Mechanical scales are composed of levers, supportin […]
Mechanical scales are composed of levers, supporting parts and connections (such as knives, knife supports, etc.) and scale heads.
The lever consists of a load-bearing lever and a force-transmitting lever. The lever material is generally forged steel, and the load-bearing lever and the force-transmitting lever of the scale with large weighing (more than 20 tons) are cast steel parts. Whether forged or cast levers, they must be aged to eliminate internal stress before they can be machined. The arrangement of the knife on the lever, in addition to determining its position according to the force ratio relationship, should also ensure the relative parallelism and perpendicularity of each cutting edge.
Knives are divided into fulcrum knives, load-bearing knives and end knives (or coupling knives).
The knife is made of high carbon steel or alloy tool steel with a carbon content of not less than 0.75~0.85%, and its hardness is not lower than RC58~65.
There are two ways to install the knife on the lever: one is to use the embedded part of the knife to make a 1:50 cylindrical pin body to be embedded on the lever; the other is to press-fit the knife on the lever by a wedge iron through a screw. superior.
In addition to the general shear and bending strength calculations for the knife, the contact stress check is also required. The contact stress of the working edge is calculated according to the length of one centimeter of the cutting edge.
The part that supports the knife is called the knife bearing, and the knife bears or transmits the load through the knife bearing. The material of the knife bearing is high carbon steel.
The installation of the knife bearing can be pressed against the support or lifting lug with a transition fit. In order to prolong the service life, the self-adjusting knife bearing can be used. Self-adjusting knives with knives can be in contact with the knives along the entire length of the blade, so damage to the knives is greatly reduced. The quenching, grinding and polishing of the knife bearing are the same as those of the knife, but the hardness must be higher, otherwise, the knife bearing will be scratched, and the frictional resistance will increase and affect the sensitivity of the scale. The hardness of the knife is slightly lower than the hardness of the knife bearing, and the cutting edge will be rounded (passivated) after long-term use, which will affect the sensitivity of the scale, but the degree of reduction is relatively small.