High-precision sandwich molding from Battenfeld

The secret of success in sandwich injection molding is hidden inside the molded parts: the use of less and lower-priced materials without compromis-ing quality standards. Injection molders taking advantage of this potential achieve a significant increase in cost-efficiency for their products. Among oth-ers, a Spanish Battenfeld customer, a well-known manufacturer of toilet seats, has seized this opportunity. In the near future he will take delivery of a new HM 10.000/7.700 + 7.700 BM B4 injection molding machine. It will be the eighth multi-component injection molding system from Battenfeld supplied to this company. This particular customer has become the market leader in Europe with the help of cost-efficient co-injection technology. The Battenfeld sand-wich system process technology has been optimized to the point of achieving a tolerance margin of only +/- 5 g for shot weights of 4,000 g.

Material cost savings through co-injection

Material costs are a major factor influencing the total cost of molded parts. Here, the co-injection process provides a solution: it offers processors numerous options to reduce the price of materials, such as molding a compact outer layer around a foamed core, or combining two different types of compact material. For example, material costs can be reduced by adding fillers or by injecting recycled material to form the core. or by adding reinforcing components to the core material,

Moreover, sandwich molding technology can frequently be used to improve the properties of molded parts. Compared to materials without reinforcing components, reductions in weight, increased rigidity or higher heat resistance can thus be achieved, together with excellent surface properties. Conductive materials such as aluminium flakes, carbon, steel or graphite fibres can be added to either the surface or the core in producing electrically shielded enclosures.

Sandwich technology also shortens the manufacturing process by opening up a vast potential for producing highly integrated parts. Several production steps, such as bonding, welding, or intermediate storage, can be dispensed with. Interesting hard-soft combinations thus become possible, for example in the automotive industry, to produce handles, linings and covers for vehicle interiors.

High precision with sophisticated machine technology

Today’s co-injection technology includes a rheologically optimized nozzle system, which permits quick, precise changeover from one material to the next through short flow-channel connections, and by reducing the mass volume in the area of concen-tric channels to a minimum. Of course, easy operation and easy access to all parts are also standard features of these modern nozzle systems.

Co-injection today also comprises process optimization, which is superbly provided by the Unilog B 4 control system in Battenfeld machines. Outstanding precision and repeatability on Battenfeld machines are achieved by one essential feature: high-precision control of the injection process, a vital factor in multi-component technol-ogy.

During the special simultaneous phase, the core material is injected through the two-channel nozzle before the injection of the surface material is fully completed. This ensures perfectly even distribution of the core material up to the end of the flow path while the mold is being filled, as well as surperb surface quality. The simultaneous phase keeps the flow front velocity constant, preventing the occurrence of pressure peaks or drops.

An additional advantage: through the cycle sequence (surface material - core mate-rial - surface material) a flawless surface consisting of 100% pure surface material is achieved, which allows for effective sealing of molded parts.

Weight fluctuations minimized by process optimization

The new HM 10.000/7.700 + 7.700 BM B4 is the third identical sandwich injection molding machine of this size delivered from Meinerzhagen to the sanitary industry, to a manufacturer of toilet seats. It brings the customer’s total equipment up to eight m

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