Modern HVAC systems use the orbiting scroll for its energy efficiency, small size and quiet operation. Both commercial and residential refrigeration systems use this technology. Orbiting scroll systems can achieve isentropic efficiencies of 70 to 75%. That’s why they are often chosen for energy saving applications.
This blog post covers the technical aspects of orbiting scrolls. It includes design theory, geometry, material selection, manufacturing methods and how to optimize performance.
What is an Orbiting Scroll?
An orbiting scroll is a spiral shaped part used in positive displacement compressors, especially scroll compressors. Unlike traditional reciprocating or rotary mechanisms, the orbiting scroll moves along an eccentric path but does not rotate. This extraordinary movement traps gas pockets and compresses them which leads to efficient fluid compression.
Operating Principle
An eccentric crankshaft drives the orbiting scroll in a circular path but the scroll itself does not spin. As it moves it forms crescent shaped pockets of gas between itself and the fixed scroll. These pockets shrink as they approach the center which compresses the gas. This procedure runs continuously, providing smooth and efficient gas compression.
Applications
Orbiting scrolls are used in more than just HVAC & refrigeration systems. They are widely used in automotive superchargers and also in certain specialized parts such as NASA’s space suit compressors where small size and high reliability is key.
Design Procedure and Considerations
A. Scroll Geometry
Wrap Profiles
Spiral compression chamber in orbiting scroll compressors is shaped by Archimedean, involute or hybrid (AI) wrap profiles. Involute curves come from base circles and help achieve smoother compression & better sealing. Archimedean spirals with linear spacing help maintain a steady pressure gradient.
Hybrid profiles combine the strengths of both. They help balance compression ratio and volumetric efficiency over different operating conditions.
When selecting a wrap profile a number of key parameters must be evaluated:
- Base circle radius (rₙₜ₍b₎): Mostly 3.0 mm
- Starting involute angle (φ₀): ±0.735 rad which determines the initial thickness of blade
- Orbiting radius (r₀ₙₜ₍o₎): 5.0 mm – based on the crank or orbital coupling
- Maximum involute angle (φₘₐₓ): Typically 8π rad (almost 4 full spirals) which gives a wrap length of about 1 m
- Scroll height: 40 mm is common in 4 kW test rigs
- Tip clearance: Kept very tight at 0.002 mm to prevent flank leakage
With optimized geometries volumetric efficiencies can go beyond 85%.
Wrap Thickness and Height
Wrap thickness is usually between 3 and 5 mm and wrap height is 40 mm. These values affect the pressure ratio, chamber volume and how rigid the structure is. Increasing wrap height increases displacement volume but also increases axial forces and material stress.
Tip Seals
Tip seals are very important in reducing wear and leakage between scroll flanks. Manufacturers use high performance polymers like metal alloys or PTFE composites for these seals. Tangential clearances are mostly below 0.002 mm. Well designed seals keep leakage low even at high speeds (1,000 to 3,000 RPM) and discharge pressures up to 8 bar.
B. Orbital Motion and Kinematics
Eccentricity and Radius
Most scroll mechanisms use orbital radii or eccentricities between 5 to 7 mm. Best value is often 7.08 mm. These dimensions keep the scrolls meshed and pockets sealed. If the eccentricity is too small, compression staging suffers. If it’s too large, the mechanism faces high radial loads.
Kinematic Simulation
Engineers use multibody dynamic tools like MATLAB or ADAMS to model scroll movement. These simulations track acceleration, displacement and velocity as the crank rotates. The results show how forces act between the Oldham coupling and the orbiting scroll. They also show how clearances cause brief rotations. This helps engineers adjust clearances & coupling shapes for low-vibration and stable performance.
C. Anti Rotation Mechanism
This mechanism stops the orbiting scroll from rotating. It keeps the orbital path precise and the scrolls meshed.
Types
- Oldham’s coupling: This uses two slots & keys set at right angles to block rotation. Engineers normally set the clearance at about 0.1 mm to keep backlash low. Oldham’s coupling works well but adds some friction. Newer designs can reduce angular velocity changes to 5 × 10⁻¹⁴°/s.
