Selecting A Mixer With Help From VORTEX Mixing Technology

Using your mixer manufacturer’s expertise and test equipment can help you select a mixer that meets your needs. This article’s first section describes hoe to determine your mixing requirements. Later section describes how to select a mixer manufacturer, how to devise and run mixing tests, and how to solicit a price quotation using a specification. The final discusses how to select a mixer.

Selecting a mixer that will effectively produce the mixture you need can be a complex process. Using the resources and expertise of your mixer manufacturer – especially the manufacturer’s test center (or rental test equipment) – can help you make the right decision. Several steps are involved, including determining your mixing requirements, selecting a mixer manufacturer, devising and running mixing tests, soliciting a price quotation, and, finally, selecting a mixer based on the information you’ve gathered.

How to determine your mixing requirements

To determine your mixing requirements, gather information about your process requirements, material characteristics, and desired results. Consider the following when gathering the information.

Process requirements. Major process requirements include the type of operation, capacity, feed and discharge devices and methods, and mixing sequence.

Type of operation. Does your process require batch or continuous mixing? Does using a specific type of mixer in one type of operation offer any advantages? For example, adding very small amounts of an ingredient in a continuous process may be more efficient using a batch “key” mixer, so called because it accurately premixes small amounts of a critical ingredient – the key mixing step – in a larger process.

Capacity. How much will you mix? With a batch process, consider the quantity in terms of batch size and the time available for mixing each batch; with a continuous process, consider the quantity in terms of hourly rates.

Feed and discharge devices and methods. What devices will you need to feed materials to and discharge them from the mixer? What methods will you need to convey materials from the process to the mixer and from the mixer to the process?

Mixing sequence. Must you mix materials in a particular sequence? If so, you may also need to feed the materials into the mixer in a particular order.

Material characteristics. Your materials’ characteristics also play a big part in selecting a mixer. Four major characteristics to consider are flow properties, sensitivity to change, abrasive or corrosive qualities, and special finish requirements.

Flow properties. Are your materials free-flowing? If they aren’t free-flowing. Will they impair the mixer’s operation by collecting in one spot in the mixer?
Sensitive to change. Can the materials tolerate physical change? Can they be easily damaged? For example, if you mix fragile crystalline materials, you can select a mixer with a gentle mixing action – such as a gently tumbling mixer – rather than a ribbon mixer. which can abrade the materials by pushing them against the mixer walls.
Do the materials undergo a phase change during mixing? If so, select a mixer that can handle phase change. For example, if you use produce inks from dry materials, you can select a mixer with a high-speed disperser; the disperser consists of an agitator whose high speed creates heat that liquefies the dry materials in the ink mixture.

Abrasive or corrosive qualities. Are your materials abrasive or corrosive? If so, you can select a mixer and components that are made of abrasion- or corrosion-resistant materials, such as stainless steel, or are lined with polymer or rubber.

Special finish requirements. Do your materials or final product require a mixer whose contact surfaces have special finishes? For example, if you mix a pharmaceutical product, you can select a mixer with highly polished stainless steel contact surfaces.

Desired result. What do you want the mixer to achieve? Do you want the mixture to be homogeneous? Do you want a certain distribution of material A in material B? do you want a material A particle to be evenly coated with material B particles?

How to select a mixer manufacturer

Based on the information you’ve gathered about your process requirements, material characteristics, and desired results, you’ve probably determined what general types of mixers are suited to your needs. It’s unlikely that one manufacturer supplies every type of mixer on your list, so you need to find one or more manufacturers who supply the mixers you need and who can help you select a mixer by testing your material.

You can find one or more suitable mixer manufacturers by considering the following points.

Test center. Does the manufacturer have a test center? Testing your materials on a test center’s equipment under the test center staff’s guidance will help you assess whether a particular mixer meets your needs. A manufacturer who runs a test center is more likely to have a good understanding of general mixing principles, which can also benefit you.

If the manufacturer has no test center, the manufacturer probably offers rental test equipment you can use at your plant. If so, the manufacturer should also provide technical support to help you use the equipment and analyze the test results.

Range of mixer types. Which types of mixers are available in the manufacturer’s test center (or line of rental test equipment)?

Range of mixer sizes. Do the mixer sizes available in the test center (or rental test equipment) match your process requirements? Most mixer manufacturers build small test equipment because the small equipment is less expensive to produce than production-size equipment and uses less material. In fact, many customers prefer not to send large material samples for testing because smaller samples are cheaper to ship and raise fewer concerns about toxicity, sanitation, contamination, and confidentiality. However, for a batch process, it’s best to use test equipment that requires a sample quantity as close as possible to the material quantity you’ll mix in one batch. If test equipment this size isn’t available, test two or more different sample quantities on the available test equipment to see if the results vary for each quantity. (For a continuous process, rather than use test equipment based on sample quantity, use test equipment with a residence time similar to that our process requires.)

Test equipment features. What features are available on the manufacturer’s test center equipment (or rental test equipment)? You’ll need to know whether the test equipment includes only base models or incorporates the optional features required by your process. For example, if you need to add liquid ingredients to a bumbling mixer, you may want a test tumbling mixer equipped with a device such as a liquid feed line with a spray nozzle so you can pump the liquid into the mixer. If you need to coat or agglomerate your materials, you may want a test mixer equipped with an intensifier bar, which will help to coat one material with another.

