Tip extraction is an effective method of removing solder fumes at source via a tube attached to the soldering iron handpiece. It is a relative low cost solution, provided it is WELL MAINTAINED on a regular basis. What starts out as an efficient system can soon be nothing short of a disaster over a short space of time. Typical problems that can occur include:
1: Stainless Steel Extraction Tubes: Extraction tubes on the iron can block quickly with resin particulates – a sticky honey type residue that forms on the nib of the tube. Once this is allowed to build up it reduces the cross sectional area of the tube which then causes a restriction in the airflow, which in turn causes even more blockage until the tube is totally blocked. Once this resin cools it is extremely difficult to clean out – in fact often it can involve using a twist drill to bore out the tube or replacement is the only option. The internal diameter of the tube is also very important and should be NO LESS than 5mm. Any smaller will make it difficult to pull the correct optimum airflow of 28-30 litres/min and encourage premature blockages. The tube should be straight and have no bends that can make tube cleaning difficult. Brass cleaning brushes must be readily available to all operators at all times, and replaced when twisted and clogged with resin!
2: Silicon Hoses: The next and possibly biggest problem can be caused by the silicon hose connecting the iron tube to the under bench gland. The silicon recommended for tip extraction is not just ‘off-the- shelf’ tubing that can be found lying around or purchased from a local hose supplier. Firstly silicon hose by its very nature is heat proof which is why it is used. It is not easily burnt by a soldering iron tip at over 300 degrees C, and it is very flexible, unlike nylon tubing that has a memory and can get very stiff over time. However, clear silicon has the problem of being a large static generator which is used in an EPA has the obvoius disadvantages of holding a large voltage…not ideal.
Therefore conductive silicon hose is recommended which is carbon loaded and earthed via the stainless steel tube and the operators hand, via a wrist band and cord. It is black in colour and despite comments like ‘you can’t see when the tube is blocked if it’s black’ is unfounded, as even clear silicon will be yellow with resin particulates in a very short space of time. So, not only is conductive silicon recommended, the CORRECT TYPE of silicon is also critical.
The optimum INTERNAL DIAMETER of the silicon should be 5mm minimum and no more than 6mm. The wall thickness must not be too thick or the overall outside diameter will be too bulky to be used comfortably, this should not exceed 1mm.
This then brings us to the ‘hardness’ of the silicon tube as ordinary silicon tube would collapse at these dimensions; therefore tip extraction silicon tubing should be of a high ‘Shore A’ hardness of 60 or higher to prevent wall collapse. The next common problem with this hose becomes critical to the overall performance of the system – the LENGTH. Tests have shown that a large pressure drop is found in small bore tubing and for every 200mm of hose there can be as much as 2 litres per minute drop in air volume. Multiply this over the entire system and it can lead to major problems.
The ultimate length of the silicon hose should be no more than 1.2m in length MAXIMUM. If the installation ducting is installed correctly then 1.2m has been proven to be plenty long enough to cover a typical work area when hand soldering. More on this later, but it is not uncommon to find two or three lengths of silicon hose ‘joined together’ with all sorts of objects – pen barrels, spare extraction tubes, electricians tape to name a few!. Usually this is done by an operator because the nearest connection gland is too far away. The correct action is to extend the main trunking nearer to the operator to allow the 1.2m hose to be used as intended. See ducting section further on.
Connection Gland: The method of connecting the silicon hose to the main ducting is also critical and must not restrict the diameter or airflow at this point; therefore these should also have a minimum internal diameter of 5mm. They should not be brass or metal as warm air can condense on the metal gland which causes blockages very quickly. These glands should be secure in the pipework – ideally threaded – to prevent them falling out and should always point downwards towards the floor to prevent the hose from ‘kinking’ and blocking off the vacuum. The gland should be brought as close as possible to the operator – either left or right – and close enough to avoid crawling under the bench to enable ease of cleaning, plus the added benefit of keeping to the 1.2m length of hose as above.
Main Trunking: The ducting that carries the fumes back to the pump unit is usually between 32-50mm in diameter and sometimes ESD safe – however these are usually mounted away from any bench top area so ESD is not essential. Push fit connections make for easy relocating so this should be the preferred type. Avoid metal pipes. The ducting should be taken the shortest route and extended to reach the FRONT of each operators bench – not at the rear as this makes it difficult to attach the silicon and cleaning etc, plus the 1.2m silicon will then not reach the bench area. Avoid running ducting on top of each bench at the rear as the silicon hose is then trailing across the work area and can get pinched or trapped.
How do we calculate 28-30 litres min ? This is how : Let’s take the ideal 5.6mm bore tube (internal). Area = πr2 (in metres) = π x 0.0028 squared = 0.0000245 metres squared.
Multiply this by the airspeed (20m/s recommended for solder smoke/fumes): 0.0000245 x 20 = 0.00049 cu/m/s. Multiply this by 3600 to convert to cu/m/hr = 1.764 cu/m/hr or 29.4 litres min (28-30!)
(Do the same as above with a 4mm tube and the answer is only 15 litres min! This will not allow the fume to be captured correctly and tubes will block fast)…
