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Science Research Technology

Walther Trowal: A new era for high gloss polishing of ceramic surfaces

Vibratory finishing of ceramic components: Perfect surface finishes at surprisingly low costs

Walther Trowal: A new era for high gloss polishing of ceramic surfaces

The new polishing paste PKC is also suitable for finishing orthopedic implants.

The recently developed polishing paste trowapast PKC produces flawless mirror finishes on ceramic work pieces with surface roughness readings of ra = 0.002 – 0.005 µm. These are values, which to date could only be achieved with costly manual polishing. The new finishing process opens entirely new surface finishing possibilities in the fields of decorative ceramics and medical engineering.

Mechanical high gloss polishing on metallic work pieces has been around for many years. To date similar finishes on ceramic components were considered as impossible.

But, because they offer a substantially higher wear resistance compared to metal alloys, the significance of ceramic materials has been growing steadily. When it comes to designer, optical and consumer products, high luster finishes are a key element for their market acceptance. But smooth, shiny surfaces also have a functional dimension for components requiring low frictional resistance. Ceramics made from zirconium provide the required hardness, but smoothing and polishing them by mechanical means was so far an unsolved problem.

Generally, mass finishing is a cost effective method for polishing of a variety of work pieces. The process usually starts out with an aggressive grinding powder followed by a polishing paste that creates a high luster on the work pieces. These polishing pastes contain extremely fine abrasive particles. Unfortunately, on very hard surfaces their material removal rate is often insufficient. For instance, creating a surface reading of ra = 0.02 µm would take such a long time that it would be absolutely uneconomical.

Walther Trowal offers a range of polishing pastes or powders containing minerals with different hardness values and initial grain sizes allowing a wide spectrum of polishing applications on all kinds of materials.

The secret: Sharp edges are becoming rounded

A suitable paste product for the economical polishing of ceramic had yet to be developed. Since for several industrial sectors in recent years this challenge had become more urgent, in 2012, a cooperative of eight companies and research institutes, among them Walther Trowal, was organized with the goal to develop a process for high gloss polishing of ceramics. The project, named KeraOpt, was financially supported by the „NRW-EU-Ziel 2“ fund for industrial research.

Within the group Walther Trowal assumed the task of developing a mass finishing process that allows creating the desired high gloss polishes on ceramic work pieces in a cost effective manner.

Another project of KeraOpt was the development of ceramic inlays for injection molds that produce very fine geometrical structures combined with extremely smooth surfaces.

After comprehensive test trials Walther Trowal could identify a mineral that is suitable for these kinds of applications: Besides producing high gloss polishes on metallic components, it also produces the same type of finish on zirconium ceramics. With the new polishing paste trowapast PKC Walther Trowal has at last a product that can successfully be used for high gloss polishing of all kinds of ceramic components.

The new polishing paste contains a mineral with a relatively large grain size with an initially very high grinding effect. During the process the mineral grains wear down to smaller sizes transforming the process from intensive grinding to fine polishing.

Angelika Helten, managing the chemical lab at Walther Trowal, explains why the new paste is so effective for polishing ceramic components: „The secret is that the PKC paste is changing its technical characteristics during the course of the finishing process. While conventional mineral grains are breaking up into smaller grains with sharp edges, the new minerals are becoming rounded. Expressed simply, they do not create micro scratches on the surface but truly polish, thus producing very shiny surfaces. The result, with surface readings of ra = 0.002 to 0.005 µm, has even surprised us.“

For the ceramic mold inserts mentioned above the same approach was taken that had proven so successful for polishing metallic surfaces. Since the removal rate on ceramic is lower than that on metal, the process lasts longer and requires two different ingredients. With an initial surface roughness of ra = 0.3 µm the first stage with a grinding powder takes about 20 hours. This is followed by a second stage with trowapast PKC that lasts about 40 hours.

The result: A member company in the KeraOpt cooperative now produces the mold inlays for plastic injection molding no longer with tool steel but with ceramic. The surface readings could be reduced from ra = 0.011 to 0.002 µm.

A real success story

Another member of the cooperative is also utilizing the new polishing technology. This company produces decorative components used in the interior of vehicles, for example, gear shifters and control elements for car radios and air conditioners.

All these components, for which the final customer demanded high gloss polishes, consist of zirconium ceramics. To date these parts had to be manually polished. Now, with trowapast PKC they can be mechanically polished with a fully automatic process.

The ceramic components undergo a 72-hour grinding process followed by a 48 hour polishing step and 2 hours for the final brightening. This results in absolutely scratch-free work pieces, which after a subsequent cleaning process can be directly installed.

Christoph Cruse, the general sales manager at Walther Trowal, sees significant advantages for the customers: „The duration of the finishing process may appear very long. But it takes place without any supervision and requires a minimum of operator intervention. Since the new process allows the treatment of batches of 5,000 pieces, the costs per piece a re significantly lower than before.

New possibilities

First feedback from the customers indicates that the new polishing process represents a significant progress towards creating smooth, shiny surfaces on ceramic components. It opens a brand new field of new applications, for example for producing
-Thread guiding parts for textile machinery
-Ceramic coatings of metallic components
-Orthopedic implants
-Components for optical electronics
-Mirrors

Walther Trowal offers interested companies to test the new technology at the Trowal test lab in Haan. This ensures that the technical specifications of potential users are met, before they have to make a purchase decision.

