hp 400 mm graphite electrodes

Machining of taper threads with hp 400 mm graphite electrodes

Quality problems in the processing of 1hp 400 mm graphite electrodes

The poor processing quality of hp 400 mm graphite electrodes is mainly manifested in the following three aspects: 1) The processing accuracy of the electrode taper hole thread is not up to standard. It cannot be guaranteed that any electrode can be reliably connected with the same specification connector (that is, to maintain interchangeability); 2) The outer axis of the electrode body is not concentric with the axis of the connector hole. 3) The upper and lower end faces of the electrode are not parallel or the center line of the main body of the electrode is not perpendicular to one end face. After the upper and lower electrodes are connected, the axis appears “twisted” and the verticality cannot be guaranteed. One side of the end face is crimped tightly, and there is a gap on the other side.

Especially due to the different working principles, “American” lathes are prone to 2) and 3), while “Japanese” lathes are mainly concentrated on the processing of taper threaded holes. The following mainly analyzes the problems of “Japanese” lathes.

Common quality problems during taper hole thread processing of “Japanese” lathes are:

1) The so-called “one good and three bad” and “three good and one bad” are flattened in the “ten” direction;

2) The threaded hole is oval (that is, flat);

3) There is a small defect on the entire circumference of the conical hole;

4) Thin line shape, severe cases can lead to “fancy teeth”;

5) One end of the taper hole and the thread at the bottom of the hole is normal, and the top of the other end is incomplete;

6) Abnormal tooth shape. After the connector is screwed into the electrode hole, periodic bright spots (commonly known as “watermelon peel”) appear on the surface of the threaded teeth;

7) Convex gas in “threaded hole”

2 cause analysis

The machining quality of the hp 400 mm graphite electrodes largely depends on the performance of the machine tool. Various problems of the machine itself may lead to substandard quality of processed products. The following are some common problems of the thread processing machine itself.

2.1 Saddle

1) Improper adjustment, the roller is too high or too low. Under the premise of the same processing size of the electrode outer ring, if the idler roller is too high, the electrode processing end will rise, which is equivalent to increasing the depth of X during thread processing, and the electrode threaded hole after processing will become larger; on the contrary, If the roller is lower, the electrode processing end will sink, and the processed electrode threaded hole will also be larger. At the same time, since the electrode axis is inconsistent with the actual rotation center line, it will also affect the flatness control of the end surface.

2) The supporting wheel cannot rotate flexibly. The bearing is damaged, or the roller rubs against one side of the support.

3) Worm gear is worn or damaged, and both sides (or one side) behind the bearing sink. During the rotation of the electrode, due to the shape of the screw hole and the shape of the outer surface of the electrode on the saddle-shaped bracket (especially the one-sided sinking), the processed threaded hole is elliptical. If the joint is tightened, “parabolic” marks may even appear on the tooth surface.

2.2 Ball screw pair

1) Repair the gap of the supply system.

2) The change of the pitch error. After long-term use, due to the objective existence of mechanical wear, the gap between the mechanical transmission parts and the guide pair will inevitably increase, and the compensation value of the ball screw will inevitably change. Once the wear or repair is not carried out in time for manual compensation, the original position accuracy will not be in the factory state, which greatly reduces the processing accuracy. During the machining process, the gap between the two-axis lead screw exceeds the internal control standard, which may cause the screw hole (ie, the degree of combination) to become larger or smaller;

If the 2-axis screw clearance exceeds the internal control standard, it will cause serious consequences such as abnormal thread profile.

2.3 Machine tool guide

1) Normal wear and tear. In the process of long-term use, due to the different degrees of friction between the two contact surfaces, the surface of the friction pair will have different degrees of wear, which affects the processing accuracy and production efficiency.

2) The contact surface is very dusty. Inadequate maintenance and lubrication of the lathe.

2.4 Chuck

1) The jaws are not tight. The three claws are not on concentric circles, and the chuck is full of dust.

2) The air pressure is not enough. Compressed air has high water content and low pressure. During the threading process, the claws do not clamp the electrode, which causes the electrode to deviate from the initial position longitudinally or the electrode speed lags behind the stroke X.

