws that are used for trimming, hedge laying etc. The hooked nose of the tip protector can be used to "grab" branches for cutting, and presents no great drawback since these very small saw units are not used for cuts where the bar tip is buried.

Carving bars

Chainsaw carving often makes deliberate use of plunge cuts, and cuts on the tip of the bar. By simply reducing the diameter of the chain nose, the amount of chain, and thus the force generated during a kickback, may be reduced. Specialist carving bars are available with small pointed noses.

Chain brake

Front handguard, and combined chain brake lever

Chain brakes prevent movement of the saw's cutting chain by applying a steel brake band around the driven clutch drum.[2] Clamping force for the brake band is provided by a powerful spring. The chain brake has two purposes. First, it can be used to secure the chain when changing position, moving between cuts or starting a cold saw, which requires a partly open throttle. This would otherwise lead to uncontrolled chain movement, a major hazard in older saws. Secondly, the chainbrake can activate under kickback conditions to prevent the operator from being struck by a running chain. Of course being struck by even a static chain may cause serious injury, but anything that can be done to mitigate the usually dreadful injuries caused by contact with a moving chain is of obvious benefit to operators. Kickback injuries usually occur to the head, face, neck and shoulders; when a running chain is involved, such injuries are usually very serious, often disfiguring and sometimes fatal.

The chain brake is principally operated by the top-hand guard being pushed forward to engage the brake, and pulled back to disengage. The spring-loaded action allows powerful braking under emergency conditions and can halt a chain under full power in a fraction of a second. Correspondingly, it may require considerable force to reset.

The chain brake may be activated deliberately by the operator, or automatically by the force of a kickback event. In the former, the operator usually rotates his left wrist and knocks the top hand guard forward with the back of his hand, re-setting it by reaching forward with his fingers to pull the top hand guard backwards. In the case of a kickback event the operator's left hand may be violently dislodged from the handle and the top hand guard will be thrown onto his hand, forcing activation of the chainbrake. Husqvarna models also incorporate a link between the top handle and the chain brake trigger, applying the brake if the saw's bar is forced suddenly upwards. This is known as an "inertia" chainbrake and will allow activation of the chainbrake even if the operator's left hand is not removed from the handle.

The chain brake may also be of use when sharpening a chain on a bar, as it allows robust filing to take place without the chain slipping about.

"Wrap-around" top-hand guards have made an appearance in recent years, but are unpopular.[who?] They restrict movement, and make no allowance for the fact that when the handle is gripped on the lower section of the handle (left side of the saw from the operator's viewpoint) it is usually for making lateral, right-to-left cuts. In this situation the operator's head, neck and shoulders are out of the cutting plane of the saw and will not be struck even if a kickback does occur.

Chainsaw kickback

Chainsaw kickback can occur when the tip of the bar comes into contact with a relatively massive or immovable object with the chain under power. The area of the bar tip most likely to be involved is known as the "kickback quarter". looking from the side of the bar, the kickback quarter is the 90° section of bar found between a line going along the centreline of the bar, and another line at 90° to the first, rising upwards from the centre of the nose sprocket. If this area of chain comes into contact with - for instance - a log, the chain will initially cut the wood, but will also produce a reaction force which pushes the bar upwards. As the bar rises, the chain is forced harder into contact with the wood and climbs upwards even harder. In a fraction of a second the chain may jam hard into the wood and hurl the bar upwards towards the operator, often causing very severe injury or death. The violence of a full kickback event is such that no evasive action is possible, and if the operator's head, neck or shoulders are in line with the plane of the bar, he will certainly be struck by it. At this point, he must rely on his chainbrake and PPE to save him from injury or worse.

Another form of kickback may occur where the top of the bar is used for cutting and becomes suddenly pinched by the wood moving. In this case the saw may be forced backwards towards the operator, or forced into a position where the tip is pinched and the saw transitions into a classic tip-driven kickback. Kickback may also occur as a result of a failed or improperly executed boring cut. Bore cutting is a specialised technique requiring proper training, and should not be attempted without such training.

