– Fabric production
In textile machines used, for example, for the production of fabric, certain positions in the machine structure are exposed to high mechanical wear, which means that sufficiently wear-resistant components are needed to ensure economic operation of the machine. The material selection for such components is determined by the required properties of the “thread/thread guide” system.
For processing natural fibres such as cotton and animal wool, steel or porcelain are usually acceptable as thread guide materials. Synthetic fibres, on the other hand, often require the materials used to exhibit much higher wear resistance in contact with the guide elements. In such cases, dense-sintered components made of oxide ceramics on the basis of Al2O3, TiO2 and ZrO2 are usually the first choice.
The main purpose of such ceramic parts is to expose the fibres and threads in contact with them, the technical properties of which are usually given, to only minimized stresses even at high processing rates and also to achieve a reliably long lifetime in the operating conditions. With the selective adjustment of the ceramic microstructure and its surface conditions in the area of the thread contact, this purpose can be achieved.
The microscopic appearance of an oxide ceramic sintered surface has a remote resemblance to a cobbled surface. On account of the non-complete thread contact with the ceramic, this leads to a low thread friction and therefore favourable sliding properties. If, however, geometric measurement tolerances of just hundredths of millimetres are specified by the customer, hard machining of the thread contact surface is hardly avoidable. Grinding alone leads to roughening owing to the crystallite edges being created by the process and therefore to increasing thread friction. In the contact area, the danger of damage up to thread breakage must then be expected. To minimize this risk, subsequent polishing of the ceramic contact surface is essential. Such a surface does avoid thread damage, however, it does not lead to lower thread friction on account of the complete thread contact. The optimum coordination of the machine parameters with the topographic properties of the ceramic components allows, however, even with such thread guides, processing rates of, for example, 1500 m/min in continuous operation.
The ceramic is produced starting from high-purity, inorganic powders usually with oxide ceramic process engineering with certain shaping variations (injection moulding, powder pressing, extrusion, slip casting), which enable the economic production of a wide variety of geometric shapes, sometimes followed by a green machining step, subsequent sintering at temperatures above 1500 °C and finally any hard machining required depending on the design.
The technical advantages of oxide ceramic thread guide components on the basis of Al2O3, TiO2 and ZrO2 can be summarized as follows:
- High wear resistance in high-speed processes
- Accuracy of contours
- Optimally adjustable topography of the thread contact area depending on the application
- Low frictional losses
- Hardly any thread breakage
- No contact reactions with the thread
- Low thread abrasion
- With the use of TiO2 ceramic, no electrostatic charging.
- Reliability and long lifetime over years in the operating conditions
For more than 50 years, oxide ceramic materials have been made in a multitude of geometric variations as proven components of machines and equipment in the textiles industry.