Common Defects and Solutions of Rubber Molded Products

Defects The reason what is happened How to solve
Bubble (also called “trapped air ”


The molding material solidifies the incomplete air not to discharge the mold temperature to be too high, causes the material certain ingredient to vaporize or decompose Increasing the temperature of the mold or prolonging the holding time, increasing the number of exhausts and reducing the temperature of the mold
Missing material Die fit clearance is too large or overflow hole too large release agent dosage too slow or too fast Adjust die fit tolerance and overflow hole size to adjust proper die fit temperature and pressurization time


The mold temperature is too high, the rubber has lost the fusion ability of partial vulcanization before it can fully flow in the process of mold closing Try to Reduce mold temperature




The improper temperature of curing incomplete die out process leads to over-sulfuration The improper temperature of the incomplete curing process leads to the redesign of the die by over-sulfide to improve the curing conditions, so that the ejection device is reasonable. Reduce mold temperature and curing time
Surface glossy


Mold temperature is too high or too low die surface rough


Adjust the mold temperature, generally reduce the mold temperature properly using the appropriate release agent to improve the mold surface finish, should be chrome plating
Sticky mold


Molded material without internal release agent or improper mold surface rough or new mold without grinding press pressure is too high The mold surface finish can be improved by adding proper amount of effective internal release agent, and the pressure can be reduced by pressing the glass fiber reinforced plastic powder after testing the mold


The phenomenon that the liquid or solid mixture inside the blend or vulcanizate precipitates on the surface of rubber products to form cloud or white powder due to migration. This is due to the use of sulfur, paraffin, certain antioxidants, softeners beyond their solubility in rubber. In order to prevent frost spray, the dosage of the above mixture should be appropriate, and the common sulfur spray cream can be prevented by insoluble sulfur. The proper addition of turpentine and liquid ancient Malone to rubber can increase the solubility of rubber to the mixture and reduce the phenomenon of frost spraying.

Frosting – Definition and Origin

Frost spray (blooming), also known as spray (spray), is a common quality problem in rubber processing. It refers to the phenomenon that the mixture contained in the non-sulfur adhesive or vulcanizate migrates to the surface and precipitates. Sometimes, this kind of spray is frost-like crystal, so it is used to called “spray frost “. The common frost spray is sulfur, because sulfur is the most widely used vulcanizing agent in general rubber, and its solubility in rubber is low, so it is easy to produce frost spray. In fact, from the appearance of the spray, not all of them are frosty, there are oil (softener, plasticizer) or powder (mostly fillers, antioxidants, accelerators, etc.) of substances, even carbon black ejection is also seen.

Frost spray – cream proof

Silica gel will also have frost spray phenomenon, the use of double two four vulcanizing agent (usually used in extrusion molding process) after high temperature decomposition will produce low molecular weight acid substances, which is incompatible with silicone rubber, In the storage process will be transferred to the surface of silica gel crystallization, resulting in frost spray. The main component of frost-proof agent is alkaline substance, through acid-base neutralization reaction to achieve the purpose of frost-proof.

High hardness silica gel often added more internal release agent, water will also spray white, water acidity has a deterrent effect on this

Method of making silicone rubber mould and matters needing attention

Die is one of the simplest methods in the fast mold, generally using silica gel to repeat the RP prototype, but the life is very short, only about 10-30 pieces! He has good elasticity and replication performance, using silicone rubber to copy the mold can not consider the drawing slope, will not affect the dimensional accuracy, has a good segmentation, do not need to divide the upper and lower mold can be directly poured as a whole. Then along the predetermined die line to cut out the master mold can be!

Room temperature vulcanized silicone rubber is divided into addition type and condensation type!

Special mould silicone rubber, The product is sold in double packaging, A component is rubber, B component is the catalyst. Room temperature, die strength and hardness should be taken into account, According to this, the weight of AB components is determined. At 20-25 degrees, A:B=100:1.5. At low room (but not less than 10 degrees), the B components were increased by 0.1-0.3. High room temperature reduced the B group 0.1-0.3. The specific method is to determine the total amount according to the mold volume, And then weigh A、B components proportionately, Stir well in a vessel, Yes.

Mold making: pour the prepared material into the clean object to be copied. In order to save material, the thin mold can also be brushed. To increase the tension of the mold can paste gauze and so on. It can be solidified into elastomer at room temperature of 20 degrees for 2 hours and can be used after one day.

B component is the catalyst, which is easy to be hydrolyzed by moisture, so the lid should be strictly closed after use. As soon as the 2.A、B group is mixed, the chemical reaction begins immediately, the viscosity rises gradually and can not be stopped. In order to avoid waste, it should be used immediately according to the dosage and with the use. mix ratio of 3.A、B groups, which is related to the speed of chemical reaction and the performance of the mold. B more components, the faster the reaction, the higher the strength and hardness of the product, but the lower the toughness. Therefore, weighing requires accuracy. 4. preparation, the A components should be stirred up and down evenly, and then weighing. 5. pouring method is suitable for relief, painting method is suitable for three-dimensional mold making. Cast relief mold should first make length and width are larger than the original carving length and width of 4-6 CM frame. The border should be straight and the inner surface should be smooth. During pouring, place the frame on the clean glass plate, then put the original in the frame, leaving 2-3 CM clearance on each side. (silicone rubber $61/ KG)

Note: There are bubble solutions in the process of making silicone rubber mold :1, improve the design of flange groove and exhaust system 2, increase the pressure of press 3, reduce the amount of release agent, and evenly spray 4, material control water …5, can try to add some defoamer 6, use cold runner. 7. vacuum pump with vacuum machine, the mold can increase exhaust operation.

  1. natural rubber (NR) is dominated by rubber hydrocarbons (polyisoprene) and contains a small amount of protein, moisture, resin acids, sugars and inorganic salts. It has high elasticity, high tensile strength, excellent tear resistance and electrical insulation, good wear resistance and drought resistance, good processing property, easy adhesion of other materials, and is superior to most synthetic rubber in comprehensive properties. The disadvantages are poor oxygen resistance and ozone resistance, easy aging and deterioration, poor oil resistance and solvent resistance, low corrosion resistance to acid and alkali, and low heat resistance. Use temperature range: about-60℃~+80℃. Make insulation and sheathing of tires, rubber shoes, hose, tape, wire and cable, and other common products. Especially suitable for manufacturing torsional vibration eliminator, engine shock absorber, machine support, rubber-metal suspension element, diaphragm, molded products.

copolymer of 2. butadiene rubber (SBR) butadiene and styrene. The performance is close to the natural rubber, is the largest production of universal synthetic rubber, its characteristics are wear resistance, aging resistance and heat resistance than natural rubber, the texture is also more uniform than natural rubber. The disadvantages are: low elasticity, poor resistance to bending and tear, poor processing performance, especially poor self-adhesive, low strength of raw glue. Use temperature range: about -50℃~+100℃. Mainly used to replace natural rubber tire, rubber plate, rubber hose, rubber shoes and other general products.