Kickback reducing systems

By far the most effective tool in preventing kickback is operator training. By preventing contact between the bar tip and solid objcts, kickback may be avoided. By keeping their head and body out of the cutting plane of the bar, injury may be prevented if kickback occurs. A useful tip is that if the operator can't read the logo on the side of the bar, they are too close to the cutting plane and should lean left to ensure safety.

Correct chain sharpening is paramount to safety in this context. Blunt chain cuts poorly and leads to increased operator fatigue and increased bar loading. Depth gauges filed too low make the chain grab at the wood and may negate the benefits offered by safety chain.

Chain design plays a major part in kickback reduction. Older, non-safety designs carried only teeth and depth gauges. Since these present a solid leading edge at the depth gauge should an object be suddenly forced into the chain, they can easily be made to engage fully with the foreign body and launch into a full kickback. Careful filing of the depth gauges, making a radius down to the leading edge, reduces the risk somewhat. Newer chains with ramped drive links fill in the gap ahead of the depth gauge, reducing the tendency to grab still further. Full safety chains have extra bumper links between the cutting links, maintaining nearly full depth gauge height along the full extent of the chain and reducing the risk of kickback to very low levels. Full safety (bumpered) chains are often fitted as original equipment to domestic and entry level saws. Modern "professional" chains offer far higher cutting performance than full safety chain, and offset their increased risk with an assumption of a much higher degree of operator competence. In reality they are still safer than traditional chains due to the vastly improved depth gauge design, with a deep ramp ahead of the gauge point.

Bar design is another factor in reducing kickback risk. The larger the radius of the bar tip, the greater the risk of kickback as the degree of engagement with the log (or other body) will be greater for a larger tip. Domestic class bars, climbing saw bars and entry-level professional bars usually have very small tips. Professional bars designed for logging and felling may have much larger tips as they are often used for boring cuts to free trapped timber or fell difficult trees, and a tapered, small-tipped bar will wedge easily when boring, stalling the chain. A large-tipped bar with nearly parallel sides bores easily and does not tend to jam.

While kickback prevention is a great concern in the context of chainsaw use, it is not the only means by which an operator can be injured by a saw. Local conditions, operator competence and many other factors need to be considered before undertaking sawing operations.

Safety throttle

The engine throttle is operated by the trigger under the rear handle of the saw. Unless the lock-out switch above the rear handle is also pressed, the throttle cannot move from the idle position, and the chain will not be driven.

The safety throttle prevents the chain from being driven if the trigger is accidentally pushed by an obstruction, such as a branch in undergrowth. It also prevents throttle activation when hot-starting a saw on the ground with one boot inside the rear handle. The safety throttle is an additional layer of protection in this case, since the chainbrake should be applied before starting a saw in any context.

The pictured model has an enlarged lock-out or 'dead man' switch which, when released, also activates the chain brake, thus instantly halting the running chain as well as disengaging the throttle.

On/Off switch

The on/off switch stops the engine running by preventing the ignition coil from firing. It must be clearly marked with the stop position. There must be a positive click action, so that there is no chance that the switch will change position accidentally, even while the saw is vibrating under heavy load.

If the switch were to move to the off position while the operator was in the middle of a critical cut while felling a tree, there would at least be a delay, which increases the chance that the tree might fall in an uncontrolled manner. Also, the saw might jam in the cut, requiring that the operator spend extra time under the unsafe tree freeing it. A switch failing "on" would also present a hazard, since the saw may then start inappropriately, such as when testing compression or assessing starter function.

If the operator is injured while using the saw, a bystander might have to move in to turn the saw off. The bystander may be unfamiliar with the saw and needs to be able to identify the on/off switch by its markings.

The Stihl model shown combines the choke, throttle start setting and ignition switch into one unified control lever. Other brands of saw usually have separate controls for all three, or a combined throttle start setting and choke control with a separate ignition switch.

If the switch fails to operate, a saw may be reliably stopped by operating the choke control to flood the engine.

