Failure Analysis And Design Improvement Of The Tensioning Oil Cylinder

Oil spilling of expansion cylinder happened a lot on some20Ton crawler style excavator after it came into market, which brought some adverse effect because it impact on customers’ using. By means of inspecting on dimension, hardness, tensile strength, yield strength, elongtation and contraction ratio of expansed Cylinder, we find out that yield strength less than design request causes the deformation of Cylinder. Morever, basied on stress analyzing, Increasing yield strength or thickness of material can improve the performance of Cylinder.First, after measuring outer diameter of failure cylinder of tensioning device, inspecting on hardness, tensile strength, yield strength, elongtation and contraction ratio of cylinder material, we find that yield strength of cylinder material less than design request causes the deformation of Cylinder. Since the temperature and pressure of spray water, and property of cooling medium, heating time are according to drawing request. We find that we can improve the yield strength of cylinder by changing the way that cylinder went into cooling medium. The best way is put one cylinder per time that yield strength can up to686Mpa.Second, we tried on new material STKM780which has large welding heat affect zone, that will affect on quality of Cylinder. Beside, lessweldability, limited by material interior diameter, causes less assurence of the welding at the bottom of Cylinder. As a result, STKM780can not used on Cyliner trial-produce.Then, we analyzied the stress of single cylinder and find that stress become greater when thickness of cylinder material become thiner. This reaserch proved that we can improve the performance of Cylinder by increasing yield strength or increasing thickness of material when designing expansion device of certain vehicle. By increasing thickness of Cylinder material, keep the same interior diameter, increase outside diameter from100mm to107.1mm, make the yield strength of Cylinder material meet the design request without changing material. At last the FTA outcome through ANYSYS and trial installation shows that after increasing the material thickness the max stress is143Mpa, less than material allowable stress and meets design request also working demand of yield strength, which avoid yield failure in general working situation.