Injection moulding process efficiency largely depends on the performance of the cooling system. To optimise changeover times (SMED) and minimise failures, maintenance departments are increasingly replacing traditional hose clamps with self-gripping systems. Although Push-On technology is well known, it nevertheless requires proper technical practice and informed parameter selection to ensure leak-tightness and operational safety.
Operating principle: physics instead of screw-type mechanics
The essence of the Push-On system is the elimination of external clamping elements (ferrules, worm-drive clamps or brackets). Connection tightness is achieved through the specific interaction between the hose material and the connector tail geometry.
The nipple dedicated to this system has specially profiled barbs. During assembly, a suitably selected rubber compound expands slightly as it is pushed over the barbs. Once seated, the material "relaxes", tending to return to its original shape, which generates the clamping force. Importantly, an increase in the internal medium pressure in the hose additionally presses the hose wall against the connector barbs, increasing frictional force and system tightness.
Applications in plastics processing: temperature control and multi-couplings
Although Push-On systems are used in pneumatics and low-pressure hydraulics, their role is particularly important in temperature control circuits of injection and blow moulds. Why?
- Space saving: In modern moulds the density of cooling channels is high. Traditional hose clamps take up space and have sharp edges that can damage adjacent hoses or injure operators' hands. A Push-On hose is flush with the connector contour, which is crucial when using multi-couplings where sockets are positioned very close to each other.
- Medium identification: It has become standard practice in the industry to use blue hoses (supply) and red hoses (return), which facilitates verification of correct connections by operators.
Connection cross-section – Push-on ferrule + self-gripping hose
Hose material: NBR/PVC and textile braid
Hoses dedicated to Push-On systems must meet stringent material requirements. A standard rubber hose will not operate correctly in this system.
Key design parameters include:
- Inner and outer layer: Compounds based on nitrile rubber (NBR) and PVC are most commonly used. This provides resistance to hydraulic oils, glycol, as well as weathering and abrasion (which is important with continuous hose movement).
- Reinforcement: A textile braid is used, providing pressure resistance while maintaining the flexibility required for installation.
- Silicone-free: This is crucial in plants where mouldings are subsequently painted or metallised – the hose must be free from silicone particles so as not to cause defects in the applied coatings.
Limit parameters and technical constraints
For process engineers and maintenance specialists, knowing the operating limits of this technology is essential. The Push-On system is a low-pressure solution.
- Working pressure: For TFNBR hoses it is 15 bar. The safety factor for these hoses is 4:1, which provides a large margin against burst, but it is important not to exceed the nominal pressure.
- Type of load: The Push-On system is not suitable for applications with pulsating pressure. Sudden pressure spikes (hydraulic shocks) can weaken this connection.
- Temperature: Operating ranges differ depending on the medium. For example, for TFNBR hoses:
Air: up to +110°C,
- Water: up to +100°C,
- Hydraulic oil and glycol: up to +70°C.
Exceeding these values accelerates rubber degradation, which can lead to loss of elasticity and, consequently, loss of tightness of the self-gripping connection.
Example components with a Push-on ferrule dedicated to a self-gripping hose
Summary – operational benefits
The use of the Push-On system in injection moulding plants streamlines production processes. The system eliminates the need for hose clamps, which shortens mould set-up time and prevents leaks resulting from incorrect clamp installation. It also improves ergonomics and protects operators from cuts caused by sharp clamp edges. Proper system operation requires the use of compatible components: hoses and connectors with a profile designed specifically for Push-on technology.