Centrifugal clutch

The centrifugal clutch disengages the chain from the engine when the engine is only at idling speed, engaging the drive automatically when the throttle is squeezed and the engine is at full speed. The purpose of this clutch is to avoid having a moving chain when the saw is idling and temporarily not cutting. At idle the chain should not move.

Many rear-handled chainsaws are used in a state, owing to poor maintenance, where there is some clutch drag and so the chain does move slowly at idle. For top-handled saws though, this is extremely dangerous and the clutch (and chain brake) on such a saw must always be functioning correctly.

Some early chainsaws used a manual clutch instead, but this is long obsolete. Anti-vibration system rubber bush metal spring

Excessive vibration over long periods can cause the user to develop hand-arm vibration syndrome (HAVS), or white finger. This is a potentially permanent and debilitating industrial injury. To reduce vibration, saws are divided into two parts. One part is a rigid assembly of the cutter bar and engine. This part vibrates strongly when the chain is cutting. The other part is a rigid assembly of the handles and controls of the machine, the part the user holds. These two rigid assemblies are joined together by mounts which provide spring suspension and damping.

Both metal springs and rubber bushes can be used to provide suspension. Metal springs are more robust and longer wearing, but rubber bushes provide damping in addition to a spring action.

Many modern saws incorporate electrically heated handles. This can help prevent HAVS by encouraging circulation to the fingers. Husqvarna models with this option have a "G" suffix after the model number.

Rear handle

Rear-handled chainsaw and two-handed grip

The front and rear handles of a typical "rear handle" chainsaw are widely spaced,so as to provide enough leverage for good control,[6] and also to provide some degree of control in the event of a kickback.

The operating controls of the chainsaw, such as the throttle and the engine stop (or on/off) switch, are placed so that they may operated whilst retaining a good grip on the rear handle.

It is impossible to use a rear-handled chainsaw single-handed. Their balance is such that this is not merely unwise, but so impractical as to be beyond a reasonable chance of it even being attempted.

Top-handled chainsaws

Top-handled chainsaws are a form of chainsaw whose safety is deliberately compromised in order to permit them being used single-handed where this is essential. They are restricted to working at height, such as up a tree.In all other cases, it should be possible to arrange the cutting task so that it can instead be carried out with two hands and the safer rear-handled chainsaw.

In the top-handled saw, the rear handle and its operating controls are moved to the top of the saw.This gives a balance to the saw such that it can now be used one-handed. The front handle remains the same. The chain brake lever is usually separate, rather than being combined into the protective hand guard.

In most cases, the top-handled chainsaw is used two-handed.It is only used single-handed when this is essential, such as when one hand is required for climbing.At ground-level, top-handled saws should not be used.

Owing to the nature of work at height, and the difficulty of continually re-starting the saw, the engine will often still be running when it is not used for cutting at that moment. For this reason it is particularly important that the centrifugal clutch is operating correctly so that the chain doesn't rotate when the engine is idling.The chain brake should also be engaged manually when not actually required,which is why top-handled saws usually have an easy brake control lever.

In many jurisdictions, use and even purchase of top-handled chainsaws is restricted to those holding the relevant certificate of competence in their use.

Rear hand guard

The rear hand guard protects the users right hand from being struck by a snapped or derailed chain.It also allows the rear of the saw to be held down by the operator's boot for starting. This is especially useful for cold engines, and larger (70 cc+) saws.

Exhaust

The exhaust directs the hot and noxious gases coming from the engine away from the user. A faulty exhaust increases noise, decreases engine power, can expose the user to unsafe levels of exhaust gases, and can increase the chance that the user could accidentally touch extremely hot metal. Most models feature a spark screen which is integrated into the muffler. The spark screen prevents sparks from being discharged from with the exhaust and potentially igniting sawdust. The spark screen also reduces noise.

Hand/Eye/Ear Defender Symbols

Warning labels

In the EU at least, it is a legal requirement that chainsaws carry certain standardized warning labels which warn of the dangers of kickback as well as making clear the need for protective clothing.

