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What is the best type of mixer for my application? Regardless of what people have told you, or what you have read, there is a best mixer for each application. Each excels in a different type of concrete:
Twin Shaft - Lots of concrete at high speed, low wear, low maintenance. Designed for rough, tough jobs like dam building and ready-mix. Handles aggregate sizes to several inches. Does not discharge completely, so not good for mixes of different type or color. End of shift cleanout is slow and difficult (unless our high pressure washout system is used). Performance on dry cast mixes is not as good as the best planetary mixers. Gives the highest throughput of concrete in a given floor space, can double plant output without modification to hoppers, scales, belts etc. Most models have single discharge door; exception is Ocmer Ocmix RG which has a double door option. "Compulsory mixing" action gives high quality concrete with maximum strength.
Turbine - High quality precast, especially wet cast mixes. Medium speed, medium wear, medium maintenance. Designed for precast. Good cleanout but sensitive to blade adjustment and wear. Good for colored mixes. Simple mechanical system. Easy to install moisture sensors in floor. Up to 4 discharge doors. Most models not fast enough to create "Compulsory mixing", so concrete not as high in quality or strength.
Planetary / countercurrent - Highest quality precast, especially dry cast, block, pavers, architectural. Medium to high speed, medium wear, medium maintenance. Designed for precast, block, pavers. Good cleanout, good for colored mixes. More complex mechanically but best models very reliable. Easy to install moisture sensors in floor. Up to 4 discharge doors. "Compulsory mixing" action gives high quality concrete with maximum strength.
Rotating pan - most of these type mixers are obsolete. Good for precast, both wet and dry cast. Mixing action similar to planetary but mechanically complex, high maintenance. Difficult to install moisture sensors. Single discharge door. Most models not fast enough to create "Compulsory mixing", so concrete not as high in quality or strength.
Drum / tilt up and transit mixing trucks - Slow, poor mixing action takes many revolutions to attain good homogeneity. Critical on charging sequence, requiring initial addition of water to wet blades and help remove deposit from previous batch. Cannot be completely discharged, difficult to clean out and maintain.
Ribbon/Spiral blade - The 'old standard' for precast and block plants. Slow, poor mixing action takes many minutes for good mix. Very little end to end action, so charging method and water entry is critical to avoid variation within discharged batch. Non-compulsory action. Reliable with low maintenance cost. [Top]
Why does the Ocmix RG have a more "rounded" body than others of the same size? When mixing a heavy load in a twin-shaft mixer, the tremendous torque of the mixer shafts tend to twist the mixer body - it squirms slightly. Many years of experience in these mixers has shown that this squirming can twist the shaft seals and bearings out of line, causing excessive wear over time. The seals are designed to allow this movement and the more cylindrical top section is a stronger basic shape that makes the Ocmix RG stiffer; it holds its shape even with full loads of extreme mix designs, such as in concrete for dam applications, resulting in longer life and lower maintenance.
Longer life with less down-time. [Top]
Why do we say the gearbox runs cooler? It's a fact that the Ocmix RG gearbox runs cooler than several others, and as a result does not require an oil cooling unit. This reduces its complexity and increases reliability while reducing its price. We say that this is due to its 2-stage design, but this is a simplification. In fact, it is due to the higher efficiency of this particular gearbox, which in turn is mainly due to the 2-stage design.
The speed of the motor, 1750 rpm, must be reduced to allow the mixer shaft to turn at 24 to 27 rpm. This is done with a 2:1 belt reducer followed by a 36:1 gear reducer. Every pair of gears creates a little friction which results in power loss. If everything else is equal, each set of gears will add to the total power loss, so the higher the number of stages, the higher the power loss. Take model RG4500, which uses two 75 HP motors. Each motor consumes 55 KW (55,000 watts) when running at full load. If each stage of the gear reducer looses just 0.5% of the power in friction, a 2-stage reducer will dissipate 1% of 55,000 or 550 watts in heat. A 3-stage reducer will dissipate 50% more, or 820 watts - almost equivalent to the electric heater you might have for warming a cold room! Luckily the mixer is not fully loaded 100% of the time, so the power dissipated will only be at this level for short periods of time. The average power dissipation raises the temperature of the gearbox, gears and oil to a proportional amount above ambient; thus if the 2-stage example gives a temperature rise of, say 60 deg. C above an ambient of 20 deg. C, its temperature will stabilize at 80 deg. C. The 3-stage example will give a rise of 90 deg. C and its temperature will stabilize at 110 deg. C. If the oil starts to disintegrate at 100 deg. C, damage will eventually occur unless extra cooling is used.
