Posted in | Materials Analysis

Improving The Sustainability Abrasives Manufacturering

In today’s competitive market place, improved productivity and maximised profits are often at the top of the list of priorities for any company. However, increasing concern about the environmental impact of manufacturing is now coming to the forefront, especially within businesses that are already making real efforts to improve their sustainability and responsibility for the world we live in.

Market leading abrasives manufacturer, Saint-Gobain Abrasives Ltd, is such a manufacturer and has long been aware of its responsibility to the environment, contributing with an on-going commitment to reduce the carbon footprint of its products and processes.

Elimination of pore inducers

The development process of every product considers the well-being of all those involved in its manufacture and use, taking into account the inclusion of the best raw materials. A good example of this occurred in the early 2000s, when creep-feed grinding became popular for machining exotic materials such as nickel alloys used in turbines for aircraft and power generation.

To achieve high stock removal rates, it required the use of grinding wheels with extra-porous vitreous bonds. The additional porosity was needed for efficient chip clearance and to ensure that coolant diffused more readily through the wheel structure to the interface with the workpiece, reducing burning and improving the surface finish. It is especially important in the aerospace industry and for other safety-critical applications, where only the highest quality is acceptable.

In standard vitrified bonded grinding wheels, porosity is controlled by the packing of the grains. In the case of high performance wheels for creep-feed grinding, however, the greater porosity could not be produced naturally by the abrasive particles alone. An artificial pore inducer was therefore introduced into the grinding wheel manufacturing process.

The most common pore inducer added to the mix was naphthalene, a polyaromatic hydrocarbon that happens to be ideal for the purpose. One reason is that, after it has done the job of controlling the inter-grain voids and keeping them artificially large, the naphthalene is easily removed as the wheel cures, due to its low evaporation temperature.

The use of artificial pore inducers like naphthalene requires substantial energy consumption as vapours must be treated and eliminated to prevent their release into the environment. Making a porous grinding wheel without the use of naphthalene would allow for significant energy savings, reducing both cost and carbon footprint. The Holy Grail at the time was therefore to develop a process for producing naphthalene-free, high porosity grinding wheels.

The research and development department at Saint-Gobain Abrasives consequently set about finding a solution. It utilised a uniquely-shaped, extruded ceramic grain in the wheel mix which, coupled with a new manufacturing process, avoided the use of naphthalene or any other artificial pore inducer.

ALTOS

The major breakthrough resulted in the group launching ALTOS under the Norton brand label, the first creep-feed grinding wheel not to require a pore inducer. The formulation is based on elongated ceramic grains, called TGX, which have the appearance of long cylinders with an aspect ratio (length to diameter) of 8 to 1, in contrast to conventional grains which have a ratio of between 1.2 and 1.5 to 1.

The unique shape of the grains allow for a low packing density during manufacture creating a naturally open structure for high porosity and superior permeability to coolant. The engineered, micron size structure of the grain allows it to microfracture in a controlled way, resulting in long wheel life and lower power consumption at high metal removal rates. This resulted in reduced cycle times and increased productivity for users whilst Saint-Gobain Abrasives were able to maintain their desire to become a greener manufacturer by eradicating the use of naphthalene within the ALTOS product.

Today, ALTOS is still the ‘Best in Class’ product for burn-free, creep feed grinding for high production rates. Compared with standard wheels, cycle times are reduced by up to 50 per cent and form holding is improved, which reduces the need for dressing and in turn leads to less wheel wear, by as much as three or four times.

VORTEX™

ALTOS was followed in 2004 by the VORTEX™ product line, which moved naphthalene-free pore inducement technology further forward. The innovative, patented grain technology creates interconnected voids to provide a structure that maximises coolant permeability and chip clearance. It was another big leap ahead in grinding wheel manufacture.

In 2012, VORTEX™2 raised the bar again. The grinding wheels, which use the same engineered 3D grain spacing as VORTEX™, benefit from a new bond that optimises the spacing of the fused alumina grain and allows for increased profile holding, leading to even higher metal removal rates, a further reduction in friction, longer dressing intervals and more parts per wheel.

VORTEX™2 grinding wheels show up to 40 per cent increase in longevity, cycle time reductions of up to 60 per cent due to increased depths of cut, and improved retention of the dressed form across the width of the wheels. This allows for higher metal removal than the previous generation of wheels.

