Compression Molding

Rubber Compression molding

Compression molding is one form of molded silicone rubber parts. Compressing preformed silicone rubber in a mold with a press during the compression process, Silicone rubber is forced into the mold cavity to form the final product during this process, any excess rubber is pushed into the flash and trim gate allowing easy cleanup once the rubber is set.

Compression molding works best for medium hardness compounds in low volume production. Silicone rubber can be difficult to insert into more complex mold designs. And Soft and Hard silicone rubber compounds don’t do well in the compression molding process.

But Silicone rubber compression molding offers advantages over other methods

  • Cost-effective Tooling
  • Maximized cavity count
  • The short set-up time that saves on short production runs
  • Economical process for medium precision
  • the least amount of waste in comparison to other molded rubber processes. 

Compression molding can be a cost-effective solution when:

  • Having silicone rubber industries manufacture the Tooling.
  • the cross-section of the part is very large and requires a long cure time.

Compression molding is used for anything from simple silicone rubber o ring to the most complex silicone parts.

If compression molding isn’t the best fit for your project, Ukong can offer a variety of other molded silicone rubber products through injection or transfer molding.

 

Injection Molding

Liquid silicone injection molding

Injection molding process involves rapidly injecting an exact amount of Silicone rubber from a tube or cylinder into a closed heated mold, the injection press closes the heated mold and applies pressure to keep the mold closed during the injection and curing cycles, the screw then injects the silicone rubber through the nozzle into the mold. the silicon rubber travels through the mold via a system of runners and sprues and finally enters the mold cavities through a gate, it then fills and packs the cavities to form the desired part rubber.

Injection molding offers economical advantages including:

  • short molding cycle
  • Lower unit cost
  • high dimensional tolerances
  • An absence of flash
  • little scrap or waste.

If you’re interested in what Ukong can do for your company email us at sales@ukongtech.com

 

Transfer Molding

Rubber transfer molding

Transfer molding combines the advantages of injection molding with the ease of compression molding. the process of transfer molding involves placing a rubber and a chamber at the top of the mold and then pushing through sprues into a heated mold.

Transfer molding offers several advantages over other methods,

  • shorter production cycles
  • maintains close dimensional tolerances than compression molding
  • provides uniformity to the molded products
  • fast mode setup.

 

 

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Silikon shore hardness

There are two most common Durometer scale, Shore A for flexible elastomers(range in hardness from very soft to medium, and to hard with almost no flexibility at all.) and Shore D for hard elastomers(hard rubbers, hard plastics). Before producing silicone items, It is very important to select the correct shore hardness of liquid silicone for different applications.

Shore A 0-degree application: it can be used for filling mould of super-soft silicone rubber mold, making of imitation prosthesis, such as mask, penis, sex articles, silicone rubber sheet, making of the soft gasket.

Shore A 5-degree application: it can be used for filling mold of super soft silica gel mould, making hand-made soap and candle silica gel mould, making imitation prosthesis products, such as mask, penis, sex articles, and silica gel sheet, making soft gasket products.

Shore A 10-degree application: can be used for soft silica gel mold filling mold production; hand soap, candle silica gel mold production; simulation of the production of prosthetic products, such as silica gel hands, feet, masks, penis, sex products, silica gel sheet, and soft gasket production.

Shore A 15-degree application: can be used for soft silicone mold filling mold production; hand soap, candle silicone mold production; simulation of the production of prosthetic products, such as silicone hand, foot, mask, penis, sex products, silicone skin, and soft gasket production.

Shore A 20-degree application: can be used for food-grade candy chocolate mold or single mold manufacturing; epoxy, polyester resin, polystyrene, vinyl plastic, paraffin wax, and other materials mold; Small cement components, cultural stone, concrete, gypsum, and other products of mold manufacturing; 3d printing mold production, candle manual soap pouring mold production; mechanical properties of waterproof sealing use.

Shore A 25-degree application: can be used for food-grade candy chocolate mold or single mold manufacturing; epoxy, polyester resin, polystyrene, vinyl plastic, paraffin wax, and other materials mold; Small and medium-sized cement components, cultural stone, concrete, gypsum, and other products of mold manufacturing; 3D printing model production, candle manual soap pouring mold production.

Shore A 30-degree application: can be used for metal crafts, alloy car and other precision mold manufacturing; epoxy, polyester resin, polystyrene, vinyl plastic, paraffin, and other materials mold; Large cement components, cultural stone, concrete, gypsum, and other products of mold manufacturing; high-precision hand plate model design, rapid prototyping design; used in vacuum bag multi-mold spraying class production.

Shore A 40-degree application: can be used for metal crafts, alloy car, and other precision mold manufacturing, as well as fixture protection; epoxy, polyester resin, polystyrene, vinyl plastic, paraffin, and other materials mold; Large cement components, cultural stone, concrete, gypsum, and other products of mold manufacturing; high-precision hand plate model design, rapid prototyping design; lost wax casting process of silicone mold production; product measurement reference production.

