The influence of molten iron superheat on the quality of malleable steel pipe fittings

The hot metal overheats, which is the primary condition for improving the quality of malleable steel pipe casting. Research on the metallurgical properties of molten iron found that cast iron still maintains an inhomogeneous state for a long time after melting. The specific reason is not fully understood for the time being. It is generally believed that molten iron contains a variety of impurities, some of which hinder the dissolution of graphite, so that solid graphite crystals dissolve too slowly in molten iron, resulting in non-uniformity of performance and organization. High temperature and overheating can speed up the dissolution of carbon and the homogenization of molten iron. The molten iron can get a series of benefits after entering high temperature and overheating.

The primary indicator of molten iron quality is the temperature of molten iron. Regarding the influence of molten iron overheating temperature on the quality of malleable steel pipe fittings, there have been different opinions in recent decades. One view is that the higher the molten iron superheat temperature, the better, which can refine the graphite and improve the mechanical properties of the casting; the other view is that the molten iron superheat temperature has a critical temperature. When the value exceeds this value, the quality of the casting decreases with the increase of the overheating temperature.

Although the casting process temperature of malleable steel pipe parts is not high, most of them are between 1260 and 1400 degrees Celsius. But from the point of view of obtaining high-quality molten iron, it should have a higher melting temperature. High temperature smelting ensures high iron tapping temperature, Fe, Si, Mn burns less, furnace conditions are stable, chemical composition fluctuations are small, high temperature smelting, S, Q, H, N and inclusions in the molten iron will be reduced, and the charge Bad heredity will be reduced.

1) At high temperature, the activity of carbon increases, and the activity of silicon decreases. The deoxidation effect of carbon on FO, MnO, SO2 and other oxides is dominant, which promotes the reduction of oxides, thereby effectively clearing the non-metallic inclusions in the molten iron. .

2) The hydrogen and nitrogen molecules in the molten iron are easily concentrated in the CO bubbles formed by deoxidation at high temperatures, and escape from the molten iron with the bubbles, thereby effectively clearing the gas in the molten iron.

3) At high temperature, the kinematic viscosity of molten iron decreases, the mass transfer is accelerated, and it is easy to achieve homogenization in convection and electromagnetic stirring.

Only the molten iron that has undergone high-temperature heat treatment can cast excellent malleable steel pipe fittings. The molten iron is released at high temperature and low temperature casting is the prerequisite to ensure the quality of malleable steel pipe castings.

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What are the surface inspections of casting products?

1. Liquid penetration testing

Liquid penetration testing is used to inspect various opening defects on the surface of castings, such as surface cracks, surface pinholes and other defects that are difficult to find with the naked eye. Commonly used penetrant detection is color detection, which is to wet or spray a colored (usually red) liquid (penetrant) with high penetrating ability on the surface of the casting. The penetrant penetrates into the opening defect and quickly wipes off the surface penetrant. Then spray the easy-drying display agent (also called developer) on the surface of the casting. After the penetrant remaining in the opening defect is sucked out, the display agent is dyed, which can reflect the shape and shape of the defect. Size and distribution. It should be pointed out that the accuracy of penetrant detection decreases with the increase of the surface roughness of the tested material, that is, the lighter the surface, the better the detection effect, and the surface detection accuracy of the grinding machine is the best, and even intercrystalline cracks can be detected. In addition to color detection, fluorescent penetrant detection is also a commonly used liquid penetrant detection method. It needs to be equipped with ultraviolet light for irradiation observation, and the detection sensitivity is higher than that of color detection.

2. Eddy current testing

It is suitable for checking the defects below the surface which are generally not more than 6-7mm deep. There are two types of eddy current testing: the placement coil method and the through coil method. When the test piece is placed near a coil with alternating current, the alternating magnetic field entering the test piece can induce a current (eddy current) flowing in an eddy current direction perpendicular to the excitation magnetic field in the test piece. The eddy current will Generate a magnetic field opposite to the direction of the exciting magnetic field, so that the original magnetic field in the coil is partially reduced, which causes the change of the coil impedance. If there are defects on the surface of the casting, the electrical characteristics of the eddy current will be distorted, thereby detecting the existence of the defect. The main disadvantage of eddy current testing is that the size and shape of the detected defect cannot be displayed visually. Generally, only the surface position and depth of the defect can be determined. In addition, it is not as sensitive as penetrant detection for detecting small opening defects on the surface of the workpiece.