Scabbard

The cutter chain is sharp enough to cause injury even when it is not being driven. The scabbard covers the chain when the saw is in storage or being transported. It also protects the chain from damage, for instance blunting by contact with concrete floors.

Air Compressors

An air compressor is a machine that is capable of converting electrical power into kinetic energy, specifically by utilizing compressed air. When this air is released in a quick burst, it releases an amount of kinetic energy that can be harnessed for a number of purposes, including pneumatic device activation, air transfer (such as filling a tire), and cleaning operations.

Air compressors work in two phases: the compression operation and the release operation. There are multiple methods of compressing air, including reciprocating pistons, rotary screws and centrifugal compression. Compression release, or air delivery, varies as well, and is measured in cubic feet per minute. Generally, the more horsepower a compressor is capable of, the more powerful the air delivery.

Air Compression Methods

Positive-displacement compressors are the more common type of air compressors available for hobbyists, small-scale applications and industrial-scale applications, although other types, including rotating impeller compressors, are still commonly used. A positive-displacement compressor essentially relies on part of the device performing an intake of air, and then minimizing the amount of space in the chamber to pressurize the air molecules. When the air is released, a valve opens and the compressed air quickly discharges.

Piston-type compressors are fairly common. These compressors use the motion of a piston to introduce air into a chamber through an intake valve. An automotive-type piston is a clear example. An automotive-type piston consists of a crankshaft connected to a rod, which is topped by a cylinder inside another cylinder. The crankshaft base revolves in a small circle. The connecting rod remains in a fixed position in relation to the crankshaft, but it operates in a hinged manner with the cylinder, allowing the cylinder to remain vertically or horizontally oriented at all times. When the crankshaft is at its lowest revolution point, the rod drops the cylinder as well. When the crankshaft turns further, the rod rises, pushing the cylinder up. This constant motion perpetuates an up-and-down path for the cylinder, and allows for air intake and release.

The exterior cylinder is topped with an inlet port, an outlet port and two valves housed in three chambers. One chamber is the inlet chamber, one chamber is the outlet chamber, and between them is the pistons cylindrical chamber. When the piston drops, the inlet port allows air to fill the space in the cylindrical chamber through an inlet valve. When the piston rises, the inlet port does not allow air to pass back through into the inlet chamber, so the air travels through the outlet valve into the outlet chamber. The repetition of this process forces more and more air into the outlet chamber, causing more compression. When the user releases the outlet chamber, air delivery occurs.

Other positive-displacement compressors use a different method of compressing their air chambers. Rotary screw compressors create an air chamber between helical screws and their housing. When the screws turn, the air chamber volume reduces, compressing the air between the screws. Vane compressors consist of a slotted rotor within a slator, the fixed housing area for the rotor. Because of the blade orientation on the rotor, the rotor revolution pushes air into a chamber and works to compress the volume with each subsequent blade rotation.

Most all positive-displacement compressors use oil as a lubricant for compressor motion as well as a solid seal for the compressed air. All of these devices must account for this oil introduction by removing oil before release. If the oil isn’t separated from the compressed air, contamination may occur in the form of “oil carryover.”

A non-positive-displacement compressor example is a centrifugal compressor, which uses dynamic compression in operation. A centrifugal compressor spins an impeller, a type of rotor, to accelerate the air within, and then a diffuser to decelerate the air. This deceleration causes the pressure on the air to rise. This air heats up during the process and must be cooled by an intercooler.

Air Compressor Applications

Air compressors are used in a variety of commercial and industrial applications. Typically, commercial air compressors are designed to work with various tool attachments in order to provide pneumatic power. A variety of electric tools use the air compressor, including blo-guns, nail guns, air staplers, air sanders, spray guns and sandblasters. These tools usually have industry standard attachments so they can be hooked up to a variety of air compressor brands. Air compressors can also be used to fill tires and other items with air.

