Selecting the abrasive
When selecting the grade of grinding paper , it is important to note that grit and micron paper are graded according to different scales . For grit paper , the number on the back indicates the number of grains within a certain area . A low number means a small number of large grains and a coarse abrasive . With micron paper , the number refers to the size of the individual grain . A low number indicates that the particles are small and that we have a fine abrasive . This means that the scales indicating the grade of the abrasive operate in opposite ways for grit and micron paper . 100 grit and 100 micron provide roughly the same rate of abrasion . But beyond that , the two scales work in opposite directions . Grit paper is generally used to make the surface perfectly flat and micron paper to work up a smooth surface . The finest grades of micron paper can produce very smooth surfaces .
Alternatives to abrasive paper
If the seat material is very hard , diamond abrasive can be the solution . This is available as metal grinding heads with the diamond abrasive permanently attached . Because the diamond abrasive is very hard , there is no need to replace the grinding
material . The same grinding heads are just used over and over again . Another alternative is cubic boron nitride ( CBN ). This can be tried if even diamond fails to make an impact . Both diamond and CBN are extremely hard materials . They have the same structure , but diamond is made up of pure carbon , while CBN consists of boron and nitrogen . CBN is often the better choice when working with steel , as steel has a high affinity to carbon . The steel can absorb carbon atoms from the diamond and erode the grit . CBN , on the other hand , does not contain any carbon .
Light machines make light work
“ I have used both the modern , lightweight type of valve grinding machines and more sturdy , traditional designs and the difference is like night and day . The newer designs are far easier to work with ,” says Rickard Nyberg , technical support manager at Vimab , Sweden ’ s largest valve service company . “ Traditionally designed machines are heavy and cumbersome and can be extremely difficult to get into tight spaces . The modern machines I work with now , by contrast , are lightweight , easy to handle and simple to set up . With their multiple grinding heads they achieve very effective abrasion . “ They also have nifty little features that make the work easier . For instance , there
VALVE GRINDING
is no need to remove the whole rigging to grind the reverse side of the wedge in a gate valve – you can just raise the machine , flip the it over 180 ° and start again on the other side . You can also grind gate valves and globe valves with the same machine , which is a great advantage .”
Improved efficiency
With a light weight machine , you can today achieve the same surface finish with an in-situ repair as you would from a workshop repair using much heavier equipment . The explanation is the circle of individual grinding heads powered by shafts from a central grinding head . This provides accurate , controlled grinding action . Combined with appropriately selected abrasive materials , this will give excellent results in a short space of thim , ideal for improving the efficiency of valve service jobs in any application .
About the company LarsLap International is a manufacturer of valve grinding machines with individually driven grinding heads . The company , based in Sweden , provides machines , abrasives and systems to service a wide range of valves for users all around the world . www . valve-world . net Valve World June 2024
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