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MK Plastics Rohacell

It is by no surprise that ROHACELL® still dominates in the area of high-grade lightweight sandwich construction. ROHACELL®’s success can be attributed to the following:

  • Excellent mechanical properties over a wide temperature range, even at low densities
  • High temperature resistance up to 220°C
  • Unique compressive creep behavior for processing up to 180°C and 0.7 MPa
  • Excellent dynamic strength
  • Cell sizes that can be tailored for each processing method

Here at Emkay Plastics we stock many thicknesses of tight tolerance cast Acrylic and the following Rohacell products:

  • Rohacell IG - UF
  • Rohacell IG - F
  • Rohacell WF
  • Rohacell HF

The superior quality the Rohacell offers enhances product manufacturing and you the customer get the benefits.
Click below to find out more about the properties of Rohacell.

What is Rohacell?

Rohacell is a closed-cell rigid expanded foam plastic based on PMI (polymethacrylimide), which does not contain any CFCs. The natural colour of Rohacell is white.

Rohacell has excellent mechanical properties, high dimensional stability under heat, solvent resistance, and particularly a low coefficient of heat conductivity. The strength values and the moduli of elasticity and shear are presently not exceeded by any other foamed plastic of the same gross density.

Machining
Rohacell IG is machined by means of high-speed tools designed for wood or plastics, without the use of lubricants. Dust must be carefully removed by vacuum. Common planing machines used for wood can also be used to plane edges and surfaces.

Milling
Grooves, rebates and other profiles can be cut with a routing cutter. With due care the material can be cut to lap joint widths of 2.00mm. Parts matching the contours of a template can be done with a suitable milling cutter.

Cutting
Thin sheets are cut with a knife. Thicker sheets can be scored halfway through and then broken. A particularly clean fracture is obtained by breaking the sheet at the edge of a table or desk.

Sawing
Circular saws are used for cutting sheets to size. Band, compass and jigsaws can be used for complex shapes

Stamping
Parts can be stamped out of thin sheets (max. 10.00mm thick). The maximum sheet thickness depends on the Rohacell grade used.

Sanding
Sanding can shape the foam sheet, using a steel template fixed to the sheet. Sanding is either done with an abrasive belt or by hand. For large parts a board covered with abrasive paper is used, which is drawn across the template by hand.

Thermoforming
Rohacell becomes thermoelastic and can therefore be shaped at a temperature of 170-190C. The required forming temperature depends on the degree of shaping and the density. Care must always be taken to see that the hot air sweeps uniformly over both sides of the Rohacell and that no heat is allowed to accumulate. The forming temperature must be accurately controlled in order to prevent secondary foaming. Cracks may form when shaping is too fast or done at too low a temperature.

Embossing
Another possible method of shaping is cold and hot embossing. For cold embossing the required shapes and profiles are pressed into the material during which time foam is compressed beyond its maximum compression strength. For hot embossing a heated embossing tool at 160-180C is pressed in to the foam. A nearly closed surface forms during hot embossing therefore polyethylene or PVC films can be sealed directly to the surface without any adhesive.

Cold shaping
It is possible for sheets to be cold bent. For this purpose the foam plastic sheets are lined on one side with a thin, flexible skin (e.g. aluminium sheet) and bent in such a way that the skin absorbs the tensile forces. With this process the attainable bending radii is about twice the sheet thickness.

Painting
Rohacell can be painted or sprayed with most commercial paints (including nitro-cellulose lacquers). Emulsion paints of the kind used in the building trade are unsuitable because Rohacell does not resist alkaline media.

Bonding
All reaction adhesive systems are suitable for bonding Rohacell IG to itself or to other materials

If you require any further technical information on any of the above, please do not hesitate to contact either Steve or Paul in the sales office.

