Welcome to Misumi's new 19-Minute Webinar Series.
For those of you here that are new to Misumi,
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Configurable components solve the designer's dilemma.
A designer has two choices for components; Standard
or Custom. Standard components have a limited selection
and often forced designers to compromise their designs.
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and convenient. The other choice is Custom.
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available at www.misumiusa.com.
Now I'll turn it over to our Misumi engineer.
Hi, my name is Vince Chan. I'm a Product Engineer for the Standard Components
team.
In today's webinar I will talk about the composite bushings offered by Misumi,
also called oil-free bushings. In today's topics, we are going to cover the basic
definitions of composite bushings,
the shapes and material combinations available at Misumi,
overall performance data, and application examples.
At the end I will show you how to select the component and download the 3D CAD model from
the Misumi website.
Composite bushings are essentially
plain bearings useful as a collar or a sleeve,
but what separates composite bushings from plain
bushings is that they're constructed by a combination of materials
that enhance their friction characteristics. Such combinations may be;
brass embedded with graphite, bronze with impregnated lubricants,
multilayered composite, or Teflon resin.
They can generally function as simple motion elements
for either rotary or sliding applications.
Generally for linear and rotary applications,
ball integrated bearings are still the superior choices
thanks to their very low-friction ball rolling mechanisms.
Composite bushings are inferior in terms of friction characteristics.
However, in applications where high efficiency is not critical,
they can function as simpler alternatives to ball bushings.
The unique material combinations are designed such that they will be self-
lubricating.
This is characterized by the bushings ability to transfer microscopic amounts
of materials to the sliding surface,
creating a film that lubricates and reduces the friction
over the length of travel without having to externally apply
lubrications.
In addition to being self-lubricating, low maintenance, and
easily switchable between rotary and linear application,
composite bushings are also formidable for high surface pressure
applications,
can possess a versatile range of operable temperatures,
it is thin-walled compared to most ball-integrated bearings, making it a space
saving component. And finally, when composite bushings are used,
the wear will not result in catastrophic failure.
Unlike ball bushings, some amount of contamination will not critically affect
their performance.
Let's browse through some of the composite bushings available at Misumi.
For brass with impregnated graphite you can choose from six basic designs;
straight, shoulder, flange, washer, integrated with housing,
or integrated with pillow block housing. ID from 5 to 100 millimeters,
and 8 to 100 millimeters in depth. For bronze with impregnated
lubricant, we offer three basic shapes;
straight, shoulder, and flange. ID ranging from 5 to 30 millimeters,
and depths from 8 to 70. For multilayered composite bushings,
five designs are available; straight, shoulder, flange,
housing, washer, and integrated with pillow block style.
ID from 3 to 50, and depths from 6 to 60.
These bushings are commonly made by layers of filler-added Teflon,
center bronze, and tin-plated steel.
Resin bushings materials can be either teflon or polyacetal with
special fillers; are available in straight,
shoulder, washer. and integrated with housing or pill blocks;
available in 3 to 50 millimeter ID, and 3 to 50 millimeter
depth. And last but not least, cast iron bushings
with special solid lubricants available in the forms of straight, shoulder, flange,
and with 1018 steel housing;
6 to 30 millimeter ID and 6 to 60 millimeter
depths. Let's review some highlighted performance specs.
Brass with embedded graphite bushings are perfect for clean room
applications. Their main properties that make them suitable for clean rooms are
that they will not absorb water,
and there are no lubricants to contaminate the environment.
Particles that may enter the bearing become embedded
into the liner, thus eliminating shaft damage.
In the un-lubricated condition, they have an operational regime
of -40 to 150 degrees Celsius
and with friction coefficient as low as .05,
while operating at 24.5 megapascal of pressure
on 1045 steel. There are also the high precision and thin-wall types
available. They maintain high abrasion resistance and low friction coefficient
under high-speed conditions.