3. Magnetic particle testing

It is suitable for detecting surface defects and defects several millimeters deep below the surface. It requires DC (or AC) magnetization equipment and magnetic powder (or magnetic suspension) to perform detection operations. Magnetizing equipment is used to generate a magnetic field on the inner and outer surfaces of the casting, and magnetic powder or magnetic suspension is used to display defects. When a magnetic field is generated within a certain range of the casting, the defects in the magnetized area will produce a leakage magnetic field. When the magnetic powder or suspension is sprinkled, the magnetic powder is attracted, so that defects can be displayed. The defects displayed in this way are basically defects that cross the lines of magnetic force, but they cannot be displayed for long-length defects parallel to the lines of magnetic force. For this reason, the magnetization direction needs to be constantly changed during operation to ensure that various defects in unknown directions can be detected. .

4. Radiographic testing

Generally, X-rays or γ-rays are used as the radiation source, so equipment and other ancillary facilities are needed to generate radiation. When the workpiece is exposed to the radiation field, the radiation intensity of the radiation will be affected by the internal defects of the casting. The intensity of the radiation emitted through the casting varies locally with the size and nature of the defect, forming a radiographic image of the defect, which is developed and recorded by radiographic film, or real-time detection and observation through a fluorescent screen, or detection by a radiation counter.

5. Ultrasonic testing

It is used to check internal defects. It uses sound beams with high-frequency sound energy to propagate inside the casting. When it encounters internal surfaces or defects, it reflects and finds defects. The magnitude of the reflected sound energy is a function of the directivity and properties of the inner surface or defect and the acoustic impedance of this reflector. Therefore, various defects or the sound energy reflected by the inner surface can be used to detect the location, wall thickness or surface of the defect The depth of the next defect. Ultrasonic testing, as a widely used non-destructive testing method, has its main advantages in: high detection sensitivity, which can detect small cracks; and large penetration capability, which can detect thick section castings. Its main limitation lies in: it is difficult to explain the reflection waveform of the disconnected defect with complex outline size and poor directivity; for undesirable internal structure, such as grain size, structure, porosity, inclusion content or fine dispersion Precipitates, etc., also hinder the interpretation of the waveform; in addition, the standard test block should be referenced when testing.

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What are the valve installation requirements?

1. Before installing the valve, carefully check whether the model and specifications of the valve used are consistent with the design;

2. According to the valve model and factory manual, check whether the valve can be used under the required conditions;

3. When lifting the valve, the rope should be tied to the flange connection between the valve body and the bonnet, and not tied to the handwheel or valve stem, so as not to damage the valve stem and handwheel;

4. When installing the valve on a horizontal pipeline, the valve stem should be vertically upward, and the valve stem should not be installed downward;

5. When installing the valve, it is not allowed to use the forced pairing connection method to avoid damage due to uneven force;

6. Rising stem gate valves should not be installed in damp underground places to avoid corrosion of valve stems.

Assembly requirements

The cleaned parts must be sealed and stored for installation. The requirements for the installation process are as follows:

1. The installation workshop must be clean, or set up a temporary clean area, such as newly purchased color striped cloth or plastic film, to prevent dust from entering during the installation process.

2. Assemblers must wear clean cotton overalls, cotton caps, no leakage of hair, clean shoes on feet, plastic gloves on hands, and degreasing.

3. The assembly tools must be degreased and cleaned before assembly to ensure cleanliness.

Decho is a professional supplier on valves , If you need any , pls contact us by email [email protected]

Problems that should be paid attention to when installing grooved pipe fittings

At present, the grooved pipe joint connection method is gradually promoted in various types of building installations. Its fast and reliable characteristics are being recognized by colleagues in the installation industry, and it is also widely used in fire protection engineering construction. However, what problems should be paid attention to when connecting rigid clamps and flexible clamps with different connection methods?

1. Install the rigid clamp on the DN≤250 pipeline according to the product manual provided by the manufacturer. Generally, satisfactory results can be obtained.

2. When connecting flexible clamps on DN≥300 pipelines, pay attention to the following installation details:

1) Quality of incoming steel pipe:

The tolerances of the outer diameter, wall thickness uniformity, and out-of-roundness of the pipe ends of the incoming steel pipe cannot exceed the standard requirements. When loading and unloading the steel pipe, it is necessary to prevent the deformation of the nozzle.

2) Measurement and visual inspection of pipe end before pressing groove:

Before the pipe end is grooved, check whether the end face of the nozzle is perpendicular to the center line of the pipe, whether the tolerance of the out-of-roundness of the nozzle exceeds the standard, and whether the burrs around the nozzle are removed and polished, such as the out-of-roundness or deformation of the nozzle , It must be removed.

