The plasma arc combustion mode of surfacing raw material for gate valve processing

The plasma arc combustion mode of surfacing raw material for gate valve processing

Forging, forging, forging steel valve simply said is mainly used for forging stainless steel gate valve, forging steel refers to the selection of forging method and produced by a variety of forging and casting steel parts.
The relative quality of forged steel valve stainless steel castings is high, can withstand the impact force effect, plasticity, toughness and some other aspects of the physical properties are higher than stainless steel castings, so whenever some important machine parts should be used in forged steel, forged steel is generally used for high pressure pipeline.
With a delicate mechanism, suitable for high pressure work characteristics.
Forging is one of the two components of casting. The key parts with high load and complex working nature in mechanical equipment are mostly cast steel parts, which are simple and can be cold-rolled welds, except for aluminum profile plates.
Welding holes and as-cast looseness of metal composites can be eliminated by forging.
Accurate selection of forging check to improve product quality, cost control has a great relationship.
The main forging materials are carbon steel, stainless steel plate and carbon steel.
Forging ratio refers to the ratio of the total cross-section area of the metal material before the deformation to the die breaking area after the deformation.
The original state of raw materials includes casting, round rods, shape memory alloys and metal powder.
The physical properties of steel castings are generally better than those of the same raw materials. Forging is made by pressing the metal embryo with forging equipment, so that the shape of the alloy embryo can be changed to obtain a processing technology with certain shape specifications and good physical properties.
Forging steel valve structure processing technology: valve body quality and characteristics directly affect the service life of gate valve operation and safety factor.
Therefore, the forged valve body should be used under the premise of poor working environment or high safety requirements of gate valve.
For DN50 stop valve, stop valve, check valve, etc., most of the domestic use the overall forging forming after welding on both sides of the flange process, there are also manufacturers connected flange forging together.
But for 2 inches above the small caliber valve body, because of the lack of forging required by the super heavy multi-directional forging machine equipment, want to achieve industrialization of large overall forging parts there is a certain difficulty. Therefore, many manufacturers from the import of large and medium-sized valve body casting, or with some companies in other countries to develop the application of forged valve body parts.
Taichenson shared a new technology application of shearing extrusion for valve body of large and medium sized forged steel valve. By taking advantage of its advantages of environmental protection, energy saving and labor saving, according to the experimental research on valve body forming technology, the technology index of shearing extrusion for valve body was obtained.
The whole process of shear – extrusion forming should take shear deformation as the main process of metal plastic processing. The basic structural mechanical characteristic of the forming technology is that the applied force can be reduced.
In turn, it greatly reduces the number of tons of machine needed for the whole process of forming.
FIG. l shows the basic principle of scissor-extrusion forming of branch and fork parts.
The diagonal line on the figure shows the shear deformation zone in the shear – extrusion forming process.
Not only does it produce a larger shear deformation around the oblique line.
The rest of the entire trichoderm produces a relatively small variety of variants. Under the influence of the needle.
The metal in the middle part of the two shear bands flows into the concave cavity of the grinding tool in a similar way, and the fork is produced.
For the cut-off valve body with two forks shown in Figure 2.
Is to cut a extrusion forming the upper branch fork and then forming the lower branch fork, 2 branch fork forming can also be carried out in a stroke arrangement of the needle. Before the valve body to carry out the scientific research of the sciss-extrusion production and operating process test, the first selection of t / 3 feet of the shrinkage part to carry out the physical simulation scientific research, get the reference process index of the sciss-extrusion forming, so as to formulate the main parameters of the production and operating process test.
Take the processing technology of DN100 cut-off valve body as an example, according to the scientific research of production operation process test.
The process index of DNlOOmm cut-off valve body with 20 steel shear extrusion material is obtained as follows: the heating temperature of the hair embryo sample is 1200℃, and the heating temperature of the grinding tool is 100 ~ 300″C.
High purity graphite liquid agent is selected as lubricant.
