Product category:
Seals
News Release from: Freudenberg Simrit LP | Subject: Merkel sealing system
Edited by the Engineeringtalk Editorial
Team on 03 April 2006
Two-stage seal improves moulding
efficiency
Ferromatik Milacron equipped one of its high-performance injection moulding machines with two different hydraulic sealing systems with a view to comparing the two systems directly.
Cycle times are a key factor in the efficiency injection moulding machines This explains why the cylinders that open and close injection moulding machines are subjected to such stress
This article was originally published on Engineeringtalk on 18 Feb 2003 at 8.00am (UK)
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Ferromatik Milacron, a renowned manufacturer of injection moulding machines, equipped one of its high-performance injection moulding machines (a K-Tec) with two different hydraulic sealing systems (each from a leading supplier of seals) with a view to comparing the two systems directly.
In order to ensure that the sealing systems were subjected to exactly the same loads, one of the machine's driving cylinders was equipped with the sealing system from one manufacturer, and the other driving cylinder with the sealing system supplied by the other manufacturer.
The leakage oil from each cylinder was collected separately.
After 139 operating hours (101,000 cycles), one of the cylinders showed first signs of leakage.
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After 665 operating hours (470,500 cycles), one litre of leakage oil had been collected at this cylinder.
After approximately 1150 operating hours (800,000 cycles) the volume of collected leakage oil at this cylinder had risen to an unacceptable 3 litres.
The sealing system that was used on the other cylinder and was subjected to exactly the same load was supplied by Merkel Freudenberg Fluidtechnic.
By this stage of the test, it had not leaked a single drop of oil.
The leaking sealing system on the other cylinder was then replaced with a Merkel sealing system identical to the one used on the leak-free side.
The piston rod and cylinder remained the same.
However, the cylinder was mounted at an angle of 0.2mm/m with a view to testing the performance of the Guivex guide tapes in this sealing system when subjected to high lateral forces.
After over 1900 operating hours (approximately 1.2 million cycles) for the replacement sealing system that was subjected to lateral forces and a total of 3080 operating hours (2 million cycles) for the sealing system on the other side that had not been replaced since the start of the test, not a single drop of leakage oil had been collected at either of the Merkel Freudenberg Fluidtechnic sealing systems.
This high-performance sealing system is the result of consistent development work and comprises the following elements: a primary seal, the Omegat OMS-MR-PR with pressure relief; a secondary seal, the T20 U-packing; the PT1 double wiper; and Guivex guide tapes.
The primary seal in this sealing system is the Merkel Omegat OMS-MR-PR, which is made of a special PTFE compound.
This material is highly resistant to wear and boasts both low friction and outstanding dimensional stability and, consequently, extrusion stability.
The secondary seal, a Merkel T20 U-packing made of polyurethane, is capable of returning the oil film that got past the primary seal, which is an inherent feature of the system, back to where it came from.
With different inward and outward motion speeds, it sometimes happens that the amount of returned oil is smaller than the amount that is dragged out.
The pressure in the sealing gap can, as a result, quickly exceed the pressure in the main hydraulic area and damage the primary and secondary seals.
A patented pressure relief groove in the Merkel-Omegat OMS-MR-PR primary seal prevents this from happening.
The design of the PT1 double wiper used in this system ensures two things: first, that the wiper lip protects the sealing system against dirt and dust from outside, and secondly, that the sealing edge is capable of further reducing the film of residual oil that escapes from the secondary seal.
The excess oil accumulates as a meniscus at the sealing edge and is drawn back into the system with the inward motion.
The Guivex guide tapes, which are capable of compensating for high lateral forces - which were artificially created in this test by mounting the cylinder at an angle - are made of the highly durable composite material HG 650.
Thanks to the patented Guivex geometry, the guide tapes are capable of distributing the forces in an optimum manner.
No damaging edge pressures occur.
This facilitates the return of hydraulic oil between the guide bush and the counterface, which in turn reduces friction and wear.
All these individual components in the sealing system are adapted to suit each other perfectly.
Every single sealing element has a specific function that ensures that the overall sealing system performs so well.
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