Since 1931 Walther Trowal is developing and producing modular as well as custom engineered solutions for a wide range of surface finishing applications.

Initially only making vibratory finishing equipment, over the years Walther Trowal has continuously broadened its product range and today offers a wide portfolio of equipment and services for improving all kinds of surfaces, e.g. mass finishing, part cleaning, shot blasting and drying of a wide spectrum of work pieces, last but not least, the coating of mass produced small parts.

Walther Trowal offers not only various types of equipment but complete surface treatment systems: By linking the various equipment modules and automating the complete process, we are able to precisely adapt our process technologies to the technical requirements of our customers. This also includes various types of peripheral equipment and process water cleaning and recycling systems. Of course, we also offer comprehensive pre- and after-sale service like sample processing in one of our demonstration labs and global repair and maintenance service.

Walther Trowal supplies customers in various industries around the world. These include automotive and aerospace, medical engineering and wind power generation.

Firmenkontakt
Walther Trowal GmbH & Co.KG
Georg Harnau
Rheinische Str. 35-37
42781 Haan/Germany
+49 2129.571-209
+49 2129.571-225
g.harnau@walther-trowal.de
http://www.walther-trowal.de

Pressekontakt
VIP Kommunikation
Regina Reinhardt
Dennewartstraße 25-27
52068 Aachen/Germany
+49.241.89468-24
+49.241.89468-44
reinhardt@vip-kommunikation.de
http://www.vip-kommunikation.de

English Press Releases

Dengeling more productive than grinding, polishing and shot peening

Dengeling more productive than grinding, polishing and shot peening

High-speed hammering: The Starrag process peening produces a micron-precise final contour.

high-speed hammering of steel surfaces as turbine blades realizes roughness values of just 0,2 µm (Ra) reliable and accurately, dengeling with special machining center: higher productivity than frictional grinding, polishing, shot peening, no rework, upgrade possible.

High-speed hammering demonstration
Rorschacherberg – There was one demonstration at the „Airfoil Technology Days 2014“ in July that attracted a constant stream of visitors. On a machine tool , Starrag was demonstrating the dengeling process that renders any form of finishing of blades unnecessary. A ready to install component is produced in a single clamping.

CNC controlled dengeling achieves lowest roughness
Dengeling is generally a manual method that is particularly widespread in agriculture, where it is used to smooth and sharpen the blades of scythes or sickles by hammering. Instead of a hammer, the Starrag process uses a special electrically powered tool to give a component its final profile with micrometer accuracy in a machining centre. „The dengeling tool essentially behaves in the same way as a normal tool that is fitted and controlled by the CNC,“ explains Product Manager, Michael Koller. „At the Airfoil Technology Days 2014 I used an LX 051 to demonstrate how it can replace polishing.“ The key benefit of the alternative to grinding is that roughness values of just 0.2 micrometer (Ra) can be achieved reliably and repeated accurately.

More precise, more targeted, more controlled than shot peening
During machining, a pulsed impact ball hammers rapidly (up to 600 Hz) and with huge power. Dengeling changes the original structures of the boundary layers on the surface to a depth of 10 mm. Initial practical tests show that the process is more precise, more targeted and more controlled than the widely used shot peening method. „We are currently working flat out to upgrade all of our so-called blade machines – so all the machines in the LX series“, Koller says. This upgrade will enable all turbine blade manufacturers to replace polishing, frictional grinding and shot peening with the dengeling process, thus making massive reductions in their process chain and cycle times. It is incredible how Starrag has used the latest technology to breathe new life into the old-fashioned process of Dengeling.
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The Starrag Group is a world technological leader in the manufacture of precision machine tools for milling, turning, drilling and grinding small, mid-sized and large workpieces in metal and composite materials. Its customers include international corporations operating in the aerospace, transport, industrial and energy markets. Its portfolio of machine tools is supplemented by technical and customer services, which substantially add to customers“ productivity.
Its products are marketed under the following strategic brands: Berthiez, Bumotec, Dörries, Droop+Rein, Heckert, Scharmann, SIP, Starrag, TTL, WMW. The group of companies, with its headquarters in Rorschacherberg, Switzerland, operates production sites in Switzerland, Germany France, the United Kingdom and India, along with sales and servicing companies in many other countries.
The Starrag Group is quoted on the SWX – Swiss Exchange (STGN).

Starrag AG
Dipl.-Ing. Michael Schedler
Seebleichstraße 61
9404 Rorschacherberg
+41 (0) 71 858 8111
info@starrag.com
http://www.starrag.com

rgt redaktionsbüro gerd trommer
Gerd Trommer
Johannishofweg 7
D-64579 Gernsheim
06258 932010
presse@rgt-gg.de
http://www.rgt-gg.de

Science Research Technology

Walther Trowal significantly reduces non-productive times for deburring of internal part surface areas

Walther Trowal significantly reduces non-productive times for deburring of internal part surface areas

The VG 25 finishing system with peristaltic pump, abrasive media storage tank and vibratory work bowl

Closed loop media handling increases productivity

At METAV 2014 Walther Trowal presents the innovative VG 25 vibratory finishing system for deburring & grinding the complex and delicate internal surface areas of high value components. The proven MV surface finishing machines have contributed to drastically reduce processing times for fine grinding and polishing. Now, with the new VG equipment and its closed loop media transport system, Walther Trowal goes one step further by practically eliminating the non-productive times for media and part handling.

