The basic method of bellows manufacture is not complicated, and every bellows manufacturer forms his bellows convolutions in one of two ways:either by mechanical forming, or by hydraulic forming. The principle is the same for both. First of all a sheet of suitable material (usually stainless steel) is selected to withstand the pressures and temperatures specified and which will resist the known corrosive influences. This sheet is then cut, rolled to pipe size and weided longitudinaly. The quality of the butt weld stock sheet into cylinders prior to convolution forming is of paramount importance to bellows life. Recognising this, we have developed our own automatic welding machines which are an engineering achievement in our own right.This machines produce a weld which is a strong as the parent metal, but does not thicken the material. Absence of either factor could seriously affect bellows life. The next stage is to form convolutions. This can be done either by roll-forming the convolutions between external and internal wheels, or by forcing the tube radially under hydraulic pressure into required convolution profile. This can reinforcing rings fitted into the convolution roots depending on pressure resistance and movement requirements.An important development in design of bellows was the intoduction of more than one ply of metal in each construction. It was discovered that by making bellows piles of thin-gauge metal rather then form one sheet of thicker gauge slock, flexibility and stress loading through movement could be extended further up the pressure range. Multy-ply bellows are a standard features of our designs.
Quality assurance is very important point in expansion join production and is achived through total project, technology manufacture and test procedure. Meintenance and quality assurance system is realised in according with factory's quality assurance programme based at ISO:94. 1994 lrqa London approved Programe and aplication of Quality Assurance programe and issued ISO 9001 certificate. For system continuing the following activities are performed:
-Internal audits (internal auditors have LR's certificates)
-Rewiew of the system is done every 6 months by LRQA (London, Köln)
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Equipment for destructive testing in our lab includes the following:
a) Fatigue test
b) Burnst test
c)Exemination of mechanical properties of material and welds (tensile strenght, elongation, impact, yield point)
d) Exemination of cemical composition-spectrofotometer
e) Metalografic microscope with equipment for photography (x 800)
f) Lab examination of base materials, welds
g) Examination of spring rate
Equipment for NDT includes the following:
a)Radiography
b) Penetrants examination
c) Ultrasonic examination
d)Magnetic particle testing
e) Hydraulic and pneumatic pressure testing
Every 4th year approvals in presence of classification societies representatives is carried out:
-Loyd's Register of Shipping-London, Zagreb Office
- Bureau Veritas-Paris, Rijeka Office
- Det Norske Veritas- Pula Office
- Croatian Register of Shipping-Split
- RWTÜV
- abs
Acording to those examination we realise type approvals with which we prove constant level of quality. Besides type approvals our customers can ask for inspection or classification society for each special order.
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