Teutrine GmbH has established itself as a reliable service partner for multi-faceted engineering, assembly and repair solutions for cement plant operators and plant engineering contractors. Companies from the chemical and wood-processing industries, from the waste disposal and power station sector also form part of Teutrine's customer base.
The ongoing performance increases and availability of process plant in the cement and mineral industry result in an increased need for large spare part stocks with resultant higher costs for procuring parts. The degree of wear in plant components that are subjected to heavy-duty operation increases exponentially. As a service partner and in very close customer contact, Teutrine GmbH from Oelde,
Westphalia, Germany, has solution strategies for greater planning assurance in the realm of maintenance and repairs. The upshot above all is an increase in lifetimes of highly stressed machine components.
In this regard a significant role is played by mobile processing machines for clients' on-site applications. Of major importance for the success of on-site operation is efficient preparatory work. Matching the mobile Teutrine processing machinery to clients' needs must be researched and precisely clarified in order that workshop quality can be achieved on site in reality.
1. Introduction
The case discussed here is a roller-press, the grinding rolls of which are equipped with hardened metal studs. Teutrine GmbH examined the options to even out the unevenly worn metal studs by means of grinding.
Problem posed: Roller-presses work with a configuration of two opposed grinding rolls. One roll is installed in a fixed position and the second roll is activated by a hydraulic cylinder in order to adjust the refiner gap or in the case of coarse grain, to ease off. The hydraulics even out one-sided stresses and the pressure is increased on the side experiencing greater stress.
As a result of this process the rolls or the hardened metal studs are subjected to various degrees of wear, in this case mainly in the centre of the roll. This leads to the refiner gap becoming too large, the required particle distribution not being attained in the grinding process and a resultant loss of quality. The main research served to clarify the following aspects:
1.1 Hardness of the metal studs
How can the roller surfaces of the rolls which are furnished with metal studs of a very high material hardness (Vickers hardness of over 900 HV-50) be treated?
Mobile treatment
Is mobile refurbishment possible on site at the customer's plant? Which processes can be developed for refurbishment of the mill without cost-intensive disassembly and reassembly of the grinding rolls?
1.2 A cost-effective process that extends operational lifetimes
Does mobile processing on site really harbour a cost-effective alternative and considerable savings-potential for the customer? Special attention had to be paid to this aspect, as this initially makes the purchase of new grinding rolls unnecessary.
2. Technology
These questions caused Teutrine GmbH personnel to find new solution channels. In a relatively short time, complex engineering with diverse tests and machinery technology were carried out. The following gives a few examples of the basic trials.
2.1 Water-jet cutting trial
Processing of the hardened metal studs by means of water-jet with a cutting width of approximately 1.5mm at a pressure of 3000bar.
For this process a very high energy requirement of 3000bar is needed, see Figure 1. The water-jet separates the very hard material whereby the high jet energy can only be absorbed in a water reservoir, see Figure 2. The disadvantages are that this process is very dangerous and the water has to be controlled. Each stud has to be hit individually. It is unsuitable for grinding installations in the cement industry!
2.2 Trial grinding with a conventional abrasive media
The trial by means of conventional abrasive discs in various grain sizes was evaluated as positive but the lifespan is very poor and as a result abrasive disc
consumption is very high, irrespective of whether abrasive media with corundum or composite ceramics are employed, see Figure 3. A further disadvantage of this treatment method is the generation of extremely high temperatures that, once again, reduce the bonding of the studs to the base material.
3. Execution
After a series of workshop trials, a special grinding cup wheel with composite diamond was developed for this application, see Figure 4.
The processing unit in module form 'Single-Execution', see Figure 5, was constructed in such a way that simultaneous application options for fixed and free roll (and different roll lengths) are given. Also, value was attached to its compact construction for worldwide employment and transport option by airfreight.
A further variant on surface refurbishment of rolls with hardened metal studs is the 'Twin-Machine' with two processing units, see Figure 6. This form of refurbishment on site permits a significant reduction in downtime.
4. Application and execution
The pre-cleaning of the rolls takes place by means of sand blasting, (see Figure 7), to remove slag remains or other residues which have built up in the spaces between the studs during grinding operations.
Subsequently the assembly of the mobile treatment unit takes place, whereby one unit is fixed in front of both the stationary roll and the free roll, see Figure 8. The alignment accuracy stands at around 0.01mm.
The rolls are then measured and the highest hardened metal stud is marked as a reference mark, see Figures 9 and 10.
The rolls are turned with the existing auxiliary mill drive and treated simultaneously with both of the high-precision grinding units. A frequency control allows the calibration of the diamond disc's rotational speed as well as optimal progress of the processing unit.
The special abrasives are cooled with water. Circulation of the cooling water is done using pumps, see Figure 11.
5. Conclusion
Depending on the degree of wear on the rolls the treatment practised by Teutrine on site can be repeated many times over.
In the case of on-site processing, the cost-intensive disassembly and reassembly of the grinding rolls and the refurbishment of the old roll at the original manufacturer's plant both become superfluous.
The refiner gap can again be correctly adjusted and the optimal grain size for the material is re-established.
The advantages for the operator are very easy to see. Among these are short downtime of the roller press, plus through the roll refurbishment measures described above, a new investment in replacement rolls was postponed for more than two years.