3) Press groove processing:

For long steel pipe pressing grooves, support brackets must be installed, and ball bearing support points are installed on the brackets to reduce the fluctuation of pipe rotation during groove pressing. Strictly press the groove depth, which must meet the requirements of the product manufacturer’s instructions. During operation, attention should be paid to the rate at which the groove depth is gradually reached, and the mold that exceeds the service life should be replaced in time. When carrying, hoisting, loading and unloading the finished pipes, the pressure groove of the pipe mouth should be protected to avoid deformation.

4) Appearance quality of approach clamp:

Since large-diameter clamps are manufactured by ball milled cast iron sand molds, the manufacturing accuracy is affected by various factors. Therefore, the appearance should be sampled

5) Matters needing attention when installing the clamp:

The installation quality of the clamp, especially the installation quality of the flexible clamp, depends on the above-mentioned requirements: that is, the material of the pipe, the shape size, the deformation of the nozzle, the quality of the pressure groove, the quality of the clamp itself, and the size Ensure that all clamps are inserted into the groove.

6) Attention should be paid to the installation of large-caliber flexible clamps with DN≥300 and above:

Inspection of the material and appearance of the rubber sealing ring: The rubber sealing ring of each manufacturer varies according to the medium used, and its manufacturing material and formula are different, but the installation unit must ask the manufacturer for the same product quality commitment and rubber seal as its unit engineering service life The physical and mechanical performance test report of the ring should be free from damage and deformation in appearance inspection. Bubbles, impurities, cracks, and uneven defects on the rubber sealing surface are not allowed.

3 Installation of grooved pipe fittings:

a. Touch the grooves and holes by hand and observe with eyes for a week. There should be no remaining burrs, breakages, or cracks.
b. Lubricant is spread around the rubber sealing ring and then clamped on both ends of the steel pipe by hand. At this time, ensure that the tension around the rubber sealing ring is basically the same.
c. Two pieces of grooved pipe fittings, tighten the bolts symmetrically on both sides, so that the gap between each groove is basically equal. When it is close to tighten and not in close contact with the rubber seal ring, use both hands to rotate the grooved pipe fittings to make the entire pipe and the sealing ring evenly contacted. Observe that each piece of the grooved pipe fitting has entered the groove, and then tighten the bolts symmetrically and successively. . When tightening, the sealing ring is found to be wrinkled and raised, and the sealing ring should be replaced.

4. It is necessary to ensure that the convex edge of the grooved pipe fits into the groove and then tighten the bolts symmetrically on both sides.

This “knocked-in” means that the protruding embedment located on the protruding edge of the grooved pipe fitting and having the same height as the depth of the pipe groove should be flush with the concave embedding that appears after the nozzle is pressed. The flange of the finished clamp sometimes appears too thick, deformed, or even twisted too much. If it can be repaired on site, it can be repaired. If it cannot be repaired, it can only be discarded and replaced with another. This requires on-site operators to observe and inspect one by one, and basically meet the requirements before installing to avoid rework.


Decho is a professional supplier on grooved pipe fittings . If you need any , pls contact us by email [email protected]

Advantages and disadvantages of Dacromet bolts

Dacromet bolt is the transliteration and abbreviation of English DACROMET. Dacromet is a new kind of surface treatment technology. Compared with the painful electroplating technology, Dacromet can be said to be a kind of “green plating”. So, what are the advantages of Dacromet bolts compared with other bolts?


1. Although the thickness of the Dacromet film is only 4-8μm, its anti-rust effect far exceeds the traditional electro-galvanizing, hot-dip galvanizing or paint coating method, so Dacromet bolts also have excellent anti-corrosion properties. Rust effect.

2. Dacromet’s processing technology determines that Dacromet bolts will not appear hydrogen embrittlement, so Dacromet bolts are very durable.

3. Dacromet bolts are very resistant to high-temperature corrosion, and the heat-resistant temperature can be as high as 300℃. The traditional galvanizing process is far inferior to it.

4. Good adhesion and recoating performance: The coating on Dacromet bolts can produce good adhesion with the metal substrate in contact, and it has strong adhesion with other coatings. The processed parts are easy to color. The bonding force with the organic coating even exceeds that of the phosphating film.

5. Dacromet bolts will not produce gas and sewage that are good for the natural environment during the entire process of production, processing and coating coverage, and no subsequent treatment is required, which greatly reduces the treatment cost.


Although Dacromet bolts have many advantages, some of its disadvantages cannot be ignored.

1. Some Dacromet bolts contain chromium ions that are harmful to the environment and human body. Chromium ions can cause very serious consequences, especially the role of hexavalent chromium ions that can cause cancer, which should be paid attention to.

