Talk about the difference between forged and cast steel valves for stainless steel valve leakage fault types summary

Talk about the difference between forged and cast steel valves for stainless steel valve leakage fault types summary

Cast steel refers to all kinds of steel castings produced by casting method. A type of casting alloy. Cast steel is divided into three categories: cast carbon steel, cast low alloy steel and cast special steel. Cast steel is mainly used in the manufacture of some complex shape, difficult to forge or cutting forming and require high strength and plasticity parts. Forging steel refers to various forging materials and forgings produced by forging method. Forged steel parts have higher quality than cast steel parts, can withstand large impact, plasticity, toughness and other aspects of mechanical properties are also higher than cast steel parts, so all some important machine parts should be made of forged steel parts.
Cast steel refers to all kinds of steel castings produced by casting method. A type of casting alloy. Cast steel is divided into three categories: cast carbon steel, cast low alloy steel and cast special steel. Cast steel is mainly used in the manufacture of some complex shape, difficult to forge or cutting forming and require high strength and plasticity parts.
Forging steel refers to various forging materials and forgings produced by forging method. Forged steel parts have higher quality than cast steel parts, can withstand large impact, plasticity, toughness and other aspects of mechanical properties are also higher than cast steel parts, so all some important machine parts should be made of forged steel parts.
Forged steel valve and cast steel valve difference:
The quality of forged steel valve is better than that of cast steel valve, can withstand large impact force, plasticity, toughness and other aspects of mechanical properties are higher than cast steel, but the nominal diameter is relatively small, generally in DN50 below. Casting valve pressure grade is relatively low, commonly used nominal pressure for PN16, PN25, PN40, 150LB-900LB. Forged steel valve grades: PN100, PN160, PN320, 1500LB-3500LB, etc. Cast steel is mainly used in the manufacture of some complex shape, difficult to forge or cutting forming and require high strength and plasticity parts.
Casting is liquid forming, and forging is a plastic deformation process, forging forming workpiece can improve the internal structure of the organization, good mechanical properties, uniform grain, important difficult workpiece must be forged, casting will cause segregation, organizational defects, of course, casting has his advantages, forming complex workpiece forging is not easy to open mold, has taken casting.
Forging valve (forged steel valve) Introduction:
1. Forging can be divided into:
(1) Closed mode forging (die forging). The forging can be divided into die forging, rotary forging, cold heading, extrusion, etc. The metal blank is placed in the forging die with a certain shape to obtain the forging. 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 blank metal) and hot forging (forging temperature is higher than the recrystallization temperature).
(2) Open forging (free forging). There are two ways of manual forging and mechanical forging. The metal blank is placed between the upper and lower two anvil blocks (iron) and the impact force or pressure is used to deform the metal blank so as to obtain the required forgings.
2, forging is one of the two components of forging, mechanical load is high, severe working conditions of the important parts, the use of forgings, the shape of the simple available rolling welding parts, except the profile plate. Welding holes and loose casting of metal materials can be eliminated by forging.
3, the correct choice of forging ratio to improve product quality and reduce costs has a great relationship. Forging materials are mainly carbon steel, stainless steel and alloy steel. Forging ratio refers to the ratio of the cross section area of the metal before deformation to the die section area after deformation. The original state of materials include ingot, bar, liquid metal and metal powder.
4. The mechanical properties of forgings are generally better than those of castings of the same materials. Forging is a processing method to obtain a certain shape and size with better mechanical properties by applying pressure to the metal blank with forging and pressing machinery to make the metal blank produce plastic deformation.
Casting valve (cast steel valve)
1, there are many kinds of casting, according to the modeling method of ordinary sand casting and special casting:
① Ordinary sand casting, including dry sand, wet sand and chemical hardening sand 3 types.
(2) Special casting, according to the casting material can be divided into special casting of ore and special casting of metal materials;
Special casting with metal as casting material, including: pressure casting, metal mold casting, low pressure casting, continuous casting, centrifugal casting, etc
Special casting with natural mineral sand as mold material includes: truthful casting, investment casting, shell casting in casting workshop, mud casting, negative pressure casting, ceramic casting, etc
2. Casting is a kind of metal hot working technology. Casting production has better comprehensive mechanical properties, wider adaptability of casting production, and low blank cost.
3. Casting is the basic process of modern machinery manufacturing industry. It is to melt the metal into liquid and pour it into the casting mold.
4. The casting process usually includes:
(1) Prepare the casting mold (the mold used to make liquid metal become solid casting, the quality of the casting mold directly affects the casting quality), casting mold according to the number of use can be divided into disposable type, multiple type and long-term type, casting mold according to the material: metal type, sand type, mud type, ceramic type, graphite type, etc.
② Melting and casting of cast metal, cast metal mainly cast iron, carbon steel and stainless steel, etc.;
(3) Casting treatment and inspection, casting treatment includes casting surface foreign matter and core, treatment of protrusions (burr grinding, cutting and pouring risers and seam treatment, etc.), casting heat treatment, shaping, rough machining and rust treatment, etc.
5, the shortcomings of casting production mode, casting will produce noise, harmful gas and dust and pollute the environment, and the required materials (such as modeling materials, metal, fuel, wood, etc.) and equipment (such as core making machine, metallurgical furnace, molding machine, sand mixing machine, shot blasting machine, etc.) more.
