Common Quality Problems and Prevention Methods in ...

Dec. 09,

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Valve grinding is a light finishing method with a very small cutting volume, and generally, there are few grinding rejects. Valve sealing surface because the dimensional accuracy is not very high, grinding scrap is rarer. Sealing surface grinding often occurs in the geometry is incorrect, surface scratches and pulling grooves and other defects. Common defect forms, causes, and prevention methods are shown below.

Defect form: Scratch

Cause 1: Abrasive mixed with individual coarse abrasive particles

Prevent method 1: Use the water sedimentation method to sort the abrasives and strengthen the storage of abrasives.

Cause 2: Dust, iron chips, or other debris are mixed in the abrasive

Prevent method 2: The container of abrasive should be covered, and the configuration should be kept clean.

Cause 3: The workpiece is not clean or has burrs

Prevent method 3: The sealing surface should be deburred and cleaned before grinding

Cause 4: The lapping machine or grinding tool is not clean

Prevent method 4: the best primary research machine and fine research are very separate, and pay attention to the lapping machine and research tool cleaning

Cause 5: Too much dust in the workshop

Prevention method 5: Establish a closed grinding room and keep it clean.

Defective form: incorrect geometry

Cause 1: Improper grinding motion

Prevention method 1: Improve the grinding motion

Cause 2: Abrasive is too thick or unevenly applied

Prevention method 2: Use thinner abrasive and pay attention to uniform application

Cause 3: Uneven grinding pressure

Prevent method 3: Even and consistent force when grinding by hand

Cause 4: Poor processing accuracy in the previous process

Prevention method 4: Improve the processing accuracy of the previous process and pay attention to prevent the deformation of the workpiece

Cause 5: Grinding time is too long

Prevention method 5: Reduce the grinding allowance, try coarser abrasives or improve the grinding speed and increase the grinding pressure

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Cause 6: inaccurate grinding tools

Prevention method 6: frequent inspection and repair of the grinding tool, the grinding tool wears out too fast can be replaced with other wear-resistant materials

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Defect form: knife marks

Cause 1: The quality of the previous process is not good, the luminosity is too low

Prevention method 1: The workpiece should be ground before grinding, and the luminosity should not be lower than 6 when using fine turning.

Cause 2: Abrasive is too coarse

Prevent method 2: use fine abrasives

Cause 3: The cutting heat generated during grinding is too high

Prevention method 3: reduce the grinding pressure, reduce the grinding speed and often add abrasive

Know about Metals Kingdom Industry Limited

Metals Kingdom Industry Limited is a professional manufacturer of Testing and Repair Equipment for Valves & Pipes since . Our Portable Valve Grinding Machine, Valve Test Bench Connecting rod synchronous telescopic mechanism, Portable Pipe Beveling Machine, Pipe Beveling and Cutting Machine all gained the National Patent for utility models in and , our factory passed ISO Quality Management Certificate in , and got the Certificate of Material Supplier by China National Petroleum Corporation and National Power Corp.

Amongst the various valve maintenance best practices to follow, grinding and lapping is high on the priority list as the procedure achieves a dense, flat surface. This effectively seals the valve seat surface in the valve body and on wedge/gate/globe/slide, to completely seal the valve&#;s metal-to-metal seat area.

An Essential Procedure

Valve reconditioning can be carried out in-situ, with the valve still fitted to the pipeline system, or in the workshop. In-situ valve lapping and repair tends to be more efficient, as it eliminates the need to remove the valve from the system. The only time workshop maintenance is more efficient is when a major valve rebuild is required.

In-situ valve maintenance requires that the bonnet is removed, and that sufficient space is available around and inside the valve body. To make the best use of the available space, ensure that the equipment you buy is light-weight, able to fit in tight spaces, as well as easy to attach. Your time onsite should be spent grinding the valve, not mounting the valve grinder.

Grinding equipment for use in the workshop needs to be easy to operate and adjust, versatile for use on several applications, and be able to extend capabilities with additional accessories for specialized applications.

Preparing for the Procedure

The following step-by-step procedure describes how to prepare the valve, as well as the basic steps to take in valve grinding and lapping:

1. Cover the area under and around the valve with plastic sheeting to prevent loss of parts and to contain dirt and grease.

2. Begin dismantling by removing any lagging. Clean the outside of the valve. Remove any rust and paint from nuts and bolts. Lubricate the bolts with penetration oil. Try to avoid any damage to the fasteners &#; even just one damaged nut will add an inordinate amount of downtime and cost.

3. Dismantle the interior parts of the valve. Clean, check and mark to ensure correct refitting. Clean the inside of the valve body, removing rust and any residual liquid. Check gaskets for cracks, corrosion, and defects.

4. Start the grinding by machining any large defects on the surface of the valve seat. Grind defects with portable valve grinders, using appropriate abrasives based on seat material and condition.

5. Remove grinding dust from the valve.

6. Leak-test the valve, ensuring it meets current standards.

7. Reassemble and refit the valve to its original position. Make sure the actuator still works.

8. Finally, write a report on the performed procedure.

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