Scraper rings – seals of this type are one of the types of auxiliary rings that are used in the sealing industry as an auxiliary seal for primary seals, which determine the tightness of the entire system. The reciprocating rings that fulfill this task include the scraper ring, it has a protective function, preventing solid or liquid contaminants in the form of liquids, dust, mud or dust from getting inside the entire system. Thus, they protect the entire hydraulic system from contamination. Sealing products, such as scraper and scraper and sealing rings, play the greatest role in places where the dustiness of the room is very high, e.g. in mines, agriculture, construction machinery. Wherever there is a risk, the machine can be damaged, the scraper ring comes in handy. They are located between the contamination environment and the primary sealing point.
Metal scraper and scraper – sealing ring
Metal scraper and scraper-sealing rings are special single-acting sealing rings with two different scraper lips, one thin metal and one thicker elastomeric. The lips scraping the seals are positioned one after the other and are housed in a small metal housing. Scraper rings with a metal scraper lip are products designed to remove stubborn dirt as well as ice particles. The elastomeric outer lip of this type of seal is designed to enhance the overall effect of scraping dirt from the tools. It is very effective in removing sand particles, water and other unwanted foreign particles. These scraper rings have two lips smaller than the nominal diameter of the piston rod, which guarantees adequate pressure of the seals. On the other hand, the metal lip is elastically embedded in the housing, thanks to which it can move freely and thus compensate for any deflections of the piston rod.
- very easy installation in open grooves,
- thanks to the metal housing it allows for a firm seat in the groove,
- Shows high abrasion resistance,
- very high scraping efficiency of these products, even with strongly adhering contaminants such as ice or mud.
The operating temperature of this type of seals is from -40 ° C to + 120 ° C.
Z scraper rings
They are used to seal drives and valve bodies. For removing external contamination from elements working in reciprocating motion. The flexible form of the ring allows for simple and reliable installation in the groove.
- simplification of the design of the piston
- shortening the length of the cylinder liners
- reduce the dead length of the cylinders
- easier assembly
The use of scraper rings as seals and their types
Scraper rings are installed in cylinder seal systems to prevent contamination of the hydraulic fluid. In continuous operation, they reciprocate the extended piston rods to scrape off dirt, foreign particles and moisture. When these types of products do their job, they go back to where they belong – inside the cylinders. Failure to install scraper rings could cause permanent damage to other rings, but also to seals, for example, which play an important role in the correct operation of the machine and in maintaining proper compression in it.
There are three most important types of sealing rings, differing in the material from which they are made. Z-rings are made entirely of rubber, ZW seals are manufactured with a metal stiffening insert, ZZproducts are characterized by an external metal casing. The latter are used when a greater fit of the seal is required. By means of a metal housing, the entire element becomes less flexible and therefore more adherent.
What are scraper rings?
The group of ring seals includes three basic types. These are sealing rings, or so-called pistonseals, whose task is to prevent exhaust gas leakage. The second type of seals are compression-scraper rings, whose task is to stop gases from passing through the first type of rings. The third and last type of seals are scraper rings, which prevent excessive oil from entering the space above the cylinder by scraping it off the cylinder liner. It should be remembered that as a result of improper assembly of the seal, it may break, and may directly result in scratching the cylinder surface and significant compression drops.
What could be the causes of damage to the hydraulic seals?
As we know, when we use tools such as hydraulic cylinders, we expose them to various types of external factors and various loads, often in difficult and aggressive environmental conditions. As a rule, difficult operating conditions and improper operation cause the actuators to be damaged in various ways. Typical cylinder failures include loss of tightness in the stuffing box and external leakage after sealing the piston rod, and internal leakage in the cylinder after sealing the piston. The main causes of these failures are:
- bending or deformation of the cylindrical surface of the piston rod caused by transverse loads,
- wear or damage to the piston rod surface as a result of solid contaminants entering the seals or as a result of corrosion.
- wear of the cylinder bearing surface resulting from the use of contaminated oil or caused by the ingress of external contaminants into the cylinder chamber,
- contaminated oil – oil contamination is most often the result of the lack of use or incorrect selection of the oil filter.
- extreme temperatures that cause seals to deteriorate, crack, delaminate, harden, crumble and swell.
- incorrectly selected hydraulic oil causing undesirable chemical reactions with the material of seals, leading to their premature degradation,
- too high operating pressure – exposes the seals to rapid wear and destruction. Exceeding the allowable pressure may damage the seals’ support rings as well as the retaining elements,
- too low operating pressure – can cause leaks with seals made of materials other than polyurethane, where there is no damping of the flowing fluid.