Conveyor belts are of utmost importance in modern industries. Their absence can slow down material transportation and make it less efficient. However, you’ll often see PIW written in the specification of these belts. This term can be confusing, especially if you’re buying a belt. This brings a question: What is PIW in conveyor belts?
For example, there are conveyor belts with specifications of 330PIW/3 or 440PIW/4. If you don’t understand PIW, you won’t be able to understand the strength and capability of the belt. Remember, PIW represents how much pulling force one inch of conveyor belt width can withstand. In this article, I’ll discuss everything about PIW and its conversion for EP belts.
What is the PIW of the Belt?
PIW is an abbreviation of “Pounds Per Inch of Width”. In simple terms, this term indicates the belt’s resistance to pulling force. A belt with 200PIW means that one inch of belt width can withstand a maximum of 200 pounds of force. Beyond this limit, the belt may stretch, tear, or fail.
PIW is an imperial unit and is commonly used in the USA and Canada. You won’t see this unit actively used in Asia, where the metric system is standard. Interestingly, many consider it PIW to show the overall strength of the conveyor belt, which is wrong. Instead, this unit only indicates the strength of an inch in width. Additionally, conveyor belts consist of multiple layers.
These include an internal layer, a carcass consisting of ply, and an external rubber layer. The PIW only measures the width of the internal fabric layer (ply) and indicates its strength. These internal fabric layers, or plies, form the belt’s carcass. A belt with a single ply in the middle layer will have lower PIW than one with multiple plies in the carcass.
Simply put, more ply means more PIW and vice versa. The PIW varies depending on the types of conveyor belt. For example, the belt used in a light-duty application will have a smaller PIW. This means they will withstand lower force per inch in width. On the other hand, there are some heavy-duty belts made for transporting heavy, abrasive, or sharp materials. Their PIW is high because they must withstand high forces and are very durable.
PIW with respect to Different Belt Specifications
Let’s understand the PIW in different conveyor belt types. First, suppose a conveyor belt with a PIW of 150. This belt can withstand a pulling force of 150 pounds per inch of width when the total width is 24 inches.
Total force this belt can withstand = 24 × 150 = 3,600 pounds total tensile strength
This belt is considered suitable for lighter applications. It may not withstand heavy-duty or extreme applications. Now, suppose 300 PIW conveyor belts with a total width of 36 inches.
Total force this belt can withstand = 36 × 300 = 10,800 pounds total tensile strength
The conveyor belt with PIW of 300 is considered best for medium applications. You can use such belts in the construction and mining sectors. However, the belt for heavy-duty applications generally has a higher PIW of around 600. Suppose their size is 48 inches. Here is the strength rating:
Total force this belt can withstand = 48 × 600 = 28,800 pounds total tensile strength
As you have seen, the PIW refers to the pulling force that a small area (one inch wide) can withstand. You can calculate the strength rating by considering the total size of the belt in inches. For example, multiply the belt’s total width (in inches) by its PIW to obtain the conveyor belt’s total tensile strength rating. You can use this method for all types of conveyor belts and find their tensile strength rating.
Safety Factor
In real-world conditions, the belt undergoes different loads. Sometimes they have to withstand extremely high, but expected, loads. But the conveyor belts generally don’t break and withstand the load. Why? That’s because of the safety factor that manufacturers consider when making the conveyor belt.
Safety factors indicate the total strength of the belt to what it will be exposed to during its use. In simple words, when you divide the total strength by the load it carries at a time, you’ll get a safety factor. Here is the exact formula to calculate the safety factor:
Safety Factor (SF) = Maximum Strength (Breaking Strength) ÷ Actual Working Load
For lighter belts, manufacturers use a 3:1 safety factor. For example, the above-mentioned 150 PIW belt will only be used to carry 1200 pounds instead of 3,600. The above limit is useful when the belt faces an unexpected, very high load. For medium- and heavy-duty belts, the safety factors are generally 5:1 and 7:1, respectively. Engineers or manufacturers keep this to ensure belts are always used below their maximum load capacity.
What is an EP Belt?
Конвейерные ленты EP are unique as their carcass is made of two materials. These include polyester and nylon (polyamide). The EP in their name represents polyester and polyamide, respectively. Additionally, their carcasses have multiple layers, which make them strong and durable. Interestingly, these two materials give these belts their unique properties.
