SAND CASTING EQUIPMENT.

3. Evaluation of the quality of spheroidizing agent
There are data from the reaction thermodynamics of spheroidizing elements in molten iron, reaction kinetics, quality influencing factors in the production process of spheroidizing agent, and process influencing factors in the use process of foundries. The standards for determining the quality of spheroidizing agent are as follows:
3.1 The affinity of spheroidizing elements with elements such as sulfur and oxygen in molten iron. It has strong affinity and forms a compound with it, which acts as the foreign core in the solidification process of molten iron, such as rare earth, magnesium, calcium and other spheroidizing elements. 3.2 The ability of spheroidizing elements to change the shape of graphite from flake to spherical.
3.3 The density and boiling point of the spheroidizing agent are lower than that of molten iron. The low density can automatically float in the molten iron, and the boiling point is lower than the treatment temperature of the molten iron. Magnesium can be transformed into a gaseous state at the treatment temperature, which has a self-stirring effect, thereby improving the spheroidization effect.
3.4 The magnesium oxide content in the spheroidizing agent is equal to about 10% of the magnesium content.
3.5 The spheroidizing agent is dense, no segregation, no shrinkage and porosity, and no powdering.
3.6 The spheroidizing agent has uniform particle size distribution, no powdery alloy, and obtuse-angled and deformed particles are better.
3.7 The above conditions basically cover the quality requirements during the production and use of the nodulizer, so it can be used as a unified standard for the quality of the supplier and the buyer.

4. Selection of spheroidizing agent
The quality evaluation standard of the above spheroidizing agent can also be said to be the basis for us to select the spheroidizing agent, but it is explained in accordance with the general principles and common phenomena. Specific to the selection of spheroidizing agent, we now follow the habit of our foundry. Perform analysis.
4.1 The main common problems encountered by foundries in the use of spheroidizing agents are:
4.11 The composition of the spheroidizing agent is inaccurate and fluctuates.
4.12 Nodulizer powdered alloy particle size does not meet the requirements.
4.13 Nodularizer is not dense, rises quickly, and burns seriously.
4.14 MgO content is too high, the reaction is too intense, the spheroidizing treatment is poor, and the amount of spheroidizing agent added is too large.
4.15 Decay quickly after spheroidization.
4.16 After spheroidization, the white mouth tends to be large.

