Analytical considerations of highly porous bond systems

Analytical considerations of highly porous bond systems for precision grinding


Productivity is the driving parameter for industrial grinding applications. The process is characterized by cycle time and surface quality (dimension, roughness, thermal interactions, …), and these factors are primarily influenced by the specification of the grinding tool. The right choice of the grit size, - quality and concentration, as well as the bond chemistry and the structure is carried out to optimize such a tool. Highly porous tools with a homogeneous and open porosity grain are becoming more and more important in the industry. In the following text the influence of the porosity on the grinding performance will be illustrated and explained. 

Porous structures without pore inducer

Porosity is definitely one of the most important properties of a grinding wheel in order to positively influence the performance. On the one hand the pores support the supply of coolants into the grinding zone, and on the other hand they facilitate the removal of chips and residues. Additionally, due to the thinner bond bridges in porous systems, the interaction between bond and workpiece is significantly reduced, resulting in a lower thermal degradation or damage (Fig. 1).

Fig. 1: Interaction between bond and workpiece. 
Compared to a standard bond (left) the thinner bond bridges of the Vitrium³-bond (right) leads to a significant reduction of thermal damages at the workpiece [SGA13].


Norton Vitrium3 logo

Saint-Gobain developed two special processes to create a highly porous structure without the addition of pore-inducers like naphthalene, or others, as it’s usually used in the industry. This technology has a positive impact on the properties of the tools and moreover it’s an important step towards the environmental protection. [Uppa13]

The two technologies are VORTEX and ALTOS X:

VORTEX 2: In order to achieve highly porous and homogeneous structure, Saint-Gobain developed special grits for these products. In Fig. 2 it is illustrated, that the very open structure 29 can be produced with the VORTEX 2 technology, whereas products with standard bonds won’t be robust at this level of porosity.

Fig. 2: Comparison between standard products and VORTEX 2. The Vortex-technology enables a much higher porosity than standard products, without any pore inducer [Hube12].

Another advantage is the very homogeneous, open and permeable structure of the grinding wheels, which is essential for an excellent supply of the coolant into the grinding zone. Fig. 3 shows that the addition of pore inducers in a competition product resulted in many defects and holes, while a VORTEX 2 wheel is totally homogeneous.

Fig. 3: Influence of the pore inducer on the homogeneity. With VORTEX-technology, the pores are open and equally distributed.

Norton Vortex2 logo

ALTOS X: Grinding wheels with the ALTOS X technology are produced with extruded ceramic grains. Saint-Gobain developed and manufactures these extruded ceramic grains (sintered alumina) with a different ratio of length to width;  TG = 4/1 and TGX = 8/1. The elongated shapes of the grains lead to a random orientation during the mixing process and therefore to an open porosity and a high permeability, without using any pore inducers. Calculation and models have shown that the elongated grains (rods) have the optimum shape to create highly porous structures, see Fig. 4 [Zhan06].

Fig. 4: Illustration of the highly porous structure of an ALTOS X-wheel with a random orientation of the cylindrical rods [Zhan06].
Impact of a porous structure on the grinding process

The power draw can be used for a proper analysis of the grinding process. It is influenced by micro- and macroscopic interactions between the grit, bond, and workpiece. The major components are the chip creation and grit wear, but also plowing, sliding and rubbing [Subr00].
The grinding power P’ can be described as a linear function of the specific material removal rate Q’w. As a good approximation the following linear regression can be used [Malk89]:

P‘ = Ec . Q‘w + P‘th
With P‘: specific power
Ec: specific grinding energy (= slope of the line)
Q’w: specific material removal rate
P’th: specific threshold power (= intersection with P’-axis)
 Fig. 5 shows the functional trends of the power draws for ALTOS X, VORTEX 2, and grinding wheels with white alumina (EKw). The following findings can be dawn:
Specific grinding energy Ec: The lower slope of ALTOS X and VORTEX 2 versus white alumina shows their lower specific grinding energy Ec.
That means:

  • Higher material removal rate at the same power (…“grinding faster“)
  • Lower power at the same material removal rate (…“grinding cooler“)

Especially ALTOS X shows a clear advantage at high Q’w, and also VORTEX 2 is superior to white alumina at any time. The threshold power Pth is similar for VORTEX 2 and white alumina, whereas it’s clearly higher for ALTOS X.  The threshold power Pth indicates, at which power an initial chipping process starts, that means finally at an infinitesimal small material removal rate. By looking to the region at low Q’w in Fig. 5 we see that VORTEX 2 and also white alumina require a lower power than ALTOS X and therefore this is not the region where ALTOS X should be used.

Altos X graph Fig. 5: Specific power P‘ versus specific material removal rate Q’w for white alumina (EKw), VORTEX 2 und ALTOS X with an outlook for new innovations.

What is the reason for these findings?

