Thread protection is a very important part of the thread connections of any structure. It should:
- operate reliably under all operating conditions,
- Allow multiple connection and disconnection,
- protect in any position,
- Do not extend the connector,
- do not weaken the components.
There are several ways to protect the threads from self-unscrewing. We can do this by using:
- Bendable washer on the cap and edge of the workpiece.
- Cloaked washer.
- Crown nut with pin.
- screw protection.
- Spring washer.
- Nuts and anti-nuts.
We distinguish the three most commonly used methods of securing threads:
With this method, we increase the elasticity of threaded joints by compressing the value of material subsiding. This largely prevents thread joints from loosening by maintaining the preload force. This method, however, will not prevent us from self-unscrewing the screws, caused by sliding, dynamically loaded parts. This is a medium strength protection. High stiffness spring or tapered washers are a product that exempliated vulnerable protections.
Thread protection against falling out
This method allows the threads to loosen or unscrew gently, but prevents the connection from completely disintegrating. Corona nuts, wire protections, coiles, metal or plastic thread inserts are examples of this type of thread protection. Although this method of protection usually avoids the loss of components, it is ineffective in maintaining crimping stress.
Due to the very heavy loads of the screws, the measures to prevent unscrewing of the threads must meet the highest standards. The best company that has developed the production of liquid single-component adhesives is Loctite. Loctite completely fills the microscopic spaces between the cooperating threads. Curing of the product occurs after cutting off the air supply and contact with the metal, it becomes a high-resistant, heat-resistant material. Loctite creates an inseparable connection that prevents any movement in the bolt ing. Curing the product and such a perfect combination as loctite solves the problem exactly where it is formed, that is, in the gwin itself. Loctite products are therefore among the most effective means of securing thread connections. It is very important when securing with Loctite glue to check that the entire surface of the screws is well moistened and the product is cured without interference. Let us remember that some oils or cleaning methods inhibit and even completely eliminate the cure process of Loctite adhesive. therefore, be careful what product we use to secure the threads.
Types of screws
The screw is, simply put, a threaded connecting element. These products are highly used in the construction industry as well as in the construction of machines. The product, which is a screw, differs primarily in size (diameter and length), shape (that is, the type of head). We also divide them into categories of plastics from which they are made, such as stainless steel.
What is stainless steel?
Stainless steel is a carbon-reduced steel alloy that is resistant to corrosion from both weather conditions as well as low-concentration acids and bases. Thanks to this property, stainless steel products are widely used wherever there are components. Stainless steel alloys, from which screw threaded rods, nuts, washers are produced. They owe their resistance and strength to their chemical composition. They contain at least 10.5% chromium and at most 1.2% carbon. Thanks to this composition, chromium, which is contained in steel, reacts with oxygen, resulting in a very thin, invisible, durable and corrosion-resistant layer of chromium oxide. The resulting layer has properties that allow it to rebuild itself when damaged by any external factors. Compared to other medium strength steel alloys, stainless steel is a strong leader.
Properties of stainless steel
- Corrosion resistance
- Incandescent ness
- Stylish design
- Easy to clean
- Easy to process
- Favourable strength-to-weight ratio
The strength of the screw connection is determined by the strength of the core. The strength of all bolt components must be at least equal to the strength. The screw material must be well machined, durable and above all plastic. We cannot afford to use medium-strength screws in designs. If we use a heavy-weighted product operating under fatigue or shock loads, it must be made of chrome or chromo-liquid structural steel, chromium-solid-clad steel shall be used at elevated operating temperatures. Mass-produced screws are made on forging machines. Screws are mass produced on forging machines, the corresponding diameter dimension is obtained by pushing the end of the screw forging through the die. The bolt core intended for rolling must have a thread split diameter. During the thread shaping process, the top of the thread is formed by the plastic flow of the material squeezed through the vertices of the tool outline. The desired diameter of the semi-finished product is obtained by turning, pulling or grinding. The thread is most often rolled or notched, the former has better static and fatigue strength of the core and is more resistant to wear. The height of the normal bolt head is 0.7 nominal diameter. The strength test of the product occurs after cutting off the head and checking the density of the plastic.
Mechanical properties of screws
Mechanical properties are determined by measuring the transfer of bolt loads. The properties of the bolts are exactly the same as the properties of the materials from which they were made. Their tensile strength is usually between 450-500 MPa. The steel symbol contains 1/10th of this value, for example, C1-50 or A1-50. Chrome steels, which can be improved, allow you to increase the tensile strength to 700-800 MPa. A typical example is C4-70 or C3-80 steel. Most of these elements are shaped by plastic processing. This increases their mechanical properties compared to the properties of the material. The greater the transformation, the greater the increase in endurance. This only means that bolts that have smaller diameters but have undergone a larger transformation will have a higher strength than screws with larger diameters. The typical strength of cold screws is 700 MPa. This is where the designation A2-70 comes from. If we require higher strength, then the steel bars from which the screws are made are dragged. This allows the bolt to reach a bolt strength of 800 MPa. Such material shall be marked with the symbol A2-80.
Trapezoidal bolts and nuts are widely used in machine construction. They are used wherever high positioning accuracy, self-braking, strength and heavy screw load are needed. Depending on the operating conditions, the environment, suitable materials are added to the nut and screw. The best cooperation is achieved for the steel screw and the bronze nut, which has self-lubricating properties, which extends the service life, prevents overheating of the nut and ensures the quiet operation of such a connection. In places where there is an aggressive environment or there is no possibility of lubrication of the thread, plastic nuts can be used. The material of the plastic nut is met by specific conditions. It is worth noting that the trapezoidal thread is self-braking. The strength of the nut depends mainly on its height, the higher the nut and thus the longer the thread, it can carry more weight and will have a longer service life. The thread wear of the nut is controlled by shrinking the gap between the safety nut. If the thread is broken, the safety nut takes over the load.