Kevin Knows: How Much Wire? How Much Gas?

Jan 27, 2010 2:32 PM

Our shop just got a new job to quote that includes welding 5,000 feet of 1/4 in. fillet welds. How much welding wire do I have to buy and how many gas cylinders will we go through?

Answer
I like the way this question is asked because this shop has already figured out two important variables: the size of the weld and how many feet of weld are in the job. Also, they are considering the cost of shielding gas in the quote, which is very smart. Below we will use some simple math and make the calculations necessary to get a very accurate estimation on the amount of welding wire and shielding gas needed to complete the job.

How much welding wire using weight of weld metal?
In my last column, we visited the examined how to determine the weight of weld-metal per foot of weld. Weight of weld metal per foot can be calculated, or you can find the values for fillet welds in Table 1 below. These values are taken from Table 12-1 in The Procedure Handbook of Arc Welding by the Lincoln Electric Co. The calculation for the pounds of welding wire needed for a job is as follows:

Sample Calculation #1:
Pounds of welding wire needed for 5,000 feet of 1/4-in. fillet weld with flat weld profile using values from Table 1.

Table 1. Fillet Weld

Knowing how many pounds of welding wire are needed for a welding job allows you to compare the cost of different sizes and types of welding wire. Welding wire is bought by the pound and the price per pound varies according to the type of welding wire (solid or cored), the diameter of the wire, and the type of packaging (size of spools, drums, boxes, etc.). So, an accurate quote can be generated based on your shop’s desired welding process (e.g., wire type, wire diameter and the type of packaging.)

How much shielding gas
Shielding gas use can be calculated based on the flow rate (SCFH) used during production and the hours of welding needed to complete the job as follows:

Sample Calculation #2:

A typical “E” size cylinder of 75Ar/25C02 shielding gas contains a little over 300 cubic feet of gas; therefore, you need to purchase about 13 gas cylinders for the welding job. The trick is to figure out how many welding hours are in a job. This is best calculated by using deposition rate:

• Wire diameter in inches (in)
• Wire feed speed in inches per minute (in/min)
• Efficiency (1.0 for solid wire, 0.85 for cored wire)
• This calculation is for steel only

Sample Calculation #3: Cubic feet of shielding gas needed for 5,000 feet of 1/4-in. fillet weld using 0.45 in. solid wire, at a deposition rate = 7.96 lbs/hr and a typical shielding gas flow rate of 40 SCFH.

From the first calculation, we know that we need 645 lbs of solid wire for 5,000 feet of 1/4 in. weld therefore:

You will need to plan for about 11, E-sized shielding gas cylinders for this welding job. Again, the type of shielding gas mix (75Ar/25C0₂, 100% CO₂ etc.) determines the cost of gas as well as the packaging. Knowing how many cubic feet of shielding gas will help you get the best price and service from your gas distributor.

Summary
The goal of this article is to help shops prepare accurate welding quotes using a few calculations. However going through the math and generating the numbers will also help you manage your operations for profitability. From these calculations, we know that welding at lower deposition rates and higher flow rates will cost you time and money.

I’d like to thank Regis Geisler from Lincoln Electric for inspiring this article based on his passion for helping welding shops become more profitable.

Kevin Beardsley, an Application Engineer at Lincoln Electric, is a registered Professional Engineer with 21 years of manufacturing experience. Send your questions to Kevin by e-mail to: AskKevin@penton.com.