METHODS OF CLEANING AND POLISHING KEYWORK

Many different methods of cleaning keywork after assembling have been used. The high cost of labour makes cleaning by hand uneconomical for any thing other than small-scale production. High volume production of keywork demands cheaper and quicker methods of cleaning, which are less labour intensive.

Firstly we need to establish what exactly is being removed by the cleaning and then we can look at the various techniques available.

The main cleaning problem is the surface oxide formed on the keywork during soldering. If overheating is avoided and a good flux is used the area soldered should be protected from oxidisation. The area that oxidises most is the unprotected surface immediately around the joint that is not covered by flux. The heating causes the surface to rapidly combine with oxygen in the atmosphere, forming the discoloration on the surface called oxide.

Depending on the material used for the keywork, oxidisation will also occur naturally without heat but takes much longer to form. If the keywork is to be plated then all traces of oxide must be removed along with any residue flux or grease. Any flux left during cleaning could become trapped under the plating and would rapidly cause the plate to bubble and lift. In its dry powder state the flux is fairly inert but trapped under plating or left in a joint it will start to react with the metal.

Note! None of the cleaning methods available will remove or hide excess solder or bastard cut file marks. Most tend to make shoddy workmanship more visible.

ACID PICKLE

For non-ferrous alloys the main pickle used is dilute sulphuric acid. The usual concentration of pickle is 10%, 9 parts water to 1 part sulphuric acid. One part of nitric acid is sometimes added to speed the cleaning process; this gives it “bite”. The acid pickle can be used cold but it cleans faster if either the acid is heated or the keywork is hot when placed in the acid.

Pickle is a relatively cheap method of removing oxide and residue flux but it has several drawbacks as well. The acids used are not selective in what they dissolve; they will attack clean surfaces faster than those covered in oxide. All sharp edges will show attack most, so avoid leaving keywork in acid longer than necessary.

The pickling of keywork while still hot is the most rapid. The thermal shock combined with the heating of the pickle gives a very fast cleaning action.

The main problems associated with pickling are the actual acids. In the concentrated form they are very dangerous and great care must be exercised in their storage, mixing and use. When mixing concentrated acids with water always add the acid to the water; never water to acid. During mixing, large amounts of heat are generated and the solution could even boil. By adding the acid to the water you can control and limit the reaction.

The fumes given off during use will condense on cool surfaces and produce holes in clothes and corrode any nearby tools or machinery. Where possible use acid pickle in a separate well-ventilated room. Protective clothes should always be worn, even when using dilute solutions. The spent pickle solution must also be safely disposed of. During pickling very high concentrations of metals build up in the solution, which are very poisonous.

Another problem likely to be encountered with pickling is contamination. It is important that the pickle is not contaminated with iron otherwise it turns the surface of all the pickled items “pink”. Keywork should not be pickled while it is still wrapped with binding wire, or if it has a rod screw in it. Brass, copper or plastic tweezers must be used for removing work from the pickle; extracting work just once with a pair of steel tweezers (even stainless steel) would result in the pickle being contaminated. Once contaminated the only course of action is to discard the pickle, clean the vessel and mix up a new batch.

“SAFE PICKLE”

There are so called “safe pickles” available, some are commercially available from jewellery suppliers such as Walsh’s or Cookson’s. These are essentially caustic rather than acid. They are to some extent safer, but the chemicals are still an irritant and precautions still need to be taken to prevent contact with skin and eyes. The chemicals may also damage clothing’s and furnishings. They tend to be less corrosive to tools but are still contaminated by iron so it is just as important to not use iron implements to place or remove work from the pickle or to allow any iron to be inadvertently pickled. Another safe pickle which can be used on non ferrous metals is Alum, this can be bought from Chemists shops. It works on Silver and brass but I have never tried it on Nickel silver.

Other things worth trying which can loosely be described as pickles are:

Brown sauce, Tabasco, Worcestershire sauce, malt vinegar, washing soda, drain cleaner and Coca cola.

Care has to be exercised when experimenting with any of these substances. Brown sauce, Worcestershire sauce, malt vinegar, and Coca cola are relatively safe and little harm can come to you using them. The method is to either coat the key or submerge it in the substance and leave it for some time (several days, these aren’t powerful pickles). It is however important to note that these substances are no longer fit for human consumption once they have been used for pickling. Washing soda and Tabasco are irritants and contact with eyes and prolonged contact with the skin should be avoided. Ingestion of washing soda should defiantly be avoided; the jury is still out on whether it is safe to ingest Tabasco. Washing soda will need to be heated to produce an effective pickle but avoiding contamination is still important. It’s always important to look what the active ingredients on the drain cleaner is before considering it and to look what precautions are recommended by the manufacturers. Generally not a safe option!

Cilit Bang is something else worth a try, I haven’t tried it yet but if the manufactures claims are anything to go by then if should be useful for our purposes.

SHOT BLASTING

Shot blasting is an alternate method of removing oxide and flux from keywork. The equipment necessary is more expensive to purchase and operate than acid pickle but it is more environmentally friendly. The larger machines used by heavy industry have a cabinet into which the work is introduced by a series of rollers. There it is bombarded by steel shot thrown by a spinning wheel. These machines are sometimes called wheelabrators because of the way the shot is thrown.

