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


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.



Swimming caps for braids

Swimming caps for braids

Long hair swim cap

There is no better feeling, than that where you feel one with nature simply by being in the water. Swimming is an art, it requires grace and tactic. But grace and tactic cannot stand alone, good gear is essential. A long hair swim cap is designed to grant you the advantage while you’re under water. I mean after all, who want’s hair obscuring a naturally good underwater view?

Long hair swim caps are designed with the intention of including diversity in design. Although this might sound surreal to some, hair, is as diverse in texture and length. Due to this diverse nature of hair, a “one-size fits all” does not suffice. The Long hair swim cap guarantees that each customer’s needs are taken into account.

For this reason, Long hair swim caps can vary in design and structure. The long hair swim cap design can suit women with braids, long hair that might not necessary fit in a traditional swim cap, afro hair, dreadlocks, and different black hair.

Swimming caps for braids

Swimming caps for braids takes into consideration the length and bulk of braids. It’s structured such that the braids can fit inside a large swimming cap and prevent the swimmer from having to deal with soaked heavy braids when they leave the water.

Upholding diversity in the water is not an easy fit. Ukong has strived to ascertain that a swimming hat for long hair is designed such that the women can comfortably engage their favorite sport whether the sport is undertaken for competitive or leisure purposes.

Swimming caps for dreadlocks

There are many black women and girls who have dreadlocks. Our company did not fail to factor in this aspect of hair. A swim cap for dreadlocks ensures that every lock is tucked and protected from moisture.

Swim caps for black hair are structured with the lengths and the feel of the hair in consideration. Black hair can have very diverse textures and may fit differently in a swim cap.

Swimming caps for Afro hair

UKONG Swim caps for afro hair therefore, are strategic in ensuring that each dynamic aspect is accounted for. Thus, whether you rock a set of natural afro, dreadlocks, long hair whether treated or not, and even in instances where you have decided to opt for the more conventional braided look, there is a long hair swim cap designed specifically for you.

Swimming caps for long hair have been long overdue. They are essential innovations as they represent a marginalized group that had never been before factored in in sports. The long hair swim cap addresses diversity.

Swimming hats for long hair that are exceptionally designed by UKONG are diverse. The company integrated a varied color gradient and informed different sizes to the swim caps. This was an intentional choice that was strategic to include swimming caps that were made with a toughened silicone to offer durability.

Each long hair swim cap has a watertight seal that prevents water from seeping through into the hair. Thus, throughout your swimming exercise you’re guaranteed to maintain dry and healthy hair underneath your swim cap regardless of how much rigorous exercises you undertake underwater.


Silicone tubes are often used in industries and applications where heat and electrical conductivity are prominent. Although the third-party test report is the core to confirm the silicone tube has fire-retardant capabilities. There are also some simple test ways and you can test them anywhere. After the combustion test, the fire-retardant silicone tube has a higher ignition point.

We prepare fire-retardant silicone tubing and regular silicone tubes to test the ignition point.

First of all, we need to prepare a stable naked light, it is recommended the alcohol lamp as this is a piece of more reasonable testing equipment, while the lighter test results are not stable, so it is not recommended. The flame-retardant silicone tube and other silicone tubes can be burned on an alcohol lamp at the same time, there are obvious differences from the burning point, and combustion time, after burning.

Ignition Point: Put the flame-retardant silicone tube in the outer flame of the alcohol lamp from 500 to 600 ° (the flame is divided into the outer flame, the inner flame, and the Flame Center) . The ignition point of the flame retardant silicone tube is 50~80s.

and other non-flame-retardant silicone hoses into the outer flame about the 30s will be burning up. This test found that the flame-retardant silicone tube burning point is more than twice, and its instantaneous burning point is as high as 1000 degrees centigrade or above.

At present, the burning temperature of household appliances is basically below 1000 degrees centigrade, so the flame-retardant silicone tube used in daily life is almost not instantaneous combustion.

