Batching Systems from China Longxinzhiye can batch more ingredients at a faster pace to keep up with the mixer and Weight Feeder.Larger numbers of ingredients are used.

Just going to larger and larger weight feeders isn’t necessarily the answer. As more ingredients are used, each ingredient constitutes a smaller percentage of the batch.

Maximizing batching efficiency clearly takes a systems approach.

Today’s high-capacity mixing systems require multiple batching scale to allow enough time to weigh each ingredient properly (Figure 1).

Each of these scales is a system unto itself–grounded corn, major ingredients, minor ingredients, bulk bag ingredients, micro-ingredients, and liquids. All of these systems must be coordinated to produce an accurate batch.

Screw Conveyor Design

Screw conveyors are the most common feeding system used in feed mills, and this is the place to start in designing an efficient Longxinzhiye batching system.

Screw conveyors deliver ingredients to the scale hopper by volume, not weight.

The volume the conveyor delivers to the scale hopper is determined by the pitch of the flighting as it leaves the area of the ingredient bin outlet.

The pitch of the flighting is the ratio of the flight spacing to the diameter of the flighting (Figure 2).

A proper weight feeder design requires that the pitch under the bin outlet area start small, then increase as the conveyor moves product along the bin outlet.

Pitch should not exceed 2/3 for light or normal ingredients or 1/2 for heavy or low-volume ingredients used in small amounts.

A top shroud at least two flighting diameters long should be installed in the weight feeder just beyond the bin outlet.

This forms a tubular area around the flighting that allows the screw to meter out each ingredient more accurately.

Beyond the shroud area, the flighting spacing should be increased to full pitch (1 / 1 ratio) all the way out to the weight feeder discharge.

This allows the screw conveyor to run less than full for more accurately control of the discharge cut off.

Limit feeder speeds to 100-105 rpm.

Weight feeder Sizing

Weight feeders must be sized properly in order to deliver ingredients into the scale hopper within the targeted mixing time. This is figured out in six steps:

1. Determine the maximum average capacity the system will be required to deliver in tons per hour.

2. Determine the system’s design capacity. Include an efficiency factor to cover lost time increments that always occur in any system.

3. Determine the maximum weight of each batch to be placed in the mixer and Weight Feeder.

4. Use this information to calculate the size of the mixer, based on cubic capacity required, and total time required for each batching/mixing cycle.

5. Make assumptions about the time required to discharge the scale into the mixer and Weight Feeder, the time to discharge the mixer, and dead time between the stopping of each weight feeder and the starting of the next feeder.

6. Use this information to determine a target screw weight feeder time for each formulation used in the plant, or at least for several of the most used formulations.

Example

Let’s take a feed mill that is required to produce an average of 60 tph, using a 4-ton mixer producing a formula from eight dry ingredients.

First, you always have to oversize the design to account for lost production due to variable factors–80% efficiency is a good target. So 60 tph /0.80+75 tph design capacity.

To meet this design target of 75 tph, the mixer would have to process 18.75 batches per hour (75/4).

In every hour, there are 60 minutes, so divide 60 minutes by 18.75 cycles to calculate the cycle time of 3.2 seconds.

Multiplying 3.2 minutes per cycle by 60 seconds per minute, you arrive at a cycle time of 192 seconds.

Now assume a scale discharge time of 15 seconds, mixer discharge time of 15 seconds, and a 4-second dead time for each of eight ingredients (32 seconds).

Subtract all of this from the 192-second cycle time, and you get 130 seconds for your target weight feeder screw time.

Figure 3 provides screw weight feeder sizes selected for each ingredient used in the batch and the amount of time needed to place each ingredient in the scale hopper.

Size your weight feeder to meet the target time.

Retrofitting

The budget may not be there for a new batching controler, but there are several ways to speed up existing systems:

Install a second batch scale hopper to weigh a portion of the ingredients. Feeder screws will have to be separated so each serves only one scale.

If the same ingredient is available in more than one bin, run both weight feeders at the same time. Program your controls to allow one weight feeder to stop shortly before the second to maintain final weight accuracy.

In stall a variable speed drive for the largest weight feeder screw motor, plus a selection system so the drive may be connected sequentially to individual feeder motors. That way, you can start and operate a feeder at much higher speeds, then slow it down as the desired weight is approached to maintain accuracy.

Enlarge bin discharge openings and put in larger weight feeders. This should be the last resort because of the expense.

This article is based on a presentation by Professor Fred Fairchild, associate professor in the Department of Grain Science and Industry, Kansas State University, Manhattan, and Feed batching Equipment News columnist.

Written by Grain Journal Editor Ed Zdrojewski

He spoke in May at the American Feed Industry Association’s 1997 National Production School in St. Louis, MO.

Recent developments in batching control and mixing technology provide a large number of benefits to feed millers, but they also require millers to rethink their approach to efficient batching. Among these developments:

Batches are getting larger. Not too long ago, three tons was the industry’s standard batch size. Today, mixer and Weighing Feeders handle six, eight, even 14 tons at a time.

Mixing has gotten faster. Newer mixer and Weight Feeders can adequately mix the larger batch size in 60 to 90 seconds.

Modern batching systems involve multiple feeders, and it’s essential that weight feeder discharge rates be controlled accurately at faster and faster batching rates.