个人感觉翻译的有些许生硬.
比如第一句这样翻译或许好一些：
托辊是带式输送机的重要部件,种类多,数量大.(不要The,因为带了the的话是特指某一个或者某一些输送机）
Carrying rollers are important parts of belt conveyors.The types and quantity of carrying rollers are vary.
第二句感觉这样会顺溜一点：
它占了一台带式输送机总成本的35% 托辊,承受了70%以上的阻力,因此托辊的质量尤为重要.
Carrying rollers take 35% in the total cost of belt conveyors and they bear 70% of resistance,therefore the quality of carrying rollers is crucial.
第三句这样会好一点：
托辊的作用是支撑输送带和物料重量
CRs are used to support belts and the weight of materials sitting on the belts.
第四句我个人没什么建议,觉得挺好.
第五句：
减少输送带同托辊的摩擦力,对占输送机总成本25%以上的输送带的寿命起着关键作用.
Reducing the friction between CR and belt plays a vital role to the duability of the belt which takes 25% in the total cost of conveyors.
接下来,第六句基本上没啥改动,只是做了些小修正：
虽然托辊在带式输送机中是一个较小部件,结构并不复杂,但制造出高质量的托辊并非易事.
It is not easy to manufacture high quality CRs though CR is a relatively small and simple part.
最后一句其实也没有必要改动,不过老衲还是忍不住小改了一下：
判断托辊好坏的标准有以下几条：托辊径向跳动量；托辊灵活度；轴向窜动量.
The criteria of determine the quality of CRs is as below:
Ratial runout;
Flexibility;
Axial movement.
如果lz觉得有帮助,就给个好评吧.