Figure 1. The correct abrasive will complete jobs faster. Source: Norton/Saint-Gobain Abrasives

When an operator enters the doors of a roll grinding shop, it is typically with the intention of shaping rolls that will work for a wide range of purposes. The operator, of course, has to follow specified safety procedures, and ensure proper machine setup. Checks are then performed throughout the process to ensure the total indicated runout (TIR) is correct, that the roll is being shaped correctly and that countless other aspects are maintained, all of which an experienced operator knows, and those who are newer to the job will soon learn.

But is that grinding operation really set up correctly? While a competent operator can produce acceptable results — which is the ultimate goal — it is also quite possible that a machine is not running at the utmost efficiency. With the right setup, it may be possible to use grinding wheels for longer intervals before changing them out, producing better surface finishes and completing jobs with high quality at faster completion rates.

Quality vs material removal rate

To function, a grinding operation must be set up correctly. The wheel speed, infeed, traverse and roll speeds are set within a certain range to avoid damaging the roll, wheel or other equipment. Different types of grinding wheel/coolant/speed combinations can nominally perform this task, but finishing a job and working at peak performance are two different things. There are several aspects to examine when optimizing a process.

First, one must consider the inherent tradeoff between speed of operation and surface finish. Infeed rate, which is the speed at which a wheel moves into the roll — with specifications in either µm or µm/minute — dictates, in part, the material removal rate (MRR) for the roll. The higher the infeed, the higher the MRR, and thus productivity. Conversely, slower infeed rates mean better surface finishes and lower wheel wear. Here, low values are generally considered to be less than 25 µm, while high values are greater than 50 µm.

Cut width (in mm/rev) dictates how much wheel overlap — roll surface area that is ground more than once as the wheel travels across a roll — takes place during a grinding operation. Like infeed, the greater the cut width (up to the point where there is no overlap and the wheel actually misses some roll surface each pass), the greater the MRR, but the lower the surface finish quality. The overlap, specified as a percentage, is dictated by the roll speed in RPM as well as the traverse/cross-feed speed in mm/min.

One might assume that both infeed and cut width should be kept very low in order to produce the best results. However, since lower speeds mean more grinding time, the price for such operations would need to be increased proportionally. Because of this, it is important to adhere to customer specs in order to keep an operation profitable, while providing a quality product at a fair price.

Machine setup

Once finish and MRRs are decided upon to align with the customer’s needs, it is time to consider what tools and settings can be used to optimize the process.

Coolant

It is important to ensure that the correct grinding fluid is applied to the operation, and to the correct area. Nozzle dimensions should cover the complete face of the wheel, without leaving out any particular area as it performs the operation. Coolant speed should match up with the wheel surface speed, which is directly related to the flow rate. Ensure that uncontaminated water is used here, and that the pH is less than 10 — above which point organic bonds can be degraded.

Wheels

A wide variety of options exist for wheel selection. Conventional abrasive wheels come in several variations of aluminum oxide, or silicon carbide. Norton also offers a variety of engineered grain materials to meet different needs. NQ engineered microstructure ceramic grain, for example, offers excellent MRR and wheel life, along with good surface finish. The Vortex/38AA grain structure, conversely, offers “only” good MRR and wheel life, but excellent surface finish.

According to a report, when choosing grinding equipment: “Abrasive consumables only account for about 3 percent of a total manufacturing budget, while machinery, labor, and overhead translate into 80 percent of that budget.” It stands to reason that if more capital is dedicated to wheel selection and proper coolant application, the cost savings from other aspects of the operation could more than justify the expense.

Storage

name="_Hlk49326087">Norton/Saint-Gobain Abrasive wheels come with an identification label marked on the side that contains a material index, batch number and expiration date. This last number is important as resin bond wheels do attract moisture and should be speed tested after expiring to ensure the wheel still works properly.

Maintenance

Even with proper wheel, coolant and speed setup, if the machine itself is not running well, the results will be poor. While operator setup and process checks will help with some of these issues, it is important to have a machine on a preventive maintenance schedule to replace wear parts, perform cleaning and address other issues that require significant machine down time. Beyond scheduled maintenance, a predictive maintenance program can take this to the next level, allowing staff to schedule when the machine is showing signs of wear before it actually affects the process.

Figure 2. Norton abrasive wheels provide optimal service life and performance for any grinding application. Source: Norton/Saint-Gobain Abrasives

Norton: Here to help

While it is evident that roll grinding operations need to be expanded with an eye toward improvement, all too often, the overwhelming goal is to get that next job out. As such, the safer bet is to do things “the way they have always been done,” rather than explore a technology that is only vaguely familiar.

Yet, the benefits of perfecting a process can be massive. Norton, founded in Worcester, Massachusetts, in 1885, and now supported by parent company Saint-Gobain, employs a team of applications engineers who can help with these improvements. Whether to introduce customers to innovative grinding products, or to offer a second look at a process, Norton experts strive to form long-term relationships that can help with customer challenges. Contact them today.