2. The coating surface color of Dacromet bolts is single, only silver white and silver gray, which is not in line with today’s personalized society. Although there are other ways to add color to it, there are some troubles after all.

Decho is a professional supplier on dacromet bolts , if you need any , pls contact us by email [email protected]

Precautions for Dacromet bolt application and causes of rust

Dacromet bolts are bolts with Dacromet plated on the bolt surface. It is a new type of surface treatment technology. Compared with the traditional electroplating process, if you only compare the anti-corrosion and oxidation functions, hot-dip galvanizing and mechanical galvanizing are better choices. However, in addition to these two points, these two surface treatment methods make it more difficult to match the bolt and the nut due to the thickening of the surface of the bolt. Therefore, considering more aspects, Dacromet bolts are a better choice.

Dacromet bolts still use a kind of “green plating” bolts. It is more environmentally friendly than ordinary galvanizing, mechanical galvanizing and hot-dip galvanizing and will not cause pollution.

Pay attention to the following items in the process of using Dacromet bolts:

1. Dacromet bolts will age rapidly when exposed to light, so the coating process should be carried out indoors.

2. If the baking temperature of Dacromet bolts is too low or too high, it will lose its anti-corrosion ability. Therefore, Dacromet bolts should be baked in a suitable temperature range.

3. The life cycle of Dacromet bolts is very short and should be used up as soon as possible.

4. Dacromet bolts have poor wear resistance, so they should be sealed with other wear-resistant coatings after the bottom coating.

Reasons for the rust of Dacromet bolts

Also pay attention to the rust of Dacromet bolts. There are four reasons for the rust of Dacromet bolts:

1. Use treated Dacromet bolts with lock washers. Due to the different corrosion potentials of the two metal materials, Dacromet bolts with lower potentials are more likely to be corroded.

2. The coating on the surface of the Dacromet bolt is not evenly covered, and the rust will start in the uncovered area.

3. Because the pretreatment did not remove the rust on the rough embryo, red rust will appear from under the coating.

4. Dacromet bolts are not resistant to acid and alkali, so the acid and alkali environment is also the cause of rust.

Decho is a professional supplier of dacromet bolts , if you need any , pls contact us by email [email protected]

What problems are prone to occur during the use of Dacromet bolts?

When people use Dacromet bolts, there will always be problems of one kind or another. Let’s analyze together what causes such problems.

1. Material reasons:

The threads of Dacromet bolts made of stainless steel, aluminum alloy and titanium alloy often lock or jam. These types of metal alloys have good ductility and are fundamentally different from materials such as carbon steel. The specific differences are as follows: Dacromet bolts have anti-corrosion properties, and when the surface is damaged, a thin oxide layer will be produced on the metal surface to prevent further and deeper corrosion. When the Dacromet bolt is locked, the pressure and heat generated between the teeth will destroy and erase the chromium oxide layer between them, causing the metal teeth to directly block or shear, and then adhesion occurs. When the adhesion phenomenon continues, the Dacromet bolt will be completely locked and can no longer be removed or locked. Usually, this series of blocking, cutting, pasting and locking actions will happen in a short time. Therefore, understanding the characteristics of the product and following the correct operation method is the first step to prevent Dacromet bolts from locking.

2. Reasons for the jam:

(1) When assembling and matching bolts and nuts produced by the same heat number, the possibility of Dacromet bolt locking will increase.

(2) The influence of thread accuracy. The matching of external thread grade 6H and internal thread 6H will increase friction.

(3) In the material composition, the higher the copper content, the higher the possibility of thread locking. However, due to the deformation of cold forging, materials with higher copper content may be used when manufacturing Dacromet bolts. The materials used may cause the Dacromet bolts to be locked.

The above are the problems that may occur during the use of Dacromet bolts and the reasons for these problems. I hope it can be helpful to everyone.

Decho is a professional supplier of bolts and nuts. If you need any , pls contact us [email protected]

What are the methods to clean Dacromet bolts?

Heat treatment technology is an important part of advanced manufacturing technology and also plays a very important role in the development of Dacromet bolts and high-end mechanical equipment. As we all know, there is no “chemical composition” will not be called a material, similarly, without “heat treatment” can not be called a material. Through heat treatment technology, the performance of Dacromet bolts can be greatly improved. But there is a problem that cannot be changed by heat treatment, and that is the rust of Dacromet bolts.

Sometimes it is found that the dacromet bolts fixed on the machine are rusty or dirty. In order not to affect the use of the machine, how to clean it has become a very important issue. This makes the performance of Dacromet bolts inseparable from the cleaning agent. Only regular cleaning and maintenance of Dacromet bolts can better play its role. Therefore, here are some commonly used cleaning agents to help you clean up daily.

