After the initial cutting operation and the stone sheets production, longitudinal and transverse cuts are made and thus the plate dimensions will be determined. The length is responsible for cutting the stone lengthwise and takes the waste on both cut sides, and the produced stone width is determined in this section. The head performs the transverse stone cutting and the produced stone length is determined in this section. Usually, different milling machines are used to convert stone large sheets into different plaques. In large factories, it is more common to use gate mills, which usually have a disk with a diameter of 50 or 60 cm. Up to 10 sheets are stacked on the milling table. After setting the device to the desired dimensions, the cutting operation is performed. In longitudinal and transverse cuts, the plaques dimensions must be completely perpendicular to each other, and this depends on the ability and milling machine skill or the accuracy of automatic devices in the final cut. In this item absence, the stone slabs will have seams and cracks during work, which will cause the unsightliness of the worked stones.
The Fourth Stage: maintaining and Polishing Operations
After cutting the stone sheet in the form of plaque, the sanding and polishing stage begins. The sanding and polishing unit task is to wear and polish the production stone. Healthy stones are polished by automatic sub and small and unhealthy sheets are polished by hand tools. Maintain and polishing manual machines have a very small production capacity compared to automatic machines. In automatic devices, stone plates are placed on the conveyor belt. Stone plaques are collected at the end of the line after passing under the sub and polishing heads. Usually, the plaques width should not be more than 40 to 60 cm. Otherwise, the sheets are sanded and polished by the Maintain sheet machines that can sand up to 180 cm. To polish the stones, artificial compact materials made in special shapes are used, which are called morsels in the term. In order for these pieces to be installed on the device, a special adhesive is used on the disc. Different bits are used to polish the stone: • Bit number zero: to get the stone initial scratch • Bite number one: to catch a rock wave • Bites number two and three: to scratch again • Bits number four: to catch small scratches and rock waves • Acid bite: yellow color and for the stone shine • Wave catching bite: red color and for catching rock waves • Prepayment Bit: Black color and for stone initial payment • Bite: To soften the stone Maintain mortars are divided into two categories, magnesium mortar and resin mortar, according to the mortar used type. Magnesium mortar type is the most common adhesive agent in subsand pieces due to its ceramic properties and slow setting. Resin mortar is used in sub-resin, sub-acid and stone polishing final stages and the final product is of very good quality. According to the stone type to be polished, maintain pieces are divided into two categories: hard maintain and soft maintain. Due to their high hardness, hard stones (granites) should be sanded gradually and in several stages so that there is no excessive pressure on the stone surface and scratches are not created on it. Maintain hard pieces (granites) have a smaller cross-sectional area than maintain soft types, and during maintain, more water should be used on the contact surface between the stone and the piece so that the so-called stone does not burn; Therefore, the maintain hard pieces shape should be such that water flows easily in the contact place between the pieces and the stone, but less water is needed in maintain soft pieces than maintain hard pieces. Modern sanding and polishing machines work automatically and can have several heads. Two of these numbers are diamond plates that scrape or grind the first uneven stone plate surface part. Then the rest of the heads do the sanding and polishing in the same order. Some sub and polishing machines have a smaller number of sub heads. It depends on the type of work to be done. Sub and polishing system in hard and soft stones is not much different except for the difference in consumables. Due to the high hardness of igneous rocks, their grinding and polishing operations are difficult, which increases their cost. In some production lines, subbing and polishing steps and turning the sheet into a reverse plate are performed. That is, if a factory is equipped with a Maintain sheet machine, it will first be sanded and polished, and then it will be turned into a plate. In the last few years, due to the stones consumption with a thickness of one centimeter in foreign markets, the sanding and polishing machine has been made with great delicacy and precision for this purpose, which can easily sand and polish a thickness of one centimeter.
Sources: Atai, M., (1352), Construction stones, Technology Shahrood University, 1397
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