- Cross head mechanism: This guides a sliding cross head along a straight track. It provides strong stability, removes rotational backlash as well as improves wear resistance over time.
- Pin and slot designs: Here a pin attached to the orbiting scroll slides inside a slot in the housing. It is compact and simple but needs precise alignment to work well.
Design Considerations
- Friction reduction: Designers try to minimize sliding contact by using low friction materials such as PTFE or applying surface treatments like hard anodizing.
- Wear resistance: Clearances are kept under 0.2 mm. Ceramic coatings or hardened steel are common for these parts.
- Lubrication needs: Continuous lubrication is required. System oil usually supplies a film at contact points to stop metal parts from wearing against each other.
D. Finite Element Analysis (FEA)
Use modal & harmonic FEA tools like SolidWorks or ANSYS to see how stress distributes across the scroll. Look for peak stresses in the involute wraps when they are under pressure loads that can be hundreds of MPa. Do a dynamic vibration analysis to find the natural frequencies. This will help you avoid resonance.
Use S‐N curves to calculate fatigue life. Apply Darveaux or Goodman methods to see how cracks start and grow under cyclic axial and radial loads which are normally 1‐2 kN.
E. Refrigerant Compatibility
Selection Criteria
Choose refrigerants with specific heat ratios, right thermodynamic properties, density and pressure‐temperature characteristics. These support best compression.
Choose refrigerants with low global warming potential (GWP) to minimize environmental impact. Non‐flammable options like R454B and R32 are good for this purpose.
Design Adjustments
Select sealing materials that can withstand chemical exposure and limit diffusion. Match spiral‐tip seals and O‐rings to the refrigerant you use. Make sure the lubricant works with the chosen refrigerant. Some refrigerants require synthetic oils that have the correct viscosity and miscibility. Use oil‐lubricated scroll contact surfaces to reduce wear.
Designing an orbiting scroll requires attention to geometry, sealing, motion control and material choices. To meet all these technical demands consider working with a specialist like Richconn. Our engineers have deep knowledge in every aspect of the design procedure.
Manufacturing Procedure of Orbiting Scroll
Manufacturing of a precision orbiting scroll has a number of well defined steps. This guide explains the procedure from raw metal to a finished and fully functional scroll geometry.
1. Material Selection
Manufacturers select aluminum alloys like A356/SiC composites for applications that need high thermal stability and low weight. For heavy duty or high load applications, steel or cast iron is used as these materials offer better wear resistance and strength.
2. Fabrication Methods
Casting
Fabrication process starts with precision casting to create the spiral body of the scroll. Choice between ductile iron and aluminum‐silicon alloys depends on targeted application. Casting produces a near‐net shape which minimizes material waste.
Machining
CNC milling follows to define the scroll wrap’s contours with high accuracy. Operators use precise tool paths and controlled cutting speeds to maintain tight tolerances. For example a cutting speed of 230 m/min with through‐tool coolant keeps tool wear low. Machining continues until surface roughness is less than Ra < 0.7 μm.
3. Surface Treatments
Electroless nickel‐phosphorus (Ni–P) plating is applied to aluminum scrolls. The coating has 3‐50 µm thickness and 3‐13% phosphorus. It increases hardness up to 750 HV. This treatment provides wear resistance and even coverage on complicated shapes. After plating sulfuric acid anodizing is applied to aluminum wraps. In result 5‐15 µm oxide layer is created. This layer improves wear durability, corrosion resistance as well as retains lubricity.
4. Assembly
Component Alignment
Put the scroll in its eccentric shaft. To stop unwanted rotation add an anti rotation device or Oldham coupling. Simulation data showed that there was 53% drop in orbital acceleration spikes when coupling’s key structure was improved. This made motion more stable.
Sealing
Insert tip seals into machined grooves to create an axial seal. Normally molded PEEK/PTFE o‐ring or C spring seals are used for this purpose. This seal is similar to piston rings in reciprocating machines.
