Grinding and polishing of stone

The grinding process is generally divided into five processes: rough grinding, semi-fine grinding, fine grinding, fine grinding, and polishing.

Polishing is the last process of stone grinding and processing. As a result of this process, the surface of the decorative stone will have greater ability to reflect light and good smoothness, and the inherent pattern and color of the stone will be displayed to a greater extent.

1. Stone grinding and polishing methods and tools

Stone polishing method:

One method is to mix loose abrasives with liquid or ointment to form a polishing suspension or polishing paste as a polishing agent, and use a suitable device to add to the abrasive or workpiece for polishing. The abrasives used include diamond powder, silicon carbide powder and white corundum powder. Different abrasives should be matched with abrasive tools of different materials. When using silicon carbide abrasives, gray cast iron abrasives should be used, and when diamond abrasives are used, tin-plated abrasives are better. Another method is to use bonded abrasives, that is, use diamond, silicon carbide or white corundum powder as abrasives and bonding agents to make abrasive blocks by sintering, electroplating or bonding. Fixed to the grinding disc to make a polishing grinding head. Small grinding blocks are generally bonded with materials such as asphalt or sulfur, while large grinding blocks are connected to the grinding disc with dovetail grooves.

The disadvantage of using loose abrasives for polishing is that the abrasives must be added to the workpiece manually or with a metering device, so the abrasives are not uniformly distributed, and they need to be operated by skilled technicians to achieve high quality standards. The use of polishing heads has many advantages: uniform abrasive distribution, good polishing quality and stable quality, easy to achieve continuous operation, high polishing efficiency, and generally the polishing time is 30% less than using loose diamond abrasives.

The essence of stone grinding is that under the action of human or mechanical force, the rotating grinding disc continuously feeds the stone material vertically, and the two friction and wear in the contact area gradually smooth the uneven surface of the plate surface layer. Since granite rocks are generally harder, the hardness of abrasive tools must exceed the hardness of stone. Generally speaking, six sets of abrasive tools are used to complete the grinding, grinding and polishing process. The first two abrasive tools need to perform forced positioning grinding to level and control the thickness of the plate; the latter abrasive tools are respectively subjected to processes such as rough grinding, fine grinding, grinding and polishing.

According to the diameter, the shape, number and arrangement of the grinding blocks, the binder used in the abrasive and the particle size of the abrasive, the grinding head has different structures. There are many kinds of grinding head diameters ranging from 4 to 12 inches, and the most commonly used is 10 inches. The shape of the grinding block is straight, oblong, umbrella, ring, etc., and straight and oblong are the most common. The number of grinding blocks depends on the diameter of the grinding head and the size of the grinding blocks, ranging from a few blocks to ten blocks. The most common arrangement of grinding blocks is radial, but there are also spiral arrangements. Binders used in abrasives include metal binders, resin binders, magnesia and polymers. The range of abrasive particle size used by various manufacturers is different. For diamond abrasives, there are 30 meshes for rough grinding heads to several μm for polishing heads.

Mamoru Nakayarna and others from the Department of Mechanical Engineering, Osaka University, Japan, used a 6-inch grinding and polishing head when studying granite stone polishing technology. ) Is the grinding head structure of the diamond grinding block using powder metallurgy binder (metal bond), and the grinding block is straight. This kind of grinding head is used for rough grinding, and the diamond grain size is 40 mesh, 60 mesh and 100 mesh respectively. ) Is a grinding head structure suitable for the use of thermosetting resin bond diamond grinding blocks, the grinding blocks are oblong. This kind of grinding head is used for fine grinding and polishing. Diamonds of 200 mesh and 500 mesh (equivalent to 74μm and 30μm) are used for fine grinding, and diamonds of 1000 mesh and 2000 mesh (equivalent to 15-25μm and 6-10μm) are used for polishing.

In the early 1990s, the British company HASELTINE LAKE improved the structure of the grinding head and improved its working performance, reducing the original five processes to two. The grinding head used in the procedure is made of a 120/140 mesh diamond, brazed, electroplated or sintered on a metal disc. The grinding head used in the second process is made of 200/300 mesh diamond with resin binder to make umbrella-shaped grinding block, and then this umbrella-shaped grinding block is made by molding or bonding it to the support plate. . The total area of the umbrella block generally accounts for 2% to 5% of the area of the grinding head. Using the above-mentioned improved grinding head saves processing time and reduces costs.

2. Influencing factors of stone grinding and polishing quality

There are many varieties of stone, and the difference in physical properties, chemical composition, grain size and mineral crystal composition have an impact on the polishing quality. Due to the different crystal quality of stone, uneven surface will be formed during polishing. Stones with larger grains have more uneven polishing than those with smaller grains, so small grains are easier to polish than large grains.

The feed rate of the polishing head has a great influence on the polishing quality. Studies have shown that with the increase of the feed rate of the polishing head, the surface gloss of the stone will decrease, but if the feed rate is too low, it will accelerate the wear of the head and reduce the production efficiency. .

The operation mode of the polishing head should be coordinated with the operation mode of the rough grinding and fine grinding head. The operation mode of the grinding head is divided into vertical and horizontal and the degree of density. Generally speaking, the operation mode A is used for rough grinding; A+B operation mode is used for fine grinding, and A+B+C+D operation mode is used for polishing. According to the specific conditions, the grinding can be repeated once to obtain a higher surface gloss.