Machining surface finish

Surface finish is another term for surface roughness. The surface finish is put forward according to the human visual point of view. Meanwhile, the surface roughness is put forward according to the actual surface micro-geometry. Because of its conformity with international standards (ISO), China adopted surface roughness after the 1980s and abolished surface finish. After the promulgation of the national standards for surface roughness GB3505-83 and GB1031-83, the surface finish is no longer used.

There are corresponding comparison tables for surface finish and surface roughness. Roughness has a calculation formula for measurement, while smoothness can only be compared with a model gauge. Therefore, the roughness is more scientific and rigorous than the finish.

Machining surface finish and surface roughness comparison table

Inspection Rules of Gray Cast Iron

•  Inspection rights

1. The supplier quality department has the right to inspect and accept or not the castings.
2. The buyer may request re-inspection of castings when necessary.
3. The supplier is responsible for the authenticity of the inspection results; and submits the production record documents when required by the buyer.

• Inspection location

1. Except for the agreement between the supplier and the buyer, the supplier carries out final inspection generally.
2. When the supplier and buyer dispute the quality of castings, the inspection may be carried out by a third party. And the third party should has laboratory qualification.

• Division of sampling batches

The supplier must test the castings for chemical composition, mechanical properties, and metallography in batches. The batch is divided as follows:

1. Castings cast by the same molten iron from the same furnace constitute a sampling batch.
2. Castings casted from the same ladle of molten iron constitute a sampling batch.
3. The maximum weight of each sampling batch is 2000 kg of castings after cleaning. The sampling batch may changes upon agreement between the supplier and the buyer.
4. If the weight of a casting is larger than 2000 kg, it will become a single sampling batch.
5. Within a certain time interval, if the furnace charge, process conditions, or chemical composition changes, all castings cast by molten iron during this period, no matter how short the time interval, are regarded as a sampling batch.
6. When continuously melting a large amount of molten iron, the maximum weight of each sampling batch shall not exceed the weight of castings poured within 2h.

In addition to the provisions of 10.3.2, if a grade of molten iron has a large amount of melting, and adopts a system-controlled melting technology and strict monitoring of the production process, and can carry out a certain form of process control on a bale (furnace) basis, such as chilling tests, chemical analysis, thermal analysis, etc., upon agreement between the supplier and the buyer, several batches of castings may also constitute a sampling batch.

• Test times

At least once of each sample test.

• Evaluation of test results

1. When testing the tensile strength, first use a tensile specimen to test, if it meets the requirements, the batch of castings is qualified in the material; If not, you can take another two samples from the same batch for re-testing.
2. In case the results of the re-inspection all meet the requirements,  the material of this batch of castings is still qualified. If one of the re-inspection results still fails, this batch of castings were preliminarily judged to be unqualified. At this time, one casting should be taken out of the batch. And the cast body sample should be cut out at the site agreed by the supplier and the buyer for tensile strength testing. If the test result meets the requirements, it can still be judged that the batch of casting materials are qualified; if the body sample test result fails to meet the requirements, it can be finally determined that the batch of casting materials is unqualified.

• Effectiveness of the test

When the test result does not meet the requirements due to one of the following reasons, the test is invalid.

1. Improper installation of the sample on the testing machine or improper operation of the testing machine.
2. The surface of the sample has casting defects or improper cutting (such as sample size, transition fillet, roughness does not meet the requirements, etc.)
3. The sample breaks outside the parallel section.
4. There are casting defects on the fracture after cutting the sample

At this time, the supplier should repeat the test according to 10.5.1 and 10.5.2, and replace the data of the defective sample with the obtained results.

•  Saving test data

The supplier shall check in accordance with this standard, and be responsible for the accuracy and authenticity of all test results completed. The supplier shall use its own or other reliable equipment to save all complete test and inspection records, for further review.

• Sample storage

If the buyer has no special requirements, the supplier should store the same batch of tensile specimens and untested specimens  for more than three months from the date of filling in the test report.

Ductile Cast Iron EN-GJS-400-15/GGG40

EN-GJS-400-15 ductile iron is a very common material in European standard DIN EN 1563.

It is equal to GGG40 in DIN 1693, QT400-15 in China, A536 60-40-18 in USA ASTM, GS400-12 in Italy, FCD400 in Japan, FGS400-12 in France, FNG42-12 in Belgium, SJK-400 in Norway and ISO 1083 400-15.

Now, let me introduce its mechanical properties, chemical composition, foundries and castings to you.

Properties of EN-GJS-400-15/GGG40 cast iron

Tensile strength ≥ 400 Mpa.
Yield strength ≥ 250 Mpa.
Elongation ≥ 15%.
No impact requirement.

Hardness of EN-GJS-400-15/GGG40 cast iron

The hardness of this ductile cast iron grade is between 130-180 Brinell hardness.

Density of EN-GJS-400-15/GGG40 cast iron

The density of this ductile iron grade is about 7.3 g/cubic centimeter, or 7.3 kg/liter.

Chemistry composition of EN-GJS-400-15/GGG40 cast iron

According to the standard DIN EN 1563 and DIN 1693, the foundries could adjust the chemical composition as long as the mechanical and physical properties of the castings could meet the requirements in Standards.

The following chart is an approximate chemical composition range for your reference.

Foundry of EN-GJS-400-15/GGG40 cast iron

These ductile iron castings were produced by Yide Casting in China.

Cast Iron Wheel Hub Shell

Engine Base Ductile Iron

Auto Part Cast Iron Bracket

Ductile Iron Auto Parts

Ductile Iron Casting Auto Flange

Cast Iron Fire Truck Parts Casting

How to Prevent Ductile Iron Castings from Bursting in Winter

The quality of ductile iron castings is generally evaluated by the spheroidization rate.

