Grain handlers are looking for ways to increase the capacity of old and new bucket elevators. 4B is helping them achieve their goal.
Pulley size, material characteristics, and terminal velocity are all factors that influence a bucket elevator’s capacity. However, bucket discharge is one of the most common causes of capacity loss.
This can be caused by incorrect belt speed in relation to the pulley diameter, the wrong elevator bucket for the material, or the wrong head shape.
Centrifugal discharge is normally used for grain and other materials which are handled at medium to high belt speeds. The material starts discharging from the bucket at about 10 o’clock from the horizontal and continues discharging around the pulley in arcs towards the head cover and outlet until empty.
It is necessary to design the head cover so that the material slides smoothly along the cover to the outlet, minimising the amount of dust created and material damage. A flat top cover design and any break in the head cover, such as explosion vents or gaps, will make the material rebound onto the pulley.
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This will result in material back legging and/or down legging.
There is a minimum and maximum centrifugal belt speed for each different bucket size and pulley diameter.
4B recommends using a range of bucket types for this application, including bottomless and low-profile buckets.
Ray-Carroll County Grain Growers, 2.8-million-bushel country elevator in Missouri, USA needed to increase receiving capacity in order to better accommodate its growing customer base. The challenge was to upgrade the receiving system without shutting down operations. Twenty million bushels of corn are received at this facility every year.
4B Components engineering group analysed the existing elevator legs and designed an improved solution. The company installed 4B Jumbo CC-S 16×8 low-profile buckets were installed that were spaced around 20cm apart. The low-profile design allowed Ray-Carroll to install the buckets closer together resulting in the ability to add 224 additional buckets per leg. To handle the increased load of the additional buckets, rubber belting was installed with 4B BC belt splice clamps, designed for heavy-weight belts.
The millwright team installed the new buckets on the two legs in two days. By working on one leg at a time, the other remained operational, and the elevator was able to receive grain throughout the process. Before the upgrades, the two legs each ran at 8,500 bph capacity. Now, each leg can handle 15,000 bph, an increase of approximately 75 per cent throughput.
There are two other types of discharge: centri-gravity, and gravity. Centri-gravity discharge is normally used for discharging powders, pellets, cement, and fragile materials at slow speeds. The elevator buckets start to discharge at top dead centre (12 o’clock) and continue until approximately 50° afterwards.
Gravity discharge is typically used for discharging sluggish, aerated materials which basically fall out of the buckets at around the 2 o’clock position. Slow running continuous elevator buckets can be used for gentle handling of fragile materials.
While bucket discharge is an important part of the process, there are other factors to consider that can also affect a bucket elevator’s capacity.
To facilitate the discharge of material from the elevator head, the outlet should be large enough for the required capacity and should be at minimum 45° from the head shaft for grain and low-friction particles. For other products such as meals, cement, sticky materials, and wood chips, the outlet should be at 50° to 55°.
Proper belt tension also helps to avoid belt slippage on the drive pulley. A lagged head pulley will help reduce slip and wear on the belt. 4B recommends installing belt slip, belt misalignment and bearing temperature monitoring systems to help with safety and maintenance requirements.
Most boot pulleys for grain are smooth surfaced, but for sticky meals which build up on the inside of the belt and cause belt stretch as well as other belt issues. A wing type pulley allows the surplus material to fall through the wings instead of building up between the pulley and the belt. A wing type pulley also reduces damage to pellets.
If the bucket elevator isn’t designed to handle the specific application requirements, it can cause issues. 4B found this when a malting company wanted to utilise an existing grain elevator to transport green malt.
After installation, it was apparent the elevator was problematic and not functioning as expected. The installed buckets were CCS127 buckets, which replaced the obsolete J127 HDP buckets that were originally installed.
After some discussion with 4B, the prognosis was the pulley may be too small for the projection of the CCS12x7 bucket. This was expected to be cured by installing CCS 12×6, but the problem persisted, although not as bad.
After a site visit, it was apparent the elevator was set up to transport free-flowing grain. This setup was incorrect for handling green malt, which, by nature, is wet and sticky and does not flow well. The product was not fully discharging into the outlet but was in fact falling down the return leg back into the boot.
4B recommended two minor alterations to solve this problem: modify the outlet by lowering it into a suitable position to ensure complete discharge of the product from the bucket into the outlet and reduce the rotation per minute of the pulley to give the correct discharge stream.
After implementing both these modifications, the problem completely disappeared. The feedback was positive and the elevator ran smoother with less loading on the motor. The batch time was reduced to the point where it is now the most efficient part of the process.