The base fights the mixer
Every newton-meter a mixer puts into the product comes back out through its base. Size a mixer base for the motor power alone and it will be fine until the day the product thickens, torque spikes, and the base finds out.
We size mixer bases for the full torque at the agitator shaft, with a service factor for startup and upset conditions. On viscous products that is often double the running torque, and the base has to survive it without rocking on its anchors.
The startup torque is the one that matters. When the motor starts against a full tank of viscous product, the torque can spike to 250 percent of rated for the first few seconds. The base has to hold through that spike without the anchor bolts loosening.
Anchored, grouted, level
Mixer bases get the full foundation treatment: machined mounting pads for the mixer drive, anchor sleeve positions laid out to the civil drawing, and grout holes so the void under the base fills properly.
For tank-top mixers we build the bridge beams instead, span-rated for the mixer weight plus the bending from shaft runout. The flange drilling is matched to the tank nozzle the mixer bolts to.
On floor-mounted mixers the base sits on a concrete plinth. The plinth has to be deep enough for the anchor bolt embedment, and the base has grout holes so the void fills. Without grout the base rocks on the high points of the concrete and the anchor bolts loosen.
Tank-top vs floor-mounted
Floor-mounted mixers sit on a base on the floor next to the tank. The mixer shaft goes through the tank wall on a stuffing box or a mechanical seal. The base carries the mixer drive and the bearing housing.
Tank-top mixers sit on a bridge beam across the tank. The mixer hangs from the bridge, shaft down. The bridge is span-rated for the mixer weight plus the bending moment from shaft runout, which is the side load the shaft puts on the bridge when the product is uneven.
The bridge flange drilling matches the tank nozzle. On some tanks the nozzle is on the top head, on others it is on a bracket welded to the side. We need the nozzle drawing to position the flange holes.
Product attributes
| Material | Q235B / Q345B carbon steel, heavy section |
|---|---|
| Sizing | Full agitator torque with service factor for startup and upset |
| Startup torque | Rated to 250 percent of running torque |
| Provisions | Anchor sleeves, grout holes, machined drive pads |
| Types | Floor-mounted base, tank-top bridge beam |
| Bridge | Span-rated for mixer weight plus shaft runout bending |
| Flange | Drilling matched to tank nozzle drawing |
| Finish | Shot blasted Sa2.5, anti-rust primer |
| Certificates | ISO 9001, ISO 3834, AWS D1.1 |
| Lead time | Samples 15 to 25 days, batch 30 to 45 days |
Frequently asked questions
Why do you size the base for more than the running torque?
When the mixer starts against a full tank of viscous product, the startup torque can spike to 250 percent of rated torque for the first few seconds. When the product thickens during mixing, the torque goes up again. If the base is sized for running torque only, it survives until the day the product thickens. We size for the upset condition so that day does not break the base.
What is the difference between floor-mounted and tank-top?
A floor-mounted mixer sits on a base on the floor, with the shaft going through the tank wall on a seal. A tank-top mixer sits on a bridge beam across the tank, with the shaft hanging down. The bridge is span-rated for the mixer weight plus the bending from shaft runout. The flange drilling matches the tank nozzle.
Why do mixer bases need grout holes?
Without grout the base sits on the high points of the concrete pad and rocks on the anchor bolts. The grout fills the void between the base and the concrete, distributing the load. Grout holes in the base plate let the grout flow through and fill the void. Without grout, the anchor bolts loosen under the torque reaction.
Can you build a tank-top bridge beam?
Yes. The bridge is span-rated for the mixer weight plus the bending from shaft runout. The flange drilling is matched to the tank nozzle drawing. Send us the nozzle dimensions and the mixer weight and we size the beam.
What mixer information do you need to quote?
Mixer model or shaft torque, mixer weight, and whether it is floor-mounted or tank-top. For tank-top we also need the tank nozzle drawing and the span. For floor-mounted we need the anchor bolt pattern from the civil drawing.
Working with us
We are a 7,000 square meter fabrication shop in Qingdao with 20 years of export experience, mostly to Australia. Welding runs under ISO 3834 with welders qualified to AWS D1.1, and quality is documented to ISO 9001 from material certificate to final dimensional report. Drawings and specifications stay confidential. Mixer model or shaft torque. Either works for a quote.
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