Flame-retardant silicone tubing has a high ignition point and is difficult to ignite (see below)

Other silicone tubes have a low ignition point and will ignite or even expand the flame when exposed to an open flame, accompanied by smoke (see below)

Combustion time: ordinary silicone tube in the combustion will accelerate and expand the height of the flame and combustion area, is not flame retardant effect which is the same as other ordinary silicone materials, after removing it from the ignition source, the ordinary silicone tube will burn on its own for a period of time about the 20s, and in the silica gel pipe ashes can be found after the sporadic flame and then extinguished. Through the in-kind combustion test, it can be clearly observed that the flame-retardant silicone tube will not spread and enlarge the flame after it is ignited by an open flame, it can extinguish itself within 3s when it is removed from the fire source. No Flame and no spark ash will appear, so it can extinguish the scattered flame automatically.

The flame-retardant silicone tube will not burn even when it is ignited and will self-extinguish when the ignition source is removed.

For other ordinary silicone tubes, the height and width of the fire source will be enlarged after the burning of other silicone tubes

After burning: extruding silicone products will appear white solid powder after burning, after burning, the inner temperature of the ordinary silicone tube will be higher, and even there will be sparks that can not be put out quickly. It needs to be completely extinguished in a few seconds. Therefore, the ordinary silicone tube can not play the role of flame-retardant in household appliances. While the flame-retardant silicone tube can effectively control the speed of flame diffusion and good self-extinguishing effect.

As the silicone itself is a relatively high burning point compared to other materials, even ordinary silicone tubing is superior to other materials in terms of both burning speed and burning point, the flame-retardant silicone tube is a special silicone material specially developed for the purpose of protecting against combustion, and its effect is obvious to all.

Silicone tube

There are many simple ways to treat the dust surface of silicone tubes. The simplest way is to put the silicone hose lying flat in a clean environment with the circulation of air to weaken the adsorption value, the longer the silicone tube is placed, the weaker the adsorption capacity, which is why for a period of silicone hose dust-free, while the new silicone rubber tubing is on the side of the dust-suction.

Therefore, for manufacturers, the storage environment requirements for silicone tubes are quite strict, no matter from any process of silicone, we should avoid sticky dust. Once the adhesion of too much dust will seriously affect the quality and delivery efficiency, so if the silicone tube which has been covered with dust, must be cleaned.

Dust treatment method one: Alcohol Wipe is one of the more extensive methods, the advantage is affordable and easy to operate. The silicone hose pipe surface after an alcohol wipe will be much cleaner, but at the same time, alcohol will stimulate the adsorption value of silicone and lead to the silicone sticky dust speeding up again. so it is suggested that after wiping with alcohol, it needs to be quickly packed into a clean and sealed environment, for example, PE bags, cartons, etc., Do not re-exposed to dust environment. And alcohol is one of the dangerous chemicals that need professional training before the user can use it.

Method two: Wipe with white gas. white gas in compression molding, liquid silicone rubber injection process is used frequently. the advantage is that white gas cleaning ability is very strong, especially for silicone products, a small drop of white gas is excellent when wiped with an absorbent cotton cloth. However, it should be noted that white electric oil has certain corrosion properties but is quickly dried by air, therefore, the operator needs to wear gloves when using white electric oil to wipe the dust on the surface of the soft silicone tubing, and can not wipe the silica gel tube for a long time because it will corrode the surface of the silica gel tube and lead to the increase of the positive and negative tolerances of the product size. So we should wipe and dry the silicone tube using white electric oil.

Method three: Just Place in water. after the dusty silicone tube cooled down, put it into the clean water and add a small amount of bleach, a few minutes later, we can directly wipe it. The advantage of this method is that it is easy to operate and does not have extra cost. Most important, the silicone tube should be cooled down completely,  otherwise, it will cause the product tolerance reduction to the lower limit. As it needs extra time to dry the silicone tubing by mechanical or natural air-drying, it will affect the product delivery.

Method four:  with Matt surface. The glossy product has a strong adsorption value, while the matt surface is not. The matt surface touches rough, the advantage is that these rough surfaces effectively insulate the enhanced adsorption value, but the glossy surface looks more shiny and beautiful.

