Quality Control Of Float Glass Melting Furnace Construction

 ① The variety, specification and performance of all materials or finished products entering the construction site of the glass melting furnace project, such as refractory materials, furnace building materials, steel, steel components, etc., shall comply with the current national product standards and design requirements.

 ② All steel components, processed parts and fabricated parts entering the construction site shall meet the design requirements and relevant specification requirements. The installation unit and the supervision unit shall inspect and accept them. If necessary, personnel can be dispatched to the factory for supervision.

 ③ Fire-resistant materials, furnace building materials, steel, etc. used in the construction site shall have quality certification documents and test reports. The monolithic refractories for furnace building shall also have instructions for use. Materials with quality objections shall be re-inspected. Materials can only be used if they are qualified, and unqualified materials shall be removed from the site.

 ④ Steel components and refractory materials shall be stacked neatly to prevent deformation and messy stacking. Magnesium bricks that are easily deteriorated by moisture shall not be exposed to moisture. Monolithic refractories, binders, etc. must be stored separately and shall not be confused. Refractory materials shall be protected from rain. During transportation and handling, they shall be handled gently and shall not be collided.

  ⑤ The measuring instruments and tools used for steel structure fabrication, assembly and quality inspection shall be regularly inspected and comply with the relevant regulations of the national metrology department. Process inspection shall be carried out during the fabrication and processing process, and only after passing the inspection shall the next process be allowed. The fabrication, processing, assembly, splicing and installation of steel structures shall comply with the design requirements and the current relevant national standards and specifications.

 ⑥ The completed steel structure components shall be derusted in a timely manner, and painted with anti-rust paint or anti-rust liquid as required by the design to avoid corrosion of the steel structure components during transportation and use. Threaded components shall also be provided with protective sleeves to prevent damage and unusability. During transportation and storage, steel structure components shall be stacked reasonably to prevent deformation from affecting installation.

 ⑦ Steel structure components shall be fabricated according to the drawings, with smooth and flat edges, and no burrs or unevenness. Round holes must be drilled, and on-site cutting into holes is not allowed. All welding quality shall meet the requirements of current national standards, and the welding quality shall comply with the provisions of the *Code for Construction Quality Acceptance of Steel Structure Engineering* (GB50205-2001).

 ① First, the positioning dimensions such as the longitudinal centerline of the melting furnace, the centerline of No. 1 small furnace, and the design elevation handed over by the civil engineering unit shall be reviewed, and permanent positioning shall be carried out. These are key positioning dimensions for the construction of the melting furnace, and the positioning shall be as accurate as possible, with the measurement error controlled within 1mm.

 ② The elevation of the top of the concrete column supporting the melting furnace shall be carefully checked and controlled within the negative tolerance range of the design elevation. Positive tolerance is not allowed, and it is generally controlled at -3~-4mm. If there is a positive tolerance, rectification must be carried out. The secondary casting of the column top plate must be dense, and no hollow shell phenomenon is allowed.

 ③ The fabrication of the main beam must be checked to comply with the design requirements. After hoisting in place, the elevation of the top surface of the main beam shall be checked, and the elevation of the top surface shall be controlled within the negative tolerance range of the design elevation, generally controlled at -3mm. If controlled according to the design elevation, the superposition of allowable errors of the secondary beam on the main beam, the stack beam and stack bricks on the secondary beam, and the bottom bricks of the tank will eventually cause the elevation of the top surface of the tank wall bricks to exceed the design elevation range, resulting in too small a gap between the tank wall bricks and the hook bricks, bringing hidden dangers to the melting furnace and affecting production due to the excessive elevation of the glass liquid level.

 ④ When measuring the elevation of the top surface of the main beam, great attention shall be paid to measuring the highest point of the top surface of the main beam. A spirit level can be used to find the highest point of the top surface, because the secondary beam is placed at the highest point of the main beam, as shown in the following figure.

 During actual construction, many construction units fail to pay attention to this and often measure the center position ② of the main beam. Although the elevation of the main beam is appropriate, after installing the secondary beam, it is found that the elevation of the top surface of the secondary beam is too high, and this is the reason. During the fabrication of the main beam, welding deformation may cause the top surface of the main beam to incline or twist. As a result, the center position ② is not the highest point of the top surface of the main beam. The same applies to the installation of secondary beams: the highest point of the secondary beam must be measured; otherwise, the designed elevation of the stack beam will rise. Therefore, it is very necessary to ensure that the main and secondary beams are fabricated flat, straight, and free of distortion.

 ⑤ After the installation of the secondary beam, the elevation should be controlled within the negative tolerance range of the design elevation, generally between -2~-3mm. For areas where the elevation exceeds the standard, clips can be used to tightly attach the secondary beam to the main beam or temporarily fixed by spot welding. The temporary welds should be removed before kiln drying.

 ⑥ The stack beam should be placed flat and straight on the secondary beam. The claws of the insulation support plate should be spot-welded under the stack beam. First, place the stack beam upside down, weld the claws, and then turn it back for installation to prevent welding deformation. Some construction units use full welding instead of spot welding, which causes deformation of the stack beam. This is an incorrect practice and must be noted. Some construction units install the stack beam first, lay the stack bricks, and then weld the claws. This is also incorrect. First, welding is troublesome, and second, there is no room for adjustment after welding deformation. Graphite grease should be applied between the stack beam and the secondary beam, and between the secondary beam and the main beam to facilitate the expansion and displacement of the furnace bottom.

  ⑦ After the installation of the main beams, secondary beams, and stack beams is completed, they should be inspected and accepted. Only after passing the inspection can the next construction process proceed.

 ① The melting section columns entering the site shall comply with relevant steel structure fabrication specifications and design requirements. The full-height bending of the columns shall not exceed 5mm, the flange inclination shall not exceed 2mm, the flatness shall not exceed 3mm, and there shall be no torsional deformation.

 ② The columns shall be hoisted into position according to the positioning dimensions. The positioning error shall not exceed 2mm. The columns shall be installed vertically with an inclination not exceeding 1mm, and temporarily fixed after adjustment. Considering that heavy loads such as breast wall support plates, arch waste beams, and breast wall masonry will be installed on the columns, to prevent the columns from tilting inward, based on installation experience, the columns can be tilted outward by about 4mm during verticality adjustment, so that they can remain vertical after heavy loads are installed. Another method is to weld adjustable flange screws to the angle irons used for temporary fixing to adjust the verticality of the columns at any time. Some construction units only temporarily fix the columns after adjusting their verticality. After installing the breast wall support plates and arch waste beams, the columns tilt slightly inward but this is not taken seriously and the verticality is not adjusted in time. Only after the breast wall is masonryed is it found that the columns and breast wall are tilted inward. By then, adjustment is impossible, directly affecting the masonry quality of the side arch bricks and main arch in the subsequent processes. This must be noted during column installation.

 ③ After the installation and adjustment of the columns are completed, components such as connecting beams, upper and lower palm irons, jacking plates, jacks, breast wall support plates, arch waste beams, and platform supports can be installed.

 ④ The breast wall support plates shall be fabricated flat, straight, without bending or twisting. During installation, the elevation of the top surface of the support plates shall be controlled within the positive tolerance range of the design elevation, ideally +2mm above the design elevation. The expansion joints between the support plates shall meet the requirements, generally 20mm. Adjacent support plates shall be of the same height, and the spacing from the columns shall comply with the design requirements, generally 90mm.

 ⑤ The fabrication of arch waste beams shall comply with the design requirements. The contact surface with the side arch bricks shall be flat, and the fabrication unit shall plane it if conditions permit. During installation, the elevation, span, and angle of the arch waste beams shall all meet the design requirements. Slight adjustments can be made based on the masonry conditions of the breast wall to ensure proper positioning of the side arch bricks. The arch waste beams must be tightly supported against the columns. Any gaps must be filled with thin steel plates of different thicknesses; other materials are not allowed to prevent loosening of the arch waste beams during main arch masonry.

 ⑥ The ability of the side arch bricks to fit tightly against the arch waste beams and align with the breast wall during masonry directly reflects the fabrication and installation quality of the steel structure, as well as the masonry quality of the breast wall. Errors in the fabrication and installation of columns, arch waste beams, and breast wall support plates, as well as errors in breast wall bricks and masonry, can cause the side arch bricks to fail to fit tightly against the arch waste beams or align with the inner edge of the breast wall. By observing the masonry of the side arch bricks, the installation and masonry quality of previous processes can be evaluated. There are many such examples in construction. For instance, during the masonry of side arch bricks in a melting furnace, it was found that the bricks protruded 3cm from the breast wall. Inspection revealed that the spacing between the two breast walls did not meet the design requirements, but rectification was impossible, so the thickness of the side arch bricks had to be ground down by 3cm to avoid affecting the construction quality of the main arch. During the pre-assembly of side arch bricks in another melting furnace, gaps were found between the bricks and the arch waste beam plane. Inspection showed that the installation angle of the arch waste beam did not meet the design requirements, necessitating reinstallation and adjustment of the beam.

 ① The stack bricks shall be laid flat and straight, with the elevation controlled within the negative range of the design elevation, generally -3~-2mm. Sufficient expansion joints shall be reserved between stack bricks, and all mortar and debris in the expansion joints shall be cleaned out.

 ② Before laying the tank bottom bricks, relevant equipment and tools shall be prepared. The joints of the tank bottom bricks shall be located at the center of the stack bricks. Positioning dimensions shall be marked on the stack bricks, with the longitudinal centerline of the melting furnace and the centerline of No. 1 small furnace as the reference, to draw positioning control lines for each row or several rows of bricks. Laying shall be carried out according to the control lines, and sufficient expansion joints shall be reserved. Suction cups shall be used as much as possible during laying. Dust at the expansion joints shall be cleaned up in time, and the joints shall be sealed tightly with adhesive tape to prevent debris from entering. Care shall be taken during installation to avoid damaging the edges and corners of the bricks manually. After construction, colored striped cloth and plywood shall be laid in time. The elevation of the top surface of the tank bottom bricks shall not be controlled at the middle position of the furnace, but only at the position where the tank wall bricks are placed, generally controlled within the range of the design elevation and -1mm. Areas exceeding the elevation shall be ground flat.

 ③ Before entering the site, the tank wall bricks shall be pre-arranged and numbered by the manufacturer, and an arrangement diagram shall be provided. During construction, the bricks shall be laid according to the numbers, neatly, straightly, with uniform joints, and triangular joints shall be adjusted. The positioning dimensions shall be controlled within 2mm.

 ① The breast wall and hook bricks in the melting section are usually made of electrofused zirconia corundum bricks, which are pre-arranged and numbered by the manufacturer, and an arrangement diagram and physical photos are provided. During construction, they are laid according to the numbers. The breast walls, hook bricks, and gap bricks in the clarification section and cooling section are usually made of high-quality silica bricks. Zircon bricks or isolation mortar are commonly used to isolate the corundum bricks and silica bricks to prevent contact reactions between the bricks.

 ② The gap between the hook bricks and the tank wall bricks shall comply with the design requirements. It is better to be larger than smaller to prevent the tank wall bricks from expanding and breaking the hook bricks. Expansion joints shall be set strictly according to the design requirements. The installation dimensions of all parts of the breast wall shall be constructed according to the drawings. Before laying the breast wall bricks, the flatness of the breast wall support plate shall be checked. The top surface of the hook bricks shall be laid flat and straight, and the level shall be checked with a spirit level at all times to avoid tilting. The inner arc surface at the bottom of the hook bricks shall have a gap of more than 5mm from the support plate. The expansion joints shall be sealed tightly with adhesive tape. The distance between the breast wall and the centerline of the melting furnace shall be strictly controlled, as the dimensional error of the distance will directly affect the laying of the side arch bricks.

 ③ Before laying the rear gable of the melting section and the front and rear gables of the cooling section, it shall be checked whether the support plates are flat, whether the elevations are accurate, whether the arch brick dimensions are standard and flat, and whether the double hook bricks have cracks, etc. Expansion joints shall be set according to the design requirements, and sufficient expansion space shall be reserved at the corners between the gable hook bricks and the longitudinal hook bricks to allow mutual expansion during thermal expansion.

 ④ The rear gable arch and the outlet arch are key parts of the melting furnace, and special attention shall be paid during laying. It shall be checked that the arch bricks and arch foot bricks have no cracks or distortion, and pre-arrangement shall be carried out before and during laying. In actual construction, there was a case where the arch foot bricks had cracks, and the arch foot bricks broke during kiln drying, causing the gable arch to loosen and the gable to crack, bringing hidden dangers to the melting furnace. Therefore, the arch bricks and arch foot bricks at key parts must be inspected, and unqualified bricks must be replaced. Laying shall be carried out more carefully. The wall shall be laid flat and straight, and the parts that need to be dry-laid must be dry-laid to facilitate the expansion and displacement of the wall.

 ① The main arch is a key part of the melting furnace and must be carefully masonryed. A construction plan shall be formulated in advance, and tools such as arc template boards and straightedges shall be fully prepared. The formwork support of the arch wooden mold shall be carefully checked to ensure foolproof safety, and attention shall be paid to fire prevention. The wooden mold support shall have a stable and firm structure, and the arc and chord height of the wooden mold must comply with the design requirements. The arc surface shall be checked for consistency, the arch top shall be horizontal, and the concave-convex surfaces must be planed flat. When necessary, a 2mm-thick plywood shall be laid on the mold surface to prevent grout leakage.

  ② After the wooden mold support is qualified, control lines shall be marked out, and the position of each arch section shall be separated by small wooden strips. The arch bricks shall be pre-arranged before masonry, the size of the mortar joint shall be determined according to the pre-arrangement, and the position control lines for each row of bricks or every 3 rows of bricks shall be marked on the arc surface. Masonry shall be carried out according to the control lines. Each row shall be controlled by a tension line during masonry, the angle of the brick surface shall be checked with an arc template at any time, and the flatness of the brick surface shall be checked with a straightedge. In the masonry of arch bricks, it is strictly forbidden to invert the large and small ends, and the arch bricks shall be kneaded and pressed to ensure full mortar. The location of the thermocouple hole bricks shall be accurately set. The locking bricks shall be appropriate and not too tight to avoid damaging them. After locking the bricks, the joints shall be grouted with thin mortar.

 ③ After the main arch masonry is completed, the tie rods shall be tightened in a timely manner, and all temporary fixings shall be removed. Generally, the height of the arch bricks from the wooden mold surface can be 0.15% of the arch span. The tie rods do not need to be too tight. According to experience, sometimes the tie rods are tightened until the main arch is separated from the arch mold with a gap of 4-2mm. A tie rod tightening plan shall be formulated before tightening, and preparations for personnel, equipment, and tools shall be made. Experienced personnel shall be assigned to command uniformly. How many buckles to tighten each time, the interval time, etc., shall be arranged and clearly explained in advance. In one kiln drying case, excessive tightening of the tie rods caused defects such as peeling, corner chipping, and cracking on the inner side of the arch bricks, affecting the quality of the main arch and requiring replacement of the defective arch bricks. During the tie rod tightening process, the changes in the main arch shall be observed at any time, and any abnormal conditions shall be dealt with in a timely manner. The formwork can be removed only after the arch bricks have shown no changes for 12 hours after separating from the mold surface.

 Finally, the masonry quality of the main arch shall be checked. Inverted large and small ends, defective or cracked arch bricks, and excessive end joints shall be replaced and rectified in a timely manner. In actual construction, the phenomenon of arch bricks "slipping" ("slipping" here refers to displacement) after kiln drying occasionally occurs. The causes may include inverted large and small ends of arch bricks that were not detected, excessive mortar joints during masonry, uneven laying of each row of arch bricks, or significant deviations in the thickness of arch brick dimensions. When thick and thin bricks are laid in the same row, the thin bricks are most prone to slipping. Therefore, making obvious identification marks on the large ends of arch bricks is an effective way to prevent slipping. Even so, one or two bricks may still have inverted large and small ends in each construction, so careful final inspection is essential.