Shore A 50-60 degree application: can be used for metal crafts, alloy car, and other precision mold manufacturing, as well as fixture protection; epoxy, polyester resin, polystyrene, vinyl plastic, paraffin, and other materials mold; Large cement components, cultural stone, concrete, gypsum, and other products mold manufacturing; high-precision hand plate model design, rapid prototyping design; product measurement reference production.

The hardness described above is only for the most extensive use. For special uses, it is important to know the part or product that you will be molding clearly.

Lfgb Fda silicone

LFGB (Lebensmittel-, Bedarfsgegenstände-und Futtermittelgesetzbuch, or “ “food, tobacco products cosmetics and other commodity management laws”), is the most important basic legal document in German food hygiene management. The specific LFGB standard: German Food, Articles of Daily Use and Feed Code of September 1, 2005 (LFGB), Section 30 & 31 with amendments and Regulation (EC) No 1935/2004 of the European Parliament and of the Council of 27 October 2004.

LFGB test requested, including extractable components, sensorial examination odour and taste test, Lead and Cadmium, Volatile organic matter(VOM) and Polycyclic aromatic hydrocarbons(PAHs) Content.

Test RequestedConclusion
German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Extractable ComponentsPASS
German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments-Sensorial examination odour and taste testPASS
German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Lead and CadmiumPASS
German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Volatile organic matter(VOM)PASS
Polycyclic aromatic hydrocarbons (PAHs) ContentPASS

German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Extractable Components

Test Method:    With reference to 61. Mitteilung über die Untersuchung von Kunststoffen, Bundesgesundheitsbl 46 (2003) 362.

Simulant UsedTimeTemperatureMax.Permissible LimitResult of 001Comment
Distilled Water4.0hr(s)100℃0.5%(w/w)<0.1%(w/w)PASS
3% Acetic Acid (W/V) Aqueous Solution4.0hr(s)100℃0.5%(w/w)<0.1%(w/w)PASS
10% Ethanol (V/V) Aqueous Solution4.0hr(s)100℃0.5%(w/w)<0.1%(w/w)PASS

Notes: %w/w = percentage of weight by weight

German Food, Articles of Daily Use and Feed Code of September 1, 2005 (LFGB), Section 30 & 31 with amendments-Sensorial examination odour and taste test

Test Method:    With reference to DIN10955:2004, direct contact method.               No.of panelist:6

Test Item(s)Limit001
Test mediaDistilled water
Test Temperature (℃)100
Test time (hr)4
Sensorial examination odour (Point scale)2.51.0
Sensorial examination taste (Point scale)2.51.0
Comments  PASS

Notes: Intensity scale(rounded at 0.5): 0 – no perceptible difference, 1 -just perceptible difference, 2 -slight difference, 3 -marked difference, 4 -strong difference

German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Lead and Cadmium

Test Method:     Microwave digestion (GZTC CHEM- TOP-004-01), analysis was performed by ICP-OES.

Test Items(s)LimitUnitMDL001
Cadmium (Cd)mg/kg2ND
Comment   PASS
Lead (Pb)mg/kg2ND
Comment   PASS

Notes: 1.mg/kg =milligram per kilogram of sample  2.MDL=Method Detection Limit  3.ND=Not Detected(less than MDL)  4.★=Absent

German Food, Articles of Daily Use and Feed Code of September 1,2005(LFGB), Section 30 & 31 with amendments and BfR recommendation -Volatile organic matter(VOM)

Test Method:    With reference to 61. Mitteilung über die Untersuchung von Kunststoffen, Bundesgesundheitsbl 46 (2003) 362.

Test Items(s)LimitUnitMDL001
Test Temperature200
Test Timehr(s)4.0
Volatile organic matter (VOM)0.5%(w/w)0.1ND
Comment   PASS

Notes: 1. %w/w = percentage of weight by weight  2.MDL=Method Detection Limit 3.ND=Not Detected(less than MDL)

Polycyclic aromatic hydrocarbons (PAHs) Content

Test Method:   With reference to AfPS GS 2014:01 PAK, analysis was performed by GC-MS.

