Defects of furan resin sand castings and their countermeasures

1.Porosity and pinholes

Causes：

• Too much resin is added, and the nitrogen content in the resin is too high
• The solvent of the alcohol-based paint contains deteriorated alcohol, contains more water, or the concentration of the paint is too low, and the drying is not thorough after ignition
• The water-based paint is not fully dried
• The molding process is not good. Among them, the factors that have a greater impact are: the pouring speed is too slow; the ventilation plan is poor; the pouring system size is not proportional; the pressure head is too low
• The loss on burn of the recycled sand is too high
• The box is poured too early before the molding (core) is fully solidified, resulting in excessive initiation. o Improper molding operation. Such as core iron exposed, core head drilling iron, etc

Measures to prevent pore defects In response to the above reasons, take the following corresponding countermeasures:
Select resin with low nitrogen content and try every means to reduce the amount of resin added, that is,

(1) select raw sand with rounded particles, moderate particle size, low micropowder content and low acid consumption;

(2) add coupling agent;

(3) select resin with good strength performance and appropriate curing agent, etc., and try to reduce the amount of resin added to less than 1.2% of the sand weight. Pay attention to the solvent quality of the paint; stir the paint thoroughly before painting, and the concentration should be greater than 30 “Be; ignite and dry immediately after painting.

After using water-based paint, it should be baked at a temperature less than 180 ° C for more than 1-2 hours to ensure that the paint is fully dried. When formulating the mutual art plan, pay attention to increasing the pouring speed and reasonably and effectively design ventilation; master the design principles of fast, closed, bottom pouring, and non-turbulent flow.

Control the loss on ignition of recycled sand below 3.0-3.5%. The main measures are to reduce the sand-iron ratio as much as possible, select excellent regeneration equipment, and pay attention to the management of regenerated sand.

The core is best used every other day, and the casting should be painted and poured 4-6 hours after molding.

Strictly operate the molding (core) and mold matching. The core bone should not Leakage, the core head must have measures to prevent iron drilling, so as to avoid choking and causing pore defects. The above mainly discusses the intrusion type pore defects caused by the furan casting itself. In actual production, the proportion of pores caused by factors such as molten iron temperature and smelting quality is also not small. Attention should be paid to specific analysis and remedies.

2.Mechanical sand adhesion and veining

Causes:

• Improper distribution of molding sand aggregate particle size and too low compactness during molding (core)
• Low refractoriness of the coating and insufficient coating thickness

When the amount of new sand is large, it is easy to produce iron seepage and veining, especially when the SiO2 content of the new sand is very high.

The low strength and poor surface stability of the molding sand caused by improper molding operation promote the occurrence of sand adhesion veining. If the molding sand is used for more than the usable time, the head sand of the continuous sand mixer When tailings are used as surface sand, the surface stability is reduced and the sand temperature is too high when repairing the surface of model sand (core).

Measures to prevent sticking sand and veining For the above reasons, take the following corresponding countermeasures:

Make the particle size distribution range of sand appropriately widen. For example, when 30/70 mesh sand is selected, the concentrated distribution of grains of sand is dispersed to four sieve numbers of 30, 40, 50, and 70. When shaping (core), ensure the compactness of the surface sand in each part. Pay special attention to the dead corners and other parts that are not easy to compact.

Ensure the quality of the coating, especially the heat resistance, aggregate fineness, solid content (concentration or Baume) and other properties. At the same time, the coating operation must ensure the quality and thickness of the coating and prevent missing coating.

Recycling of old sand is to reduce and prevent mechanical adhesion. The most effective measure for sand and veins.

Pay attention to the operation to ensure the strength and surface stability of the casting (core). When mixing sand, the sand temperature should be controlled below 40C.

Add an appropriate amount of iron oxide powder or use chromium ore sand to the sand. The pouring temperature should not be too high.

3.Sand blasting and sand holes

Causes:

• Rough surface of the gate, lack of coating or insufficient coating thickness are often important reasons for sand holes caused by sand blasting
• Improper molding (core) operation causes poor surface stability. If the compaction is insufficient, the mold (core) surface is rough, the repair or filling of the hanging climbing does not reach the strength and bonding firmness is not enough, the molding sand that exceeds the usable time, etc., may cause sand blasting and sand hole defects

Countermeasure:

• The gate rod should be smooth
• The horizontal gate and the inner gate are best made with horizontal samples