The polyester fabric is present in the lengthwise (warp) direction in the plies. On the flip side, nylon is present in the crosswise (weft) direction, making it a strong layer. The presence of multiple layers in the carcass makes these conveyor belts strong and durable. They can withstand loads and do not break easily under tensile forces.
Interestingly, these belts are rated by maximum breaking strength. It is measured as N/mm (Newtons per millimeter) of width. For example, an EP belt with a breaking strength of 100 N/mm. This means that a 1 millimeter-wide belt can withstand a maximum force of 100 newtons. If the force goes beyond this limit, the belt may fail.
It is worth noting that EP conveyor belt measurements (N/mm) are in metric units. It is generally used in Asia. EP belts made in Asian countries have strength ratings written in N/mm. One of the key advantages of EP belts is that they don’t stretch much. Why? That’s because they have very low elongations. This makes them perform excellently even after years
of repeated use.
How to convert PIW of the Belt into EP (N/mm) of the belt?
As I said earlier, PIW and N/mm are two different units. Although they show the same strength rating, their use is limited to specific regions. The PIW is used in the USA, and N/mm is standard in Asia, where the metric unit system is standard. So the EP belt made in the USA will have a strength rating as per PIW.
On the other hand, belts made in Asia will have a maximum breaking strength rating in N/mm. So one must know how to convert these units, making it easier to understand the exact strength rating of belts. Here is the simple formula you can use to convert PIW into EP belt:
EP (N/mm) = PIW × 0.175
Suppose you have 600 PIW conveyor belts. You can easily convert this strength rating to EP (N/mm) using the formula above. Here is the exact process:
EP (N/mm) = 600 × 0.175 = 105 N/mm
This means that a 600 PIW belt is equivalent to 105 N/mm. Similarly, the 300 PIW belt is equal to 52.5 N/mm, as confirmed by the above formula. Want to convert N/mm into the PIW? This conversion is necessary when you’re from the USA but using a belt made in Asia. Here is the formula to convert N/mm into PIW:
PIW = EP (N/mm) × 5.71
PIW to N/mm Conversion Table
As previously said, both PIW and N/mm indicate the strength of the conveyor belt. However, it is difficult to convert the strength using the formula every time, right? That’s why I am going to list the conversion table showing the most common belt PIW into N/mm. This will help you quickly understand by knowing one unit of belt.
| PIW (Pounds per Inch) | N/mm (Approx) | Closest EP Belt Rating |
| 150 | 26 | EP 250 |
| 175 | 31 | EP 315 |
| 200 | 35 | EP 315 |
| 225 | 39 | EP 400 |
| 250 | 44 | EP 400 |
| 300 | 52 | EP 500 |
| 350 | 61 | EP 500 |
| 400 | 70 | EP 630 |
| 450 | 79 | EP 630 |
| 500 | 88 | EP 630 |
How is Steel Cord Belt Strength Measured?
In the above section, I mentioned the formula for the tensile or breaking strength of the EP belt. However, there are different types of conveyor belts. One of the most rugged conveyor belts available has steel cords or cables in its carcass. These belts are unique and different from conventional conveyor belts.
One may get confused when dealing with the strength rating of such belts. However, there is no difference in the strength rating between these two types. That’s because the strength of the steel cord belt is also measured in N/mm. So you can use the formula when converting PIW to N/mm for steel-cord belts.
Steel cord belts (N/mm) = PIW × 0.175
This formula will give you the breaking strength of these belts in N/mm. When you want to convert N/mm into PIW for a steel cord belt, here is the formula to follow:
Steel cord belts (PIW) = N/mm × 5.71
The specification of steel cord belts generally includes ST. The examples include ST 1000, ST 2000, ST 3150, and more. It is noteworthy that the above formula applies to all types of conveyor belts. These include heat-resistant, cold-resistant, oil-resistant, flame-retardant belts and more.
Заключение
In conclusion, conveyor belt specifications can be written in different units. Some popular strength rating units include PIW and N/mm. These units are the standards for both EP and steel-cord conveyor belts. Belts rated in PIW are typically made in the USA, while those rated in N/mm are usually made in Asia. It is very beneficial to know the exact conversion to avoid confusion. So, regardless of where the belt is made, you’ll be able to understand its tensile or maximum breaking strength. In this article, I have thoroughly discussed the calculation and conversion of PIW to N/mm.