Pulley crowning is an essential design element for tracking control of flat conveyor and power transmission belts. A friction cover, or “rubber lagging” helps to increase the traction between the conveyor belt and the drive pulley. Used alone, these covers optimize belt performance.However, when combined with a crowned pulley, there can be undesirable performance effects such as joint degradation and premature belt wear. As a result, Habasit generally recommends avoiding this combination.
To explain why problems arise, we need to understand the interaction between the conveyor belt and a lagged, crowned pulley. Let’s start by looking at the fundamentals of how the crown works to keep a belt centered on the pulley.
Crowned pulley design
In order to produce a centering influence on the belt, a crowned pulley is designed with end diameters that are smaller than the pulley’s central diameter. This creates tapered surfaces on which the belt moves, which push its edges towards the center of the pulley. The different diameters also produce different circumferences around the pulley.
在张力下，皮带符合冠状曲线，其中施加的张力力在皮带中心区域中最大。这对应于滑轮的最大直径/周长。在操作期间，皮带和皮带轮在该领域移动在最大的接触力。随着滑轮的直径/圆周朝向其端部逐渐减小，皮带轮上的带路径的长度和接触力比例地减小。虽然皮带轮的锥形锥形末端变化，但是在这些端部的皮带边缘必须继续与皮带中心一起移动。结果，皮带的边缘滑动滑轮的锥形端部，并且它们如此更大的情况下，在带路径长度的差异最大的情况下。这些区域中的接触力减小有助于促进滑动。在皮带和皮带轮的锥形端部之间的这种滑动件产生摩擦反应和将带式边缘推向其中心的力。
Let’s look now at what can happen when a pulley is both crowned and lagged.
Buckling
When a lagged pulley is crowned, the friction forces increase – and this is when the potential for problems begins. If there is sufficient friction force from the lagging, the greater centering effect can cause the belt to buckle in the center and rise up off the surface of the pulley. Ultimately, the belt can buckle completely and fold over.
The stick-slip effect
随着带和冠辊之间的摩擦力增加，外带边缘与滑动的电阻比例地增加。例如，如果皮带摩擦从钢带表面0.15增加到0.35的滞后，则耐滑动抗性增加〜133％。这意味着由于外带边缘在外带边缘处的抵抗力增加，边缘将具有更大的倾斜倾斜，以在皮带的中心后面拖动并产生皮带的横向偏转（变形）。
喋喋不休
There can also be damage to the lagging as a result of the stick-slip effect, or “chattering”. This occurs when the outer belt edges resist slip due to static friction hold, but then break the friction hold and suddenly spring forward, pulled by the center area of the belt. As the belt slips, it rubs forcefully against the surface of the lagging material, producing abrasions in the form of flat spots on the lagging. In more extreme cases, under high-stress belt operation, the belt joint may deform to the point of failure. The vulcanized lagging material can also experience reversion, and become soft and sticky, leaving rubber residue on the conveyor belt, slider bed and/or rollers.
皮带施工和张力在这种效果中发挥着关键作用，因为它们有助于确定幅度，严重程度和擦伤的数量。例如，横向刚性皮带不会像更横向柔性的带状一样变形，并且沿着较短的距离延长较短的较短，较小，更加抖动的颤动标记。另一方面，在高张力下的皮带将产生更大的摩擦力，抵抗滞后，使其保持快速，最终磨损更大，留下更少但更大的颤振。
Conveyor belt construction
What’s the best way to deal with these problems if a design situation requires a crowned and lagged pulley? One answer is to think very carefully about the belt construction and specify a highly durable rubber, such as carboxylated nitrile rubber (XNBR), or crosslinked polyurethane with a brushed or ground finish, in the 80-90 Shore A hardness range. This offers less friction than the commonly employed 70 Shore A, and thus minimizes abrasion.
了解滑轮冠的功能的原理和皮带轮和冠式皮带轮之间的动力学可以帮助您优化腰带和输送机的性能，从而可以提高腰带维护间隔并延长皮带使用寿命。如果您有任何其他问题，请下载ourEngineering Guideorcontact us!
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