Pumps are acknowledged workhorses in industrial liquid-handling applications, but there is another technology that, while not necessarily as highly recognized as the pump, plays a pivotal role in critical industrial liquid-handling applications. This technology is the portable mixer, and properly designed and engineered mixers can provide the operator with many years of service in a wide variety of blending or mixing operations.
Like any piece of industrial equipment, portable mixers only operate at their highest level of efficiency, effectiveness and reliability if the proper model and style is specified for the specific mixing or blending task. Therefore, there are a number of operational variables that must be taken into consideration when specifying a mixer.
Neptune™ suggests considering the full range of portable mixers – and has created a Mixer Selection Guide to assist in the process – with the best selection ultimately being the one that can satisfy the specific needs of the operation as related to the following categories:
- Style: There are four basic styles: pail, which has the smallest capacity, drum, tote and light- or heavy-duty bulk tanks, which have the highest capacity. The most commonly used in industrial operations are the drum and tank styles. Most models are either gear-driven with speeds of 350 or 420 revolutions per minute (rpms), or direct-drive, with speeds of 1,750 rpm.
- Mounting: While some mixers can be permanently mounted to the drum, tote or bulk tank, in most instances a mounting clamp is used to attach the mixer to the vessel. There are three common portable mounting-clamp styles: C Clamp, which has an adjustable angle of entry that is controlled by a ball-and-socket adjustment design; Angled Riser, which provides a fixed 10-degree angle of entry into the mixing vessel; and Flange Mount, which attaches to a flange that is located on the lid of the drum, tote and bulk tank.
- Props: “Neptune recommends Square Pitch propeller, which is the most efficient prop and can displace eight inches of liquid in one revolution for tanks up to 5,000 Gallons” said Gurmeet Kharbanda, Director Product Management - Neptune.
- Shafts: Shaft lengths for most mixers are determined by critical speed. Operating at a rotational speed that is equal or close to critical speed will cause a multiplication factor on normal runout, but this will be mitigated by the speed damping that is produced by the liquid. There are, however, certain circumstances that will produce abnormal shaft vibration. These include operating the mixer through drawoff or at drawoff for a significant period of time, during the drawdown of solids, and at a natural frequency when mixing extremely light liquids that do not produce a damping effect.
Also contributing to the style of mixer that should be specified are a number of operational characteristics, including mixing rate, or the time it takes to completely “turn” the product in the mixing vessel; mixer position, whether side-mounted, center-mounted, angled, offset or requiring baffles; and liquid type, with the liquid’s viscosity and particulate levels determining proper style and orientation.
“When dealing with slurries, we recommend solids should be limited to about 10% of the volume in the vessel” said Kharbanda.
Pumps may garner a majority of the attention in industrial liquid-handling applications, but portable mixers can often play an undeniably significant role in optimizing the effectiveness of the entire production operation. As with any technology, knowing the dos and don’ts of mixer specification, as well as the handling characteristics of the liquid to be mixed or blended, will aid in selecting the technology that is best suited for the operation.