Different molding methods for metal bellows of mechanical seals

In accordance with different forming methods the metal bellow mechanical seals can be classified as: (1) Hydraulic formed metal bellows: its materials include copper alloy (brass, phosphorus bronze and beryllium bronze), aluminum alloy, austenitic stainless steel, high nickel alloy, monneel alloy, etc. The wall thickness varies from 0.06~0.5mm, and the pressure resistance is determined according to the structure, wall thickness, number of layers and materials. For example, stainless steel bellows, internal diameter of 15mm, wall thickness of 0.1mm, the number of layers is one, external pressure resistance is 1.5MPa, if the number of layers is three, external pressure resistance is 6MPa. For the high pressure type, the wall thickness is increased, the structure is changed to Ω shape, the same inner diameter (15mm), the wall thickness is 0.2mm layer, and the external pressure resistance reaches 9MPa. 

China's hydraulic formed metal bellows (single layer) of metal bellow mechanical seals in 1968 has the standard, the current standard is JB2388-78 metal bellows. The range of material varieties and operating temperature are shown in Table below.

(2)Welding metal bellows of metal bellow mechanical seals: because the welding bellows has the advantages of larger volume change rate, small axial size after compression (see Figure below), unlimited wave numbers, can be done with larger diameter, lower cost and so on. Now most of the mechanical seals use welded metal bellows. 

The materials for welding metal bellows are: austenitic stainless steel, precipitated hardened stainless steel (of PH type), titanium, high nickel alloy (such as lnconel, Hastelloy, Monel, etc.)

The thickness of the welded bellows varies from 0.07mm to 0.8mm, 1.0mm, 1.2mm, and the number of layers can also be divided into two and three layers. Inner diameter size up to 1000mm, damage pressure is up to 50MPa, and the failure pressure of special parts is up to 80MPa.

Because the welded metal bellows forming is convenient, single piece production & batchs production can be accomplished, the relative production cost is lower. At present, foreign larger sealing companies have welded bellows series mechanical seals. For example, Eagle introduced the technology of EG & G SEALOL company in the United States, has Y1~7 welded metal bellows mechanical seals, other companies have M type (rotating structure) and Q type (static structure) and MFL mechanical seals. 

Domestic Shanghai water pump factory also introduced the technology of EG & G SEALOL company to produce 676 and 670 welded metal bellows mechanical seals suitable for corrosion and granular media, which meets DIN 24960 and ISO 3069 standards. The materials and performance of type 676 and 670 sealing are listed in the table below. Shanghai water pump plant also introduced for high temperature, high pressure type 605 metal bellows seal and other purposes of the seal.

 In addition to the introduction of technology, domestic petrochemical system manufacturers have carried out the development & trial work of welded bellows mechanical seals, at the same time, there are also domestic protection of 1Cr18Ni9Ti stainless steel bellows products. For example, Shenyang Scientific Instrument Factory has welded metal bellows mechanical seals, specifications for inner diameter d8~48, outer diameter D6~65, wall thickness 0.09~0.2mm, length can be supplied according to user requirements.

Electrodeposited metal bellows of mechanical seals: its materials are nickel, copper, silver, gold and other metals. Electrodeposited is a new bellows forming process, its formed bellows wall thickness can be very thin (7.5 μ m), the inner diameter can be very small (0.75mm), the size tolerance is very small, is currently used in precision instruments. Although electrodeposited metals are mainly pure metals, it can be deposited on other metals, so as to expand the application scope. Foreign electrodeposition metal bellows mechanical seals already have a series of bellows items.

Shanghai water pump plant also introduced type 605 metal bellows seal for high temperature, high pressure and other purposes. In addition to the introduction of technology, domestic petrochemical system manufacturers have carried out the development & trial work of welded bellows, at the same time, there are also domestic production of 1Cr18Ni9Ti stainless steel mechanical bellows products. For example, Shenyang Scientific Instrument Factory has welded metal bellow mechanical seals, specifications for inner diameter d8~48, outer diameter D6~65, wall thickness 0.09~0.2mm,different lengths can be supplied according to user requirements.