Freeze Cast has an international reputation for its expertise in the manufacture of hydraulic parts. Today, we supply companies from different sectors in Europe, America, Africa and Asia, which means that we manufacture thousands of parts per year.
We manufacture products with different materials and finishes, covering a wide portfolio of sizes, weights and shapes.
We adapt to the technical and legal requirements of the customer’s sector, which are markets characterized by their concern for performance, efficiency and quality. These needs often require complex designs, which present new challenges for foundries like ours.
As a result, we receive many different orders from many different industries and countries. It is well known to our customers that we have a team of highly trained and motivated employees who are ready to take on their requests.
Projects with complex shapes and geometry are studied by our technical department. They are in charge of deciding on the feasibility of the order, and choosing the best solution for each project.
In the case of impellers, there are factors that could complicate the manufacturing process, which we pay special attention to.
Some of the parameters that influence the production of an impeller are:
HYDRAULIC OPENING
Hydraulic opening, hydraulic passage or fluid outlet are different names used to designate the area where the fluid exits the impeller.
The fluid enters the impeller at the area known as the suction eye and is expelled in a driven manner through the hydraulic outlet opening.
Geometrically controlling this area is critical to the performance of the equipment. In many cases, very narrow hydraulic passages are necessary to achieve the head and flow parameters required by the hydraulic curves of the equipment.
Narrow hydraulic openings are a major challenge for the caster, as they require ceramic cores of minimal thickness.
At Freeze Cast, this has become one of our specialities, as we have developed our own core making technology. We have extensive experience with these complex geometries.
RATIO BETWEEN THE DIAMETER OF THE WORKPIECE AND THE HYDRAULIC OPENING
If to the difficulties explained in the previous point we add a large part size (or impeller diameter) in relation to the hydraulic opening, the complexity of the process increases exponentially.
To explain it in a mathematical way: for the manufacturing of an impeller, the quotient between the diameter and the hydraulic output has to be considered, which we will call Ds coefficient.
A standard size impeller can have a Ds coefficient between 10 and 20.
It is common in the industry that from 35 onwards it is considered to be difficult to cast.
At Freeze Cast we are used to working with ratios that exceed the value of Ds 50 and 60, in some cases reaching ratios close to 80. As the impeller is already a complex part to cast for any caster, when the Ds coefficient increases, manufacturing becomes a challenge.
VANE THICKNESS AND ANGLE
Impeller vanes are a fundamental part of any impeller.
Obviously, not all impellers have the same shape or number of vanes.
During the almost 40 years of our existence, we at Freeze Cast have manufactured some 2,000 different impeller models, each having different hydraulics and therefore different vanes.
A very important variable to take into account when manufacturing an impeller is the thickness of the vanes.
A thin vane can lead to filling problems and cold metal defects. On the other hand, a thick vane can lead to problems with shrinkage porosity and hot spots.
On the other hand, the thickness ratio between the vanes and the rest of the part to be cast is also critical. This is why it is decisive to evaluate the thickness of the vanes before establishing the manufacturing parameters of the part.
Another fundamental variable is the angle of development of the vanes. In general, a large angle of development increases the difficulty of the part, makes it more difficult to manufacture the cores and reduces the accessibility of the cast part.
NUMBER OF VANES
The usual number of impeller vanes for high-energy pumps is usually between 4 and 7 vanes.
Ninety-five percent of the impellers we are dealing with have this number of vanes.
The other 5 percent are parts with a number of vanes ranging from 2-3 to 20 vanes.
In the picture below, a 15-bladed rotor is shown, in this case this part is intended for a compressor. In addition, the vanes of this part are only 2 mm thick.
It is also worth mentioning the thinness of this part, which is another of the key characteristics in the manufacture of impellers and which we will see in the next point.
WALL THICKNESS AND GEOMETRY OF THE CAST PART
Thicknesses of castings can either help or hinder the manufacture of cast components.
At first glance one might think that the thin thicknesses found in impellers are difficult to manufacture and so they are, but an equally challenging problem for the caster to solve are the variable thicknesses and certain whimsical geometries such as right angles, very frequent in the impeller designs we are faced with.
Some impeller designs feature rings in the area of the lower shroud (opposite the suction side) that add a further geometrical handicap.
MATERIALS
Speaking in terms of casting, it is obvious that the material selected for the project has a direct influence on the difficulty of fabrication. At Freeze Cast we manufacture in most families of stainless steels, carbon steels and nickel based materials.
We would especially like to mention duplex and super duplex materials. These materials have been very demanded and very fashionable in the last decades.
These materials have two different phases in their structure: an austenitic phase and a ferritic phase, which occurs at 50% approximately, hence the name duplex.
They have better corrosion resistance and mechanical properties than austenitic materials.
However, it is widely known in the industry that these materials can be difficult to use in the manufacture of components such as impellers. The right manufacturing parameters must be carefully and technically chosen to successfully manufacture components, and the processes involved in manufacturing must be carefully controlled.
At Freeze Cast we are experts in duplex materials. We have casted these metals for over 30 years, and are approved by Norsok M-650 for ASTM A-995 GR4A, GR5A and GR6A materials.
QUALITY REQUIREMENTS
Last but not least, we will mention some non-destructive quality tests which ensure greater integrity of the part and are not that easy to apply when manufacturing the impellers. These tests can be:
Visual inspection: Mandatory for all orders.
Liquid penetrant: A test that fits very well to the geometrical characteristics of the impeller and detects surface defects.
Radiographic test: Like the liquid penetrant test, this test is in high demand in the impeller industry, as it detects volumetric defects inside the material.
Magnetic particles: Detects surface and subsurface defects, but is difficult to apply in some geometries.
Ultrasonic: A quality test difficult to apply to the geometry of impellers.
CLOSING REMARKS
All projects involve one difficulty or another. If it is not in the geometry of the part, it is in the technical specifications, and if not, in the materials that make it up. That is why we have been investing in innovation for 35 years, developing processes that allow us to overcome all the barriers imposed by product design.
This process of improvement has come hand in hand with our ceramic moulds, which have proved to be perfect for the manufacture of difficult parts.
More than 50 internationally renowned customers already rely on our hydraulic parts. If you have a new design and you are looking for a foundry that is up to the challenge, contact us. If you send us your design we can assess it, at no cost or obligation, and offer you our range of processes and services.
At Freeze Cast we are looking forward to helping you, no matter how large or complex your project is.