THEORETICAL WEIGHT AND ACTUAL WEIGHT
- Definition
Theoretical weight price: Use theoretical data, apply relevant formulas to calculate weight, and then calculate the price according to this data.
Actual weight price: Calculate the price according to actual weighing data.
- Why do we have Theoretical weight and Actual weight ?
It is because of tolerance. In practical operation, the rolling of steel plates has temperature changes and the equipment also has processing gaps, which leads to the actual thickness of the actual output plates being different from the theoretical data. This is an inevitable result and cannot be avoided.
3.Tolerance range
The tolerance of stainless steel plates we often refer to is mostly negative tolerance, that is, the actual thickness is lower than the theoretical thickness. Although positive tolerance (actual thickness is higher than theoretical thickness) also exists, it is relatively rare.
The following table is the general requirements of ASTM A480 on plate thickness
From this table, we can see that under the standard ASTM A480, the actual thickness deviation is generally around 5%. But in actual operation, many Chinese suppliers will use big tolerance plates, and their actual thickness deviation is generally above 10%.
Here we can introduce the difference between Theoretical weight and Actual weight in practical application:
For example:
Case:
Mr Elon Musk want to buy Stainless steel plate to build his SpaceX Drago.
SS304, cold-rolled, 2B surface, 1.2*1220*2440mm plate, 10 tons,
Price from Supplier A: $2.02/kg, Theoretical weight price, amount USD $20200
Price from WALMAY: $2.12/kg, Actual weight price, amount USD $21200
Obviously, Supplier A is 5% cheaper than WALMAY, But the truth is this:
Theoretical weight price: The same plate with an actual thickness of 1.12mm. the supplier does not consider the actual thickness, but directly calculates the weight according to the thickness of 1.2mm to get 28.3kg/pcs, then there are 353 sheets in 10 tons. The supplier will arrange production according to 353 sheets, and the customer can only receive 353 sheets.
Actual weight price: WALMAY will calculate according to the actual thickness. When the actual thickness is 1.12mm, the calculation is 26.4kg/pcs. There are 378 sheets in 10 tons. In this case, the customer will get 378 sheets.
Therefore, When Elon Musk buys 10 tons of 304 plates from “supplier A”, he will buy 25 less plates. That is:
Theoretical weight price: $2.02/kg, USD$20,200, 353 plates
Actual weight price: $2.12/kg, USD$21,200, 378 plates
When converted to weight, affected by the thickness tolerance, the actual weight of 353 plates is far less than 10 tons, and may be only 9.3 tons or less. This is nearly 700 kilograms less than the expected 10 tons, that is 7% less.
Using this idea, when the “supplier A” use theoretical weight and “Walmay” use actual weight price. Mr Elon Musk buys from the “supplier A” at a 5% cheaper price, he feels cheaper, but in fact it is still 2% more expensive than buying from “Walmay”.
And if the “supplier A” choose big tolerance sheet. For example, the standard thickness is 1.2mm but the actual thickness is only 1.05mm, then the difference is 13%. In this case, If the price from “supplier A” is 5% cheaper than”Walmay”, the actual purchase cost to Elon Musk is still 8% higher; even if the price is 10% cheaper, the actual purchase cost is still 3% higher.
Here we can see the importance of constraining actual thickness and actual weighing settlement.
Tags : stainless steel sheet，plate
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