Grinding technology of mechanical seal sealing surface -- manual grinding and mechanical grinding

Manual grinding is mainly used for small batch production and repair of single piece. Manual grinding is labor-intensive and requires skilled operators. Mechanical grinding is used in mass production.

1、 Manual grinding The manual grinding generally adopts flat plate, which is made of high carbon cast iron. The flat plate is generally in a group of three, and the flatness of the flat plate is allowed to deviate.

1. The sand inlay and sand inlay (sand pressing) of cast iron grinding plate is to embed the abrasive particles on the surface of the grinding plate first. Sand inlay is a difficult skill to master, which is the key to ensure the quality of work. It can be done manually or mechanically, but it is difficult to ensure the quality of sand inlay by mechanical methods, so manual sand inlay is very common.

Before sand embedding, "sand removal" shall be carried out. Sand removal is to remove the used abrasive that has lost cutting effect from the surface of the grinding plate to prepare for sand embedding. Sanding is to draw two small circles with a diameter of about 10mm with stearic acid on a grinding plate, then drop 8~10 drops of kerosene and apply it evenly by hand. The two plates are combined, and one person shakes the upper plate in the shape of "∞" with both hands, so that kerosene is evenly distributed on the whole plate surface, and then two people push and pull back and forth and rotate 180 ° intermittently. The oil film thickness between the grinding plates is 0.005~0.007mm, and the abrasive sand particles are driven to the plate surface of the free plate under the force of changing direction given by the oil layer. After removing the upper grinding plate, wipe the plate surface with absorbent cotton.

2. The procedure of sand inlay is illustrated with the emery of W1 as an example.

① Wipe the two grinding plates with absorbent cotton.

② Scratch stearic acid.

③ Put the prepared grinding mixture (corundum+stearic acid+aviation gasoline) on the surface of the grinding plate, and the dosage is 15-20ml.

④ Evenly apply it by hand, and wait for the gasoline to evaporate completely.

⑤ Add 3-5 drops of kerosene and apply evenly.

⑥ Buckle one grinding plate onto the other, and let two people press the "∞" shape to shake the upper plate evenly and gently, and rotate 180 ° intermittently. Push and pull repeatedly for several times (5-10 times).

⑦ When the surface of the grinding plate is black and shiny, remove the grinding plate and wipe it with absorbent cotton.

⑧ Check with the test block. If the cutting force is strong, the stripes are dense, and the thickness is uniform, the sand embedding is completed. Generally, 4~5 times of sand embedding are required.

2、 Mechanical lapping Mechanical lapping is to grind the workpiece on a rotating abrasive tool, which is generally a round abrasive plate.

The grinding disc for mechanical grinding is usually made of cast iron, and the polishing disc is made of steel or copper. Suede and silk face plates are often used for polishing and surfacing sealing rings such as cemented carbide, copper alloy and stainless steel.

The surface of the metal grinding plate shall be flat and free from defects, and the flatness shall be trimmed to below 0.05/1000mm. The radius of the disc shall be designed to be at least twice the diameter of the workpiece to be processed. The diameter range is generally 305~1620mm (16~64in), and the thickness is about 1/10~1/6 of the diameter. The disc surface is provided with grooves, which are designed to reduce the stress and deformation of the disc surface, facilitate heat dissipation, and facilitate the removal of waste abrasives and the inclusion of wear debris during grinding.

Surface radioactive and diamond blocks are mostly used for rough grinding, concentric circles are mostly used for fine grinding, and end thread (Archimedes spiral) is mostly used for polishing.

Grinding machine is a kind of grinding equipment used in mechanical seal manufacturing industry. It is composed of bed, base, reduction box, grinding plate, control ring (also called retaining ring or correction ring), limit support frame, etc.

During grinding, the workpiece is placed in the control ring, and the plastic spacer ring is used to evenly arrange the workpiece in the control ring. The grinding pressure is applied by the weight. When the grinding plate rotates, the control ring rotates in the limit support frame. In addition to rotation, the workpiece rotates on the grinding plate along with the control ring, and the surface is continuously ground under the action of the abrasive.

Here are some common types of grinders.

