© Kieselstein International GmbH
The main reasons for wire breakage during the drawing process are surface defects. Shaving is a way to remove them. This results in further potential for raising the workability and for increased cross-section reduction.
Due to the industrial application of new materials and alloys there is a progress in the wire production business. The focus is on the development of materials as well as the improvement of technologies and processes for the production and processing of wire. One main issue is the continuous improvement of the characteristics of the workability while increasing wire quality at the same time.
Image 1) Technical process of „shaving“ © Kieselstein International GmbH
Shaving used for increasing the surface quality even today is an integral part of the production of high-tensile valve spring wire. In addition to the use for steel wire the demand for the application in the processing of non-ferrous metals has increased in recent years. One reason are the risen requirements in the wire quality and in this context the demand for a well-defined surface quality.
On the other hand some wire production technologies such as casting, create surfaces that complicate the working of the wire. A chipping processing of the defective surfaces therefore also have positive influence on the following processing steps, like wire drawing.
As picture 1 shows shaving of the wire is a chipping process. Amongst others oxides, decarburised surface layers and other defects located near the wire surface are removed during the shaving process. Modern wire shaving plants work in a diameter range from 1 mm to 22 mm. The chipping tool – the shaving die – removes between 0.02 mm and 0.5 mm of the wire diameter off the inlet material.
This results in a nearly defect-free surface of the material with a low roughness of the surface as shows picture 2. Usually this wire is processed further by wire drawing.
Casting, rolling, shaving
In the course of a scientific thesis by using the testing plant of KIESELSTEIN International the influence of shaving on the workability of non-ferrous metals using the example of magnesium alloys WE43 and AZ81 has been examined. The intention was to find out to what extent the workability is positively influenced by the chipping process. The results can be transferred to the processing of other materials as well.
The basis are activities of KIESELSTEIN International in the production of magnesium wire as semi-finished product used for production of screws for the automotive industry. The wire produced by casting and subsequent rolling is processed on the shaving plant. Afterwards it was drawn down to the final diameter. In a test the drawing of the inlet material was compared to the drawing with preliminarily shaved wire.
Image 2) Comparison of a wire cross-section polish before and after shaving © Kieselstein International GmbH
When drawing the shaved material the degree of workability on a single draft, i. e. the one-time cross-section reduction, could be increased by 15% compared to drawing unshaved material. This means that shaving reduces the number of drafts necessary from the same inlet material to the same finished diameter.
The processing of the wire can be economised. During a second test shaved and unshaved inlet material were compared on a multiple draft. Using shaved material the workability could be increased by 60% compared to unshaved material. Integrating shaving into the wire production process increases the workability of non-ferrous metals.
This allows adapting some of the processing steps such as intermediate annealing considerably. Furthermore evidence could be provided that the workability of shaved material compared to unshaved wire is improved also in a single draft. Less drawing steps become necessary in the wire production process, which results in savings of energy and costs.
Image 3) Combined drawing-/shaving plant for the processing of non-ferrous metals © Kieselstein International GmbH
The following conclusions can be drawn from the testing results:
– increased cross-section reduction on a single draft
– less drawing steps with multiple step drawing
– improved workability in general
– fewer heat treatment steps required
– higher surface quality
– more efficient production process
One further advantage is that shaving can be integrated into the drawing process of non-ferrous metals, respectively in the existing plants and machinery.
Picture 3 shows an example of a combined drawing-/shaving plant of KIESELSTEIN International GmbH for the treatment of non-ferrous metals. A shaving unit for a diameter range from 1.0 mm to 2.0 mm which has been integrated into an existing multiple step drawing plant is shown in picture 4.
Image 4) Integrateable shaving unit for a diameter range of 1 mm to 2 mm © Kieselstein International GmbH
Summary and outlook
The conclusions drawn from the results of the processing tests allow for an economisation of the technological procedure of the production of non-ferrous metals. The savings realised due to unnecessary annealing or the increase of the cross-section reduction in each processing step are considerably higher than the costs the integration of shaving into the drawing process of non-ferrous materials induces.
In addition to the improvement of the workability, the defects in the surface are removed and a defined roughness adapted to the following processing can be reached. This enables a production considerably more efficient while increasing the product quality significantly at the same time.