Structure of guide rail 2

Structural design of 3 guide rails
1. Sliding guide rail
(1) Basic form
Triangle guide rail: This guide rail can automatically compensate for wear and tear, resulting in high guiding accuracy. Its cross-sectional angle is determined by the load size and guidance requirements, generally 90 °. To increase the bearing area and reduce the specific pressure, a larger apex angle (110 °~120 °) is used to improve guidance, while a smaller apex angle (60 °) is used under the condition of constant guide rail height. If the force acting on the guide rail differs greatly in two directions, an asymmetric triangle should be used to make the direction of force as perpendicular to the guide rail surface as possible.
Rectangular guide rail: Its advantages include simple structure, easy manufacturing, inspection, and repair, wide guide rail surface, high load-bearing capacity, and high stiffness, making it widely used. But its guiding accuracy is not as high as that of triangular guide rails: the clearance between guide rails needs to be adjusted with pressure plates or inserts, and needs to be readjusted after wear.
Swallowtail shaped guide rail: The adjustment and clamping of the dovetail shaped guide rail are relatively simple, and the gap between each surface can be adjusted with a single strip. It has a small height and compact structure, but it is inconvenient to manufacture and inspect, with high friction and poor rigidity. Used in situations where the movement speed is not high, the force is not significant, and the height dimension is limited. Circular guide rail: easy to manufacture, the outer circle is ground, and the inner hole can be precisely matched by grinding, but the clearance cannot be adjusted after wear. To prevent rotation, keyway or flat surface can be machined on the cylindrical surface, but it cannot withstand large torque. Suitable for applications that can withstand axial loads.
(2) Common forms of guide rail combinations
Triangle and rectangle combination: This combination form uses triangular guide rails as the guiding surface, with high guiding accuracy, while flat guide rails have good processability, so it is widely used. There are two forms of this combination: V-flat combination and edge flat combination. V-flat combination guide rail is easy to store lubricating oil and can be used at both low and high speeds; The leveling combination guide rail cannot store lubricating oil and is only used for low-speed movement.
In order to make the movement of the guide rail lightweight and labor-saving, and the wear of the two guide rails uniform, the driving element should be located below or biased towards the triangular guide rail. Rectangle and rectangle combination: The load-bearing surface and guiding surface are separated, making manufacturing and adjustment simple. The gap between the guiding surfaces is adjusted with a strip, resulting in low contact stiffness
Double triangular guide rail: Due to the symmetrical structure, the two guide rails wear evenly, and the symmetrical position remains unchanged after wear, so the machining accuracy is minimally affected. Good contact stiffness and high guiding accuracy, but poor processability, and it is difficult to completely contact the four surfaces through scraping or grinding. If the thermal deformation of the moving parts is different, it cannot guarantee simultaneous contact of the four surfaces, so it is not suitable for use in situations with large temperature changes.
(3) Gap adjustment
To ensure the normal operation of the guide rail, an appropriate gap should be maintained between the sliding surfaces of the guide rail. If the gap is too small, it will increase frictional resistance; Excessive clearance can reduce guidance accuracy. If the clearance of the guide rail is ensured by scraping and grinding, it requires a lot of labor, and after long-term use, the clearance of the guide rail will increase due to wear and tear, requiring timely adjustment. Therefore, the guide rail should have a clearance adjustment device. The rectangular guide rail needs to adjust the gap in both vertical and horizontal directions. In the vertical direction, the lower clearance of the lower surface is generally adjusted by using a lower pressure plate. The methods include: a) scraping or grinding the joint surface of the lower pressure plate; b) adjusting the position of the strip with screws; C) changing the number or thickness of the washers:
In the horizontal direction, it is commonly used to adjust its side clearance with flat or diagonal inlay strips.
The gap between circular guide rails cannot be adjusted
(4) Clamping device
Some guide rails (such as non horizontally placed rails) require their position to be fixed after movement, so specialized locking (clamping) devices are needed. The commonly used locking methods include mechanical locking and hydraulic locking.
(5) Measures to improve wear resistance
The service life of guide rails depends on their structure, materials, manufacturing quality, heat treatment methods, as well as their use and maintenance. Improving the wear resistance of the guide rail to maintain a certain guiding accuracy for a longer period of time can extend the service life of the equipment. The measures to improve the wear resistance of guide rails include:
1) Choose a reasonable specific pressure unit area as the specific pressure, that is, P=P/S (kg/cm2)
In the formula, P represents the force acting on the guide rail in kilograms
Support area of S-rail (cm2)
From the above equation, it can be seen that in order to reduce the specific pressure of the guide rail, the weight of the moving parts should be reduced and the area of the guide rail support surface should be increased. Reduce the center distance between the two guide surfaces. It can reduce the external dimensions and lighten the weight of moving parts. However, reducing the center distance is limited by the structural dimensions, and if the center distance is too small, it will lead to unstable motion.
