Rubber Injection Molding: Based on a process intended for molding plastics, injection-molding rubber began in the mid-1960s. Rubber injection molding successfully alters the plastics process by heating the rubber and placing it under significantly more pressure per square inch of cavity surface in molding. This is different from plastic injection molding where plastic cools under less pressure. Through various innovations, injection molding has become one of the most efficient ways to create molded rubber products.
The process of injection and injection-transfer molding starts with efficient material preparation. The material is mixed in bulk then stripped immediately into continuous (abot 1.25″ wide and 0.375″ thick) strips. These strips are then fed into a screw which, in turn, fills a barrel with the appropriate predetermined amount of rubber material.
Advantages of injection molding:
Transfer Molding: As with compression molding, transfer molding requires secondary raw material preparation into pre-forms. It differs, however, in the placement of these pre forms into a “pot” located between the top plate and a plunger. When the pre-forms are placed into the pot, the mold is then closed and the material is compressed by the plunger and transferred through sprues into the cavity below. Some possible advantages of transfer molding over compression molding can include:
The primary disadvantage of transfer molding is the increase of waste or excess flash. This can be seen in
the “flash pad” or the rubber left in the pot after the transfer is cured which can either be recycled or discarded.
Compression Molding: Compression molding is a process that involves taking a rubber compound or mixed raw material and creating “pre-forms” in the basic shape of the end product. The pre-forms provide a surplus of material to be placed in the cavity, thus ensuring a total cavity fill. Once in place, the mold is then closed, applying both heat and pressure to the pre-form and allowing it to fill the cavity. When the cavity is filled, excess pre-form material spills out into overflow grooves. Following this step the rubber is then demolded, usually by hand, leaving us with the molded rubber product.
This learning must be fed back to the teams and stakeholders involved as well as disseminated to the wider departments and organization where appropriate, including patient safety teams. This might translate into organizational change, as lessons learned in the planning and delivery of the simulation intervention are adapted to different environments. Such interventions carry a risk of exacerbating the second victim phenomenon. It is therefore paramount to ensure the psychological safety of all individuals and teams involved during the trigger event.
Compression molding is often chosen for medium hardness compounds in low volume production or in applications requiring particularly expensive materials. This process helps to minimize the amount of overflow, or flash created during the rubber molding process. Also, ithe pre-forms can be difficult to insert into more complex mold designs. Furthermore, the compression molding process does not lend itself well to the material flow requirement of harder rubber compounds.
Benefits of Compression Molding:
Compression molding can be a cost effective solution in situations where the tooling already exists or the
cross-section of the part is very large and requires a long cure time.
Dr. Ben Chouchaoui
Operations Manager
WIDL Inc.
July 1, 2023
Monday – Friday
8:00 am – 5:00 pm
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Disclaimer - Dr. Chouchaoui and WIDL do not do engineering services regulated by PEO (Professional Engineers Ontario). If you need services as such please contact PEO for referrals to an engineer who does such.