Industrial strength air compressors are used to power industrial tools much like commercial varieties, but they can also be used to power larger machines and applications. For instance, petroleum is often “coked,” when carbon particles known as coke are introduced to change the behavior of the petroleum for efficiency reasons. In order to coke large amounts of petroleum, air compressors are used to power the process. Air compressors are also used in applications where purging systems are required to remove unwanted particles.

How Mailing Machines Work

Milling machines are tools designed to machine metal, wood, and other solid materials. Often automated, milling machines can be positioned in either vertical or horizontal orientation to carve out materials based on a pre-existing design. These designs are often CAD directed, and many milling machines are CNC-operated, although manually and traditionally-automated milling devices are also common. Milling machines are capable of dynamic movement, both of the tool and the workpiece, and many milling machines can perform multi-axis machining.

Because of variations in orientation, operation and application, milling machines have varying functions and different operating principles.

Tooling

Milling machines can be outfitted with a number of tool heads to accomplish different machining needs. Some of these tool heads include cutters, rounding mills, fluted mills and ball end mills. Some milling machines have rotating tool ends that can change depending on the needed task—computer programming communicates with the machine when to change its tooling.

The different tooling used in milling machines is based on material and desired shape. Because materials like wood and steel have different physical properties, different tool bits are needed to properly machine the materials. If a milling machine uses a tool bit that is not strong enough to machine steel, the tooling and even the machine itself can be damaged. Tooling that is too strong for softer materials can damage the workpiece.

The basic tooling bit on a milling machine is called the cutter. A cutter is a shaped bar that has saw teeth. The cutter rotates rapidly to cut down and shape materials. The cutter is attached to an arbor, which is sometimes called a mandrel or mandril, a shaped bar that varies in size, length and ending, and is used to hold the cutter firmly.

A milling cutter’s saw ending can be spaced, sized and oriented in many ways. Generally, the teeth are either positioned in a straight up-and-down orientation, or angled in a helical orientation. Straight teeth are preferable in operations on denser materials, while helical teeth can create very smooth cuts on softer materials. There are a variety of cutters within these categories, including dense end cutters, t-slot cutters, and angle cutters. Cutters are subject to different standardized sizes, with CAT sizes as the most commonly-used standardization category in the United States.

Types of Milling Machines

Milling machines are categorized by their orientation to their workpiece and their degree of motion.

Knee-Type

Knee-Type milling machinesemploy a vertical workspace supported by a knee, which is an adjustable vertical casting. The knee supports a saddle and can be adjusted to allow for a customizable workspace.

Plain Vertical and Horizontal

Milling machines with a standard work surface can either be oriented vertically or horizontally. The tooling assembly is generally affixed on a turret and swivel, typically positioned parallel to the workspace. The turret and swivel allow the tool to move freely around the workpiece to enforce tight tolerances.

Universal Horizontal Milling Machine

A universal horizontal milling machine differs from the plain horizontal type because it has a table swivel housing, which allows the table to move out 45 degrees from the standard horizontal position. This workpiece movement allows for easier angular or helical milling operations.

Ram-Type and Universal Ram-Type Milling Machines

A ram-type machine is used to allow the tooling to position itself on a greater range of space with regards to the workpiece. The ram-type machine has a spindle on a movable housing, which can move within a set horizontal plane. The universal ram-type milling machine includes a swivel housing that increases the range of cutting movements.

Swivel Cutter Head Ram-Type Milling Machine

With a swivel cutter, a milling machine can rotate from a completely vertical to a completely horizontal position. The worktable also moves, providing the user with a very liberal degree of motion and orientation. Many swivel cutters include both automatic or hand driven settings, increasing operation options.

Simple Guide For Machines

A Guide to Simple Machines A Guide to Simple Machines

The most elaborate machines and inventions are really derived from very basic ideas. The ideas that have come from the simple wheel, inclined plane and pulley systems have been adapted into more complex inventions such as automobiles, airplanes and other machinery.

