Tuesday, January 14, 2014

What to know when buying a Wrought Product versus a Cast Product

Today's blog is brought to you by one of our very own, Eric Grabowski.  Eric has been in the Metals Industry for over 30+ years (although he REALLY doesn't like me saying that...he says it makes him feel old!) and with the Atlas Bronze family for 15 years. We are lucky to have Eric as he is our Go-To guy when it comes to technical advice on Made to Order partsHe knows his metal!

Buying a Wrought Product


We have a number of customers who are accustomed to buying steel, stainless steel, brass, and aluminum on a daily basis.  When they buy this material they are used to ordering the size they need based on a set tolerance. Steel, stainless steel, brass and aluminum are made by either extrusion or drawing, so when you buy one of these products the outside diameter, thickness or width will typically have a tolerance that is plus (+) and minus (-). 

For example:

You need:  1" diameter Brass Rod (Wrought Product)
Tolerance: plus (+) and minus (-)  tolerance on this bar will be +/-.005.  
This means:  Diameter size will fall between .995" diameter and 1.005" diameter

Buying a Cast Product

Now say that same customer receives a request to purchase a Cast Product.  They will quickly find out that the material tolerance will follow a different set of rules. You see, with Cast Bronze Products (most popular alloys being C93200 Bearing Bronze and C95400 Aluminum Bronze) if you were to order that same 1" diameter it will typically have a tolerance over sized by as much as .090" on that diameter.

For Example:

You need:  1" diameter Bronze Rod (Cast Product)
Tolerance:  a minimum of .070" over sized
This means:  Diameter size will be at a minimum of 1.070" diameter

So what's the difference?

It is simply that Wrought Products hold a plus (+) and minus (-)  tolerance.  The bar could fall slightly above or slightly below the desired size.  On the other hand, Cast Products offer additional stock that enables a customer to finish to the desired size.  In Cast Products that additional stock added will also apply to Cored Bar and Rectangle / Plate stock. There will be extra stock added to the Outside Diameter, the Inner Diameter and on a Width and Length. 

Why knowing your finished dimensions when buying Cast Products will save you time and money?

When a customer is buying a Cast Product, we always ask, "What are your finished dimensions?".  We typically ask this because we look at all the available sizes we have in our inventory and select a size that will finish to the customer's needed dimensions.  The goal is to save the customer money on the amount of scrap generated and time in the amount of machining. Knowing a customer's finished dimensions on rectangular cut plate is especially important. We can consider the thickness, width and length and make an allowance for clean up based on the finished size of all 6 surfaces on the rectangle.

There are other reasons we ask for the finished dimensions - especially on longer lengths. As you increase in length with a Cast Bar Product you run the risk of that bar not remaining perfectly straight or flat.  This is crucial if that customer will ultimately need to machine the entire bar.  So we make larger allowances based on the length of a finished piece to ensure the customer will finish to those desired dimension. 

As a rule of thumb regarding any bronze, make sure you communicate what you are finishing to as it provides important information, that will ultimately save you time and money. 

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