2.5 Flyer body and bearing seat

1) The connection between the spindle taper hole and the comb XX handle is unreliable. It may be that the material and the taper are not matched, and the operation of replacing the v-handle is improper.

During the cutting process, the spindle taper hole and handle of the XX comb teeth will expand radially under the action of centrifugal force. As the rotation speed increases, the expansion coefficient increases, and the contact and stress state between the mating surfaces are very complicated. When the spindle taper hole and the X handle use the same material, the expansion of the former is always greater than the latter, which reduces the reliability of the connection; if the material properties of the spindle taper hole and the comb tooth XX handle do not match, the consequences will be more serious. At ordinary speeds, the above changes can generally be ignored, but when the speed is high, the radial expansion caused by centrifugal force will reduce the contact stress between the connecting surfaces, resulting in a change in the position of the XX comb handle relative to the spindle taper hole, resulting in The bending of the X tool directly affects the machining accuracy and the surface roughness of the thread under the action of the radial cutting force.

The radial gap between the spindle taper hole and the comb tooth XX handle increases in a square relationship with the increase in speed, and this change is uneven across the contact cone surface; in addition, the fly x body taper handle is long, and it is difficult to achieve a full-length seamless Cooperate. The clearance at the large end of the comb XX handle is larger than that of other parts, and the radial clearance changes in the form of a bell mouth. With the increase of the speed, the trend of the change of the bell mouth becomes more obvious. The air drying in this space will not only cause the radial runout of the X-shaped tool, but also affect the dynamic balance of the X gear system, and the connection between the spindle and the comb tooth XX handle will loosen, so that the XX comb handle will be clamped in the axial direction. Move to the rear end of the spindle under the action, resulting in axial positioning error of the X handle. Therefore, generally only 70% of the contact with the front is required, and there is often a certain gap in the rear.

If the gap between the spindle and the x-handle is offset due to increased interference to ensure high-speed and reliable contact between the spindle taper hole and the comb-tooth XX handle, excessive interference requires pulling the x mechanism to generate greater tension. The replacement of x is very unfavorable and will also cause the end of the spindle to expand, which will adversely affect the front bearing of the spindle.

2) The adjustment of comb tooth x spindle bearing is unreasonable. The main performance indicators of spindle components are rotation accuracy, stiffness and speed adaptability. In particular, it needs to be pointed out that the rotation accuracy depends on the manufacturing and assembly quality of the spindle and the bearing. If the gap is too large, the shaft will move; if the gap is too small, the bearing will heat up.

3) The plane x is not firmly fixed.

2.6 Cutting

 

3) At present, the tool (x comb) of the electrode taper hole thread is mainly made of high-speed steel, 45 steel inlaid hard alloy or full hard alloy, etc. In contrast, the high-speed steel x comb has poor durability.

1) Deformation of the X tool after grinding: The grinding of the inlaid carbide comb X generally uses an artificial diamond wheel to grind the cemented carbide part, and then uses a normal grinding wheel to grind the entire surface. Since the expansion rate of the 45ᦇ steel inlaid carbide comb x cemented carbide part is lower than that of the x frame, during the grinding process, if the feed depth, cutting speed and x stroke amount are not properly controlled, the x comb teeth will pass 4-5 times Deformation will occur after grinding, and use a plug gauge to detect the processed electrode threaded hole. The “convex” x tooth is obviously damaged. Observe the theoretical and actual taper.

3) The comb X does not match the Fei X fuselage, and the dynamic balance is poor.

2.7 Electrode body

During the processing, the electrode tripped seriously. This is mainly due to insufficient graphitization and light weight.

2.8 Other

1) Insert (plug iron). It is mainly worn or deformed, causing looseness or crawling.

2) Pressure plate (hook iron). After wear, the process jitters.

3. solve

1) Use the error compensation function of the numerical control system to compensate the pitch error and pitch error of the servo feed system within a certain range.

2) The machine tool should be checked regularly, and the friction pairs such as the guide rail should be repaired by manual scraping to maintain the due accuracy.

3) Regularly check the working status and lubrication of the comb tooth x spindle bearing, adjust the bearing clearance, and choose lubricating grease reasonably according to seasonal changes.

4) Strict process control, do a good job in the first electrode quality inspection personnel re-inspection confirmation system, and increase the frequency of self-inspection by operators.