How to Achieve Safe and Efficient Compressors via Proper Running-in
Like other machinery, screw compressors have a running-in period. During running-in, material transfer occurs on the surfaces of friction pairs with the participation of lubricant, achieving surface conditions suitable for optimal friction. This represents the traditional narrow definition of running-in.
The new broad definition of running-in refers to a process during which incompatibilities of components and subsystems including base parts, connecting pieces, pressure vessels, auxiliary systems and control systems, manufacturing and assembly tolerances, and other unreasonable factors emerge. These defects are further remedied or self-repaired to realize adaptation and self-adaptation.
This process is indispensable for mechanical products. The consequences caused by missing or inadequate running-in can sometimes be painful for manufacturers, distributors and end users.
A well-known manufacturer once encountered failures on a large 5,500 kW reciprocating compressor within one year, including fractured couplings, broken main shafts, fractured connecting rods, cracked pistons and fractured piston rods. Some fertilizer compressors even exploded and caused personnel injuries.
Common faults include cylinder scoring, abnormal air leakage of piston rings, severe leakage in packing boxes, and so on.
Screw air compressors may suffer abnormal noise, excessive temperature, heavy vibration, or even complete operational failure; damage to star wheels of single-screw air compressors also happens from time to time.
Can such severe incidents be detected as early as possible and eliminated before escalating into accidents or disasters under the quality assurance system? Even the zero-tolerance US military standard cannot rule out space shuttle catastrophes. Therefore, identifying defects and unforeseen hidden hazards during equipment commissioning and running-in at an early stage is a highly cost-effective and safest measure.
Different manufacturers adopt different running-in specifications. Back in the 1980s, Ms. Feng Yaoping, then Chief Engineer of the Planning Institute under the Ministry of Machinery Industry, shared insights after a research trip to Germany: Heidelberg printing presses leave the factory with printing counters showing 4,000 impressions. This means each Heidelberg press undergoes factory running-in and inspection with 4,000 sheets printed. Indeed, few compressor manufacturers worldwide enjoy a better reputation than Heidelberg Printing Machinery.
Compressor manufacturers should earnestly study compressor running-in and practical testing techniques to minimize running-in losses. Proper running-in and testing are related not only to the interests of manufacturers and distributors, but also to end users, especially owners of new projects.
Some compressor manufacturers attach little importance to running-in and regard it as redundant work. However, inadequate running-in may force manufacturers to bear huge costs.
Definition of Running-in
Traditional running-in theory: Machined mechanical components cannot achieve ideal matching conditions (including clearances, surface contact characteristics and states) for optimal operation. Units need to run at low speed and light load. With lubricants in place, mating surfaces gradually reach relative harmony and stability. After running-in, oil, oil filters and corresponding filters are replaced, allowing the machine to enter its optimal service stage on a new baseline. For example, the running-in period for automobiles is generally specified at approximately 4,000 kilometers of driving.
The length of the running-in period is subject to the following factors:
Design and manufacturing level of the compressor
The popularization of machining centers, especially high-precision precision machining centers, raises the machining accuracy and surface finish of components by an order of magnitude. Compressor component designs optimized for machining center processing, combined with superfinishing, polishing, coating, precision casting and strict quality control, can shorten the running-in period.
Material technologies that improve compressor reliability also help reduce running-in duration.
Compressor rotational speed
High-speed compressors feature shorter running-in periods. The running-in period of screw air compressors lasts roughly 300 hours; reciprocating air compressors require 500~1,000 hours, while large reciprocating compressors need a longer running-in time of 4,000~8,000 hours. Generally, compressors enter stable reliable operation after one year of service.
Operating environment of the compressor
Compressors operating in favorable environments with proper maintenance enjoy shorter running-in periods and better running-in results.
Running-in technology
Misconception
A prevailing misunderstanding claims: "Given current standards for mechanical design, machining and assembly technologies, components no longer require running-in to achieve good fit and operation."
In fact, modern design and manufacturing technologies have not yet eliminated the necessity of running-in. Premature omission of running-in may trigger the following problems:
a. Accelerated component wear
b. Higher failure risk
Deviations generated during machining and assembly, along with latent defects, may lead to abnormal heating, leakage, irregular wear, excessive vibration and noise, or even component jamming during running-in.
c. Easy deterioration of lubricating oil
During running-in, small mating clearances result in poor oil film quality and obvious temperature rise, which accelerates oxidative deterioration of lubricants. Abundant metal particles mix into the oil and degrade its performance. Greater frictional resistance between components also speeds up oil aging and increases oil consumption.
d. Abnormal loosening of fasteners
Smooth completion of the running-in period is critical for the subsequent service life of compressors, and pre-running-in implemented at the factory carries greater significance.