Test Item(s): Sum of 18 PAHs. Sum of 7 PAHs Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Pyrene, Anthracene, Fluoranthene. Naphthalene(NAP CAS NO. 91-20-3). Acenaphthylene(ANY, CAS NO.208-96-8). Acenaphthene(ANA, CAS NO.83-32-9). Fluorene(FLU, CAS NO.86-73-7). Phenanthrene(PHE, CAS NO.85-01-8). Anthracene(ANT, CAS NO.120-12-7). Fluoranthene(FLT, CAS NO.206-44-0). Pyrene(PYR, CAS NO.129-00-0). Benzo(a)anthracene(BaA, CAS NO.56-55-3). Chrysene(CHR, CAS NO. 218-01-9). Benzo(b)fluoranthene(BbF, CAS NO.205-99-2). Benzo(j)fluoranthene(BjF, CAS NO.205-82-3). Benzo(k)fluoranthene(BkF, CAS NO.207-08-9). Benzo(a)pyrene(BaP, CAS NO.50-32-8). Benzo(e)pyrene(BeP, CAS NO.192-97-2). Indeno( 1,2,3-c,d)pyrene(IPY, CAS NO.193-39-5). Dibenzo(a,h)anthracene(DBA, CAS NO.53-70-3). Benzo(g,h,i)perylene(BPE, CAS NO.191-24-2)

FDA testing (Food & Drug Administration Standard) is the minimum safety standard for food-contact silicone products in the US & Australia. The specific standards is: United States Federal Code, Part 21, Food and Drugs (21 CFR).

FDA test requested

Test RequestedConclusion
FDA 21 CFR 177.2600-Total extractive residuesPASS

FDA21 CFR 177.2600-Total extractive residues

Test Method:     With reference to US FDA 21 CFR 177.2600.

Simulant UsedTimeTemperatureMax.Permissible LimitResult of 002Comment
Distilled Water7.0hr(s)Reflux temperature20mg/sq.in<0.5mg/sq.inPASS
Succeeding Extraction2.0hr(s)Reflux temperature1mg/sq.in<0.5mg/sq.inPASS
n-Hexane7.0hr(s)Reflux temperature175mg/sq.in9.2mg/sq.inPASS
Succeeding Extraction2.0hr(s)Reflux temperature4mg/sq.in<0.5mg/sq.inPASS

In summary…

LFGB silicone pass more strict testing and is therefore more expensive, while FDA silicone is more widely used, but silicone that has passed LFGB testing is definitely safer.

Different countries have different standards for food-contact silicone products. LFGB is standard mainly for Europe, while FDA (Food and Drug Administration) is standard in America(though different country has their own FDA standard, but US FDA is internationally applied.) 

Our baby suction bowls, Baby self-feeding spoon, Silicone Baby Plate, Silicone teether, and other silicone baby items are produced with LFGB silicone. We also can custom products with FDA approved silicone or silicone with LFGB certification based on customer’s requirement.

swim caps print logo

There are many different printing processes on silicone products. silicone silk screen printing, silicone printing, silicone color printing, silicone transfer printing, silicone film printing.

Silicone silkscreen printing

swim caps print logo

The silkscreen is the first printing method. Screen printing requires a logo screen set. Generally, the silk screen printing ink will be thicker and brighter, and the printed pattern has a strong dimensional sense. Silkscreen printing can also print thin lines and is also suitable for large-area printing. The disadvantage is that it is low efficiency as by hand printing and only can up to print 5colors. Silkscreen can only print one color at a time, bake it. Then fix another logo screen set to print the second color.

Silicone pad printing

pad printing

It is printed by machine with a metal plate. The plate is flat, with the image chemically imprinted. The silicone pad is pressed onto the ink, picking up the image. And then the silicone pad is pressed onto the substrate, transferring the image on the silicone product.

The advantage of pad printing is that the printing speed is fast, and you can print several colors at the same time. Pad printing can be used on a variety of substrates, particularly oddly shaped objects that are difficult to screen print. The disadvantage is that the ink is slightly thinner than the silkscreen, not too bright.

Silicone color printing

CMYK printing

color printing is also called digital printing, CMYK printing. The technique used to print full-color images. The silicone ink and the silica gel itself are chemically reacted with each other, so the based product should be white. Otherwise, the logo will be discolored. If the based products in different colors, it is better to print with white ink by silkscreen printing or pad printing first, then do the CMYK printing. However, because there is dust in the printing process, when there is color printing, there will be small dust particles on the surface.

Silicone heat transfer printing

Your custom logo is printed on transfer label or film first, and then ink is thermally transferred from the label to the silicone products using heat by press machine. It can print several color logo. But the logo screen is expensive.

Silicone water transfer printing

water transfer printing

Firstly put the printed water-soluble film on the surface of the water. Immerse the silicone products into the water, the upward pressure of the water causes the ink to wrap and adhere to the item. Then removed the products from the water. It can be applied to all types of substrates with full colors printing.

Silicone film printing

kid swim caps

Cover the film on the silicone while compressing the product, without secondary processing and printing. Washable, folding, scratch-resistant grade A, dry-wearing and wet-resistant grinding A grade, excellent color printing pattern, clear and vivid color printing pattern, environmental protection

Ukong can do the above all kind of silicone printing. We carefully evaluated all methods and help you choose the right way to print your silicone products.

