【正文】 .If the scraper is new, the angle is adjusted to 228. After the regrinding of the scraper, the shorter and steeper angles are obtained for the scraper.If the scraper adjustment angle is smaller than 228, the plete scraping of the product bees difficult. Some product stays on the drum as scraping material during the scrape operation.If the angle of the scraper adjustment is bigger than 288, the scraper may abrade the drum in case of unsuitable mounting or higher pressure on the scraper During the work, the scraper is ground several times. When the width of the scraper decreases to lower than 100 mm during grinding it should no longer be used.3. Experimental procedure. MaterialsGenerally, cast iron and steel are used for drum dryers as materials in industry. In this study, AISI 4140 steel is used as a drum material. The spectral analysis of the present drum material is shown in Table 1.In addition, HSS is used for scraping knife and the chemical analysis is also illustrated in Table 1.. CoatingIn order to increase the hardness and the wear resistance, the drum is coated with the harder chromium. The hardness can reach up to 800–1000 HV. The coating thickness must be approximately – mm. After the coating process, corrosion and heat resistance could also be increased in addition to wear resistance.In the present study, steel samples (in various diameters) are firstly treated with degreasing solvent suitable for ASTM B177 C8 and then they are coated with harder chromium similar to the earlier work .. GrindingIn order to increase the surface quality and decrease the surface roughness, drum and scraping knife are ground. The selection of grinder was done according to the standard of TS 291 for surface grinding.The grinder works at the cutting speed of 25 mys and advance speed of mys. In addition, a suitable coolant (soda water) was used for surface grinding in liquid form.. Surface roughnessIn order to check the surface quality, surface roughness was measured. In this study, a profilometer was used to determine the surface roughness.. HardnessThe hardness of the drum with chromium coating is measured by the microhardness test machine. In this test, 10 N load is employed using Officine Galileo Microscan test machine. At least five microhardness are obtained from each specimen and an average value is reported. This method is suitable for very hard, brittle and thin materials.However, the hardness of the scraping knife is measured by the Rockwell test machine (RC). In this method, firstly, a preload of 100 N is employed and then a primary load of 1400 N is also applied for the process.. Electrical measurementsIn order to measure the real contact area, the electrical conductivity method is one of the processes used.In this study, a digital ohmmeter (microohm 3000) is used for electrical measurements. This device always gives the resistance value at 20 ℃ by balancing the outer temperature. Micro 500 press with puter control is employed for the obtaining of the real contact area.4. Results and discussion. Surface roughnessSurface roughness measurements are employed via profilometer and the results are shown in Table 2 for the drum and scraping knife.It is seen from Table 2 that the surface roughness of the drum and scraping knife are very close to each other. For this reason, the coupling of drum and scraping knife will work in good harmony. These values are in agreement with the general tribological rules and the previous work.After a long time working with each other, the wear of the drum with hard chromium coating (68 R Cs940HV) will be less than the softer (60 RC) scraping knife of HSS. It means that scraping knife will be blunt within3–60 h according to the type of product and working density. In this way, the knife will be worked within the angles of 22–28176。 and drying. Both steps use the heat transferred from the surface of the steamheated drums to the wet manufactured goods.Improved by the boilingtype of drying, the obtained drumdried pieces introduce outstanding wettability and are unplicated to rehydrate, qualities extremely significant for readytouse products.In this paper, drum dryers are studied due to their industrial importance and extensive application area.2. Drum dryerDrum dryer is a mechanical system, which is widely used for various sectors in industry. Basically, it has a cylindrical shape. The processed solutions and suspensions are laid on the drum dryer which is heated by steam. Then, the scraper knife scratches the drying product on the drum and the process is plete. . Working principleDifferent drum dryers are designed and one of them is shown in Fig. 1.Fig. 1. Schematic representation of top loading double drum dryer The selection of drum dryers depends on the production type and raw material. Designing of a single drum is simple, but problematic in practice, therefore, double drum dryers are widely used in industry.The gap between two cylinders of double drum dryers is one of the important working factors. If the product on the drum is very thin, it causes the loss of yield. The scraper knife damages in case of the thick product on the drum.It is difficult to measure the distance between two drums. Several methods have been developed to measure the gap for this purpose. . Scraper knife The performance of the drum depends on the scraper knife. Longer service, higher capacity, improved product quality and lower power consumption are obtained with the suitable location, adjustment and maintenance.The scraper knife is hardened and very sharp, and therefore, must be carefully kept during the mounting.Unsuitable adjustment of the scraper knife increases the power consumption and bluntness. It also causes the fracture and failure on the surface of the drum.Adjustment of the knife is done via setting bolt. If more adjustment is done, knife pressure is incre