Introduction

A relatively new standard established by the American Petroleum Institute, API 603 standards require extremely precise castings with features that are near impossible to provide in as cast condition with most other casting processes. The standard is highly stringent and as yet, very few valve manufacturers have qualified for these standards.

The casting of the gate valve body is very typical, with huge dimensional variations in wall thicknesses, and overall, a very tricky casting to produce to the stringent standards that it demands. A significant majority of foundries have struggled to perfect this casting.

At Metafore, we took on the daunting challenge of making castings weighing upwards of 240 kilograms (single piece) through our Lost Foam Sintered Shell (LFSS) Process and the results have delighted our customers.

These castings, were they to be made via the conventional sand casting route would not only be much heavier in weight, but would also have to face the following limitations:

• Core: Due to core shifting, there would be a huge increase in allowances. This was completely eliminated at our end since the LFSS is a coreless process.
• Poor preparation of the core leads to blow holes, gas porosity and other defects which are completely eliminated in the LFSS process.
• Wash/ Cut defect: In the conventional sand casting process, if the core strength is not maintained uniformly, and as desired owing to quality issues, there is a distinct possibility of cuts in the ingate areas which in turn effect the overall casting quality to a near rejection level.
• The huge thickness variation between the flange and the bore (in excess of 3x) makes metal flow, methoding and directional solidification a huge challenge to overcome in the sand casting process necessitating either chills or pads. The same is simply not required in the LFSS process.
• Machining time is higher since machining allowance is more and referencing is difficult considering the occurrence of warpage.