Glass-lined equipment basics

March 31, 2024

First, the basic knowledge of chemical enamel equipment

1. The origin of the name of chemical enamel uses the technology of enamel to composite an acid-resistant glass material with properties close to industrial glass onto a metal substrate to obtain a glass/metal composite, since the coating layer substantially retains most of the properties of the acid-resistant glass. Such as smooth, transparent, dense and non-porous, high chemical stability, etc., is not as good as ordinary enamel for daily use, so it is called "glass-lined". The production process of bismuth glass is equivalent to the enamel process, so it is still enamel. People often have different names in daily life, such as acid-resistant enamel, which is called it is particularly resistant to acid. Chemical enamel is called for its products mainly used as chemical production equipment.

2, the performance of enamel products

The enamel equipment is sprayed on the surface of the steel sheet by a glass glaze with a high silicon content, and is fired at a high temperature of 920 ° C to 960 ° C for a plurality of times, and the glass glaze is adhered to the surface of the metal tire. The performance of enamel is:

(1) Corrosion resistance: It can resist organic acid, inorganic acid organic solvent and alkaline solution with pH less than or equal to 12, but not suitable for strong alkali, HF, and phosphoric acid with temperature greater than 180 °C and concentration greater than 30%; ) Non-stick: smooth glass is not sticky to the medium and easy to clean; (3) Insulation: suitable for occasions where static electricity is easily generated during the medium; (4) Isolation: The glass layer separates the medium from the container steel, iron Ion does not dissolve into the medium; (5) Preservation: The glass layer has good preservation properties to the medium.

3, enamel equipment use conditions
The enamel layer is resistant to most inorganic acids, organic acids, organic solvents and the like, and has excellent corrosion resistance especially in mediums such as hydrochloric acid, nitric acid and aqua regia. However, it cannot be used under the following conditions:

(1) HF of any concentration and any temperature can not resist corrosion; (2) Phosphoric acid: the concentration is more than 30%, the corrosion is strong when the temperature is higher than 180 °C; (3) hydrochloric acid: the concentration is 10--20%, the temperature is greater than 150 °C (4) Sulfuric acid: concentration 10--30%, temperature is greater than 200 ° C can not resist corrosion; (5) lye: PH is greater than or equal to 12, temperature is greater than 100 ° C, can not resist corrosion.

Second, the manufacture of chemical enamel equipment

1. Chemical enamel production operation procedures
2. Substrate characteristics of chemical enamel equipment The base materials used in the manufacture of enamel glass products are mainly high-quality low-carbon steel, cast iron and stainless steel, among which low-carbon steel and cast iron are the most common. The former is used as a suitable steel for bismuth glass, and is used in a large number of equipment and containers. The latter is widely used for the manufacture of pumps, valves, small equipment and spare parts because it can cast complex parts and is inexpensive. Substrate chemical composition Mechanical properties C si Mn PS Tensile strength MPa Elongation % Yield point MPa Impact toughness MPa Steel ≤ 0.14 ≤ 0.37 ≤ 0.65 ≤ 0.035 ≤ 0.45 > 330 > 310 200 -- Welding rod ≤ 0.1 ≤ 0.12 ≤ 0.45 ≤ 0.05 ≤0.03 >430 >180 -- 80 Cast iron 3-0.35 2.0-2.6 0.4-0.6 0.1-0.5 < 0.1 (graphite carbon 2.5)

3, the requirements of the bottom tire

The quality of enamel equipment is first determined by the iron tire. Without high-quality iron tires, it is impossible to have high-quality enamel equipment. To ensure the quality of the products, the iron tires should meet the following six requirements: (1) The surface of the bottom tire should be flat, without significant mechanical defects such as tool scars, pits, interlayers, etc.; (2) The weld bead on the surface of the bottom tire should be straight, Regular, the width of the weld must not exceed 1.5 times the thickness of the steel plate. Weld joints shall be smoothly transitioned, and no defects such as slag inclusions, pores, undercuts, and incomplete penetration shall be allowed; (3) welds on the surface of the bottom tire shall be polished before blasting; (4) surface of the underlay The amount of misalignment of the butt weld is less than 10% of the thickness; (5) the flange roughness is less than 0.15% of the diameter; (6) The compression surface of the butt flange is to ensure the seal under the design pressure.

4. After the surface treatment of the bottom tire is processed, the surface quality of the substrate often fails to meet the technical requirements of the enamel, such as the oxide surface on the metal surface, the surface skin (caused during rolling), the weld defect and the machining process. Adhesive grease and dirt, etc., all affect the burning

Polishing is generally carried out on a grinder or with a hand-held grinding wheel. The requirement for polishing is to smooth the surface of the simmered surface, round the sharp corners, and grind the scale and the skin to reveal the true color of the metal.

The decarburization of the oil is to burn off the adhered grease, organic matter, etc. at a high temperature. When the carbon content of the steel plate exceeds the standard, the high-temperature surface decarburization method is also used for compensation treatment.

After the enamel equipment is damaged, it is retanning to the enamel factory, and heat treatment (dehydrogenation) must be performed to eliminate the hydrogen infiltrated into the substrate of the blasting site. Sand blasting is to roughen the surface of the bottom tire, increase the surface free energy and specific surface area, thereby improving the adhesion between the base metal and the bottom glaze.

5, tire repair

After the surface treatment of the iron tires, before the official squirting of the enamel glaze, it is necessary to carefully examine all the "defects" that do not meet the requirements of the enamel process, such as burrs, sharp corners, embossed pits, interlayers, trachoma and so on. These "faults" can be polished by hand, shovel, repair, and grinding.

