Unveiling the reasons behind the choice of metal materials for elevator counterweight sheaves
2025-07-06 22:10
1. Common Types of Elevator Sheaves
Common types of sheaves in elevators mainly include the following three: a) Cast iron sheaves, known for their robustness and durability; b) Direct-pressure MC nylon sheaves without a steel ring, characterized by their lightweight and wear-resistant properties; c) Heat-embedded steel ring MC nylon sheaves, combining the stability of a steel ring with the smoothness of nylon, exhibiting excellent performance.
2. MC Nylon Sheaves Manufacturing Process
The core manufacturing process of MC nylon sheaves is centrifugal casting. The raw materials are mainly divided into two categories: liquid caprolactam and solid caprolactam. The quality of the raw materials is crucial to the final performance of the product. The core stages of this process include vacuum dehydration of raw materials, precise control of the addition of catalysts and activators, centrifugal casting molding, and heat treatment. In China, most manufacturers tend to use solid raw materials for production, and in the heat treatment stage, boiling water is commonly used.
3. Assembly and Matching between Elevator Sheaves and Bearings
Cast iron and MC nylon sheaves differ significantly in structural design, mainly in terms of hub thickness, rim size, number of spokes, and web thickness, as well as the interference fit accuracy between the wheel hole and the outer ring of the bearing. Common assembly methods for MC nylon sheaves and rolling bearings can be categorized into two: Firstly, during MC nylon casting, a steel ring is embedded using a heat-embedding process, and then the rolling bearing is assembled onto the steel ring; Secondly, the rolling bearing is directly pressed into the precisely machined MC nylon wheel hole. The former relies mainly on the tight bonding and meshing between the steel ring and its tooth structure and the nylon material; the latter relies on precisely controlling the interference fit to obtain the necessary pre-tightening force. Ensuring sufficient and lasting stable adhesive force or pre-tightening force is the cornerstone of ensuring the smooth operation of the rolling bearing. For structures where the bearing is directly pressed into the wheel hole, the interference fit requirements for the nylon wheel hole and the bearing outer ring are much higher than those for cast iron wheel holes, and this process is significantly affected by factors such as the material's elastic modulus and thermal expansion coefficient.
4.MC Factors Causing Deformation of Nylon Sheave Holes
Several main factors leading to deformation of MC nylon sheave holes are as follows:
(1) The elastic modulus, which reflects the stress-strain relationship (i.e., softness) of the MC nylon material, is one of the key indicators for measuring its performance. Specifically, the elastic modulus plays a crucial role in ensuring the stability of the bearing in the wheel hole. In contrast, the tensile elastic modulus of cast iron is about 30 times that of MC nylon. However, the elastic modulus of MC nylon shows a certain degree of instability during manufacturing and may also change during subsequent use, with temperature being a particularly significant influence. When the tensile elastic modulus of MC nylon is small, the bearing outer ring under stress is prone to deformation or loosening in the relatively soft wheel hole, leading to accelerated bearing damage.
(2) The thermal expansion coefficient of MC nylon material is an important indicator for measuring the degree of expansion of the nylon sheave hole diameter after a temperature increase. Compared with the bearing steel outer ring, the linear thermal expansion coefficient of the nylon sheave is as high as 6 to 7 times that of the steel. In addition, the thermal conductivity of the nylon sheave is also inferior to that of cast iron, making it difficult to effectively dissipate the heat accumulated by the bearing outer ring, resulting in a significant increase in the temperature of the rolling bearing during operation. Therefore, affected by the large thermal expansion coefficient, as the temperature increases, the wheel hole size will further increase, which may lead to deformation or loosening of the bearing outer ring in the wheel hole, undoubtedly accelerating the bearing damage process.
(3) The dimensional stability of MC nylon material is significantly insufficient, especially under the attack of a humid environment, the size change of the sheave hole is particularly prominent, showing a highly unstable characteristic. Once the wheel hole size expands, the outer ring of the bearing may be squeezed and deformed, or even loosen, which will drastically accelerate the wear and tear of the bearing.
(4) When the structural rigidity of the MC nylon sheave is not strong enough (for example, the rim, web, and hub are relatively thin), under the strong force of the traction steel wire rope, all parts of the sheave will undergo significant deformation. This situation may further lead to deformation of the bearing hole, causing the bearing outer ring installed in the wheel hole to deform or loosen, thus greatly accelerating the damage process of the bearing. It is worth noting that this deformation phenomenon is directly related to the elastic modulus of the nylon material.
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