Engineering library
Practical guidance on polymers, design, tooling, production and purchasing. Start with the issue your team is solving.
How rotational molding works
Rotational molding heats a measured charge in a slowly rotating hollow mold, then cools the part before removal. Powder distribution, heat transfer, fusion and cooling work together; rotatio
Rotomolding vs injection and blow molding
Choose the process around geometry, demand, finish and assembly. Rotomolding is worth investigating for relatively large hollow parts and varied production runs. Injection molding may better
LLDPE, HDPE and resin selection
LLDPE and HDPE are common rotomolding resin families, but the family name is not a complete specification. Select a supplier grade using stiffness, impact, environmental stress cracking, pro
Reading density and melt-index data
Density and melt index help compare candidate resins, but neither replaces finished-part testing. Compare melt-index values only at the same temperature and test load. Check stiffness and im
UV resistance and outdoor colour
Outdoor service is a combination of sunlight, heat, moisture, loading and local climate. A UV-stabilized grade is a starting point, not a guaranteed service life for every colour and region.
Chemical and temperature compatibility
Identify the exact liquid, concentration, temperature and contact duration. General polyethylene chemical resistance does not validate a finished tank with stressed corners, inserts and seal
Powder quality, preparation and storage
Powder consistency affects flow, fusion and appearance. Record supplier lot, particle specification, contamination controls and storage history. Do not assume every surface defect can be cor
Recycled PE and specialty materials
A sustainability claim needs a defined material source and an appropriate application. Recycled content may change consistency, colour and mechanical behaviour; test the specified blend rath
Nominal vs minimum wall thickness
Nominal thickness describes a design target; minimum thickness defines the weakest acceptable inspected region. A part can meet its target weight and still have a thin local area. Agree a wa
Why wall thickness varies
Wall distribution depends on heat, mold geometry, material movement and loading arrangement. Start with an inspection map and process records rather than accepting total weight as proof of u
Tolerances, shrinkage and assembly datums
Specify the few dimensions that actually control assembly and explain their function. A single tolerance percentage for every rotomolded part is not a useful acceptance standard. Separate mo
Draft, corners and mold release
Design for a clear removal direction before adding cosmetic details. Internal cores, textures and deep recesses can make release more difficult than an open outer surface. Use a mold-opening
Ribs, flat panels and stiffness
Large flat panels need a deliberate stiffness and appearance strategy. Investigate contours, hollow ribs and support locations before making the entire part thicker. Injection-style narrow s
Molded-in inserts and attachment points
Define the load path before choosing an insert. Torque, pull-out, vibration, spacing and installation method all matter. Metal encapsulation should not be assumed to create a chemical bond w
Holes, fittings and leak paths
Decide which openings are formed in the mold and which are cut after molding. Plan machining datums, trim edges and access for assembly. A one-piece shell can still leak at a gasket, fitting
Tooling route, ownership and maintenance
Compare tooling routes against geometry, finish, revision risk and expected runs. Do not buy on mold price alone. Record tool identification, ownership, exclusivity if agreed, storage, maint
Process records, cooling and warpage
Record the approved material, shot weight, machine, heating, rotation, cooling and demolding conditions for the sample. Changing the cooling strategy can change dimensional behaviour. Identi
Bubbles, pinholes and surface defects
A defect is a symptom, not a complete diagnosis. Record location, frequency, material lot, photographs and the conditions of good and bad parts. Bubbles or pinholes may require checking fusi
Surface finish, colour and branding
Define visible zones and an agreed appearance sample. Texture, mold condition, pigment and handling all affect what the customer sees. Discuss molded graphics, labels and secondary finishing
Designing a robot enclosure for rotomolding
Start with a system layout that identifies sensors, batteries, cooling, maintenance and the precision chassis. Assign the molded cover a defined role instead of expecting it to provide every
Specifying a medical equipment housing
State the intended use and whether the part contacts patients, fluids or the sterile field. An external housing is not automatically a medical device approval or a biocompatible component. A
Samples, inspection and batch traceability
Sample approval should identify the exact drawing revision, material, colour, assembly and test conditions. Include critical dimensions and minimum wall checks rather than relying only on a
Packaging, container loading and landed cost
Hollow products can consume significant shipping space. Evaluate packed dimensions, nesting, fittings inside the shell and protection before freezing the design. Compare actual loading plans
What makes a rotomolding RFQ quotable?
A useful RFQ describes function, drawing revision, material or exposure, quantity, critical interfaces, tests and destination. Separate tooling, samples, recurring parts, purchased fittings