Hobson data sheet
BUMAX 88 and BUMAX 109 Stainless Fastener Data Sheet
A four-page BUMAX data sheet, distributed by Hobson, for BUMAX 88 and BUMAX 109, two premium A4 stainless fastener products. It covers composition and standards, corrosion resistance, mechanical properties and preload, fatigue, magnetic permeability, quality and marking.
What this covers
- Introduction and applications
- Chemical composition and standards
- Corrosion resistance
- Mechanical properties and preload
- Fatigue resistance
- Magnetic permeability
- Quality, marking and packing
Applies to Threaded Rod (Allthread), Hex Bolts & Set Screws, Hex Flange Nut, Hex Nut, All-Metal Prevailing Torque Nut, Socket Head Cap Screw, Socket Countersunk Screw, Flat Washer and Mudguard / Penny Washer.
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Both are made from 316L high molybdenum stainless (EN 1.4432, 1.4436, 1.4435) within the A4 definition of ISO 3506. BUMAX 109 gets its extra strength from a special manufacturing process.
- BUMAX 88 (M3 to M36): 800 MPa tensile and 640 MPa yield minimum, matching 8.8 carbon steel. BUMAX 109 (M3 to M20): 1,000 MPa and 900 MPa, matching 10.9. Standard A4-70 is 700 MPa and 450 MPa.
- PRE 27 against 25 for standard A4: BUMAX 88/109 guarantee 2.5 to 3.0% molybdenum, standard A4 only 2.0%. In a five-year roadside and coastal exposure test in Sweden, 316L high Mo pitted at one of seven sites and standard 316L at five.
- Fatigue test on M6 x 50 bolts pre-stressed to 400 MPa: BUMAX 88 reached the 10 million cycle test limit in every test at ±50 and ±55 MPa; A4-80 lasted between 0.4 and 10 million cycles at those levels.
- BUMAX 88/109 nuts are always waxed (friction about 0.08), so far less torque is needed to reach the clamp load than with standard A4, in tests on M6 bolts and nuts.
- Relative magnetic permeability at 20°C, measured on M5 screws: BUMAX 88 1.006, BUMAX 109 1.007. Used in nuclear and fusion reactors and particle accelerators.
- Delivered with full traceability and a 3.1 certificate. BUMAX 88 can also come certified to the EU pressure equipment directive (PED 97/23), and with CE marking as a structural bolt to EN 15048.
Who it helps: Engineers and buyers who need a stronger, more corrosion resistant A4 stainless fastener in place of 8.8 or 10.9 carbon steel.
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