Hollow Bar advantages for component manufacturing industries

Hollow Bar and Mechanical Tubing provide an economic and efficient means of supplying high quality raw material stock for the manufacture of radially machined components; providing a cost effective solution to the use of solid bar. 

Hollow Bar minimizes material wastage and reduces the total machining time requirements by avoiding the initial drilling operation. 

Typical manufacturers that use stainless steel Hollow Bar to make components that are used in: 

  • general engineering 
  • chemical & petrochemical plants 
  • automotive production 
  • paper production plants 
  • textile production plants 
  • food production equipment 
  • anti-friction and slide bearing production

Machining allowances & production tolerances

Hollow Bar is manufactured in the size ranges most frequently required by mechanical engineering manufacturing companies. However, in the case of Hollow Bar, the tolerance range for the outside diameter lies in the plus range, and for the inside diameter in the minus range. The wall thickness tolerance is determined by the degree of centre offset; this is due to the effect of the tolerance for the outside and inside diameter, the wall thickness and the centre offset. (See diagram below.)

In the case of Mechanical Tubing to ASTM A 511, the outside diameter and the wall dimensions generally lie in the centre of the tolerance range. Thus, when ordering product for machining it is important to take into account the differences in the tolerances between the Hollow Bar and the ASTM A 511 Mechanical Tubing specifications. In most cases the machining set up is based on centring the outside diameter.

Hollow bar Dimensional Range and Tolerances

For full details on Finish Machined dimensions download our Datasheet at www

Outside diameter rangeDimensional tolerances
mmFor the outside diameter | DFor the outside diameter | dFor eccentricity (centre offset) | EFor out-of-straightness | h
32 < D < 250 -0/+2% (min. 1 mm)+0/-2% (min. 1 mm)10%

1 mm/m

Outside diameter rangeMachining allowances
mmFor the outside diameterFor the inside diameter
32 # D # 701.0 mm1.0 mm
70 # D # 1321.0 mm1.0 mm
132 # D # 2001.0 mm2.0 mm
200 # D # 2501.0 mm2.0 mm

Note: The machining allowances are recommended minimum values and are related to short-length mechanical parts (L<2.5 x D, max. 250mm). Machining allowances for longer parts or
special machining procedures can be customised.

Materials

Standard grades

Hollow Bar and Mechanical Tubing are supplied in a range of specially selected stainless and acid-resistant standard grades chosen to cover the majority of the corrosion and processing problems that occur in day to day practice.

MST
Designation
USAEurope
EN 10216-5
Others
 UNSDesignation
(grade)
Standard
ASTM
Steel
No.
DesignationStandard
(SS)
Standard
(BS)
DMV 304S 30400MT 304
(TP 304)
A 511
(A 312)
1.4301X5CrNi18.102333304 S 15
DMV 304 LS 30403MT 304L
(TP 304L)
A 511
(A 312)
1.4306X2CrNi19.112352304 S 11
DMV 316S 31600MT 316
(TP 316)
A 511
(A 312)
1.4401X5CrNiMo17.12.2 316 S 31
DMV 316 LS 31603MT 316L
(TP 316L)
A 511
(A 312)
1.4404X2CrNiMo17.12.2 316 S 11
DMV 316 L Mos   1.4435X2CrNiMo18.14.32353316 S 13
DMV 321S 32100MT 321
(TP 321)
A 511
(A 312)
1.4541X6CrNiTi18.102337321 S 31
DMV 316 Ti TP 316 Ti 1.4571X6CrNiMoTi17.12.22350 
DMV 22.5S 31803  1.4462X2CrNiMoN22.5.3  

(…) Grade designation and/or Standard not specific for Hollow Bars.

VALIMA GRADES

VALIMA TECHNOLOGY for that extra machining advantage . 

Refining both the melting method and the extrusion process produces machining speeds up to 50% higher than standard materials- without compromising performance or compliance to standards.

The VALIMA process modifies the inclusion structure, utilising the benefit of:
Optimising the Sulphur content.

Modifying the inclusion structure to create globular, malleable, low melting point oxide type inclusions which play a significant role of self lubricating the metal-tool interface. 

Eliminating the presence of hard and abrasive inclusions which impact tool life and performance.  

Improved chip breaking with a consequent reduction of cutting edge too-tip wear.  

VALIMA
Designation
MST
Designation
USAEurope
EN 10216-5
Others
  UNSDesignation
(grade)
Standard
ASTM
Steel
No.
DesignationStandard
(SS)
Standard
(BS)
VALIMA 304DMV 304 MCS 30400MT 304
(TP 304)
A 511
(A 312)
1.4301X5CrNi18.102333304 S 15
VALIMA 304 LDMV 304 LMCS 30403MT 304L
(TP 304L)
A 511
(A 312)
1.4306X2CrNi19.112352304 S 11
VALIMA 316DMV 316 MCS 31600MT 316
(TP 316)
A 511
(A 312)
1.4401X5CrNiMo17.12.2 316 S 31
VALIMA 316 LDMV 316 LMCS 31603MT 316L
(TP 316L)
A 511
(A 312)
1.4404X2CrNiMo17.12.2 316 S 11
VALIMA 4435DMV 316 L Mos*MC   1.4435X2CrNiMo18.14.32353316 S 13

(…) Grade designation and / or Standard not specific for Hollow Bars.
* DMV 316L with 2.5 - 3% Mo.

Typical material savings

The red line represents the loss of material ‘Z’ involved when turning a solid round into a Mechanical Tube. Here 45 % of the solid round must be removed for this purpose.

The dotted line illustrates the tube length factor ‘D’, which indicates the extra length available for the mechanical parts production as opposed to solid rounds of the same weight.

The example shows a 1.8-fold tube length increase, which means that almost twice as many parts can be made from the tubular weight of material.

Standards & Norms

Hollow bar is typically manufactured acc to Mechanical Tube Standard ASTM A511.

   Wall thickness tolerance, % 
Outside
diameter
inches
Ratio of wall
thickness to
outside diameter
Outside diameter
tolerance
inches
0.109”
and under
0.109”
to 0.172” incl.
Over 0.172”
to 0.203” incl.
Over
0.203”
Cut
length in. *
Under 3All wall
thicknesses
+/- 0.023+/- 16.5 %+/- 15 %+/- 14 %+/- 12.5 %3/ 16
3 to 5 1/ 2 excl.All wall
thicknesses
+/- 0.031+/- 16.5 %+/- 15 %+/- 14 %+/- 12.5 %3/ 16
5 1/ 2 to 8 excl.All wall
thicknesses
+/- 0.047   +/- 12.5 %3/ 16
8 to 9 3/ 4 incl.5 %
and over
+/- 0.047 **   +/- 12.5 %3/ 16

(…) Grade designation and / or Standard not specific for Hollow Bars.
* DMV 316L with 2.5 - 3% Mo.