Mild metals such as aluminum can be used as mating shafts.
The casted bronze bushing are porous and soaked in
lubrication. As a result, the frequency of needing to apply external lubrications
is greatly reduced. The excel in abbrasion
and braking resistance under lubricated conditions,
and are best suited for high-speed and low load applications.
According to performance data, the coefficient of friction can be as low as
.1
under a surface pressure of 1.47 megapascal,
with a velocity of over .83 meters per second.
Multilayer bushings are excellent for high-temperature environments.
The lamination technology allows heat to transfer and dissipate away from the
running surface
through the bushings shell. Shot loads have no effect on the bushing and no damage
to the shaft.
There are suitable candidates for applications in die-casting,
welding, paper mill, textiles, foundry, and woodworking equipment.
In testing, it can withstand 2.9
megapascal of surface pressure with coefficient of friction as low as
.2 with 1045 steel as the sliding surface.
However, it is rated up to 280 degrees Celsius,
and they can withstand more load that the porous bronze bushings,
roughly 49 megapascal, but at drastically lower speed.
The polyacetal resin based bushings excel in both
load capacity and abrasion resistance.
With low static friction coefficient, these bushings provide high-velocity
properties.
In addition, they prevent stick slips and rasping noise.
One of the most important features is that these bushings conform to food
sanitation laws.
The other resin type, the Teflon-based, provide a low static friction
coefficients
on start-ups and no stick slips during operation.
These continue to maintain high abrasion resistance and low friction coefficients
under high speed conditions. They also conform to food sanitation laws and excel
in chemical resistance.
As you can see from a journal rotation test, resin based bushings generally have
higher velocity rating,
and the coefficient of frictions fall well below 0.2 in comparison
with copper center bushings or nylons with impregnated
additives.
The last category is the iron casted bushings with special lubricants.
They are suitable for moderate-low and low speed applications.
Internally you will find a pattern of spirally embedded molybdenum disulfide
lubricants.
This enables a low friction coefficient in both reciprocal
and oscillating motion. While not as versatile as the previous categories
discussed
they have a moderate temperature range of -40 to 150 degrees Celsius,
suitable for oscillating applications, and perform well in
air and oil only. For a complete reference of performance data,
visit the latest printed Misumi catalog or online and www.misumiusa.com,
then type into the search box, "bushing".
Housings with circular, square, and compact flanges
are available for many of the brass composite bushings.
They are also available in pillow blocks styles, with
single or double size lengths. Because of their simple-assembly nature, they
greatly save time
compared to conventional ball bushing pillow block assemblies.
One last type is the threaded housing built-in copper alloy bushings
that have threads machine on the body of the case
and assemble with only one piece of special nut.
It is very important to consider the tolerances of the inner and outer
diameters
when designing an application that will be using composite bushings.
For regular and thin-wall bushings, the brass and graphite composites
will typically have F7 or E7 bore tolerance.
Here are some recommended mating shaft tolerances. A shaft tolerance
of D8 is good for general high-load use,
while E7 is sufficient for general light load use.
Shaft tolerances of f8 and g6 are recommended for high-precision uses,
especially g6 for intermittent operations.
For both regular and thin-wall bushings the outer diameter will typically
have m6 or r6 tolerance.
A press-fit installation is usually recommended to afix the bushings
to a plate or housing. The housing matching hole diameter
is recommended to have a tolerance H7.
The surface conditions on the shaft are also important factors to consider
for composite bushings. Recall that self-lubrication works
by depositing lubricants to the surface of motion.
If the surface is too smooth, the lubricants will be
unable to stick to the surface. On the other hand,
if the surface is too rough the bushing may start shearing materials
on the surface. The typical Misumi linear shaft compatible for use
has a surface roughness of 0.4 RA.
You also want to be careful about the surface treatment
and depth of plating on the shaft.