The punching needle is tapered, and the punching needle aperture is ~’108mm. The samples are blank parts with flanges. The experimental equipment is lO00t clutch screw press, and the main working parameters are shown in Table l. Physical properties in forging such as.
According to the main working parameters of the punching machine and the principle of shear – extrusion process of the specimen, a set of grinding tools is formulated. Before the experiment, the required force size is calculated according to the simulation test results, the specifications of steel castings and the mechanical properties of steel castings.
After calculation and calculation, the 1O00t punching machine can meet the requirements of Qi. The forging forming of small diameter cut-off valve body is realized in large, small and medium-sized equipment, which proves that the cutting and extrusion forming process has the characteristics of environmental protection, energy saving and labor saving.
Able to form the overall forging of large and medium-sized cut-off valve body in China’s current equipment.
In addition.
The forging and forming of tee pipe and other large and medium-sized fork parts can be studied scientifically by the technology of shearing and squeezing.
Forging can be divided into: (1) closed forging (free forging).
It can be divided into free forging, rotary forging, cold extrusion, extrusion forming, etc., the alloy embryo is put into the forging die with a certain shape to force the deformation and get the cast steel. According to the deformation temperature, it can be divided into cold forging (forging temperature is normal temperature), warm forging (forging temperature is lower than the recrystallization temperature of the embryo metal) and hot forging (forging temperature is higher than the recrystallization temperature).
(2) open forging (free forging).
There are two forms of manual forging and mechanical forging. The alloy embryo is placed between the two anvil blocks (iron) and the impact force or burden is used to cause deformation of the alloy embryo so as to obtain the steel casting.
Comparison of forged and cast steel valves: Cast steel valves are used to cast steel in casting parts.
A type of casting alloy.
Steel casting is divided into three categories: cast carbon steel, forged high alloy steel and forged special steel.
Steel casting is a kind of steel casting made by casting method.
Steel castings are mainly used to manufacture some parts which are complicated in appearance, difficult to be forged or grinded and require high strength and plasticity.
The disadvantage of steel casting is that compared with forged steel, the sand hole disadvantage is larger, and the mechanism is closely horizontal, and the compressive strength is not as good as forged steel. Therefore, forged steel valves are generally used as the leading role in the key parts of the pipeline under high pressure and continuous high temperature.
Forging, forging, forging steel valve technology improvement plan: it is necessary to use the ** expansion head, to the gate valve after installation in the safety channel (safety channel aperture size tolerance for reasonable control) as the positioning reference, both sides of the expansion at the same time.
Forged steel valve body rebound force more than high pressure gate valve rebound force, valve body hole firmly wrapped high pressure gate valve, no gap, compact structure. Therefore, the axial load must be strictly controlled.
When the high pressure gate valve is pressed to the valve body, the valve body cavity must be changed in the elastic limit, to ensure that after the expansion force disappears, the valve body cavity back elasticity, fill the high pressure gate valve back elasticity, so that they stick to each other, so as to limit the very large axial load.
In order to avoid excessive installation of ground stress, the strength of forged steel valve high pressure gate valve tail material is not easy to high, good plasticity and low strength, and control the installation load.
At the same time, in order to ensure that the high pressure gate valve pressure distribution after less rebound force, there should be sufficient offset, so that the high pressure gate valve tail section length is not less than twice its thickness.
Select “after loading press” processing technology, can ensure the quality, forging steel valve high pressure gate valve production and processing is convenient, improve the high efficiency of the packing machine. The plasma arc combustion method of surfacing raw material of gate valve processing technology in the mouth feeding plasma surfacing, the powder is subjected to sufficient heating, but not to reduce the splash of the powder, so that relatively high melting rate can be obtained.
The main disadvantage of feeding powder in the mouth is that molten aluminum alloy sticks to the mouth.
Molten aluminum alloy adhering to the mouth wall or inlet and outlet to a certain total number of falling into the solution pool, resulting in melting drops, more serious when blocking the mouth hole.
