Lead Components & Assemblies
Lead Chevrons & Bricks
Lead Bricks are widely used in various applications including ballast for shipping and sub-sea cables, counterbalance weights and radiation shielding. Depending upon the application the specifications for shape and size vary. Large ballast blocks may be sized to meet the requirements of the available lifting equipment with chamfered corners to minimise snagging, whilst radiation shielding is typically sharp edged and smooth of finish to ensure a tight build, minimising the creation of shine paths, and reducing contamination traps.
In radiation shielding the brick size is typically selected after consideration of installation method, lifting equipment and, where applicable, with reference to manual handling guidelines and prevailing customer and regulatory requirements.
Bricks are produced from pure lead where cost is the key driver, or as an alloy with 4% Antimony additive were a harder, damage resistant brick is required.
A typical specification is 4% Antimonial Lead Alloy in a 8” x 4” x 2”/ 200 x 100 x 50mm (+/- 0.5mm) chevron brick form. The brick shall be sharp of edge and corner, smooth of surface and free from indentations, cracks or defects.
All chevrons are manufactured to interlock cleanly preventing shine paths. Cast arrangements are particularly useful for bulk shielding applications whilst extrusions and machined variants are better for complex geometries and a clean and easily decontaminated surface finish.
Chevrons up to 40 x 100mm may be extruded, cast or milled; beyond 50mm cast or milled products apply dependent upon the application.
Cast chevrons are usually utilized as bulk shielding material, either in ‘as cast’ form where surface finish is not of concern or in machine finished form where a clean and regular face is required to the resultant wall. The resultant chevrons are the cheapest form of product designed for manual handling and wall construction and are in, many cases, sufficient for applications including bunkers and localized temporary erections.
Extruded chevrons are created using a 500 tonnes extrusion press and are completely regular in appearance. The manufacturing process inherently compresses the lead into the required shape under force and therefore results in a product that is inherently free from defects.
Dimensions of chevrons are limited by the size of the press die and as a result they tend to be in thinner sections, as a result they are often produced in longer lengths or rails to achieve a component weight just inside the desired manual handling limit. The production process is more complicated than cast chevrons and as a result the product range is more expensive, however, the resultant surface finish and ease of assembly make them a common form of product where cast solutions are inappropriate. Due to process dynamics, chevron rails are not suitable where high contents of Antimony (over 4% Sb) are required.
Rolling a thick billet of lead to the desired width, cutting oversize and machining to finish produces milled & machined chevrons. This product is the most flexible in terms of achievable form factors and bespoke finishes, is homogenous and porosity free as a result of rolling reductions and may be produced in thicknesses up to 150 – 200mm with multiple chevrons (V, W, VW…) if required for stability. However the complexity of the manufacturing process makes them less appropriate in applications where large quantities of cheap bulk shielding are required.
Chevron Standard Forms
Typical form factors include BS 4513 specification V50 & V100 series square cut and R50, R100, R150, R200 or R250 series round cut form factors although a wide variety of current, historic, local and international standards, including legacy Eastern Bloc types, are supported in addition to bespoke or client specific forms.
Lead Bricks & Pipes
Some applications do not require chevrons to protect from the inadvertent creation of shine paths. This may be where walls are made up of multiple offset layers or where brick interfaces can be aligned to avoid coincidence with the radiation path. In such cases lead bricks may be used. Bricks are available in a variety of sizes and are typically cast, extruded or saw cut from milled sheet.
Lead pipe work is typically produced to provide contoured over cladding to existing piping installations. Depending upon the sizes, shapes and features required pipe work can either be self-supporting or encapsulated with structural members.
Leads density can be used to increase the density of bulk construction materials. Two standard forms of lead can be used in this instance: lead powder and lead shot. Lead powder is uncommon and no longer recommended. Whilst it can easily form a homogenous mix with the parent material, the mobile nature of dry lead powder requires careful consideration of the health and safety arrangements until the media becomes fixed as a result it is not considered useful in the majority of applications outside of bespoke production facilities.
Lead shot is often a realistic compromise in such situations allowing a reasonable degree of homogeneity whilst minimising the risk of inhalation during the mixing process. Shot is readily available in sizes from 1mm upwards and through careful selection of geometries, can be used to produce densities significantly in excess of standard concrete whilst being able to be cast in much the same way.
Lead filling is a technique used to provide installed fixed shielding to flasks, gamma gates, containers and structural assemblies. Royston is able to provide a filling service to third party manufacturers of steelwork, or if required by the client or designer, provide the complete service including manufacture of the assembly to be filled as well as providing the fill itself.
We are able to handle assemblies, which are physically large (size and weight) and have experience in assemblies in excess of 20 tonnes, alternatively if appropriate we are able to undertake on-site filling. Post filling services including scintillation testing can also be arranged.
For novel applications or where the constraints on lead filling are not well understood by the client, we are able to offer an advisory service to ensure that designs consider the fill process and limitations thereof. This approach can be useful in minimising the potential for voids in the finished assembly.
Royston provides a wide variety of services including filling, casting, milling, machining extruding, burning and welding. Additionally we have experience in working with suitably qualified and experienced personnel in the design, manufacture, assembly and testing of complex and bespoke assemblies. Whether you require just one step in the process or a turnkey service we are more than happy to help.