Month: April 2015

Friction Measurement

Published on by John BallLeave a comment

I had a customer wanting to reject a container off a conveyor belt.  The container held fruit, and when an optic detected a reject, they wanted to operate a solenoid to have a nozzle blow the container into the reject bin.  They had a range of containers that went from 6 oz. (170 grams) to 5 lbs (2,270 grams).  He wanted me to suggest one nozzle for all sizes, as they would automatically regulate the pressure for the full range of container sizes.  In looking at the largest size, this container will need the most force to remove.  The two factors that affects the force in this application is weight and friction.  When it comes to friction, it is generally an unknown for customers.  Here are a couple of things to help in determining the friction in your application.

Strawberry Delight
Strawberry Delight

Friction is a dimensionless number that represents the resistance created between two surfaces.  We have two types; static friction, ms, and kinetic friction, mk.  Static friction is the maximum amount of resistance before the object begins to slide.  Kinetic friction is the amount of resistance that is created when the object is sliding.  So, Static friction is always greater than kinetic friction, ms > mk.  For this application, we will have the air nozzle shoot horizontally to hit the target.  This is the most common and efficient way.

Let’s take a look our customer’s application.  We have a system to reject a non-conforming part with air.  The conveyor is a urethane belt.  The container is plastic.  We need to determine the correct nozzle to reject the 5 lb (2,270 gram) container.

Being that the conveyor belt is only 12” (30.5 cm) wide, we can determine that if we get the part moving, it will continue off the belt and into the reject bin.  The equation for the maximum amount of force required to move the container is Fs = ms * W(Equation 1).

Fs – Static Force – lbs (grams)

ms  – Static Friction

W – Weight lbs (grams)

One way to determine the amount of force is to use a spring scale.  The spring scale should have a maximum indicator to help tell you the maximum amount of force.  You will have to attach the scale to the container on the conveyor belt. Static friction is the resistance between two surfaces; so, you will have to use the same conditions as required for the operation.  Keep the scale parallel to the conveyor.  While slowly pulling on the scale, watch the dial.  Once the part begins to move, record the weight.  For the exercise above, it showed 1.82 lbs (826 grams) of force to move the 5 lb (2,270 gram) object.

Another way would be to determine the static friction, ms.  Static friction can be found by the angle at which an object starts to move.  By placing the container on a section of supported urethane conveyor belt and lifting one end of the conveyor belt until the object starts to slide, you can measure the angle or the height of the lift.  As an example, we take 3 foot (0.9 meter) of supported urethane conveyor belt and we lifted one end to a height of 1 foot (0.3 meters) before the 5 lb (2,270 gram) container moved.  To determine static friction, it is the tangent of the angle that you lifted, ms = tan(B) (Equation 2 below).  In this example, B = 20o.  Therefore Equation 2 gives us, ms = tan(20o) = 0.364.  If we plug this into Equation 1, we get the following:

Imperial Units                                                    SI Units

Fs = ms * W                                                         Fs = ms * W

= 0.364 * 5 lbs                                                    = 0.364 * 2,270 grams

= 1.82 lbs of force                                               = 826 grams of force
Now that we have the static force, we want to be slightly higher than that.  In looking at the force requirements that are in the EXAIR catalog, it shows that a model 1104 nozzle has a 1.9 lb (850 grams) of force.  This is at a 12” (30.5 cm) distance with a pressure of 80 psig (5.5 bar).  This nozzle will be able to slide the largest containers into a reject bin. With pressure manipulation, the customer can also use this same nozzle for the smaller containers.  If you have any applications that need products to be moved, you can always contact the application engineers at EXAIR to help you with a solution.

Variety of Nozzles
Variety of Nozzles

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Image courtesy of Chobist, Creative Commons License

Super Air Knife Used in Mining Application

Published on by Lee EvansLeave a comment

If you were to look at a graphical representation of the exports from some countries (such as Chile), copper, copper alloys, and other metals would dominate over 50% of the graph.  In order to get all of those metals exported out of the country, they first have to be mined and, in many cases, separated from other, undesirable items, such as rocks or dust.  And, in order to separate the materials, many end users place the products on a conveyor and blow off what isn’t wanted.

We receive calls and emails at EXAIR regularly for these types of applications.  Recently, I received one such email about an application in need of dust and dirt removal from a conveyor during a mining operation.  The conveyor belt had become overrun with dirt and debris that couldn’t be removed by conventional means.  So, the end user sought an alternative, and permanent solution.

It was at this point that the Super Air Knife was considered, and after measuring the width of the conveyor we realized a stock model 110018 would work well.  Following installation of the Super Air Knife, the dust and dirt was removed to within an acceptable level, and the end user sent me the pics below.

