summary

The basic principle of steel bar thermal flux welding is to fill the easily ignited thermal flux (usually the powder mixed with aluminum powder, iron oxide powder and some alloy elements) into the graphite crucible, and then ignite it to form an exothermic reaction to reduce the iron oxide powder to liquid molten steel. The temperature is above 2500 ℃ and passes through the sealing sheet (small round steel sheet) at the bottom of the crucible, The gap is reserved between the two reinforcements through the graphite pouring tank to melt the end face of the reinforcement and form the welded joint of the reinforcement after cooling. In order to ensure the full melting of the end of the reinforcement, a preheating metal storage chamber must be set, so that when the high-temperature molten steel initially entering the mold enters the preheating metal storage chamber after flowing through the gap between the reinforcement, the end of the reinforcement will be preheated, while the subsequent molten steel will fill the gap of the reinforcement joint, and a firm welded joint will be formed after cooling, as shown in the figure.

1 – high temperature matches; 2 – reinforcement; 3 – preheating metal storage chamber; 4 – asbestos; 5. Molding sand;
6 – sealing piece; 7 – thermal agent; 8-crucible with tapping port; 9 a crucible cover

連接工藝

(1) Reinforcement preparation. The end face of the reinforcement must be cut flat, preferably with a circular saw; When gas cutting is adopted, the oxide scale and slag attached to the end face of the cut shall be removed in advance.
(2) Sleeve fabrication. The steel sleeve is usually made of 45 high-quality carbon structural steel or low-alloy structural steel.
When designing the cross-sectional area of the connecting sleeve, the yield bearing capacity of the sleeve shall be greater than or equal to 1.1 times of the yield bearing capacity of the reinforcement base metal, and the tensile bearing capacity of the sleeve shall be greater than or equal to 1.1 times of the tensile bearing capacity of the reinforcement base metal. A certain clearance shall be reserved between the inner diameter of the sleeve and the outer diameter of the reinforcement to enable the molten steel to be smoothly injected into all corners.
When designing the length of the connecting sleeve, the shear capacity of the filling metal should be considered. The shear capacity of the filling metal is equal to the shear strength of the filling metal multiplied by the area of the outer circle of the reinforcement (the length of the sleeve multiplied by the length of the outer circle of the reinforcement). The shear strength of the filling metal can be calculated as 0.6 times its tensile strength. The bearing capacity of the base metal of the reinforcement is equal to the yield strength or tensile strength specified in the national standard multiplied by the nominal cross-sectional area. The tensile strength of filling metal can be calculated according to the tensile strength of Q215 steel 335n / m2.
When designing the internal thread or toothed groove of the connecting sleeve, it should be considered that there is a good anchoring force (bite force) between the sleeve and the filling metal. A small round hole shall be machined near the middle of the connecting sleeve so that molten steel can be injected from here.
(3) Thermal agent preparation. The main components of the thermal agent are droplet shaped or petal shaped aluminum powder and fish scale shaped iron oxide powder, and the ratio of the two shall be determined through calculation and test. In order to improve the strength of the filling metal, a small amount of alloy elements can be added if necessary. The two main components of the heat agent should be mixed evenly. If it is the purchaser’s bagged thermal agent, it shall be thrown several times before use, and it must be mixed evenly to ensure full reaction.
(4) Crucible preparation. The crucible is usually made of graphite or steel plate, and the interior is coated with refractory. The refractory consists of 3 parts of clean and fine quartz sand and 1 part of clay, plus 1 / 10 parts of colloidal material, and 1 / 12 parts of water to produce a suitable mixture. If it is mixed manually, the sand and clay must be dry before mixing. After the two materials are mixed, colloidal material and water can be added. Among them, the less water the better. Water glass is commonly used as colloidal material.
After the inner wall of the crucible is coated with refractory, it shall be dried slowly until there is no moisture; If heated to dry, the heating temperature shall not exceed 150 ℃.
When this connection method is widely used in the project, all connecting sleeves, heat agents, crucibles, disposable liners, supports, etc. of different specifications can be mass produced, packaged and supplied by special factories for convenient construction.