VORTEX 2: The highly porous structure of this grinding wheel with ist thinner bond bridges reduces the interaction and rubbing between bond and workpiece, leading to a smaller specific grinding energy Ec compared to white alumina. The threshold powers are similar, as the VORTEX 2 grit shows a similar grit fracture behaviour and sharpness like white alumina.

ALTOS X-grinding wheels are made of the extruded ceramic grain TGX. Due to its toughness and the microcrystalline structure the threshold power Pth to generate a first chip is quite high. Nevertheless, the benefits of ALTOS X are predominant at higher material removal rates Q’w: The high porosity (=low bond-workpiece interaction) and the self-sharpening effect of the ceramic grain (=efficient chip forming) allows extremely high material removal rates Q’w at low power P’, without thermal damages at the workpiece!

These properties have been proven in many tests.

Next development steps

A major target of Saint-Gobain’s development are grinding wheels for high material removal rates with low thermal damage; the blue zone in Fig. 5 shows the outlook. High porosity and strong & thin bond bridges is certainly the right concept, but additionally there are several directions taken to improve grain fracture behaviour.

Quantum Prime image

Fig. 6: SEM-images and diagram: Microcrystalline structures of previous generation ceramic grain and Norton Quantum Prime grain.

Quantum Prime logo

The Norton Quantum Prime technology represents grains with a lower toughness than the previous generation ceramic grains, which is caused by a 2nd phase in the microcrystalline structure. Therefore the fracture behaviour is significantly changed, which means that fractures and new sharp edges are formed already at a lower load. Consequently, it reduces the threshold power Pth, and the material removal rate can be 30% higher at the same power. This property guarantees the success of Norton Quantum Prime grinding wheels in many applications, for both low and high Q‘w. 

The next step is the combinations of these technologies:

VORTEX 2 + NORTON QUANTUM PRIME +VITRIUM³= NORTON QUANTUM-X … is a highly porous grinding wheel, which additionally features the improved grain fracture behaviour of the Norton Quantum Prime technology. Due to the low threshold power Pth Norton QUANTUM-X can be used at low material removal rates Q’w; but the open porosity reduces the thermal interaction, which enables the wheel to be used at higher material removal rates as well. This is a great start of versatile wheels suitable for many applications!

Norton Quantum X logo

Case studies

The following case studies show, that products to optimize the productivity are available: Higher material removal rates & lower cycle times, based on grinding wheels with a low specific grinding energy, low threshold power and high porosity:

Gear grinding with ALTOS X

-   Application: Profile grinding, Gleason-Pfauter
-   Workpiece: 18 CrNiMo, 58-60 HRC, module 10
-   Competition: Newest technology
-   Saint-Gobain: TGX 120 F13 VCF5
>   Result: Q’w + 200%, cycle time -40%, cost benefit -45%

Turbine blade grinding with NORTON QUANTUM-X

-   Application: Creep feed grinding
-   Workpiece: Turbine blades, Ni-alloy
-   Competition: Newest technology
-   Saint-Gobain: 5NQX 80 E28 VS3X
>   Result: Cycle time -50%, wheel life +40%, cost benefit -25%


An increasing productivity is generated by a higher material removal rates and the reduction of thermal damages. These components can easily be interpreted with the specific grinding energy Ec and the threshold power Pth. 
With the VORTEX 2- and ALTOS X technology, Saint-Gobain offers two product lines, which have a very high and open porosity and therefore reduced interactions between the bond and the workpiece. They enable a cool grinding process even at very high material removal rates. 
Moreover, the Norton Quantum Prime grit was developed to use these advantages at softer process conditions. Sharp edges are created at lower loads, and the lower threshold power Pth makes the products suitable for a wider range of applications.
The combination of these technologies finally leads to a new level of performance, Norton QUANTUM-X; a product which enables grinding at lower and higher material removal rates Q’w and guarantees efficient grinding without thermal damages.  


[Hube12]    Huber, C.: Innovative grinding wheels for a cooler grinding strategy, Seminar “Moderne Schleiftechnologie und Feinstbearbeitung”, 2012
[Malk89]    Malkin, S. and Guo, C.: Grinding technology: theory and applications of machining with abrasives, ISBN 978-0-8311-3247-7 1, 1989
[Sgab13]    Saint-Gobain Abrasives: Vitrium³ Reshaping the world of precision grinding, Brochure #2405, 2013
[Subr00]    Subramanian, K.: The System Approach (Modern Machine Shop Books), ISBN 978-1569902554, Hanser Gardner Publications; 2000
[Uppa13]    Uppal, S.: Grinding wheels that don’t cost the earth, Grinding & Surface Finishing, Special report 26/27, November 2013
[Zhan06]    Zhang, W. Experimental and computational analysis of random cylinder packings with applications, PhD Diss. Louisiana State University, 2006
[Sgab14]    Saint-Gobain Abrasives: Quantum Prime Performance Revolution, Brochure #4005, 2021