Lubrication
Use ISO VG 32‐68 synthetic lubricants such as PAGs, POEs or PAOs to improve flank sealing, reduce friction and protect against wear in orbiting scrolls. In high stress areas apply MoS₂/PTFE coatings for extra durability.
5. Testing and Quality Control
Performance Testing
Test the scroll’s isentropic and volumetric efficiency at pressure ratios between 2.2 and 4.0 :1. Flow rates for these tests range between 0.1 & 0.5 m³/min.
Durability Testing
Scrolls face vibration endurance and thermal cycling tests. These tests find fatigue and thermal deformation problems that can harm sealing performance.
Leakage Testing
Use sniffing, helium mass spectrometry or vacuum methods to detect leaks. These methods can find leaks as small as ~1×10⁻⁹ mbar·L/s. This procedure checks that micro clearances remain intact or not.
Performance Optimization for Orbiting Scroll
Efficiency Enhancements
Volumetric Efficiency
To increase volumetric efficiency we adjust the design tip seals and wrap geometry for better performance. CFD analysis shows that a discharge‐matched wrap profile of about 66° gives better chamber and sealing filling. This gives 4.9% isentropic & 4.1% volumetric efficiency gain.
We achieve this by parameterizing the spiral involute in CAD. We then run CFD iterations with MOST algorithms. The profile that reduces backflow and secondary vortices the most is chosen.
Mechanical Efficiency
Lowering mechanical friction is key to maintaining efficiency and performance over time. We use smooth surface finishes with Ra less than 0.7 µm to reduce contact friction. Nickel‐phosphorus coatings at critical flank interfaces help increase durability and reduce wear.
Noise and Vibration Control
Design Modifications
Balancing masses are placed on the scroll wrap to reduce orbital vibration. Silicone damping bushings fit into the Oldham coupling and absorb shocks from movement. To suppress noise from resonance, engineers can add viscoelastic or particle damping layers to the housing.
Material Selection
Gray cast iron and viscoelastic composites are chosen for their high damping ability. Constrained‐layer damping materials between layers is very effective at reducing high frequency vibration.
Reliability and Longevity
Fatigue Resistance
Orbiting scrolls continuously act under cyclic loads because of their orbital motion during compression. We use Finite Element Analysis (FEA) to design scroll profiles that reduce peak stress points. We optimize thickness in high strain areas to slow down crack formation under repeated pressure & heat. Modal analysis helps to avoid structural resonance which extends the scroll’s life a lot.
Wear Resistance
RICHCONN uses hard coatings like Diamond‐Like Carbon (DLC) to reduce surface wear and friction. DLC brings the coefficient of friction down to about 0.2 which increases long term reliability. Additional coatings like MoS₂/PTFE or electroless nickel‐phosphorus give extra sliding wear protection. Using strong base materials like alloyed steels or hardened aluminum prevents abrasive damage and galling.
To Sum Up
This has covered everything you need to know to manufacture and design an orbiting scroll for maximum performance. Accurate wrap geometry, thorough testing and the right surface treatments all add up to scroll’s long life. In the future, ongoing research and development will increase orbiting scrolls’ role in HVAC and more advanced refrigeration & industrial applications.
If you’re looking for dependable manufacturing solutions then choose Richconn. Let us handle your orbiting scroll design & manufacturing needs.
Related Questions
What effect do radius and eccentricity have on the movement of an orbiting scroll?
Changing the radius and eccentricity allows you to adjust the movement. Increasing radius increases displacement and more eccentricity gives more compression but can cause more imbalance. Balancing both is key to efficient and smooth operation.
Why use aluminum alloys for orbiting scrolls?
Aluminum alloys are a great choice for orbiting scrolls. They make lightweight components that also resist corrosion. These materials make CNC machining easier, reduce wear and improve heat transfer. Moreover they have a high strength to weight ratio for efficient operation especially in HVAC applications. Using aluminum alloys can also save cost by extending scroll life and simplifying processing.
Where can I find a manufacturer for custom orbiting scrolls?
You can contact Richconn as they manufacture custom orbiting scrolls with outstanding quality. Our team uses CNC precision and has vast material knowledge.
