Polyurethane elastomers, compared to rubber, have good abrasion resistance. As rollers, rubber rollers and even tires, polyurethane has become more and more widely used due to its outstanding wear resistance, and its market share has gradually increased. Even so, in some special fields, such as professional sporting goods accessories, wire cutting guide wheels, etc., engineers are still challenging the stronger wear resistance of polyurethane products in order to obtain longer service life.
In general, there are four ways to improve the wear resistance of polyurethane elastomers. Here we analyze or elaborate on the advantages and disadvantages of these ways:
- Selection of high wear-resistant raw materials
Some material suppliers offer prepolymers with high wear resistance. For example, according to the test data provided by a material supplier, the wear of some specific tests is less than 1/2 of that of the comparison material.
Advantages:
The process is simple, and the production is carried out according to the processing technology recommended by the supplier, and the expected performance can generally be achieved.
Shortcomings:
1. The price is expensive, the price is 2~3 times that of ordinary materials, and the price of some materials is more than 5 times that of ordinary materials.
2. Other properties such as tensile and tear properties may be lost compared to ordinary materials.
- Add high hardness powder material
Increasing the hardness of the friction surface can improve the wear resistance of the material, which is generally achieved by adding high-hardness ceramic material micropowder. These ceramic micropowders include alumina, silicon carbide, and boron nitride. In addition to ceramic materials, there are also cases of adding metal powder and diamond powder.
Advantages:
1. On the premise that the processing technology is well realized, the service life under certain friction conditions (such as the impact friction of mortar fluid) can be improved.
2. The price of certain materials and grades is relatively low, which has little impact on the cost.
Shortcomings:
1. High processing requirements: Generally, it is necessary to use a suitable coupling agent to process the powder material before adding. The coupling agent is the "bridge" between the additive and the base material. Whether the "bridge" is firm or not is directly related to the final product. The quality of the product. If the coupling agent is not properly selected or handled well, it will be difficult to achieve the desired effect.
2. Change the hardness of the product: it is necessary to introduce other materials to adjust the hardness.
3. The selection of materials and processing technology are not easy to master: Taking alumina as an example, powders with coarser particle sizes are easy to block the screen and delaminate during processing, and powders with finer particle sizes are easy to agglomerate. Cause the effect not to be up to expectations, or cause the defect of the product.
4. The cost of some materials (such as diamond) and finer ones such as nano-scale powder is too high.
- Reduce the surface friction coefficient of the product.
Reducing the friction coefficient of the material surface can improve the wear resistance of the material, which can be achieved by adding some lubricants. Typical materials include: silicone lubricants, graphite, molybdenum disulfide, polytetrafluoroethylene powder, etc., these materials have the characteristics of low friction coefficient, among which silicone belongs to liquid lubricants, graphite, molybdenum disulfide and polytetrafluoroethylene powder Vinyl fluoride powder belongs to powder lubricant.
Advantages:
1. Some materials are easy to add. For example, silicone lubricant itself is liquid, and the process of adding it to polyol, prepolymer or TPU masterbatch is simple.
2. Under good processing conditions, the surface friction coefficient of the material can be greatly reduced to improve the wear resistance of the product.
3. Generally, the amount of addition is low, and the amount of addition is %2 to 2%.
Shortcomings:
1. Surface migration: Silicone additives will migrate to the surface of the material during the placement process, reducing the friction coefficient of the material surface, and will lose the wear resistance after being placed for a long time or used for a period of time. There are also other solid lubricants dispersed near the friction surface of the product (added layer), which only improves the wear resistance near the friction surface. When the added layer is consumed, the wear resistance of the product will be greatly reduced.
2. The amount of addition cannot be increased: for powder lubricating materials, when the bulk phase distribution is required, the addition amount is small, and the wear resistance effect is not large. It is a problem common to almost all powder additive materials.
3. Dispersion defects: When trying to increase the amount of addition, it is necessary to find a suitable coupling process to treat the material, and self-lubricating materials are often stable in performance. These processes are too professional, and even if feasible, the effect is very limited.
- Add fiber material
Ideally, fibers with high modulus and high strength are distributed in the polyurethane material, which can strengthen the material and improve wear resistance. Typical materials are para-aramid (aramid 1414, hereinafter referred to as aramid) short fibers or pulp. Aramid pulp is obtained after surface fibrillation of aramid fibers, and its unique surface structure is extremely It greatly improves the gripping force of the mixture, and is suitable for use as a reinforcing fiber in friction and sealing products.
Advantages:
1. High degree of wear resistance improvement.
2. Improve tear resistance.
3. In some cases, improve the surface friction coefficient of the product.
Shortcomings:
1. The process of adding aramid fibers is relatively complicated, and there is a problem of winding between short fibers and pulp (especially pulp). Whether it is adding CPU or TPU, it is faced with the problem of how to open the winding so that it can be evenly distributed in the material question.
2. There is a problem with the compatibility of polyurethane. It is necessary to use a certain process such as plasma or coupling agent to treat the fiber to improve the compatibility of fiber and polyurethane. Similar to all treatment methods, there are also problems of limited effect improvement and timeliness. And further push up the cost of use.
3. It is difficult to increase the amount of addition. Even when the amount of addition is small, aramid pulp will obviously increase the viscosity of the prepolymer, resulting in difficulties in subsequent processing.
4. The price is high, and the price of aramid fiber itself is relatively high. In 2018, due to the strong market demand, the production reduction of the aramid giant DuPont and the domestic aramid still to be broken through several factors, the price further increased.
From the above discussion, it can be seen that whether it is the added powder or the reinforced fiber, there is a compatibility problem with the polyurethane substrate. If this problem is properly solved, at least 3 breakthroughs can be achieved:
1. Broaden the selection of added materials, such as ultra-high molecular weight polyethylene powder or fiber, which has some outstanding properties but is itself relatively inert. Materials can also be included in the selection range.
2. Substantially increase the amount of addition, and the improvement of compatibility means that the powder material is more evenly distributed in the substrate, and it is not easy to agglomerate, which simplifies the processing technology.
3. Due to the improvement of compatibility, there is no defect between the dispersed phase (additive) and the continuous phase (polyurethane) in an ideal state. In addition to improving specific properties, other comprehensive properties of the material can also be improved.