1. M650 heavy block type plane grinder This is a single-sided grinder, which uses a weight to apply grinding pressure. There are three abrasives in the control ring that are added manually. The grinding workpiece is pressurized by adding weights on the upper part, which consumes a lot of physical energy for operators. It is generally used for the grinding of medium-sized sealing rings, and is a kind of grinder that is widely used. The main technical parameters are: the diameter of the grinded workpiece can reach 240mm.

Thin thickness of workpiece: 1 mm.

Workpiece machining precision flatness 0.03 μ m, roughness Ra0 05μm。

Grinding plate diameter: 650mm, rotating speed: 10~60r/min, variable speed, motor power: 1 5~2. 2kW。

Control ring diameter X inner ring diameter: 280mm X 240mm.

Overall dimension (L x W x H): 900mmX1000mmX800mm.

Mass: 1200kg.

2. M650c air pressure grinder This grinder has the following characteristics: ① The rotation of the grinding plate is regulated by a frequency conversion motor and a reducer, which is small in size, high in efficiency, stable in operation, and low in noise. The speed ratio is 1:20, and the speed of the grinding plate is 150r/min The control board displays the speed of the motor.

② The machine has the function of running time adjustment, and the set time is 100min. When the grinder time is set, the machine starts running to the set time, and the grinder automatically stops running, so the grinding operation is more convenient and simple.

③ The adjustment function of abrasive addition is perfect. After the prepared abrasive is put into the storage tank, the electromagnetic stirring can prevent the abrasive precipitation in the abrasive. The air pressurization and electromagnetic valve in the storage tank can control the time interval of abrasive addition, which can be up to 100min. At the same time, the time of each abrasive addition can be controlled. The "minute/time" displayed on the control panel is the time interval for adding abrasive.

④ The inner diameter of the air pressure cylinder of this machine is Φ 50mm, and the air pressure can be adjusted to change the grinding pressure weight. There is an automatic alignment plate at the end of the piston rod of the cylinder which is directly pressed on the grinding workpiece. When using, the workpiece thickness of each control ring should be consistent. The soft rubber pad is padded on the top to contact the flat plate at the end of the piston rod, so as to avoid grinding deflection and uneven phenomenon. The three cylinders can control the pressing and lifting separately or simultaneously, which is convenient for operation.

⑤ There are 3 control rings in total, which can move towards the center and the edge of the grinding plate through the support frame, so as to achieve automatic disc repair. The support frame of the control ring can be adjusted inside, outside, up and down, so that the control ring can operate freely.

In addition, the machine is attached with three control rings for dressing the grinding plate, and coarse and fine emery abrasives can be used to grind the dressing plate.

⑥ When the position of the control ring changes, the pressurizing cylinder can also adjust the corresponding position through screws, so that the pressurization of the cylinder is always in the middle of the control ring.

⑦ The waste lapping fluid is easy to receive and discharge in an inclined flow channel.

Grinding diameter: 240mm.

Thin thickness of workpiece: 1mm.

Workpiece machining precision flatness 0.03 μ m, roughness Ra0.05 μ m.

The diameter of the grinding plate is 650mm, the rotating speed is 10~60rmin, the speed is variable, and the motor power is 2 2kW。

Control ring diameter X inner ring diameter: 280mm X 240mm.

Cylinder pressure: 0.2~0 6MPa。

Overall dimensions (L X W X H): 900mm X 1000mm X 800mm.

Mass: 1450kg.

3. Double sided grinder The main features of the grinder are as follows: ① The machine is a four action double sided high-speed grinding equipment. The upper and lower grinding plates rotate in opposite directions, which can grind the upper and lower surfaces of the workpiece evenly at the same time. The workpiece rotates both in revolution and rotation in the planetary gear (equivalent to the control ring mentioned above), with uniform movement track, high processing precision and production efficiency.

② The star wheel is driven by the gear, and the wear is less than that of ordinary grinder.

③ The rotation direction of the star wheel of the machine can be changed, so that the flatness of the upper and lower grinding plates can be automatically corrected. It is not necessary to remove the plate for processing correction when working for a certain time like the ordinary grinder.

