The Versatility of Pug Mill Mixers: A Look at Their Many Applications
Pug Mill Mixers, sometimes known as Stabilized Base Mixers, are double shafted, paddled machines that accept a continuous feed of two or more materials to be uniformly blended at high capacities for downstream processing or disposal. Because of their unique ability to handle high moisture content and create a uniform, consistent mixture, they can be used for applications in many industries.
Pug Mill Mixers can be used for many applications including cold-mix and hot-mix asphalt, stabilized base materials for roads, construction and road building applications, mining applications, and more. Keep reading as we dive deeper into the wide variety of industries and applications that utilize Pug Mill Mixers.
How Pug Mill Mixers Work
Pug Mill Mixers, or Stabilized Base Mixers, are designed to thoroughly blend construction aggregates with consistent moisture content for improved compaction.
Using twin shafts with intermeshing, corrugated paddles that rotate in opposite directions, these mixers create a uniform mixture by lifting and folding the material inward while moving it slowly toward the discharge point. The double shafted machine uniformly blends these materials as long as they are introduced at a controlled feed rate, providing a well-mixed, uniform discharge. Spray bars positioned near the feed end add water to achieve optimal moisture levels, ensuring the material is well-conditioned for faster, more effective compaction when laid by road crews, offering a much more efficient and consistent mix than in-place methods.
Material Handling Capabilities
Generally, Pug Mill Mixers are suited for handling a feed of up to a two-and-a-half-inch rock or solids. Operations might be mixing already separated rock and sand, or a road base material that requires a specific blend of the two. In many cases, a certain percentage of rock and sand that have been separated earlier in the process need to be reblended and mixed to create a road base suitable for good compaction. That’s where water is added, at a controlled feed rate, along with the rock and sand to ensure the right consistency and performance.
Advantages Over Batch Mixers
Unlike Pug Mill Mixers, Batch Mixers are low-capacity units. Batch Mixers may be used over Pug Mill Mixers in cases where a specific retention/mixing residence time is required or to provide a uniform blend at a low volume or capacity for downstream processing. Pug Mill Mixers and Batch Mixers differ in the sense that Pug Mills cannot hold material for a long retention period. Pug Mills are a continuous feed and discharge mixer. The retention time may be between 30-60 seconds, depending on the length of the mixer.
Pug Mill Mixer Customizations
Pug Mill Mixers have a sturdy box construction. They utilize a rectangular feed inlet with an optional hopper on top and a rectangular discharge opening on the bottom at the opposite end. There are several customizations that can be added to Pug Mills to tailor the machine to the needs of a site.
A simple addition to a standard Pug Mill is a spray bar water manifold metering system. Spray bars and a direct reading flow meter make it easy to control the product’s moisture content. The flow meter is the part of the water manifold that distributes the water to two or three spray bars.
A discharge feed chute can also be added to a Pug Mill Mixer. The discharge chute allows for the transition of material to downstream processing equipment. Typically, a chute is slightly tapered to a narrower outlet point for feeding a conveyor belt.
Lastly, there is typically a gap in between the paddle swing and the curved mixer box, so a bed of material is established. Abrasion resistant steel liners can be added to decrease and slow down the wear of the steel mixer box.
Construction & Road Building Applications
Pug Mill Mixers can be used when a new highway or replacement concrete highway is being constructed, as well as other roads, parking lots and even airport runways. When new roads are being put in, the concrete and asphalt are ripped up before digging into the subbase. Before a new concrete pour, a compacted base of a specific rock and sand blend at a certain moisture content is needed. Adding water to this mixture is necessary to provide compaction of the stabilized base material and to meet the desired moisture content.
Pug Mill Mixers can assist when it is necessary to mix aggregates with water and other stabilizing agents. Producers will often put a slight amount of cement and water into a rock and sand blend to act as a hardening agent. They can also be used for recycled asphalt pavement when reclaiming old asphalt and mixing it with new materials for sustainable reuse.
Coal Fired Power Plants
Pug Mill Mixers can be used in coal fired power plants where there are one or two waste streams. One of these waste streams is often a very fine dry fly ash that needs to be hauled to a disposal site. In order to haul this material, water may need to be added to increase the moisture content to 5-10%. Producers typically want to load out or mix fly ash at 100 tons per hour.
In coal fired power plants where there is flue gas desulfurization (FGD), dewatered lime sludge is a secondary waste product. This lime sludge is dewatered after the FGD process that is meant to prevent pollutant emissions. After dewatering equipment is used to dilute and dewater this lime and water flow, they are left with a sludge and dry fly ash. Most power plants then have permitted sites where they can dispose of this uniformly mixed lime sludge and dry fly ash. Because of the drastic difference in textures of the thickened lime slurry and dry fly ash, this is a very difficult mixing application.
EIW Pug Mills have been sold into several plants for mixing flue gas desulfurization lime sludge and fly ash. These Pug Mills excel at uniformly mixing these two difficult-to-mix materials at a high-capacity basis anywhere from 50 to 250 tons per hour.
Mining & Minerals Applications
In some applications, tailings are discharged out of a thickener. The thickener underflow in some mineral operations may be 30-40% solids by weight. There can also be a secondary waste stream of dry screened minus quarter inch fines that have not been processed. When the screened dry fines and thickener underflow need to be disposed of, a Pug Mill Mixer can be used to blend the two feed streams uniformly at capacities of up to 400 to 500 tons per hour.
Industrial Waste & Environmental Applications
In some industrial waste or municipal applications, there is a thickened, Jello-like, sludge that is a waste product. This dewatered municipal sewage sludge, or biosolids, can be mixed in a post lime stabilization application. During this process, lime is added at a specific rate to raise the pH of an acidic sludge. In some applications, biosolids may be mixed with a bulking agent to compost a dewatered municipal biosolids sludge.
Some Pug Mill Mixers can handle very lightweight bulking agents like sawdust, shredded corn stalks, woodchips or even shredded tires. These bulking agents can be mixed with a type of industrial sludge at capacities of 50 to 200 tons per hour at a very low bulk density material. This could be 50 lbs. per cubic foot or 0.8 tons per cubic meter mix bulk density mixed at a high capacity. Lightweight material such as this can be uniformly blended and either further processed or disposed of in a landfill.
Benefits of Pug Mill Mixers Across Applications
Eagle Iron Works Pug Mill Mixers utilize intermeshing paddle shafts driven by a single motor through a dual-output, timed gear reducer. This design allows the intermeshing of the paddle shafts to provide a vigorous mixing of difficult-to-mix materials. These could be wet and dry materials that require thorough mixing or blending at a high capacity anywhere from 50 to 500 tons per hour.
Eagle Pug Mill Mixers utilize a heavy-duty gear box and highly abrasion resistant paddles made from a cast iron allow. These mixers can handle abrasive feeds like sand and rock and provide continuous high capacity mixing in a variety of applications.
From construction and road building applications to power plants and industrial waste, Pug Mill Mixers are a versatile, efficient tool for a wide range of industries. They have the ability to handle high moisture content, create a uniform, consistent mixture and can be customized to meet the needs of a specific operation.
Learn more about EIW Pug Mill Mixers and download our brochure.