A Belleville washer is a conical spring washer that develops axial force as it flattens. How to use one comes down to three decisions: which way it faces, how many you stack and in what pattern, and how far you compress it. Confirm the contact faces and stack sequence on the assembly drawing, compress to the installed height that matches the required load, then verify the setting. There’s no universal “concave side up” rule and no universal tightening torque.
This guide covers installation and verification. For how disc springs work and how to choose one, see what disc springs are and how they work. “Belleville washer” and “disc spring” overlap in everyday use, but the product specification, not the name, sets tolerances, load behavior and suitability for cyclic service.
How Do Belleville Washers Help Maintain Clamping Force?
Tightening creates the preload. A Belleville washer doesn’t add to it. It adds compliance to the load path, so less force drains away when the joint settles. How much it helps depends on the stack’s stiffness near the operating point and on the spring travel available.
It doesn’t stop settlement, creep or relaxation, and it doesn’t prevent every kind of loosening. Temperature change can raise or lower preload depending on the geometry and materials, so check both the minimum retained load and the maximum load you expect in service. You’ll typically see these washers on joints with gaskets, on soft or creeping materials such as copper and aluminum, and where temperatures swing.
Worked example: preload loss after settlement
A bolted copper busbar connection is a classic case, because copper creeps under sustained load and moves with temperature. Here’s a simplified version with assumed values, not LILY application data. It’s an axial joint with no external separating load and no bypass contact, and the stiffnesses are treated as constant over the small unloading interval.
Initial preload F0: 1,000 lbf.
Settlement stiffness without the spring, k0: 500,000 lbf/in, where k0 = 1 / (1/kb + 1/km), kb is the bolt stiffness and km is the clamped-member stiffness.
Permanent shortening of the clamped stack: 0.001 in.
Belleville stack unloading stiffness ks near the operating point: 20,000 lbf/in. Adding the spring is assumed to leave the other stiffnesses unchanged.
| Joint | Force lost to 0.001 in settlement | Preload left |
|---|---|---|
| Without a Belleville stack | 500 lbf (50%) | ≈500 lbf |
| With the Belleville stack | ≈19 lbf (about 2%) | ≈981 lbf |
For this model, preload loss is stiffness times settlement. Without the spring it’s 500,000 × 0.001 = 500 lbf. With the spring, k = 1 / (1/k0 + 1/ks) ≈ 19,231 lbf/in, so the loss is about 19 lbf and about 981 lbf remains. These are model results, not a promised improvement for every joint.
The 20,000 lbf/in is a local unloading stiffness. It doesn’t tell you how far the stack is deflected from its unloaded state, so use the full load-deflection curve to confirm the initial setting, the unloading travel and the operating limits. The comparison also leaves out temperature effects, continuing creep and changes in contact stiffness.
Before You Install: Confirm the Part and the Load Path
Start with the part number and the assembly drawing. Similar outside dimensions don’t mean equivalent load curves, tolerances or fatigue life. On LILY’s JHBCKFB data sheet, for example, working load sits next to compressed height and deflection, so read them as one operating point. Compare the Belleville washers and Belleville disc springs ranges by their actual specifications, not by name, or start from the disc spring category.
| Check | Establish before assembly |
|---|---|
| Part identity | Part number, material, finish, drawing revision. |
| Geometry | OD, ID, thickness, free height, and space for the full working stroke. |
| Support and guidance | Where each edge bears; guide clearance, surface condition, alignment. |
| Load and travel | Initial load, minimum retained load, maximum permitted load, expected movement. |
| Assembly setting | Stack sequence, target installed height, tolerance, measurement method. |
Then trace the force through the assembly. A shoulder, spacer or stop can create a load path around the spring once it makes contact, so confirm the spring stays the only axial load path across the whole stroke.
Which Way Do Belleville Washers Go?
For a single washer under a nut or bolt head, the usual arrangement is crown toward the nut, rim on the joint. The nut or head loads the raised inner edge, and the outer rim bears on the joint or a support washer. That’s common practice, not a rule, so confirm it against the contact geometry on your drawing.
Flip it and things can change. With equivalent flat supports, a symmetric washer keeps the same ideal axial characteristic. Real supports rarely are equivalent. The nut’s bearing diameter, the hole size, a counterbore or a shoulder can leave an edge unsupported or cause interference in one orientation, and the nut can end up bearing on the cone surface instead of the edge. Sources online show it both ways because the answer depends on that geometry.
Describe direction relative to the nut, the joint face and neighboring washers, never just “up” or “down.” Photograph or mark the sequence before disassembly, but check it against the approved drawing, because an existing assembly may already be wrong.
Both contact edges are narrow rings that carry high local pressure. Where a support washer or hardened seat is specified, use the specified size and material. An arbitrary flat washer can bend, embed in a soft surface, or change friction, travel and thread engagement.
Series, Parallel and Combined Stacks
With identical discs, nesting them the same way makes a parallel group. Alternating directions makes a series stack. Equal parallel groups placed in series make a combined stack. The relationships below assume axial loading and negligible friction.
Side view of a disc spring stack showing the conical profiles and contact gaps.
A four-disc example
Say one disc gives about 225 lbf (1,000 N) at 0.012 in (0.30 mm) of deflection. At that same point, the ideal results are:
Four in parallel: ≈900 lbf (4,000 N) at 0.012 in (0.30 mm).
Four in series: ≈225 lbf (1,000 N) at 0.047 in (1.20 mm).
Two parallel pairs in series: ≈450 lbf (2,000 N) at 0.024 in (0.60 mm).
This is stacking arithmetic, not a LILY rating. Friction and geometric variation change what you’ll measure, and long stacks need guidance against lateral instability. Specify the actual sequence, clearances and lubrication, and don’t mix or substitute discs outside the approved design.