④ The lower grinding plate can be lifted up and down, so that the workpiece can be easily removed, and the position of the star wheel can be moved up and down, so that the star wheel and the sun wheel can be evenly worn.

⑤ The lifting of the upper grinding plate is driven by the cylinder, and the change of the workpiece weight can also be obtained by changing the cylinder pressure. At the same time, the lower grinding plate can also be disassembled by using the cylinder.

⑥ The motor adopts stepless speed regulation motor, which can start and stop smoothly, and can choose the ideal grinding speed.

The main technical parameters of the machine are as follows: the overall dimension of the equipment (length x width x height) is 1200mm x 800mm x 2350mm; The outer diameter of the grinding plate is 670mm; Five star wheels can be installed at the same time; The outer diameter of machined parts is 220mm; The thickness of machined parts is 2.5 mm; The surface roughness of machined parts can reach Ra0 1 μ m or more; The power is 3000 kW.

4. Several problems that should be paid attention to in the use of the grinder ① The grinding plate should be corrected in time. The flatness of the grinding surface mainly depends on the precision and grinding motion of the grinding plate. During grinding, the wear of the grinding plate plane is uneven. Generally, the wear of the grinding plate mostly occurs in the middle of the plate surface, that is, the middle of the surface of the grinding plate is low. This is due to the high probability of contact between the middle part and the workpiece. When the movement of the workpiece spreads all over the grinding plate but does not exceed the edge, the wear trend of the grinding plate is still that the middle part is more than the edge. If this continues, the uneven wear of the grinding plate will cause the workpiece surface to form a middle bulge. When the middle of the grinding plate is high, the middle of the product surface is concave.

For four action double-sided grinder, the rotation of control ring can be changed through the sun wheel in the middle to achieve the purpose of disc repair. For single-sided grinder, the position of control ring can be changed to repair the disc.

When the middle of the grinding plate is high, the 3 control rings should be installed as close to the middle as possible.

When the middle of the grinding plate is low, move the two control rings outward.

When the grinding plate is straight, the three control rings should be placed in the normal position.

It is convenient to check the flatness and straightness of the grinding plate by optical gap measurement method, and the measurement accuracy is high. The inspection method is: first clean the inspected part of the grinding plate, wipe off the oil film with solvent, and then contact the edge of the knife edge ruler with the inspected plane; Place a light source behind the knife edge ruler, and then observe the light leakage gap between the inspected plane and the knife edge from the front of the knife edge ruler, which can be determined by the size of the light leakage gap. If a feeler gauge is used for inspection, it should generally be less than 0.02mm.

② The clearance between the workpieces in the control ring shall be appropriate. If the clearance is too large, the workpieces will collide with each other during grinding, causing scratches or cracks. If the clearance is too small, the workpieces cannot rotate with the control ring. The friction tracks of each point on the workpiece surface on the grinding plate will be uneven, affecting the flatness of the seal ring. Sometimes, the workpieces will be jacked up, causing the grinding surface to deflect. Only by making the workpiece rotate smoothly and flexibly in the control ring, can the workpiece get a uniform friction track on the grinding plate and ensure the processing quality of the workpiece.

③ Make sure that the grinding plate is special for the plate. During the use of the grinder, attention should be paid to keeping it clean, especially in the later steps of polishing and grinding. Because the grain size of the polishing abrasive is different from that of the finishing abrasive, it is necessary to prevent the finishing abrasive from being brought into the polishing abrasive plate, otherwise there will be scratches during polishing. Therefore, the polishing and finishing processing should be separated, and no grinder should be used permanently. If polishing is not enough, clean the precision lapped workpiece, clean it with an ultrasonic cleaner, dry it in the air, and then polish it.

④ When using water-soluble abrasives, prevent the surface of the grinding plate from rusting. At the end of each work piece, take out the control ring from the grinding plate, clean and dry the grinding plate. Wipe off the rust before use the next day.

⑤ Clean the discharge channel of the grinder frequently to prevent the accumulated abrasive from overflowing into the bearing seat of the reduction gearbox.

⑥ The abrasive shall be stirred and suspended to prevent blocking the solenoid valve.