5. Common defects caused by improper application of spheroidizing agent
Casting defects such as inclusions, holes, cracks (referring to pores, keyholes, cracks, cold partitions, etc.) often affect the mechanical properties, physical and chemical properties, and processing properties of the castings, and determine the quality of the castings. Ductile iron parts may have almost all casting defects, but due to their different production methods, crystallization laws, casting properties and other casting alloys, ductile iron often has some unique defects. Xinyuanzhu Group combined with the actual casting production research of the foundry workshop shows that almost All the defects of ductile iron parts are related to spheroidizing agent. This mainly has the following aspects:
5.1 Graphite ball alienation: Irregular graphite appears in the alienation of graphite ball, such as clumps, tadpoles, worms, horns or other non-spherical shapes. This is because the local crystal growth mode and growth rate deviate from the normal growth law when the spherical graphite grows along the radiation direction. When the amount of residual spheroidizing elements in the casting exceeds the expected range, such as the residual magnesium is too high and exceeds the minimum amount required to maintain graphite spheroidization, it will also affect the graphite crystallization conditions, and it is easy to produce tadpole strong graphite. When there are more residual rare earths, high carbon equivalent molten iron is easy to produce fragments of graphite, and the concentrated area of fragments of graphite is generally called "grey spots". The emergence of vermicular graphite is due to insufficient residual spheroidizing elements or excessive titanium and aluminum.
5.2 Graphite floating: In the thick-walled ductile iron with hypereutectic composition, there is often a dense area of graphite at the top of the pouring position, that is, the phenomenon of "floating from beginning to end". This is because the density of graphite and molten iron are different, and the hypereutectic molten iron is directly precipitated Graphite is caused by the upward buoyancy. The degree of graphite floating is related to the carbon equivalent, the type and residual amount of spheroidizing elements, the solidification time of the casting, and the pouring temperature. Magnesium can increase the eutectic carbon content of ductile iron. For molten iron with the same carbon equivalent, increasing the residual magnesium content can reduce graphite floating, and the residual rare earth content is too high, which helps to promote the explosion of graphite.
5.3 Anti-white mouth: the white-mouth structure of general iron castings is easy to appear in the surface, sharp corners, and drape seams that cool quickly, while the reverse white-out defect is the opposite. The carbide phase appears in the middle section of the casting, hot joints, etc. Location. When the residual amount of spheroidizing elements is too much, it can promote the generation of anti-white defects. Rare earth elements are stronger than magnesium, and they can generally increase the degree of supercooling when the ductile iron structure is formed.
5.4 Subcutaneous pinhole: The hypodermic pinhole mainly contains hydrogen, but also a small amount of carbon monoxide and nitrogen. When the amount of residual magnesium is too high, it also strengthens the tendency to absorb hydrogen from the wet type, thereby increasing the probability of subcutaneous pinholes. In addition, the long residence time of spheroidized molten iron can also increase the number of pinholes.
5.5 Shrinkage cavities and porosity: Shrinkage cavities often appear in the final solidification part of the casting (hot joints, riser neck and casting connection, inner corner or inner gate and casting connection), which are holes hidden inside the casting or connected to the outside. . Shrinkage porosity appears macroscopically at hot joints, and most of the tiny shrinkage holes are interconnected inside the holes. Related to the spheroidizing element is that the residual magnesium and rare earth should not be too high to control, which has a significant effect on reducing the macroscopic and microscopic shrinkage. The shrinkage tendency is almost proportional to the spheroidizing element.
5.6 Black slag: it generally occurs on the upper part of the casting (pouring position), and is mainly divided into block, rope and finely broken black slag. The main component of black slag, magnesium silicate, is produced by the reaction of MgO and SiO2 in molten iron and is affected by its relative content. Therefore, one of the measures to control black slag is to reduce the residual amount of magnesium (when magnesium is added 0.15%, the total slag accounts for about 0.1% of the weight of the molten iron), and the residual rare earth has a strong affinity with oxygen, which reduces the amount of black The slag has obvious effect.
5.7 Spheroidization decline: This is due to the longer residence time of the spheroidized molten iron, the residual magnesium is gradually reduced, the slag is not removed in time, and the sulfur will return to the molten iron, reducing or even disappearing the graphite in the solidified structure, and decays into irregular Graphite, worm-like or flake graphite. This spheroidization decline is related to the low rare earth content in the spheroidizing agent or the low amount of spheroidizing agent added. However, it is not advisable to increase its addition immediately because the residual amount of magnesium is high and the amount of slag and cementite will increase, and the graphite ball will be transformed into tadpole-like graphite in the thick section. Production practice shows that the low sulfur content of raw molten iron is the most effective in preventing spheroidization and decline.
Including the defects of nodular iron parts, almost all have something to do with the composition and amount of nodulizer, but we can’t expect nodulizer to solve many problems, let alone solve all problems, because of the effect of spheroidizing elements and nodulizing agent. The added amount of spheroidizing is both pros and cons. The spheroidizing agent is only a very important factor in the stable production control system of spheroidal graphite cast iron. Only when combined with other supporting measures can the spheroidizing treatment be carried out stably.

to sum up:
The amount of spheroidizing agent added to the influence of ductile iron In the production of nodular cast iron wholesale, the amount of spheroidizing agent added directly affects the overall performance of ductile iron and the production cost of ductile iron. Since the advent of ductile iron, it has always been one of the most important issues that people have paid attention to. The amount of spheroidizing agent added directly affects the overall performance of ductile iron and the production cost of ductile iron.
Since the advent of ductile cast iron, it has always been one of the most important issues that people are concerned about. The amount of nodulizer is affected by the characteristics of the nodulizer itself, the characteristics of molten iron, the size of the casting, the thickness of the wall and the thickness of the ductile iron. Brand and spheroidizing treatment process four major factors.
The characteristics of the spheroidizing agent include the composition, specific gravity, lumpiness and metallurgical quality of the spheroidizing agent. The characteristics of the molten iron include the composition of the molten iron, especially the sulfur content, the temperature of the molten iron and the metallurgical quality of the molten iron. The spheroidizing treatment process includes the shape, size, and spheroidization of the molten iron. The degree of agent coverage and so on.
Xinyuanzhu Group only analyzes several major issues in the currently widely used processing technology containing one, rare earth, and punching. The role of spheroidizing elements The rare earth ferrosilicon-magnesium spheroidizing agent contains spheroidizing elements magnesium, rare earth, calcium, a certain amount of iron, silicon, and a small amount of manganese, aluminum, and titanium. The spheroidizing elements are Mg, Re, and Ca according to their spheroidizing ability. They all have strong desulfurization and degassing capabilities. The affinity to oxygen is Ca, Re, Ma in descending order, and the affinity to sulfur is Re, Ca, Mg in descending order. Obviously, magnesium plays the main role of spheroidization, plays the role of auxiliary spheroidization, and also plays the role of desulfurization, degassing, and purification of molten iron. The spheroidizing elements added to the molten iron have the following functions; there is a certain residual amount in the molten iron to make graphite into balls; combine with sulfide to form sulfides, which desulfurize the molten iron; react with oxygen in the air to produce oxidative burning loss .

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