Teachers have found that the study of these types of simple machines can be beneficial in learning about more complex ideas. Because of these ideas, we have assembled a number of links that can be beneficial to teachers in teaching scientific concepts that simple machines provide:

Pulleys

Pulley Activities – activities that can be used to demonstrate the principals of the pulley.

Pulleys – information on how pulleys work and the types of pulleys.

Pulley Uses – educational example of the uses of pulleys.

Pulley Example – useful experiment that students can do to learn about how pulleys work.

Gears and Pulleys Lab – lab that students can do to learn about gears and pulleys.

Wheel and Axle

Physics Concepts – useful information that can be presented to students about the wheel and axle.

Let’s Move It – informative page with educational resources to teach engineering principles.

Simple and Complex Machines – information on activities to teach about machines.

Wheel and Axle – the simple machine is described by how it works.

Work, Power and Machines – experiments and information on how simple machines function.

Lever

The Lever – physics and engineering are discussed in this informative article about the lever.

Simple Machines – information about the lever and other simple machines.

Types of Simple Machines – useful information about the lever and other simple machine types.

Lever and other Simple Machines – informative site listing various types of simple machines and their uses.

Lever – resource detailing the uses of the lever as a simple machine.

Inclined Plane

Simple Inclined Plane – useful website exploring the physics behind the inclined plane.

The Inclined Plane – good educational resource to help students understand the inclined plane.

Inclined Plane Experiment – helpful demonstration of how the inclined plane is used.

History of Inclined Plane – exploration of the physics and uses of inclined planes.

Inclined Plane and Pulley – interactive experiment on uses of the inclined plane.

Wedge

Wedge – information and examples of the uses of the wedge.

Understanding the Wedge – informative page discussing the uses of the wedge.

Wedges and Screws – useful information on this page showing how wedges and screws operate.

Wedge and Lever – informative lab showing how the wedge and lever operate.

What Do Wedges Do? – experiment showing the use of a wedge and how it works.

Lesson Plans

Lesson Plans – wide variety of lesson plans dealing with simple machines.

Simple Machines – very good resource containing lesson plans about simple machines.

Simple Machines – collection of five lessons on simple machines.

Simple Machine Web Quest – very useful site containing a web quest dealing with simple machines.

Simple Machines – unit worth of plans covering simple machines.

Simple Machine Projects

Experiments – collection of experiments covering simple machines.

Lessons – variety of lessons for students to understand the workings of simple machines.

Simple Machines – helpful collection of resources covering simple machine projects.

Understanding Simple Machines – useful information on how to understand the workings of simple machines.

Simple Machine Activities – resourceful site containing numerous activities and lessons concerning simple machines.

Using Ecm Motors in HVAC System

HVAC (Heating, Ventilating and Air Conditioning) refers to systems that heat or cool a designated environment. HVAC systems are especially important when it comes to designing large office buildings or climate controlled environments, such as some aquatic enclosures at the zoo. To achieve heating or cooling, an HVAC system depends heavily upon the quick movement of air from one location to another. AC motors have been used in past applications to serve as the primary air driving force, but they are not always the most efficient choice because they run continuously at full power. Electronically commutated motors (ECMs) were developed to offer a greater range of operability choices, and to minimize noise.

ECM Basics

ECMs are DC motors that function using a built-in inverter and a magnet rotor, and as a result are able to achieve greater efficiency in air-flow systems than some kinds of AC motors. (Although AC current is used for ECM, the ECM’s internal rectifier converts the current to DC voltage). Permanent split capacitor (PSC) motors, often used in conjunction with electronic SCR motors, are somewhat inefficient when used in air control systems because the fan motor noise requires the motor to run at less than a full load. When turned down, PSC efficiency suffers and falls in the range of 12 to45 percent. ECMs, on the other hand, maintain a high level (65 to 75 percent) of efficiency at a variety of speeds. As a result, ECMs are cost and energy efficient and can reduce operating costs. Additionally, ECMs are not prone to overheating and do not require additional measures to offset the generation of heat, as PSCs often do.

