Here at MPT Drives, we believe that
our success is a satisfied customer. TechTips is designed to
become a reference library for you to troubleshoot and solve the
most common product questions. You'll find helpful tips on getting
the most out of your investments. The information contained within
our "Tech Tips" is for informational usage only. The
information provided is based solely on our experience, it is not
intended to replace or circumvent the user manuals supplied with
our products.
| Diagnosis
of problems in Warner Electric Clutches and Brakes |
Warner
Electric Electromagnetic Clutches and Brakes are basically simple,
very reliable devices. Problems with a unit that is not
functioning are usually easy to diagnose with a few simple tools
and a little knowledge. The only tools needed to diagnose most
problems are a Screwdriver and a Volt/Ohmmeter.
Only
three things are needed for an Electromagnetic Clutch or Brake to
function: Proper
voltage, usually 90 Volts DC, Proper resistance in the
electromagnetic coil, usually about 100-1500 OHMS and a Proper
air gap between the armature and magnet or armature and rotor,
usually about 1/32”
The
most common problem with a nonfunctioning new unit
is too large of an air gap. A used unit that has been functioning
usually does not have this problem, if the gap has not been
disturbed. Once the gap is properly set, the auto gap feature
maintains the gap for the life of the unit. The gap is set, by
pressing the armature manually into the magnet or rotor. The
armature will then pop back to the proper setting, about 1/32” A
unit that is functioning will have visible motion and sometimes an
audible click when the magnet pulls the armature and closes this
air gap. The air gap can be adjusted by hand on open units, but is
a slightly more complicated procedure on Unimodules and
Electromodules. These units must be adjusted with a flat blade
screwdriver, inserted through the outer housing, and through an
oblong slot in the fan. This is best done after consulting an
instruction manual.
If
you do not have access to a Volt/ Ohmmeter you can perform a
simple test for the presence of magnetism. With the motor
power turned off and, the power to the clutch
or brake turned on, place an unmagnetised steel
screwdriver near the magnet. If the screwdriver is drawn to the
magnet, magnetism is present and voltage or resistance problems
can normally be ruled out. The air gap is the likely suspect. If
there is no magnetism, the voltage and resistance must be checked.
If
you have a Volt/Ohmmeter, set it to the 90 Volts DC scale and test
for voltage at the coil terminals. If there is no voltage, check
for voltage at the power supply output terminals. If there is
voltage at the output terminals, but none at the coil terminals,
there is a problem with the wiring or switching in between the
power supply and magnet. If there is no voltage at the power
supply output, check for voltage at the input. If there is voltage
at the input but none at the output, make sure any voltage
adjustment pots are turned up, and the fuse is not blown. No
voltage at the input indicates a problem with the wiring, fuses or
switching on the input side. If a blown fuse is replaced, and
continues to blow, check the coil resistance.
If
there is voltage at the coil terminals, but the unit fails to
function, disconnect power and remove the wiring from the coil
terminals. Set the Volt/Ohmmeter to the resistance scale. Test the
coil resistance by connecting the Volt/Ohmmeter probes across the
coil terminals. The specifications for proper resistance can be
found in the Warner Electric catalog or, can be obtained by
calling MPT Drives. (800.473.7433) Lacking the proper resistance
specification, you can use an approximate value of 280-300 ohms.
Usually when a coil fails, it will measure either zero, indicating
a shorted winding or, infinite, indicating an open winding. Zero,
or very low resistance will blow fuses in the power supply. A coil
with out of spec resistance needs to be replaced.
One
last thing, most mechanic types are used to seeing automotive
style brakes. In an automotive brake, metal-to-metal contact is an
indication of a problem. Since Warner Electric clutches and
brakes are electromagnetic, metal-to-metal contact is essential,
and is not a cause for replacement. Do not reface a
magnet or armature that looks worn. If it has worn beyond
serviceable limits the components need to be replaced.
If
you have checked and verified the presence of Proper Voltage,
Resistance and Air gap, the unit closes the air gap
when the power is on but still fails to run, check for a
mechanical jam in the driven machinery. If all of these things are
checked and the unit still fails to run you have discovered a
“Great Mystery of the Universe” Consult
MPT Drives for technical assistance at 800.473.7433
Pat
Armitage
MPT Drives, Inc.