1. Soluble emulsifying cleaner. This cleaning agent usually consists of emulsifiers, soil, solvents, builders, corrosion inhibitors and a small amount of water. The role of water in the upright cotton is to dissolve the emulsifier. This cleaning agent treatment can dissolve the dirt on the surface of the Dacromet bolts, and it will cause other substances to react during the cleaning process, leaving a layer of anti-rust film on the surface. Emulsifiers and detergents can hold the grease particles on the surface of Dacromet bolts and dissolve them in detergents containing solvents and oils.

2. Alkaline cleaner. Alkaline cleaners are actually a mixture of builders and alkaline earth metal salts of surfactants. It is a widely used cleaner. When maintaining Dacromet bolts, the pH of the cleaning agent is about 7.

The main purpose of using the above two cleaning agents is to ensure the cleaning effect, and secondly because these two cleaning agents are cheap and cost-effective.

Tianjin Decho International Trade Co.,Ltd is a professional supplier on bolts and nuts products . If you need any , pls contact us by email [email protected]

Dacromet bolts play a very important role in the development of the machinery industry

Looking at the development trajectory of the world, we can intuitively see that the current industry is different from the past industry development. It is closely related to our production and life. Our life is inseparable from the development of the machinery industry. The development of the machinery industry is inseparable from the development of Dacromet bolts. No matter how small our Dacromet bolts are, they are unobtrusive. Once the machinery industry cannot continue to use them, serious consequences will occur. It cannot be said that the entire machinery industry is completely paralyzed, at least, most of its industries will suffer a huge blow. Nothing will go smoothly, it may affect the progress of the project. If the situation is serious, the entire project may not be able to continue without Dacromet bolts.

What incredible things will happen if Dacromet bolts are lost in mechanical engineering. In the investigation of the entire machinery industry, almost all relevant personnel believed that Dacromet bolts are a small part, but they shoulder considerable responsibility. It is very important in engineering operations, it is necessary to link, you can use it wherever you need it. It can be said that if there is no Dacromet bolt, the link cannot be carried out, which will slow down the progress of the entire project.

Once the Dacromet bolt is ignored, it will cause a lot of trouble. If you use it, but don’t see its location correctly, some accidents may happen. For example, if the connection is not tightened, when the object is lifted, if the object is heavy, it may break, resulting in a construction accident. If this happens, you need to treat and check the Dacromet bolt carefully during use, so that this kind of situation can be avoided.

Decho is a professional supplier on Dacromet bolts. If you need any , pls contact us by email [email protected]

Some tips on buying gasket products

At present, gaskets will also be widely used in many industries. Regardless of their small size, they can play a very important role. So how do we choose when we need a gasket?
1. The type and scope of gaskets should conform to the design documents and current effective standards of the country and related industries. Changes in gasket materials and usage standards must be approved.

2. There are many factors that affect the selection of gaskets. Generally, on the premise of ensuring safe operation, you can try to choose a gasket that is cheap, easy to manufacture, easy to install and replace.

3. The thickness of the gasket depends on the specific situation. Generally speaking, if the sealing surface is well treated and the pressure is not too high, a thin gasket should be used. However, when the internal pressure is high, the washer is too thin, which is not conducive to the extension of the bolt, and the rebound of the washer is too small to achieve the required amount of recovery, which may cause leakage. Therefore, when the pressure is higher, a thicker gasket should be selected.
4. In order to ensure the interchangeability of gaskets, the specifications and materials should be unified as much as possible when selecting models. When considering meeting the requirements for use, specifications and materials should be combined as much as possible, and unnecessary problems should be avoided.

5. It is not allowed to use edgeless high-strength gaskets under the conditions of medium gas and high pressure, and corrugated gaskets are also not allowed to be used on serpentine and grooved flanges.

6. Special requirements should be paid attention to. If a certain medium does not allow mixing of fine fibers, fiber gaskets should not be used. If some parts will vibrate violently, you need to choose a gasket with strong vibration resistance, resilience and durability.

7. The gaskets connected to the valve and flange at the bottom of the liquefied balloon tank should be spiral wound gaskets with metal protective rings.

8. When using gaskets, they should be used in a fully annealed state, and softer materials should be used as much as possible. The hardness of the gasket should be lower than the flange sealing surface.

9. The replacement principle of gaskets on imported equipment is to replace the types and materials as they are. When the gasket form or material needs to be replaced due to special reasons, approval is required.

Decho is a professional supplier on gasket products, if you need any , pls contact us by email [email protected]