This example is a simplification and we have neglected some smaller effects such as the different ratio of the reducers in the example, which tends to level the difference somewhat. Nevertheless, the RG's 5-year gearbox guarantee shows that we are very confident in its ability to perform without an oil cooler, even when running non-stop and fully utilized for many hours each day. [Top]
Why a reduced discharge door? By reducing the width of the normally full width door, the normally long discharge chute can be cut down proportionally. This reduces the height of the mixer above the truck or bucket, which in turn reduces the cost of the plant substantially. In existing plants, it can increase the headroom under the discharge spout, enabling higher discharge positions to be used.
Unlike other models of reduced door, which use a standard, very small door on even the largest sizes of mixer, Ocmer's door is approximately 2/3 the standard width, with this ratio maintained on all sizes of mixer. Although the height and cost saving is not as impressive, the discharge time is maintained at very little more than the standard discharge time, keeping throughput essentially unchanged. [Top]
Does the area above the discharge door get mixed properly? In a word, YES. The very intense mixing action sweeps the material through this area before it has time to stop, allowing it to mix with the rest of the batch. There is a step of less than 2" high between the mixer floor and the discharge door, however, and a concern has been raised that a small fillet of unmixed material can lie along the trailing edge. This is highly unlikely in practice because the mixing action pushes material across this area from both sides. To eliminate any possibility for concern, however, the edge of the floor and liner can be chamfered.
Complete mixing and thorough cleanout means no unmixed or stale concrete. [Top]
Filling to total capacity and faster mixing time means a lot more throughput for the price, or a smaller mixer, which saves money. [Top]
What is the difference between Filling Capacity, Uncompacted Output and Compacted Output? When the mixer is filled to its DRY FILLING CAPACITY, as the stone, sand and cement mix, the air spaces between stone chunks get filled with sand, and the air spaces around the sand grains get filled with cement. The density goes from about 100 lb/cu. ft. to 150 as it is mixed. Even the spaces around the cement powder get filled – with water. The whole volume reduces by 20% or more as a zero slump mix is made. But this zero slump mix still has lots of air spaces in it. If discharged in this state, you get an UNCOMPACTED YIELD of 20% less than the mixer capacity. When the mix is vibrated in the mould or form, all this extra air is expelled and it compacts by a further 15 to 20% to give the COMPACTED YIELD, which is 2/3 of the dry filling capacity.
What does this mean to the user? It depends on the application:
If the user needs 3” slump or less, the container (Tuckerbilt or bucket) capacity must hold the UNCOMPACTED YIELD.
If the user needs 6” slump or more, the container (Tuckerbilt or bucket) capacity must hold the COMPACTED YIELD.
If the user needs something in between, the container (Tuckerbilt or bucket) capacity must hold something IN BETWEEN. Use your judgment. [Top]
How long will the mixer last before I have to replace the liner tiles? If you use the mixer 5 days per week, single shift, and depending on the type of aggregates used, expect to replace the centre section of tiles after 1 1/2 to 3 years. This is equivalent to between 100,000 to 200,000 batches. Note that Ocmer's ni-hard tiles are Italian made and have high (and expensive) nickel content, making them CERTIFIED 600 Brinell, unlike others that use Chinese tiles of inferior hardness.
Ocmer Quality throughout [Top]
Why do Ocmer mixers not use cleaning rings on their shafts? Heavy steel cleaning rings are used by many other manufacturers, but Ocmer generally does not use them because of the damage they can do to the arm hubs. A properly designed paddle, arm and hub is self-cleaned by the intense mixing action - there are no dead spots and at the end of the day, little or no buildup should be evident on these parts. Exceptions occur, and when a special, sticky mix requires them, the rings are added.
Better solutions through better engineering and innovation. & [Top]
Do you stock parts in North America? A full stock is kept at our North American Headquarters, ready for next day delivery across the continent. This stock includes all wear parts and most other parts, including gearboxes, for every model sold in North America, including those sold through our dealers. Call us with your model and serial number for prices on any parts that you need.
Can I buy parts on credit? Of course - all it takes is the establishment of a credit account if you don't already have one with us/p>
The customer comes FIRST at Ocmer North America & [Top]
How do you price your products, is shipping included? Some companies price their products in Euros because it is more convenient for them. But you could work out the exchange to Dollars, then find it has changed by the time it is delivered and you end up paying more. Scale-Tron's policy is to price everything in Dollars; you are guaranteed to pay the price we agreed at the time of order, even if the Euro goes up.
Your other unknown when buying European products is the shipping cost. Again, we don't ship FOB our European port for the same reason. You only pay the shipping from the east coast port of entry that is most convenient. We can give you a close estimate for this if you wish.
No hidden costs. [Top]
Concrete mixer facts and information © 2006 Robin Shepherdson, Eng.