Most of the linear shafts will be induction hardened
with considerable depths of hardening on the surface,
compatible for use with either ball bushings
or composite bushings. However,
for some linear shafts, they will have non-hardened soft cores,
supplemented only by a thin layer of hard chrome plating.
This layer is very thin, only about 10 microns or so.
In such cases, if linear ball bushings were used,
this thin plating may crumble under the hardened ball bearings,
whereas composite bushings will be more forgiving on such a
surface. The part number for the composite bushing
is simply consisted of the material code,
inner diameter, and the length. Let's look at
a few application examples. A basic example
is a linear mechanism driven by a ball screw
or a lead screw, guided by a system of parallel shafts
and two or four ball bushings. The function of the ball bushings can be
potentially
replaced by composite bushings, depending on the operating environment,
load, frequency, and whether if high efficiency is required.
For single shaft mechanisms, the shaft can serve as a motion guide
involving linear or rotary motion, or as a linear guide by restraining the rotation.
Tither long linear bushings or oil-free bushings for intermittent motions
should be selected to obtain linear stability and high load capability.
One key advantage of ball bushings is that they're capable of reaching
substantially higher speed.
However, the bearings can often suffer from ingress of
dirt, dust, and other contaminants that that will score the shafts.
They also require frequent lubrication. On the other, hand by implementing
oil-free composite bushings, the problem of shaft
surface wear is eliminated and the frequency of applying lubrications
can be minimized.
Another good example is using composite bushings as linear bearings
in 3d printers. The primary advantages
over ball bushings are lower-cost, lower weight,
and less maintenance.
Saw dust and high temperatures are adverse to a woodworking machine.
Composite bushings can cope with large amounts of wood dust
and high temperatures. They are dry-running, which
is an indispensable feature in dusty environments.
Composite bushings are not only use in factory automation
or manufacturing, they're also found sporting equipment,
such as rear suspension mechanisms in a mountain bike.
Another sporting equipment that uses composite bushings are found in ski
bindings.
The main advantage for both mountain bike and ski bindings jis that they're
very well suited
in wet, muddy, and cold conditions. It being low weight is a
desirable characteristic for competitive sports.
Now let us see an example of finding a composite bushing
from the Misumi USA website. Suppose I have a simple linear guiding mechanism
driven by an air cylinder. I am using a ten millimeter diameter shaft with a g6
tolerance.
It will be a low-speed application where precision is non-critical,
and I want it to be as less hassle as possible.
This is a perfect scenario to use a composite pushing.
Here I am on the Misumi USA website.
Composite bushings will fall under the Factory Automation category,
so I will go ahead and click on the Automation Components link.
In this pictorial index under the linear motions category
I should be able to find the oil-free bushings. Click on it,
and it will direct me to the main selection page for oil-free bushings.
In this page I can select the type of oil-free bushings I would like to use;
multilayer composites, metal alloy base,
or resin base. I would like to use a brass
composite bushing. Once I'm in the metal alloy bushing page,
I can browse through this list and see which styles suit my application the best.
Suppose I want a simple bushing with flange.
Now that I am in the detailed product page for this material and style of bushing,
I can start selecting the parameters I need from the configuration panel
on the left,
such as the operating environment, bore diameter,
outer diameter, overall length,
and flange type. When all necessary parameters are selected,
the part number will automatically generate itself.
You have essentially found the part you need. One important step is to visit the
specifications table
and ensure that it meets your requirements.
You can also click on the technical information tab
and further review the performance data of the bushings.
Last but not least, you should be able to click on the CAD Model button near
the top
right to download a model for your assembly. Be sure to have your login information
ready.
Enter you username, password, and the link should be available for you to access
the CAD files.
Various CAD file formats are available,
such as Pro/E, Inventor, or SolidWorks.
This concludes our presentation on composite bushings.
Thank you for joining us today. Thank you,
and we hope you enjoyed today's webinar. All of Misumi's configurable components
and one million products are available
at www.misumiusa.com.
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