How to Set Preload From Load-Deflection Data
Preload is the force in place before service load arrives. Pick it from the force window your joint needs, not from a percentage of flat load, and not by tightening until the washer looks flat.
- Define the force window. Include settlement, temperature change and service movement.
- Pick the right curve for the material, stack, temperature, and loading or unloading.
- Find the matching compression. A nonlinear curve doesn’t have one constant stiffness across its working stroke.
- Convert it to installed height between clearly defined measurement faces.
- Set an acceptance range that covers spring tolerance and measurement uncertainty.
Stack deflection S = H(free) − H(installed)
Use the same stack and the same measurement faces for both heights. Bolt stretch and seating also take up joint movement, so total joint movement isn’t the same as spring deflection.
Reading a real LILY data sheet
JHBCKFB is a small part, used here only to explain the data sheet fields, not as a recommendation for a particular bolted joint. Its drawing dimensions the thickness (0.007 in) and the overall height (0.013 in) separately.
| Parameter | Catalog value |
|---|---|
| Material | High-carbon steel |
| OD / ID | 0.187 in / 0.093 in |
| Thickness | 0.007 in |
| Height | 0.013 in |
| Compressed height at working load | 0.010 in |
| Deflection at working load | 0.003 in |
| Working load | 6 lbf |
| Flat load | 10 lbf |
The height difference, 0.013 − 0.010 = 0.003 in (0.076 mm), matches the working deflection at 6 lbf (about 26.7 N). With the thickness subtracted, the nominal cone height is 0.013 − 0.007 = 0.006 in, so the working deflection is roughly half of it.
These are rounded nominal values. They don’t give you a complete curve, a force tolerance or a fatigue rating, and two rounded end points can’t prove the shape of the curve. Get the applicable load-deflection data before you set another operating point or let the part control a critical load.
How to Install Belleville Washers, Step by Step
- Make it safe. Isolate the equipment and release stored spring force using the approved procedure.
- Inspect. Look for cracks, corrosion, damaged edges, burrs and permanent set. Match replacements to the specified part number.
- Prepare seats and guides. Clear debris, check clearances, and use only the approved lubricant.
- Build the sequence. Count discs and groups, then check the end-disc orientation against the drawing.
- Compress axially. Keep the stack aligned and stay inside the permitted stroke.
- Measure and record. Use calibrated equipment. Log installed height, conditions and, if specified, measured force.
A listed flat load isn’t automatically the installation load. Some products are designed for specified flattened conditions and others need reserve travel, so follow the operating limits of your part. “Fully flat” is neither a universal target nor a universal failure.
Verify Clamping Force: What Each Measurement Tells You
In a simple stationary joint with no external separating load and no bypass contact, a spring in the bolt’s axial path carries the same force as the bolt. Under service load, bolt tension and residual clamping force can differ, so check the joint load model first.
| Method | Useful evidence | Limit |
|---|---|---|
| Installed height | Estimates force from the stack curve. | Depends on curve tolerance, seating, friction, measurement accuracy. |
| Load cell or fixture | Measures force in the instrumented path. | Must represent real supports and conditions. |
| Bolt elongation | Estimates bolt tension. | Needs bolt-specific calibration and temperature control. |
| Torque record | Shows the process was followed. | Doesn’t establish spring force or residual clamping force. |
NASA’s Fastener Design Manual, RP-1228 covers fastener torque, lubricants and platings, which is where much of the torque-preload scatter comes from. A torque validated for one friction condition won’t carry over to another. Where force accuracy matters, validate the assembly with the specified measurement method.
Common Installation Problems
| What you see | What to check |
|---|---|
| Unexpected force at target height | Part identity, disc count, sequence, curve revision, lubrication, measurement faces. |
| Tilted stack or uneven contact marks | Seat alignment, guide interference, debris, support dimensions. |
| Load falls after operation | Seating, joint settlement, relaxation, temperature, plastic deformation. |
| Nut feels tight before expected compression | Thread interference, shoulders, stops, other contacts. Check before adding torque. |
Replacement or Application RFQ Checklist
Send these with your inquiry:
Existing part number, drawing or clear stack photos
Target load and travel (or installed height)
OD, ID, thickness and free height
Material and finish
Temperature and exposure conditions
Duty cycle and reason for replacement
Quantity
For corrosive environments, look at corrosion-resistant Belleville disc springs and confirm the material against the actual exposure. If you don’t have the curve or installation setting, send us your application details before choosing a substitute.
Frequently Asked Questions
Do I need a flat washer with a Belleville washer?
Only if the design calls for one. A hardened flat washer is common against soft or easily marked surfaces, or over an oversize hole, but it also changes friction and travel. Follow the drawing instead of adding one on your own.
Can a Belleville washer replace a locking device?
Not by itself. It helps hold preload as the joint settles or moves, which is why it’s used where vibration and temperature change, but holding axial load and positively locking a fastener are different jobs. If the joint specification calls for a locking method, keep it unless an approved redesign and testing say otherwise.
How can I tell a Belleville washer is installed backwards?
Compare it with the drawing or your earlier photos first. A backwards washer often shows contact marks on the wrong edge or has the nut sitting on the cone surface, and the installed height or force won’t match what the stack should give. Measure before you decide, because a wrong disc count can look the same.
Should I retighten the joint after its first operating cycle?
Only if the maintenance procedure calls for it. Unplanned retightening can raise the load or use up the spring travel you have left. For a scheduled recheck, follow the specified temperature, unloading and measurement conditions.
Can I reuse washers removed during maintenance?
Check the product instructions and your inspection criteria first. A washer can look fine and still have lost load. Where reuse is allowed, verify dimensions and load behavior against the acceptance limits, and replace anything with unknown history.
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