Why Meter Augers Matter?

At first glance having to choose between 10 different metering augers when configuring your new Bourgault Air Cart may seem daunting. However, the decision ultimately comes down to just a few things:

>   UHMW OR NICKEL-PLATED STEEL FLIGHTING?

Ultra-High Molecular Weight polyethylene is quite simply an amazing material. It’s resistant to corrosive chemicals, has an extremely low rate of moisture absorption, and similar to Tefl on, nothing sticks to it! If you are going to utilize seed treatment on any product being metered through a tank, UHMW is your choice so that product doesn’t build up and change the amount being delivered. The downside with UHMW is its toughness, or lack there-of. The edges of the fl ighting will tend to “flare” due to friction with the product. Following multiple seasons of use the overall diameter of the flighting may cross a specified minimum diameter and require replacement under Bourgault’s extended warranty policy on metering augers.

The nickel-plated steel version of the metering auger shines when it comes to its durability and ability to handle abrasive materials. However, it has a higher risk of build-up on the auger. Bourgault’s overall recommendation is UHMW in all tanks except one that will typically be dedicated to phosphorous fertilizer use.

>   SINGLE-FLIGHT (1X), DOUBLE-FLIGHT (2X), OR HIGH-OUTPUT (HX)?

Since Bourgault’s 9000 Series air carts are designed with at least 4 separate tanks of varying capacities, the appropriate metering auger selection is typically based on the tank size. Bourgault strives to maximize your productivity through tank sizing, thus low application rate products go in smaller tanks with higher rate products in larger tanks. Also, with 4 or 5 tanks many seeding scenarios utilize multiple tanks for a single product, allowing the application rate to be split between tanks, which again matches the tanks size - you wouldn’t put a high-output metering auger on a small tank as it would run out almost immediately!

The Positive Displacement Metering (PDM) system is incredibly versatile, providing large application rate overlaps between the different metering auger types:

For the 2 larger tanks on your 9000 A/C a 1X metering auger will cover almost all seeding scenarios! Only if you are looking to apply more than 200 lb/ac through a single meter would a HX be selected.

>   IT’S NOT ALL ABOUT MAXIMUM RATES!

Although maximum application rates tend to be the first thing customers are concerned with, the minimum rate is just as important! There are two main considerations:

• Variable Rate: when using VR both the maximum and minimum application rates of your prescription need to be achieved. In the below example a 1X is the correct choice:

• Auto-Sectional Control (ASC): As the ASC sections turn off, the metering auger needs to slow down to achieve the target application rate as the effective width of the machine has just been reduced. In the VR example above let’s assume the prescription minimum application rate is 80 lb/ac across an 80 ft machine that has 8 X 10 ft sections. If the 1X metering auger is turning at 160 RPM to achieve the 80 lb/ac on the full 80 ft, once a single section turns off it will need to slow down to 7/8 of 160 RPM = 140 RPM to apply that same 80 lb/ac over what is now 70 ft. Turn off 3 sections, and it must slow to 5/8 of 160 RPM = 100 RPM and so on until there is just 1 section left seeding and the meter is operating at 1/8 of 160 RPM = 20 RPM.

>   METERING AUGER LIMITATIONS VS METER DRIVE LIMITATIONS

• The Positive Displacement Meter (PDM) is EXTREMELY versatile and can operate effectively at very low RPM’s without pulsing. It can also run at an exceptionally high RPM (850 RPM) without cavitation (cavitation means the auger doesn’t fill properly if it turns too fast, resulting in output that is less than what was achieved at a lower RPM). A key factor is that the output is linear for changes in RPM, which allows the system to accurately predict the application rate from a single calibration point. This is critical for both variable rate and auto-sectional control where the rotational speed will be changed to meet target application rates.
• The hydraulic metering drive is also tremendously capable, and can operate at speeds from as low as 10 RPM uniformly to as fast as 500 RPM! In order to create this large difference in operating speeds, a range sprocket selector was needed. Knowing what each metering auger type can apply as a minimum and maximum in a particular range is extremely important as the range sprockets cannot be changed on the fly. The overall metering auger speeds are as follows:
  • Low Range: 5 RPM through 200 RPM
  • Medium Range: 10 RPM through 425 RPM
  • High Range: 20 RPM through 850 RPM

>   HOW FAST IS MY METERING AUGER TURNING?

• Everything with the PDM metering augers comes down to one thing – the calibration factor. The calibration factor is the weight of product metered by the auger with each revolution, therefore a calibration factor of 0.276 equates to 0.276 lbs of product per revolution of the metering auger. The different versions of metering augers are capable of metering the same product, they just have a different throughput and therefore a different calibration factor:
  • HX – Wheat = 0.408 lb / revolution
  • 1X – Wheat = 0.276 lb / revolution
  • 2X – Wheat - 0.156 lb / revolution

Special Note: Product density does impact the calibration factor. Lighter product has a lower calibration factor when compared to denser product. Wheat has an average density of 52 lb/ ft³, whereas barley has an average density of 43 lb/ft³ – thus a typical calibration factor for barley with a 1X auger is 0.234 (vs 0.276 for wheat with a 1X).

• The other factors that determine how fast your metering auger turns are as follows:
  • Desired application rate
  • Working width of the seeding implement
  • Ground speed

Thus to seed wheat at 180 lb/ac with a 1X metering auger on a 76 ft machine at 5 mph the metering auger will be turning:

As an engineer I love a good formula! However not many people want to run through the math for all of their scenarios, and it truly isn’t necessary 99% of the time when making confi guration decisions! Using all of the above factor, a simple table can be used to allow our customers to make the correct decisions with their new 9000 I Series Air Cart. This is a large table as it accounts for various seeding speeds and working widths, however only one section of the table will be applicable so then it becomes simple to make the right decision.

Below is a sample of that table:

>   THEN WHAT ABOUT THE LO AND VL METERING AUGERS?

As you can see from the above table, the 2X metering auger cannot meter low rate product such as canola or inoculant in an ASC situation. Any tank intended to apply less than 10 lb/ac needs to have a Low Output (LO) or a Very Low Output (VL). The LO was the standard when ASC was released over 10 years ago to seed 5 lb/ac of canola at 5 mph. With the introduction of the TriMax, customers can lower their seeding rate due to the reduced mortality rate, creating the need for a VL auger. Unless you are utilizing your canola / inoculant tank to top-up your fertilizer capacity in other seeding scenarios, the VL has become the new standard of choice. Our Order Desk staff is always prepared to work with our dealerships to ensure that you, our customer, has confi dence that your machine will function properly in ALL of your seeding scenarios right from the get go!

By Brad Hicks, P. Eng Inside Sales, Product Customer & Service Leader