Some of the most common problems we encounter during site visits to oilseed extraction plants around the world relate directly to improper press settings. Since screw type expeller presses rely on friction and continuous pressure to extract oil, variables affecting these forces need to be monitored and adjusted over time to maximize production and minimize waste. Too often, operators depend on their experience of running a particular machine, monitoring motor current and knowing when to push or back off production to ensure the system doesn’t get overloaded. As parts wear, operators can not only make adjustments for better, more efficient output but also extend the time between rebuilds. Let’s look at the three critical settings to ensure you’re getting the most out of your bulk materials while keeping the press at peak output and efficiency.
1. Mass flow rate
The first measurement we take when visiting any site – assuming material preparation and moisture content are correct – is the mass flow rate of material into the press. Expeller screw presses are extremely sensitive to throughput, and if the configuration of the plant does not include a weights and measures system, operators must calculate mass flow rate manually to ensure throughput does not exceed the recommendations set by the press manufacturer.
In typical plant design, a screw conveyor feeds the expeller press, with the speed of the material controlled by adjusting a VFD, or variable-frequency drive. If the plant does not have the equipment to weigh the material continuously, the operator can use a timer to measure the amount of material collected in a container within a given timeframe at multiple feed setpoints, until matching the maximum throughput of the press. At each setpoint, the operator can calculate the mass flow rate by dividing the mass of the material collected by the unit of time.
Most oilseed processing companies monitor the average current of the expeller press motor to ensure the operator does not feed more material than the motor can handle. But the mass flow rate is just as important to regulate internal pressure in the press – both to maximize production and minimize the risk of damaging mechanical parts during processing.
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2. Press shaft speed
The primary goal for every oilseed processing company we serve is to extract the most, highest-quality oil possible from the seed material while consuming the least amount of energy. Depending on the material our client is processing and its state before feeding it into the press, we’ll work with them to determine the ideal torque for their specific application. By understanding the relationship between the speed of the main drive motor and the gear reducer, we can control the speed of the shaft.
Why is shaft speed of the pressing screw important? If the screw is turning too fast, the operator can feed more material into the press in a given timeframe, but the oil does not have enough time to separate from the meal. At slower shaft speeds, there is more torque available to extract the oil at a higher rate, leaving less oil in the meal. But if the shaft turns too slowly, there won’t be enough material feeding into the press to generate the internal pressure needed for oil extraction. For peak efficiency, Anderson establishes the shaft speed in our manufacturing facility to provide the ideal torque for the amount and type of material being fed into the press. Once shaft speed is established, we do not recommend making changes to the shaft RPM without first contacting one of our Anderson process engineers since this could negatively impact throughput and oil recovery. Finally, we recommend documenting these settings for each seed type and batch for later reference.
3. “A-gap” in the drainage cage
One of the most common issues we encounter at a client site involves maintenance of the drainage cage. Depending on the process, the drainage cage will need to be rebuilt every six months to one year. Screw press cages have numerous replacement parts, and if a rebuild isn’t completed correctly, the gap between the inside diameter of the cage and the outside diameter of the shaft can be too large, allowing product to flow backward and the press failing to sustain proper internal pressure.
At Anderson, we’ve established standards for setting the “A-gap” in the drainage cage and provide shim kits for setting the proper diameter for each application. Depending on the material being processed, the shims make up for variances in tolerances inside the cage and establish the gap for maintaining appropriate internal pressure and flow of the oil. All of our “A-gap” standards have been documented over many decades for reference during drainage cage maintenance and rebuilds.
The Anderson International difference
With the Anderson Expeller® series presses, operators can easily make changes to settings to accommodate different sizes, shapes or types of seeds and nuts. Before purchasing an oilseed press, make sure the manufacturer’s equipment gives operators the flexibility to monitor and make adjustments over time to maximize oilseed extraction and minimize waste.
Finally, since each setting impacts other settings, be sure to keep records and remain patient when locating the best setting for each type of seed, or even each batch within a seed type. Changes in moisture content or other characteristics may also require changes to press settings for the most efficient oil recovery.
As we’ve learned from more than a century of oilseed equipment manufacturing, operating a press is true art – grounded in science.
Have additional questions? Reach out today.