SF-1 PTFE Composite Thrust Washers for Industrial Door-Hinge Knuckles
For an SF-1 PTFE composite thrust washer between industrial door-hinge knuckles, specify which face slides, which face is supported and how the washer is restrained. Check the door’s axial load path separately from the radial pin reactions. A thin steel-backed washer is a sliding bearing component, not automatically a structural shim, radial guide or interchangeable solid-PTFE ring.
The application is a drawing-defined industrial hinge with slow angular movement and an axial sliding interface. Selection requires the hinge designer’s load and retention requirements; this article does not certify a hinge assembly or imply approval for a particular door standard.
Identify the complete washer construction
An SF-1-style washer commonly combines a metal backing, a porous bronze intermediate layer and a PTFE-containing sliding mixture. Specify the exact supplied material, fillers, total thickness, layer arrangement, outside finish and any lead-content restrictions. The SF-1 family name alone does not establish a proprietary formulation or compliance status.
GGB’s DU reference describes a specific steel-backed, bronze-sinter, PTFE-and-lead material and reserves DU as a protected product designation. It must not be used as a claim that every SF-1 washer has the same properties.
[1]| Part | Working interface | Purchase-order check |
|---|---|---|
| Steel-backed PTFE composite thrust washer | Specified polymer face against a suitable moving counterface | Layer orientation, full backing support, retention and axial load. |
| Solid PTFE or another polymer ring | A different through-thickness material construction | Creep, support, temperature, dimensional stability and approved duty. |
| Plain metallic spacer or shim | May locate parts without intended sliding | Structural thickness and clamping role; do not assume a sliding-bearing rating. |
| Radial pin bushing | Supports the pin’s cylindrical sliding surface | Pin reaction, journal clearance and alignment; distinct from the axial washer. |
Door weight and hinge moment are separate load questions
A vertical hinge assembly must balance the door’s weight and the moment caused by its offset centre of gravity. The way axial force is shared between hinge knuckles depends on the supports, tolerances, adjustment and stiffness. It is not automatically equal across every visible washer.
Consider an original static illustration: door weight W = 400 N, horizontal centre-of-gravity offset a = 0.50 m, and vertical spacing h = 1.20 m between two effective radial reaction points. Assume a rigid idealisation and omit wind, operator forces, acceleration, closer loads and impact.
| Quantity | Calculation or constraint | Meaning |
|---|---|---|
| Weight-induced overturning moment | W × a = 400 × 0.50 = 200 N·m | Must be balanced by the hinge/frame system. |
| Ideal opposing radial reactions | F = W × a / h = 166.7 N at each reaction point | A radial couple; not the axial load on each washer. |
| Total vertical reaction | Sum of axial support reactions = 400 N in this ideal case | Load sharing needs the actual knuckle and support arrangement. |
These assumed values are not a hinge rating. They demonstrate why dividing door weight equally among washers or using the radial pin reaction as washer thrust can be wrong. Ask for the maximum washer reaction and radial pin reactions over opening, closing, stop contact and any specified external-load cases.
For an annular washer, nominal axial pressure can be screened using F divided by its effective contact area. Account for the actual counterface footprint, holes and interrupted support. A whole-ring average does not evaluate tilt, edge contact or long-term deformation.
Put the sliding layer against the intended moving face
SKF’s composite-bearing catalogue calls for steel-backed thrust washers to seat with their backing against the housing wall. It also describes full supporting surfaces, counterface coverage and anti-rotation location for its washer arrangements. These are useful design principles; use the actual supplier drawing rather than importing SKF dimensions into an SF-1 order.
[2]For the hinge, mark the stationary seat and moving knuckle on a section drawing. Show the polymer working face explicitly. If the washer is allowed to spin at its steel-backed seat, an unintended second rubbing interface can appear. Confirm the location method, clearances and which component carries any retaining feature.
A locating hole, pin or screw must not leave a proud edge in the working envelope. Check its recess relative to permissible wear, as well as the seat’s flatness and the washer’s remaining section. Choose retention through the approved design; do not add a hole through the layer as an assembly shortcut.
If both hinge faces must slide relative to an intermediate part, review that arrangement separately. Flipping a one-sided washer cannot create two approved polymer sliding faces, and stacking rings changes the axial fit and retention.
Keep alignment, clamping and lubricant decisions explicit
Set washer thickness and seat depth through the hinge’s axial stack. The pin fastener should not unintentionally clamp the sliding interface or remove required movement clearance. A spacer may carry clamp load while a separate washer carries sliding thrust; identify these roles on the drawing.
Inspect the knuckle faces for tilt, burrs, weld distortion, paint or coating build-up and rough contact. The counterface must meet the selected material’s finish and hardness requirements. Retain pin alignment and the specified radial guide rather than asking a flat washer to correct a tilted hinge.
State opening angle, cycles, dwell, door orientation and exposure to dust, washdown or corrosion. Dry-running approval and any initial lubricant belong to the supplied grade and duty. Tin plating on an exposed steel backing does not establish a stainless backing or a universal wet-service rating.
Do not add grease only because the old hinge squeaked. Check layer orientation, unintended clamping, counterface damage, contamination and the supplier’s lubrication instructions. Changes to grease or cleaner require compatibility review for the complete material system.
For first-article acceptance, agree seated thickness, hole location, retention, axial movement and loaded opening effort through the operating angle. Include any defined rest period and environmental conditioning. Wear inspection and replacement limits belong to the hinge’s approved maintenance plan.
Frequently asked questions
Can the steel-backed side run against the moving knuckle?
Follow the supplied washer design. In the one-sided construction discussed here, the polymer face is the intended sliding face and the backing needs its specified support; unintended sliding at the back requires a separate review.
Does each washer carry door weight divided by the hinge count?
Not automatically. End support, adjustment, stiffness and tolerances determine the axial reaction distribution. Obtain the design load on the actual washer.
Can a thicker washer remove all hinge play?
First separate axial movement, radial clearance, pin wear and frame misalignment. Changing thickness can introduce clamping or alter engagement, so retain the approved axial stack.
Is tin-plated SF-1 the same as a stainless-backed washer?
No. An exterior coating and the backing metal are separate specifications. State the actual backing and exposure requirements.
Request a drawing review
Send the hinge section identifying stationary and moving faces, washer ID × OD × total thickness, seat and retention details, axial and radial reactions, counterface materials and finish, angular duty, environment, lubrication, quantity and inspection requirements.
Send your drawing for review or email sales@boniubushing.com. BONIU confirms manufacturing feasibility, material availability, documentation and quotation scope for the specific enquiry. This guide is not a stock listing or a record of BONIU testing for the illustrated application.
Technical references
- GGB: DU metal-polymer bearings. Manufacturer-specific construction and protected product designation; not SF-1 equivalence.
- SKF: composite plain bearings, catalogue 6110 EN. Washer support, counterface coverage, retention and backing orientation, printed pages 23 and 26. Not a BONIU hinge rating.
Source descriptions and proprietary product data belong to the cited organisations. They are not BONIU ratings, certifications or test results. Calculations and application checklists in this article are engineering analysis under the stated assumptions. Confirm the supplied part and complete assembly against the approved drawing.