Barlog Plastics KEBABLEND RS 49.1800 PA12 for Radiation Shielding is an injection-moulding compound based on polyamide 12 filled with a tungsten filler system. The designation RS 49.1800 identifies the radiation-shielding series and a nominal composite density of 4.90 g/cm³, which is determined according to ISO 1183-1:2019. The grade is supplied as cylindrical granules and is used for photon-radiation shielding in diagnostic X-ray housings, collimators, isotope handling tools, nuclear maintenance fixtures, and non-destructive testing equipment. The main functional difference from unfilled PA12 is the deliberate increase in density and high-Z filler content; this converts a mechanically tough polyamide into a stiff, highly filled shielding material with lower ductility, higher melt viscosity, and higher machine wear. The main difference from lead sheet is processability: complex housings can be moulded as a single consolidated part with ribs, snap fits, bosses, and cable reliefs, without cutting, bending, or bonding lead.

Because the polymer matrix is PA12, water uptake at saturation is significantly lower than that of PA6 or PA66. Under ISO 62:2008 immersion conditions, unfilled PA12 typically reaches about 1.5% water absorption, while PA6 can absorb 9–10%. The tungsten filler reduces moisture-related dimensional change further because the inorganic phase occupies volume and constrains the matrix. The trade-off is a large loss in elongation and notched impact strength compared with unfilled PA12. Mechanical data should therefore be taken from the current Barlog Plastics technical datasheet for RS 49.1800, with dry-as-moulded and conditioned values reported to ISO 527-1:2019, ISO 178:2019, and ISO 179-1:2010.

How Does the Tungsten Filler Alter Photon Attenuation Compared with Unfilled PA12?

The attenuation of a narrow photon beam is expressed as I = I₀ exp[−(μ/ρ) ρ t], where μ/ρ is the mass attenuation coefficient, ρ is density, and t is thickness. The linear attenuation coefficient μ = (μ/ρ) ρ determines the thickness required for a given reduction in transmitted intensity. Unfilled PA12 has low effective atomic number and density 1.01 g/cm³; therefore it is not useful as a primary X-ray barrier. RS 49.1800 increases both density and effective atomic number through the tungsten filler. Tungsten has Z = 74 and a high photoelectric cross-section in the diagnostic energy range; the resulting compound is a practical polymer-based shield.

Lead-equivalence values are not intrinsic. The same specimen can exhibit different lead-equivalence factors at 70 kV, 100 kV, 120 kV, or isotope gamma energies. Qualification should follow the broad-beam geometry of IEC 61331-1:2014 or the purchaser’s equivalent national standard. The measured value is influenced by filler dispersion, wall thickness, weld lines, and local density gradients. For these reasons, specifying RS 49.1800 as “2.0 mm Pb equivalent” without stating the beam quality and filtration is technically incomplete.

For a fixed transmitted intensity ratio, the required shield thickness decreases as the linear attenuation coefficient increases. Because lead has higher density and Z than the tungsten-filled PA12 compound, a lead sheet provides more attenuation per millimetre. The RS 49.1800 wall is therefore thicker than a lead-sheet shield for the same lead equivalent; the engineering advantage is the consolidation of shielding and mechanical housing. Published lead-equivalence data for this specific configuration is limited to the manufacturer’s application validation; product developers should generate attenuation curves on moulded plaques representative of the final gate and weld-line locations.

Filler particle size, particle size distribution, and surface treatment determine the balance between melt viscosity and filler separation. Coarse tungsten filler can raise the sedimentation rate in a molten pool; if residence time is too long or back pressure too low, filler separation can produce local density gradients. Typical production parameters therefore hold melt temperature at the low end of the recommended window and use a reverse barrel temperature profile to reduce shear heating. High back pressure without excessive screw speed improves dispersion but increases shear work; the indicated back pressure range of 0.5–1.0 MPa should be treated as a starting point.

The PA12 matrix melting peak in an unfilled state is in the range 172–180 °C under ISO 11357-3:2018, and the crystallization peak is typically near 140–150 °C. The filled compound has a similar matrix melting point but a lower specific heat per unit volume of polymer and higher thermal conductivity due to the tungsten filler. The higher thermal conductivity can reduce cycle time in thick sections but also promotes faster skin formation; injection speed and gate freeze time must be adjusted. Published data for the exact thermal conductivity of RS 49.1800 is limited; the manufacturer’s datasheet should be consulted for heat transfer calculations.

On production injection-moulding machines, the high melt density changes shot-weight calculations and screw recovery behaviour. A screw of 40 mm diameter and 120 mm stroke has a geometric swept volume of approximately 151 cm³; at a nominal solid density of 4.90 g/cm³, that corresponds to a shot mass near 740 g, compared with roughly 153 g for unfilled PA12. Machine selection based on polystyrene shot capacity therefore underestimates the required barrel capacity. The general-purpose three-zone screw should be replaced or protected with a bimetallic barrel, hardened screw, wear-resistant check ring, and wear-resistant nozzle tip. Field experience with comparable tungsten-filled PA12 on 20:1 L/D screws has shown screw recovery time increases of 30–50% relative to unfilled PA12 at the same back pressure, because the compound is both denser and more viscous.

Injection Moulding of a High-Density PA12 Grade on Production-Scale Equipment

Pre-drying is mandatory. Residual moisture above 0.10% by weight can hydrolyse the PA12 matrix and cause surface splay. Sealed bags can normally be dried at 80 °C for 4–6 h in a desiccant dryer with a dew point of −30 °C or lower. If pellets are exposed to ambient air above 50% relative humidity for more than a few hours, the drying time should be extended. Melt temperature is generally held between 220 °C and 260 °C. The lower bound is set by melt homogeneity and the upper bound by PA12 degradation; residence time above 260 °C should be kept below 8 min and the melt should not exceed 280 °C. Injection pressures of 80–120 MPa and holding pressures of 40–70 MPa are typical for thick-walled shielding parts. Mould temperatures between 40 °C and 80 °C are used; the upper value improves weld-line strength but increases cycle time and ejection difficulty.

