MOPS ,COMPOUNDS,FINISHING DIFFRENT METALS AND PLASTICTS

poliMop Construction.

There are many methods of mop construction but for the purposes of this article we will concern ourselves with the two main methods:-

• Open - these are made from whole discs of fabric with a centre assembly of leather washers stapled together or for the smaller types, a stitched centre. These mops present a flexible surface to the work being polished and are generally used for semi-finishing and final colouring depending on the type of fabric used.
• Stitched - these are used for general purpose and heavy duty polishing where stiffness of mop is required. They may also be dressed with glue or cement and abrasive as described in the previous article. Any type of mop can be stitched but the term usually applies to the type of mop made from assorted pieces of coloured or white cotton cloth in various grades. It also applies to the Sisal stapol mops as they are invariably stitched. The mop sections usually have a thickness of approximately ¹/₂" and are concentrically machine stitched and the complete mop is made up of one or more sections.
• The method of stitching varies depending on the amount of stiffness required and are generally in three categories: Open stitched - General purpose, close stitched roughing and scurfing and Very close stitched for heavy duty work.
• In addition to the names which describe the fabric or method of construction, mops may also be described as: Brown unbleached: White cutting: Finishing, swansdown, colouring.
• The brown, unbleached cloth (calico) mops are in the main used for general purpose polishing and are made from specially woven, long, stapol cotton to ensure maximum life.
• White cutting mops are made from stiff, white fabric which incorporates a special dressing which reinforces the fabric, keeping the mop stiff and reducing fraying to a minimum. These mops are usually used for initial polishing where a rapid cut is required.
• Finishing, swansdown and colouring mops are made from special, soft, unbleached cotton cloth and are used chiefly for the final finishing or colouring operations, using a lime finish or rouge composition. Swansdown is the softest type for the polishing of jewellery.
• To prepare a new mop prior to use on a polishing spindle and before applying any composition, the mop should be placed on the spindle and a mop dresser or wire brush held against the periphery as the mop revolves. This ensures true running and levels the face and also causes the threads to be knitted together, giving a smooth, velvet-like surface.

Polishing Compositions.

• A polishing composition consists of an abrasive such as tripoli, calcined alumina, aluminium oxide, rouge or lime, together with a grease bond.
• The grease content of the composition serves a number of purposes. It holds the abrasive particles together in the composition block, helps the abrasive to be retained on the mop face and acts as a lubricant during the polishing operation. Polishing compositions are usually found in bar form so that they can be easily applied to the polishing mop. To be effective and economical in use the composition must soften under frictional heat from the mop, just sufficiently to enable the abrasive to be taken off by the mop and to give a clean cut on the surface being polished.
• Cheap compositions containing, e.g. lustre, are generally used for the preliminary polishing of non-ferrous metals such as Copper, Brass, Pewter, etc.. It can be used on aluminium but will not give a very bright finish as aluminium requires very sharp cutting abrasives.
• Aluminium oxide compositions such as Carbrax and Satene from Cannings or Cetem Brown are mainly used as a cutting medium for bright finishing operations prior to the final finishing or colouring operation and may be used on Steel, Stainless, Aluminium and non-ferrous metals.
• Calcined alumina based compositions, e.g. Hyfin by Cannings or Cetem Blue or White, were originally developed for the polishing of stainless steel but are now widely used for the final polishing and colouring of steel and non-ferrous metals, especially aluminium on which it excels.
• A lime based composition such as Cannings' Peerless is traditionally used on non-ferrous metal after tripoli polishing to colour or clear the polished surface. 'Clearing' removes any grease smears and reveals the polished finish.
• Rouge compositions are used for the ultra-fine polishing of precious metals such as gold and silver and can be used on other non-ferrous metals when colouring where extra brilliance is required.

Final colouring and finishing - polishing applications.

Where a mirror finish is required a further polishing stage is necessary. This is usually known as the 'colouring' or 'finishing' stage. For this operation an unbleached calico mop, e.g. B or G quality, is generally used with a calcined alumina based composition such as Cannings Hyfin, Chrome Gloss or Cetem Blue or White, or even a rouge composition. The term colouring as previously stated in the first part is applied purely to the final finishing operation and is not a cutting operation as in the previous two stages. Hence the use of very soft mops.

Polishing Steel.

With steel pressings or bright drawn bar or tube it may only be necessary to use a single polishing operation before electroplating, i.e. no abrasive finishing or final colouring stages. For this polishing operation a sisal mop used with an aluminium oxide composition such as Cetem Brown is ideal. A good, bright reflective finishing is generally achieved with this in one operation. If, however it is felt a much brighter finish is required then a further colouring stage, using a calico B mop with a fused alumina compound such as Cetem White or Blue, will achieve a bright, mirror finish. If an abrasive finishing operation is required - start with 90 or 100 grit through 150/180 grit and finish with 220 or 250 grit aluminium oxide.

