Abrasive belt production process

The production of abrasive belts generally includes four processes: raw cloth processing, large roll manufacturing, large roll post-processing and conversion. These four processes are described as follows:

1.Original fabric processing

The bases used for abrasive belts include cloth, paper and composite bases. Paper, except for waterproof samd paper, generally does not need to be treated. Composite bases are a combination of paper and cloth, which are sometimes purchased directly from suppliers or completed on the original cloth processing line or large roll manufacturing line of the abrasive belt production plant. Here we mainly explain the main processes of cloth base treatment such as scraping, singeing, dewaxing, dyeing, impregnation and scraping, stretching, calendering, etc. Different processes are selected according to different requirements.

(1) Shaving and singeing

Scraping and singeing are the processes of removing lint, keps, impurities and other defects on the surface of the original cloth. The surface of the grey cloth is scraped clean by a spiral scraper, and then the lint on the surface of the grey cloth is burned off by a high-temperature flame, making the surface of the grey cloth smooth and flat.

(2) Desizing and degreasing

Desizing and degreasing is to remove the size on the cotton yarn and the wax in the cotton fiber. It is removed by soaking in alkali solution. The cotton cloth after desizing and degreasing is easy to absorb and penetrate the size.

(3) Dyeing, impregnation and slurry scraping

Since the sanding belt has a relatively low requirement for the base color, dyeing, impregnation and slurrying are combined, that is, the dye for dyeing is directly impregnated and added to the slurry to achieve the purpose of dyeing. Water-resistant products must be impregnated with resin materials, while general non-water-resistant products are impregnated with animal glue.

(4) Stretching

Stretching includes longitudinal and transverse stretching. Longitudinal stretching removes part of the elongation and reduces the elongation of the finished product. Transverse stretching has shaping and stenting effects to ensure that the width of the processed cloth is controlled within a certain range.

(5) Calendering

Calendering is the final step in the processing of raw cloth, which aims to make the cloth flat and smooth, thus ensuring the uniformity of glue coating.

2.Jumbo roll manufacturing

Jumbo roll manufacturing includes major processes such as trademark printing, gluing, sand planting, gluing, and drying. These processes are all completed on one production line, which is a linked production line.

(1) Trademark printing: This process is to print the factory trademark, abrasive particle size, model and relevant factory regulations on the back of the cloth or paper base. The printing must be clear, legible, beautiful and easy for users to identify relevant data of the product, such as the direction of the abrasive belt when overlapping.

(2) Gluing: including primer and re-coating. For example, the amount of coating (primer and re-coating) and the amount of sanding are all automatically scanned on modern production lines and their information is fed back to the automatic adjustment control device. In the past, many large enterprises used β-ray penetration measurement, but its stability, safety and accuracy were poor. Recently, some well-known sandpaper, sand belt and sand cloth roll enterprises have made major technical changes and successfully adopted the γ-ray online measurement of the American NDK company. Its measurement accuracy is 0.25mm and the measurement error is ±0.25%. The measurement accuracy, stability and safety are superior to the previous measurement system. It is equipped with a touch-screen monitoring display and automatic feedback control, plus automatic temperature control on the drying line, forming a complete sandpaper, sand belt and sand cloth roll measurement quality control system, which can ensure the stable quality of each batch of products. The thickness of the primer and re-coating in production is implemented by controlling the gap between two pairs of rollers.

(3) Sand planting: There are two methods of sand planting, one is gravity sand planting and the other is electrostatic sand planting. Gravity sand planting relies on the abrasive's own gravity to plant sand on the rubber layer, so the arrangement of the abrasive on the rubber layer is relatively messy and has no definite directionality. Electrostatic sand planting is to use the electrostatic magnetic field to polarize the abrasive and attract it to the rubber layer, so the abrasive is arranged in an orderly manner, and the edges and tips of the abrasive face outward, which is very advantageous. Since the axis direction of the abrasive must form a certain angle with the substrate, the orientation of the abrasive on the substrate surface forms a sawtooth-like structure, so the abrasive can fully achieve the best effect on the surface of the sand belt, and the grinding ability will inevitably be enhanced. Since electrostatic sand planting is not suitable for coarse particles (coarser than 40#), this part of the abrasive must be completed by gravity sand planting.

(4) Drying: Large rolls must be dried before planting. Drying equipment has the characteristics of fully enclosed drying and enclosed drying with humidity control function. Fully enclosed drying should have high drying temperature and long drying time. In order to reduce the diffusion heat and fully utilize the heat cycle to improve the heat efficiency, the centralized treatment of harmful exhaust gas and reduce environmental pollution, the fully enclosed drying form is beneficial to the production of sanding belts, and generally has a capacity of more than one kilometer, which is conducive to the characteristics of resin glue drying temperature and long drying time. Drying equipment with humidity control function is to make the sanding belt lose physical moisture under high temperature and long-term baking, which causes the sandpaper to become brittle. A humidifying device is added in the lead-out area of ​​the sandpaper to keep the water content of the sandpaper balanced with the normal state. Therefore, the sandpaper should have this function in the drying process.

4.Post-processing of jumbo rolls

After the abrasive cloth is rolled out from the drying room, it must go through a series of treatments before entering the conversion process. The post-processing of the large roll includes post-curing, storage, humidification, and bending. After these treatments, the performance and quality of the abrasive cloth (paper) can reach the predetermined goals.

1) Post-curing. The large roll of sandpaper (paper) transferred from the drying room has only completed the pre-curing stage and the abrasive has been positioned due to the low temperature and short time in the drying room. However, from the perspective of the phenolic resin curing reaction, it has only reached the B stage. If it is truly cured, it will require a higher temperature and time to become an insoluble and infusible resin in the C stage, and its quality can achieve the desired effect.

(2) Storage. After the large rolls are cured at high temperature for several hours, the phenolic resin binder will produce an imbalance of internal stress due to the asymmetry of the cross-links formed on the polymer chain during the curing reaction, forming the so-called "internal reaction force" that causes the surface of the emery cloth to deform, become uneven or twisted. This defect will gradually disappear on its own after a certain period of storage, and the surface of the emery cloth will become smooth and straight. It is best to store large rolls in a warehouse with constant temperature and humidity, which will achieve better storage results.

(3) Humidification. Whether it is a roll of sandpaper or a roll of sandpaper, it must contain a certain amount of physical moisture under normal conditions. When this moisture is lost to a certain extent, the sandpaper or sandpaper will become brittle. When a large roll of sandpaper is baked at high temperature in a curing furnace, the loss of moisture is also relatively serious, resulting in a certain degree of brittleness. Therefore, humidification is used to restore the moisture contained in the sandpaper and improve its flexibility and toughness.

(4) Flexibility The abrasive belt is also called a flexible abrasive. To achieve flexibility, one is to select a base material and a binder that are both flexible materials. In this way, the product itself is very soft and does not need to be flexibly bent, which is a relatively difficult task. The second is to perform flexibility. In order to deal with difficult-to-grind materials, large grinding volume processing and heavy-load grinding must use a base with a thicker and heavier thickness, and a thermosetting resin with high bonding strength and high heat resistance. In this way, the flexibility of the belt itself will be improved, but the belt is generally soft but still hard at the microscopic level. This is the task to be accomplished by mechanical flexibility. Simply put, the role of mechanical flexibility is to produce tiny cracks on the surface of the abrasive belt, thereby making the entire abrasive belt soft.

4.Conversion

The so-called conversion refers to the process of converting abrasive cloth rolls into abrasive belts or discs, sheets and other shaped products.