1 Polishing principle
The polishing process is carried out on a special machine tool, the polishing machine. There are two heat-treated alloy cast iron plates (referred to as polishing plates) on the polishing mill. Concentric semi-circular grooves are pre machined on the working surface, as shown in the following figure. During operation, the smooth grinding plate continuously extrudes and grinds the ring belt and the two poles of the ball billet in the plate groove under a high working pressure (20 ~ 40t) and a certain rotating speed (80 ~ 200R / min), and removes the metal surplus, so that the ball billet gradually obtains the same surface quality and geometric accuracy as the soft grinding process, and then directly performs heat treatment.
2 Polishing mechanism
2.1 Grinding function of smooth grinding plate
The pre grinding effect of the polished plate is related to the internal metallographic structure of the polished plate and the external process conditions during processing.
In service, the main metallographic structure of the polished plate is martensite, carbide and graphite. Martensite and carbide are hard brittle phases; The strength and hardness of graphite are close to zero. It is like a hole in the plate, cutting the matrix and adapting to stress concentration.
When the steel ball moves along the plate groove under a certain pressure, it will move relative to the surface of the plate groove. Due to the action of dislocation and impact, the graphite and the matrix of hard and brittle phase on the surface of the plate groove are broken and peeled off quickly, forming many small pits, uneven, and the convex irregular part is mainly martensite, which is hard and brittle and becomes a large number of small edges. When the steel ball moves relative to the plate groove, under the action of pressure, these convex edges grind the metal on the surface of the steel ball like the abrasive grains of the grinding wheel.
In the process of light sealing, the graphite and hard and brittle abrasive particles on the surface of the plate groove are constantly broken and falling off, and the circulating washing of the cleaning liquid causes the plate groove surface to constantly generate and reveal new edges, thus maintaining the continuous grinding ability of the light grinding plate.
To sum up, the grinding effect of the smooth grinding plate depends on the metallographic structure in the plate on the one hand, and on the other hand, there must be appropriate external process conditions: a certain pressure, the ball and the plate groove move relatively, and the cleaning liquid is continuously washed.
2.2 Peeling form of metal on the surface of steel ball
In the process of polishing, the small edge raised on the surface of the plate groove can be vertically cut into the ball surface under the action of pressure, and the tangential force makes the edge move tangentially relative to the ball surface. Therefore, the surface of the steel ball is sheared, ploughed or cut, causing the metal to wear and fall off, leaving visible fine groove marks on the surface of the steel ball. Therefore, the falling off of the metal on the surface of the steel ball belongs to abrasive wear, and the grinding of the surface of the steel ball by the polishing plate can be regarded as a kind of fixed metal abrasive wear.
3 Finishing of three light grinding plate
Generally, the grinding wheel, i.e. the smooth grinding plate, is trimmed with the grinding wheel knife. The method is to stop the machine first, remove the fixed plate, fix the dressing frame (the grinding wheel knife with some left-hand and some right-hand spiral teeth) on the fixed plate, start the machine tool to rotate the grinding wheel and push the fixed plate, use the friction force of the grinding wheel to the grinding wheel knife to drive the grinding wheel knife to rotate, and trim the grinding wheel groove section (its depth has reached or exceeded 1 / 2 of the steel ball diameter), The groove depth of the grinding wheel is reduced to ensure that the grinding wheel can continue grinding.
With this trimming method, the following defects exist:
1) The consumption of grinding wheel blades is large. Generally, 5-6 grinding wheel blades are a group, and they are scrapped after being used twice; The trimming times are frequent, and each shift shall be trimmed 1-2 times; The operation is laborious and the labor intensity is high.
2) The grinding wheel needs to be shut down for dressing. After dressing, the grinding wheel fragments need to be cleaned. The efficiency is low and the auxiliary time is long.
3) Because of manual operation, the depth of the grinding wheel groove after dressing is different, so it is difficult to reach the ideal depth.
4) The edge of the grinding wheel groove is easy to crack and the groove shape is incomplete after dressing with the grinding wheel cutter, and the steel ball is easy to be gnawed and scratched during regrinding.
5) When dressing the grinding wheel with the grinding wheel cutter, the noise is large, the dust is large, and the vibration force is strong. During the dressing process, the main shaft of the machine tool and the guide column of the fixed plate are greatly impacted, causing certain damage to the equipment.
Make use of the notch in the fixed plate that is necessary for the circular processing of the steel balls (the steel balls are not grinded here during grinding), install the diamond strip dressing device (referred to as the dresser) shown in the above figure directly in the middle of the notch, and fasten it to the flange of the grinding machine. A driving device drives the slider to make a reciprocating motion perpendicular to the spindle axis of the grinding wheel, The Diamond Bar clamped on the slide block by the transition block is closely attached to the grinding wheel plane and reciprocates with the slide block. During normal grinding, there is always a certain pressure F between the fixed plate and the grinding wheel. When the groove of the grinding wheel consumes a distance of △ X, the fixed plate presses the steel ball and moves △ X (excluding the grinding amount of the steel ball and the consumption of the guide plate), and the diamond bar also moves △ X toward the grinding wheel, that is, the dressing amount of the grinding wheel is △ X (excluding the consumption of the diamond bar). Therefore, by dressing the grinding wheel with diamond bars, the grinding and grinding wheel dressing can be carried out simultaneously, and the groove depth of the grinding wheel can be kept basically unchanged during the grinding process.
More about WBM Steel Ball:
Bearing steel balls are important basic components in the industry. Bearing steel balls have a long history of use in the precision bearing industry and life, and are more widely used. It can be said that steel balls exist in most places where there is rotation, commonly known as steel balls and balls. Steel balls are widely used in bearings, hardware, electronics, iron art, mechanical equipment, electric power, mining, metallurgy and other fields.
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WBM has obtained the certificates of ISO9001:2000 and ISO/IATF16949, The outstanding reputation of WBM is built on our core management principles: technical innovation, high output quality and efficiency, hard-working, meeting and beyond clients’ expectation. WBM spares no effort in creating maximum value for customers.