We continue our series called: The Basics, with an in-depth review of the different diamond bond types. In our first article on industrial and synthetic diamonds, we highlighted the importance of selecting the proper grade diamond for the task, but the bond that holds the diamond is equally as important.
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There are four common diamond bonds: resin bond, sintered bond, electroplating and vacuum brazing, shown in the image below. In this article we will first cover resin bonded tools commonly known as resin polishing pads. But before we delve into some specifics, it's important to understand some basic mechanics.
Resin bond, sintered bond, electroplating, vacuum brazing.
The bond serves two important functions. First, is that it holds or contains the diamond grit in place for the crystal to be able to cut, grind, shape or polish. Second, the bond needs to progressively wear in order to expose new, unused crystals to the surface. Working materials can range greatly in hardness and abrasiveness. The rate of diamond exposure is dependent on the density, type of bond and the working material. Paring the correct bond with the working material is critical for performance and tool life.
Resin bonded diamond tools or resin polishing pads are made by mixing diamond grit with various formulations of resin powders to produce a solid homogenous, multi-layered bond commonly used for very light grinding and polishing.
Visible diamond grit suspended in a resin bond
There are three major resin bond types: marble, granite and concrete resin bond. Each resin bond is specifically formulated to enhance the performance of the tool on the material. Each of the materials vary widely in their density, hardness and abrasiveness, so selecting the correct resin formulation is critical.
Marble, granite and concrete.
Marble and other natural stones in the marble category such as limestone and travertine are all soft and delicate stones that require a specifically formulated matrix. Marble scores between 4 and 5 on the Mohs hardness scale and is comprised of metamorphosed limestone. Typically marble resin bonded tools are run wet to diminish the heat build-up and subsequent resin transfer onto the surface. The resin wears at a slower rate as to not prematurely exposed new diamond crystals that can heavily scratch the delicate surface.
Granite on the other hand can be up to twice as hard as marble scoring between a 6 and 7 on the mohs hardness scale. Granite is an igneous rock that contains quartz crystals. A resin bond designed for granite will wear efficiently to expose new diamond crystals to effectively grind and polish the surface. These pads typically have a higher tolerance for heat and are proportionately denser to tackle a harder surface. The quartz and density of the granite requires a more robust matrix and a higher-grade diamond.
It might be important here to slide in a quick note on engineered stone. Engineered stone is a composition of quartz crystals and resin binder that make it very difficult to polish. In addition to the tough quartz crystal, the resin binder has a tendency to burn polishing pads not specifically designed for engineered stone. Special high-heat tolerant resins need to be used to avoid marking the surface.
Concrete is characterized as a very abrasive material that can vary widely in hardness depending on the local aggregate used. Typically resin bond tools designed for concrete are run dry and require a high-heat resistance. In addition, they need to be of a higher density to withstand the weight of a concrete machine that can weigh up to 10 times more than a marble machine. Concrete pads also run on planetary machine heads, which means that they rotate many times more than a stone resin pad.
Diamond resin bonded pads have greatly evolved over the years as new applications, new materials and new machines come on to the market. While it may appear on the surface that all resin polishing pads are created equal, it is certainly not the case. Understanding how these products are made and what constitutes a high-performance product can mean all the difference.
In the next installment of The Basics, we will discuss the sintered bond.
The invention relates to the technical field of precision grinding and polishing consumables, in particular to a formula and a manufacturing method of a diamond grinding pad.
Background
The grinding scheme of a diamond (diamond) grinding pad and water instead of a grinding disc and grinding fluid is a trend of the development of the grinding industry, and has the advantages of reducing waste liquid discharge, being more convenient to use, good in stability and the like; however, the existing diamond polishing pad generally has the defects of poor self-sharpening property, poor uniformity and serious scratch.
CN.9 belongs to a superhard resin grinding wheel, which is prepared from the following raw materials in parts by weight: 15-25 parts of epoxy resin liquid, 15-20 parts of diluent, 0.5-1 part of coupling agent, 0.5-1 part of hollow sphere, 40-60 parts of diamond and 10-15 parts of curing agent. According to the invention, through carrying out oven foaming and sieving on the hollow balls, the porosity and the aperture of the grinding wheel can be well controlled, the porosity of the prepared grinding wheel can reach 50-60%, and the aperture is 100 plus one 200 mu m, the prepared grinding wheel has high structure uniformity, can be continuously self-sharpened without trimming, has high porosity and good chip capacity, has a low substrate surface damage layer, has good grinding performance on substrate materials, improves the processing efficiency and reduces the processing cost. But is only suitable for high-speed and rapid cutting and is not suitable for low-speed grinding and polishing.