Cast Iron.

Iron castings are generally treated using abrasive belts or scurfs. The grade of abrasive necessary for the initial stage will depend upon the surface condition and may be as coarse as 60 or 90 grit, aluminium oxide being the best abrasive due to its superior cutting abilities. The abrasive operation is carried out as previously' described and for the final abrasive operation a 220-240 or 320 grit abrasive should be used depending on the finish required, the abrasive being lubricated with a good bobbing grease. Where a brighter finish is required the casting may then be polished with a sisal mop in conjunction with an aluminium oxide polish such at Cetem Brown, as for steel. There may be, however, a tendency for the casting structure to be opened up.

Stainless Steel.

Stainless steels are usually more difficult to polish than ordinary plain or mild steel but the use of a good quality aluminium oxide polish such as Cetem Brown and a sisal mop will ease the process. Depending on the condition of the metal prior to polishing, an abrasive finishing operation may be required - use only aluminium oxide belts, flap wheels or abrasive dressed scurfs as emery is not hard or sharp enough for this material. Step down through the grit sizes as for steel or cast iron. For final finishing use only calcined alumina such QS Cetem Blue or White with a white stitched mop. Where Cetem Brown has previously been used only a light polishing should be required. If an extremely high reflective finish is required, a final colouring operation may be carried out using Chrome-Gloss with an unbleached calico mop such as B or G quality.

Non-Ferrous Metals.

Brass Castings generally require an abrasive finishing operation, using felt bobs or scurf mops dressed with emery or aluminium oxide (when using aluminium oxide it is recommended to use two grades finer). Generally it is necessary to start with 100 or 120 emery and finish with 180 grit. Many components may be finished with abrasive belts or flap wheels. Alternatively Cetem Brown may be used with a sisal mop if the surface is not too rough. After bobbing or abrasive finishing the castings are greased mopped with a Tripoli composition such as Lustre with a hard coloured or white stitched mop. To clear the surface and bring up a high reflectivity the brass can then be finished with a calcined alumina composition, e.g. Cetem Blue or White, on an unbleached calico B mop. As an alternative a rouge composition can be used. On brass with a good initial surface it may be possible to obtain the required finish using Cetem White on an unbleached calico mop without the need for a previous greased mopping operation.

Aluminium & Zinc Based Alloys.

Aluminium sand castings are initially abrasive finished using belts, flap wheels, felt bobs or stitched mops dressed with abrasive. Use only aluminium oxide grits with a good binder or adhesive as emery tends to embed itself in this material and can cause dragging or tearing of the metal. This is due to the fact the aluminium is an abrasive and clinging material and requires very sharp cutting edges to machine it. After the abrasive finishing operation a bright finishing stage is required using an aluminium oxide composition such as Cetem Brown on a sisal or white stitched mop followed by a final colouring operation using Cetem Blue or White with a soft, unbleached calico G mop. If a satin or matt finish is required, Cetem Brown used with a sisal mop gives a finish suitable for satin anodising. On aluminium castings, where the cast dimpled finish is to be retained but is required to be brightened up, a Fibral satinising mop can be used dry, without any polish. These come in coarse, medium, fine and very fine grades aluminium oxide impregnated grit.

Polishing Plated Deposits.

Nickel plated articles from an ordinary dull plating solution require finishing if a reflective surface is desired. For this purpose Peerless polish is used on an unbleached calico mop. Small articles and where deposits are thin a soft Climax or Swansdown mop may be used. Most dull nickel deposits are soft and easily finished to a high reflectivity. Where hard deposits are encountered then a fast cutting white stitched mop may be used, care being taken when polishing corners and projections to avoid cutting the deposit. Alternatively Cetem White, Blue, or Chrome Gloss may be used with a soft calico G mop but not on thin deposits.

Chrome Plate.

Chrome deposits should be bright from the bath but can be coloured if necessary with a Basil leather mop and Peerless composition. Where chrome deposit is dull or has dull patches Cetem While or Blue should be used on an unbleached calico B or G mop to produce a brilliant surface. This composition may also be used to remove any burnt portions of the chrome deposit and bring up the required finish. For final colouring Chrome Gloss may be used on an unbleached calico B or G mop.

Plastics.

