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Reliability, Precision, Speed


Spinneret holes are tiny and usually appear en masse. To be able to measure them precisely and efficiently, Walter Uhl and his team have developed an inspection microscope that is over seven meters long. The complete system is designed, produced and assembled in Asslar.

You wouldn’t believe all the places UHL microscopes are used – in a highly diverse range of industries and business fields all over the world. Expectations are always high, the technical requirements extremely specific. Walter Uhl knows that. But after all, this is the reason why customers approach the company Walter Uhl technische Mikroskopie GmbH & Co.KG in the first place. “If the slogan had not already been invented, I would say ‘Nothing is impossible’, says the company owner, “particularly when it comes to high-quality optical metrology for unusual measuring tasks and special customer-specific configurations.”

The most recent product of the Asslar measuring microscope manufacturer evolved from just such an unusual measuring task: the inspection of spinnerets, which are used in industrial production of textile fibers. Spinneret plates can be as long as 7.5 meters and accommodate more than 35,000 holes, so-called capillaries, of varying geometries and diameters up to 250 micrometers. Homogeneous fiber production quality depends on the measurement of every single capillary. And, as in other industries, measurements have to be reliable, precise and as fast as possible.

UHL’s solution to this challenge is unique. The basic mechanical construction consists of a linear axis with separate modules measuring 80 cm in length. The length of the instrument can be adapted to the size of the spinneret plates. For inspection, the plates are clamped in a fixture. From here, the fully automated spinneret inspection system takes control. In a first step, the entire spinneret is scanned and all hole positions are captured. Even at this early stage, information can be obtained on the condition of the holes. Then, using a higher magnification, either a hole-by-hole 100 per cent check or a random check of the spinneret can be performed, depending on requirements. During inspection, any dirty holes are cleaned with compressed air from a blowing station and then inspected again. Obstinate dirt can be removed manually with fine tools, using the live image for reference.

Each spinneret has a unique number for unambiguous and complete documentation of all measurement and inspection results. After a complete inspection run, an easy-to-read analysis module displays the results in the form of various charts or a text protocol.

The capability of UHL as a medium-sized enterprise to create such an unusual measuring system is one of the company’s core competences, the product of many years of experience and persistent enlarging of its expertise. “We have spent years developing some of the parts of the system and we keep on developing them further,” comments manager Malte Bernard. “We have thus acquired a sort of construction kit with which we are able to meet practically any customer requirement.” This has led to a whole number of inspection microscopes for different applications, for instance the benchtop models PR2 and PR3 for visual checking of small quantities, or the PR5 series for the inspection of so-called ring spinnerets, which works with high-resolution video technology.

The PM4 spinneret inspection microscope is naturally a premier league product – and earns this status in every respect. Most of the mechanical components are made of cast aluminum to prevent fluctuations in the measurement results over long periods of time. The motorized axes were also designed with the corresponding degree of precision. Special fixed-magnification optics with integrated ring illumination deliver excellent imaging quality. The measuring accuracy for a 10x objective is 1 micrometer – for spinneret capillaries with a diameter of approx. 250 micrometers this is not only desirable but mandatory. The inspection microscope thus easily detects any deviations within the specified tolerances.

The spinneret inspection microscope weighs around 1.5 tons. For customers it is a heavyweight investment, but it pays off in no time at all. After all, measuring quality means manufacturing quality. Two PM4 models have meanwhile left the assembly hall in Asslar in the direction of Mexico and Brazil, one has remained in Germany. At the ITMA, the world’s leading textile machinery fair, Walter Uhl was able to make some important contacts and convince several reputed companies in the textiles industry. UHL is already working on new orders, exhibiting the qualities its customers have come to expect: reliability, precision and speed.


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