CN115647948A - Grinding method for super-hard coating hammer-type valve rod with large length-diameter ratio - Google Patents

Abstract

A grinding method of a hammer-type valve rod with a superhard coating and a large length-diameter ratio relates to a grinding method of a valve rod. The invention aims to solve the problems that the center of gravity of a workpiece is biased, the workpiece vibrates in machining and the machining quality cannot meet the design requirement in the grinding machining of the existing hammer type valve rod. According to the invention, through the innovation of the processing method, the central bracket is arranged at the joint of the valve rod shaft section and the valve rod head shaft section, so that the stability of the processing process is improved, the high-precision processing is realized, the processing quality of a product is improved, and the damage to equipment is reduced; when a workpiece is clamped, the jacking force is reasonably selected, so that the workpiece is prevented from being bent due to overlarge jacking force of the centre or clamping is prevented from being unstable due to undersize jacking force of the centre; before grinding a workpiece, the outer circumferential surface of the support position of the shaft section of the valve rod is ground, so that the precision of the support position is ensured, a foundation is laid for subsequent processing, cutting parameters are reasonably selected according to a processing process, and the processing quality and the yield are improved. The invention belongs to the technical field of valve rod processing.

Description

A grinding method for a hammer-type valve stem with a superhard coating and a large length-to-diameter ratio

technical field

The invention relates to a grinding method for a valve stem, in particular to a grinding method for a hammer-type valve stem with a superhard coating and a large aspect ratio, and belongs to the technical field of valve stem processing.

Background technique

The hammer-type valve stem is mainly used in ultra-high pressure steam turbines and is the core component of the steam turbine. The function of the rod is to control the closing of the steam turbine. If the processing accuracy of the hammer valve rod is not up to the requirements, the unit will not be closed tightly during use, resulting in air leakage, which will affect the normal operation of the entire unit.

The high temperature and high pressure environment during the operation of the steam turbine has great corrosion damage to the surface of the hammer valve stem. In order to ensure that the surface of the hammer valve stem can better bear high temperature and high pressure, it is necessary to spray chromium carbide coating on the outer circumference of the shaft section of the valve stem. The hardness reaches 1200HV. Such a high hardness coating adds great difficulty to the grinding process. The diameter of the shaft section of the valve stem head is 293.51mm, and the length of the shaft section of the valve stem is 1568mm, but the diameter of the shaft section of the valve stem is only 79.79mm, the aspect ratio reached 19.7.

In the process of using the conventional cylindrical grinding method, there are the following technical difficulties:

1. The diameter of the shaft section of the valve stem head is large, and the center of gravity of the hammer-type valve stem is seriously biased to the side of the shaft section of the valve stem head after being clamped. , At the same time, severe vibration will also have an impact on the main shaft and grinding wheel of the grinding machine, reducing the service life.

2. The length of the shaft section of the valve stem accounts for 2/3 of the overall length of the hammer-type valve stem, and the coating hardness on the outer peripheral surface is high. During the grinding process, vibrations often occur and the stability is poor, resulting in out-of-tolerance cylindricity and coaxiality. The surface roughness does not meet the design requirements.

Over the years, technical personnel of many enterprises have carried out various attempts, but cannot find a kind of suitable method to overcome above-mentioned difficulty all the time. Therefore, providing a new grinding method for the above-mentioned technical difficulties has become an urgent problem to be solved by those skilled in the art.

Contents of the invention

The purpose of the present invention is to solve the problems that the center of gravity of the work piece deviates, vibrates during machining, and the machining quality cannot meet the design requirements in the grinding process of the hammer-type valve stem. Furthermore, a grinding method for a hammer-type valve stem with a superhard coating and a large length-to-diameter ratio is provided.

The technical solution of the present invention is: a grinding method of a hammer-type valve stem with a superhard coating and a large length-to-diameter ratio, which is specifically carried out according to the following steps:

1. Position the workpiece on the cylindrical grinding machine by double-top clamping method;

2. Adjust the top tightening force generated when positioning the workpiece in step 1;

3. Use a central bracket to support the workpiece, and the central bracket is installed at the end where the shaft section of the valve stem is connected to the shaft section of the valve stem head;

4. Grinding the outer peripheral surface of the shaft section support of the valve stem;

5. Use a micrometer to measure the cylindricity of the grinding surface in step 4, and proceed to the next step if the cylindricity is less than 0.02mm;

6. Grind the shaft section of the valve stem on the workpiece processed in step 5 until the diameter of the shaft section of the valve stem is 79.79mm, the cylindricity is less than or equal to 0.02mm, and the surface roughness is below Ra0.4μm, then proceed to the next step one step;

7. Grind the shaft section of the valve stem head on the workpiece processed in step 6 until the diameter of the shaft section of the valve stem head is 293.51 mm, the cylindricity is less than or equal to 0.02 mm, and the surface roughness is below Ra0.4 μm, then proceed to the next step one step;

8. Use a dial indicator to measure the coaxiality between the shaft section of the valve stem head and the shaft section of the valve stem after step 7.

