Due to the advantages of good thermal stability, brittleness, high rigidity and controllable porosity, the ceramic bond has the advantages of high strength, good self-sharpening, easy dressing, and strong chip capacity. Widely used in automobile, aerospace, aviation and precision cutting tool manufacturing industries. The strength of the ceramic bond sand and wheel mainly depends on the strength of the ceramic bond itself and the bond strength between the bond and the abrasive particles. The composition of the bonding agent is an important factor that affects the strength of the ceramic bonding agent and the bonding strength between the bonding agent and the abrasive grain interface.

Nano rare earth oxide reinforced and toughene

The ceramic bond CBN abrasive has high speed, high efficiency, high precision, low grinding cost, green environmental protection and other excellent properties. It is a research hotspot of scientific researchers in various countries in the world in recent years, and its development speed is very fast. The performance of CBN abrasive tools depends largely on the performance of ceramic binders, but the brittleness of ceramic binders will reduce the service life of CBN abrasive tools and increase processing costs. Therefore, it is necessary to strengthen and toughen the combination of ceramics, improve the microstructure of CBN grinding tools, and improve their comprehensive performance.

There are many toughening methods of ceramics combined with good agents, such as phase change toughening, metal toughening, fiber toughening, and second phase particle dispersion toughening. In addition to the above toughening mechanism, there are also methods for introducing rare earth oxides. There are a lot of research results in this area, such as:

The effects of Li2O3, CeO2, and Y2O3 on the refractoriness and flexural strength of ceramic binders were explored. It was found that La2O3 had a greater influence on the refractoriness of ceramic binders, and Y2O3 had a better effect on the strength of ceramic binders.

.Introducing a certain amount of Y2O3 into the calcium aluminum silicon glass-ceramic system can reduce the refractoriness of the ceramic binder and increase the flowability. At the same time, Y2O3 has the effect of inducing crystallization.

XIA et al. Introduced an appropriate amount of Y2O3 into the ceramic binder, which not only improved the fluidity of the binder during the bonding process, but also increased the content of β = quartz solid solution in the binder and improved its mechanical properties.

At present, there are few studies on the use of rare earth oxides to improve the fracture toughness of ceramic superabrasives. In the study, the Na2O-B2O3-Al2O3-SiO2 system was used as the basic ceramic binder, and different nano rare earth oxides (CeO, Sm2O3, Y2O3, La2O3, Er2O3) were added to strengthen and toughen the binder to explore different rare earths. The influence of oxides on the microstructure and fracture toughness of ceramic binders.

The following results are obtained through research and analysis:

(1) When the volume fraction is 2% Er2O3, the flexural strength of the bond sample is the highest, reaching 194MPa, which is 17.6% higher than that of the base bond.

(2) CeO, Sm2O3, Y2O3, La2O3, Er2O3 all have a toughening effect on the basic binder. When the volume fraction of 5% ER2O3 is added, the fracture toughness of the binder sample is up to 2,7MPam1 / 2, the ratio Base bond increased by 108, 2%

(3) The composite binder containing 2% volume fraction of ER2O3 wets the CBN abrasive particles well, and its flexural strength is 102 MPa.

(4) According to XRD analysis, the main phase of the basic binder is cristobalite, and its corresponding diffraction peak intensity is very high. The incorporation of nanometer rare earth oxide changed the main crystal phase of the sample, and transformed the cubic structure quartz phase with larger expansion number into the hexagonal structure quartz phase with smaller expansion coefficient. This may be one of the reasons that the fracture toughness of the sample is significantly improved after adding the nano rare earth oxide.

(5) Through SEM observation, further comparison found that the samples containing CeO2, Sm2O3, Y2O3 have more holes, and the Li2O3 and Er2O3 samples have fewer holes on the surface, which may be one of the reasons for the difference in fracture toughness of the samples .

(6) From the observation of the fracture morphology of CBN abrasive with Er2O3 added ceramic bond, it can be seen that the ceramic bond added with Er2O3 is ideal for the wetting and bonding of CBN abrasive particles. The bonding agent spreads evenly between the abrasive particles. There are evenly distributed stomata. These pores will play the role of chip holding, cooling liquid and lowering the surface temperature of the workpiece when the CBN grinding tool grinds the workpiece, preventing the workpiece from being burned.

The influence of different wetting agents on the molding performance:

The binders, abrasives, and fillers in ceramic mixture abrasives are mostly particles or powders, all of which are barren materials. When mixing, in order to make the molding material have a certain formability, wetting agent that acts as a temporary wetting and bonding function needs to be added. There are many types of wetting agents for CBN abrasives, such as dextrin solution, polyvinyl alcohol solution, sodium carboxymethylcellulose solution, etc., all of which belong to the type of organic matter, with good wetting properties. It can be burned out in the middle, but the adhesion is poor, the strength of the wet blank of the abrasive is low, and there are inorganic types such as water glass. This type of wetting agent has good adhesion performance and high strength of the wet blank of the shaped abrasive. Causes pollution and is not easy to control.

In recent years, we have conducted many researches on the wetting agent for ceramic bond abrasives and the molding performance of the mixture. Zhuo Jianming et al. Studied a new type of modified oil emulsion wetting agent, and obtained loose, well-preserved molding materials. The molded products are self-hardening, and the wet blank has a fast drying and high dry strength.

