The general fuel filter adopts a star filter paper folding structure. Inside this type of fuel filter, the folded filter paper is connected to both ends of the plastic or metal filter. After the dirty oil enters, it passes through the layers of the filter outer wall After filtering, the filter paper reaches the center, and clean fuel flows out. This filter paper generally uses corrugated fuel filter paper. Higher-end engines use high-precision filter paper and spiral fuel filters. Unlike star-shaped fuel filters, the filter paper is wrapped around the center tube. The space utilization rate is high. Within the same space size, it can accommodate a larger The filtering area is generally 3 times that of a star filter. After the dirty oil enters, it is directly filtered through the filter paper and flows out, and the foreign particles are retained in the filter paper groove. The performance of this fuel filter is more superior, which can make the filtration accuracy of fuel higher. The main research contents of high-precision filter paper: ①selection of pulp raw materials; ② determination of process parameters; ③ selection of creping scraper; ④ selection of wet strength agent; ⑤ application of water-resistant glue. The technical indicators of high-precision fuel filter paper are shown in Table 1: The production process flow is shown in Figure 1: 1. Process ratio: (1) 50% of rainbow fish coniferous wood pulp; (2) 50% of Bowater coniferous wood; (3) Dosage of wet strength agent: 5% (for absolute dry pulp); (4) Dosage of surface water repellent (6% concentration): 20% 2. Determination of process parameters In order to take into account the relationship between paper strength, pore size, and air permeability, the pulp must also be beaten. Appropriate tapping degree is conducive to ensuring the bonding force between the fibers and can reduce the maximum pore size. After repeated comparisons, we believe that when the pulp tapping degree is at 17 ° SR, the various indicators of papermaking are closest to the requirements, and the final parameter of the pulping is 17 ° SR and the wet weight is 9-10g. 3. Selection of wrinkle scraper The wrinkling of filter paper is mainly to increase the effective filtering area of ​​the filter element, and there are a large number of grooves on the paper to accommodate more dirt and prolong the service life of the filter. What determines the depth of the wrinkle is the thickness and angle of the wrinkle blade. After testing the actual paper pattern produced, when the thickness of the wrinkle blade is 1.0 mm and the wrinkle angle is 25 °, the wrinkle depth of the filter paper meets the requirements. 4. Application of water-resistant glue All other filter papers are coated with water-resistant resin on the surface, so that the finished paper has sufficient strength and water-resistant performance to ensure the subsequent processing of the filter element. However, the high-precision filter paper has been wrinkled before the sizing machine. If the surface sizing technology of the general filter paper is used and the water-resistant rubber material is immersed again, the wrinkle will disappear or become shallow. Therefore, how to apply water-resistant glue on paper has become the technical key to high-precision filter paper production. After many considerations, the application of water-resistant rubber compound by surface spraying has achieved good results. 4. Features of high-precision filter paper: (1) A high-strength and oil-resistant latex layer is evenly sprayed on the surface of the filter layer, which increases the strength, stiffness and oil resistance of the fuel filter paper, thereby improving its filtration accuracy and life; (2) The hot air drying method of the drying tunnel is adopted to maintain the permeability and bulk of the filter paper, and the dryness is greatly improved after drying. A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone. Hanging Chalkboard,Custom Chalkboard,Portable Chalkboard,Wood Framed Chalkboard Jinan Tri-Tiger Technology Development Co., Ltd , https://www.tigerwoodproduct.com
A blackboard can simply be a board painted with a dark matte paint (usually black, occasionally dark green).Matte black plastic sign material (known as closed-cell PVC foamboard) is also used to create custom chalkboard art.Blackboards on an A-frame are used by restaurants and bars to advertise daily specials.
A more modern variation consists of a coiled sheet of plastic drawn across two parallel rollers, which can be scrolled to create additional writing space while saving what has been written. The highest grade blackboards are made of a rougher version porcelain enamelled steel (black, green, blue or sometimes other colours). Porcelain is very hard wearing, and blackboards made of porcelain usually last 10–20 years in intensive use.
Lecture theatres may contain a number of blackboards in a grid arrangement.The lecturer then moves boards into reach for writing and then moves them out of reach, allowing a large amount of material to be shown simultaneously.
The chalk marks can be easily wiped off with a damp cloth, a sponge or a special blackboard eraser usually consisting of a block of wood covered by a felt pad. However, chalk marks made on some types of wet blackboard can be difficult to remove. Blackboard manufacturers often advise that a new or newly resurfaced blackboard be completely covered using the side of a stick of chalk and then that chalk brushed off as normal to prepare it for use.