Pre-running-in
Pre-running-in refers to a series of ultra-precise procedures implemented before formal running-in, aiming to shorten the running-in cycle and reduce running-in losses. Many world-famous compressor brands have fully or partially adopted such procedures.
Fundamental solutions to eliminate running-in faults include: designing compressor components suitable for machining center processing; deploying sophisticated manufacturing equipment; applying superfinishing, polishing and coating processes; adopting running-in enhancers; and enforcing strict quality assurance controls. Optimized pre-running-in conditions help units pass the running-in phase smoothly.
New Technologies for Compressor Running-in
Design and manufacturing level of the compressor
The popularization of machining centers, especially high-precision precision machining centers, raises the machining accuracy and surface finish of components by an order of magnitude. Compressor component designs optimized for machining center processing, combined with superfinishing, polishing, coating, precision casting and strict quality control, can shorten the running-in period.
Material technologies that improve compressor reliability also help reduce running-in duration.
Compressor rotational speed
High-speed compressors feature shorter running-in periods. The running-in period of screw air compressors lasts roughly 300 hours; reciprocating air compressors require 500~1,000 hours, while large reciprocating compressors need a longer running-in time of 4,000~8,000 hours. Generally, compressors enter stable reliable operation after one year of service.
Operating environment of the compressor
Compressors operating in favorable environments with proper maintenance enjoy shorter running-in periods and better running-in results.
Running-in technology
Misconception
A prevailing misunderstanding claims: "Given current standards for mechanical design, machining and assembly technologies, components no longer require running-in to achieve good fit and operation."
In fact, modern design and manufacturing technologies have not yet eliminated the necessity of running-in. Premature omission of running-in may trigger the following problems:
a. Accelerated component wear
b. Higher failure risk
Deviations generated during machining and assembly, along with latent defects, may lead to abnormal heating, leakage, irregular wear, excessive vibration and noise, or even component jamming during running-in.
c. Easy deterioration of lubricating oil
During running-in, small mating clearances result in poor oil film quality and obvious temperature rise, which accelerates oxidative deterioration of lubricants. Abundant metal particles mix into the oil and degrade its performance. Greater frictional resistance between components also speeds up oil aging and increases oil consumption.
d. Abnormal loosening of fasteners
Smooth completion of the running-in period is critical for the subsequent service life of compressors, and pre-running-in implemented at the factory carries greater significance.
Methods to Ensure Smooth Compressor Running-in
A set of specialized technologies guarantees effective running-in. Foreign manufacturers are highly proficient in these techniques. Some domestic compressor manufacturers have mastered part of the relevant technologies, while others lack such capabilities, leading to large gaps in compressor reliability and performance.
Key technologies to ensure smooth running-in:
1. Anti-seize coatings or anti-seize compounds
Anti-seize coatings/compounds represent a vital foreign mechanical technology. During assembly, high-friction areas are coated with anti-seize materials to protect friction pairs. A wear-resistant protective film forms on friction surfaces to reduce dimensional loss during running-in, accelerate the running-in process and lower subsequent performance attenuation rates.
Most domestic manufacturers are unfamiliar with this technology, creating a technical gap between domestic and imported compressors.
2. High-performance lubricants
Adopting high-performance compressor oil can minimize problems during running-in. Foreign air compressor manufacturers widely use PAO synthetic oils, and some have adopted ester oils and silicone-based oils. High-performance lubricants strengthen lubrication performance with improved anti-oxidation and anti-wear properties. They further reduce oil carryover in compressed air and boost energy efficiency, targets difficult to achieve with ordinary mineral base oils.
3. Special factory test procedures
The air end is the most failure-prone part during screw compressor running-in. Comprehensive systematic testing of air ends before final assembly maximizes the detection of hidden defects.
a. Short-duration low-speed dry friction testing for air ends is beneficial. Low-speed dry friction easily exposes improper fitting of screw air ends. Vibration and noise data measured during low-speed dry friction can be compared with benchmark data of qualified air ends and normal operating parameters to evaluate air end integrity.
b. Equip the air end test bench with large-size motors and frequency converters to expand overspeed test ranges and guarantee excellent air end performance.
c. Test compressor vibration, noise, input power and air delivery capacity. Compare measured data with benchmark air end parameters to assess overall compressor quality.
Topics Worth Reflection
On-site compressor failures at the customer’s premises are extremely troublesome. Once a fault occurs, manufacturers must devote capital, manpower and communication resources to resolve the issue. Even after settlement, negative impressions will remain.
Manufacturers should adopt advanced running-in technologies inside factories to simulate potential on-site faults in advance and eliminate them. Although such practices increase time and cost, they constitute a wise strategy.
The necessity of innovative running-in concepts appears less prominent for medium and low-grade compressors, yet it is far more important for premium brand compressors. Applying new running-in technologies improves compressor performance parameters, stabilizes and extends the service life of high-performance operation, and enhances overall reliability.
The new broad definition of running-in refers to a process during which incompatibilities of components and subsystems including base parts, connecting pieces, pressure vessels, auxiliary systems and control systems, manufacturing and assembly tolerances, and other unreasonable factors emerge. These defects are further remedied or self-repaired to realize adaptation and self-adaptation.
This process is indispensable for mechanical products. The consequences caused by missing or inadequate running-in can sometimes be painful for manufacturers, distributors and end users.
A well-known manufacturer once encountered failures on a large 5,500 kW reciprocating compressor within one year, including fractured couplings, broken main shafts, fractured connecting rods, cracked pistons and fractured piston rods. Some fertilizer compressors even exploded and caused personnel injuries.
Common faults include cylinder scoring, abnormal air leakage of piston rings, severe leakage in packing boxes, and so on.
Screw air compressors may suffer abnormal noise, excessive temperature, heavy vibration, or even complete operational failure; damage to star wheels of single-screw air compressors also happens from time to time.
Can such severe incidents be detected as early as possible and eliminated before escalating into accidents or disasters under the quality assurance system? Even the zero-tolerance US military standard cannot rule out space shuttle catastrophes. Therefore, identifying defects and unforeseen hidden hazards during equipment commissioning and running-in at an early stage is a highly cost-effective and safest measure.
Different manufacturers adopt different running-in specifications. Back in the 1980s, Ms. Feng Yaoping, then Chief Engineer of the Planning Institute under the Ministry of Machinery Industry, shared insights after a research trip to Germany: Heidelberg printing presses leave the factory with printing counters showing 4,000 impressions. This means each Heidelberg press undergoes factory running-in and inspection with 4,000 sheets printed. Indeed, few compressor manufacturers worldwide enjoy a better reputation than Heidelberg Printing Machinery.
Compressor manufacturers should earnestly study compressor running-in and practical testing techniques to minimize running-in losses. Proper running-in and testing are related not only to the interests of manufacturers and distributors, but also to end users, especially owners of new projects.
Some compressor manufacturers attach little importance to running-in and regard it as redundant work. However, inadequate running-in may force manufacturers to bear huge costs.
Definition of Running-in
Traditional running-in theory: Machined mechanical components cannot achieve ideal matching conditions (including clearances, surface contact characteristics and states) for optimal operation. Units need to run at low speed and light load. With lubricants in place, mating surfaces gradually reach relative harmony and stability. After running-in, oil, oil filters and corresponding filters are replaced, allowing the machine to enter its optimal service stage on a new baseline. For example, the running-in period for automobiles is generally specified at approximately 4,000 kilometers of driving.
The length of the running-in period is subject to the following factors:
Design and manufacturing level of the compressor
The popularization of machining centers, especially high-precision precision machining centers, raises the machining accuracy and surface finish of components by an order of magnitude. Compressor component designs optimized for machining center processing, combined with superfinishing, polishing, coating, precision casting and strict quality control, can shorten the running-in period.
Material technologies that improve compressor reliability also help reduce running-in duration.
Compressor rotational speed
High-speed compressors feature shorter running-in periods. The running-in period of screw air compressors lasts roughly 300 hours; reciprocating air compressors require 500~1,000 hours, while large reciprocating compressors need a longer running-in time of 4,000~8,000 hours. Generally, compressors enter stable reliable operation after one year of service.
Operating environment of the compressor
Compressors operating in favorable environments with proper maintenance enjoy shorter running-in periods and better running-in results.
Running-in technology
Misconception
A prevailing misunderstanding claims: "Given current standards for mechanical design, machining and assembly technologies, components no longer require running-in to achieve good fit and operation."
In fact, modern design and manufacturing technologies have not yet eliminated the necessity of running-in. Premature omission of running-in may trigger the following problems:
a. Accelerated component wear
b. Higher failure risk
Deviations generated during machining and assembly, along with latent defects, may lead to abnormal heating, leakage, irregular wear, excessive vibration and noise, or even component jamming during running-in.
c. Easy deterioration of lubricating oil
During running-in, small mating clearances result in poor oil film quality and obvious temperature rise, which accelerates oxidative deterioration of lubricants. Abundant metal particles mix into the oil and degrade its performance. Greater frictional resistance between components also speeds up oil aging and increases oil consumption.
d. Abnormal loosening of fasteners
Smooth completion of the running-in period is critical for the subsequent service life of compressors, and pre-running-in implemented at the factory carries greater significance.
Pre-running-in
Pre-running-in refers to a series of ultra-precise procedures implemented before formal running-in, aiming to shorten the running-in cycle and reduce running-in losses. Many world-famous compressor brands have fully or partially adopted such procedures.
Fundamental solutions to eliminate running-in faults include: designing compressor components suitable for machining center processing; deploying sophisticated manufacturing equipment; applying superfinishing, polishing and coating processes; adopting running-in enhancers; and enforcing strict quality assurance controls. Optimized pre-running-in conditions help units pass the running-in phase smoothly.
New Technologies for Compressor Running-in
Design and manufacturing level of the compressor
The popularization of machining centers, especially high-precision precision machining centers, raises the machining accuracy and surface finish of components by an order of magnitude. Compressor component designs optimized for machining center processing, combined with superfinishing, polishing, coating, precision casting and strict quality control, can shorten the running-in period.
Material technologies that improve compressor reliability also help reduce running-in duration.
Compressor rotational speed
High-speed compressors feature shorter running-in periods. The running-in period of screw air compressors lasts roughly 300 hours; reciprocating air compressors require 500~1,000 hours, while large reciprocating compressors need a longer running-in time of 4,000~8,000 hours. Generally, compressors enter stable reliable operation after one year of service.
Operating environment of the compressor
Compressors operating in favorable environments with proper maintenance enjoy shorter running-in periods and better running-in results.
Running-in technology
Misconception
A prevailing misunderstanding claims: "Given current standards for mechanical design, machining and assembly technologies, components no longer require running-in to achieve good fit and operation."
In fact, modern design and manufacturing technologies have not yet eliminated the necessity of running-in. Premature omission of running-in may trigger the following problems:
a. Accelerated component wear
b. Higher failure risk
Deviations generated during machining and assembly, along with latent defects, may lead to abnormal heating, leakage, irregular wear, excessive vibration and noise, or even component jamming during running-in.
c. Easy deterioration of lubricating oil
During running-in, small mating clearances result in poor oil film quality and obvious temperature rise, which accelerates oxidative deterioration of lubricants. Abundant metal particles mix into the oil and degrade its performance. Greater frictional resistance between components also speeds up oil aging and increases oil consumption.
d. Abnormal loosening of fasteners
Smooth completion of the running-in period is critical for the subsequent service life of compressors, and pre-running-in implemented at the factory carries greater significance.
Methods to Ensure Smooth Compressor Running-in
A set of specialized technologies guarantees effective running-in. Foreign manufacturers are highly proficient in these techniques. Some domestic compressor manufacturers have mastered part of the relevant technologies, while others lack such capabilities, leading to large gaps in compressor reliability and performance.
Key technologies to ensure smooth running-in:
1. Anti-seize coatings or anti-seize compounds
Anti-seize coatings/compounds represent a vital foreign mechanical technology. During assembly, high-friction areas are coated with anti-seize materials to protect friction pairs. A wear-resistant protective film forms on friction surfaces to reduce dimensional loss during running-in, accelerate the running-in process and lower subsequent performance attenuation rates.
Most domestic manufacturers are unfamiliar with this technology, creating a technical gap between domestic and imported compressors.
2. High-performance lubricants
Adopting high-performance compressor oil can minimize problems during running-in. Foreign air compressor manufacturers widely use PAO synthetic oils, and some have adopted ester oils and silicone-based oils. High-performance lubricants strengthen lubrication performance with improved anti-oxidation and anti-wear properties. They further reduce oil carryover in compressed air and boost energy efficiency, targets difficult to achieve with ordinary mineral base oils.
3. Special factory test procedures
The air end is the most failure-prone part during screw compressor running-in. Comprehensive systematic testing of air ends before final assembly maximizes the detection of hidden defects.
a. Short-duration low-speed dry friction testing for air ends is beneficial. Low-speed dry friction easily exposes improper fitting of screw air ends. Vibration and noise data measured during low-speed dry friction can be compared with benchmark data of qualified air ends and normal operating parameters to evaluate air end integrity.
b. Equip the air end test bench with large-size motors and frequency converters to expand overspeed test ranges and guarantee excellent air end performance.
c. Test compressor vibration, noise, input power and air delivery capacity. Compare measured data with benchmark air end parameters to assess overall compressor quality.
Topics Worth Reflection
On-site compressor failures at the customer’s premises are extremely troublesome. Once a fault occurs, manufacturers must devote capital, manpower and communication resources to resolve the issue. Even after settlement, negative impressions will remain.
Manufacturers should adopt advanced running-in technologies inside factories to simulate potential on-site faults in advance and eliminate them. Although such practices increase time and cost, they constitute a wise strategy.
The necessity of innovative running-in concepts appears less prominent for medium and low-grade compressors, yet it is far more important for premium brand compressors. Applying new running-in technologies improves compressor performance parameters, stabilizes and extends the service life of high-performance operation, and enhances overall reliability.