Method Five: Coating with anti-dust oil. This is the best way to protect silicone tubes from dust, and after coating the surface touch smoothly.  But it is difficult to spay even as the silicone tube is circular, which leads to the coating cost being expensive. and the coating is not environmental.

Method Six: Quickly air-dry. silicone pipe dust absorption mainly occurs in the product which has residual heat. Quickly air-dry is suitable for the products which have to be second vulcanized, such as food-grade and medical silicone tubes. It is also suitable for regular silicone products. We can use high-power electric fans to speed up the cooling, then the dust adsorption ability of the silicone tube is weakened.


silicone phone case

Why new silicone product look yellow?

There are three reasons, curing agent, processing technology and raw materials are poor quality

  • Curing agent

The performance of the curing agent can be divided into general and anti-yellow. It is applied in the following two aspects:

The general one is non-anti-yellowing curing agent, it can be used for non-exposed silicone products which are relatively dark colors or low color requirement.

The other one is an anti-yellow curing agent, it can be used for silicone products that need to be exposed to light or certain chemicals or lighter and brighter colors, and a higher requirement of colors.

  • Processing technology

During molding, the clear silicone turns yellow. The main problems are

  1. Mold’s temperature is too high
  2. Vulcanizationtime is too long
  3. Turn yellow after the second Vulcanization
  • Raw materials are of poor quality

Sometimes we add an anti-yellow curing agent to the silicone rubber, but the clear silicone products still look yellow after molding. It may be the silicone rubber material’s anti-yellowing ability is too poor. The only solution is to change the raw material.

Although the excellent weather ability and anti-aging properties of silicone products. However, sometimes silicone products turn yellow after molding. In order to prevent this kind of situation, we should choose the correct curing agent. During processing, we should strictly control the temperature of tools and their curing time, and pay attention to the raw material resistance of yellowing.

silicone phone case

Why clear silicone cases turn yellow over time?

Clear phone cases are normally made from silicone that is popular for its inexpensive and flexible properties. Unfortunately, these silicone turn yellow as they age. The main reason is because of the ultraviolet radiation of the light. If you usually use your smartphone with the case outdoors, the case will turn yellow after long-time exposure to the light. Of course, UV radiation is not the only element that can cause the silicone to age. This natural process is accelerated when they are exposed to excessive amounts of chemicals, light, and heat.

In addition to this, the constant friction during normal use, and the sweat on the hand or the oil on your face cause the oxidation reaction will also turn the cell phone cases yellow.

Rather than just being a stain, the yellowing is part of the material degradation. But yellowing does not affect its basic use such as hardness and service life.


How to remove the yellowness of silicone cases at home?

how to remove yellownessDetergent powderpaint thinner

Take an empty bowl with tissue paper in it.

Put the Detergent powder in the bowl, mix water & detergent powder, add more tissue paper( tissue papers will help to stick to the cover and will remove it better), then add vinegar in the mixture, stir it well. Now put a yellowness silicone cover in it. Leave it for 5 minutes. Then add paint thinner. Leave it for 5 minutes again, stir it well and cover it with tissue, leave it for 20 to 30 minutes. Finally, take the silicone case out, it looks good and transparent again.

silicone overmolding

Overmolding refers to a process used to combine at least two materials to create one object part or design.

Today, two technologies can be used to create overmolded objects: Injection molding and 3D printing

Injection molding is the most common process used for over-molding more recently. Some 3d printing technologies are being used to over mold objects of the two, Overmolded parts typically consist of a substrate and the overmolding material, or sometimes more materials. one material is commonly known as the substrate, it is either partially or fully covered by a second material or materials referred to as the overmolded material.

The substrate material can be just about anything, metal, plastic, glass, and so on. The overmolded material is often silicone rubber or thermoplastic material. The over molding process often results in either a chemically bonded part of the materials are mechanically interlocked.

Overmolding offers several benefits. one, in particular, is that it can eliminate secondary operations when building parts thereby reducing manufacturing costs. It is often used to deliver a specific feel to a product such as softening edges or delivering a more pleasant feel or giving users a firm but soft grip. In brief, the injection overmolding process works like this.