ECMs are also relatively low-maintenance; the use of true ball bearings reduces the need for oiling, and varied start-up speeds reduce stress on mounting hardware. The operating range is significant enough to enable one ECM to replace two induction-style models, which simplifies the replacement, maintenance, and installation processes, and minimizes product choices. However, not all ECM motors run at variable speeds and selection depends heavily upon application specifications. The initial cost of an ECM can be high, but is typically balanced by overall energy savings in the long run.

ECM in HVAC Systems

When considering an ECM for application in an HVAC system, there are several factors to keep in mind. Although ECMs are often selected because many models run at variable speeds, in certain condenser applications it is preferable to select and ECM that runs at a fixed speed—an ECM running at a fixed speed s in a condenser unit still uses less energy than a typical PSC motor running at a fixed speed in a similar unit. As a result of increased energy savings, a condenser operating with an ECM will have a higher SEER (seasonal energy efficiency ratio) rating. In other HVAC units, an ECM can run at variable speeds but depends on a controller that pre-programs speed, including the rate at which the motor ramps up. Whereas typical PSC motors start and almost immediately run at full capacity, an ECM can start slowly and stop slowly, which can help reduce humidity. Additionally, the control can be set to alter the amount of air an ECM motor drives through the system, which enables a greater range of possible air-flow rates.

A typical ECM operating in an HVAC system will go through several stages, as determined beforehand by a manufacturer or a preprogrammed controller. In its first stage, and ECM runs at a lower speed to remove humidity (this is especially important in a cooling system). Next, the ECM reaches its designated peak speed, as specified for the application, maintaining high efficiency despite any shifts in operating speed. When the ECM stops, it can be programmed to stop slowly (called a soft stop).

How Wood Chippers Work

Wood chippers (or tree shredders) are frequently used in industrial lumber applications to reduce wood into chips or sawdust, as part of wood recycling or as part of a manufacturing process. Wood chippers are also used by those in the agricultural industry during property and land maintenance, or to aid in clean up after a storm or meteorological event. Typically, wood chippers are comprised of several distinct parts, including a hopper, a collar, a chipper, and a collection bin. An internal power source, typically a combustion engine, can range from 3 to 1,000 horsepower, depending on the size and type of chipper.

How Wood Chippers Work

Regardless of the size or make, wood chippers all function in the same basic manner. An internal engine, either an electric motor or a fossil-fuel engine, powers the device. A gearbox uses pulleys and v-belts to connect the engine to a set of knives—the pulley enables the engine to control the speed at which these blades rotate, and the v-belt transmits the power from the engine. Internal gears within the gearbox also help control speed and power.

Wood chippers typically have two separate chutes for processing wood. The first chute, the smaller of the two, shreds branches into chips. The second, larger chute features blades and additional devices, such as hammers, to turn excess plant material (such as leaves) into mulch. Based on the kind of blades within the chipper, a user can determine the type and thickness of wood the chipper is capable of handling. Typically, the larger the machine, the larger the load it can handle. Blades can either function on separate shafts or intermesh. If several blades are rotating on independent shafts, the wood will be repeatedly cut down the branches as they are passed through the blades at a fast pace. Intermeshed blades are somewhat slower, but are somewhat self-feeding as they draw the branches into the blades themselves. Additionally, intermeshed blades produce consistently sized chips.

Types of Wood Chippers

There are several kinds of wood chippers, ranging from those designed for residential use to larger, industrial models.

High-Torque Roller

High-torque rollers tend to be low-speed. Because they are also powered by an electric motor they are quiet, which makes them a popular choice for residential applications. Additionally, they are self-feeding, and some offer anti-jamming features.

Drum

Drum chippers are named for the large, motor-powered drum located at the center of the machine. The drum draws material in, like a feeder, and chips material while moving toward the output chute. The process is very fast and loud, and carries significant safety risks. Because the drum and engine are directly connected, any kind of drum jam can subsequently affect the engine, causing the engine to stall and pieces of wood to become lodged in the drum. Additionally, operators must exercise care when feeding the machine so as not to get clothing or appendages caught in drum, which can cause extreme injury or death. Some models offer additional safety features, which help ensure operator safety while also minimizing the sound of the machine.

