CONVENTIONAL CONCAVES

Imagine taking an engine that was designed to power a tank and using it in a racing car. It wouldn't have a chance. Now imagine taking a concave that was designed to thresh corn and using it to thresh a crop with small seeds and straw.

Regardless of the crop you are harvesting concaves always have two jobs to do. Thresh and separate. Thresh, or free the seeds, and then separate those seeds from everything else that went into the combine along with the seed.

Of all the different crops that are grown in North America, as well as being the largest crop, corn is also one of the easiest to thresh.

With corn you've got a 3" diameter cob covered with kernels as big as the end of your thumb. With the kernels sitting out in the open they are easy to thresh and, because there's no straw or chaff to deal with, the concave doesn't have any problems separating the empty cob from the kernels. The kernels fall through the openings in the concave and the big empty cob travels on through to the walkers.

When a combine leaves the factory, and if there happens to be a 1/4" difference in tolerance from one side of the concave to the other, it really won't affect threshing performance all that much if all you grow is corn. But if you grow crops other than corn, problems will begin. While the 1/4" difference in tolerance doesn't really affect performance with a 3" diameter corn cob, that 1/4" difference is big enough to let an entire head of wheat pass through and not be threshed.

In most conditions corn is so easy to thresh that the entire concave is not all used. With the 13 bar concave that came in most Deere combines from 1973 to 1984, only the middle seven were used for threshing. The front three and back three fell away from the circle. We feel this was intentional, in order to let the big corn cobs through, but it sure makes it hard to do a decent job in anything else but corn.

While the front and back of the concaves, for the new John Deere conventional combines, no longer fall away from the cylinder they are manufactured to a 27 1/2" circle. In almost every crop, except corn, a 27 1/2" concave is simply too big for a 26" diameter cylinder. Corn is about the only crop that can be threshed with that kind of a gap. These concaves may get you through in corn but you'll begin to have threshing and separating problems as soon as you pull into almost every other crop. With most other crops the seeds are a lot smaller and concave tolerances are more critical.

Remember it is more difficult for the concave to do its job when the seeds are locked inside a head and there's straw and chaff.

That is why every HARVEST Concave is precision bored to a diameter exactly 1/8" larger than the cylinder. HARVEST Concaves are manufactured and precision bored to the highest standards.

With HARVEST Precision Bored Concaves the entire concave fits the cylinder allowing the entire concave to be used for threshing and separating--exactly what is needed for all the crops that are more difficult to thresh and separate.

HARVEST Concaves are also built heavier and stronger. They start out as a precision concave and because they are stronger they keep their shape and remain a precision part. This is especially important when harvesting crops with straw or smaller seeds.

As we have already stated concaves have two jobs to do--thresh and separate. Because the concave has two entirely different functions to perform, HARVEST Concaves have two entirely different areas, a threshing area and a separation area.

For threshing you need an area that is closed and capable of holding the heads long enough for the seeds to be rubbed out or threshed. For separation you need an open area that will allow the seeds to fall away and be separated from the straw.

On HARVEST Concaves the threshing area, or the first third of the concave, is covered with Filler Plates.

The Filler Plates hold the heads in the wedge between the concave and the cylinder so they can be threshed completely and not pushed through the concave and onto the shoe or walker in the form of unthreshed heads. Without Filler Plates white caps and unthreshed heads are knocked through the front third of the concave. Without Filler Plates threshing is done by the impact of the cylinder bars striking the heads and not by gentle rubbing.

To thresh cereal grains properly the concave also needs more bar above the Filler Plates. The wires have to be placed deep enough to allow a minimum of 3/8" of bar above the Filler Plates to form a deep enough pocket to hold the heads long enough for the cylinder bars to rub the seeds out of the head.

Because some crops are more difficult to thresh than others, HARVEST Concaves use Filler Plates to increase or decrease the size of the threshing area. In hard to thresh crops you add as many Filler Plates as are required to allow enough time for the heads to completely thresh out. With easy to thresh crops, like barley, you remove some of the Filler Plates. In the hardest to thresh crops, like grass seed, canary seed, green flax or heat shriveled spring wheat, you may need five to ten Filler Plates. In barley or canola you may only have to use one or two Filler Plates.

The Filler Plates allow you to fine tune your concave to obtain maximum threshing and separating performance. It only takes about five minutes to add or remove a Filler Plate. The concave does not have to be removed.

The separation area of the concave, the back two-thirds, is open to allow the grain to fall through. HARVEST Concaves have larger 2" wire spacing in the separation area. These wider openings greatly improve separation.

Now we're not suggesting that if you only grow corn you can go into a harvest season with a bent or worn out concave. That's just not good practice.

Because HARVEST Concaves are manufactured and precision bored to the highest standards you know they will give you the best performance regardless of the kind of crop you are harvesting.

In all crops, except sunflowers and wet corn, set the concave to form a wedge, open at the front and closed at the back. Set the front concave-to-cylinder clearance according to your crop. With most crops that would be 3/4". A bumper crop needs a larger opening, about 1", and a light crop needs a smaller opening, about 1/2" The rear concave-to-cylinder clearance should be set at almost zero.

At the front of the wedge the Filler Plates in the concave hold the heads in place so they can be properly threshed. As the wedge closes the cylinder bars push the straw up the concave towards the back beater. At the same time they also accelerate the seeds through the openings in the back two-thirds of the concave.

When setting your concave for sunflowers the wedge is not as critical. Set the front and back of the concave slightly less than the thickness of the pad, tight enough to take the seeds out but not so tight that the pods break up.

In corn set the front of the concave slightly smaller than the diameter of the full cob and the back slightly smaller than the diameter of the threshed cob. This will ensure a gentle rubbing, rolling action upon the cob. The objective is to keep the cob whole.

Remember - wet corn needs a slightly larger concave-to-cylinder clearance and slower cylinder speeds to keep the cob whole.

Because HARVEST Concaves are precision bored to a perfect circle it is important that your cylinder bars also describe a perfect circle. One high bar is enough to significantly increase walker loss, white caps and cracked kernels. Every new HARVEST Concave comes with a shim kit to true your cylinder bars. We feel that more problems can be prevented in the cylinder and concave than anywhere else in the combine.

You will be surprised to learn that the cylinder bars of all combines, will vary as much as 1/8" of an inch in thickness. Experience in the field has proven that the maximum out of round a cylinder can be for grain crops is .0030" between highest and lowest bar. If you have a grain that is particularly hard to thresh, or if you harvest seed crops such as alfalfa, then it should be no more than .0020".

Consider what happens in grain crops if you have one high bar in your cylinder. Every time that cylinder bar comes around, it wipes the concave clean with the following result:

  • an excessive amount of grain will be thrown on the walkers.
  • there will also be partial heads on the walkers.

To compensate for the unthreshed heads, the only thing the operator can do is turn the cylinder faster. Now three things happen:

  • more threshed grain will be thrown on the walker.
  • there will be some unthreshed heads on the walker, along with some cracked kernels.
  • the straw will be chopped.

Almost all cracked kernels or damaged seed comes from running the cylinder too fast.

By truing your cylinder bars, using a HARVEST Concave and setting it as we have discussed you will achieve a noticeable increase in your combine's capacity, a noticeable decrease in your combine's losses and a noticeably cleaner sample in the tank.

Copyright © 2007 Harvest Services Ltd.