The more rounded, finer, and evenly distributed graphite, the smaller the splitting effect on the metal matrix. And the smaller the stress concentration caused, the better the performance of ductile iron. Process quality control of ductile iron castings is very important. It is necessary to inoculate and spheroidize the molten iron, do a pre-furnace test, and strictly control the composition. Meanwhile, add appropriate inoculants and nodulizers according to the weight of the molten iron. At the same time, strictly control the pouring time of each ladle of molten iron. Thus in order to prevent graphite decay in the later stage of pouring.

Ductile iron castings are based on mechanical properties as the acceptance criteria. After pouring, sampling for performance tests can promptly find out whether the castings have quality problems. The problems include inoculation, poor spheroidization, or graphite decline. In addition, winter is the season where casting quality problems occur frequently. The low ambient temperature will cause the molten iron to cool too quickly. This will result in supercooled graphite or excessive pearlite. Therefore, we should pay attention to the heat preservation of the casting after casting the molten iron in winter.

Now, let me introduce how to prevent ductile iron from bursting in winter in detail.

The matrix structure of ductile iron parts is mainly included ferrite and pearlite, and a small amount of cementite and phosphorus eutectic as well. Castings with more ferrite content and less pearlite content have good toughness and low strength. Otherwise, the castings have high strength and poor toughness.

Many equipments and objects are also repellent to winter, and ductile iron castings are also a typical one. What is the threat to ductile iron castings in winter? In fact, the main problem is that ductile iron parts will explode in a low temperature environment. The temperature in winter will definitely be lower, but this will not affect the performance of ductile iron parts themselves. It is mainly because of the special composition of the object that it has both good toughness and steel strength. Therefore, it is also ideal in terms of elongation, and it can operate normally even at low temperatures.

However, the fluid medium in the ductile iron parts will not be able to withstand the threat of low temperature. And under this circumstances the castings may burst. In order to avoid such problems, if the critical point of the fluid is relatively low, we can add some antifreeze appropriately. Or take proper heat preservation treatment for ductile iron castings. Those preventions are effective.

If you want to solve the problem at the source, you can also choose a ductile iron material with a better low-temperature anti-freezing material from the beginning. However, the requirements and conditions for the technical process are very harsh. Yet the investment cost will be relatively high. Thus this must be carefully considered.

Yide casting is a leading casting foundry in China, with 27 years’ experience, produces top quantity ductile iron castings. If you are interested in our cast iron, please feel free to contact us for more details on casting.

Appearance Inspection Method of Ductile Cast Iron

Ductile cast iron is a high-strength cast iron material whose comprehensive properties are close to steel. Based on its excellent properties, it has been successfully used to cast some parts with complex forces and high requirements for strength, toughness and wear resistance. Ductile cast iron has rapidly developed into a cast iron material second only to gray cast iron and widely used. The so-called “substituting iron for steel” mainly refers to ductile iron.

Generally, the technical requirements of ductile iron castings mainly include: mechanical properties, geometric shapes and dimensions, surface quality and defects.

The appearance of ductile iron parts is not allowed to exist the following defects:

1. Macroscopic defects such as pores.

2. Sand inclusion.

3. Slag inclusion.

4. Porosity or shrinkage.

5. Microscopic defects such as poor spheroidization and excessive crystal grains.

Ductile cast iron parts should not be too dry or too wet. Too dry will cause the mold to fail to fall off. And too wet to easily fall off. After the molding sand of ductile iron parts is molded, the internal surface should be dried with a coating agent. So as to prevent the molten iron from impacting the sand mold and causing the sand, and mud to enter the inside of the cast iron. The method of drying the coating agent for ductile iron parts is generally igniting and drying. Because the coating agent is containing alcohol, cold iron is added to some sand molds. The role of cold iron is to accelerate cooling and reduce shrinkage.

The inspection of ductile iron parts includes appearance inspection, magnetic particle inspection and ultrasonic inspection.The appearance inspection is a heavy work in ductile iron parts, which requires a lot of grinding cooperation.

Generally speaking, the appearance inspection requirements of ductile iron parts should meet the following points:

1. No cracks, no welding, no surface non-metallic inclusions and sanding.

2. Surface cleanliness reaches Sa 2.5.

3. Surface roughness reaches A2.

4. Pores reaches C2.

5. Cold barrier reaches D1.

6. No mechanical scratches.

In the appearance inspection of ductile iron parts, we should pay special attention to the difference between surface pores and surface blisters.

Generally, surface pores are smooth and regular on the inner wall. While the surface blisters are relatively irregular and contain more dust or sand and other nonmetallic impurity. If the surface recesses of ductile iron castings are pores, it can be compared with the SCRATA test block. If it is judged to be the surface blisters, they generally need to be polished and repaired, because the roots of most blisters will extend into the metal. When the shot peening effect of ductile iron parts is not good, the roughness will not meet the requirements. If there are oxide scales on the surface of ductile iron parts and large-area surface defects that are difficult to polish, such as smears, re-shot blasting or polish should be considered. Because this type of defect will affect the appearance inspection, and it is particularly easy to miss the inspection of the surface sand.

Do you understand the above knowledge points about ductile iron castings? If you need to know more about ductile iron castings, please pay attention to our website.

Yide casting is a leading casting foundry in China, with 27 years’ experience, produces top quantity ductile iron castings, if you are interested in our casting fitting, please send us a drawing file, and please don’t hesitate to contact us for more details.