Sales Engineer
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|
In order to assure the correct
shaft alignment of both sides in a coupling application, each side
of the coupling should be installed with the capscrews in the
coupling individually tightened to a snug position, and then
tightened to the proper recommended torque value with a torque
wrench. Only after the first shaft is installed in its portion of
the coupling should the same process be repeated for the second
shaft. This sequence of installation will assure that the individual
shafts are properly aligned with the coupling itself, and with each
other. An improper installation may result in less than optimal
concentricity value as measured by TIR, possibly causing component
vibration and damage.
Source: Tech Tip from Collars &
Couplings, Inc.
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| Sizing
or Re-Sizing V-Belt Drives |
V-Belt drives
have always been an integral part of our business here at MPT
Drives. With the increased use of VFD’s in the HVAC Industry,
their popularity has waned slightly, but there are still thousands
of V-belt drives in the field.
Many times, these
drives need to be changed, sometimes by changing one of the sheaves,
sometimes a complete new drive is required. That is where MPT Drives
comes in. We are more than happy to help. To adequately advise you
on the best option for you, we need the following information:
1.
Motor HP
2.
Required Fan RPM
3.
All information about the existing drives (Sheave diameters,
belts size, shaft diameters)
4.
Is there a belt guard or belt tube in place?
5.
Is an increase in speed going to adversely affect your
motor’s amp draw?
Whenever
possible, we will try to reuse the existing equipment. Just changing
one sheave and maybe a set of belts will decrease down time and
reduce costs. There are times when you need to replace the whole
drive. If that is the case, we will make up to ten selections and
make a recommendation as to what we think may be right for you. To
accomplish this, we use Browning Edge® software. This software is
available either on CD or on the Web. Based on the information we
enter, The Edge® program will make up to ten selections to try to
fit the specifications. They are listed in order of cost, least
expensive on up.
One word of
caution to customers using the Edge® software on their own;
although Emerson-EPT will stand behind any drive selected by their
software, the least expensive drives are shown first. Although it
may appear attractive to save money on the initial drive, proper
installation and maintenance are critical to keeping the drive
running properly. Sometimes the savings are quickly eaten up by the
higher maintenance costs. As with any product, proper maintenance is
essential to V-Belt drives, but it may be more cost effective to
spend a little more on a less “finicky” drive. We will be happy
to lend our guidance to help you make your selection.
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| Torque
Limiters- Mechanical Vs. Electronic Devices |
Most
machines can be damaged by mechanical jams (overloads) Often a
machine’s designers mistakenly believe that the heaters, called
“overloads” in a motor starter, or the over-current protection
in a variable speed drive, will protect the machine from mechanical
overloads caused by jams. These devices are designed to protect
against electrical overloads, they should be thought of as
functioning as a fuse. They are not intended to function as a
mechanical overload protection device.
The three
main reasons that these devices cannot be relied on to provide
mechanical overload protection are: 1) Current based devices must be
sized to accommodate startup current inrushes. Starting currents can
be as high as 600 % of the full load current. 2) Amperage (Current)
change, is not linear with respect to actual motor load change, and
usually will not reliably react fast enough to protect the driven
equipment. 3) Many of these devices are deliberately designed to be
a time-delayed feature.
Mechanical
drive components are better protected with the installation of a
dedicated torque-limiting device. Some common mechanical torque
limiting devices are: Shear Pins, Friction Clutches,
and Ball-Detent Clutches. Mechanical Torque Limiting Devices
have an advantage over Electronic Torque Limiters only in small
sizes, when they are inexpensive by comparison to the electronic
version. Mechanical devices have many disadvantages, regardless of
their size. Many designs are difficult to reset. In a shear pin
design, the old pin must be removed. The pin liners must then be
aligned, and a new pin must be inserted. If a proper shear pin is
not readily available, any pin of a similar size is often inserted
in place of a proper shear pin. If this happens, all overload
protection is obviously lost. In a Friction Clutch installation,
when an overload setting is exceeded, the clutch will slip. These
devices will quickly overheat, and wear out, if not detected soon by
plant personnel. Each time a friction clutch slips, the overload
setting is reduced by wear. Ball Detent Clutches need to have a
proximity switch, or limit switch associated with them, to shut off
the drive, when they are tripped by an overload. If this switch
fails, or is out of position, the Ball Detent Clutch will quickly
fail.