Another way to reduce the pressure on the guide rail is to use an unloading device, which increases the rebound or hydraulic force in the opposite direction of the guide rail load to offset some of the load borne by the guide rail.
2) The commonly used guide rail materials for selecting suitable materials include cast iron, which is cast as a whole with the guide or moving parts, and is commonly made of gray cast iron. It has the advantages of low cost, good processability, and high thermal stability. Under good lubrication and protection, it has a certain degree of wear resistance. The commonly used ones are HT200~HT400, with a hardness of HB=180~200. Increasing the carbon and phosphorus content in cast iron appropriately and reducing the silicon content can improve the wear resistance of the guide rail. If gray cast iron cannot meet the wear resistance requirements, wear-resistant cast iron can be used, such as high phosphorus cast iron, with a hardness of HB=180~220 and a wear resistance performance about twice that of gray cast iron. If a certain amount of copper and Qin are added to form phosphorus copper Qin cast iron, its wear resistance is about twice as high as that of gray cast iron. However, high phosphorus cast iron has high brittleness and casting stress, and is prone to cracking. Therefore, appropriate casting processes should be adopted
In addition, low-alloy cast iron and rare earth cast iron can also be used.
Steel - rails on high demand or welded frames, commonly made of quenched alloy steel. The wear resistance of quenched steel guide rails is 5-10 times higher than that of ordinary gray cast iron. Commonly used methods include 20Cr steel carburizing quenching and 40Cr high-frequency quenching.
The methods for embedding steel guide rails include:
Screw connection should prevent the screws from being sheared: To avoid holes on the guide rail (which may accumulate dirt and accelerate wear), inverted screws are generally used. When it is structurally inconvenient to insert screws from below for fixation, the method shown in Figure 21-16 can be used. After tightening the screw, grind the hexagonal head flat so that there is no gap between the screw hole on the guide rail and the screw head.
Use epoxy resin for bonding, with a gap of no more than 0.25 millimeters between the bonding surfaces. Adhesive guide rails have a certain degree of adhesive stiffness and strength, as well as a certain degree of impact resistance. The process is simple and the cost is relatively low. Plastic - using polytetrafluoroethylene as the substrate and adding different fillers as the guide material. It has wear resistance, vibration resistance, and low coefficients of dynamic and static friction (0.04) It can eliminate low-speed crawling phenomenon and achieve good results in practical applications. 3) Heat treatment is often used to improve the wear resistance of cast iron guide rails by quenching the surface of the guide rails. Surface quenching methods include flame quenching, high-frequency quenching, and electrical contact quenching.
4) Lubrication and protective lubricating oil can form a very thin oil film between the guide rails, prevent or reduce direct contact between the guide rail surfaces, reduce friction and wear, and extend the service life of the guide rails. At the same time, lubrication can prevent "crawling" for low-speed motion, and reduce frictional heat and thermal deformation for high-speed motion. The lubrication methods for guide rails include pouring cups, oil cups, manual oil pumps, and automatic lubrication. The protective device of the guide rail is used to prevent cutting, dust and other dirt from falling onto the surface of the guide rail, so as to avoid scratching, rusting and premature wear of the guide rail. To this end, a scraper is installed at the end of the motion guide rail: various styles of protective devices are used to prevent the guide rail from being exposed.
(6) Verification of structural dimensions
1) Verify the impact of temperature changes on the clearance between guide rails. When working in environments with significant temperature changes, the clearance between guide rails should be checked after selecting the accuracy and fit. In order to ensure that the guide rail does not get stuck during operation, the minimum clearance of the guide rail should be greater than or equal to zero, that is, the minimum clearance of the Amin20 guide rail is calculated using the following formula:
Amin=Dmin [1+ak (t-to) - dmax [1+az (t-to)] (mm), where t-working temperature (C)
T0- Temperature during manufacturing (C)
Dmin - Minimum size of containment component at to (mm)
Dmax - maximum size of the enclosed component at to (mm)
AK - Linear expansion coefficient of containment material (1/C)
AZ - Linear expansion coefficient of the contained material (1/C)
To ensure guidance accuracy, the maximum clearance Amax of the guide rail should be less than or equal to the allowable value, that is, the maximum clearance Amaxs [Amax] of the guide rail is calculated using the following formula:
Amax=Dmax [1+ak (t-to)] - dmin [1+az (t-to)] (mm), where Dmax - maximum size of the containment component at t0 (mm) dmin - minimum size of the containment component at to (mm) 2) Non self-locking condition and calculation of guide rail clearance
After initially determining the structural form and size of the guide rail, attention should be paid to the direction of the applied force and the position of the point of action, striving to minimize the tilting moment of the guide rail. Otherwise, the friction force of the guide rail will increase, wear will accelerate, thereby reducing the flexibility and guiding accuracy of the guide rail, and even causing the guide rail to get stuck.