6. Cast steel is divided into three categories: cast carbon steel, cast low alloy steel and cast special steel.
① Cast carbon steel. Cast steel with carbon as the main alloying element and small amounts of other elements. Carbon content less than 0.2% for casting low carbon steel, carbon content 0.2% ~ 0.5% for casting medium carbon steel, carbon content more than 0.5% for casting high carbon steel. With the increase of carbon content, the strength and hardness of cast carbon steel increase. Cast carbon steel has high strength, plasticity and toughness, low cost, used in heavy machinery to manufacture parts to bear large loads, such as rolling machine frame, hydraulic press base, etc. In the railway rolling stock for the manufacture of large force and impact bearing parts such as pillow, side frame, wheels and coupler, etc.
② Casting low alloy steel. Cast steel containing manganese, chromium, copper and other alloying elements. The total amount of alloying elements is generally less than 5%, which has greater impact toughness and can obtain better mechanical properties through heat treatment. Casting low alloy steel has better performance than carbon steel, can reduce the quality of parts, improve the service life.
③ Casting special steel. Alloyed cast steels refined to suit special needs are of a wide variety, usually containing one or more high alloying elements to obtain a particular property. For example, high manganese steel containing 11% ~ 14% manganese can withstand impact wear, and is mostly used for wear-resistant parts of mining machinery and engineering machinery. Stainless steel with chromium or chromium nickel as the main alloying element, used in corrosion or high temperature conditions above 650℃ working parts, such as chemical valve bodies, pumps, containers or large capacity power station turbine housing.
Summary of failure types for stainless steel valve leakage
The sealing surface of stainless steel valve is mostly stainless steel. In the grinding process, due to the improper selection of grinding materials and incorrect grinding methods, it not only reduces the production efficiency of the valve, but also affects the quality of the product. According to the characteristics of stainless steel materials, the selection of materials with strong labor intensity and wear resistance, and in the processing of abrasive crushing still affect the quality of the product.
The valve to the workpiece grinding is first of all to the grinding tool nesting, and then with the help of abrasive particles and grinding liquid mixed composed of grinding agent to achieve the purpose of grinding processing. Grinding force refers to the force acting on the unit grinding surface area, which is applied to the tool and the force acting on the processed surface through the abrasive particles. If the pressure is too small, the grinding effect is very small. The increase of the pressure, the grinding effect will be enhanced, and the grinding efficiency will be improved. However, when the pressure increases to a certain value, the phenomenon of saturation occurs, and the grinding efficiency generally reaches a large value. If the pressure per unit area continues to increase, the efficiency decreases.
Stainless steel valve leakage problem can not be underestimated, we make a small summary of the following problems, I hope it will be helpful to your use process:
1. Stainless steel valve connection leakage
First of all, it is necessary to check whether the valve and the valve connection bolt are tightened. If they are not tightened, the gasket ring and the flange sealing groove surface are not fully combined, which often leads to leakage. Check the bolts and nuts in sequence and tighten all the bolts until the gasket rings are tightly compressed. Secondly, the size and accuracy of the gasket ring and flange sealing groove surface should be checked. If the sealing contact surface size is wrong or too rough, the gasket ring should be repaired or updated. Moreover, check whether there is some corrosion, sand holes, sand holes or impurities in the contact surface of the gasket ring and flange sealing groove. If there are such defects, it should be repaired, repaired or cleaned accordingly.
2. Stainless steel valve cover leaks
Valve cover leakage, mainly manifested in the leakage of packing seals. First of all, check whether the seal is selected correctly and whether it matches the sealing groove. If there are such problems, replace the sealing ring or repair the sealing groove. Second, check whether the sealing parts appear burr, fracturing, torsion and other phenomena, this case to replace the sealing parts. In addition, check whether the sealing surface of each sealing groove is rough or has other defects. If there are defects, the defects should be eliminated or the damaged parts should be updated.
The valve cover or bracket has packing to be sealed by compression. The installation of these packing should be checked. If it is found that the upper and lower packing is installed upside down, it should be removed and re-installed in accordance with the correct method. Moreover, check whether the precision of the contact surface of the seals meets the specified requirements.
3. Stainless steel valve body cavity decent leakage
Valve body in the casting process, sometimes there will be sand holes, sand holes and other casting defects, it is difficult to be found in the machining process, once the pressure is applied, the hidden casting defects will be exposed. In this case, it is necessary to repair welding, repair or update.
4. Stainless steel valve seat valve plate leakage
Leakage at the seat plate is a common occurrence when installing or servicing valves. Generally, it can be divided into two categories: one is the sealing surface leakage, the other is the sealing ring root leakage.
First of all, the precision of the sealing surface contact between the seat and the valve plate should be checked. The sealing surface should be at least ground. If the surface accuracy is found to be too rough, it should be removed and ground again. Secondly, check whether there are pitting, indentation, sand holes, cracks and other defects on the sealing surface. In this case, the valve plate or seat should be replaced. For the seat with the pressure spring, the elasticity of the pressure spring should be checked to meet the requirements. If the elasticity is weakened, the pressure spring should be updated. Moreover, check whether the T-shaped connection between the valve plate and the valve stem is too loose, resulting in the inclination of the valve plate in the process of compression. In this case, the valve plate should be removed and adjusted to the appropriate size.
The internal opening of the valve body is easy to enter welding inspection, iron filings, impurities and other foreign bodies during the installation process. Such sundries should be cleaned before installation. If you forget to clean or clean not thoroughly, it will cause the valve plate to close less than the expected depth and leakage, in this case, remove the valve body to clean again.
The stainless steel valve seat should be installed with the best installation tool, and the seat should be checked to ensure that it is installed in place. If the thread is not screwed to the desired depth, there will be leakage at the seat. In this case, the seat should be installed again with the best tool.