Gate location controls the position of weld lines. Weld lines in highly filled grades can reduce tensile strength by 20–40% compared with unwelded sections and may create local filler orientation that reduces local shielding density. In a radiation-shielding housing, weld lines should not be located in sealing faces, in thin sections, or along the primary beam path. A central fan gate or sequential valve gating is preferred for large covers. Hot runners are possible, but the manifold and nozzle tips must be specified for abrasive compounds. Gate diameters below 1.0 mm can produce excessive shear heating and filler separation. Venting depth above 0.02 mm risks flash due to the compound’s high density and the high injection pressures used; vacuum-assisted venting is beneficial for large components.

Machine selection should also consider screw torque. Because the melt density is approximately 4.9 times that of unfilled PA12 and viscosity is higher, the plastication load at a given screw speed is greater than a general-purpose PA12 job. A high-torque drive and a screw design with low-shear mixing sections are preferred. Shots should not exceed 60–70% of the barrel capacity for homogeneous melt quality. The hopper should be closed or fitted with a dry-air purge to minimize moisture re-uptake during long production runs.

Post-mould dimensional stability in RS 49.1800 is governed by the crystalline structure of PA12 and the high filler volume. Mould shrinkage is significantly lower than unfilled PA12 because the tungsten filler constrains contraction. Shrinkage is anisotropic; values in the flow direction are generally lower than transverse values. A mould temperature of 80 °C and adequate holding time are required to minimize tolerance variation. If parts are annealed after moulding, secondary crystallization or stress relaxation can cause additional dimensional movement; dimensional inspection should be performed after representative conditioning, not immediately after ejection.

PA12 is selected as the matrix because it has lower water absorption and better dimensional stability than PA6 and PA66, and because PA12 retains good resistance to aliphatic hydrocarbons, oils, greases, and many cleaning agents used in medical and industrial environments. The tungsten filler can reduce chemical resistance slightly because the filler-matrix interface may permit ingress of aggressive media. In applications with repeated disinfectant exposure, the finished part should be compatibility-tested with the specific agent, since PA12 may stress-crack in contact with polar solvents or strong acids at elevated temperature.

When a Radiation Shield Must Replace Lead Sheet in Complex Enclosures

Lead sheet requires secondary cutting, bending, or bonding, which generates lead dust and raises occupational hygiene requirements. RS 49.1800 PA12 converts the shielding layer into an injection-moulded part that can include integrated snap fits, screw bosses, ventilation louvres, and internal ribs. The wall thickness must be calculated for the specific photon energy, but a lead-free polymer-tungsten shield will generally require a greater wall thickness than lead. For diagnostic X-ray energies, the required multiplication factor relative to lead is normally greater than 2 and must be confirmed by measurement under IEC 61331-1:2014 conditions. The design freedom can nevertheless reduce total system mass and part count because separate mechanical housings and lead linings are combined.

The material is not a replacement for borated polyethylene in neutron shielding. In mixed neutron-photon fields, RS 49.1800 is used as the photon-shielding layer in a laminate with hydrogen-rich neutron-shielding material. Compared with barium-sulfate-filled PA12, RS 49.1800 offers a higher density and higher effective atomic number, which produces more attenuation per millimetre at diagnostic X-ray energies. Compared with unfilled PA12, the compound has much lower ductility and should not be used for snap-fit arms requiring large deflection unless the design is adapted to the material’s modulus and strain-at-break. Unfilled PA12 typically has a tensile modulus around 1.4 GPa and a high elongation at break, frequently above 50%. Tungsten-filled PA12 with a density near 4.90 g/cm³ is expected to exhibit a tensile modulus in the region of 8–10 GPa and a strain at break below 3%, reflecting the transition from a ductile polyamide to a particulate-filled composite. The exact values vary with filler content, particle size, and surface sizing. These differences mean that design rules developed for unfilled PA12 snap fits and living hinges are not applicable; structural simulations should use the actual stress-strain curves measured according to ISO 527-1:2019, not generic PA12 databases.

Material Verification, Batch Release and Compliance Matrix

Incoming material quality is verified against the manufacturer’s batch release certificate and the buyer’s agreed specification. The following table lists the standard test methods relevant to RS 49.1800 PA12 for Radiation Shielding. Compliance with lead-free shielding requirements does not follow from material composition alone; the final component must be evaluated against the applicable device or installation standard. The material is formulated without metallic lead, but downstream RoHS compliance depends on the component category and applicable exemptions under RoHS Directive 2011/65/EU. REACH screening under EC No 1907/2006 should be requested from the supplier for the specific production lot.

Operational boundaries include avoidance of amine-based additives or flow modifiers that can attack the PA12 matrix at melt temperature; such additives may cause gas evolution, surface defects, or premature degradation. The grade should not be diluted with unfilled PA12 regrind on shielding-critical parts, because dilution reduces filler concentration and therefore density and lead equivalence. Regrind content should be established by radiological measurement and not mechanical strength alone. For critical shielding housings, a conservative regrind limit of 20% is applied unless the moulder has radiological data demonstrating otherwise. Moisture-exposed pellets must be re-dried before processing. Final parts should be radiographically checked in the gate and weld-line regions, because standard injection-moulded test bars do not reproduce local filler orientation or density variations present in a real shielding wall.