With injection molding technology, substrate parts are molded first, the molded parts are either placed into a different mold or placed back into the injection molding machine, where the second material or materials is injected once cooled this object is removed from the mold, then you have an over molded part.

The 3d printing technology is typically jetting where two or more materials are jetted concurrently onto the part during the layer-by-layer build process. The types of products that are over molded include tool hand grips like drills scissors, Screwdrivers, personal care products, cell phones, and anything needing market differentiation. For more information about the silicone overmolding process, please visit Ukong website.


Silicone products

The silicone has many excellent characteristics and functions. But silicone belongs to the production of synthetic raw materials, the different proportion of ingredients in the materials will have a different functional effect, and what reasons for the aging in silicone rubber products? Following are some reasons for aging in silicone cases.

Contact medium aging

Exposure to moisture in the air, or other conditions, such as the external insulation of electrical power systems, in salt-contaminated areas, is extremely susceptible to salt spray, therefore, it is necessary to study the aging performance under this condition. In addition, some silicone rubber products which come into contact with oil are tested to improve their oil resistance.

The aging of silicone rubber under different kinds of oil is due to the mechanical damage of aging on one hand, and on the other is the degradation of cross-linking system, which results in low molecular weight materials. The presence of fluid can reduce the coefficient of friction, but it can also accelerate the chemical degradation of the silicone rubber, thus accelerating wear.


Thermal oxidative aging

Natural rubber (NR) for capacitor seals, EPM, EPDM, Styrene-butadiene, butyl rubber, silicone rubber (NVQ), and so on, are all of these forms of thermal-oxidative aging during use. NR containing a lot of unsaturated double bonds, under the combined action of heat and oxygen, the VULCANIZATE will degrade, the molecular chain and cross-linking bond will be cracked and broken, resulting in aging.

Thermal oxidative aging is both a radical and an oxidation reaction. Under anaerobic thermal aging conditions, free radical decomposition occurs, and the lower the bond cleavage energy, the faster the decomposition, when molecules break down and form free radicals, then the main chain breaks and forms cross-links, producing all kinds of gases. In ultraviolet aging, molecules absorb ultraviolet light and activate certain functional groups, and decomposition or through the energy transfer in other functional groups, such as decomposition, through the formation of active groups and reaction.

The oxidative decomposition of side-chain organic groups in silicone rubber occurs mainly in the anaerobic high-temperature open environment, which leads to the hardening of silicone rubber, while in an oxygen-free high temperature closed environment, the main chain fracture reaction occurs mainly, the formation of volatile cyclic polysiloxane, resulting in softening of silica gel products. The oxidation of side-chain methyl and the degradation and fracture of the main chain are the main reactions of silicone rubber at high temperatures.

Fatigue Aging

The fatigue aging of silicone rubber case is that the aging phenomenon of silicone rubber products under the action of a certain frequency and periodic stress, which is caused by the change of the molecular structure of silicone rubber material, that is, force and heat effect. (due to the rubber in a number of deformation, hysteresis phenomenon, so that the internal silicone causing heat )


Ozone aging

Ozone content in the atmosphere is very low, in the aging process of silica gel, ozone attack silica gel molecules, silica gel expansion and dispersion resulting in surface cracks. Ozone reacts with double bonds in silica molecules to form Ozonide and peroxide, which in turn regenerates ozonide. The Ozonide is broken down into free radicals by the action of heat and light, leading to a chain growth reaction. In addition, the silicone rubber under stress will produce molecular fracture, but not the formation of Ozonide, the phenomenon of cracking and aging.

By studying the effect of ozone on different kinds of tread rubber, including natural rubber, oil-filled methyl-styrene-butadiene rubber, and the blend of isoprene rubber and cis-1,4-polybutadiene rubber, etc., the service life of silicone rubber decreased and decreased rapidly in the short time of ozone action, which proved that silicone rubber had obvious degradation at the beginning of ozone action. Along with the Ozone Action Time extension, the service life drops slowly. This may be due to the degradation process slowing down during the deepening phase of polymer decomposition.