What if the main ram is scored on my Single Stage press?

In the life of a Single Stage Press you may encounter a score mark in the main hydraulic cylinder. This damage could have multiple causes. Possible causes include but are not limited to contamination in the hydraulic system, metal parts liberated by hydraulic components and metal shavings of hard chrome from the rod itself.

These contaminants find their way to the lowest point in any actuator, hose or tank and in many cases stay there indefinitely. However, if the contamination gets into the bottom of the main cylinder, the result could be a scored rod.

There were 2 types of seals used in main cylinders supplied by Milnor. These are Vee Packing and U-Cup seals. The U cup seal has a lower friction on the rod but only one seal lip prevents a leak. The Vee packing has multiple seal lips but does create more friction load on the rod.

The Vee packing can be tightened by removing shims from the rod gland ring and tightening the bolts. This causes further compression of the vee packing and as a result creates more friction to the rod. In the early years it was thought that you only had to tighten the seals to fix a leak but some evidence has been found that over tightened Vee packing can actually pull chrome off the rod. This results in chrome embedded in the seal pack and may indeed cause rod scoring as the hard chrome gets stuck in the seal pack and grinds into the rod itself. So, our advice is to replace the seals rather than tighten them.

Around 2010 Milnor began using a rotating ram device with the intention to help diaphragm life on presses that saw uneven cakes caused by small loads. With the advent of this device, any contamination in the rod seal will affect the rod in every indexed position of the rotating mechanism. As a result we have seen minor scoring in some rods around the entire rod rather than in just one place on the rod. In these cases we have recommended that the rotating mechanism be disabled to prevent widespread damage. It is also worth noting that rods with substantial scoring have been made nearly "leak-proof" by replacing the seal pack and disabling the rotating mechanism.

Finally, if a rod does leak some fluid, it can surely still be used. The main concern is that there be no oil on the goods being processed. We have seen oil mops (oil absorbent pads) used to absorb oil and prevent any oil on the goods. When this is no longer a viable solution, a new seal pack can be installed and if this is not satisfactory, a complete cylinder replacement may be required.

Milnor stocks remanufactured hydraulic cylinders that have been milled, chromed and rebuilt with new seals. These are normally in stock for any model press Milnor has manufactured. These parts are available at a reduced price based on the pending the return of the failed cylinder. Cylinders can be remanufactured with an approximate 4 week lead time if the press can be taken out of production for the lead time. If not a replacement cylinder is a viable choice for repair. Check with Milnor customer service for pricing of this option.

Gary Lazarre
1/28/2013

Other related details can be found in the maintenance bulletin "Hydraulic Maint" dated 2010.

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