Cast-Fab Technologies produces ductile iron castings which range in size from just a few pounds up to about 80,000 pounds.We have produced larger ductile iron castings, in my own experience at Cast-Fab, even up to 1 63,000 pound shipping weight. On a regular basis we produce castings weighing 40,000 pounds.
In regard to the 40.3 specification, we first began shipping castings made to this specification in 1996. However, we laid the groundwork for this as early as 1994.
To start this discussion on the castings made to the specification 40.3, I would like to talk for a bit about the historical beginnings of the specifications themselves.
The so-called "DIN" specifications actually refers to the issuing authority for the specifications, which is much like ASTM (American Society for Testing Materials) in the United States. In Germany a similar organization exists, known as "Deutshe Industrie Norman," or the initials DIN.
DIN 1693, Part 1, was first issued in September 1961. I have not studied the 1961 issue, but I understand it cam about from research in Germany from about 1955 through 1959. The specification is similar to ASTM specification A536, in that this one specification number covers several grades of combinations of tensile strengths. Similar to A536 the grades in DIN 1693 are ranked according to their mechanical properties. Also like A536 the numbers used to designate the grades are a type of shorthand indicating the strength of the grade. Of course the measuring units are in metric, instead of Imperial units.
The original specification I referred to DIN 1693 which was issued in September 1961 had sever lower tensile grades classified within the specification, namely GGG-38, GGG-42 and GGG-45. For example GGG-42 would refer to a ductile iron with a tensile strength of 420 N/mm. So the number in the grade is multiplied by 10 and the result is the minimum tensile strength, in N/mm2.
In 1973 the DIN 1693 specification was revised again. Two ferritic grades were combined - GGG-38, and GGG-42 into the GGG-45. Also, the increasing importance of guaranteed impact values led to the conclusion of the 40.3 grade in DIN 1693 Part 1. |
Molding Practice
To produce the large castings normally associated with the 40.3 specification, rigid sand molds and cores are necessary. Chemically bonded sands, mixed correctly and well rammed, are necessary. Without good practice, mold wall movement can occur which introduces microporosity in the attached test bars.
Test bars should be positioned vertically in the mold. In doing so, any dross or slag will normally be on one end of the bar, instead of the area where the test pieces will be removed. The length of the bar is a good item to discuss with the customer before starting production. The length will be dependent on the gage length of machined tensile test bars, including the gripping method. It is best to allow an extra 15 to 25 mm if possible.
Positioning bars in the cope should not be done. The drag is the best area to place test bars.
If a bar must be placed horizontally, the test pieces should be cut from the lower two-thirds of the bar only.
Attached bars can be made as part of the pattern, or ram-up cores can be used to make the bars. Each method has an advantage. With pattern made bars the position is controlled, the location is controlled, and the cost to make the bar itself is minimal. With ram-up cores the bars can be placed lower in the mold, but the possibility now exists for leaving the bars out during molding, or variation in location and position from casting to casting. Also the costs go up since an extra operation is needed to make the core. We consider the advantages of both in our placement decision.
I think it is important to attach two bars on very large castings. This provides more material for all the tests, and extra material to be used in case of a problem in testing.
Test bars must be made of sand of the same type as the casting. Avoid locations also where cooling rates will be influenced by gating systems, risers or chills.
Lastly, the bars should not be removed until the heat treating is concluded. Some customers want to witness bar removals.
In our experience we have never had a purchaser specify where the bar is to be placed. Some purchasers do like sketches or photos of bar placement for their records, however. So usually it is the manufacturers choice to attach the bar in a suitable location.
Although the bar thickness is specified exactly, there is some latitude in design of bar width. We have always opted for a wider bar. This represents large castings better and gives more raw material to machine test bars out of. |
