Note 56: Mass Spec Maintenance & Cleaning Utilizing Micro-Mesh® Abrasive Sheets

By John J. Manura

INTRODUCTION

We have had many requests over the years for a fine grit sandpaper to clean quadrupole rods and other mass spectrometer source parts. Most commercially available sandpapers or emery papers were too coarse or degraded too rapidly. We had several reports of some mass spec servicemen using a fine abrasive product to clean quadrupole rods, so we set out to find a source of a fine abrasive cloth for various uses in cleaning mass spectrometer parts, in particular for cleaning quadrupole rods, source slits and other source parts. The product we eventually decided to market is known as Micro Mesh Cushioned Abrasives.

Table 1 - Micromesh Abrasives

 

Product No.	Description	Color
MM-1500	4" 6" sheet, 1500 Grit	Violet
MM-1800	4"x 6" sheet, 1800 Grit	Pink
MM-2400	4"x 6" sheet, 2400 Grit	Grey
MM-3200	4"x 6" sheet, 3200 Grit	Blue
MM-3600	4"x 6" sheet, 3600 Grit	Green
MM-4000	4"x 6" sheet, 4000 Grit	Yellow
MM-6000	4"x 6" sheet, 6000 Grit	Orange
MM-8000	4x 6 sheet, 8000 Grit	Red
MM-12000	4x 6 sheet, 12000 Grit	Green

Micro Mesh not like conventional abrasive sheets or sandpaper. In the case of Micro Mesh products, there is a cloth backing upon which a thin latex film is applied. The various sizes of aluminum oxide crystals are adhered onto the film in such a manner that the crystals are held in a resilient matrix, as opposed to a hard matrix. This construction allows the crystals to remain adhered to the backing even when used under pressure. What is unique about the cushioned abrasives is that they do not produce any random deep scratches. Instead, they produce an extremely uniform scratch pattern over the entire work surface. The cushioned Micro Mesh abrasives also have an extremely long life, since the crystals will continue to cut effectively until they eventually become dull and lose their sharp cutting edges. This product line was initially developed to remove scratches and to polish the acrylic windows on aircraft, but additional applications have included polishing all metals, plastics, PTFE, Vespel® and many other natural and synthetic materials. The normal procedure involves the use of a range of abrasive sheets. By beginning with the coarser grits and successively using finer grits, mirror finishes can be obtained.



Figure 1 - Micromesh can be used to clean mass spec probe rods.

The starting grit size is determined by how deep the scratches or imperfections are in the item you are cleaning. On cleaning items, as mass spectrometer direct probes (Fig. 1), it may be necessary to begin with the coarsest grits of abrasive to remove the deep scratches. Once you begin cleaning with a specific mesh size, you must continue the cleaning process with the next finest mesh size. It is important that none of the intermediate mesh sizes are skipped. Each successive grit size must be used in mesh size order to remove the scratches from the previous mesh size. By using the successive mesh sizes all the way down to the 12,000 mesh size, a mirror finish can be obtained (Fig. 2). This finish is finer than the finish which could be obtained even with buffing wheels and without the mess. The Micro-Mesh abrasives can be used either wet or dry, depending on your preference. Most users prefer to use the sheets dry without any water or other lubricant. Individual sheets can be washed out and used again. The Micro-Mesh products may cost more than ordinary sandpaper, but it produces finishes ten times finer and lasts 10 to 20 times longer. Every sheet is color coded (see Table 1) for easy reference and has the grit size written on the reverse side. Grit sizes range from 1500 grit to 12,000 grit. The higher the grit number, the finer the cutting action. The finer meshes are ideal for cleaning and polishing source slits and quadrupole rods.



Figure 2 - Micromesh can be used to clean mass spec metal filaments.



Figure 3 - Cleaning Source Slit With Micromesh

Other uses of the Micro-Mesh abrasives include the cleaning of source slits (Fig. 3) which cannot be cleaned by other materials since they would round the slit edges or remove too much metal. Cleaning quadrupole rods and other source parts is easily accomplished with minimal surface metal removal. SEM sources can also be cleaned in a similar manner. A related product is the Micro-Mesh polishing board (Fig. 4). This emory board sized polisher contains three of the finer grits and is ideal for reaching into tight spots, and for general instrument part cleaning where an abrasive sheet with a stiff backing is preferable. The Micro-Mesh boards are used just like the Micro-Mesh sheets, starting with the coarsest area and working toward the finest area. In our shop we use these boards for cleaning the electrodes on our spotwelders and also for cleaning filament posts. These boards are also useful for cleaning quadrupole rods. The Micro- Mesh polishing board has three different polishing surfaces on its two sides. On the side with the two sections, the dark granular gray, section is the coarsest grit and should always be used first until as many as possible of the visible scratches have been removed. The neighboring white section is the next finest grit and should be used next. This section will further smooth the rough edges and scratches caused by the first grit. Finish polishing with the opposite side of the polishing board. This side is medium gray and is the finest abrasive. This should remove the finest scratches. If not, it may be necessary to back-track to the coarser grits and repeat the operations. Remember that the polishing board is primarily for tight areas and corners and cannot be expected to do as complete a job as the Micro-Mesh sheets. It can however, do a fine job in places that are hard to reach.



Figure 4 - Micromesh Polishing Boards

Directions For Using Micro-Mesh Abrasives

1 . Wipe off the object to be cleaned with a rag or cloth. Any loose, hard material left on the subject could possibly cause deep scratches which may prove difficult to remove.

2. Begin with the lowest number grit required to remove the scratches. (begin with the 1500 grit if the surface is fairly rough). Polish in straight lines completely covering the area to be polished. Further polishing with subsequent grit sizes should be done at right angles to the previous grit until the scratches and imperfections are no longer clearly visible. If the scratches or imperfections are very deep, it will probably be necessary to first sand the area with conventional 200 grit emery paper to prepare the surface for subsequent cleaning with the Micro-Mesh Abrasives.

3. After two to three minutes of polishing with the Micro-Mesh cloth, begin using the next highest grit number (next finest grit) of Micro-Mesh abrasive cloth and repeat the procedure in step 2. Remember to always work at right angles to the direction of polishing with the previous abrasive grit size.

4. Wipe off the object to be cleaned with a rag or cloth between abrasive grits to remove any loose, hard material left on the object.

5. Continue working with successively finer grits until the finish you desire is attained. Continuing all the way to the 12,000 grit sheet will produce a bright mirror finish on most smooth metals. A bright, shining surface can sometimes be achieved quicker depending on the metal and the initial condition of the surface. For additional information on the availability of the Micro-Mesh products, please refer to Scientific Instrument Services complete catalog.

For additional information on Micro Mesh including availability, visit our WEB pages on Micromesh or see our catalog.

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