The pin mixer, a horizontal, continuous mixer, is perhaps most well known for the role for which it was originally developed: processing carbon black.
In the carbon black industry, pin mixers provide a highly effective means of converting a dusty, difficult-to-handle material into small, dust-free granules with improved handling characteristics.
Today, nearly a century after it was invented, the pin mixer’s diverse processing capabilities have led it to be used in a wide variety of industrial settings, not just as a stand-alone processing device, but also as a method for preconditioning material in a larger agglomeration process.
The Pin Mixer as a Stand-Alone Device
As a stand-alone device, the pin mixer can accomplish three goals: mixing, pelletizing, and densifying.
Mixing
Not surprisingly, given its history, the pin mixer is the device of choice for combining ultra-fine materials with a liquid binder to produce a homogeneous mixture. The pin mixer is capable of combining multiple solid and liquid feed components to yield a uniform product. It is regularly used as a mixing unit throughout many industries for dust wetting/dust suppression, and for preparing a uniform mixture of disparate components.
The intense spinning action of the mixer also lends itself to homogeneously combining dry feedstocks without the use of a liquid binder, a process often referred to as dry blending.
Pelletizing
In addition to its mixing capabilities, the pin mixer also provides an efficient and continuous option for converting dust and fine particulates into free-flowing, dust-free granules. When processed in a pin mixer, these granules are typically referred to as micro pellets.
The granules resulting from micro pelletizing are within the range of 20 to 60 mesh, and more dense than material processed in some alternative mixers, such as the pugmill mixer.
Pellets are produced through agitation agglomeration with the aid of a liquid binder.
Densifying
The pin mixer is also widely recognized for its ability to provide significant densification to material fines. This is a result of the intense spinning action that occurs in the mixer. When looking to agglomerate powder or fines, the pin mixer provides greater densification with less binder than other agitation agglomeration methods.
Through adjusting retention time, along with other process variables, the mixer can be used to meet all three of these objectives, or just one.
As a singular processing unit, the pin mixer is highly customizable and widely used to process carbon black, coal dust, catalysts, filter media, pigments and dyestuffs, ceramics, and specialty powders, among other materials.
Paint pigment micro pellets produced in a FEECO Pin Mixer
The Pin Mixer as a Preconditioning Device
As a preconditioning device, pin mixers are used no differently than as a stand-alone unit. The unique combination of capabilities (mixing, pelletizing, and densifying), the pin mixer offers makes it ideal as a preconditioning device in a larger agglomeration process, particularly when preceding a disc pelletizer (pan granulator).
When paired with a disc pelletizer, the pin mixer provides the larger agglomeration process with a uniform, homogeneous mixture of dense seed pellets. The addition of the pin mixer offers several benefits to the process:
Enhanced Size control
The pin mixer allows for liquid and solid feed rates to be precisely controlled. When paired with a disc pelletizer, enhanced control over particle size can be achieved.
Dust Suppression
As pelletizing on a disc typically occurs in open air, fugitive dust can be a problem. When a pin mixer precedes the disc pelletizer, the mixing of binder and feedstock occurs in the sealed environment of the pin mixer. The seed pellets discharged from the mixer and fed to the pelletizer are de-dusted, avoiding fugitive dust concerns.
Decreased Binder Requirement
Operations that utilize a disc pelletizer alone create pellet density through added binder, with density increasing as a result of the rolling action. In contrast, pin mixers use mechanical motion to densify pellets, so pelletizing plants using a mixer to precondition feed for the disc pelletizer require less binder.
Increased Production
When a pin mixer is added to a disc pelletizing operation, production is often increased because the bulk of the moisture needed can be added in the pin mixer. The incorporation of moisture is much faster in a pin mixer compared to a disc pelletizer, which requires a controlled, gradual moisture feed to avoid upset conditions. This significant decrease in time, courtesy of the pin mixer, allows production to be increased.
Improved Product Uniformity and Crush Strength
As disc pelletizers do not provide thorough mixing of solid and liquid feed, binder distribution can be uneven when using a disc pelletizer without a preconditioning step. The turbulent mixing action of the pin mixer, however, produces a homogeneous blend of liquid and solid feedstock, so pellets are uniform from one to the next. Since the binder is a significant contributor to end product crush strength, an even distribution of the binder also ensures that all pellets will have the desired crush strength with less variation.
The pin mixer as a preconditioning device prior to a disc pelletizer is used throughout various industries to process a wide range of materials, from fertilizers and soil amendments, to chemicals and industrial products.
Synthetic gypsum soil amendment pellets produced in the FEECO Innovation Center using a pin mixer and disc pelletizer combination
Pin Mixer Testing
As every material (and even the same material from different sources) responds differently to agglomeration, testing is often an important part of developing a successful pin mixer operation, whether the mixer will be used by itself, or in combination with other equipment. The FEECO Innovation Center offers batch- and pilot-scale testing for pin mixers both as a stand-alone device, as well as part of a disc pelletizer or drum agglomerator setup.
Batch pin mixer used for testing in the FEECO Innovation Center
Testing collects key process and material criteria for producing a product with the desired specifications. Variables that are defined during testing include:
- RPMs
- Binder formulation
- Binder feed rate and spray location(s)
- Solids feed rate
- Particle size distribution
- System pressures
- Temperature
By working with these key criteria, in combination with characteristics of the material, numerous particle characteristics can be controlled, including:
- Attrition
- Bulk density
- Compression
- Crush strength
- Green/wet strength
- Flowability
- Physical characteristics
- Particle size distribution
- Solubility
- Temperature
Conclusion
While the pin mixer was developed for use in the carbon black industry, the diverse capabilities in mixing, pelletizing, and densifying that it offers have pushed it into a wide array of other industries and applications. The pin mixer is effective both as a stand-alone processing unit, and in partnership with additional agglomeration equipment, where it offers several benefits.
FEECO is the leading provider of custom pin mixers, having supplied hundreds of mixers since our founding in 1951. All FEECO pin mixers are engineered and fabricated around the characteristics of the material to be processed for an optimal processing solution. FEECO can also provide custom disc pelletizers and complete agglomeration lines.
If you are unsure if a pin mixer is right for your project, we can assess your unique material and run comprehensive testing to establish feasibility and assist in the design of a commercial-scale unit or production line. For more information on our pin mixers and agglomeration systems, contact us today!