Casting is a manufacturing, constitute an integral part of the believe that most of the manufacturers will bother to defects of casting
Ductile iron castings manufacturer small make up today as dear friends some remedial measures are discussed.
1, retention time: after inoculation to pouring out between the residence time is too long, for the precipitation of graphite is provided, generally the time should be controlled within 10 min.
2, compactness of sand mold: if the compactness of sand mould is too low or uneven, so that after pouring the metal under the action of static pressure or expansion force, produce the phenomenon of cavity expansion, the original metal enough feeding and cause shrinkage of casting to produce shrinkage.
3, pouring temperature, in general, the higher the pouring temperature, the greater the tendency of graphite on the floating, this is because the casting is advantageous to the precipitation of graphite is liquid for a long time.
4, poured riser and chill: if the pouring system, riser and chill Settings, liquid metal can't guarantee the directional solidification;
In addition, the number of the riser, size, and the connection with the casting when no, will affect the feeding effect of risers.
5, melting process, liquid metal to progress the melt temperature, fitting for the calm, to facilitate the buoyancy and extraction of non-metallic inclusions.
Factories to control phosphorus content less than 0 08%.
In addition, if the wall thickness change too hardcore, isolation of thick section is not feeding, make produce porosity shrinkage tendency increases.
Because the density of graphite is smaller than iron liquid, under the drive of magnesium vapor, graphite floating into the upper casting.
These defects affect the function of casting, casting rejection rate increased.
And high sulfur content in liquid iron, castings are prone to slag.
6, pouring system, gating system design should be reasonable, with functions of slag, can make the liquid metal filling mold smoothly, makes every effort to avoid splash and turbulent flow.
If 7, sand, sand surface adhesion have extra sand or coating, they can be of oxide synthetic slag and liquid metal, lead to slag.
Sand mold with uneven density, compactness type low wall surface easily metal corrosion and the formation of low melting point compounds, resulting in casting slag.
High phosphorus content in 8, phosphorus, iron, extend the solidification range, low melting phosphorus eutectic solidification at the end at the same time not supply, and make the casting shell, therefore has a tendency to increase the shrinkage cavity, shrinkage.
9, rare earth and magnesium: research thought of slag in recent years mainly because of the element such as magnesium and rare earth oxide and, therefore should not be too high residual magnesium and rare earth elements.
10 and compactness of the mould should be average, intensity is enough;
Tanks should be blowing off the sand mold.
Steel compared with the corresponding organization, the plastic is lower than steel, fatigue strength close to the general medium carbon steel, showed up to 0, 7 ~ 8, 0 is almost 2 times the general carbon steel, and capital is lower than steel, so its application has become increasingly widespread.
Thus, residual magnesium quantity and residual quantity of rare earth can increase the chilling tendency of nodular iron, the graphite expansion is reduced, so when their content is higher, also can increase the shrinkage cavity, shrinkage tendency.
It should be pointed out that the main reason for the high carbon equivalent is to produce graphite floatation, but not the only reason, casting size and thickness is also the important factors influencing the graphite floatation.
In order to prevent the occurrence of these defects, it is necessary to analyze it and precision forging, sums up the various influence factors, puts forward prevention measures, can effectively reduce the generation of defects, the progress of the casting mechanical function and produce benefits.
In this temperature range, with temperature rise, magnesium and rare earth absorption rate increased.
11, control of iron liquid ingredients: try to reduce the sulfur content in the molten iron (
, right amount add rare earth alloy (
0 1% ~ 0 2%)
To purify the molten iron, reduce residual magnesium and silicon content, the quantity as much as you can.
In addition, the activity of the carbon equivalent can be progressive ductile iron, is beneficial to the feeding.
12, pouring temperature, pouring temperature is too low, the metal liquid metal oxides by metal liquid viscosity is too high, not easy to rise to the surface and the liquid metal in the residual;
When temperature is too high, on the surface of the metal liquid slag become too weak, not easy since the liquid surface, often with the liquid metal flow type.
Empirical formula to produce high quality castings C % % si + 1/7 & gt;
13, temperature, pouring temperature is high, is beneficial to the feeding, but too much will increase the liquid contraction, adverse to eliminate shrinkage cavity, shrinkage porosity, so should choose according to details of reasonable pouring temperature, is 1300 ~ 1350 ℃.
The actual yield, the pouring temperature is too low is one of the main cause of slag.
But progress carbon equivalent, should not make the casting produces graphite floating and other defects.
And magnesium is a strong not disorderly carbide elements, hinder the graphitization.
14, silicon: in under the premise of same carbon equivalent, appropriate lower silicon content, may help reduce the tendency of graphite floatation.
Druschitz and W.
Chaput studies have found that if shorten the coagulation time, follow the pouring temperature, graphite floating tend to be lower.
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