Disc

A disk chipper features a disc, typically steel, with cutting blades attached. Material is drawn from the hopper via hydraulic wheels, and then moved toward the spinning disc. As the disc rotates, the blades encounter the wood, the material sliced into chips. With industrial disk choppers, the disc can be as large 160 inches in diameter, with an engine of up to 5,000 horsepower.

General Types of Bearing and How They Work

Generally speaking, a bearing is a device that is used to enable rotational or linear movement, while reducing friction and handling stress. Resembling wheels, bearings literally enable devices to roll, which reduces the friction between the surface of the bearing and the surface it’s rolling over. It’s significantly easier to move, both in a rotary or linear fashion, when friction is reduced—this also enhances speed and efficiency.

How Bearings Work

In order to serve all these functions, bearings make use of a relatively simple structure: a ball with internal and external smooth metal surfaces, to aid in rolling. The ball itself carries the weight of the load—the force of the load’s weight is what drives the bearing’s rotation. However, not all loads put force on a bearing in the same manner. There are two different kinds of loading: radial and thrust.

A radial load, as in a pulley, simply puts weight on the bearing in a manner that causes the bearing to roll or rotate as a result of tension. A thrust load is significantly different, and puts stress on the bearing in an entirely different way. If a bearing (think of a tire) is flipped on its side (think now of a tire swing) and subject to complete force at that angle (think of three children sitting on the tire swing), this is called thrust load. A bearing that is used to support a bar stool is an example of a bearing that is subject only to thrust load.

Many bearings are prone to experiencing both radial and thrust loads. Car tires, for example, carry a radial load when driving in a straight line: the tires roll forward in a rotational manner as a result of tension and the weight they are supporting. However, when a car goes around a corner, it is subject to thrust load because the tires are no longer moving solely in a radial fashion and cornering force weighs on the side of the bearing.

Types of Bearings

There are numerous different kinds of bearings that are designed to handle radial load, thrust load, or some combination of the two. Because different applications require bearings that are designed to handle a specific kind of load and different amounts of weight, the differences between types of bearings concern load type and ability to handle weight.

Ball Bearings

Ball bearings are extremely common because they can handle both radial and thrust loads, but can only handle a small amount of weight. They are found in a wide array of applications, such as roller blades and even hard drives, but are prone to deforming if they are overloaded.

Roller Bearings

Roller bearings are designed to carry heavy loads—the primary roller is a cylinder, which means the load is distributed over a larger area, enabling the bearing to handle larger amounts of weight. This structure, however, means the bearing can handle primarily radial loads, but is not suited to thrust loads. For applications where space is an issue, a needle bearing can be used. Needle bearings work with small diameter cylinders, so they are easier to fit in smaller applications.

Ball Thrust Bearings

These kinds of bearings are designed to handle almost exclusively thrust loads in low-speed low-weight applications. Bar stools, for example, make use of ball thrust bearings to support the seat.

Roller Thrust Bearings

Roller thrust bearings, much like ball thrust bearings, handle thrust loads. The difference, however, lies in the amount of weight the bearing can handle: roller thrust bearings can support significantly larger amounts of thrust load, and are therefore found in car transmissions, where they are used to support helical gears. Gear support in general is a common application for roller thrust bearings.

Tapered Roller Bearings

This style of bearing is designed to handle large radial and thrust loads—as a result of their load versatility, they are found in car hubs due to the extreme amount of both radial and thrust loads that car wheels are expected to carry.

Specialized Bearings

There are, of course, several kinds of bearings that are manufactured for specific applications, such as magnetic bearings and giant roller bearings. Magnetic bearings are found in high-speed devices because it has no moving parts—this stability enables it to support devices that move unconscionably fast. Giant roller bearings are used to move extremely large and heavy loads, such as buildings and large structural components.