Considerations for Ejecting Parts with an Air Nozzle: Weight and Friction

I had a customer wanting to reject a container off a conveyor belt.  The container held yogurt, and when an optic detected a reject, they wanted to operate a solenoid to have a nozzle blow the container into a reject bin.  They had a range that went from 4 oz. (113 grams) for the small containers to 27 oz (766 grams) for the large.  He wanted me to suggest one nozzle for all sizes, as they would automatically regulate the pressure for the full range of products.  In looking at the largest size, this container will need the most force to blow off the conveyor.  The two factors that affects the force in this type of application is weight and friction.  When it comes to friction, it is generally an unknown for customers.  So, I was able to help with a couple of things to determine the friction force.

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 move or slide.  Kinetic friction is the amount of resistance that is created when the object is moving or sliding.  So, Static friction is always greater than kinetic friction, ms > mk.  For this application, we will use an air nozzle to “shoot” horizontally to hit the rejected product.

Let’s take look at our customer’s application.  We have a system to reject a non-conforming part with air.  The conveyor has a urethane belt.  The container is plastic.  For the largest container, they have a weight of 27 oz. (766 grams).  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 a container is below as Equation 1.

Equation 1

Fs = ms * W

Fs – Static Force in ounces (grams)

m– Static Friction

W – Weight in ounces (grams)

One way to determine the amount of force is to use a scale similar to a fish scale.  The scale should have a maximum indicator to help capture the maximum amount of force.  You will have to place the object on the same belt material because different types of materials will create different static forces. Keep the scale perpendicular to the object, and slowly pull on the scale.  Once the part begins to move, record the scale reading.  For the exercise above, it showed 9.6 oz. (271 grams) of force to move the 27 oz. (766 gram) object.

Another way would be to calculate 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, you can lift one end until the object starts to slide.  The height of the lift can be measured as an angle.  As an example, we take 3 feet (0.9 meter) of supported urethane conveyor belt, and we lifted one end to a height of 1 foot (0.3 meters) before the 27 oz (766 gram) container moved.  To determine static friction, it is the tangent of that angle that you lifted.  With some right triangle trigonometry equations, we get an angle of 19.5o.  Thus, ms = tanq or ms = tan(19.5o) = 0.354.  If we plug this into Equation 1, we get the following:

Imperial Units                                                    SI Units

Fs = ms * W                                                         Fs = ms * W

= 0.354 * 27 oz.                                                = 0.354 * 766 grams

= 9.6 oz. of force                                              = 271 grams of force

1″ Flat Super Air Nozzles

Now that we have the static force, we want to be slightly higher than that.  In looking at the force requirements that are published in the EXAIR catalog, it shows that the model 1126 1” Super Flat Air Nozzle has a 9.8 oz. (278 grams) of force at 80 PSIG (5.5 Bar).  This force is measured at a 12” (30.5 cm) distance with a patented .015” (0.38mm) shim.  So, this nozzle will be able to slide the largest container into the reject bin.

1″ Flat Super Air Nozzle shims

To expand on the benefits in using the EXAIR Flat Super Air Nozzles, the force can be changed easily with a regulator or with a Shim Set.  This is a unique feature as most competitive flat nozzles do not allow you to do this.  The patented shims control the force rating in a wide range with lower air consumption and lower noise levels; making them safe and efficient.  So, if this manufacturer decided to produce other sizes in the future, then they could change the shim to target even larger containers.  The flexibility of using the EXAIR Flat Super Air Nozzles allow you to increase or decrease the force by just removing two screws and changing the thickness of the shim inside.  EXAIR does offer a pack of shims with different thicknesses which are called a Shim Set.

With air pressure or shim manipulation, the customer could use the same nozzle for the yogurt containers.  If you have any applications that need products to be rejected quickly, an Application Engineers at EXAIR will be happy to help you with a solution.

John Ball
Application Engineer
Twitter: @EXAIR_jb

Photo: Yogurt by BUMIPUTRAPixabay Licence

Super Air Knife Improves Plastic Injection Molder Process

EXAIR commonly works with plastic injection molding companies. They produce top quality plastic parts from both commodity and engineering-grade resins for many diverse industries. The customer reached out to us with a problem. A mold that they were running was having some issues. The parts were not releasing and ejecting properly, causing the need to use a mold release, which was slowing down the process by a manual operation to the process.  Also, the parts were seeing push pin marks, causing cosmetic issues with the parts.  The customer wanted to explore using compressed air to blow the parts free.

Plastic Injection Mold
Typical Plastic Injection Mold

Based on the mold size and layout, a pair of 12″ Super Air Knives was installed.  The knives are oriented to blow straight down along the face of the mold, one knife per part tree.  The strong laminar flow of air hits the parts causing them to release and drop without the use of release agents.  Also, the push pin marks are within normal standards, eliminating the the cosmetic concerns.

gh_Super Air Knife 750x696

This is just one example of how intelligently using compressed air can help improve a process.  By using air knives for wide areas or using a 1″ Flat Super Air Nozzle for very small parts, or anywhere in between, we can help to solve your part ejection issues and make your process run better, faster, and with higher quality.

1″ Flat Super Air Nozzle with Changeable Shims

If you would like to talk about Super Air Knives, Flat Nozzles or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
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Twitter: @EXAIR_BB


Injection Mold Photo – “Creative Commons Injection Mold” by Mitch Barrie is licensed under CC BY-SA 2.0

Part Ejection Improved by Choosing the Right Air Nozzle

Recently, I was able to work with a gentlemen from a stamping company that produces small metal stamped lids for the cosmetic industry.  He was frustrated because the current blow off setup, a copper tube and nozzle (shown below), was too weak and narrow to be effective with parts ranging from 1″ to 2.5″ wide.  Whenever a lid did not get completely discharged, the machine would jam and double hit on the next cycle, ruining (2) parts in the process, not to mention, potentially damaging the the tooling.

After reviewing the process, which is very high speed, we wanted a strong, concentrated blast of air that matched the part profile to maximize the air flow contact patch.  We agreed the model HP1125 – 2″ High Power Flat Super Air Nozzle would be a good nozzle to implement and test.  In addition to the Nozzle, the customer ordered the model HP1132SS Shim Set, to allow for flow and force adjustment of the nozzle to obtain the best possible performance under production conditions.  The HP1125 nozzle provides 2.2 lbs of force with the standard .025 patented shim installed, and can be decreased or increased by changing the shim to .020″ or .030″ thick. Preliminary testing has proven successful, and reliability testing and data collection is underway.

2 Inch Flat
2″ Flat Super Air Nozzle

EXAIR has available, the Air Nozzles Blowoff Guide, a handy reference with 23 pages of technical data for OSHA safe nozzles and Safety Air Guns for every application imaginable.

blowoff guide
The EXAIR Air Nozzles Blowoff Guide

To discuss your part ejection, blowoff, cooling or drying application, feel free to contact EXAIR and one our  Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web
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Twitter: @EXAIR_BB