SF-1 PTFE Composite Split Bushings for Pneumatic Cylinder Rod Guides
An SF-1 PTFE composite split bushing can be considered for a pneumatic-cylinder rod guide when the installed clearance, rod surface, lateral reaction and lubrication condition suit the selected formulation. The guide is a radial sliding bearing, not a pressure seal. A matching diameter alone does not prove that a replacement will control rod deflection or preserve smooth low-speed movement.
This guide addresses the front-head guide around a reciprocating piston rod. It complements BONIU’s general SF-1/SF-2 comparison by examining guide span, seal alignment and installed-bore acceptance in this specific assembly.
Separate the material family from a branded application claim
GGB describes DU® as a steel-backed, porous-bronze, PTFE-and-lead composite suitable for linear as well as other sliding movements. It reserves DU as its own product designation. This is a manufacturer reference, not evidence that an unspecified SF-1 bush has the same formulation, compliance status or ratings.
[1]A useful procurement trap appears in PERMAGLIDE’s pneumatic-cylinder example: its rod bearing is P200, installed with initial grease. Its material page describes a distinct lubricated composite family; confirm the exact sliding-layer formulation against the current supplier specification. The application example therefore cannot validate a dry PTFE/SF-1 substitution.
[2][3]For an SF-1 enquiry, obtain the backing specification, sliding-layer formulation, any lead-content requirement, coating and approved lubrication condition. A tin- or copper-coloured outside finish does not identify the sliding layer.
Compare the actual guide construction
| Construction | Application question | Evidence to request |
|---|---|---|
| Steel-backed PTFE composite split bush | Does this exact formulation support the rod duty in the intended dry or lubricated state? | Material identification, installed bore limits, counterface requirements and duty-specific review. |
| Lubricated composite, such as the cited P200 example | Can the specified grease, pockets and sealed arrangement be retained? | Initial lubrication procedure, compatible grease and assembly instructions for that product. |
| Machined metal guide bush | Will oil or grease reach the loaded zone throughout the stroke? | Alloy, groove geometry, feed route, clearance and wear acceptance. |
| External rod guidance | Is the side load or overhang better supported outside the cylinder? | Assembly load path, permitted misalignment and cylinder-maker approval. |
Analyse guide reaction before increasing bushing length
The actuator’s axial force is not the radial guide load. An off-axis tooling force, mounting error or gravity acting on an extended rod can create bending. The piston guide and front-head guide share this reaction according to their separation, stiffness and contact conditions; the distribution changes with stroke.
For an initial engineering screen, average projected pressure is p = R / (d × L), where R is the radial reaction, d the rod diameter and L the effective loaded guide length. This expression assumes a uniformly loaded projected area. A bent rod or an angularly misaligned housing can concentrate contact near one edge, so the calculated average is not a permissible-pressure check by itself.
Send the maximum extension, unsupported load position, cylinder orientation and external-guide arrangement with the load. If the rod is carrying a substantial bending moment, review the assembly rather than simply ordering a longer bush: additional length may increase sensitivity to angular error.
Review reversals, creep speed and seal behaviour together
At each reversal the sliding speed passes through zero. A cycle-average speed can hide the acceleration, dwell and breakaway conditions that affect a positioning cylinder. Record stroke, cycles per minute, peak speed, dwell under load and the lowest controlled speed separately.
If motion becomes jerky, inspect seal drag, rod condition, contamination, pneumatic control and alignment as well as the bearing. A low published bearing friction figure does not predict the breakaway force of the complete sealed actuator. For short repeated strokes, identify the portion of rod repeatedly passing through the loaded guide and the wiper’s ability to exclude particles.
Changing from greased to dry service changes the tribological system. Confirm compatibility with assembly grease, air-system oil carry-over and cleaning agents. Keep lubricant choices within the seal and bearing suppliers’ instructions.
Inspect the installed bore, not only the loose bush
A thin-wall split bush closes and conforms when pressed into its housing. Specify the housing bore and its material, the rod diameter range, the acceptance temperature and the required installed clearance. Measure the bore after installation with a method that does not damage the liner; a loose-bush diameter is not the sole release criterion.
Provide an entry chamfer, remove burrs and use an aligned press tool that supports the bushing end. Review split orientation against the supplier’s instructions and the known load direction. Confirm the head housing is not distorted by clamping, threaded retention or nearby fasteners.
Do not import a machining allowance from a different composite material. PERMAGLIDE’s machining guidance specifically concerns P202; it is not a general reaming instruction for PTFE composites.
[4]Record rod coating, hardness, roughness measurement direction, corrosion and scratches. Assess surface finish and clearance together against the selected supplier’s specification. The general BONIU fit guide provides a starting checklist, not a universal numerical fit for every cylinder.
Frequently asked questions
Can an SF-1 guide bush replace the rod seal?
No. The guide supports a specified radial reaction and alignment; the seal contains pressure. Confirm both components and their separate grooves on the cylinder drawing.
Is DU the standard name for every PTFE composite bush?
No. DU® is GGB’s protected product designation. SF-1 is used by suppliers for a composite-bushing family; request the actual formulation and specification rather than assuming brand equivalence.
Should a tight installed bush be reamed?
Do not assume there is a machining allowance. Check the housing, installed bore, rod and layer specification first. Obtain explicit supplier instructions before removing sliding-layer material.
Can a rod-guide bushing correct a long overhung load?
A guide can carry only the load and alignment for which the assembly is designed. An external linear guide or changed cylinder mounting may be needed; increasing bush length alone is not a verified solution.
Request a drawing review
Send the front-head section drawing, rod diameter and coating, housing material and bore limits, installed-clearance requirement, stroke and speed profile, side-load position, maximum extension, seal arrangement, lubrication, quantity and inspection needs.
Send your drawing for review or email sales@boniubushing.com. BONIU reviews manufacturing feasibility, material availability, documentation and quotation scope for the particular enquiry. This guide does not confirm stock, a certified material batch or approval for a named machine.
Technical references
- GGB: DU metal-polymer bearings. Branded material construction, linear motion and product-identity context.
- PERMAGLIDE: piston-rod bearing in pneumatic cylinders. P200 application with initial lubrication; not an SF-1 rating.
- PERMAGLIDE: P200, P202 and P203 materials. Product-specific lubricated composite family and construction information.
- PERMAGLIDE: machining the sliding layer. Product-specific P202 allowance; not transferable to an SF-1 liner.
The cited manufacturers describe their own products and material references. Their ratings, tests and certifications are not BONIU specifications. The application analysis, calculations and enquiry workflow here are engineering guidance; final limits require review of the actual assembly.