Most
mechanical overload protection devices are located in the open, and
are subject to “Adjustment” by the machine operators. Often this
means that they are set to their maximum setting, which usually
renders them useless, eliminating their function as a torque
limiter.
Electronic
overload protection devices are generally divided into two main
categories, Current Monitors, and Power Monitors.
Current Monitors are less sophisticated devices that measure the
current draw of the drive motor. The main limitation of
current-based devices is that changes in current, lag behind the
changes in the actual load, as seen by the drive motor. This means
that they are slower to react to an overload. The better electronic
overload protection devices are Power Monitors. These devices look
at both current and voltage, and apply a mathematical formula to
determine the actual power produced by drive motor. Typically this
measurement is done every eight milliseconds, as the sine wave
crosses the zero point. These devices are far more accurate, and
much faster reacting than current-based overload protection devices.
Their performance far exceeds the performance of any mechanical
overload device. Power Monitor load limits can be set in several
important ways, an ultimate high limit, a rate of change limit, and
for some applications, a low limit. A high limit can be used for
gradual increases in load, a rate of change will detect sudden
increases, such as are seen in a jam condition, and low limits are
used in detecting conditions like dry pumps, or failed drive
components. These limits are easily set; all you need to do is
monitor the load seen by the running machine, and set the limits
somewhat higher (Or lower) than the normal condition. You then need
to observe the operation, to ensure that there are no nuisance
trips. If nuisance trips occur, a gradual adjustment is needed,
until the nuisance trips are eliminated. When any of these preset
limits are exceeded, an output relay changes state. This is normally
used to shut off the drive motor, and can be used to sound an alarm,
light a warning etc.
Power
monitor devices have many advantages over conventional mechanical
torque limiting devices. They are less expensive than large
mechanical torque limiters. Because they can be mounted in a locked
enclosure, they are resistant to unauthorized “Adjustment” Many
power monitors have output functions, that will output an analog
signal that is relative to load. This can be recorded to catch
changes in machine load, such as bearing condition, broken, or dull
cutting tools, and many others. There are also models that can be
monitored by computer.
Protection
from mechanical jams should be designed into any machine that could
be damaged from such an event. Power monitors are the best
performing solution, and can be less expensive to install, and
operate than many common mechanical overload devices. For more
information on overload protection devices, contact your MPT Drives
sales representative.
Pat
Armitage
MPT Drives, Inc.
Sales Engineer
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| What
is Horsepower? What is Torque? |
There
is a lot of discussion about horsepower and torque. I find most
people don’t really have a clear understanding of exactly what
each of these terms actually mean. We are usually exposed to these
terms early in life, about the time we begin to get interested in
cars. We read in automotive magazines dynomometer test reports, that
a particular car produces X amount of horsepower and torque. I find
that most people look at the horsepower numbers, but usually ignore
the torque figures. I think that this is because people believe
that they understand what horsepower is but that they have no clue
as to what torque is. What most of us really know about horsepower
and torque is that more is better; at least when it comes to our
cars.
Horsepower
is a measurement of kinetic energy, and torque
is a measurement of force. Either one can be
derived from the other with the appropriate formula.
Torque
x Rpm / 63025 = Horsepower
Or
Force
x Velocity / 33,000 = Horsepower
Horsepower
x 63025/ rpm = Torque
Torque
can be present at zero rpm, in which case the horsepower would be
zero.
Without the element of time,
(revolutions per Minute) there is no energy.
If
you think about it, it might seem strange that we rate motors in
terms of how they compare to horses. As it turns out there is a
logical, historical explanation, for this comparison. James Watt,
the inventor of the steam engine, needed a way to rate his steam
engine in terms of its output power. He concluded that an obvious
way would be to rate it against the competition of the day, the
horse. He was working at a coal mine at the time, and observed that
a mine pony could lift 22,000 lbs of weight, one foot, in one
minute. (Note the element of time in the rating)
He arbitrarily raised
that figure 50% to approximate what he thought a horse might be able
to do. So, One Horsepower is the ability to lift 33,000 lbs, one
foot, in one minute.