SAK in belt blow off 1
Model 110018 mounted above a conveyor
SAK in belt blow off 2
After the 110018 Super Air Knife

If you have an application that may benefit from an EXAIR solution, contact one of our Application Engineers.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Force And Flow…Which One Is The Right Tool For The Job?

Published on by Russ BowmanLeave a comment

If you’re even a casual, occasional reader of the EXAIR Blog, you know we write an awful lot about efficiency…namely, the ability of engineered products to conserve compressed air, while optimizing its effectiveness. Oftentimes, these blogs are inspired by a conversation we’ve had with a user of simple and inexpensive (but wasteful and unsafe) blow off devices, such as open-end tubing, or drilled pipes. The first thing the caller wants to talk about is the force produced by one of our products…will it be the same as what’s being currently used?

The quick answer is no. In fact, if you’re looking for maximum force, there’s no better way to get it than simply blowing compressed air out the end of an open pipe. This has to do with nothing more complicated that grade school science – converting the potential energy (due to the compression of the air) to kinetic energy (what happens when it’s put into motion.) See, with an open-end blow off, almost all of the potential energy is converted to force. Plain old brute force. And it works GREAT for blowing stuff around…the larger the opening, and the higher the supply pressure; the more air will flow, and faster. Thing is, to produce a good blow off, you don’t need maximum force.

EXAIR’s Intelligent Compressed Air Products are engineered to use some of that potential energy of the compressed air to entrain large amounts of “free” air from the surrounding environment. That’s the purpose of the jets recessed between the fins of our Super Air Nozzles, and the Coanda profile of our Air Knives, Air Wipes, & Air Amplifiers.

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.
EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

These designs reduce the amount of compressed air that is used, which reduces the load on your air compressor, which makes everyone happy (OK, maybe not that happy, but pretty happy still.) They also mean that your blow offs will be quieter, and safer.

Perhaps your application calls for higher force. If that’s the case, EXAIR’s Air Knives, Air Amplifiers, and Air Wipes can be fitted with thicker shims for additional flow and force. So can our Flat Super Air Nozzles. And our largest High Force Super Air Nozzles are capable of generating up to 23lbs (10.4KG) of force.

Perhaps, though, your application calls for the highest force that can only be achieved with an open-end blow off. If that’s the case, you can still meet OSHA compliance through the use of extra protective equipment, pressure relief valves, guarding devices, etc. But the costs of those measures can make the cost of engineered products pale in comparison, so I highly recommend you make sure of what you need.

If we can be of any assistance with that, give us a call.  We can discuss your application, and get you the right tool for the job.

Russ Bowman
Application Engineer
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Truck Headlight Assembly Relies on EXAIR Static Eliminators

Published on by exaircorpLeave a comment

This week I was contacted by an automation company who was contracted to assemble new truck headlights. The 2 parts in the process are the lens and the body and they are brought into a machine on 2 separate lines running parallel to each other. A robot arm picks up the lens and holds it in place against the body while a thin layer of glue is placed around the edge. The finished product is then sent down line where it travels under an inspection light to check for any captured debris and to ensure a proper seal. It was at this point they noticed residual internal dust on both pieces which caused an inspection fail and created a large amount of rework and/or scrap, so they called EXAIR for help.

The customer set up an online meeting where they were able to show an illustration of the process. Since these parts are plastic, their potential for holding a static charge increases. These lenses are also recently removed from the mold which may also be causing a static charge as they are separated from the mold. At the time of the call the lenses were brought in 2 at a time, face down over an opening in the bottom of the table where they use compressed air to blow them clean. The customer had not considered that static may be holding the dust on the surface of the lenses and that a static elimination process could provide a solution. The opening under the lenses was approximately 12″ (300mm) long x 6″ (150mm) wide so I recommended using our Model # 111012, 12″ Super Ion Air Knife and mounting the unit under the opening, directing the airflow blow out the inside of the lens. The Super Ion Air Knife produces a high velocity, laminar sheet of ionized airflow across the entire length of the knife capable of dissipating 5kV in .018 seconds when 6″ away and operating at 80 PSIG supply pressure.

Super Ion Air Knife
Super Ion Air Knife available up to 108″ in one-piece construction.

For the body application, the parts were again brought in 2 at a time, face down but there were (2) smaller openings, approximately 4″ (150mm) x 4″ (150mm) so I recommended using (2) of our Model # 7194-9362, Stay Set Ion Air Jets and mounting one unit at each opening. blowing back up inside the body.  The Stay Set Ion Air Jet produces a more focused ionized airflow and allows you to bend the hose to deliver the airflow to the critical area.

7294-9362
Stay Set Ion Air Jet easily directs ionized airflow and holds position.

Since both processes are being performed in close proximity, on one machine, they were able to use our Model # 7940 Power Supply (115V, 50/60Hz) with 4 outlets to operate all 3 ionizers, simplifying the setup and installation.

If you are experiencing a static issue in your facility, give us a call, we are here to help.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN