Light Duty Line Vac For Part Rejection

Today I worked with a long standing customer that was interested in using the Line Vac technology to provide a method for part rejection.  The parts come out of a bin and travel to the next station for final assembly.  There is an accept/reject analysis system along the way, and it was decided that the Line Vac would offer an easy way to remove the part from the conveyor and transport it to a reject bin.

The parts are very small, with 0.093″ to 0.187″ OD and 0.178″ to 0.335″ lengths.  Part weights were 0.27 grams or less, so a very small and light weight item.  Maximum part processing was estimated at less than 6 parts per minute, so low speed and low transfer rates apply.  The final piece of information was the distance for conveyance, and here it was only a few inches up and then 4′ over to the reject bin.

Based on all the information about the parts, the process and the transfer distance, it was determined that the 3/4″ Light Duty Line Vac would be an ideal choice for the application. The unit is available as part of the  model 132075 Light Duty Line Vac Kit, which includes a Automatic Drain Filter Separator and a Pressure Regulator.  The Pressure Regulator is especially important in this application, as it will allow for pressure adjustment to provide the best performance while keeping the compressed air usage to a minimum.


The EXAIR Family of Line Vacs


EXAIR manufactures 3 styles of Line Vac- Light Duty, Standard, and Heavy Duty with either smooth bore hose or NPT threaded ends.  They are offered in 4 types of materials- Aluminum, Type 303 and Type 316 Stainless Steel, and a hardened alloy construction. An important factor in material selection is the abrasiveness of the material to be conveyed.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can help your process, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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How Much Force Does It Take?

In case you weren’t aware, the answer to “How much force does it take?” is always going to be, ALL OF IT.   At least that is what we generally think when trying to blow product off a conveyor belt or diverting parts into bin, etc. Speed and efficiency play a direct role in to what nozzle or blow off device you should use in order to get the job done and be able to repeat the process.

The question we are often asked by customers is, “How much force to I need to move this?”  That is a question that we cannot often answer without asking more questions.  The good part of this is, there is a formula to calculate just how much force you need to move an object.   A good video explaining friction is shown below.

In order to answer the question of how much force do I need, we really need to know all of the following:

Weight of the object
Distance from target
Is it on an incline or level
Distance needed to move
Then, the usually unknown variable, the coefficient of friction between the target and what it is sitting on.

Often times it is the thought process of, my target weighs 5 pounds, I need 5 pounds of force in order to move it from the center of this conveyor belt to the edge, this is not the case.   If you wanted to lift the object over a break between two conveyors then you would need slightly more than 5 pounds in order to ensure you are lifting the front edge of the unit high enough to meet the other conveyor.

Whether you know all of the variables or only a few, if you need to get an object moved and you want to try using compressed air to do so, give us a call and we will help you find the best engineered solution for your application.  Then, we’ll back all stock products with a 30 day guarantee if you don’t like how the system performs – but rest assured, we get it right almost every time.

30 Day Guarantee

The EXAIR 30 Day Guarantee

Brian Farno
Application Engineer Manager

Friction Measurement

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)

m– 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
Twitter: @EXAIR_jb


Image courtesy of Chobist, Creative Commons License

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