Torque, is a force,
tending to cause rotation. It is measured in terms of pounds, or
ounces; acting on a lever arm, measured in terms of feet, or inches.
(The metric system uses Newton Meters) This lever arm is connected
to a shaft that can rotate. Most mechanical power transmission
components are rated in terms of
“Pound Inches” or, “Inch Pounds” There is some
argument as to which variant is correct, as for me; I consider them
to be interchangeable. Smaller mechanical power transmission
components are often rated in terms of “Ounce Inches” or “Inch
Ounces” Again, interchangeable terms a far as I am concerned. One
“Foot Pound” or Twelve “Inch Pounds” of torque is a
one-pound force, applied to a lever arm, one foot, or twelve inches
long, connected to a shaft, that tends to cause rotation of the
shaft.
So, why should you
care? All driven machines require horsepower and torque to
drive them. Lets look at two simple machines, an elevator (Vertical
lift), and a chain conveyor (Horizontal move). For simplicity, we
will drive both with a 24” pitch diameter (12” radius) headshaft
(drive) sprocket. Both will have the same load of 1000 lbs. I will
calculate the required Horsepower and Torque for both, at 50 feet
per minute, and 100 feet per minute. Also for simplicity, I will
disregard the weight of the chain in all examples.
The
Elevator: A 24” pitch diameter
sprocket, lifting 1000 lbs of weight suspended from it, equals 1000
foot lbs, or 12,000 inch lbs of torque.
Force
x lever Arm = Torque
1000lbs
x 12” lever arm = 1000 ft lbs or, 12000 inch lbs
(The
force acts on the radius of 12”, the effective
length of the lever arm)
To
determine the horsepower, the element of time (speed) is required.
Chain
Pull (cp) x Feet Per Minute (fpm) / 33,000 = Horsepower
1000cp x 50fpm / 33,000 = 1.515hp
1000cp x 100fpm / 33,000 = 3.03hp
Note
that doubling the speed, doubles the required horsepower,
but the torque remains the same.
The
Conveyor: We are not lifting the load,
so a coefficient of friction is applied, that lessens the load.
Think of it in terms like this, you can’t lift your car, but you
can push it. It takes a lot less force to push, or pull, than to
lift the same weight. I will apply an extremely conservative
coefficient of friction to the total weight that the conveyor will
move (multiply the load weight by 0.2).
1000lbs
x 0.2 = 200lbs
So, a
force of 200lbs of chain pull is required at the 24”pitch diameter
(12” radius) headshaft sprocket. Again I use the same formulas:
Force
x Lever arm = Torque
200
lbs x 12” radius sprocket = 200 ft lbs or, 2400 in lbs
Chain
Pull (cp) x Feet per Minute (fpm)/ 33,000 = Horsepower
200lbs
cp x 50 fpm/ 33,000 = .303hp
200lbs
cp x 100 fpm/33,000 = .606hp
Again,
doubling the speed requires doubling of the required horsepower,
but the required torque remains the same, regardless of the speed.
Ratios,
whether by gears, belts, chain and sprockets or anything else, are
usually thought of as speed reducers, or less often, as speed
increasers. They should be thought of more in terms of what they do
to torque. A speed reducer is a torque increaser and vice
versa. The laws of physics dictate that a change of speed via a
ratio, proportionally changes the torque, as a factor of the ratio.
Disregarding the friction in the system, the torque is multiplied or
divided as a factor of the ratio. Thus, a 5:1 speed reduction
ratio, multiplies the input torque 5 times, (A mechanical
advantage) and a 1:5 speed-increasing ratio would reduce
the torque 5 times. (A mechanical disadvantage)
I hope this provides a
clear explanation of what Horsepower and Torque actually mean. Do
you need to actually remember all of this? NO! Your job is to
be an expert in what your company expects you to know, our job is to
be an expert in horsepower and torque. When these things need to be
determined, call The Drive Experts at MPT Drives Inc.
We will do the calculations, when it comes to deciding what
your machinery requires. When we do our job, we help you do
yours.
Pat
Armitage
MPT Drives, Inc.
