What causes the rough surface of castings? Is there any effective solution?

Reasons: 1. The embedded material particles are coarse and not delicate after stirring.

2. Roasting. If the heating rate is too fast, the expansion difference will occur at different positions in the cavity, which will cause the inner surface of the cavity to peel off.

3. The maximum temperature of roasting is too high or the roasting time is too long, which makes the inner surface of the cavity too dry.

4. The roasting of the casting is not sufficient during the die-casting production, and when the molten metal is injected, it causes the decomposition of the embedding material, produces more gas, and produces pitting on the surface of the casting.

5. After the molten metal is injected, the local temperature in the cavity is too high, and the surface of the casting is locally rough.

Solution: 1. Don't overmelt the metal.

2. The roasting temperature of the mold should not be too high or too low.

3. Coat the wax type with a liquid to prevent burning.

4. Avoid the phenomenon of depression in the direction of the casting road.

There are many reasons for the roughness of the surface of the casting: the embedded material particles are coarse and not delicate after stirring; If the roasting temperature rises too fast, the expansion difference occurs at different positions in the cavity, which makes the inner surface of the cavity peel off; The maximum temperature of roasting is too high or the roasting time is too long, so that the inner surface of the cavity is too dry, etc., the solutions are: do not over-melt the metal; The roasting temperature of the mold should not be too high or too low; Casting companies such as Jincheng Precision Co., Ltd., which coat wax molds with liquids to prevent burning, are doing a good job in these areas.

Steel castings in the production of not only pay attention to the quality of the problem, but also the appearance of the product also needs to pay special attention, the following is a list of specific reasons for the rough surface of the casting:

1. The particle size of molding sand and core sand is too coarse;

2. The compactness of the sand mold and sand core is low or uneven;

3. The coating quality of the core is poor, the coating thickness is uneven, and the coating peels off;

4. The pouring temperature and pouring height are too high, and the metal hydraulic pressure is large;

5. The height of the upper box or pouring cup is too high, and the hydrostatic pressure of the metal liquid is large;

6. Molding sand and core sand contain too much clay, binder or fusible additives, low fireability and poor thermal conductivity;

7. There are too many ridges in the core sand of the reused sand, too much fine crushed sand, dust, dead clay and iron * sand in the reused sand, and the sintering temperature of the molding sand is low; Orb sand.

8. The casting is unpacked and sanded too late, forming solid hot sticky sand, especially thick castings and high melting point alloy castings;

9. The molten metal has good fluidity and low surface tension. For example, the phosphorus and lead content in the copper alloy is too high, and the phosphorus, silicon and manganese content in the cast steel is too high;

10. The oxides and low-melting compounds in the molten metal react with the molding sand to generate low-melting point compounds such as ferrous silicate and ferrosterite, reduce the surface tension of the molten metal and its fluidity, so that the low-melting point compounds and molten metal penetrate into the sand grain gap through the capillary action mechanism, and in the process, the sand particles are continuously eroded, so that the sand particle gap expands, resulting in mechanical sand sticking or Layan chemical sticking sand.

Common defects in castings and their causes are:

1. Stomatae. The cause of pores is that there is too much moisture in the molding material or a large amount of gassing substances; The air permeability of molding sand and core sand is poor; The pouring speed is too fast.

2. Trachoma. The causes of sand hole are: insufficient strength of molding sand; insufficient compactness of molding sand; pouring speed is too fast, etc.

3. Shrinkage porosity. The reason for the leakage of the hole is that the casting is poorly replenished during the solidification process.

4. Sticky sand. The reason for sand sticking is the poor fire resistance of the molding sand or the high pouring temperature.

5. Cracks. The reason for the crack is that the wall thickness of the casting is very different; improper opening of the gating system; The new difference between the sand mold and the core, etc.

Brief introduction of castings: castings are metal forming objects obtained by various casting methods, that is, the smelted liquid metal is injected into the pre-prepared casting mold by pouring, injection, suction or other casting methods, and the objects with a certain shape, size and performance are obtained after cooling and subsequent processing methods such as grinding.

Casting use: The use of castings is very wide, has been used in hardware and the entire mechanical and electronic industry, and its use is becoming an expanding trend. The specific industries used are construction, hardware, equipment, construction machinery and other large machinery, machine tools, ships, aerospace, automobiles, locomotives, electronics, computers, electrical appliances, lamps, etc.

The surface of any machined part is actually not a completely ideal surface, because the machined surface always has a certain degree of microscopic unevenness, residual stress, cold hard bending and metallographic structure changes. Although such problems only exist in extremely thin surface layers, they intricately affect the accuracy, wear resistance, retention of mating properties, corrosion resistance and fatigue strength of mechanical parts, thus affecting the performance and service life of the product. Therefore, it should first understand its impact on the performance of the part.

