Adhered matter and wear in precast concrete production

Adhesions and wear that occur at transition points and on discharge funnels, mostly result in unscheduled downtimes. Cost-intensive repairs on the greater part of the production processes can be prevented with effective wear protection. Possible applications can be considered by the example of a precaster.

Adhesions and wear that occur, for example, at transition points and on discharge funnels, mostly result in unscheduled downtimes. Cost-intensive repairs on the greater part of the production processes can be prevented with effective wear protection. Possible applications can be considered by the example of a precaster who manufacturers wall and floor elements and stairs, among other products.

The production process can be described as follows: binders and aggregates, and possibly admixtures, are mixed with water in a pan mixer. Next, the mix is transported, in rotary buckets, to a concrete spreader, which then distributes the concrete to the awaiting receiving points.

In this process alone, there are already at least three sensitive places that pose a risk for a reliable production process:

1. The pan mixer

2. The rotary bucket

3. The concrete spreaders.

The mixer – optimizing, conversion, process monitoring

Correct adjustment and continuous monitoring of the mixing tools, in connection with the correct mix ratio and the suitable mixing time, are the basics for optimal and consistent mix results.

The mixing tools differ depending on the manufacturer, mixer type and construction years, mounting and wear behavior. Because stocking and storage of a large number of different mixing tools are complex and expensive, the wrong paddles are frequently used for lack of availability. Owing to the use of wrong paddles, the wear in the mixer is primarily at the wall or bottom of the mixer, the replacement of which is expensive and time-consuming. “This is exactly where we begin with our universal mixing tools that can be used with every pan mixer. Their use automatically reduces storage costs,” explains Detlef Bauer, Managing Director of the company Pucest protect GmbH.

To improve the mixing behavior of a pan mixer, Pucest offers its customers the possibility of mixer optimization: the pan mixer is optimally adjusted on location at the customer’s site. The paddles and arm arrangement are checked and adjusted to provide a uniform mixing line during mixing and to reduce the mixing time. Due to the improved arrangement of the paddles and the arms, the wear is primarily at the paddles – which can be replaced at lower cost. This eases the wear on the mixer bottom and the external walls.

When there is no control of the mixing tools

Optimization of a mixer is worthy of consideration only when the mixer is still in good working order and when the bearings of the mixing tools are not out of alignment. Bearings that are out of alignment frequently result in concrete ingress into the rotor, which hinders the arms from moving and results in loss of their elasticity – and, in turn, in increased wear.

To save high costs due to the complete replacement of the mixer, Pucest offers conversion of the mixer with its universal mixing arms, which prevents ingress of concrete into the rotor.

In the first step, the customer is provided with a so-called “black box,” which records the complete mixing processes to millisecond precision and thus provides accurate information on the possible causes of an irregular mixing process.

The mixer is converted based on the analysis of the data recorded. At first, the existing arm lead-throughs on the rotor are closed and the rotor fitted with adaptor panels. The adaptors enable fitting of the new Pucest universal mixing arms. These, according to the manufacturer, have a decisive advantage over the original: the new arm system provides optimal preset of the cushioning elements, which do not have to be readapted. Another advantage is the modular configuration of the mixing arms.

The operator of the mixer is thus given the possibility of optimally adjusting the arm in a matter of only a few minutes to achieve an ideal mixing line and mixing period. Furthermore, the wear is directed into the paddles, reducing wear on mixer bottom and mixer walls. Following conversion, the “black box” remains with the customer so that improvement of the mixing process can be precisely analyzed together with the concrete manufacturer.

Rotary bucket and concrete spreader

Another essential component of the production chain is the rotary bucket in which the concrete, via a bucket conveyor, is transported to the concrete spreader. The mixer discharges the mix through a funnel and into the bucket. During charging, transport and discharge, the buckets are exposed to permanent friction and impact wear. Here, in order to prevent expensive downtime, it is effective to provide utilization of Pucest 12-mm wear-protective cladding (85° Shore A) with cast-in perforated aluminum sheet, which is excellently suitable for cladding round segments.

The concrete spreader, too, is permanently exposed to friction and impact wear by the mix. Here, too, utilization of Pucest wear plates is also recommended.

Cleaning – the be-all and end-all against wear

For the application described with the foregoing example of the precaster, installation of the high-pressure Pucest Easy Cleaner system can be highly recommended in two critical places of the production process.

Several 3D nozzles driven by water pressure are installed in the cover of the pan mixer and take over the cleaning work. Two preset wash programs enable the plant operator to include intermediate cleaning between the two mixing processes and to initiate final cleaning at the end of the workday. Another Pucest easy cleaner is installed above the concrete spreader, which is fitted with nozzles adjusted for two-dimensional cleaning only.

In addition to continuous cleaning, which reduces adhesion and wear, the unit is designed to provide the workers with greater protection. For one, they must no longer climb into the mixer for cleaning to manually remove adhered matter. Secondly, an automatic system immediately interrupts automatic cleaning when the cover of the mixer is opened.

All of the measures described above, correctly installed, can notably reduce production downtimes and, in addition, save the company enormous costs.

CONTACT
Pucest protect GmbH
Zwischen den Wegen 5
63820 Elsenfeld/Germany
+49 6022 264010

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