Sales Engineer
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Taper
Bushing systems were originally conceived so that
manufacturers and distributors could carry a smaller
inventory, and save both time and money versus machining
finished bore components. There are other benefits to these
systems. Bore sizes can be changed quickly. Tapered bushings
clamp onto the shaft. The tapered OD of the bushing fits into
a tapered ID of a drive component. When the bushing is
tightened, the bushing clamps onto the shaft. This provides a
much better connection than single, or even multiple setscrew
style connection.
There
can be some confusion between the various bushing systems
commonly available on the market in the US. The terms “Taper
lock”, and “QD” are often used universally to describe
any bushing, much like Kleenex is used to describe any tissue.
The three major bushing systems on the market in the US are: Split
taper, QD, and Taper lock. Each of these
systems has it’s advantages and disadvantages.
Split
Taper: (primarily marketed by Browning) This bushing looks
much like a QD bushing at first glance. The split taper
bushing, like a QD, is a flanged type bushing. The main things
that differentiate it from the QD are: The barrel (tapered
portion) of this bushing is split in two places, with the
split ending before it enters the hub. The bushing is keyed to
the shaft, and the OD of the barrel is keyed to the drive
component as well. This design will drive, even if the
fasteners become loose. This keyed connection is it’s
primary advantage. Disadvantages to the Split taper bushing
are: Any flange-type bushing takes up more room on the shaft.
The split Taper bushing’s fasteners can be inserted from the
flange side only.
QD
(primarily marketed by Woods and Dayco) This bushing also is a
flange-type bushing, and at first glance looks like a Split
Taper Bushing. The main differences between this bushing and a
Split Taper are: This bushing is split once, and the split
extends through the flange. The advantage of this bushing
system is: It can
be mounted in two ways. Standard mount: Fasteners
inserted through the flange, into threaded holes in the drive
component. Reverse mount: Fasteners inserted through
the drive component, into threaded holes in the flange. This
feature can make installation easier. The disadvantages are,
there is no keyed connection on the barrel OD, causing
slippage if it becomes loose. In large bore sizes, the keyway
is shallow or nonexistent.
Taper
lock (primarily marketed by Dodge) This bushing looks much
different from the other bushing systems, it is a flangeless
style bushing. The flangeless design is it’s advantage,
taking less shaft space for use in space restricted designs.
The disadvantages are: This bushing often cracks when
installed or removed often making it a one-time use device.
Installation is difficult. Part of the published installation
procedure requires the installer to hammer on the large end of
the bushing, after tightening the fasteners, and then
retighten the fasteners. This hammering and retightening is
often overlooked by the installer, and can result in the drive
component coming loose, and falling off the rotating shaft. |
SPLIT TAPER®
Bushing
QD®
Bushing
TAPER BORE®
Bushing
All
taper bushings offer the advantages of ease of removal, clamp
to the shaft, ease of changing bore sizes, and less expense
than finish machining. It is their individual disadvantages
that determine which bushing system is best for any particular
application.
Most
bushing systems offer hubs that are finish machined with their
particular taper already bored in them. This makes them easy
to apply, by welding them into a drive component.
There
is another type of shaft connection device that is gaining in
popularity. They are commonly used in Europe. They are
generically referred to as “Shaft locking devices”
Ringfeder
and Fenner primarily market this shaft locking type of device
in this country. This device fits into a straight counter bore
in the drive component, and is internally and externally
expanding. This locks the device to both the shaft, and the
drive component. These devices use no keyway, and that is
their primary advantage. This allows machine builders to save
the expense of cutting keyways, possibly use smaller shaft
sizes, and allows for infinite adjustment of drive components
for timing purposes. The disadvantage of these devices is
mainly cost. They are more expensive than standard taper
bushings.
Most
applications will benefit from using one of these systems,
versus machining costs. Their clamping to the shaft can ease
maintenance, and prevent setscrews from marring expensive
shafts. Review the disadvantages of each system before
deciding on which would best suit your application.
Pat
Armitage
MPT Drives, Inc.
Sales Engineer
|
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V-Belt
Maintenance
Advanced Bearing School
Coupling
Comment #201, Parthiv Amin - Mill Products Manager