MU

MU material structure

Multilayer bushing (dry Sliding Bearings) MU bearings are self lubricated material and are a three layer composite product.

  • PTFE Modified antifriction surface layer 0,01 mm minimum thick (without lead, complying with the European Parliament’s “ELV” directive 2000/53/Ec);
  • Porous bronze layer 0,20 ÷ 0,35 mm thickness;
  • Low carbon steel supporting strip 0,50 to 2,70 mm thick depending on the size of the bush. The steel is plated for corrosion protection (Tin or Zinc 2 ÷ 8 μm).

Structure of the composite material:

Layer Average analyses of the material Thickness of layer
Sliding layer PTFE Fabric 10μm
  • (Minimum)
Intermediate layer CuSn11 Sintered 200÷350μm
  • (Average Peak)
Connecting layer Cu 1÷3μm
Supporting shell Low Carbon Steel (EN 10139)
  • Cu = 0,080 Max
  • Mn = 0,40 Max
  • P = 0,03 Max
  • S = 0,03 Max
0,50 ÷ 2,70 mm
  • (Depending on Dim. of the Bearing)
Protective Layer Sn or Zn 2÷8μm

Operating Conditions

Dry

Oil

Grease

Water

Process fluid

Very Good Very Good Fair Fair Fair

Availability

Characteristics

MU structure combines in the best way the mechanical strength of the steel, the bronze thermal conductivity and PTFE low friction. The performance given without lubricants are the following:

  • Working surface acceptable specific static pressure: Max 250 N/mm2;
  • Working surface acceptable specific dynamic pressure: Max 140 N/mm2;
  • Maximum sliding speed (dry): 2,5 m/s (500 fpm);
  • Maximum sliding speed (oil): 10 m/s (2000 fpm);
  • Working temperature from: -200°C to +280° C (-328°F to +536°F)
  • Friction factor from 0,02 to 0,20;
  • Clear fluids like oil or water permit higher values for speed and specific pressure;
  • Friction factor not affected by “stick - slip” effect;
  • High chemical resistance to industrial fluids and gases (we recommended to make previous test for new application / project).

Special Items

Apart from bushings ISO 3547 (DIN 1494) and thrust washers, the MU can be supplied as many other technical items, between them we indicate the followings:

  • Bushings and washers at customer request measures;
  • Counter - roller bushings with the sliding surface on the outside diameter;
  • Special items at customer’s drawing.

Performance

MU bushing service life depend mainly from the load factor P x V (N/mm 2 · m/s). Practical cases have shown that a working load factor of 2.5 to 3,6 (N/mm2 · m/s) is admissible for short periods. Long service life are suited with load factors ranging from 0.2 to 1.8 for continuous movements and 0.1 to 0.9 (N/mm2 · m/s) for alternate movements.

Friction

MU friction factor principally depends from the specific load, the sliding speed and from the working temperature; very important it is also the material and the counter piece superficial degree of finishing.

Sliding Speed V ( m/s ) Specific Load P (N/mm2) Friction Factor
up to 0,001 140 0,02
from 0,001 to 0,005 from 140 to 62 from 0,04 to 0,07
from 0,005 to 0,05 from 62 to 11 from 0,07 to 0,1
from 0,05 to 0,5 from 11 to 1 from 0,1 to 0,15
from 0,5 to 2,5 1 from 0,15 to 0,2

Wear

During operation the MU bushing shows a first running - in phase when some of PTFE compound transfers on counter piece which normally is of steel alloy. Other counter pieces of stainless steel, chrome plated steel and hard anodised aluminium can improve MU service life. As counter piece have to be avoided bronze, aluminium, phosphatized and nickel plated steel to optimise MU durability surface roughness must not exceed 0.4 um. Where possible MU bushing preliminary tests have to be carried out to make sure about the influencing factors of each application; our technical department is willing to supply additional information and data request.

Mounting

Base procedure for bushings mounting is to force them into their seats; there are same suggestion to follow:

  • Machine a 1 mm seat lead - in with an angle of 20° (±5°);
  • Clean and burr the pieces to couple;
  • Lubricate external bushing surface before mounting;
  • Check alignment between seat and bushing centre lines;
  • When 2 bushing are needed their junctions must be aligned;
  • Use a proper sized mandrel when possible;
  • Mounting can be done with hydraulic or mechanical tools;
  • The mounting force (F) in Newton is shown in the attached table.
Bushing Nominal Thickness 0,50 ÷ 1,00 mm F = 300 x L (Length of bush)
Bushing Nominal Thickness 1,00 ÷ 1,50 mm F = 500 x L (Length of bush)
Bushing Nominal Thickness 1,50 ÷ 2,00 mm F = 700 x L (Length of bush)
Bushing Nominal Thickness 2,00 ÷ 2,50 mm F = 900 x L (Length of bush)

When mounting larger bushes it is advisable to use a mounting tool to support the bush.

The tool diameter should be 0,3 ÷ 0,4 mm more than the bush diameter.

If the bush is secured by using an adhesive, care must be taken to ensure that good quality adhesive are used and that it does not get onto the sliding surface.

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