The demand for better part quality and lower cost per part has driven advances in grinding technology both in machine tool design and wheel performance. Grinding professionals are more aware than ever before of the critical role coolant plays in efficient grinding processes and the need for a well-designed coolant strategy.
To meet these demands machine manufacturers are increasing the pressure and flow rate of their pumps and adding high-pressure cleaning nozzles to their coolant systems. But all this increased flow and pressure along with higher wheel speeds and cleaning nozzles puts more coolant into the air in the form of a mist that must then be extracted.
As asupplier of grinding wheels, Norton | Saint-Gobain Abrasives engineers have seen this trend play out in the Higgins Grinding Technology Center (HGTC; Northborough, MA) when testing newly developed abrasive products. The HGTC is where Norton R&D engineers test newly-developed abrasive products to ensure superior performance before introduction into the market.
All types of grinding products from ultra-high precision products used in the electronics industry, to precision abrasives used in the aerospace and automotive industries, to coated abrasive and rough grinding product used in primary steel manufacturing are tested here. The HGTC was established in 1993 to advance the understanding of the science of grinding and how to best apply abrasives products in manufacturing processes. It currently employs close to 20 researchers and has 20 machines including two robots.
In 2014, to reduce the environmental impact of activities at this facility, a team was established to achieve ISO 14001 certification. During the site evaluation, the centralized mist collection system that services the grinding machines was identified as needing improvement.
In 2011, when Norton Abrasives moved the HGTC to Northborough from their Worcester facility the centralized mist collection system was moved and connected to the 12 machines used for wet grinding tests. Some of these machines were running water soluble oil while others used straight oil coolant. After the system extracted and filtered the air, it was returned into the room.
During their audit of the facility the ISO 14001 team identified a number of ways to improve the mist collection system. One big concern was worker safety, should one of the seals in the duct work fail and coolant accumulate on the floor creating a slipping hazard.
In addition, a system upgrade would provide an opportunity to include an absolute or HEPA filter to remove all of the very fine mist from the air, exceeding OSHA standards, before it was returned to the room. Operating costs of the old system were high and included proper disposal of used fluids and filters, coolant and filter replacement, collector maintenance, and electricity costs. Even when only one wet grinding test was running, the system was drawing air from all the machines, increasing electricity costs, as well as significantly adding to the noise level in the room.
The Northborough Research and Development Center’s operations team then evaluated several alternative solutions for improving mist collection. The first option was to replace the old central system filter with a new filter and make any necessary repairs to the duct work. The second was to install individual units at each machine. The advantages of small units at each machine included lower overall energy cost, since each system would only operate when a test was actually running on the machine. Also, the units would only be servicing one machine and any recovered coolant could be returned to the machine. To avoid any health risks, replacement units needed to meet stringent air quality standards.
After reviewing all the options, the team members determined that the best solution was to place small mist collectors at each machine. Their next step was to search for potential suppliers.
Norton discussed the situation with two companies that specialize in mist eliminators. The potential suppliers were given the opportunity to install one unit on a machine. Each unit was run for a period of one month and evaluated for removing mist from the machine enclosure, noise, discharge air quality, and potential maintenance issues.
After the month-long trail the decision was made to proceed with the supplier with a system featuring self-cleaning Disc Stack technology. The units remove 100% of the particulate from the air down to 1 μm before it enters a final-stage HEPA filter. The disk technology actually separates the fluid from the air versus collecting it. The HEPA filter performance is monitored by measuring the pressure drop across the filter and alerts the operator with LED lights when the filter needs to be changed. Therefore, filters are replaced only when necessary thereby ensuring consistently low operating costs and improved air quality.
Once the products were selected, engineers visited the HGTC and measured each machine to determine the correct size unit. A total of 12 units were purchased and installed in 2015. Since their initial installation over $6000 in energy savings, $7000 in coolant replacement cost, and $7500 savings in maintenance and hazardous waste disposal costs have been realized for a total savings of over $20,000 per year. The potential slipping hazard related to oil leaking onto the floor from the duct work was eliminated, and with the addition of the HEPA filters, air quality has improved and now exceeds OSHA standards. After approximately 18 months of single shift operation, none of the HEPA filters have needed replacement.
As an added benefit, at some machines the noise level dropped to 73dB from more than 90dB while on the old central system, making it much easier to carry on a conversation and promote hearing safety. Another unexpected benefit recently realized was that when a new grinding machine was installed, no modification to a central system was required, nor were any tests running on other machines disrupted.
Grinding processes are more productive than ever before thanks to developments in wheel and machine technology. With these improvements come challenges to protect the environment and the employees who run the machines. By being aware of new technologies we can meet those challenges and deliver value to our customers while protecting worker health and safety, and the environment.
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