WORKING POLICRIL TUBES
Policril tubes generally can be mechanically worked with the same tools and methods used for light metals, normally it is not required to use lubricants, in the case of excess heating water or emulsion oil can be used.
A normal metal hand saw can be used; better and quicker results however can be obtained by using a band saw or a circular saw. In the case of the band saw a speed of 800 – 1200 metres per minute is recommended with a blade 3:7 teeth per cm and a peripheral speed of 2000-3000 m/min. It is necessary to remember that the thicker the tube, the less number of teeth required. To avoid splintering it is necessary that the sharpening be uniform, whilst to avoid localised overheating compressed air or water can be used for cooling, normally however this is not required.
Drilling is done with normal twist drill bits used for metal, well sharpened and quite flat (approx 110°).
The optimal cutting speeds are:
Diameter 1.6mm 7000 revs/min
Diameter 6.35mm 1800 revs/min
Diameter 12.70mm 900 revs/min
To avoid breakage when the drill bit emerges from the other side, it is necessary that the drill progresses slowly in order to reduce the suction effect of the drill bit as it enters the thickness of the tube. To achieve this, it is best to utilise a drill with a manual progression command which enables you to control any eventual overheating. It is however advisable to lubricate with water or oil. To achieve large holes the use of a milling cutter is recommended.
The normal turning process used for non iron metals such as bronze and aluminium are suitable for Policril tubes; for the finishing a speed of 900 revs/min is recommended with a progression of 1/5 mm/rev and also a cut of 1/50 rev/min. The utensils used can be of common steel and the most adequate characteristics are:
Cutting angle 60°
Back slope angle 10°
Clearance angle 20°
It is good practice to avoid sharp edges and drastic section variations. The shavings should be eliminated with a jet of air or another method in order to avoid scratches. For lubrication during cutting water or oil can be used.
The same progression and cutting speeds used for non iron metals are recommended. Concave cutters give a good finish which can be further improved by using an adequate lubricant.
THREADING AND TAPPING
Both can be carried out during turning or manually by utilising standard screw plates and taps for metals, ensuring not to use excess force and lubricating with emulsion oil or another lubricant. Normally roughing tools give a better result than finishing tools and avoid sharp edges which tend to favour breakage.
GRINDING AND SANDING
Both can be done manually utilising middle files suitable for metals or sand paper. Sanding machines can also be used but it is important to avoid localised overheating.
Excellent and rapid results are obtained using a polishing machine with buffer disks at a rotation of 1000 revs/min, with a yellow abrasive paste initially and then a white paste for brilliance at the end, ensuring not to apply too much pressure on the disk in order to avoid the surface overheating.
Seeing as the tubes are often polished using polishing machines, before gluing it is absolutely essential that, where possible, the tube is heated in an oven at 55-60°C for at least 6 – 7 hours; this is necessary in order to eliminate any tension in the material created during polishing. If instead it is not possible to put the tubes in an oven, it is possible to eliminate tension in the material by heating only the surface which needs to be glued with heated plates, paying attention that the heat is not excessive to avoid deformation. The above mentioned process guarantees that the solvents normally contained in glues do not cause crazing or frosting.
Heating at a temperature 130-150°C renders Policril tubes plastic like and flexible as if of plastic rubber and in this condition they can curved into any shape. Once cooled down they maintain the shape created.
The heating of the material can be carried out with electric or gas ovens or infrared rays. It is essential to avoid overheating which may damage the tubes beyond repair.
Air pressure bending in twin female mould halves is the most indicated method for continuos production and when a high quality finish is requested.
With this system it is possible to achieve a perfectly circular section. The air pressure is maintained by using conical caps which are applied at the two extremities of the tube.
These caps are made up of a flange which has the same internal diameter as the external diameter of the tube and a cap with a conical trend (15° – 20°) which is inserted inside the tube. One of these caps needs to have a watertight grip, whilst the other a nozzle to allow the emission of pressurised air.
Whilst maintaining the air pressure, the piece is allowed to cool for a few minutes, after which the air pressure can be released and the mould opened. This method can also be used for numerous shapes, even irregular ones.
Our company is at the client’s disposal for any support or advice required in order to guarantee the perfect bending of our tubes.
JOINING POLICRIL TUBES
The different segments of a Policril tube can joined together other with various methods depending on the final application:
Head to Head Joint: the simplest type of joining where the extremities of the tubes to be joined are glued together utilising a suitable glue.
Sleeve joint: where the end of a tube is softened by heating with a suitable oven and then widened by utilising a wooden form in order to achieve a glass type shape which should have an internal diameter equivalent to the external diameter to the tube which needs to be joined. After which the tubes are glued with a suitable adhesive.
Flange Joint: this type of bonding is suitable for tubes with a large diameter and when the option to detach the tubes is required. The flanges are obtained from acrylic sheets, in a suitable thickness, and should have an internal diameter equivalent to the external diameter of the tubes to be joined then they are glued together. The flanges should have holes suitable for the bolts to be inserted and it is necessary to insert between the flanges a type of washer in a suitable material.
Filed joint: this type of bonding is obtained by utilising a standard metal file. It is advisable when bonding tubes with a thin wall thickness to insert in the extremity of the tube a timber support in order to avoid it being squashed.
Socket joint: utilised for filed tubes which allows also the possibility to detach the tubes or even simply by creating a sleeve with an internal diameter equivalent to the external diameter of the tube to be joined and then gluing with chloroform. It is also possible to join formed pieces as this method does not require any particular precautions for installation, especially in milking-machine applications where normally a great number of tubes are utilised.
Policril tubes are produced in a large range of standard diameters normally in a length of 2030mm and it is also possible to produce other “supplementary” or “special” diameters to order. The tubes are also produced in standard colours and opal, and with a sample any type of colour match is also possible.
Quotations and technical suggestions are supplied on request.