 

Rohacell Profile

 

 

Property Profile PMI foams

1. Free from CFC, halogens and bromine

2. Ease of machining, no special tooling required

3. Thermo formability

4. 100% closed cell structure

5. Compatibility to any matrix system (wet and prepreg)

6. High heat distortion temperature, 180-240c

7. Outstanding strength-to-weight ratio

8. Outstanding creep compression resistance

9. Classified to be non-toxic acc. To AIRBUS standard AITM

10. Low smoke density

11. No release of corrosive emissions when burning

12. Thermal recycling

Rohm Rohacell Approvals

1. 144 Specifications worldwide

2. 95% aerospace industry (24 years of experience)

General Specifications:

1. DIN ISO 9001 / EN 29001

2. DNV (Det Norske Veritas)

3. Lloyds Register

4. FAA Approval ‚ McDD

5. MIL Specifications

Internal and external Audits:

16 Audit

1. McDD

2. Westland,

3. Kawasaki

4. Gulfstream

5. Northrop

6. NFT

7. TUV-CERT

 

Properties Unit Rohacell      
31 IG Rohacell        
51 IG Rohacell        
71 IG Rohacell        
110 IG          
           
Density Kg/m3 32 52 75 110
Compressive          
Strength Mpa 0.4 0.9 1.5 3
Tensile          
Strength Mpa 1 1.9 2.8 3.5
Flexural          
Strength Mpa 0.8 1.6 2.5 4.5
Shear          
Strength Mpa 0.4 0.8 1.3 2.4
Elastic          
Strength Mpa 36 70 92 160
Shear          
Modulus Mpa 13 19 29 50
Elongation of          
Break % 3.5 4 4.5 4.5
Heat distortion          
Temperature oC 180 180 180 180

 

1) The values were measured per pendicular to the sheet surface.
2) At higher temperatures, reverse foaming of the oriented cell structure set in.

 

 

 

Rohacell Sales Range

On stock grades

We can cut Rohacell to any size or thickness needed. We offer a cutting service for Rohacell you may have which needs cutting down to size.


Tolerances are +/-0.5mm

Rohacell Grade Minimum-Maximum Sheet Size Minimum to Maximum Sheet Thickness
IG-F
31 IG-F 1300mm x 630mm, 1300mm x 1300mm,
2600mm x 1300mm
1mm - 140mm
51 IG-F 1300mm x 630mm, 1300mm x 1300mm,
2600mm x 1300mm
1mm - 140mm
71 IG-F 1300mm x 630mm, 1300mm x 1300mm,
2600mm x 1300mm
1mm - 130mm
110 IG-F 2160mm x 1100mm 1mm - 100mm
WF
51 WF 2500mm x 1250mm 50mm/100mm
71 WF 2500mm x 1250mm 50mm/100mm
110 WF 2160mm x 1100mm 50mm/80mm
HF-UF
(51) HF-UF 2500mm x 1250mm 1mm - 80mm

Rohacell stock bought to order

Rohacell Grade Minimum-Maximum Sheet Size Minimum to Maximum Sheet Thickness
31 HF 2500mm x 1250mm 1mm - 110mm
71 HF 2500mm x 1250mm 1mm - 80mm
51 Rima 2500mm x 1250mm 1mm - 80mm
71 Rima 2500mm x 1250mm 1mm - 70mm
110 Rima 2160mm x 1100mm 1mm - 65mm
51 Rima-HT 2500mm x 1250mm 1mm - 80mm
71 Rima-HT 2500mm x 1250mm 1mm - 70mm
110 Rima-HT 2160mm x 1100mm 1mm - 65mm
51 Rist-HT 2500mm x 1250mm 1mm - 120mm
71 Rist-HT 2500mm x 1250mm 1mm - 110mm
110 Rist-HT 2160mm x 1100mm 1mm - 80mm
71 XT 2500mm x 1250mm 1mm - 110mm
110 XT 2160mm x 1100mm 1mm - 95mm
71 XT-HT 2500mm x 1250mm 1mm - 110mm
110 XT-HT 2160mm x 1100mm 1mm - 95mm
51 WF-HT 2500mm x 1250mm 1mm - 120mm
71 WF-HT 2500mm x 1250mm 1mm - 110mm
110 WF-HT 2160mm x 1100mm 1mm - 95mm
51 S 2500mm x 1250mm 1mm - 80mm
71 S 2500mm x 1250mm 1mm - 70mm
110 S 2160mm x 1100mm 1mm - 65mm
31 HP 2500mm x 1250mm 1mm - 80mm
110 HP 2160mm x 1100mm 1mm - 40mm
31 HP-HT 2500mm x 1250mm 1mm - 80mm
110 HP-HT 2160mm x 1100mm 1mm - 40mm
SL 71 2500mm x 1250mm 1mm - 90mm
SL 110 2160mm x 1100mm 1mm - 75mm
71 SL-HT 2500mm x 1250mm 1mm - 90mm
110 SL-HT 2160mm x 1100mm 1mm - 75mm
50 WIND-F 2500mm x 1250mm 1mm - 120mm
60 WIND-F 2500mm x 1250mm 1mm - 100mm
80 WIND-F 2500mm x 1250mm 1mm - 100mm
100 WIND-F 2160mm x 1100mm 1mm - 90mm

