Umbrella Valve also knowns as Umbrella Valve Seals, Umbrella Check Valve, Rubber Umbrella Valve and Liquid Silicone Valves, is mainly made from high-tensile solid silicone (HTV) or liquid silicone rubber (LSR) materials, also made from other rubber materials like Neoprene, EPDM, Fluorosilicone, Nitriles etc. The production of silicone rubber umbrella valves involves a striking balance between efficiency and quality. To achieve this balance, different manufacturing processes must be considered and compared to determine which process better matches the product's particular needs.

Umbrella Valve Compression Molding Process

Compression molding also uses pre-formed material. It is used to mold all elastomers and durometers. Compression molding requires heating up of silicone rubber raw materials in the mold. A pressure is applied in compression molding and should be maintained during cooling.

The process of compression molding: First, an appropriate amount of the polymer and necessary additives are thoroughly mixed and loaded between upper and lower parts of the mold. Both parts are heated up and only one is movable. Second, the compression mold is closed, heat and pressure are applied. When the cavity is filled, excess material fills the mold’s overflow grooves. Third, after curing is complete and the mold is opened, demolding is performed to remove any flashing.

What is Liquid Silicone Check Valve Injection Molding ?

Injection molding is one of the most common manufacturing processes for silicone and rubber parts. The first injection mold system, patented in 1872, the original injection-molding machine worked like a large hypodermic needle, using a plunger to inject plastic through a heated cylinder and then into the mold. Over time, the industry expanded, increasing the demand for inexpensive mass-produced products, which encouraged the injection-molding process to evolve.

The process of injection molding is as follows:

Silicone injection molding feeds uncured silicone into a rotating screw. A controlled amount is pulled into the injection unit, where the silicone is pre-heated and plasticized.

This material is then injected into a mold cavity through a gate and runner system. The silicone is held under high pressure and at an elevated temperature to achieve curing or vulcanization. When curing is complete, molded rubber parts are removed or ejected from the mold's cavities.

How Rubber Umbrella One Way Valve Transfer Injection Molding Works?

Transfer injection molding is similar to injection molding service and is generally known as a simpler injection molding variation. Transfer injection molding, like injection, pushes material into a mold with a sprue, but instead of a screw injector, it uses a plunger.Transfer injection molding begins by place the rubber raw material in a transfer chamber prior to entering the mold. The mold is then closed and a plunger compresses the material. As heat is applied, pressure forces or “transfers” the uncured  rubber through sprues into the mold’s cavities. Multiple cavities can be used within transfer molding since the material is entering the mold after the mold is closed. The mold remains closed during curing and is later opened to remove silicone rubber parts for trimming, a secondary process that removes unwanted overflow material called flash.

Advantages of Umbrella Valve Compression Molding, Injection Molding And Transfer Injection Molding

LSR Injection molding: 

• Supporting high volumes of parts that require medium-to-high levels of precision. (higher precision than converted LSR compression molding).

• Decreasing labor processing time and shorten vulcanizing time about eighty seconds for one shot. Because the silicone rubber is pre-heated, it flows readily into mold cavities and supports decreased cure times. 

• Valve without burrs, minimum parting line, and reduced material waste.

• Tolerance can achieve 0.01mm.

• Supporting overmolding products and providing high levels of control and consistency.

Transfer injection molding: 

• Tolerance is better than comprssion molding.

• Reducing risk of contaminating color parts because of pre-forms cutting by hand, reducing equipment costs and time dependency with solid casting material.

• Cheaper mold costs than LSR iniection mold, and can match the existing compression mold templates.

• Allows for Metal Inserts: this procedure is suitable for items that have metal inserts; 

• Sharper Edges: Because of the higher pressures, the transfer molding process can achieve sharper edges and cutoffs than injection molding.

Compression molding: It is a good choice for very hard or difficult-to-flow materials because it doesn’t need to push the silicone rubber through sprues, gates, or runners. Meanwhile the mold cost is cheap than transfer mold & LSR injection mold, mold-making time will also be shorter, which is good for fast-prototype.

Disadvantages of Umbrella Check Valve Compression Molding, Injection Molding and Transfer Injection Molding

Injection molding:

• Mold cost: Injection molds price is the most highest when compare to compression mold and transfer mold. 

• High Setup Costs: Injection mold machines are far more costly than transfer molding machines, and the setup cost is also high, processing process is much more complex.

• Sharp corners: LSR Injection Mold are less capable for manufacturing products with sharp corners, most of the molds prefer to avoid it.

Transfer injection molding:

• Waste material: Transfer injection molding usually generates more waste owing to the greater sprue and overflow channels. When thermosetting materials are used, the scraps produced are not reusable.

• Slow: Because of the time taken to preheat the materials before transfer and the lower volume, the production speed is much slower than injection molding.

• Smaller Quantity: Since transfer injection molding machines cannot handle as many cavities as injection molding machines, fewer units are made per cycle.

Compression molding: 

• It can't achieve automatic demold, so requires longer demoulding time for labor process and vulcanizing, also need to remove flash manually, for thick product or the product that require low temperature vulcanization, the molding time can up to 450seconds.

• Valve with burrs, flash, and waste material during de-moulding.

• Limited precision.

Better Silicone can offer the one-stop service of silicone rubber umbrella valves for your products. From Umbrella Valves design support, manufacturability & moldability analysis, mold-making, Umbrella Valves production, inspection, packaging etc. If you have any need, please feel free to contact us.