CN.6 discloses a method for preparing a superhard resin grinding wheel, which comprises the following steps: firstly, drying the hollow spheres in an oven at the temperature of 80-100 ' for 0.5-4h, uniformly mixing the hollow spheres with diamond, and then sieving the mixture through a 100-mesh and 120-mesh sieve; secondly, stirring and heating the epoxy resin liquid for 2-5 minutes in a water bath at the temperature of 70-80 ', adding a diluent and a coupling agent, continuously stirring and heating for 5-10 minutes, adding the mixture of the hollow spheres and the diamonds obtained in the step I, and continuously stirring and heating for 5-10 minutes; thirdly, reducing the temperature of the water bath in the second step to 55-60 ', uniformly mixing the diluent and the curing agent, adding the mixture into the slurry obtained in the second step, uniformly stirring, pouring the mixture into a mold, hardening the mixture for 3-8 hours at 80-90 ', and then curing the mixture; cooling the material solidified in the step III to room temperature, demoulding to obtain a grinding wheel ring, and processing to obtain the superhard resin grinding wheel. But is only suitable for high-speed and rapid cutting and is not suitable for low-speed grinding and polishing.
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Disclosure of Invention
The invention aims to solve the technical problems of high mixing difficulty, poor uniformity, poor cutting performance, serious grinding scratch and the like of the conventional nano injection molding material, and provides a formula and a manufacturing method of a diamond grinding pad.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the formula of the diamond grinding pad comprises the following raw materials in percentage by weight:
10 to 30 percent of diamond powder
20 to 60 percent of adhesive
10 to 30 percent of hollow glass beads
0 to 20 percent of other fillers
0.5 to 3 percent of auxiliary agent.
In the invention, the hollow glass beads have the function of reducing the resin strength of the adhesive, and the manufactured resin grinding pad can increase self-sharpening property. The hollow cavity of the hollow glass bead can store part of water after being opened in the grinding process, and the part of water plays a role in cooling and lubricating in the grinding process, so that deep scratches caused in the grinding process are reduced. In addition, as the surface energy of the smooth sphere of the hollow glass bead is smaller, the hollow glass bead is not easy to agglomerate when being added into resin, and the viscosity of the resin is hardly increased, so that the mixing and the use are convenient; after the mixed material is vacuumized, the porosity of the material is generated by the hollow glass beads, and the porosity of the grinding pad is stable and uniform.
In the technical scheme, the diamond powder is one of single crystal, polycrystal and polycrystal-like, and the particle size of the diamond powder is 1-50 microns. The particle size of the diamond dust determines the efficiency and roughness of the grinding.
In the technical scheme, the adhesive is one or more of thermosetting phenolic resin, epoxy resin, urea resin, acrylate and polyurethane. In the invention, the adhesive is used for bonding all the components, so that the grinding pad is convenient to form.
In the technical scheme, the other fillers are one or more of calcium carbonate powder, talcum powder, wollastonite powder, aluminum hydroxide and kaolin. In the present invention, the other fillers function to improve the compounding viscosity and the strength of the polishing pad.
In the technical scheme, the auxiliary agent is one or more of a coupling agent, a cross-linking agent, a flatting agent, a thickening agent, a wetting agent and a defoaming agent. In the invention, the wetting agent is used for improving the surface wettability of the powder and the mixing uniformity. The coupling agent has the functions of reducing the viscosity of the synthetic resin melt, improving the dispersion degree of the filler to improve the processing performance, and further ensuring that the product obtains good surface quality and mechanical, thermal and electrical properties. The cross-linking agent is used for generating chemical bonds among linear molecules, so that the linear molecules are mutually connected to form a net structure, and the strength and the elasticity of the product are improved. The leveling agent can effectively reduce the surface tension of the resin product and improve the leveling property and uniformity of the resin product. The thickener functions as a dispersion medium instead of an organic solvent.
In order to further solve the defects of the prior art, the invention also provides a method for manufacturing the diamond polishing pad, which comprises the following steps according to the formula:
step one, premixing: adding the adhesive, the diamond powder, the hollow glass beads and other fillers into a mixing tank in proportion, stirring and heating to 50 ';
step two, main mixing: opening a low-shear mixer, controlling the shear force to be less than 20Mpa, preventing the hollow glass beads from being broken, adding the auxiliary agent, dispersing the mixed material for 30min, and improving the viscosity and the uniformity of the mixed material;
step three, bubble removal: after the material mixing is finished, opening a vacuum device to remove bubbles mixed in the material;
step four, forming: adding the materials into a grinding pad die, and curing and molding.
In the above technical scheme, in the first step, the stirring speed is 60-100rpm, and the stirring time is 15-30 min.
In the above technical scheme, in the second step, the stirring speed during mixing is 300-600 rpm.
The invention has the beneficial effects that: the precision grinding machine can meet the precision grinding of workpieces made of glass, ceramics, sapphire and the like, only uses water as a lubricating coolant during production, and has good grinding force and stability, low grinding surface roughness and less deep scratches.
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