In order to avoid the above situation, the tungsten pole and the nozzle hole should have a high coaxiality to ensure that the alloy powder is sent out evenly from the nozzle. In addition, the total flow of powder gas should be appropriate, not causing cyclone movement.
(1) Plasma arc combustion mode (1) Combined plasma arc: non-migrating arc is used for heating alloy powder: migrating arc can not only warm alloy powder, but also melt the surface of the original material.
For self-fusible alloy powder surfacing, because of the high powdery melting point, the effect of non-migrating arcs is not obvious: when surfacing fine powder with relatively high melting point, the effect of non-migrating arcs is obvious.
The surfacing welding of thin and small parts mostly adopts combined plasma arc.
(2) Transferable plasma arc: Since non-transferable arc does not play a vital role, in many places only transferable arc is used to carry out surfacing, which can save a set of switching power supply.
(3) The combined plasma arc of series electric arc: it has the advantage that the positive ion arc generated between the nozzle and the lower part is not easy to expand the blowing force of the cyclone on the molten pool, which can effectively limit the melting depth.
Although this arc heating is relatively dispersed, it can still maintain sufficient specificity. The plasma arc with this method is used to manipulate the current flow of positive ion arc. If the current flow increases, the nozzle ablation is more serious, but the development of water cooling heat dissipation, this situation can be improved.
The plasma arc method is rarely used in China.
(2) Powder delivery method At present, two kinds of powder delivery methods are used: powder delivery inside the mouth and powder delivery outside the mouth. In the nozzle feeding plasma surfacing, the powder is subjected to sufficient heating, but also to reduce the splash of the powder, can obtain relatively high melting rate.
The main disadvantage of sending powder in the mouth is that molten aluminum alloy sticks to the mouth.
Molten aluminum alloy adhering to the mouth wall or inlet and outlet to a certain total number of falling into the solution pool, resulting in melting drops, more serious when blocking the mouth hole.
In order to avoid the above situation, the tungsten pole and the nozzle hole should have a high coaxiality to ensure that the alloy powder is sent out evenly from the nozzle. In addition, the total flow of powder gas should be appropriate, not causing cyclone movement. In the nozzle plasma surfacing, the alloy powder is not sent into the plasma arc outside the nozzle, which effectively solves the problem of dripping and nozzle blocking. The melting depth under the similar standard is smaller than the mouth feeding powder, this is because when the mouth feeding powder, the powder cyclone in the nozzle has been significantly heated, and blown directly to the solution pool, resulting in a larger additional blowing force: and when the mouth feeding powder, the additional blowing force caused by the powder gas is reduced.
The main disadvantages of sending powder outside the mouth are large powder dispersion level and low aluminum alloy stacking rate.
(3) Plasma surfacing steam and alloy powder usually use pure hydrogen working gas (also known as positive ion gas, arc stabilizing gas), powder gas and protection gas.
Hydrogen plasma arc has low current, stable ignition, small tungsten electrode and nozzle ablation.
Some overseas applications are 70% hydrogen and 30% helium as gas or powder gas, which makes the working voltage of plasma arc rise, and thus has high power and production efficiency.
Nitrogen also works well as a protective gas, but it’s rare and expensive.
Under the premise of ensuring sufficient specificity and symmetry of plasma arc to send out alloy powder, the total flow of working gas and powder delivery gas should be limited as far as possible, so as to reduce the cyclone blowing force. The protection gas needs sufficient total flow to be effective. Because the alloy powder of plasma arc surfacing is mostly self-fusible, no protective gas can not have a significant impact on the quality of surfacing, but the nozzle is very easy to be spilled out of the molten pool metal sand dirty.
The finer the particle size distribution of alloy powder for surfacing, the easier it is to melt, but too fine powder is difficult to reach powder.
Too thick powder is not easy to melt, but also easy to fly out of the surfacing area, so that the powder loss.
The suitable size range is 0.06 to 0.112mm (120 to 230 mesh/ft).
In order to avoid the powder melting in the nozzle resulting in plugging conditions, in China is also used fine powder (40-120 mesh/ft) surfacing.