Compared with the prior art, the present invention has the following effects:

1. Through the innovation of the processing method, the present invention installs the center bracket 2 at the junction of the valve stem shaft section 1 and the valve stem head shaft section 3, so as to improve the stability of the processing process, realize high-precision processing, and improve the processing quality of the product. Reduce damage to equipment.

2. The present invention rationally selects the clamping force to prevent the bending of the workpiece due to excessive clamping force at the tip or unstable clamping due to too small clamping force at the tip.

3. Before grinding the workpiece, the present invention firstly grinds the outer circumferential surface of the support of the shaft section 1 of the valve stem to ensure the accuracy of the support and lay a foundation for subsequent processing, and rationally select cutting parameters according to the processing process to improve the processing quality ,Yield.

4. The present invention adopts an intermittent grinding method during the grinding process to prevent the center hole from being damaged by the tip grinding, resulting in a decrease in machining accuracy.

Description of drawings

Fig. 1 is a schematic flow sheet of the present invention;

Fig. 2 is a processing schematic diagram of the present invention, in the figure: 1, valve stem shaft section, 2, center bracket, 3 valve stem head shaft section.

Detailed ways

The technical solution of the present invention will be described below in conjunction with the accompanying drawings and through specific implementation methods. Apparently, the implementations described below are only some, not all, implementations of the present invention. Based on the implementation manners in the present invention, all other implementation manners obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

Specific embodiment 1: This embodiment is described in conjunction with Fig. 1 to Fig. 2. A grinding method of a hammer-type valve stem with a superhard coating and a large aspect ratio in this embodiment is specifically carried out in the following steps:

1. Position the workpiece on the cylindrical grinding machine by double-top clamping method;

2. Adjust the top tightening force generated when positioning the workpiece in step 1;

3. Use the central bracket 2 to support the workpiece, and the central bracket 2 is installed at the end where the valve stem shaft section 1 is connected to the valve stem head shaft section 3;

4. Grinding the outer circumferential surface of the shaft section 1 support of the valve stem;

5. Use a micrometer to measure the cylindricity of the grinding surface in step 4, and proceed to the next step if the cylindricity is less than 0.02mm;

6. Grinding the valve stem shaft section 1 on the workpiece processed in step 5 until the diameter of the valve stem shaft section 1 is 79.79mm, the cylindricity is less than or equal to 0.02mm, and the surface roughness is below Ra0.4μm, proceed to the next step;

7. Grind the shaft section 3 of the valve stem head on the workpiece processed in step 6 until the diameter of the shaft section 3 of the valve stem head is 293.51mm, the cylindricity is less than or equal to 0.02mm, and the surface roughness is below Ra0.4μm. proceed to the next step;

8. Use a dial gauge to measure the coaxiality between the valve stem head shaft section 3 and the valve stem shaft section 1 after step 7.

In this embodiment, the two supporting claws of the center bracket 2 are arranged at 90°, and the two supporting claws are against the outer circumferential surface of the valve stem shaft section 1, and each supporting claw can be adjusted along the diameter direction of the valve stem shaft section 1 . Such setting, on the one hand, ensures that the center bracket 2 provides stable support for the workpiece, ensures that the center of gravity of the workpiece does not deviate, and improves the processing quality; on the other hand, prevents the grinding wheel from interfering with the center bracket 2 during grinding.

Specific embodiment 2: This embodiment is described with reference to Fig. 1 to Fig. 2 , and the tightening force in step 2 of this embodiment is selected as 0.8N. This setting prevents the workpiece from being bent due to excessive top tightening force or unstable clamping caused by too small top tightening force. Other compositions and connection methods are the same as those in Embodiment 1.

Specific embodiment 3: This embodiment is described with reference to FIG. 1 to FIG. 2 . The grinding processes of step 4, step 6 and step 7 of this embodiment all include rough grinding, semi-fine grinding and fine grinding. Other compositions and connection modes are the same as those in Embodiment 1 or 2.

Specific embodiment four: This embodiment is described in conjunction with Fig. 1 to Fig. 2, in step four and step six of this embodiment:

During rough grinding, the workpiece speed is 20r/min, the feed rate is 0.005mm/r, and 0.02mm fine grinding allowance is left;

During semi-fine grinding, the workpiece speed is 30r/min, the feed rate is 0.01mm/r, and 0.02mm fine grinding allowance is left;

During fine grinding, the workpiece speed is 30r/min, and the feed rate is 0.005mm/r.

This setting is because during rough grinding, the roundness of the chromium carbide coating on the outer circumferential surface of valve stem shaft section 1 is poor, and the grinding is in an intermittent state. parameters, to round the product; then slightly increase the depth of cut and feed to improve processing quality and processing efficiency; finally, when entering fine grinding, select cutting parameters with small depth of cut and low feed to ensure the final processing accuracy. Other compositions and connection relations are the same as those of the specific embodiment 1, 2 or 3.

