Archive for month: February, 2021

What should I pay attention to when using gaskets with flange connections?

Definition of gasket:

The gasket is made of paper, rubber sheet or copper sheet. It is a material placed between two planes to strengthen the seal. It is a sealing element arranged between static sealing surfaces to prevent fluid leakage. When the flange sealing surface is matched with the gasket, the following points should be noted:

1. Thread of flange

Thread is the main direction of flange surface roughness, such as: multi-direction, recording spiral, serration and other surface finish patterns should be as close as possible to the center line of the gasket to be consistent, such as round flanges. The surface texture should be processed into concentric circles or recording spirals to avoid straight lines passing through the flange surface. If there is a straight line across the sealing surface, it will become a direct leakage path. If the gasket needs to be used in conjunction with the flange, then you need to pay attention to this point.

2. Waviness of flange

The waviness is the deviation from the overall flatness. Under normal circumstances, there is no need to consider the waviness problem, but there are two situations that require special attention, because excessive waviness is also a difficult problem to solve.

3. Roughness of flange

Roughness refers to the average value of unevenness calculated from the center of the flange surface, in units of tenths of inches (or meters). For serrated flange surfaces, the typical roughness is 125-500 microinches, while for non-serrated flange surfaces, the roughness is 125-250 microinches. For flanges that are too rough, it is usually impossible to seal the gasket, so you can only choose the softest possible gasket; on the other hand, it is difficult to seal the surface of the flange with a high degree of polishing. This kind of flange should also be avoided because of the sealing The surface needs to have enough “bite marks” to provide enough friction to prevent the gasket from being blown out or extruded or excessive creep.

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A nut is a nut, a part that is screwed together to fix it with a bolt or screw. According to different materials, the components used in the manufacturing machinery of nuts are divided into several main types such as carbon steel, stainless steel, and non-ferrous metals (such as copper).

The locknut consists of two parts, each part has a staggered cam. Since the inclination angle of the inner wedge design is greater than the angle of the bolt and nut, this combination is tightly bitten into a whole. When vibration occurs, it can prevent the protruding parts of the loose nut from staggering and generating lifting tension, thereby achieving the combined anti-loosening effect.

Embedded nuts are brass nuts made of various embossed wires. The embedded knurled brass nuts we usually contact are all processed by precision automatic lathes.

The main method of operation for embedded knurled copper nuts is injection molding. After heating, it is embedded in plastic parts or directly injection molded. If injection molding is used, the melting point of the nut needs to be higher than 200°C, so that the embedded nut is melted by heat. After inserting the plastic part, the temperature rises rapidly.

After injection molding, the plastic body rapidly cools and crystallizes. If the temperature of the embedded nut is still high, you can pour it into the place where the copper nut contacts the plastic part and starts to loosen or crack. Therefore, copper nuts can be used instead of carbon steel nuts in the injection molding of embedded nuts.

There are two methods to form the external die knurling of the embedded copper nut. One is to use copper raw materials to draw patterns and then produce them on upper equipment. Usually, the figure drawn in this way is straight, the other is to use a round copper material. In the production process, the round copper material is directly embossed. This processing method can produce some non-standard size knurled copper nuts. The embossing shape of the embedded copper nut can be selected by the user, such as mesh or various scroll patterns.

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A nut is a nut, a part that is screwed together to fix it with a bolt or screw. The materials are divided into carbon steel, stainless steel, non-ferrous metals (such as copper), etc.

Nuts are parts that tightly connect mechanical equipment. Through the internal thread, nuts and bolts of the same specification can be connected together. The working principle of the nut is to self-lock through the friction between the nut and the bolt. However, the reliability of this self-locking will be reduced under dynamic load. In some important occasions, we will take some anti-loosening measures to ensure the reliability of the nut lock. One of the anti-loose measures is to use anti-loose nuts.

There are also three types of lock nuts:

1) Use two same nuts to tighten the same bolt, and increase the tightening torque between the two nuts to make the bolt connection reliable.
2) Special lock nuts need to be used together with lock washers. The special lock nut is not a hexagonal nut, but a round nut in the middle.
3) Drill threaded holes from the outer surface of the nut to the inner thread surface for screwing in small-diameter countersunk screws. The purpose is to tighten the centripetal force to prevent the lock nut from loosening.

There is a small piece of copper inlaid on the lock nuts with better quality currently on the market. The copper piece matches the thread of the lock nut on the inner surface of the nut to prevent the radial jack screw from directly contacting the locking thread and damaging fasten the screw nut. This kind of locknut has gradually begun to be applied to the shaft end locking of rotating parts, such as anti-loosening of the bearing at the mounting end of a ball screw.

