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Lines and machinery in the production of automotive air conditioning ducts (2)

The requirements that arise in systems using CO2 as a refrigerant do not bypass air-conditioning tubing either. One method is to manufacture a duct from AEM rubber [2] reinforced with a steel braid, which contains a corrugated, flexible stainless steel tube inside. A duct made in this way can operate with an operating pressure of 170 bar at a temperature of -40÷150°C. It provides zero permeability, high pressure and temperature resistance and meets DIN 74106 specifications.

Rubber hose production line with corrugated steel hose inside

Start of the process – precision cutting of corrugated hose

The stainless steel corrugated hose is supplied in reels on drums with different burl diameters. The length of the hose on a single reel is 400÷1100m. Transport of the cutting component is provided by decoilers with an auxiliary feeding system that regulates the tension and thus minimizes the effect of material stretch on the actual length of the cut piece. A chipless cut must be made precisely on both sides at a specific point in the wave, which is tested using a vision system. The manufacturer’s specifications specify ranges for the length and outside diameter of the cut piece. The infeed roller system ensures optimum distance from the cutting head and proper tensioning of the hose to reduce the possibility of deformation.

Nipple assembly, welding and electrochemical passivation

Sections of corrugated hose of the appropriate length then go to an automatic station for assembling nipples on both sides. These are also made of stainless steel. The process of TIG orbital welding in an argon atmosphere takes place here. After the electric arc is extinguished and the protective atmosphere is emptied, the turntable with the component is automatically returned to the base position. The workpiece moves to the next station for electrochemical passivation of the welds. An electric drive puts the component into rotary motion and a pneumatic system moves the weld cleaning heads closer. Electrochemical passivation is particularly effective for stainless steel welds and provides optimal corrosion resistance. Excess liquid used in the process is collected by a system of acid-resistant tanks. A number of parameters are measured and checked, such as the path of the nipple assembly, the speed of electrode rotation during orbital welding, the welding current, the rotation speed of passivation heads or the conductivity of the passivation bath.

Mounting the steel hose in the rubber hose

The steel hose prepared in this way can be mounted inside a rubber hose of adapted length. A special hole is also made in the rubber later secured with a silicone band. Finally, D-rings are put on the steel nipples. The machine ensures that the parts are assembled without deformation or scratching, and at the right level of cleanliness. The assembled workpiece is blown out and any impurities go into the appropriate chamber. The extension of the nipples from the rubber hose is checked using a profilometer. The presence of D-rings is also checked and the path and, optionally, the strength of the assembly of the steel hose into the rubber hose is measured.

Sub-assembly of the ties and crimping of the ends of the block and connector

Each complete hose consists of two lugs and a section of pre-assembled hose. Ties are put on the rubber part, which are crimped at the next station. The ends are bent into a preset shape and are topped with a block and connector. The assembly operation involves sliding the ends from the side onto the nipples and crimping the connectors around the nipple connection. Loading is done manually, while assembly and unloading are automatic. It is possible to integrate with a manipulator or robot that receives the assembled cables.

Crimping of stainless steel ties

The cable is manually pre-positioned. The machine automatically extends the ties assembled at the earlier station. The position of the ties results from the product reference. Verification of the correct positioning of the cable tie follows, and the crimping operation is performed. Ovalization is optionally checked.

Machines for wire bundling and flow test

A/C wires are grouped into bundles of different numbers, e.g., two-piece or five-piece. The picking station allows assembly by simultaneously pushing the wires against the appropriate flange. This operation is followed by a purge and automatic flow test with dry filtered air without oil mist. It is to check whether the cross-section of any of the component hoses has been narrowed or completely clogged.


[2] AEM – ethylene acrylic rubber

ELPLC SA machines and lines

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