Electrical properties

Electrical properties

Dielectric constant and loss tangents of ROHACELL

ROHACELL Frequency, GHz
Dielectric constants 2.5 5 10 26.5
31 1.05 1.043 1.046 1.041
51 1.057 1.065 1.067 1.048
71 1.075 1.106 1.093 1.093
Loss tangent        
31 <0.0002 0.0016 0.0017 0.0106
51 <0.0002 0.0008 0.0041 0.0135
71 <0.0002 0.0016 0.0038 0.0155

 

The excellent dielectric values of ROHACELL are a major advantage for its use in radomes and antenna engineering.

The moisture pick-up of ROHACELL without skins does not really influence the remarkable specific properties of ROHACELL in antenna applications since the water molecules are fixed in the imide groups and are unable to oscillate freely.

When ROHACELL is covered with skins as usual, the skin material influences the properties of the antenna more than ROHACELL itself. The change of the antenna properties by water absorption of the skins must also be taken into account as the water molecules may oscillate freely here.

X-Ray Transmission


X-ray transmission of ROHACELL
Aluminium-equivalent measurements were carried out with 100 kV X-ray on various ROHACELL specimens. The graph shows curves measured for ROHACELL grades31, 51 and 71. Only the given readings for the indicated thickness were measured for ROHACELL 110, P 170 and P 190.

ROHACELL Thickness In. (mm) Al-equivalent In. (mm)
110 1.9 (48) 0.17 (0.44)
p 170 1.1 (28) 0.16 (0.39)
p 190 0.9 (23) 0.15 (0.35)





X-ray transmission of ROHACELL (100kV)

Compressing Rohacell

Surface compression

ROHACELL sheets with an integral structure are produced in a press which can be cooled and heated. A cold suitably over sized ROHACELL sheet is placed between heated platens at 320-356of (160 - 180oc) and then the press closed immediately.

The specific molding pressure should be about 30% less than the compressive strength of the particular ROHACELL grade at 68of (20oc) As the heat penetrates into the ROHACELL sheet, the outer cells correspondingly give way and are squeezed flat.

The procedure gives a higher density in this layer. The molding time depends on the desired degree of compression until the thickness stop is reached. The sheet must now be cooled to about 176of (80oc) before it can be taken out of the press. This prevents the flattened cells from recovering their original shape (fig 34). The method also serves for partial compression ol molded articles (fig. 35).

In practice, this procedure is also utilized for sandwich parts with thin skins in order to increase the bending stiffness of the sandwich. Another important fact is that the indentation resistance is considerably improved through the higher density of the edge zones. During hot curing of the adhesives or resins, the outer surface is compressed until the desired thickness stop is reached.

Molding with complex exterior contours

After heating the ROHACELL part to be molded to the forming temperature (338 - 374of (170 - 190oc) depending on material grade). it is placed in a heated mold and brought to the required geometrical form by compression. The molding must be cooled down to about 176of (80oc) before it can be taken out of the mold.

The described method is far more cost-effective than other techniques, because there is no machining to a precise exterior contour.