What is Rubber Injection Molding?

What is rubber injection molding? At its most basic level, an injection molding press consists of an injection unit, hydraulic system, clamping system, a heating system, and software powering each element.

Injection Unit

The injection unit includes a metal screw within a heater-jacketed barrel. The screw forces heated rubber past its tip and into the heat-jacketed injection barrel, where it is held while the material in the mold cures and is queued before the next injection cycle. The combination of the ram and the screw allow for the molten rubber compound to be moved towards a nozzle. The nozzle injects through a hole made in the top half of a closed mold. This hole connects to smaller holes, or gates, which enter the cavities of the mold. The number, size, and pattern of gates will vary depending on the design of the part.

Hydraulic System

The hydraulic system controls the clamping and ancillary systems such as the screw and injector unit. In addition, it controls the operation of the ejector bars. Sufficient oil pressure must be supplied in order to operate all the press functions that are likely to be required at the same time.

Clamping system

The next element, the clamping system, includes two halves of a press that will: open each part of a mold, allow the placement of inserts, close the mold sections, and finally close and securely clamp the mold sections together during the ensuing injection and curing cycle.

Heating System

The heating system includes electric heating elements that are zoned with separate temperature controls applied to each zone. Using the electric heating elements, it is possible to limit temperature gradients across the platen to plus or minus 1-degree Celcius. The temperature gradients across the mold are less predictable and depend upon the mold geometry and construction, settings of the zones, and ambient conditions around the press. Thus, temperature control of the platen depends on all of the elements within the platen being operational.

Software in rubber injection molding

Finally, the software. The heart of the software system is a programmable logic controller or PLC, which programmed with the operational commands that work the electro-mechanical operation of the injection molding process. It is the PLC that provides the logic for automatic and semi-automatic operation, controlling the stop and start of pumps, adjusting pressures, reading micro-switch positions and all the other functions of the machine.

rubber injection molding diagram

Rubber injection molding offers the best process control set-up of any molding technique. Generally speaking, the injection units of injection molding machines perform similarly to plastic injection machines. The compound is fed to the barrel usually as a continuous strip, but the material can also come in a granulated form that is fed through a hopper similar to plastic injection molding. The mastication in the injection screw, and the stresses from being forced through a runner and sprues at high velocity preheats and lowers the viscosity of the compound, thus offering flow and cure time advantages over conventional molding methods. The manner in which material is handled handling sets the stage for automation. When combined with an insulated delivery system, injection molding yields a very cost-competitive process. One of our primary focuses as a rubber injection molding company is to meet your demand in the quickest and most efficient manner. Using our state of the art injection rubber molding machines, we reduce cycle times and in turn the cost that it takes to manufacture our customer’s parts.

As a company specializing in rubber injection molding, the process provides the most accurate and controlled method of molding rubber and silicone parts. When precise tolerances matter, injection molded rubber products are the best way to ensure accurate results for each part manufactured. Our highly automated process also allows for short-run rubber molding of parts that can be provided on-demand with short lead times.

Advantages of Rubber Injection Molding

1. High level of automation

2. Fast, high quantity production

3. Reduced cycle time

4. Air entrapment is significantly reduced

5. No complex preform is needed

6. Cure temperatures used can be much higher than those used for compression or transfer molding

7. Reduced waste where the flashed material is significantly reduced or eliminated.

8. Reduction in backrind because  the temperature of the compound entering the cavity is closer to the molding

9. Reduction in manual labor

10. Preheating the compound in the screw before it enters the cavities allows the material to flow more easily into the cavities.

Contact Poly-Tek today for all your custom molding needs!