The VG 25 finishing system effectively removes burrs from complex parts with difficult to reach surface areas including internal passages. It ensures that delicate part contours are not compromised and fragile ribs or cross-sections are not damaged. Even the inside of bore holes with diameters of less than 3 mm can be completely deburred.

Brand new is the closed loop system for transporting the grinding media. With this innovative and unique concept Walther Trowal could significantly reduce the non-productive times for loading and unloading the work pieces: After completion of the deburring process a suction pump removes the whole media batch from the work bowl allowing easy removal of the finished work piece from the magnetic fixturing plate and placement of a new raw part in the work bowl.

The first VG systems have proven that the complex internal surface areas of aluminum or titanium components weighing 30 – 40 kg (66 – 88 lbs) can be automatically and efficiently deburred within 2 to 4 hours. In comparison, manual deburring of the same parts takes at least one week.

Lose burs in components used for the operation of complex systems, for example, hydraulic valve blocks for the aerospace industry, can cause system failures with catastrophic consequences. For this reason, such components require careful and complete deburring of all their internal passages.

The Walther Trowal MV finishing systems have demonstrated to be highly effective for such deburring tasks. And, compared to the Abrasive Flow Machining (AFM) with a grinding paste, or the ECM electrochemical deburring, the capital expenditure for the MV equipment with part fixtures and the operating costs (including consumables) are considerably lower.

In the MV machines the work piece handling had already been streamlined by simply placing the parts mounted to a special fixture on a magnetic plate in the work bowl where they are electro-magnetically clamped. With the VG systems Walther Trowal implemented further significant improvements.

However, the grinding medium, a mix of aluminum oxide and water, proved to be quite a challenge for the Trowal engineers. Because of its high abrasivity aluminum oxide is an excellent deburring medium but, at the same time, it can cause considerable wear on all machine components exposed to it during the finishing process, like for example, pumps piping and hose connections. To minimize the wear rate when pumping the corundum/water slurry Walther Trowal uses highly wear resistant materials and a special peristaltic pump.

After a raw work piece is placed onto the magnetic plate, the work bowl is flooded with water. Then the media/water slurry is pumped from a storage tank into the work bowl. Upon completion of the finishing process the slurry is pumped back into the storage tank. For removal of any residual abrasive particles from the work piece surface, the system is flooded with clean process water.

Technical highlights:

The work bowl of the multi vibrators, model range MV and VG, is equipped with an integrated magnetic plate. The work pieces, mounted onto a special fixture, are placed on this magnetic plate and held in a stationary position with an electromagnetic clamping device. This causes the clamped parts to vibrate at the same frequency as the work bowl generating a very fast relative movement between the work pieces and the grinding media and producing an intensive but, at the same time, gentle deburring/grinding effect. The result: Perfectly deburred and ground surface areas at significantly lower processing times.

At the center of these innovative finishing systems are three high speed vibratory motors which allow changing their rotational direction and RPM as well as their position. They are running at very high speeds but produce extremely low amplitudes. Since the directional effect of the induced vibrations is overlapping, the MV and VG vibratory systems produce excellent isotropic finishes on complex and/or delicate components, especially on surface areas which cannot be reached with conventional vibratory finishing methods.
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Facts about Walther Trowal

For more than 80 years Walther Trowal has been a pioneer and market leader in various surface treatment technologies. The company offers modular and custom engineered solutions for a wide range of surface treatment problems.

Initially only making vibratory finishing equipment, over the years Walther Trowal has continuously broadened its product range and today offers a wide portfolio of equipment and services for improving all kinds of surfaces, e.g. mass finishing, part cleaning, shot blasting and drying of a wide spectrum of work pieces, last but not least, the coating of mass produced small parts.

Walther Trowal offers not only various types of equipment but complete surface treatment systems: By linking the various equipment modules and automating the complete process we are able to precisely adapt our process technologies to the technical requirements of our customers. This also includes various types of peripheral equipment and process water cleaning and recycling systems. Of course, we also offer comprehensive pre- and after-sale service like sample processing in one of our demonstration labs and global repair and maintenance service.

Walther Trowal serves customers all over the world in many industries, for example, automotive, aerospace, medical implants and wind energy.

Walther Trowal GmbH & Co.KG
Christoph Cruse
Rheinische Str. 35-37
42781 Haan/Germany
+49 2129.571-231
c.cruse@walther-trowal.de
http://www.walther-trowal.de

VIP-Kommunikation
Regina Reinhardt
Süsterfeldstrasse 83
52072 Aachen/Germany
+49.241.89468-24
reinhardt@vip-kommunikation.de
http://www.vip-kommunikation.de