Hydraulic head for high pressure pumps
Hydraulic head in IDI isothermal ductile iron for high-pressure piston pumps
Application sectors and benefits of a hydraulic head in IDI produced by Zanardi Fonderie
This case history showcases the development and production of a hydraulic head in IDI800-6 isothermal ductile iron for water-driven high-pressure piston pumps, typically employed for industrial uses, such as cleaning surfaces, ships, various types of pipes, water treatment, as well as for deburring, cutting and removal of cement, asphalt and paint from stone, cement or metal surfaces and for cutting solid materials.
Application sectors of an isothermal ductile iron (IDI) hydraulic head
The reference sector is industry, especially the steel and iron, chemical and petrochemical, construction and water treatment sectors.
Benefits of isothermal ductile iron IDI compared to GJS600-3
+60% working pressure
Increase in maximum working pressure from 250 bar to 400 bar.
Minimum impact on machinability
Isothermal ductile iron IDI800-6 has a slightly higher hardness compared to EN-GJS-600-3, but is more uniform in the variation in thickness and with a much narrower range. This meant that the IDI800-6 solution does not represent a problem from a machinability point of view.
Design time frames
Thanks to the co-design with Zanardi Fonderie’s technical department, the IDI800-6 solution enabled the customer to meet the tight deadlines imposed for introducing the new version of the head on the market.
Same size and weight
The IDI800-6 solution made it possible to avoid increasing the weight and overall dimensions of the existing version.
Minimum impact on costs
All this was achieved with sole additional cost of the thermal treatment which resulted in a 60% increase in working pressure without have to redesign a new component, thus limiting the overall design costs whilst guaranteeing interchangeability.
The problems solved thanks to a hydraulic head made of isothermal ductile iron (IDI)
The component described in this case history derives from the existing head for high flow rates, but differs from this version in terms of the type of suction and supply valve units, now optimised for high pressure. It has been designed to reach a pressure of 400 bar compared to the 250 bar of the current version.
The customer needed to launch the new version of the hydraulic head as quickly as possible. To succeed in doing this, we worked on a co-design with the customer whilst respecting the foundry requirements and thus, introduced some size modifications as well as opting to change the material to achieve the higher performance required.
The goal of increasing performance meant that the GJS600-3 spheroidal graphite iron, a material previously used for high-capacity heads, was no longer suitable for the new stress levels. The decision was, therefore, taken to upgrade the material, opting for a spheroidal graphite iron with a yield stress of around 500 Mpa.
The benefits obtained by using a hydraulic head in isothermal ductile iron (IDI)
These piston pumps are capable of working at pressures of up to 1500 bar with absorbed power up to 150 HP. Choosing high-performance and high-quality materials for the construction of the head, the key component, therefore, to achieving these levels of performance, is of fundamental importance. Isothermal ductile iron IDI800-6 proved to be the best material for the versions with pressure up to 400 bar.
Starting material for high flow rates (pressure of 250 bar)
Fatigue limit σAG; PS50%
The new solution assessed for achieving the high pressure goal (400 bar)
Fatigue limit σAG; PS50%
Tensile and fatigue test performed on test specimens obtained from separately cast samples Ø25 mm. The fatigue limit on smooth surfaces (R-1) was obtained by testing Ø6.5 mm smooth test specimens machined with the Short Stair Case method (run out at 5ML of cycles). In reality, the workpiece has a variable thickness.
Why isothermal ductile iron IDI800-6 satisfied the customer’s requirements
Isothermal ductile iron IDI800-6 ensures greater fatigue performance and mechanical features compared to GJS600-3 spheroidal graphite iron. Given the absence of binding agents and, therefore, segregation in the metal matrix, these features were uniformly maintained on all the thicknesses after the thermal treatment. Moreover, the hardnesses proved to be more uniform in the thickness variations, so the hardness range was narrower and only just higher than that of GJS600-3, thus ensuring an excellent compromise in terms of machinability. The absence of alloying agents also meant the cost was only slightly higher than that of the original spheroidal graphite iron solely due to the additional thermal treatment.
The working requirements requested by the customer and bench tested were:
- Working pressure of 400 bar
- Uniformity of the micro structure between the surface and core and all the thicknesses
- Internal and surface integrity
- Good machinability
- Compliance with the deadlines for the market launch
- Low cost increase compared to the GJS600-3 solution
- 1500 bench working hours (the equivalent of 5·107 operating cycles)
- On test bench at a rotation speed of 550 rpm (max absorbed power 150hp)
- No “cavitation pitting”
IDI800-6, in this case, proved to be the best material compromise between technology and cost effectiveness for production of the hydraulic head. Nickel plating was introduced as an alternative to other corrosion protection treatments during the validation stage.
Spheroidal graphite iron comparison: Construction methods and techniques of an IDI isothermal ductile iron hydraulic head
The co-design work, managed entirely Zanardi Fonderie’s staff, played a key role in producing a hydraulic head in IDI for the industrial sector which resulted in a 60% increase in working pressure.
An exchange of ideas between the customer’s and Zanardi Fonderie’s technical departments proved important right from the preliminary design stages. This enabled the designers to make comparisons and share, on the one hand, the stress resistance requirements, and the industrialisation requirements of the foundry, on the other. The goal, which was duly achieved, was to produce a product sample in as little time as possible (whilst complying with the size and integrity requirements requested by the customer), minimising the risk of having to make radical design changes to achieve the goal.
From a mechanical point of view, an in-depth examination was performed on the tensile state of the component, EAE (Environmentally Assisted Embrittlement) induced by contact with fluids, contact fatigue phenomena, the effect of surface treatments and, lastly, the requirements for internal and surface integrity.