Continuous operation tests. Does the manufacturer offer mixing tests for continuous operation? If you need a continuous mixer, you may be able to get by with only a batch mixing test, because it’s easier and cheaper to run a batch test and relatively easy to size a continuous mixer from the batch test. However, using a continuous mixing test is generally better because the test makes it easier to reproduce your operation conditions and test variations in your feed materials.

Auxiliary equipment for continuous operation tests. Does the manufacturer have the auxiliary equipment – such as hoppers, feeders, and weighing equipment – required for continuous mixing tests? Does the auxiliary equipment offer the capacity you need?

Lab analysis equipment. What lab analysis equipment does the manufacturer offer? Can the manufacturer analyze the material to see if the desired mixture has been achieved? Mixing tests in a test center are most effective when test data can be analyzed on-site during the tests, rather than at your plant after the tests, because on-site analysis permits testing modifications as the tests are run.

How to devise and run mixing tests

Once you’ve selected one or more mixer manufacturers, you need to devise and run the mixing tests. Plan to use a series of mixing tests rather than a single test because you’ll be testing each mixer’s ability to provide reproducible results.
Work with each manufacturer when devising the test series so that the results provide several types of information about a mixer’s ability to meet your needs. The test series should help you assess the impact of small changes in process parameters, such as humidity, which can help you determine the mixer’s optimal operating conditions. For a batch mixer. the test series should help you determine how easily the mixer can be fed and discharged, how much material remains in the mixer after a batch is discharged, and how easily the mixer can be cleaned. For a continuous mixer – as long as you provide enough material to supply a long, frequently sampled test run in the mixer – the test series should help you determine how the equipment handles variations in feed materials.

Running the test series will probably take a few days or weeks. If the manufacturer has both a test center and rental test equipment, as many do, part of the series can be conducted at the test center and part at your plant using the rental test equipment. (Tests at your plant typically reveal more information about the mixer’s performance under your operating conditions.) Several representatives from your plant – the plant engineer, the mixer operator, and a representative of your plant’s product development staff – should attend the tests to gather as much information as possible. Expect to pay a fee if part of the test series is run at a test center, because a well-equipped test center is expensive to set up and operate. However, some manufacturers rebate part of the fee against an equipment order.

During the test series, supply the manufacturer’s testing staff with as much information as you can about your materials, process, and desired results. Also ask the testing staff about the equipment’s operation, components, operating limits, advantages, and disadvantages. If the manufacturer fully understands what you need and you understand the capabilities of the equipment used in the test series, it’s more likely you’ll be able to work together to find a mixer that meets your criteria.

How to solicit a price quotation using a specification

After the mixing tests are completed and you’ve determined that one or more mixer manufacturer can supply the equipment you need, solicit a price quotation from each manufacturer.

To do this, submit a detailed specification to each manufacturer. If possible, ask each manufacturer for a copy of whatever document (generally a questionnaire) it offers to customers to help identify the customers’ needs; then base your specification’s content on this document, which generally asks about the customers’ mixing requirements. As precisely and succinctly as you can, specify your requirements, including the mixture you require, the sample quantity you’ll use to test the mixer’s performance, your plant’s available space and electrical capacity, the throughput capacity your process requires, and any construction materials and finishes required for the mixer’s contact surfaces. Make sure you send identical information to each manufacturer.

How to select a mixer

Finally, you’re ready to choose a mixer. After comparing the test results and price quotations from different manufacturers and, perhaps, for different mixers, you’ll probably find that more than one mixer can satisfy your criteria. If two or more mixers seem equally suited to your needs, you may be tempted to select the least expensive one. However, while price is important, this approach ignores some other, less tangible factors that strongly influence a mixer’s suitability for a given application. To make the best choice, consider the following design criteria and other factors.

Design criteria. The mixer you choose should meet some or all of the following design criteria. Arrange the criteria in order of priority for your mixing requirements, and then review each mixer you’re considering in terms of how it meets the criteria.

The mixer should:
• Suit your process.
• Meet all criteria listed in your specification.
• Be well-constructed.
• Be easy to clean.
• Have components that are easy to access and maintain.
• Provide easy material sampling.
• Meet your safety requirements.
• Reduce risk of material contamination.

Other factors. Next, consider the following less tangible factors. These factors can help you assess a mixer’s cost benefit over time and thus help you determine which mixer can best meet your needs.
• Manufacturer’s reputation. Does the manufacturer produce high quality mixers? Has the manufacturer supplied mixers that satisfactorily met other customers’ requirements?
• Manufacturer’s ability to service the mixer. Can the manufacturer promptly service the mixer and supply parts when necessary?
• Auxiliary mixer features available. Can the manufacturer supply the auxiliary features your process requires?
• Operating life of your process equipment and the mixer you select. How does the expected operating life of your process equipment (or the expected life of your manufacturing process itself) compare with the proven operating life of the mixer you select? For example, if you expect the operating life of your process equipment (or manufacturing process) to be shorter then your mixer’s, you should select a mixer versatile enough to be used later in another process.

Conclusion

You can successfully choose a mixer if you make use of your mixer manufacturer’s expertise and test center (or rental test equipment) and follow an organized selection process. The mixer manufacturer not only can help you devise and run mixing tests, but can work with you throughout the selection process to ensure the mixer you select cost-effectively meets your mixing requirements.