We selected glycerin as the regulator of the looseness of the molding compound, and studied the looseness and fluidity of the molding compound after adding glycerin and the strength of the wet and dry blanks pressed by the molding compound. The results show that after adding glycerin, the molding compound The liquidity has been greatly improved, and the annual organization's uneven scrap rate has been reduced from 5,40% to 2,00%.

We made a comparative analysis of the factors that affect the wet-dry strength of the ceramic abrasive body. The results show that the wetting agent has the greatest influence on the wet-dry strength of the green body.

Using dextrin liquid as a comparison, we discuss the mixing uniformity, loose density, looseness of four new wetting agents, such as polyvinyl alcohol solution, polyethylene glycol aqueous solution, and isobutylene maleic anhydride copolymer aqueous solution, to the ceramic bond CBN abrasive molding material. The effect of wet billet strength and tissue uniformity. the result is:

(1) Comparison of loose density of molding materials

The loose density of the molding material has a significant impact on the moldability of the abrasive. The better the looseness, the better the fluidity, and the easier the feeding of the abrasive during the molding process. The loose density test results of the five kinds of wetting agents are shown in Figure 3.

Comparison of loose density of different types of wetting agent molding materials

It can be seen that the bulk density of the molding materials mixed with PAM is the largest, which is 51,14% higher than that of the molding materials mixed with dextrin; the use of ISOBAM-110 mixture is followed by an increase of 16,59% compared with dextrin; PEG-6000 has the lowest compounding compound. This is because when PAM and ISOBAM-110 are used as wetting agents, the bonding agent forms a uniform coating layer on the abrasive surface, and there is no agglomeration formed by the bonding agent or the bonding agent and the abrasive. The particle size of the mixture is uniform and consistent. In the process of natural accumulation, it has good fluidity and can evenly fill the voids; however, the molding compound mixed with PEG-6000 has a binder agglomeration phenomenon, and the adhesion between the abrasive particles is serious, resulting in different particle sizes inside the molding compound and poor fluidity. Therefore, the bulk density is also smaller.

(2) Comparison of the strength of wet blanks of CBN test strips

Another important indicator to measure the performance of the wetting agent is the wet green strength of the abrasive. If the wet blank is not strong enough during the manufacturing and handling of the abrasive tool, it will cause direct damage or invisible damage to the abrasive tool. The picture shows the test results of the wet blank strength of CBN test strips with different types of wetting agents.

Wet strength of CBN test strips with different types of wetting agents

It can be seen from the figure that the CBN test strip wet blank with dextrin as a wetting agent can withstand a fracture length of 18,13 mm; PAM has a fracture length of 24,49 mm, an increase of 35,08% compared with dextrin. The breaking length of ISOBAM-110 is next, which is 17.71% higher than dextrin, and the breaking length of PVB is the smallest. This shows that the use of PAM and ISOBAM-110 as a wetting agent can effectively improve the strength of the wet billet and greatly improve the yield of the abrasive, while PVB as a wetting agent has a tendency to reduce the strength of the wet billet.

Effects of adding Li2O

In the preparation of ceramic bond grinding wheels, alkali metal oxides are often introduced into the bond as a flux, thereby effectively reducing the refractoriness of the bond and increasing the high-temperature fluidity of the bond. The excessive addition of alkali metal oxide increases the thermal expansion coefficient of the bonding agent and reduces the bonding strength of the abrasive. Therefore, the amount of alkali metal oxide added should be controlled within a relatively low range.

The Na2O = B2O3-Al2O3-SiO2 series ceramic bond was selected as the basic bond, and the fire resistance, fluidity, flexural strength of the abrasive and the interface between the bonding agent and the abrasive particles were studied by the addition of La2O to the basic bonding agent. Impact. The following quotes the effect of adding Li2O on the refractoriness and fluidity of the binder and the strength of the binder.

(1) With the increase of Li2O content, the refractoriness of the binder is significantly lower than when it is not added; the refractoriness of the binder in the range of 0-6wt% when Li2O is added changes drastically, and then the change in refractoriness tends to be flat. This is mainly because Li2O acts as a network changer, which breaks the Si-O bond in the glass network and reduces the structural tightness of the glass network, so the softening temperature of the glass and the refractoriness of the bonding agent decrease accordingly.

(2) The fluidity of the binder increases with increasing Li2O content, and the fluidity of the same component increases with increasing temperature. The addition of Li2O reduces the refractoriness of the binder, causes the binder to melt, and the viscosity decreases, thereby increasing the fluidity of the binder. As the temperature of the binder of the same component increases, its high-temperature viscosity decreases, so Its liquidity is further increased.

(3) The analysis found that the strength of the test strip increased first and then decreased, and the maximum value appeared when the Li2O content was 5wt%. This may be because with the increase of Li2O content, the refractoriness of the bonding agent is significantly reduced, and the fluidity of the bonding agent at the firing temperature is gradually improved, thereby facilitating the uniform distribution of the bonding agent around the abrasive and improving the bonding between the bonding agent and the abrasive To improve the strength of the abrasive strip.

However, when the content of Li2O exceeds a certain value, Li2O, which is a modified body of the network, has an enhanced destructive effect on the network and reduces the strength of the bonding agent. On the other hand, a large amount of Li2O makes the bonding agent's refractoriness too low, and its fluidity too large, which may easily lead to excessive burning of the abrasive tool and loose structure, thereby reducing the strength of the abrasive tool test strip.