  1. cis-butadiene rubber (BR) is a cis-structured rubber formed by polymerization of butadiene. The advantages are: good elasticity and wear resistance, good aging resistance, excellent low temperature resistance, small heat under dynamic load, easy metal bonding. The disadvantages are low strength, poor tear resistance, poor machining performance and self-adhesion. Use temperature range: about -60℃~+100℃. Generally used with natural rubber or styrene-butadiene rubber, mainly to make tire tread, transport belt and special cold-resistant products.
  2. isoprene rubber (IR) is a cis-structured rubber formed by polymerization of isoprene monomers. Chemical composition, solid structure and natural rubber similar, properties are very close to natural rubber, so synthetic natural rubber. It has most of the advantages of natural rubber, aging resistance due to natural rubber, elasticity and strength slightly lower than natural rubber, poor processing performance, high cost. Use temperature range: about -50℃~+100℃ can replace natural rubber to make tires, rubber shoes, hose, tape and other universal products.
  3. neoprene (CR) is a polymer formed by monomer emulsion polymerization of neoprene. This rubber molecule contains chlorine atoms, so compared with other universal rubber: it has excellent anti-oxygen, anti-ozone, non-flammable, self-extinguishing after ignition, oil resistance, solvent resistance, acid and alkali resistance, aging resistance, good air tightness, etc. Its physical and mechanical properties are also better than natural rubber, so it can be used as general rubber, but also as special rubber. The main disadvantages are poor cold resistance, large specific gravity, high relative cost, poor electrical insulation, easy to roll, easy to burn and easy to stick die. In addition, the stability of raw glue is poor, not easy to preserve. Use temperature range: about-45℃~+100℃. It is mainly used in the manufacture of cable sheaths with high ozone resistance and aging resistance, as well as various protective covers and protective covers; oil resistant, chemical corrosion resistant hose, tape and aircraft lining; rubber products for flammable underground mining, as well as various molded products, sealing rings, pads, binders, etc.
  4. butyl rubber (IIR) is a copolymer of isobutene and a small amount of isoprene or butadiene. the biggest characteristics are good air tightness, good ozone resistance, aging resistance, high heat resistance, long-term working temperature can be below 130℃; can resist inorganic strong acid (such as sulfuric acid, nitric acid, etc.) and general organic solvents, good vibration absorption and damping characteristics, electrical insulation is also very good. The disadvantages are poor elasticity, poor processing performance, slow vulcanization speed, poor adhesion and oil resistance. Use temperature range: about -40℃~+120℃. Mainly used as inner tube, water tube, balloon, wire and cable insulation layer, aircraft equipment lining and shockproof products, heat-resistant transport belt, heat-resistant aging rubber products.
  5. copolymer of butadiene rubber (NBR) butadiene and propylene. It is characterized by excellent resistance to gasoline and fatty hydrocarbon oils, second only to polysulfide rubber, acrylate and fluorine rubber, and superior to other general rubber. Good heat resistance, air tightness, wear resistance and water resistance are good, strong adhesion. The disadvantages are poor cold resistance and ozone resistance, low strength and elasticity, poor acid resistance, poor electrical insulation and poor polar solvent resistance. Use temperature range: about-30℃~+100℃. Mainly used in the manufacture of various oil-resistant products, such as hose, sealing products and so on.
  6. copolymer of hydrogenated butadiene rubber (HNBR) butadiene and propylene fine. it is obtained by the double bond in NBR butadiene hydrogenated in whole or in part. Characteristics are high mechanical strength and wear resistance, heat resistance is better than NBR when crosslinked with peroxide, other properties are the same as butyl rubber. The disadvantage is that the price is higher. Use temperature range: about-30℃~+150℃. Mainly used for oil-resistant, high-temperature sealing products.
  7. copolymer of ethylene propylene rubber (EPM\\EPDM) ethylene and propylene, generally divided into binary ethylene propylene rubber and EPDM. Features are ozone resistance, UV resistance, weather resistance and aging resistance, ranking first in general rubber. Electrical insulation, chemical resistance, impact elasticity is very good, acid and alkali resistance, small specific gravity, can be high filling fit. Heat resistance up to 150℃, resistance to polar solvents-ketones, esters and so on, but not to aliphatic hydrocarbons and aromatic hydrocarbons, other physical and mechanical properties slightly superior to natural rubber but better than styrene-butadiene rubber. The disadvantage is that self-adhesion and mutual viscosity are very poor, not easy to bond. Use temperature range: about -50℃~+150℃. Mainly used for aircraft equipment lining, wire and cable foreskin, steam hose, heat-resistant transport belt, automotive rubber products and other industrial products.
