1 Trimmed: to make the surface of the suction cup smooth and the outer dimensions meet the requirements.
2 Special processing: such as using some special pricess on the surface of the suction cup, to made the performance of the special-purpose products improved;
3 The suction cup product containing the fabric skeleton needs to do the hot stretching cooling and cooled under inflation pressure after vulcanization,to ensure the product size, shape stability and good performance.

1. Triming of the suction cup mold after vulcanization

When the rubber suction cup is vulcanized, the rubber material will flow out along the parting surface of the mold to form an overflow burr, we also call it burr or flash. The thickness and size of the burr are determined by the structure, precision and the parallelism of the machine plate mold and the amount of glue remaining. The edge of the suction cup produced by the current infinite mold is particularly thin, and sometimes it can be removed directly when it is taken out of the mold, or just gently wiped off. However, this kind of molds are costly and vulnerable. Most rubber suction cups require trimming after vulcanization.

There are several ways to trim,

1. Manual trimming method: manual punching, scraping, boring, cutting, scraping,
2. Normal temperature mechanical triming: punching, cutting, grinding
3. Low temperature mechanical triming method: shot blasting, drum trimming, vibration trimming, shaking, swing trimming, brush trimming, centrifugal impeller blasting

Manual trimming

Manual trimming is an ancient method of trimming, which involves manually punching the burrs with a punch; removing the burrs with scissors, scrapers, etc. The quality and speed of manual trimming are depends on people. The geometry of the finished product must conform to the product drawing requirements and must not be scratched, scratched or deformed. Before trimming, you must know the trimming position,technical requirements, the correct trimming method and how to use the tools.

1. Mechanical trimming

Mechanical trimming refers to the process of trimming rubber suction cup products by using various special machines and corresponding process methods. It is currently a more advanced method of trimming.

(1) Mechanical punching and trimming remove the burr of the suction cup by using a pressure machine and a die punching knife. This method is suitable for the suction cups which burr can be placed on a die punching plate. This method is generally used for the suction cup with high gel content and low hardness.This can reduce the unevenness of the edge after the knife cutting and the side surface depression due to the large elasticity of the product;

As for the lower rubber content with higher hardness. The product can be directly cut by the knife die method. In addition, die cutting also have two method, cold cutting and hot cutting. Cold cutting refers to punching at room temperature. It will need the equipment with higher die cut pressure, and the quality of punching is better. Hot cutting refers to punching at a higher temperature. It should prevent the high temperature from contacting the product for too long which will affect the product quality.

(2) Mechanical cutting and trimming is suitable for the trimming of larger-sized products, using cutting tools. General cutting machines are special machines, and different products use different cutters. For example, after the tire is vulcanized, there got some strips in different lengths on the surface of the exhaust eyes and the exhaust line. The strip must be removed by using a grooved tool under the condition of tire rotation.

(3) Mechanical grinding and trimming For suction cups with inner and outer rings, grinding is usually used. The grinding blade is a grinding wheel with a certain thickness of the particles. The precision of grinding and trimming is low, the grinding surface is rough and there may be residual sand particles, which affects the use effect.

(4) Low temperature shot peening are generally used for the high quality small suction cup. The product is rapidly cooled to below the brittle temperature with liquid nitrogen or dry ice, and then the metal projectile or plastic projectile sprayed into at high speed to break the flash and remove the trimming.

(5) Low temperature brushing and trimming, which removes the burrs of the frozen suction cup by means of two nylon brushes rotating around a horizontal axis.

(6) Low temperature drum trimming which is the earliest adopting the method of freezing trimming. The impact force generated by the rotation of the drum and the friction between the products are used to break and fall off the edge of the product which has been frozen to below the embrittlement temperature. The shape of the drum is generally in octagonal, that will increase the impact force in the drum. The rotation speed of the drum should be moderate, and the addition of the abrasive can improve the efficiency. For example, the trimming process of the rubber plug of the electrolytic capacitor should use this low temperature drum to trim.

(7) Low-temperature vibration trimming, also known as vibration freezing and trimming, the products are spirally vibrated in a circular sealed box, and there is a strong impact by abrasive between the products, which causing the frozen embrittlement broken. The low-temperature vibration trimming is better than the low-temperature drum trimming, its product damage rate is low.

(8) Low-temperature swinging and shaking trimming are suitable for small,micro-products and products that containing metal bamboo frames. It can be used with the abrasive to removed the edges, corners, burrs in the grooves of the product.

