Causes of defects
1) Casting and mold design
Sharp corners are easy to cause modeling breaks or scratches.
Deep concave holes are likely to cause poor compactness of the sand mold, porous sidewalls, and damage the sand mold when the mold is pulled out.
2) Mould
Molds that affect the compactness of the scouring sand, such as small-diameter recessed holes, will cause the scouring sand to become soft near the loose parts.
The rounded corners are too small, and the sculpting process is broken (injured).
The mold itself is too rough; especially the sidewall, it is easy to strain the sand mold when the mold is drawn.
The insufficient draft angle can easily cause damage to the sand mold when drafting.
Mould sticking may be the effect of the reaction of the paint and sand or the release agent on the mold itself.
The thickness of the hot core box mold is uneven, resulting in uneven heating.
3) Sandbox and its preparation
Any conditions that will cause the sand to be soft, such as the box belt design (the sandbox wall is bent diagonally) or the sandbox is too small.
4) Pouring and riser system
Pouring risers that lead to hot joints, these phenomena will produce mechanical or chemical sticky sand.
The formation of an inner gate with a high metal flow rate will produce sand washing near the inner gate, and sand holes will also be produced in other parts of the casting at this time.
5) Molding sand
The moisture of molding sand is too high or too low, too high moisture will cause mold sticking; too low moisture of green sand will reduce the strength and cause sand washing.
Hot sand will cause the self-hardening resin sand or sodium silicate sand to harden too fast and reduce the strength of the sand mold, or cause the moisture of the wet mold sand to evaporate and affect the strength.
Improper configuration of molding sand is the main factor causing rough surface; the main reasons are too coarse molding sand or improper particle size distribution.
There are too many low-melting materials in the molding sand, which is easy to cause chemical sand sticking at this time.
The content of carbon material in the molding sand is too high, a gas disturbance occurs during pouring, and the surface of the sand mold is cavities due to the burning of the carbon material.
Poor fluidity of molding sand, resulting in poor compaction.
An excessive amount of release agent.
6) core making operation
The sand is too coarse.
The core box is not clean-such as a residual mold release agent or mold sand.
All the reasons for the poor compactness of the sand core-this may be the main reason.
Improper use of paint, such as low Baume of paint or uneven application.
Excessive hardening of the sand core, for example, the temperature of the shell mold sand is too high or the time is too long to cause the sand mold to become brittle, or the water glass sand core is blown excessively to pulverize the sand core, etc.
Improper handling will scratch the surface of the sand core.
7) Modeling and fitting work
Poor compaction of the sand mold is the main reason for the rough surface of the casting.
The mold is the dirty-the same reason as the sand core.
Improper use of paint; for example, the uneven application will cause paint peeling and peeling, and paint Baume is too low.
Improper repair, such as poor tightness, excessive moisture, etc.-should start with avoiding repair.
An excessive amount of release agent.
8) Metal composition
Among the metal components, the metal component (or its oxide) that is easy to react with the molding sand is too high; this will cause chemical sticking; therefore, olive sand should be used for casting of manganese steel. Alloy steel with high chromium content should use chromium sand.
9) Melting operation
As long as the pouring temperature and metal composition are mastered, the melting operation has no effect on the surface roughness of the casting.
10) Pouring operation
For sand molds, too high a metal pouring temperature will cause sand sticking.
Improper skimming of the ladle caused oxides to enter the cavity and react with the molding material.
11) Other
Foreign inclusions.
Improper cleaning of castings, such as too thick shot blasting, insufficient time, etc.