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Bolt fasteners have become a very important part of the mechanical field, which means that we usually need to pay attention to the maintenance and maintenance of bolts, so that they can play the greatest role in the mechanical field. If they are not standardized in use, they will reduce Its service life. For the maintenance of bolts, we should do the following

1. When heating the standard parts, it should be noted that they should be stacked reasonably. If there is a deviation, the standard parts will be slightly oxidized in the quenching oil, and there will be a phenomenon of discoloration when the tempering is delayed. , If you use ether to soak it again, oily impurities are very likely to appear.
2. Standard parts are generally cleaned with silicon-hydrochloric acid cleaning agents after quenching. They must be cleaned first and then rinsed. Be careful when rinsing them, and thoroughly check the rinsing tank to avoid leaving other substances. In the above, and the water used for rinsing must be changed frequently, otherwise the products produced may have quality problems.
3. When the standard parts are about to be heat-treated, they must be cleaned thoroughly, especially the alkaline substances remaining on the surface of the standard parts. If the impurities cannot be completely removed, the standard will be removed at high temperature. The part is burned, and when it is tempered again, it will make the standard part a waste.
4. If the quenching oil cannot be replaced in time when it is in use, it will cause pollution residues and black stripes on its appearance, which will cause its appearance to be very unsightly.

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Carbon steel weldability and its test evaluation

1. Welding:

A process in which two objects are combined between atoms to form an inseparable whole by heating or pressing, with or without filling materials.

2. Weldability:

refers to the ability of homogeneous or dissimilar materials to be welded to form a complete joint and meet the expected use requirements under the conditions of the manufacturing process.

3. The four major factors that affect weldability are:

material, design, process and service environment.

4. The principles for assessing weldability mainly include:

①Assess the tendency of welding joints to produce technological defects, and provide a basis for formulating reasonable welding procedures;

②Assess whether the welded joints can meet the requirements of structural serviceability; design new welding test methods to meet the following requirements The stated principles: comparability, pertinence, reproducibility and economy.

5. Carbon equivalent:

The content of alloying elements in steel is converted and superimposed according to the equivalent of several carbon content, which is used as a parameter index to roughly evaluate the cold crack tendency of steel.

6. Oblique Y-shaped groove butt joint crack test:

The purpose is mainly to identify the cold crack tendency of the first layer of low-alloy high-strength steel welds and HAZ, and it can also be used to develop welding procedures.
1) Preparation of the test piece, the thickness of the welded steel plate δ=9-38mm. The grooves of the butt joints are processed by mechanical methods, and the two ends of the test plate are welded within a range of 60mm, and the two-sided welding is adopted. Take care to prevent corner deformation and incomplete penetration. Ensure that there is a gap of 2mm at the weld of the sample to be welded in the middle.
2) Test conditions: The electrode selected for the test weld matches the base metal. The electrode used should be strictly dried. The diameter of the electrode is 4mm, the welding current (170±10) A, the welding voltage (24±2) V, and the welding speed ( 150±10) mm/min. The test welds can be welded at various temperatures, and the test welds are welded only one line without filling the groove. After welding, let it stand and cool down for 24 hours, and then take samples and conduct crack detection.
3) Detection and calculation of crack rate. Use the naked eye or hold a 5-10 times magnifying glass to detect whether there are cracks on the surface and section of the weld and heat-affected zone. It is generally believed that when the surface crack rate of low-alloy steel “Xiaotieyan” test is less than 20%, cracks generally do not occur.

7. Latch test:

purpose, mainly to evaluate the hydrogen-induced delayed cracking tendency of steel. With other equipment, it can also measure reheat crack sensitivity and laminar sensitivity.
1) For the preparation of the test piece, take the welded steel processing or cylindrical bolt test bar, take samples along the rolling direction and indicate the position of the bolt in the thickness direction. There is a ring or spiral gap near the upper end of the test bar. Insert the pin test rod into the corresponding hole of the bottom plate so that the notched end is flush with the surface of the bottom plate. For plug test rods with annular notches, the distance a between the notch and the end surface should be such that the penetration depth of the weld bead is tangent to or intersects with the cross-sectional plane of the notch root, but the penetration of the notch root circumference shall not exceed 20%. For low alloy steel, the a value is 2mm when the welding heat input is E=15KJ/cm.
2) In the test process, according to the selected welding method and strictly controlled process parameters, a layer of surfacing weld bead is melted on the bottom plate, the center line of the weld bead passes through the center of the sample, and the penetration depth should be such that the tip of the notch is located in the heat affected zone In the coarse-grained region, the weld bead length L is about 100-150mm. When welding, the cooling time value t8/5 value of 800-500℃ should be measured. When welding is not preheated, load it when it is cooled to 100-150℃ after welding; when preheating before welding, it should be 50- higher than the preheating temperature. Load at 70°C. The load should be applied within 1 min and before cooling to 100°C or 50-70°C higher than the preheating temperature. If there is post-heat, load it before post-heat. When the test bar is loaded, the bolt may break within the duration of the load, and record the load time.

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