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The amount of shrinkage mainly depends on the coefficient of thermal expansion difference between the suction cups material and the mold material at the vulcanization temperature. The main influencing factors are the vulcanization temperature，the type of raw rubber in the rubber mixture and the type and amount of filler.

1. How to calculate the vulcanization shrinkage rate of the suction cup? And how to make sure the exact shrinkage rate of the suction cup?

There are many ways to determine the vulcanization shrinkage rate. Such as linear expansion coefficient method and rubber Shore A hardness method.

1. Factors affecting the shrinkage of rubber compounds

There are many factors which can affect the shrinkage of the suction cup, such as the shape of the rubber suction cup (different parts of one suction cup shown the different shrinkage), the vulcanization temperature and the processing method. Here are some key factors below,

1). The hardness of the material

Hardness increased will caused the shrinkage of the rubber decreases. The hardness between 75 and 85 shoreA are the lowest shrinkage.

2). Rubber varieties

Rubber with different molecular structures has different effects on shrinkage. For example, when the same amount of reinforcing agent (20 parts of semi-reinforcing carbon black) is added, the shrinkage ratio of various vulcanized rubbers obtained by vulcanization at different temperatures is: fluororubber > silicone rubber > ethylene propylene diene rubber > styrene – Butadiene rubber>Natural rubber>Butyl rubber> Neoprene rubber. The specific shrinkage data of several rubbers at different temperatures are as follows,

Natural rubber 1.4-2.4
EPDM rubber 1.6-2.2
Styrene – Butadiene Rubber 1.5-2.0
Neoprene 1.3-1.8
Butadiene rubber 1.4-2.0

3). Filler effect on the shrinkage

The filler in the rubber mixture also has a large effect on the shrinkage of the suction cup. In particular, increased fillers will caused the shrinkage decreased. In addition, the difference in the type of filler will also effect on the shrinkage rate of the suction cup. Since the linear temperature coefficient of the filler material is small, it is much more close to the shrinkage of metal mold.

4). Vulcanization temperature

The vulcanization temperature effect on the shrinkage rate of the product. The vulcanization shrinkage rate increases while the temperature increases. The shrinkage rate can be lowered by appropriately lowering the vulcanization temperature. The vulcanization shrinkage of several rubber raw materials increases as the vulcanization temperature increases.

5). Skeleton material

When the suciton cups has a fabric skeleton, the shrinkage ratio of the cotton skeleton product is from 0.2% to 0.4%. The shrinkage of the polyester matrix product is from 0.4% to 1.5%, and the shrinkage of the nylon skeleton product is from 0.8% to 1.8%. The more layers you got, the smaller the shrinkage will be. The metal parts has a small shrinkage ratio, the metal-facing side shrinks, the shrinkage is from 0 to 0.4%, and the unidirectional adhesive product shrinkage is from 0.4% to 1.0%.

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Heat treatment

Practice has shown that the heat treatment for some rubber suction cups in a hot air medium can stabilize the physical and mechanical properties, making the cross-linking structure more perfect, eliminate the internal stress generated by the molding vulcanization. And it can greatly reduce the compression permanent deformation and improve the service life. For example, a product such as silicone rubber, fluororubber, acrylate rubber can be subjected to secondary vulcanization. In addition, some medium-resistant suction cups can be heat-passivated in some media to improve their dielectric properties.

1. Surface chemical treatment

For some suction cups, surface halogen treatment can improves its surface hardness, it will not affect the elasticity and strength of the whole material, but improves its service life. Halogenation treatment with chlorination solution, preparation of aqueous solution with 24% chlorine water and hydrochloric acid, rinsing the suction cup, chlorination in chlorination for a certain period of time, neutralization with sodium chlorate, and wash it with water to make it clean and then put in the oven to dry.

1. Surface coating

The surface coating of the suction cup are designed to improve its surface properties. Such as improve the lifting unsaturated rubber resistant to ozone and weathering resistance; Polyurethane coating can lift the weather resistance and oil resistance of isoprene rubber, styrene butadiene rubber, butadiene rubber; polytetrafluoroethylene polyimide coating can firmly reduce the static and dynamic friction coefficient of the rubber product. The coating can be carried out by electrostatic spraying, immersion film formation, filming, osmosis film formation, etc.

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