1 The effect of surface quality on wear resistance is well known, when the two interacting surfaces move relatively, because friction will consume a lot of useful energy, about 1 3 of the world's energy is consumed by useless friction. The main cause of frictional resistance is due to the rough and uneven surface of the parts. The rougher the surface, the greater the coefficient of friction and the more severe the wear.

If the machining surface of the part is rough and uneven, when the two parts rub against each other, not all the surfaces are in contact, but only some convex peaks are in contact. According to the test, the actual contact area of the machined surface after turning and milling is 15% and 20%; The finely ground surface is 30% 50%; The surface that has been super-fined, skillfully ground and ground is 90% 97%. Real [ooo

The higher the different surface roughness values, the rougher the surface.

than the accuracy is one level higher.

Drawings have different requirements.

For example, the technical requirements for part drawings usually include:

Requirements for blanks. For example: casting Bichun parts and forgings are not allowed to have casting (forging) defects; Fillet is not injected; Draft slope, etc.

Requirements for heat treatment. For example; Quenched and tempered HRC28---32; Quenching HRC45---50; Wait.

Surface treatment. Such as: non-processing surface coating anti-rust primer. Wait.

Other requirements that need to be explained in writing.

1. The higher the surface roughness value, the rougher the surface.

6 than the accuracy of one level higher.

3. The commonly used surface roughness values are05, 25, 50, in microns.

4. Mechanical drawings often have: geometric tolerances and surface treatment.

1. The higher the surface roughness value, the rougher the surface.

6 than the accuracy of one level higher.

3. The commonly used surface roughness values are05, 25, 50, in microns.

4. Mechanical drawings often have: geometric tolerances and surface treatment.

The main causes of surface roughness during part machining are friction between the tool and the workpiece surface, built-up edge and vibration of the process system.

There are several factors that affect the surface roughness of machined parts produced by a machining center, and there are several steps that can be taken to improve the surface roughness: Optimize cutting parameters: Adjusting cutting parameters such as cutting speed, feed rate, and tool sharpness can help produce a smoother surface on machined parts.

Use high-quality cutting tools: High-quality cutting tools with well-maintained cutting edges and correct geometry can produce a smoother surface on the machined part. Reduced cutting forces:

Reducing cutting forces helps to reduce surface roughness by reducing energy and vibration during machining.

This can be achieved by optimizing cutting data, reducing cutting speeds, or using more advanced cutting tools. Use proper cooling and lubrication: Proper cooling and lubrication can help reduce heat accumulation during machining and reduce residual stresses in machined parts, both of which can help improve surface roughness.

Proper machine maintenance: Regular maintenance of the machining center, including regular cleaning and inspections, helps to minimize wear and tear on machine components and ensures that the machine is in optimal operating condition, which can help improve surface roughness.

Generally, it includes degreasing and rust removal and activation, two processes, the quality of pretreatment is the key to the success or failure of blackening at room temperature, that is, the degreasing must be thorough, and the surface activation is moderate (that is, the fresh metal surface is exposed, and there is no excessive corrosion). For castings, pay attention to the following three points:

Remove the oxide scale by mechanical means. Such as: rolling, sandblasting, polishing, grinding, etc. Some castings are treated by this method, and then cleaned with water, which can be directly blackened or other anti-rust treatments. ②

Start by soaking or washing with clean water. Before the workpiece is chemically degreased and rusted, the workpiece is cleaned (soaked) first, one is to clean the workpiece first, and the other is to fill the pores on the surface of the workpiece with water, which is convenient for cleaning after chemical treatment. Degreasing, rust removal and activation.

Due to the pores on the surface of the casting, it is difficult to remove after being polluted, especially the oil stain, and the poor treatment will have an impact on the entire anti-rust treatment and fail to achieve the expected purpose, including iron, copper, aluminum, etc. and its alloy castings. There are many ways to remove oil. Such as:

Chemical degreasing, mechanical degreasing, baking degreasing, ultrasonic degreasing, electrolysis and organic solvent degreasing, etc. Rust removal and activation are generally treated with hydrochloric acid solution or dilute sulfuric acid (15 20%) at medium temperature.

1.Pre-treatment: sandblasting.

2.Final treatment: plating or oxidation or spraying.

QPQ treatment can be carried out, mainly anti-rust.

1. Porosity: too much moisture or a large amount of gassing substances in the molding material; The air permeability of molding sand and core sand is poor; The pouring speed is too fast.

2. Sand hole: the strength of molding sand is not enough; insufficient compactness of molding sand; pouring speed is too fast, etc.

3. Shrinkage porosity: the casting is poorly repaired during the solidification process;

4. Sticky sand: the fire resistance of molding sand is poor or the pouring temperature is too high;

5. Cracks: the wall thickness of the casting varies greatly; improper opening of the gating system; The new difference between the sand mold and the core, etc.

This is complicated, please refer to the relevant casting manual.