The smaller machines which are used for our type of work consist of a cabinet with a hinged door through which the work is placed and one or two thick rubber gloves built into the cabinet sides. The work is placed into the cabinet and the door closed. The work is then held and manipulated by the operator's hands inside the rubber gloves. The cleaning material used is an abrasive that is blown at the work through a nozzle with air from a small compressor. The surface finish and cleaning rate is controlled by the particle size and type of abrasive used.

ULTRASONIC CLEANERS

Ultrasonic cleaning units are used for degreasing and final cleaning of intricate items. The jewellery and electronic industries make extensive use of ultrasonic cleaning machines for cleaning watches and circuit boards. Due to the cleaning action the items do not have to be stripped or disassembled prior to cleaning.

Ultrasonic cleaners work by vibrating the cleaning fluid in the tank at a high frequency so dislodging the particles from the item being cleaned. Anything placed in the cleaning tank also vibrates which assists the removal of surface oxides. These cleaners can be used with a variety of cleaning fluids depending on the application. Solvent-based cleaning fluids are used for removing grease, and ammonia based for removing oxide. The larger units have heaters fitted to increase the cleaning action and refrigeration coils above the tank to condense the liquid evaporated by the heating.

BARRELLING OR TUMBLING

Barrelling is used to remove surface oxide and improve the surface finish. The barrel used is usually hexagonal in cross section and it is this shape which imparts the tumble action. The drum is only part filled with the items to be cleaned, water and a barrelling media to suit the particular application. The barrel is very slowly rotated and because the barrel has corners the work is carried up with the drum until it falls back into the bottom. This tumbling action rubs the work together with the tumbling media removing the oxides and polishing the surface.

The tumbling process is very slow and could take several days to complete depending on media used and surface finish required. Tumbling is not a selective cleaning process and needs careful use to avoid loosing too much detail. The tumbling media used for cleaning is usually triangular shaped ceramic chips which grind away at the surface and steel balls or pins which polish. T. W. Howarth the oboe makers clean all their keywork to a 400 grit finish and then barrel tumble for a final finish before plating. The only work polished on a mop is the actual touches of the keys which all have a rounded shape.

A recent development of tumbling is the use of shallow barrels that rotate horizontally, these are said to give a much quicker cleaning action than the traditional barrel style.

POLISHING MOPS

Polishing mops are sometimes used before and after plating to give the keywork its final polish. Depending on the type of mop and compound used this polishing process can remove large amounts of material. Buffing is often seen as a tempting soft option when it comes to cleaning keywork. It looks deceptively easy to do, but it requires a lot of practise to buff successfully without ruining the work. The main problem is the way the buff catches edges and rounds any sharp corners.

The machine we have in our workshop is only intended for light occasional use. The larger industrial machines have continuous rated motors of up to 5 hp and air extraction systems to remove lint and particles from the workshop environment. Extended spindles can be fitted to polish the inside of saxophone bells etc.

Protective clothes and eye protection must be worn at all times. Due to way the mop revolves if the work is offered to the wrong part off the mop it could pull the work out of the operator’s hand resulting in damage to the work and operator. Always buff using the lower section of the buff where it will only pull the work away from you and not throw it at you. The biggest danger when using a buffing machine is loose items of clothing etc. becoming entangled with the revolving spindles and dragging the operator into the machine. All bare spindle between buffing mop and motor should be guarded, a free turning tube is the usual method of guarding the spindles.

Various types of mops and polishing compounds are made to cover the range of application. In general the hard mops such as calico mops are used with the coarser polishing compounds and the soft mops, swans down are used for the fine finishing compounds. Some mops are stitched to make them “stiffer” or harder.

POLISHING COMPOUNDS

Tripoli - A general purpose compound suitable for use on most materials. Will produced a good finish but can vary depending on supplier of compound.

Hyfin - Supplied for finishing stainless steel and plastics. Produces a very good finish on nickel silver and brass, superior to Tripoli.

Rouge - Used for final finish on silver, gold and none ferrous. alloys. Produces very fine finish. Several different types are available some are cleaner to use than others.

Vonax - Intended for perspex and ebonite but produces a very good finish on blackwood.

The golden rules to producing a good finish are: keep one mop for each compound and different material. Keep compounds separate from one another and away from dust and contamination etc.

The mops gradually wear away with use, but the mop surface can become badly clogged with compound and metal. To re-surface mop, cut it down by holding a stiff wire brush against the face of the revolving mop and then re-apply fresh compound. A special tool called a mop rake can be bought or made for this purpose, as its name suggests it has a number of teeth with break up the tangled fibres on the edge of the mop and cleans out the caked compound and waste. It is also possible to carry out this possess with the back edge of a tenon saw, ask for a demonstration of this if you are unsure.

Other types of wheels and compounds can be used when it is necessary to remove greater amounts of material. Hard rubber wheels with abrasive bonded into rubber are used for finishing steels etc (violinmakers use this type of wheel for sharpening knife blades). Soft rubber wheels with abrasive bonded in are used for cleaning most materials. The wheels are made from the same materials as the blocks that we use to clean keys etc. Being flexible and soft they adapt to shape being cleaned. Coarse carborundum compounds are sometimes used on hard felt mops to remove deep marks etc prior to finishing.