Specific embodiment five: this embodiment is described in conjunction with Fig. 1 to Fig. 2, in the step seven of this embodiment:

During rough grinding, the workpiece speed is 15r/min, the feed rate is 0.005mm/r, and 0.03mm is left for semi-fine grinding allowance;

During semi-fine grinding, the workpiece speed is 20r/min, the feed rate is 0.01mm/r, and a fine grinding allowance of 0.02mm is left;

During fine grinding, the workpiece speed is 15r/min, and the feed rate is 0.005mm/r. The other components and connections are the same as those in Embodiment 1, 2, 3 or 4.

Specific Embodiment 6: This embodiment is described with reference to FIG. 1 to FIG. 2 . The grinding processes of step 4, step 6 and step 7 of this embodiment all adopt the intermittent grinding method. This setting prevents the tip from being overheated for a long time, and prevents the tip from grinding and damaging the center hole, resulting in a decrease in machining accuracy. Therefore, regular downtime is required during processing. The other components and connections are the same as those in Embodiment 1, 2, 3, 4 or 5.

Specific Embodiment 7: This embodiment is described with reference to FIG. 1 to FIG. 2 . The coaxiality in step 8 of this embodiment is 0.02 mm. The other components and connections are the same as those in Embodiment 1, 2, 3, 4, 5 or 6.

The present invention has been disclosed above in a preferred embodiment, but it is not intended to limit the present invention. Any person familiar with the art will not deviate from the content of the technical solution of the present invention. Modifications, equivalent changes and modifications all still belong to the scope of the technical solution of the present invention.

Claims (7)

1. a grinding method of a superhard coating large length-to-diameter ratio hammer type valve stem, is characterized in that: the method is specifically carried out in the following steps: 1. Position the workpiece on the cylindrical grinding machine by double-top clamping method; 2. Adjust the top tightening force generated when positioning the workpiece in step 1; 3. Use a central bracket to support the workpiece, and the central bracket is installed at the end where the shaft section of the valve stem is connected to the shaft section of the valve stem head; 4. Grinding the outer peripheral surface of the shaft section support of the valve stem; 5. Use a micrometer to measure the cylindricity of the grinding surface in step 4, and proceed to the next step if the cylindricity is less than 0.02mm; 6. Grind the shaft section of the valve stem on the workpiece processed in step 5 until the diameter of the shaft section of the valve stem is 79.79mm, the cylindricity is less than or equal to 0.02mm, and the surface roughness is below Ra0.4μm, then proceed to the next step one step; 7. Grind the shaft section of the valve stem head on the workpiece processed in step 6 until the diameter of the shaft section of the valve stem head is 293.51 mm, the cylindricity is less than or equal to 0.02 mm, and the surface roughness is below Ra0.4 μm, then proceed to the next step one step; 8. Use a dial indicator to measure the coaxiality between the shaft section of the valve stem head and the shaft section of the valve stem after step 7. 2. A method for grinding a hammer-type valve stem with a superhard coating and a large aspect ratio according to claim 1, wherein the clamping force in said step 2 is 0.8N. 3. The grinding method of a hammer-type valve stem with a large length-to-diameter ratio of superhard coating according to claim 1, wherein the grinding steps of step 4, step 6 and step 7 all include rough grinding , semi-fine grinding and fine grinding. 4. the grinding method of a kind of superhard coating large aspect ratio hammer valve stem according to claim 3, is characterized in that, in described step 4 and step 6: During rough grinding, the workpiece speed is 20r/min, the feed rate is 0.005mm/r, and 0.02mm fine grinding allowance is left; During semi-fine grinding, the workpiece speed is 30r/min, the feed rate is 0.01mm/r, and 0.02mm fine grinding allowance is left; During fine grinding, the workpiece speed is 30r/min, and the feed rate is 0.005mm/r. 5. the grinding method of a kind of superhard coating large aspect ratio hammer valve stem according to claim 3, it is characterized in that, in described step seven: During rough grinding, the workpiece speed is 15r/min, the feed rate is 0.005mm/r, and 0.03mm is left for semi-fine grinding allowance; During semi-fine grinding, the workpiece speed is 20r/min, the feed rate is 0.01mm/r, and a fine grinding allowance of 0.02mm is left; During fine grinding, the workpiece speed is 15r/min, and the feed rate is 0.005mm/r. 6. The grinding method of a hammer-type valve stem with a large aspect ratio of superhard coating according to claim 1, characterized in that, the grinding procedures of step 4, step 6 and step 7 all adopt intermittent Grinding method. 7. A method for grinding a hammer-type valve stem with a superhard coating and a large aspect ratio according to claim 1, wherein the coaxiality in the eighth step is 0.02 mm.

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