  8. Silicone rubber (Q) is a special rubber with silicon and oxygen atoms in its main chain. The main features are high temperature resistance (up to 300℃) and low temperature resistance (minimum-100℃). It is the best resistant rubber at present. The disadvantages are low mechanical strength, poor oil resistance, solvent resistance and acid and alkali resistance, more difficult to vulcanize, more expensive. Use temperature :-60℃~+200℃. It is mainly used to make high and low temperature resistant products (hose, seals, etc.), high temperature resistant wire and cable insulation layer, because of its non-toxic and tasteless, but also used in food and medical industry.
  9. Fluorine rubber (FPM) is an organic elastomer formed by copolymerization of fluorine-containing monomers. High temperature resistance up to 300℃, acid and alkali resistance, oil resistance is the best oil rubber, radiation resistance, high vacuum resistance, electrical insulation, mechanical properties, chemical corrosion resistance, ozone resistance, atmospheric aging resistance are excellent. The disadvantages are poor processability, expensive cold tolerance and low elastic permeability. Use temperature range :-20℃~+200℃. Mainly used in the defense industry to manufacture aircraft, aircraft on the vacuum, high temperature, chemical corrosion resistance of sealing materials, hose or other parts and automotive industry.
  10. Polyurethane rubber (AU\\EU) has elastomers formed by polymerization of polyester (or polyether) with diisocyanate compounds. It is characterized by good wear resistance, is the best in all kinds of rubber; high strength, good elasticity, excellent oil resistance. Ozone resistance, aging resistance, air tightness and other excellent. The disadvantages are poor temperature resistance, poor water and alkali resistance, poor aromatic hydrocarbons, chlorinated hydrocarbons and ketones, esters, alcohols and other solvents. Use temperature range: about-30℃~+80℃. Make tires next to parts, gaskets, shockproof products, and wear-resistant, high-strength and oil-resistant rubber products.
  11. Acrylate rubber (ACM\\AEM) is a polymer of ethyl acrylate or butyl acrylate. It is characterized by good heat and oil resistance and stable performance in lubricating oil containing sulfur, phosphorus and chlorine additives. At the same time, aging resistance, oxygen and ozone resistance, UV resistance, good air tightness. The disadvantages are poor cold resistance, water resistance, steam resistance and organic and inorganic acids, bases. In methanol, ethylene glycol, ketone ester and other water-soluble solution expansion. At the same time, poor elasticity and wear resistance, poor electrical insulation, poor processing performance. Use temperature range: about-25℃~+150℃. Can be used to manufacture oil-resistant, heat-resistant, aging-resistant products, such as seals, hose, chemical lining.
  12. Chlorosulfonated polyethylene rubber (CSM) is an elastic polymer obtained by chlorination and sulfonation of polyethylene. Oxyfast aging resistance is excellent, weathering resistance is better than other rubber. Flame retardant, heat resistance, solvent resistance and resistance to most chemicals and acid and alkali resistance. Electrical insulation is good, wear resistance is similar to styrene-butadiene rubber. The disadvantage is poor tear resistance and poor processing performance. Use temperature range: about -20℃~+120℃. It can be used as sealing material on ozone generator to manufacture oil-resistant seals, wire and cable prepuce, oil-resistant rubber products and chemical lining.
  13. Chloroether rubber (CO\\ECO) is a polymer that is either homopolymerized by epichlorohydrin or copolymerized by epichlorohydrin with ethylene oxide. It is characterized by excellent resistance to fatty hydrocarbons and chlorinated hydrocarbon solvents, alkali resistance, water resistance, aging resistance, ozone resistance, poor elasticity and poor electrical insulation. can be used as hose, seal, film and container lining, oil tank, cots, make oil seal, water seal, etc.

Chlorinated polyethylene rubber (CM or CPE) is an elastic polymer made of polyethylene by chlorine substitution. The performance is close to that of chlorosulfonated polyethylene rubber, which is characterized by good fluidity and easy processing, excellent weather resistance, ozone resistance and corona resistance, heat resistance, acid and alkali resistance and oil resistance. The disadvantages are poor elasticity, large compression deformation and low electrical insulation. Use temperature range: about -20℃~+120℃. wire and cable sheath, hose, tape, cots chemical lining, etc.

There are bubbles on the surface of rubber products.

  1. water (add calcium oxide when mixing)
  2. not fully vulcanized, not ripe looks bubble.
  3. there are more impurities in vulcanizing agent, the impurities of small molecules become decomposed ahead of time, and the residual products of bubbles
  4. the mold itself exhaust design is unreasonable, rubber punching line gas can not be discharged in time!

Disperse 5..

  1. rubber plasticizing time is long. There are also bubbles when the product is vulcanized.


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