What Are Our Concerns About Bearings（58）

Q1:Is the valve blank cast or sand cast?

A:There are mainly the following points about the difference between castings and forgings:

Castings are materials cast in a mold as a whole, its stress distribution is uniform, there is no limit to the direction of compression.

The forgings are made up of the same direction of force pressure, its internal stress is directional, can only bear directional pressure.

Forgings and forgings of the same material and the same wall thickness are superior to castings in terms of strength and crystal phase structure.

For valves, the wall thickness of castings of the same pound class and material is thicker than forgings. Its compressive strength is equal to the forgings.

Casting requirements for casting process are relatively high, the biggest characteristic is that you can make a more complex shape, the structure of the valve body and the flow channel are irregular, casting can be one-time molding, as long as the process passes, you can cast a large diameter valve body.

The density of forgings is better, but for too complex flow channels and shapes can not be formed at a time, often need to be modular, separate forging and welding together, so the size of the forgings is limited.

Forgings often fail to produce complex, streamlined channels. The flow channel is processed by turning, and many sharp corners are formed inside the transition, which is easy to cause uneven stress and cracking.

At the same time, the design of modular welding, forging valve seat caliber is relatively fixed, in some valve sizes, its caliber is small, affecting the flow capacity. The increase of valve resistance and the reduction of the efficiency of the whole system.

Due to the limitations of large size valve forging process, at the same time to save costs, many manufacturers usually use the body center part of the casting, both ends of the forging structure.

Whether castings, forgings. In processing, there is a possibility of product defects.

The main defects of castings are trachoma, bubble and so on. The main defects of forgings are large grain size, cold hardening phenomenon, cracks, cracking and so on.

In order to obtain qualified product quality, the corresponding casting needs heat treatment to eliminate the stress in the casting process, and X-ray, magnetic particle inspection, penetrant inspection and other detection methods are used.

For forgings, this requires strict heat treatment of the weld and the corresponding detection means to ensure. Forgings often require ultrasonic examination. In addition, it should be mentioned that the welding process is very strict, and the qualification of welding engineers is also the key to ensure the quality of products.

No matter what kind of raw material the valve uses, the manufacturer needs to have strict quality control procedures, standard testing procedures to ensure the quality of the valve.

Q2:Are there any standards for tempered and tempered samples?

A:GB/T13320-2007 is the metallographic structure rating diagram and evaluation method of steel die forgings. The depth of hardened layer and hardness test samples of quenched and tempered parts are not standardized

Q3:Why is ultrasonic testing more common than magnetic particle testing for castings?

A:Ultrasonic inspection and magnetic particle inspection, the purpose is different. Ultrasonic inspection mainly detects internal defects of workpiece, while magnetic particle inspection mainly detects surface defects such as cracks. The surface of the casting is not easy to crack, and the surface of the casting is rough, and it is not suitable for magnetic powder, so the casting is generally not required for surface detection.

Q4:After the 42CrMo forgings are normalized, how many grades can the grain size reach?

A:Even coarse grain can be corrected by subsequent heat treatment. Normalizing is merely a foundation for quenching.

Q5:How to keep processing allowance 45 steel forgings?

A:Generally, when free forging, 5mm machining allowance is left for rough machining on one side;  When die forging, 3mm machining allowance is left for rough machining.  

Q6:What is the difference between GB/T642-91 and JB/T1270-93?

A:GB/T642-1999 chemical reagent potassium dichromate  

Technical standard for shaft forgings JB-T1270-93  

Q7:What are the most common standards of stainless steel?

A:This g industry has GB/T4237-2007, GB24511 GB4238 NB/T47010  

GB13296 and so on plate, forgings, pipes and other standards.  Various industries with stainless steel are not the same, so the standard is also much  

Q8:How to classify industrial pipes according to pressure? What criteria to cite?

A:According to the pressure mode, it is divided into external pressure vessel and internal pressure vessel  

1. External pressure container  

When the internal pressure of the container is less than an absolute atmospheric pressure (about 0.1mpa), it is also called the vacuum container  

2. Internal pressure vessel (according to the design pressure P points)  

Low pressure (L) container 0.1mpa ≤ P < 1.6 MPa  

Medium pressure (M) container 1.6 MPa≤ P < 10.0 MPa  

High-pressure (H) container 10 MPa≤ P < 100 MPa  

Ultra high pressure (U) container P ≥100MPa  

Specification standard for pressure vessels —  

Such as China’s GB150 “Steel Pressure Vessel”  

JB4732 “Steel pressure Vessels — Standard for analysis and Design”  

JB/T4735 “Steel Welded Atmospheric Vessel”  

Technical regulations pressure vessel safety technical supervision regulations, etc  

Q9:What is standard duralumin?

A:Standard duralumin:  

A medium strength alloy in the aluminum-copper-magnesium series, Chinese brand 2A11(LYll), US brand 2017.  It is one of the earliest duralumin alloys, used in structures in various forms before 2024(American grade) alloys.  Today, 2All alloys are mainly processed into bars for forging and die forging.  

The main alloy composition (%) is A1, Cu(3. ~ 84.8), Mg(0.4 ~ 0.8), Mn(0.4 ~ 0.8).  The main strengthening phase is θ(CuAl2) phase, and there is a small amount of S(Al2CuMg) phase when the impurity silicon content is low (see aluminum alloy phase).  

The melting temperature of standard duralumin alloy in industrial production is 720 ~ 760℃, the casting temperature is 700 ~ 725℃, and the homogenization temperature is 495℃.  Hot plastic deformation performance is good, can be processed into plates, tubes, bars, profiles and forgings, hot rolling temperature 390 ~ 440℃, extrusion temperature 400 ~ 460℃, forging temperature 350 ~ 470℃.  The effect of heat treatment is large, quenching temperature is 500±51℃, natural aging is generally used, and qualified performance can be obtained above 96h.  

The typical mechanical properties of 2All alloy at room temperature are as follows: under annealing condition, roar is 180MPa, σ0.2 is 70MPa, δ 20%;  Under quenching and natural aging, σb is 425MPa, σ0.2 275MPa and δ 20%.  Medium corrosion resistance in the atmosphere, seawater corrosion resistance, aluminum coating, anodizing treatment and paint can improve the corrosion resistance.  Can not braze and gas welding, but argon arc welding, but low welding performance, spot welding performance is better.  The cutting performance of annealed material is low, and that of fully aged material is good.  

The alloy is used in the manufacture of moderate strength structural parts, such as aircraft skeleton, fixing joints and propeller blades in the aviation industry;  Manufactures all kinds of structural parts and accessories in the construction, shipbuilding and vehicle industries.  

Q10:What is meant by ASTM A105 ASME B16.11 standard?

A:ASTM A105 is the material standard for pipe wrought carbon steel materials, such as flanged, plug-welded and threaded pipe fittings, equivalent to no. 20 steel forgings  

ASTM B16.11 Insert Weld or thread type is the standard for forged pipe fittings.