In modern industrial transmission, polyurethane belts occupy a special niche due to their unique elasticity, oil and petrol resistance, and the ability to be quickly repaired without dismantling the equipment. In 2026, the demands on service autonomy have increased: an engineer must be able to not only select the optimal profile but also perform high-quality heat welding directly on-site. The correct selection of characteristics—from Shore hardness to reinforcement type—directly impacts the line's efficiency and repair intervals.
With 20 years of experience supplying drive solutions, Belting Rezina provides customers with not only high-quality components but also comprehensive technical support for integration and service.
Shore Hardness: How Hardness Determines Traction Capacity
Thermoplastic polyurethane (TPU) hardness is a fundamental parameter that determines the balance between the friction coefficient and the load-bearing capacity of a belt. Three hardness grades are most common in the industrial sector.
Comparative analysis of the hardness of elastomers (Table 1)
| Marking | Shore hardness | Coefficient of friction | Main purpose |
| 85A (Green/Transparent) | Average | High | Light loads, transportation of glass and tiles. |
| 90A (White/Orange) | Above average | Average | General purpose, medium drive loads. |
| 95A (Blue/Red) | High | Short | Heavy loads, work in abrasive environments. |
Shore hardness affects how a belt behaves in a pulley. Soft belts (85A) provide excellent traction, which is important for inclined conveying, but are more susceptible to stretching. Hard compounds (95A) have low surface adhesion but are capable of transmitting significant torque without deformation. Belting Rezina specialists recommend 90A as the optimal industry standard for most conveyor systems.
Reinforcement: a balance between strength and flexibility
A standard polyurethane belt is homogeneous and highly elastic, allowing it to be used without tensioners. However, in certain applications, reinforcement is necessary.
When a cord is required:
- Long wheelbase: To eliminate the effect of the belt “sagging” under its own weight.
- High positioning accuracy: Reinforcement reduces the elongation coefficient to almost zero.
- High starting loads: The cord prevents the belt from breaking during sudden starts.
Cord types:
- Polyester: Provides good flexibility and resistance to cyclic loading. Ideal for systems subject to frequent flexing.
- Steel: Provides maximum rigidity. However, the steel cord limits the minimum pulley diameter and makes the belt less resistant to corrosion in humid environments.
It's important to remember: reinforcement is always a compromise. If the pulleys in your system have a small diameter, the cord can cause premature belt failure due to internal stress.
Technical emphasis: bending geometry
The minimum pulley diameter directly depends on the belt cross-section (diameter) and its rigidity. Ignoring this parameter leads to overheating of the material during bending and the destruction of the polyurethane's molecular bonds.
Dependence of the minimum pulley diameter (Table 2)
| Belt diameter / Profile section | Min. pulley diameter (85A) | Min. pulley diameter (95A) |
| Round 5 mm | 45 mm | 60 mm |
| Round 10 mm | 90 mm | 120 mm |
| Klinovaya (SPA/A) | 100 mm | 140 mm |
Welding Technology: The Physics of Thermal Welding
The main advantage of TPU is its ability to weld "infinitely." In the field, the quality of the joint determines the reliability of the entire line.
Connection methods:
- Butt weld: The simplest method. The belt ends are cut at a right angle, melted on a mirror, and pressed together. The joint strength is approximately 60–70% of a whole belt.
- Overlap joint: Requires pre-milling of the ends. Increases the contact area, which increases strength to 80%.
- Z-stitch: The most reliable method for flat and wide belts, providing maximum molecular adhesion area.
A critical error is overburning the material. When polyurethane overheats above $+240°C$, destruction (carbonization) occurs. The rubber turns black and becomes brittle, and gas bubbles form within the seam. Such a joint will burst under the first load. A proper seam should be transparent (or the color of the belt) with a neat bead of flash around the perimeter.
FAQ: Frequently Asked Questions
1. Is it necessary to use glue when welding polyurethane belts?
No. Polyurethane belts are bonded by molecular diffusion under heat. Using glue will only weaken the joint, creating a foreign layer.
2. How quickly can the conveyor be started after belt welding?
It is recommended to wait at least 10–15 minutes for the weld to cool completely at room temperature. Forced cooling with water is prohibited, as it causes internal stress in the polymer.
3. Is it possible to weld reinforced belts?
Yes, but the joint strength will be determined solely by the strength of the polyurethane, as the cord inside the seam remains interrupted. To maintain the cord's strength, special mechanical fasteners are used.
4. How to determine if the belt is overheated during welding?
If acrid smoke appears upon contact with the welding mirror and the melted polyurethane turns brown or black, the temperature is too high.
Selecting a polyurethane belt is a balance between material hardness, pulley geometry, and splice quality. Understanding the physics of thermoplastic processes allows engineers to efficiently repair and upgrade lines with minimal time investment.
Benefits of working with Belting Rezina:
- Direct deliveries of certified belts from leading brands.
- Wide stock assortment of all types of profiles and hardnesses.
- Professional selection of components according to your technical requirements.
Leave a request for belting.uz or get a consultation from a specialist on selecting drive solutions right now!