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Increasing the Strength and Reliability of Press Fits


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Retaining compounds increase the strength and reliability of traditional press and shrink fits. Retaining compounds improve the distribution of stress, which increases maximum load transmission and performance. They create a physical barrier that eliminates fretting, oxidation and galvanic corrosion, which increase service life.
Recent chemical advances in retaining address assembly process variables including gaps, surface finish and cleanliness ensuring consistent performance. Application equipment provides repeatable precision dispensing.
• Recent innovations in retaining: tolerance, higher temperature resistance, primerless formulas
• New data on retaining advancements: test results on strength, oil and chemical tolerance
• How to use retaining compounds to augment a press fit for increased reliability
• Application case histories for retaining including cost and performance

Published in: Technology, Business
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Increasing the Strength and Reliability of Press Fits

  1. 1. Increasing the Strength and Reliability of Press Fits
  2. 2. Before We Start  This webinar will be available afterwards at & email  Q&A at the end of the presentation  Hashtag for this webinar: #DWwebinar
  3. 3. Moderator Presenter Q&A Miles Budimir Doug Lescarbeau Robert Dunkel Design World Henkel-Loctite Henkel-Loctite
  4. 4. Increasing Strength & Reliability of Press Fits Doug Lescarbeau Anaerobic Technology Director, Henkel Corporation Robert Dunkel Technical Service Director, Henkel Corporation November 14, 2013
  5. 5. Agenda • Mechanical retaining • Retaining compounds • Performance • Application process • Disassembly • Recent innovations • Application case histories
  6. 6. Mechanical Retaining Methods There are three common mechanical methods used to join cylindrical components such as gears, bearings, shafts and hubs: Types of Fits Mechanical-Drive Assembly Interference Fit Assembly Tack in Place Assembly
  7. 7. Mechanical Drive Assemblies Set Screw Pin Keyway Spline Shaft The most common mechanical-drive assembly is the conventional key/keyway. Other mechanical-drive assemblies are set screws, pins and spline shafts. All transmit torque levels related to their mechanical interlocking: Set screw << pin << keyway << spline shaft All are easy to assemble or disassemble.
  8. 8. Mechanical Drive Limitations • Notch effect creates high stress concentration in the area of the screw, key, pin or spline. • Backlash, inherent in most designs, results in relative movement leading to abrasive wear • High machining costs result due to additional manufacturing steps • Uneven distribution of mass will affect balance
  9. 9. Interference Fit Assemblies D1 >> d2 d>D e.g. H7/k6 Press Fit Taper Fit Shrink Fit Press fit: interference is created because the shaft is larger in diameter than the hole into which it is pressed. Taper fit: interference is created when the fastener is tightened so the parts are drawn together. Shrink fit: The hub is expanded with heat or the shaft is shrunk with cold before parts are assembled. Interference is created when parts return to normal temperature.
  10. 10. Limitations of interference fit assemblies, e.g. taper fits, press fits, shrink fits • Material, surface and design restrictions rely on friction alone to transmit torque • Close tolerances required to achieve specific load capacity results in high machining costs • Micro-movement can cause fretting corrosion that will accelerate wear and increases the risk of part failure • Surface galling makes disassembly difficult/ impossible • High stress in components, due to interference fits, plus operational loads can lead to part failure
  11. 11. Tack in Place Assemblies Connections by welding or soldering are high strength assemblies, but complete load is carried by the small welding area.
  12. 12. Limitations of welded or soldered tack in place assemblies • Only compatible metals can be joined • Heating of the material can create distortion, residual stresses and structural degradation in welded areas. • Disassembly difficult/impossible • Additional costs due to need for specialized equipment, e.g., laser welding, energy • Need for specially trained personnel, e.g., Welders • Welding usually requires secondary cleaning and grinding operations.
  13. 13. Retaining Compounds • Single component adhesive • Fill gap between joined parts • Make use of complete contact area • Good adhesion to metal surfaces • High cohesion of the adhesive layer • Provide high shear strength
  14. 14. Retaining Compound Options Augment Mechanical Retaining • Higher load transmission and better performance with existing designs and geometry. • Equal performance with relaxed tolerances. • Reduce the size and weight of an assembly. Replace Mechanical Retaining • High-strength products can carry high loads. • Because there is 100% contact, load and stress is distributed evenly over the joint. • All voids are filled, which prevents corrosion and fretting.
  15. 15. Design Tools Proprietary RetCalc+ software models Retaining Compound performance Input • 6 Joint Design Factors • 3 Retaining Compound Factors Output • Axial load rating • Torque rating
  16. 16. Cost Benefits • Reduce or eliminate expensive machining operations. • Eliminate some surface finishing requirements. • Prolong equipment life through better fatigue and corrosion resistance. • Fill gaps so machining tolerances can be widened. • Help lower overall assembly and maintenance costs. • Simplify assemblies by reducing use of circlips, keys, dowels or threads. • Can eliminate the need for mechanical retainers. • Minimize machine downtime, ensuring an earlier return to service.
  17. 17. Retaining Compounds Comparison to Mechanical Assembly Methods Retaining Compounds: • Increase assembly reliability. • Produce more accurate, rigid assemblies. • Eliminate backlash in keys and splines. • Prevent small diameter shaft distortion. • Increase strength of mechanical retaining methods. • Eliminate fretting corrosion. • Seal against environmental corrosion. • Eliminate high assembly stresses. • Reduce variations in load transmission. • Allow dissimilar materials to be assembled more easily. Interference (press fits or shrink) fits and taper fits • Rely on friction alone to transmit torque; therefore, they are limited by material, surfaces and design. • Close tolerances are needed to obtain specific load capacities, leading to higher production costs. • Interference fitting creates stresses in the components that can lead to failure, particularly when combined with operational stresses. Keyway and spline assemblies • Cause high stresses due to the “notch effect” that occurs. • Result in high machining costs and backlash. Welding and soldering • Only compatible metals can be joined. • Heating of the material can lead to residual stresses and structural degradation and distortion. • Requires skilled labor and secondary cleaning and grinding.
  18. 18. Application Process Dispensing Equipment provides process control Manual Semi-Automatic Automatic
  19. 19. Disassembly Bearings assembled with Retaining Compound can be disassembled with industry standard bearing disassembly tools and techniques, including bearing pullers and hydraulic presses. Another technique is to heat the parts well above the service temperature [to 250°C (482°F) for most products] and disassemble while the parts are hot.
  20. 20. Voice of Customer & Market Research • Market research identified improvement opportunities • Performance • Primerless • Oil Tolerant • Higher Temperature • Selection • Simplify selection • Global product range
  21. 21. Innovation Temperature upgrade • • Upgraded Temperature to 360ºF (180ºC) Improvements measured via heat aging
  22. 22. Innovation Oil Tolerance • Tested on steel pins and collars with light contamination
  23. 23. Innovation Primerless • Improved performance on all materials
  24. 24. Innovation Primerless • Improved strength development thru gap
  25. 25. Innovation Performance summary Retaining components are often inactive surfaces. Primerless simplifies the assembly process. Health and safety has changed industry cleaning procedures. Oil tolerant delivers more consistent strength. Smaller, higher power components operate hotter Higher 180oC (360oF) rating withstands the temperature
  26. 26. Selection • Five products • Globally available
  27. 27. Applications
  28. 28. Electric Motor Assembly Situation US motor manufacturer wanted to improve brushless motor assembly Solution Parts slip together and are bonded in place with a retaining compound. Challenges • Assembly is subject to high torsional stresses • Must resist lubricating oils Benefits • Retainer increases strength • Relaxed tolerances reduced part cost • Slip fit simplifies component alignment versus press fit
  29. 29. Wheel Suspension Shaft Coupling Situation Solution Urban public transport company in Belgium needs to secure pins for the wheel suspension. Challenges The pin in the hole has too much tolerance so it is susceptible to corrosion and wear. Benefits • Cost savings. Pins last 400,000 km instead of 100,000 km • Corrosion is prevented • Retainer distributes stresses providing highly reliable bond • Robust process. Performs even if parts have light oil contamination
  30. 30. Heat Exchanger Assembly Situation Heat exchanger tube repair required time consuming and costly. Challenges • Must withstand refrigerant fluid and thermal environment. Benefits • Faster process than brazing • Bonding, unlike brazing, does not require skilled labor Solution Heat exchanger tubes are inserted into the tube sheet using a slip fit with retaining compound applied to the outer diameter of the tube.
  31. 31. Threaded Inserts Situation A manufacturer of large air bearings wanted to eliminate spot welding threaded inserts. Solution Inserts are bonded into place with a retaining compound. No cleaning or priming required. Challenges • Parts have an have oily film • Must be ready for further processing within minutes Benefits • Lowered production cost • Eliminated hazardous fumes emitted during welding galvanized • Reduced work in process and plant floor space for process
  32. 32. Athletic Prosthetic Leg and Foot Situation Prosthetic equipment maker needs to secure bearing for competitive sports equipment. Solution Bushings and stainless steel bearings are coated with retaining compound, then press fit into place. Challenges • Repetitive high impact conditions • Thermal cycling from weather extremes • Durability to protect athlete Benefits • Joint strength is increased because retainer augments strength of press fit • Retainer provides 100% contact which distributes stresses, improves reliability • Bearing assembly seats are sealed preventing corrosion
  33. 33. Thank you! As a thank you for participating in the webinar, you’ll receive a free copy of the Retaining Compound Design Guide in the mail.
  34. 34. Questions? Henkel-Loctite Design World Miles Budimir Phone: 440.234.4531 Twitter: @DW_Motion Doug Lescarbeau Henkel-Loctite Robert Dunkel
  35. 35. Thank You  This webinar will be available at & email  Tweet with hashtag #DWwebinar  Connect with  Discuss this on