ULTRA HIGH MOLECULAR WEIGHT P-E IDLER
VERNIER/DIRTWHACKER CONVEYOR IDLER
Upon a request from an Escom power station who suffered catastrophic loss, and associated down-time of a power station unit and costs of entire tear-drop conveyor belts due to wear on steel idler being in use, a set of idlers was developed and manufactured from Ultra High molecular Weight Poly Ethylene together with a bearing/seal combination to cope with a dusty and acidic wet environment. The solution resulted in extending the average life of an idler from a few weeks to about two years. These extremely favourable results obtained in the above application as well as a similar application on a diamond mine, together with requests from these and other customers, prompted us to develop our present conveyor idler.
A major influence at the time was the Blinkpan experience where 9 years previously similar tubing was imported, idlers made by a company that ceased to exist years ago, and installed in an overland coal conveyor. If our bearing seal combination was used at that time, a much longer life would have been realized since the bearings on these idlers started to fail while the shells were still in an as new condition, with machining marks along the tube length that were still visible. Equally good results obtained in platinum mine confirmed the durability of this material.
In discussing the features of our system, we invite the reader to look at the individual components of the idler.
An Ultra High Molecular Weight Polyethylene tube with initial dimensions of 133 OD and 94.5 ID is used.
After assembly, machined to 128 mm along its entire length, resulting in no run-out, a perfect environment with the benefits of smoother running and longer bearing and conveyor structure life.
Uhmwpe has a low coefficient of friction and together with the fact that it does not react chemically with any substance, results into the benefit that no material sticks to the outside of the idler. Where material does not adhere to the outside of the idler, smooth running results, again a longer bearing and structure life. In a man-carrying application it has an additional benefit of less discomfort and worker acceptance. An additional benefit on conveyors carrying different products is that contamination becomes more manageable.
The material has an excellent resistance to impact and has a memory capability to return to the machined size and shape. We make use of this feature by using our standard idler as an impact idler, far outperforming idlers specifically designed as impact idlers. This results in lower inventories with the associated financial benefits.
The combination of high abrasion resistance, high impact resistance and a low coefficient of friction results in a long life of the idler shell, making the idler cost effective against any other known competitor. This material will outlast ordinary polyethylene by at least 5 times under all conditions.
In a test conducted by the S.A.B.S. a toxicity index of 2.3 resulted. A value below 3 is considered to be of low toxicity. The material has excellent chemical resistance, and is suitable for underground operation according to SABS tests. With the addition of additives, an anti-static capability is possible.
End caps are made from 30 % glass filled nylon for strength and impact absorption.
Depending on the conditions where the idlers are being installed we use a combination of either 2 labyrinth seals per side or one labyrinth seal and a double lip oil seal per side.
In a 1 meter submerged, in dirty water, application these seals worked more than 2 months before the idler failed. This may sound a short period, however, standard steel idlers lasted only 2 to 3 days, resulting in frequent replacement under very difficult conditions.
The idler has 2 sealed bearings, 6206 2RS, with dynamic load ratings of 19500 N each.
We make use of a 32 mm shaft, machined to 30 mm diameter for the bearings and to 25 mm at the ends, in favour of a 25 mm shaft having 50% of the deflection of the latter under similar conditions. Machining under the bearing and seal area improve conditions for electroplating. The shaft can be ordered for either 18 or 22 across flat installations and is electro-plated for a longer life. Different arrangements can be made to accommodate a non standard frame.
Stationary on the shaft, stone guards protect the seals from product lodged between the frame and idler as well as forming a very effective side labyrinth seal itself.
Electronic tracking of the data of each idler is possible by means of an internal, thus protected and tamper free affordable transponder, a portable scanner together with a computer and the relevant software. Although not sold by us, the latter is available and can be expanded to a complete plant database incorporating idler details.
Our customers are having excellent results. As a further bonus, labour saving from less frequent idler changes result as well as a much lighter idler. Most important, this idler cannot cut your conveyor belt under normal circumstances.
|Notice the material build-up on steel idlers|
|No material build-up on UHMWPE idlers|
BACKGROUND INFORMATION ON UHMWPE
Materials – UHMW-PE
Ultra High Molecular Weight Polyethylene (UHMW-PE), a lesser known engineering plastic, has certain unique combination of properties, which makes it a very attractive material for the application under consideration. These include
- Extremely high abrasive wear resistance, and in many cases better than steel. UHMW-PE is not a hard plastic when compared to Nylons and Acetals and has less wearing effect on materials it is in contact with than the “harder” plastics. The molecular structure allows foreign particles to become imbedded in it and thereby reducing the wear on the contact body.
Comparison of Abrasion Resistance
2. Very low coefficient of friction, second only to PTFE. Should a bearing seize, the belt will slide over the conveyor idler with minimum wear to the belt or roller. UHMW-PE also provides an extremely effective “non stick” surface. One of the major applications for UHMW-PE is the lining of hoppers, chutes, silo’s and bins where problems are encountered with material sticking to the sides. Sticking of materials to conveyor idlers is encountered and the choice of UHMW-PE as the liner or contact surface could overcome this type of problem.
Comparison of Coefficient of Friction
3. UMMW-PE has an extremely high impact strength, which retains good values down to very low temperatures. In notched impact tests according to ISO 179, no specimen fracture was obtained. Because of its exceptional toughness, UHMW-PE withstands some impact stress without cracking, even at the temperature of liquid helium (-269º C).
Comparison of Impact Resistance
Other unique properties of UHMW-PE include:
- Chemically and corrosion resistant & Sound absorbing
VERNIER-DIRTWHACKER IDLERS FOR SICON TUBE/TEAR-DROP CONVEYOR
A selection of 89, 105 dia drum- and 125 dia biscuit Sicon Idlers manufactured from reprocessed UHMW-PE except the lower left 125 biscuit idler which was manufactured from virgin UHMW-PE material. Notice the 5 mm wear indicating hole in this idler.
Once again we use UHMWPE for the drum section which will be in contact with the belt. Reprocessed UHMW-PE has the unique feature that it’s properties improve with re-use.
Shaft: The shaft is produced from 26 mm 070M20 (EN3) material mm which has been machined all over. The shaft is then zinc plated and yellow passivated.
Bearings: Two 6205 2RS Bearings.
Seals: In addition to the seals of the bearings, a double lip oil seal is installed to prevent the penetration of dust into the bearing cavity. Further more the front end has a solid face to prevent penetration of foreign particles into the bearing cavity.
Inspection hole: A hole is drilled into the drum section 5 mm from the OD so that wear can be inspected and managed.
Our idlers have been used with enormously good results over the last ten years at tube conveyor installations. Huge successes have been attained under hazardous and detrimental conditions. A further use is that for roller at the side of the belt to assist in belt training. The drum idlers with a heavy wall, enjoy a long life
OUR PRODUCT HAS NEVER CUT A COSTLY TUBE CONVEYOR BELT!!!!
Using the UHMWP-E tube we manufacture a 100 mm 1ong 128 dia idler with various stub shaft diameters/lengths to use on flex-wall/bucket conveyors. 100 mm long idlers are kept in stock but longer lengths can be accommodated.
Shells for the 128 dia idlers 100 mm long.