Liquid silicone rubber overmolding

TPE over-molding widely used in the thermoplastic elastomer industry. In recent years, with the rise of liquid silicone applications and the excellent properties of liquid silicone rubber materials, TPE over-molding products are gradually being replaced by liquid silicone rubber. The liquid silicone rubber has excellent comprehensive performance. LSR has high-temperature resistance than thermoplastics, soft-touch, high quality of materials meet with the medical-grade requirements. It is the best soft material for over-molding and injection molding and two-color injection molding.

Silicone over-molding is a process that is used to cover, bond, or encapsulate an existing part with silicone material.

Liquid silicone rubber overmolding silicone overmolding

 

The main advantages of liquid silicone over-molding

The liquid silicone rubber(LSR) material has excellent slip resistance and soft elastic touch, which can improve the touch feeling of the product and enhance the grip.

liquid silicone rubber has different hardness range Shore 10-90A according to the physical properties of the product, as well as suitable physical properties (such as abrasion resistance, adhesion, melt index, etc.). A variety of possible material application options are available for different products.

Liquid silicone rubber is an environmentally friendly raw material. It does not contain phthalates, halogens, and does not include 38 SVHC substances of REACH. It meets the environmental testing standards of ROHS, REACH, NP, EN71, and PAHS, and can fully meet the environmental protection requirements.

 

Liquid silicone rubber over-molding processing technology

Silicone rubber over-mold injection molding process involves two steps wherein a completed plastic or metal entity is placed into the mold site of an LSR mold, after which the LSR is over-molded directly onto the part.

The injection molding temperature is different depending on the hard material. The commonly plastic substrate is PC or PA, and aluminum alloy can also be over-molded by liquid silicone rubber.

 

Common problems and solutions for liquid silicone rubber over-molding processing

1) Lack of silicone – the product is trapped air, or the silicone is not enough.

2) blunt, overflow edge – increase the clamping force; reduce the injection pressure.

3) Poor viscosity – choose the right adhesive. Check the plastic or metal substrate is clean.

4) out of shape during Injection molding – lowering the molding temperature; using a high-temperature resistant substrate.

 

Ukong is a liquid silicone product OEM/ODM manufacturer. We are committed to the development of new processes for liquid silicone (LSR) products and custom products. We have advanced molding techniques such as the high speed of injection molding, short vulcanization time, automatic, self-removing, and no burrs.

Our products including the liquid silicone rubber baby care, medical liquid silicone products, mobile phone 3C waterproof accessories, automotive electronic accessories, liquid silicone kitchen products, industrial sealed liquid silicone Products, etc. and has rich experience in the liquid silicone rubber over-molding parts. (liquid silicone rubber to plastic, liquid silicone rubber to metals, liquid silicone rubber to glass or ceramic, silicone two-color products)

 

What is the difference between liquid silicone rubber(LSR) and solid silicone rubber?

Liquid Silicone Rubber is Liquid, Solid silicone rubber is solid and no fluidity. The finished Liquid Silicone Rubber and solid silicone rubber are not easy to distinguish. Liquid silicone rubber finished products has high transparency and odorless with injection feeding mouth, While the finished products of the solid silicone rubber have low transparent.

 

Solid Silicone Rubber

Silicone Rubber

Solid silicone rubber can be made into all kinds of silicone products after vulcanization. Comparing with the injection molding process, the most advantageous of compression molding is the lower cost. The solid silicone molds are cheaper, and the raw materials are also less expensive. Processing is highly variable, so that, a wide range of different parts can be made with a few basic silicone grades.

But the disadvantage is that the manual operation, the self-demolition mold line has no liquid perfection, and the most softness of the product only reaches about 20 degrees.

How to store the Solid Silicone Rubber

  •  Store in closed containers in cool rooms at 0- 30 °C
  • Do not expose to direct sunlight
  • Keep separate from organic rubber and crosslinker chemicals

 

Liquid Silicone Rubber

Liquid silicone rubber

The liquid silicone is liquid. In the production process, the liquid silicone raw material is injected directly into the mold cavity. The process can be fully automated. It does not need to involve a lot of labor. The product is sealed and processed. Therefore, It produces high-quality parts without secondary finishing, and the processing speed is fast. Injection molding is suitable for complex part geometry. Liquid Silicone Rubber is widely in Medical and Baby Care Products.

The disadvantage is that the cost is high, the mold development cost is expensive, and it is uneconomical for the production of small-batch products!

How to store the Liquid Silicone Rubber

  •  Store in closed containers in cool rooms at 0 – 30 °C
  • Higher average temperatures may shorten the shelf life
  • Do not expose to direct sunlight
  • When opening the container, make sure that no dirt falls onto the surface of the rubber

We manufacture silicone components with solid silicone rubber and liquid silicone rubber. We will assist you in choosing the right economical material for your projects.