ANSI MH27.1 is the "American National Standard for Patented Track Underhung Cranes and Monorail Systems". Patented track is a runway or monorail section that has a special hard alloy steel bottom tee section that is generally 3.25" or 3.33" in width and has a flat flange. The minimum tread hardness is 195 Brinell. Click here for more information on Patented Track.
Patented track is used because it has a common flange width so that a variety of trolleys and end trucks can run on the same track profile. Because of the hard tread surface, the track has great durability. It is not uncommon to find patented track that is 30 to 40 years old and is still in satisfactory condition.
One of the key principles to achieving extended service life is employing trolleys and endtrucks that are designed to equally share wheel loads as they ride on the patented track tread. In fact, ANSI MH27.1 mandates that "Carrier yokes shall be of the swiveling type." For example, the endtruck trolley shown in the figure below is from an Acco Louden crane.
Notice how the endtruck trolleys (item 2) are constructed so that they swivel and pivot about the endtruck load bar bearing washer (item 6) which contacts a forged pivot pin welded to the endtruck load bar. This swiveling and pivoting arrangement ensures that the load at each wheel as it contacts the patented track tread is equal and thus the wear on the patented track tread will be even between each side.
Compare this to the Harrington endtruck in the figure below.
|THIS DESIGN DOES NOT MEET ANSI MH27.1|
This endtruck is used by some on patented track because it is less expensive to produce than endtrucks with trolleys that swivel and articulate. Notice that it's construction consists of a wheel with bearing affixed to a rigid shaft. The rigid shaft is then mounted to the web of the endtruck channel. There is no way for the load on the endtruck to equalize between the wheels on one side of the track and the other. If there is any vertical misalignment between the pin to endtruck connection during fabrication (which there most certainly will be despite even the best manufacturing tolerances) one wheel will be imparted a greater load than the other. In addition, any axial misalignment of the shaft will cause the wheel to contact the track surface at an angle instead of in a truly flat orientation.
The inability of this endtruck configuration to equalize wheel loadings will lead to uneven wear of the patented track tread and accelerated endtruck wheel wear, thus shortening both the track and endtruck life.
ANSI MH27.1 also requires that "Wheels have a minimum tread hardness of 375 Brinell." Harringtons endtrucks are only 200 to 250 Brinell. They do offer an option, at an additional price and increased lead time, to have the wheels hardened to 350 to 375 Brinell.
CONCLUSION - To maximize the life expectancy of you patented track purchase, endtrucks and trolleys should be used from the patented track manufacturer that swivel and pivot and meet the full requirements of the ANSI MH27.1 specification.