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Sicoma |
TWIN-SHAFT MIXERS - SICOMA STRENGTH SHAFT SEAL
Other twin shaft mixers have gained a bad reputation for poor shaft seals and bearings, requiring replacement every few years. Sicoma realized at the outset that these items were weak points and decided to eliminate these problems in their mixer design. This has been achieved; shaft seals and bearings typically last for the life of the mixer. Of course, like anything else in the concrete industry, the mixer needs to be maintained as instructed, but nothing special, other than topping up the grease and oil levels, needs to be done.
| Most twin shaft mixers have a small gap between the rotating part and the fixed part, called a Labyrinth; to prevent concrete entering this gap, grease is pumped out. As the shaft flexes with load, however, air pockets open, which fill quickly with concrete. The concrete then blocks grease flow, which preferentially flows through the best seal - the one with the lowest pressure. Wear and failure of the blocked seal follows quickly. |
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| In comparison, Sicoma's patented Strength Seal uses a tough rubber
disc pushing against a hardened steel cone. This forms a one-way
valve; the pressure of concrete pushes against the rubber, closing
it even more firmly against the cone. The small amount of grease,
at high pressure, is necessary only to keep the cone and disc
lubricated. A small, fixed volume of grease is metered to each
seal in sequence, ensuring that each is correctly lubricated. Shaft flexing has no effect on this seal. |
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| The seal and the bearing are not in the same housing, as is the case in many other mixers. If the seal should ever fail, grout forcing its way out does not destroy the seal on the bearing; it drops out of the cavity, leaving the bearing and its lubrication seals intact. In the picture, the shaft seal is at right, with its grease feed tube at the top. The bearing is a left, with its oil refill cap and level indicator plainly visible. Oil is used for bearing lubrication, since it lasts for years and can be replenished easily without the overpressure that can damage bearing lube seals when grease is pumped in. |
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What is the "Triple Shaft Seal"?
The first seal is the one shown above - the yellow rubber disc. This forms the seal between concrete inside the mixer and the outside world. On the outside end of the shaft, a housing (just below the grease tube above) retains the grease. To prevent the grease escaping out of this housing, a second rubber seal is installed between housing and shaft.
Since the grease in this type of seal is under high pressure, the secondary seal tended to leak slightly, which is not serious but looks unsightly. Purely for this cosmetic reason, a third, high pressure seal is installed behind the second one. This whole arrangement is patented by Sicoma and is not available from any other manufacturer.
The Sicoma Strength Shaft Seal is so effective that in a test, it was run for 3 months under normal production without grease, with no failure. After dismantling, the rubber sealing disc had become discolored due to the friction and high temperature, but the seal was fully intact and there was no noticeable wear to rubber disc or steel cone.