VITRIUM3

A hallmark of the manufacturing processes for the open-matrix wheels described so far was that the bonds require a lower firing temperature than most conventional vitrified bonds containing artificial pore inducers, which significantly reduces energy consumption and the carbon footprint.

Earlier this year (2013), after years of research and development, Saint-Gobain Abrasives brought to market the NORTON VITRIUM3 bond with a cutting edge technology that allows it to be fired at lower temperatures. The bond improves the performance of precision grinding wheels, resulting in 20 per cent faster metal removal and a 30 per cent increase in wheel life, compared to standard wheels. VITRIUM3 bond can be used with various types of grain, from the proprietary NORTON QUANTUM ceramic to conventional aluminium oxide and does not require the use of pore inducers to create high level porosity.

VITRIUM3 is the company’s toughest bond to date, adhering strongly to the grains whilst allowing the extra porosity to do its job. VITRIUM3 bond provides grain adhesion and holding power that is far superior to those of any other bond. Specifically designed to be used safely at high speeds, despite there being less bond material retaining the abrasive, VITRIUM3 bond reduces friction and burning, as there is less bond-to-component contact during grinding. This new, versatile technology can be applied to all precision grinding practices, including creepfeed grinding.

Environmental regulations are constantly evolving and becoming stricter. With ALTOS, VORTEX™2, AND VITRIUM3, Saint-Gobain Abrasives is anticipating future regulations that could reduce the use of substances like naphthalene as pore inducers.

The welfare of people making and using abrasive cutting and grinding wheels is Saint-Gobain Abrasives' prime concern. All manufacturing sites are ISO 14000 approved and are required to show significant year-on-year improvements in waste reduction, energy management and scrap levels, but most importantly in safety.

Furthermore, as a founding member of the international Organization for the Safety of Abrasives (oSa), all products are developed, manufactured and tested in accordance with EN12413, the European safety standard for bonded abrasive products.

Optimisation of process, productivity and quality

Saint-Gobain Abrasives is not only committed to improving its own environmental impact but also that of customers using its products. The manufacturer works in partnership with customers to improve grinding efficiencies as well as reducing environmental impacts through the free service of the Process Solutions Program (PSP). Dedicated engineers visit to analyse the user's grinding operations with a view to increasing productivity, reducing manufacturing costs per part and improving quality.

The point Saint-Gobain Abrasives makes is that the machining consumable accounts for only three per cent of manufacturing costs, so the impact that its price has on the total is small. However, cutting 60 per cent off cycle times reduces cost per part by more than 45 per cent, while fewer wheel changes also significantly raises productivity and machine utilisation. It is on these areas that Saint-Gobain Abrasives focuses attention during its Process Solutions Program (PSP) analysis. Quality enhancement and scrap reduction also impact heavily on the bottom line and are similarly targeted.

One of the tools used by Saint-Gobain Abrasives' applications and diagnostics engineers in PSP audits is the Field Instrumentation System (FIS), a portable tool designed to monitor and measure the grinding process to provide accurate information to help maximise performance.

The system is particularly useful for monitoring and recording creep-feed grinding cycles and minimising thermal damage. Grinding power as well as normal and tangential grinding forces can be measured to optimise the process. FIS shows how the heat generated affects workpiece and process integrity and indicates ways to optimise coolant flow rate, pressure and nozzle design to produce top quality parts.

Conclusion

Saint-Gobain Abrasives takes seriously the need to reduce energy consumption and waste at customers' factories as well as its own and has been successful in achieving this goal. Apart from the environmental aspect, the manufacturer knows that the policy is good for business, in the light of frequent and substantial rises in the prices of energy and raw materials.

As customers move to the ALTOS, VORTEX™2 and VITRIUM3 products, they see large increases in productivity and reductions in power drawn from their grinding machines. It is because, compared with traditional creep feed grinding wheels, the amount of energy to remove the same amount of material decreases significantly, reducing power consumption and energy costs. It also allows older and less rigid grinding machines to be used more productively, without loss of component accuracy.

Saint-Gobain Abrasives’ grinding wheels have resulted in a significant reduction in wheel wear. Increases in product lifetime of between 50 and 100 per cent have been reported compared with standard wheels. It is due to greater edge profile holding, slower wheel wear rate and lower dressing frequency and duration, which in turn offer a reduction not only in downtime but also in energy consumption.

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