• Although many plastics are moulded with an in-built gloss, polishing is sometimes still required. Not all plastics are suitable for polishing and most reflective results are obtained on plastic having a rigid surface and relatively high softening temperatures. Wax-like materials such as polythene and resilient materials such as PVC are difficult to polish. In view of the wide range of plastics available they may be broadly divided into two groups, i.e. Thermoplastics, which soften on heating such as ABS, Polycarbonate, Polystyrene, Nylon and Acetates, and Thermosetting which permanently set on heating, e.g. Epoxies, Bakelite, Melamine, Perspex, and Polyurethane. The equipment required is basically the same as for metals. Large mops are usually preferred because they generate less frictional heat through being more flexible due to their higher surface speed. A large open mop remains cooler because any point on its periphery makes contact with the plastic less frequently than its corresponding point on a smaller mop revolving faster but having the same surface speed. For the actual polishing process in which scratches are obliterated and a high gloss is imparted, mops of unbleached calico B or G quality are generally used. These can be used with a tripoli based composition such as lustre. A final clearing operation is carried out with a mop of much softer fabric such as Climax or Swansdown. This is used with a special composition, formulated specifically for plastics such as Vonax. This will remove the excess of greasy composition and clear the surface of smears and give increased 'depth' of finish, it is most important to use as large a mop as possible and light pressure to avoid overheating and softening of the surface of the plastic. Plastics which respond best to polishing are as follows: Perspex, Tufnol, Epoxies, Casein, Bakelite, Formica, Polyester, Polyurethane.
• Remember, polishing is a skill and the best results can only be achieved with experience and practice.
• If you have any polishing problems you can rely on Cetem to help you and to give good, sound, practical advice. Cetem use only the best industrial quality materials which cannot be obtained through retail outlets. We also supply to the trade and can set you up if you intend to start your own polishing business. We can supply large industrial size mops, polishing machines, abrasive belt machines, coated abrasives, grinding wheels, loose abrasives - in fact anything used in the polishing industry. Come to Cetem for all your polishing and abrasive materials. We try to supply your every need.

CETEM RESTORATION SERVICE

Cleaning Finned Heads and Barrels.

• Cleaning cylinder heads and barrels at home is a very laborious task and satisfactory results are difficult to achieve on iron, and impossible on alloy without enlisting the services of a specialist.
• A few weeks ago I stripped a Triumph T100 engine (the one with close-finned all alloy head and barrels). Time was, as they say of the essence as it was Friday night and I intended fitting the head, barrels and pistons to my own machine next day.
• The engine was the oiliest I have ever seen as the external rocker drain pipes had been leaking, the fins were painted matt black and were thickly coated with burnt-on oil and road dirt. The ports and combustion chambers were heavily encrusted with carbon. By 10 p.m. I had the lumps on the bench with valves and cam-followers out ready to start cleaning. After some browsing around the cans and bottles in the garage looking for something stronger than paraffin, I started to search the kitchen and got my oily hands on an aerosol of "Shift" Magic Three Minute Oven Cleaner with a large warning on the label "do not allow to come into contact with aluminium or painted items". This must be good stuff I thought. So I put head and barrels in the oven and settled down to watch the last bit of "News at Ten".
• When heating alloy components to fit bearings, valve guides etc., I aim for 100 C. and avoid heating much above this unless a very tight bearing is refusing to budge when reasonable forces are applied. Avoid heating with a flame if possible. The temperature is easily checked using "Bethel's right hand rule" i.e. lick the tip of the forefinger of the right hand and touch it momentarily onto the hot alloy, if it sizzles (i.e. water boils) then component has reached 100 C. If finger blisters it is too hot! Using oven gloves I removed the hot items from the oven and placed them on an old table in the -'garden. I then sprayed "Shift" all over them, well into fins and ports. Violent effervescing followed and my vital parts disappeared in thick choking fumes. Very nasty ! I stepped smartly back out of harm's way and remember thinking how fortunate that the parts were only off a Triumph. After a few minutes the activity subsided and I got the parts under the hot tap (don't use cold water as they are still hot at this stage). As if by magic all the Shift was rinsed away (yes Shift) along with carbon, paint and oil revealing finning still intact. Most of the carbon from the combustion chambers and ports had disappeared. Much encouraged by this I spent some time scratching nooks and crannies deep inside the finning with various implements; then gave the parts another dose of treatment. This time I learned why "Shift" must not be used on aluminium: it turns it black! The ammonia in the cleaning agent reacts with the clean aluminium (I'm guessing now) and turns it dull grey in colour. So next morning found me sitting on the doorstep of my nearest friendly auto engineering firm where they let me use their bead blaster in exchange for green folding drinks vouchers, which the owner pops into his back pocket. I found the black/grey discolouring disappears instantly under the bombardment of nylon beads, and as head and barrels were quite clean apart from this I soon had them in as-new condition.
• To summarise then, oven cleaner can be useful for cleaning very dirty aluminium heads and barrels which are to be subsequently bead blasted, giving a significant saving in bead blasting time. It can also be used to remove carbon from ports and combustion chamber. and piston crown avoiding the damaging scratching and scraping usually resorted to. On an iron barrel or head it will remove carbon, oil and old paint without the discoloration problem.