6, simmering glaze

After the iron tire is repaired, it can be sprayed and simmered. Spraying can be done by hand or by mechanical (semi-automatic) spraying. The consistency of the glaze consistency of the two is different, which is based on the experience of the operator, because the diameter of the spray gun, the air pressure for spraying and the consistency of the glaze are interrelated. The main point of the squirting glaze is to make the head glaze uniform and uniform, and the thickness value is controlled to be 200 ± 50 μm after firing. After the bottom glaze is sprayed on the iron tire, it is dried. Generally, it is naturally dried. It can also be dried in the drying room and slowly baked in the front of the furnace or on the side of the furnace. Care should be taken to prevent rapid baking, which can cause cracking of the powder layer. After the powder layer is dried, it can be fired in a firing furnace. The firing temperature of the bottom glaze is high. In order to make the bottom glaze firmly adhere to the iron surface, the firing temperature should not be lower than 880 ° C when using the three-in-one glaze. In order to achieve the above requirements between the iron tire and the bottom glaze, the temperature of the firing furnace must be controlled to above 920 °C. In order to improve efficiency, the optimum firing furnace temperature is 960 to 980 °C. The firing of the bottom glaze must be carefully mastered, that is, it cannot be burnt enough (commonly known as burning), and it cannot be burned (commonly known as fire). The former is not well sealed, and the latter will burn the bottom glaze. The moderately glazed glaze should be colored and hooked, and the surface is smooth and bright without bubbles. After the first glaze is burnt, if the quality is qualified, the glaze glaze can be smeared; if it is not qualified, it needs to be repaired. If the burning is serious, the second glaze needs to be squirted. When squirting the bottom glaze for the second time, it should not be sprayed too thick, and the total thickness of the glaze should be controlled to be less than 350 μm. When it is thicker, it will affect the effective thickness of the glaze layer.

7. After the glaze enamel enamel is burnt, the quality can meet the requirements and the glaze can be glazed. The true corrosion protection layer of enamel equipment is the glaze layer. The glaze layer is sprayed and simmered similarly to the bottom glaze. The thickness of the glaze layer is generally about 1 mm. Depending on the requirements of use, if heat transfer is considered, the enamel layer should be made thinner, and the enamel layer should be thicker when the medium used without heat transfer is severely corroded. Japan allows a maximum thickness of 2.55mm, and China's standard stipulates that it must not exceed 2mm and the thinnest is 0.8mm. To reach the specified thickness of the porcelain, the glaze on the product should be squirted many times. The thickness of each pass is preferably thinner. However, considering the production efficiency, it should not be too thin. Generally, it is better to control the thickness of each pass by 2mm. If the surface condition of the metal is good, the weld seam is not problematic, and the sneezing process is finely ground, then the sneeze can reach the specified thickness after three to four glazes. In order to ensure the quality of simmering, every sneeze must be checked to check whether there are dark bubbles, pinholes, etc. on the porcelain surface. Once found, it should be polished and repaired. Pinholes and dark bubbles for straight metal surfaces should be ground or even repaired. Any place where the bottom metal is repaired must be refilled with glaze. The above fixes must be mastered by each sneeze operator.

8, inspection

Since most of the enamel equipment is used in harsh corrosive environments, the quality inspection of the products is very strict. Inspection and inspection requirements are determined according to the grade requirements of the product itself. For specific requirements, see ZB G94004-87 and zB G94005-87 standards. See Table 2 for the test method. The product can be assembled or packaged after passing the inspection. The parts that need to be assembled shall be inspected after assembly. Only the qualified parts will be considered as qualified products before they can be packaged. The equipment should be allowed to stand for more than half a month before sale to eliminate residual stress. Project technical index test method porcelain layer thickness 0.8~2.0mm With non-magnetic thickness gauge, according to GB7991---87 for measuring withstand voltage 20000V (DC) without breakdown with AC spark generator according to GB7993---87 for resistance The pressure meets the design requirements pressure water pressure test, the method GB7994---87 according to the appearance of the porcelain layer quality and color is basically the same, the surface is smooth, no explosion porcelain, fish scale cracks, dark bubbles, tank body, canopy on the upper surface of the can not exceed Three pieces, foreign matter ≤ 8mm2, two pieces should not be ∠ 100mm in the bright light or 100W low-voltage illuminating light at 600mm, observe from the porcelain surface 600mm and record the result deformation tolerance flange maximum and minimum diameter difference ≤ 0.1% Dg Use the meter ruler to measure the maximum outer diameter and the minimum outer diameter of the flange. The difference is used as the elliptical degree. The flange roughness is allowed to be ≤0.3%. Dg The maximum gap between the plane and the standard plane is measured by the feeler gauge as the unevenness of the agitating hole flange. The surface level a allows ≤10 lid to be buckled to the horizontal surface, then the ruler is placed on the flange surface of the mixing hole, and the height of the platform at the outer circumference of the flange of the lid is measured by a right angle triangle. High value Calculate with the lowest value tga≈△hmax/Dg Flange compression surface width ≥10mm With thickness ≤5mm ruler, over-diameter placed on the flange to rotate 180o, measure the compression surface (when continuous gap ≤0.5mm) The radial full-bounce packing seal at the upper end of the width stirrer is allowed to be ≤0.30mm. The stirrer is mounted on the inspection frame and the stirrer is rotated. The square meter is used to measure the tube non-straightness on the contact surface between the stirrer main shaft and the stuffing box (including the thermometer sleeve). 〕 Allow ≤ 0.3% L Use a ruler to measure the maximum gap between the pipe and the ruler.

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