Concrete mixer types
The heart of a concrete mixing plant is the mixer, upgrading a mix design’s several raw materials to a product of high value: concrete.
The mixer market is global providing users with a wide range of different mixer types and models.
The most common models are:
- Countercurrent planetary mixer
- Free fall drum mixer
- Single shaft mixer
- Twin-shaft mixer
Performance, efficiency and versatility are the characteristics required for a mixer to be able to mix nowadays concretes. Additionally state of the art technology and high quality are needed for economics and longevity.
Each mixer, of course, has its own properties and characteristics as there are dimensions, volume, power, weight, mixing technology and application.
The mixer to a high extent determines the construction of the whole concrete mixing plant. To achieve the best possible results in matters of production capacity and user-friendliness not only the mixer but all transport and dosing equipment as well as the scales and the surroundings must be dimensioned accordingly.
Inner workings of a twin-shaft mixer.
Inner workings of a countercurrent planetary mixer.
Parameters effecting to mixing of concrete
Efficiency of the mixing process has a big impact on how quick and intensely cement, water and additives can be homogenized with the aggregates.
Intense and efficient mixing is required to reach targets as there are good workability, compressive strength, impermeability and frost resistance of the concrete.
Generally, mixing times vary between 30 to 120 seconds depending on the concrete mix design and the raw materials used, specifications of the relevant standards, the mixer type, the state of the mixing tools and the batch size. To find out the best mixing result for a concrete mix design the production needs to be controlled and tests of the properties of fresh and hard concrete have to be carried out.
There are some "parameters", which can be controlled/adjusted by the plant’s operator:
- Sequence of emptying scales
- Waiting times between discharging different materials
- Position and state of the mixing arms (proper mechanical adjustment at regular intervals minimize wear and maintain the mixing efficiency)
- Total mixing time
- Speed of the mixing arms (if the mixer motors are equipped with frequency inverters)
The actual result of the mixing process and consistency of the concrete mix can be monitored visually by an HD-camera installed in a dust proof housing placed on the mixer, or by following the motor power displayed on the control computer screen. The reading varies according to the consistence of the concrete mix.
Mixer covers often are also equipped with an inspection hatch allowing to take a look inside the mixer through a steel mesh during the mixing process.
It is necessary to carry out preventive maintenance on base of the maintenance program as specified by the manufacturer, under regard of the mixer's actual operating hours provided by the control system.
Motor sizes range from 15 up to 75 or more kilowatts and several hundred kilowatts if 2 or 3 motors are in use, leading to enormous power inside the mixer and respective danger during operation. Safety regulations and operating instructions must therefore must be followed strictly.
The figures below illustrate the movement of the mixing arms of a twin-shaft and countercurrent mixer.
The best mixing result and the designated properties of a mix can only be achieved if materials are dosed according to the mix design, as exact as possible, with repeating precision of the dosing equipment and weighing accuracy of the scales on highest possible level.
Tecwill offers a wide range of versatile mixing solutions for different purposes, such as the production of ready-mixed concrete, shotcrete, as well as high quality wet concrete, SCC and UHPC for precast plants, not to forget earth-moist concrete for block and paver factories.
The Tecwill WillControl control system helps to achieve high-quality repeating precision, allowing to discharge various raw materials into the mixer in the desired quantity, order and time.
The system also anticipates the need for the maintenance of the mixer and other plant equipment.
For further information please contact Teemu Tuominen.