Guide analyses for a few acid-proof
steels
Bumax products are manufactured from Swedish steel SS 14.2343, equivalent
to EN 1.4436. The carbon content is no more than 0.03% and the alloy content
- chrome, nickel and molybdenum - is higher than in A4 EN 1.4401, the
most common steel grade used for A4 fasteners.
Bumax steel is often called 2343/316L Hi Mo which gives the products
corrosion properties and strength beyond the norm. The table below shows
the chemical composition of acid-proof steel. It includes A4 AISI 316
and 316L – the usual for fasteners – and the acid-proof steel
of the Bumax products.
| Steel type |
C max |
Cr |
Ni |
Mo |
| A4 (316) |
0,080 |
16,0-18,0 |
10,0-14,0 |
2,0-3,0 |
| A4 (316L) |
0,030 |
16,0-18,0 |
10,0-14,0 |
2,0-3,0 |
| BUMAX 88 |
0,030 |
16,5-18,5 |
11,0-14,5 |
2,5-3,0 |
| BUMAX 109 |
0,030 |
16,5-18,5 |
11,0-14,5 |
2,5-3,0 |
| BUMAX Hard |
0,030 |
16,5-18,5 |
11,0-14,5 |
2,5-3,0 |
Corrosion properties
The most common types of corrosion in acid-proof steel are pitting, crevice
corrosion and general corrosion. The steel’s chemical composition
has a major effect on the corrosion properties, with the superior properties
being mainly provided by the alloying elements chrome (Cr), nickel (Ni)
and molybdenum (Mo). The low carbon content (C) is of some importance
but it is at higher temperatures where low carbon content is essential.
Laboratory tests show that our variant of SS 14.2343 – from which
the Bumax products are made – is superior to standard A4 316/316L
in all media and types of corrosion.
Mechanical properties of Bumax
Hard fasteners
Bumax Hard acid-proof fasteners Hardness in HV 0,05
Tightening torque and forces
In order for a screw joint to work satisfactorily, it is important that
it is fitted correctly. This also applies to Bumax Hard Taptite.
The tables show the breaking torque of the screw, the
recommended tightening torque and approximate thread forming torque. The
tables also show suitable hole diameters for safe function.
Torque and strength for Taptite
| Thread |
Breaking torque
Nm min
|
Tightening torque
Nm Rek
|
Thread forming torque
Nm approx. |
| M3 |
4,5 |
1,3 |
0,7 |
| M4 |
7,9 |
3 |
1,8 |
| M5 |
13 |
6 |
3,5 |
| M6 |
20 |
12 |
8 |
| M8 |
30 |
25 |
15 |
| M10 |
52 |
49 |
28 |
Bumax Hard Taptite
Bumax Hard Taptite is a self-tapping/thread forming screw. Thanks
to its special trilobular shape, its conical entry thread and its good
surface hardness, the Bumax Hard Taptite can form metric threads
in structural steel and cold-rolled, austenitic, stainless steel with
a hardness of up to approx. 200 HV. The special Taptite shape is shown
in the figures below.
Taptite trilobular geometry
C=External circle diameter
D=Trilobular diameter
K=Ovality
Thread shape and entry thread
Hole diameters – drilled or punched holes
| Material thickness or thread length for Taptite screws |
| Thread |
0,1-1,5 |
1,51-2,5 |
2,51-4 |
4,1-6,5 |
6,6-10 |
10,1-15 |
| M3 |
2,7 |
2,8 |
2,8 |
2,85 |
|
|
| M4 |
3,65 |
3,65 |
3,7 |
3,75 |
3,8 |
|
| M5 |
|
4,6 |
4,7 |
4,7 |
4,75 |
|
| M6 |
|
5,5 |
5,6 |
5,6 |
5,65 |
5,7 |
| M8 |
|
|
7,5 |
7,5 |
7,6 |
7,7 |
| M10 |
|
|
9,3 |
9,3 |
9,4 |
9,5 |
With punched holes in austenitic stainless steel, deformation
hardening can cause a hardness of more than 200 HV at the hole edge, and
therefor fitting problems may occur.
Bumax Hard Self Tapping (ST)
Bumax Hard ST screws have a conventional plate screw thread and differ
from usual stainless plate screws thanks to their high surface hardness.
Hole diameters and plate thickness (T) for Bumax
Hard ST thread
| T |
Screw diameter |
| |
ST2,9 |
ST3,5 |
ST4,2 |
ST4,8 |
ST5,5 |
ST6,3 |
| <0,56 |
2,2 |
2,6 |
|
|
|
|
| 0,56-0,63 |
2,3 |
2,7 |
3,2 |
3,7 |
|
|
| 0,64-0,75 |
2,3 |
2,8 |
3,2 |
3,7 |
4,3 |
|
| 0,76-0,88 |
2,4 |
2,8 |
3,2 |
3,8 |
4,3 |
4,9 |
| 0,89-1,25 |
2,4 |
2,8 |
3,3 |
3,8 |
4,4 |
4,9 |
| 1,26-1,38 |
2,5 |
2,8 |
3,5 |
3,9 |
4,5 |
4,9 |
| 1,39-1,75 |
2,6 |
2,9 |
3,8 |
3,9 |
4,6 |
5,0 |
| 1,76-2,25 |
|
3,0 |
3,8 |
4,0 |
4,7 |
5,2 |
| 2,26-3,0 |
|
3,2 |
3,9 |
4,1 |
5,0 |
5,3 |
| 3,1-4,0 |
|
|
|
4,4 |
5,1 |
5,8 |
Stock and special
Stock Bumax Hard have the superior Torx grip and range from M3 -
M8. Self tapping (ST), i.e. plate screws, are stocked with diameter range
ST2.9 - ST5.5.
Because we make Bumax Hard products at our factory, we can also
offer special manufacture according to customer needs and requirements.
Bumax Hard can be made to several designs, regarding different head
shapes and grips.
ISO 9001 and QS 9000
Quality always has top priority at Bulten Stainless, and we target our
work to continuously improve our quality. Activities are controlled by
our quality assurance system which is certified by TÜV to ISO 9001
and QS 9000 – a system used by the major actors in of the automotive
industry.
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